同济大学机械工程专业英语翻译

目录
UNIT 1 ADVANCED ENGINEERING MATERIALS 1
UNIT 2 HEAT TREATMENT OF METALS 6
UNIT 3 CASTING PROCESSES 15
UNIT 4 FORGING PROCESSES 21
UNIT 5 POWDER METALLURGY 26
UNIT 6 INJECTION MOLDING 32
UNIT 7 METAL CUTTING 38
UNIT 8 GRINDING 45
UNIT 9 LAPPING POLISHING 49
UNIT 10 SURFACE ENGINEERING 51
UNIT 12 DRILLING AND MILLING 63
UNIT 13 JIGS AND FIXTURES 68
UNIT 14 LIMIT AND TOLERANCES 72
特种加工工艺（ⅠⅡ） 77









UNIT 1 Advanced Engineering Materials

Types of Materials材料类型

Materials may be grouped in several ways Scientists often classify materials by their state solid liquid or gas They also separate them into organic (once living) and inorganic (never living) materials材料种方法分类科学家常根状态材料分：固体液体气体材料分机材料(生命)机材料(未生命)
For industrial purposes materials are divided into engineering materials or nonengineering materials Engineering materials are those used in manufacture and become parts of products工业效言材料分工程材料非工程材料加工制造成产品组成部分工程材料
Nonengineering materials are the chemicals fuels lubricants and other materials used in the manufacturing process which do not become part of the product非工程材料化学品燃料润滑剂加工制造程成产品组成部分材料
Engineering materials may be further subdivided into ①Metal ②Ceramics ③Composite ④Polymers etc工程材料进步细分：①金属材料②陶瓷材料③复合材料 ④聚合材料等等

Metals and Metal Alloys 金属金属合金

Metals are elements that generally have good electrical and thermal conductivity Many metals have high strength high stiffness and have good ductility 金属通常具良导电性导热性元素许金属具高强度高刚性良延展性
Some metals such as iron cobalt and nickel are magnetic At low temperatures some metals and intermetallic compounds become superconductors某金属磁化例铁钴镍极低温度某金属金属化合物转变成超导体
What is the difference between an alloy and a pure metal Pure metals are elements which come from a particular area of the periodic table Examples of pure metals include copper in electrical wires and aluminum in cooking foil and beverage cans 合金纯金属区什？纯金属取元素周期表中特定位置元素例电线中铜制造烹饪箔饮料罐铝
Alloys contain more than one metallic element Their properties can be changed by changing the elements present in the alloy Examples of metal alloys include stainless steel which is an alloy of iron nickel and chromium and gold jewelry which usually contains an alloy of gold and nickel合金包含止种金属元素合金性质通改变中元素存改变金属合金例子：锈钢种铁镍铬合金金饰品通常含金镍合金
Why are metals and alloys used Many metals and alloys have high densities and are used in applications which require a high masstovolume ratio 什金属合金？许金属合金具高密度需较高质量体积场合
Some metal alloys such as those based on aluminum have low densities and are used in aerospace applications for fuel economy Many alloys also have high fracture toughness which means they can withstand impact and are durable
某金属合金例铝基合金密度低航空航天节省燃料许合金具高断裂韧性意味着起击耐
What are some important properties of metals
Density is defined as a material’s mass divided by its volume Most metals have relatively high densities especially compared to polymers 金属重特性？密度定义材料质量体积数金属密度相较高尤聚合物相较言
Materials with high densities often contain atoms with high atomic numbers such as gold or lead However some metals such as aluminum or magnesium have low densities and are used in applications that require other metallic properties but also require low weight高密度材料通常较原子序数原子构成例金铅然诸铝镁类金属具低密度需金属特性求重量轻场合
Fracture toughness can be described as a material’s ability to avoid fracture especially when a flaw is introduced Metals can generally contain nicks and dents without weakening very much and are impact resistant A football player counts on this when he trusts that his facemask won’t shatter断裂韧性描述材料防止断裂特出现缺陷时断裂力金属般缺口凹痕情况显著削弱抵抗击橄榄球运动员相信面罩会裂成碎片
Plastic deformation is the ability of bend or deform before breaking As engineers we usually design materials so that they don’t deform under normal conditions You don’t want your car to lean to the east after a strong west wind 塑性变形断裂前弯曲变形力作工程师设计时通常材料正常条件变形没愿意阵强烈西风汽车东倾斜
However sometimes we can take advantage of plastic deformation The crumple zones in a car absorb energy by undergoing plastic deformation before they break然时利塑性变形汽车压皱区域断裂前通历塑性变形吸收量
The atomic bonding of metals also affects their properties In metals the outer valence electrons are shared among all atoms and are free to travel everywhere Since electrons conduct heat and electricity metals make good cooking pans and electrical wires 金属原子连结特性影响金属部原子外层阶电子原子享处移动电子导热导电金属适合做烹饪锅电线
It is impossible to see through metals since these valence electrons absorb any photons of light which reach the metal No photons pass through阶电子吸收达金属光子透金属见没光子通金属
Alloys are compounds consisting of more than one metal Adding other metals can affect the density strength fracture toughness plastic deformation electrical conductivity and environmental degradation 合金种金属组成混合物加金属影响密度强度断裂韧性塑性变形导电耐环境退化等性
For example adding a small amount of iron to aluminum will make it stronger Also adding some chromium to steel will slow the rusting process but will make it more brittle
例铝里加少量铁更强样钢里加铬减缓生锈程较脆

Ceramics and Glasses陶瓷玻璃

A ceramic is often broadly defined as any inorganic nonmetallic material． By this definition ceramic materials would also include glasses however many materials scientists add the stipulation that ceramic must also be crystalline陶瓷通常概括定义机非金属材料定义陶瓷材料应包括玻璃然许材料科学家添加陶瓷必须时晶体物组成约定
A glass is an inorganic nonmetallic material that does not have a crystalline structure Such materials are said to be amorphous玻璃没晶体状结构机非金属材料种材料称非结晶质材料

Properties of Ceramics and Glasses陶瓷玻璃特性

Some of the useful properties of ceramics and glasses include high melting temperature low density high strength stiffness hardness wear resistance and corrosion resistance高熔点低密度高强度高刚性高硬度高耐磨性抗腐蚀性陶瓷玻璃特性
Many ceramics are good electrical and thermal insulators Some ceramics have special properties some ceramics are magnetic materials some are piezoelectric materials and a few special ceramics are superconductors at very low temperatures Ceramics and glasses have one major drawback they are brittle许陶瓷电热良绝缘体某陶瓷具特殊性：磁性材料压电材料特殊陶瓷极低温度超导体陶瓷玻璃缺点：容易破碎
Ceramics are not typically formed from the melt This is because most ceramics will crack extensively (ie form a powder) upon cooling from the liquid state 陶瓷般熔化形成数陶瓷液态冷时会量破碎(形成粉末)
Hence all the simple and efficient manufacturing techniques used for glass production such as casting and blowing which involve the molten state cannot be used for the production of crystalline ceramics Instead sintering or firing is the process typically used 玻璃生产简单效—诸浇铸吹制涉熔化技术晶体物组成陶瓷生产作代般采烧结焙烧工艺
In sintering ceramic powders are processed into compacted shapes and then heated to temperatures just below the melting point At such temperatures the powders react internally to remove porosity and fully dense articles can be obtained
烧结程中陶瓷粉末先挤压成型然加热略低熔点温度样温度粉末部起反应孔隙十分致密物品
An optical fiber contains three layers a core made of highly pure glass with a high refractive index for the light to travel a middle layer of glass with a lower refractive index known as the cladding which protects the core glass from scratches and other surface imperfections and an out polymer jacket to protect the fiber from damage光导纤维三层：核心高折射指数高纯光传输玻璃制成中间层低折射指数玻璃保护核心玻璃表面擦伤完整性破坏谓覆层外层聚合物护套保护光导纤维受损
In order for the core glass to have a higher refractive index than the cladding the core glass is doped with a small controlled amount of an impurity or dopant which causes light to travel slower but does not absorb the light 核心玻璃覆层折射指数中掺入微控数量减缓光速会吸收光线杂质搀杂剂
Because the refractive index of the core glass is greater than that of the cladding light traveling in the core glass will remain in the core glass due to total internal reflection as long as the light strikes the corecladding interface at an angle greater than the critical angle 核心玻璃折射指数覆层全反射程中光线射核心覆层分界面角度界角核心玻璃中传送光线保留核心玻璃中
The total internal reflection phenomenon as well as the high purity of the core glass enables light to travel long distances with little loss of intensity全反射现象核心玻璃高纯度样光线强度损耗传递长距离成

Composites复合材料

Composites are formed from two or more types of materials Examples include polymerceramic and metalceramic composites Composites are used because overall properties of the composites are superior to those of the individual components复合材料两种更材料构成例子聚合物陶瓷金属陶瓷复合材料复合材料全面性优组成部分单独性
For example polymerceramic composites have a greater modulus than the polymer component but aren’t as brittle as ceramicsTwo types of composites are fiberreinforced composites and particlereinforced composites例：聚合物陶瓷复合材料具聚合物成分更模量陶瓷样易碎复合材料两种：纤维加强型复合材料微粒加强型复合材料

Fiberreinforced Composites纤维加强型复合材料

Reinforcing fibers can be made of metals ceramics glasses or polymers that have been turned into graphite and known as carbon fibers Fibers increase the modulus of the matrix material 加强纤维金属陶瓷玻璃已变成石墨称碳纤维聚合物纤维加强基材模量
The strong covalent bonds along the fiber’s length give them a very high modulus in this direction because to break or extend the fiber the bonds must also be broken or moved着纤维长度强结合力价结合方予复合材料高模量损坏拉伸纤维必须破坏移种结合
Fibers are difficult to process into composites making fiberreinforced composites relatively expensive纤维放入复合材料较困难制造纤维加强型复合材料相昂贵
Fiberreinforced composites are used in some of the most advanced and therefore most expensive sports equipment such as a timetrial racing bicycle frame which consists of carbon fibers in a thermoset polymer matrix 纤维加强型复合材料某先进昂贵运动设备例计时赛竞赛行车骨架含碳纤维热固塑料基材制成
Body parts of race cars and some automobiles are composites made of glass fibers (or fiberglass) in a thermoset matrix
竞赛汽车某机动车车体部件含玻璃纤维(玻璃丝)热固塑料基材制成
Fibers have a very high modulus along their axis but have a low modulus perpendicular to their axis Fiber composite manufacturers often rotate layers of fibers to avoid directional variations in the modulus纤维着轴高模量垂直轴模量较低纤维复合材料制造者旋转纤维层防模量产生方变化

Particlereinforced composites微粒加强型复合材料

Particles used for reinforcing include ceramics and glasses such as small mineral particles metal particles such as aluminum and amorphous materials including polymers and carbon black加强微粒包含陶瓷玻璃类矿物微粒铝类金属微粒包括聚合物碳黑非结晶质微粒
Particles are used to increase the modulus of the matrix to decrease the permeability of the matrix to decrease the ductility of the matrix An example of particlereinforced composites is an automobile tire which has carbon black particles in a matrix of polyisobutylene elastomeric polymer微粒增加基材模量减少基材渗透性延展性微粒加强型复合材料例子机动车胎聚异丁烯造橡胶聚合物基材中加入碳黑微粒

Polymers聚合材料

A polymer has a repeating structure usually based on a carbon backbone The repeating structure results in large chainlike molecules Polymers are useful because they are lightweight corrosion resistant easy to process at low temperatures and generally inexpensive聚合物具般基碳链重复结构种重复结构产生链状分子重量轻耐腐蚀容易较低温度加工通常较便宜聚合物
Some important characteristics of polymers include their size (or molecular weight) softening and melting points crystallinity and structure The mechanical properties of polymers generally include low strength and high toughness Their strength is often improved using reinforced composite structures聚合材料具重特性包括尺寸(分子量)软化熔化点结晶度结构聚合材料机械性般表现低强度高韧性强度通常采加强复合结构改善

Important Characteristics of Polymers聚合材料重特性

Size Single polymer molecules typically have molecular weights between 10000 and 1000000gmol—that can be more than 2000 repeating units depending on the polymer structure 尺寸：单聚合物分子般分子量100001000000gmol间具体取决聚合物结构—2000重复单元
The mechanical properties of a polymer are significantly affected by the molecular weight with better engineering properties at higher molecular weights聚合物分子量极影响机械性分子量越工程性越
Thermal transitions The softening point (glass transition temperature) and the melting point of a polymer will determine which it will be suitable for applications These temperatures usually determine the upper limit for which a polymer can be used热转换性：聚合物软化点(玻璃状转化温度)熔化点决定否适合应温度通常决定聚合物否限
For example many industrially important polymers have glass transition temperatures near the boiling point of water (100℃ 212℉) and they are most useful for room temperature applications Some specially engineered polymers can withstand temperatures as high as 300℃(572℉)例许工业重聚合物玻璃状转化温度接水沸点(100℃ 212℉)广泛室温某特制造聚合物受住高达300℃(572℉)温度
Crystallinity Polymers can be crystalline or amorphous but they usually have a combination of crystalline and amorphous structures (semicrystalline)结晶度：聚合物晶体状非结晶质通常晶体状非结晶质结构结合物(半晶体)
Interchain interactions The polymer chains can be free to slide past one another (thermoplastic) or they can be connected to each other with crosslinks (thermoset or elastomer) Thermoplastics can be reformed and recycled while thermosets and elastomers are not reworkable链间相互作：聚合物分子链彼滑动(热塑性)通交键互相连接(热固性弹性)热塑性材料重新形成循环热固性弹性材料
Intrachain structure The chemical structure of the chains also has a tremendous effect on the properties Depending on the structure the polymer may be hydrophilic or hydrophobic (likes or hates water) stiff or flexible crystalline or amorphous reactive or unreactive链结构：分子链化学结构性影响根结构聚合物亲水憎水(喜欢讨厌水)硬软晶体状非结晶质易起反应易起反应



UNIT 2 Heat Treatment of Metals

The understanding of heat treatment is embraced by the broader study of metallurgy Metallurgy is the physics chemistry and engineering related to metals from ore extraction to the final product 热处理理解包含冶金学较广泛研究冶金学涉金属矿石提炼产物物理学化学工程学总称
Heat treatment is the operation of heating and cooling a metal in its solid state to change its physical properties According to the procedure used steel can be hardened to resist cutting action and abrasion or it can be softened to permit machining 热处理金属固态加热冷改变物理性操作采步骤钢通硬化抵抗切削磨损通软化允许机加工
With the proper heat treatment internal stresses may be removed grain size reduced toughness increased or a hard surface produced on a ductile interior The analysis of the steel must be known because small percentages of certain elements notably carbon greatly affect the physical properties合适热处理应力细化晶粒增加韧性柔软材料覆盖坚硬表面某元素(尤碳)微百分极影响物理性必须知道钢分析
Alloy steel owe their properties to the presence of one or more elements other than carbon namely nickel chromium manganese molybdenum tungsten silicon vanadium and copper Because of their improved physical properties they are used commercially in many ways not possible with carbon steels合金钢性质取决含碳外种种元素镍铬锰钼钨硅钒铜合金钢改善物理性量许碳钢适方
The following discussion applies principally to the heat treatment of ordinary commercial steels known as plain carbon steels With this process the rate of cooling is the controlling factor rapid cooling from above the critical range results in hard structure whereas very slow cooling produces the opposite effect列讨针称普通碳钢工业钢言热处理时冷速率控制素高界温度快速冷导致坚硬组织结构缓慢冷产生相反效果

A Simplified Ironcarbon Diagram简化铁碳状态图

If we focus only on the materials normally known as steels a simplified diagram is often used 果注意力集中般说钢常简化铁碳状态图
Those portions of the ironcarbon diagram near the delta region and those above 2 carbon content are of little importance to the engineer and are deleted A simplified diagram such as the one in Fig21 focuses on the eutectoid region and is quite useful in understanding the properties and processing of steel 铁碳状态图中三角区含碳量高2部分工程师言重删图21示简化铁碳状态图焦点集中析区理解钢性处理十分

The key transition described in this diagram is the decomposition of singlephase austenite(γ) to the twophase ferrite plus carbide structure as temperature drops 图中描述关键转变单相奥氏体(γ) 着温度降分解成两相 铁素体加渗碳体组织结构
Control of this reaction which arises due to the drastically different carbon solubility of austenite and ferrite enables a wide range of properties to be achieved through heat treatment控制奥氏体铁素体碳溶解性完全产生反应通热处理获范围特性

To begin to understand these processes consider a steel of the eutectoid composition 077 carbon being slow cooled along line xx’ in Fig21 At the upper temperatures only austenite is present the 077 carbon being dissolved in solid solution with the iron When the steel cools to 727℃(1341℉) several changes occur simultaneously理解程考虑含碳量077析钢着图21xx’线慢慢冷较高温度时存奥氏体077碳溶解铁里形成固溶体钢冷727℃ (1341℉)时时发生干变化
The iron wants to change from the FCC austenite structure to the BCC ferrite structure but the ferrite can only contain 002 carbon in solid solution 铁需面心立方体奥氏体结构转变体心立方体铁素体结构铁素体容纳固溶体状态002碳
The rejected carbon forms the carbonrich cementite intermetallic with composition Fe3C In essence the net reaction at the eutectoid is austenite 077C→ferrite 002C+cementite 667C析出碳金属化合物Fe3C形成富碳渗碳体质析体基反应奥氏体077碳→铁素体002碳+渗碳体667碳

Since this chemical separation of the carbon component occurs entirely in the solid state the resulting structure is a fine mechanical mixture of ferrite and cementite Specimens prepared by polishing and etching in a weak solution of nitric acid and alcohol reveal the lamellar structure of alternating plates that forms on slow cooling种碳成分化学分离完全发生固态中产生组织结构种细致铁素体渗碳体机械混合物通磨弱硝酸酒精溶液中蚀刻制备样显示出缓慢冷形成交互层状薄片结构
This structure is composed of two distinct phases but has its own set of characteristic properties and goes by the name pearlite because of its resemblance to mother of pearl at low magnification种结构两种截然状态组成身具系列特性低倍数放时珠母层类处称珠光体

Steels having less than the eutectoid amount of carbon (less than 077) are known as hypoeutectoid steels Consider now the transformation of such a material represented by cooling along line yy’ in Fig21 含碳量少析体(低077)钢称亚析钢现种材料着图21中yy’ 线冷转变情况
At high temperatures the material is entirely austenite but upon cooling enters a region where the stable phases are ferrite and austenite Tieline and levellaw calculations show that lowcarbon ferrite nucleates and grows leaving the remaining austenite richer in carbon较高温度时种材料全部奥氏体着冷进入铁素体奥氏体稳定状态区域截线杠杆定律分析知低碳铁素体成核长剩含碳量高奥氏体
At 727℃(1341℉) the austenite is of eutectoid composition (077 carbon) and further cooling transforms the remaining austenite to pearlite The resulting structure is a mixture of primary or proeutectoid ferrite (ferrite that formed above the eutectoid reaction) and regions of pearlite
727℃(1341℉)时奥氏体析组成(含碳量077)冷剩余奥氏体转化珠光体作结果组织结构初步预析铁素体(析反应前铁素体)部分珠光体混合物

Hypereutectoid steels are steels that contain greater than the eutectoid amount of carbon When such steel cools as shown in zz’ of Fig21 the process is similar to the hypoeutectoid case except that the primary or proeutectoid phase is now cementite instead of ferrite析钢含碳量析量钢种钢冷时图21zz’线示初步预析状态渗碳体取代铁素体外余类似亚析钢情况
As the carbonrich phase forms the remaining austenite decreases in carbon content reaching the eutectoid composition at 727℃(1341℉) As before any remaining austenite transforms to pearlite upon slow cooling through this temperature着富碳部分形成剩余奥氏体含碳量减少727℃(1341℉)时达析组织前说样缓慢冷温度时剩余奥氏体转化珠光体

It should be remembered that the transitions that have been described by the phase diagrams are for equilibrium conditions which can be approximated by slow cooling With slow heating these transitions occur in the reverse manner 应该记住状态图描述种转化适合通缓慢冷似衡条件果缓慢加热相反方式发生种转化
However when alloys are cooled rapidly entirely different results may be obtained because sufficient time is not provided for the normal phase reactions to occur in such cases the phase diagram is no longer a useful tool for engineering analysis然快速冷合金时完全结果没足够时间正常状态反应发生种情况工程分析言状态图工具

Hardening淬火

Hardening is the process of heating a piece of steel to a temperature within or above its critical range and then cooling it rapidly 淬火钢件加热超界温度范围然快速冷程
If the carbon content of the steel is known the proper temperature to which the steel should be heated may be obtained by reference to the ironiron carbide phase diagram However if the composition of the steel is unknown a little preliminary experimentation may be necessary to determine the range 果钢含碳量已知钢件合适加热温度参考铁碳合金状态图然钢成分知道时需做预备试验确定温度范围
A good procedure to follow is to heatquench a number of small specimens of the steel at various temperatures and observe the result either by hardness testing or by microscopic examination When the correct temperature is obtained there will be a marked change in hardness and other properties
遵循合适步骤种钢试件加热温度淬火通硬度试验显微镜检查观测结果旦获正确温度硬度性明显变化
In any heattreating operation the rate of heating is important Heat flows from the exterior to the interior of steel at a definite rate If the steel is heated too fast the outside becomes hotter than the interior and uniform structure cannot be obtained 热处理作业中加热速率重热量定速率钢外部传导部果钢加热太快外部部热均匀组织结构
If a piece is irregular in shape a slow rate is all the more essential to eliminate warping and cracking The heavier the section the longer must be the heating time to achieve uniform results 果工件形状规消翘曲开裂根加热速率缓慢截面越厚加热时间越长达均匀结果
Even after the correct temperature has been reached the piece should be held at that temperature for a sufficient period of time to permit its thickest section to attain a uniform temperature加热正确温度工件应温度保持足够时间厚截面达相温度

The hardness obtained from a given treatment depends on the quenching rate the carbon content and the work size In alloy steels the kind and amount of alloying element influences only the hardenability (the ability of the workpiece to be hardened to depths) of the steel and does not affect the hardness except in unhardened or partially hardened steels通定热处理硬度取决淬火速率含碳量工件尺寸非淬硬钢部分淬硬钢外合金钢中合金元素种类含量仅影响钢淬透性(工件硬化深层力)影响硬度

Steel with low carbon content will not respond appreciably to hardening treatment As the carbon content in steel increases up to around 060 the possible hardness obtainable also increases 含碳量低钢淬火处理没反应着钢含碳量增加060附硬度增加
Above this point the hardness can be increased only slightly because steels above the eutectoid point are made up entirely of pearlite and cementite in the annealed state Pearlite responds best to heattreating operations and steel composed mostly of pearlite can be transformed into a hard steel
超析点钢完全珠光体退火状态渗碳体组成高点硬度增加珠光体热处理作业响应基珠光体组成钢转化成硬质钢

As the size of parts to be hardened increases the surface hardness decreases somewhat even though all other conditions have remained the same There is a limit to the rate of heat flow through steel 条件保持变着淬火零件尺寸增加表面硬度会降热量钢中传导速率限
No matter how cool the quenching medium may be if the heat inside a large piece cannot escape faster than a certain critical rate there is a definite limit to the inside hardness However brine or water quenching is capable of rapidly bringing the surface of the quenched part to its own temperature and maintaining it at or close to this temperature淬火介质冷果工件中热量特定界速率更快散发部硬度会受明确限制然盐水水淬火够淬零件表面迅速冷身温度保持接温度
Under these circumstances there would always be some finite depth of surface hardening regardless of size This is not true in oil quenching when the surface temperature may be high during the critical stages of quenching种情况零件尺寸表面总定深度硬化油淬情况油淬时淬火关键阶段零件表面温度然高

Tempering 回火

Steel that has been hardened by rapid quenching is brittle and not suitable for most uses By tempering or drawing the hardness and brittleness may be reduced to the desired point for service conditions．快速淬火硬化钢硬易碎适合数场合通回火硬度脆性降低条件需程度
As these properties are reduced there is also a decrease in tensile strength and an increase in the ductility and toughness of the steel The operation consists of reheating quenchhardened steel to some temperature below the critical range followed by any rate of cooling 着性降低拉伸强度降低钢延展性韧性会提高回火作业包括淬硬钢重新加热低界范围某温度然意速率冷
Although this process softens steel it differs considerably from annealing in that the process lends itself to close control of the physical properties and in most cases does not soften the steel to the extent that annealing would The final structure obtained from tempering a fully hardened steel is called tempered martensite然程钢软化退火相回火适合严格控制物理性数情况会钢软化退火种程度回火完全淬硬钢终组织结构称回火马氏体

Tempering is possible because of the instability of the martensite the principal constituent of hardened steel Lowtemperature draws from 300℉ to 400℉ (150℃~205℃) do not cause much decrease in hardness and are used principally to relieve internal strains 马氏体淬硬钢成分稳定性回火成低温回火 300℉400℉(150℃~205℃)会引起硬度降减少部应变
As the tempering temperatures are increased the breakdown of the martensite takes place at a faster rate and at about 600℉(315℃) the change to a structure called tempered martensite is very rapid The tempering operation may be described as one of precipitation and agglomeration or coalescence of cementite 着回火温度提高马氏体较快速率分解约600℉(315℃)迅速转变称回火马氏体结构回火作业描述渗碳体析出凝聚聚结程
A substantial precipitation of cementite begins at 600℉(315℃) which produces a decrease in hardness Increasing the temperature causes coalescence of the carbides with continued decrease in hardness渗碳体量析出开始600℉(315℃)硬度降温度升会碳化物聚结硬度继续降低

In the process of tempering some consideration should be given to time as well as to temperature Although most of the softening action occurs in the first few minutes after the temperature is reached there is some additional reduction in hardness if the temperature is maintained for a prolonged time 回火程中考虑温度考虑时间然数软化作发生达需温度初分钟果温度维持段延长时间会额外硬度降
Usual practice is to heat the steel to the desired temperature and hold it there only long enough to have it uniformly heated通常做法钢加热需温度仅保温正均匀受热

Two special processes using interrupted quenching are a form of tempering In both the hardened steel is quenched in a salt bath held at a selected lower temperature before being allowed to cool These processes known as austempering and martempering result in products having certain desirable physical properties两种采中断淬火特殊工艺回火形式两种工艺中淬硬钢允许冷前先选定较低温度盐浴淬火两种分称奥氏体回火马氏体回火工艺产品具特定需物理性

Annealing 退火

The primary purpose of annealing is to soften hard steel so that it may be machined or cold worked退火目坚硬钢软化便机加工冷作加工
This is usually accomplished by heating the steel too slightly above the critical temperature holding it there until the temperature of the piece is uniform throughout and then cooling at a slowly controlled rate so that the temperature of the surface and that of the center of the piece are approximately the same通常钢加热稍高界温度温度保持工件全部均匀受热然受控速率慢慢冷样工件表面部温度似相
This process is known as full annealing because it wipes out all trace of previous structure refines the crystalline structure and softens the metal Annealing also relieves internal stresses previously set up in the metal程称完全退火前组织结构痕迹细化晶粒软化金属退火释放先前金属中应力
The temperature to which a given steel should be heated in annealing depends on its composition for carbon steels it can be obtained readily from the partial ironiron carbide equilibrium diagram The heating rate should be consistent with the size and uniformity of sections so that the entire part is brought up to temperature as uniformly as possible 定钢退火温度取决成分碳钢言容易局部铁碳合金衡图加热速率应截面尺寸均匀程度相协调样整零件均匀加热需温度
When the annealing temperature has been reached the steel should be held there until it is uniform throughout This usually takes about 45min for each inch(25mm) of thickness of the largest section达退火温度钢应保持温度等全部均匀受热时间般零件截面厚度计英寸(25mm )约需45分钟
For maximum softness and ductility the cooling rate should be very slow such as allowing the parts to cool down with the furnace The higher the carbon content the slower this rate must be柔软性延展性冷速率应该慢零件炉子起冷含碳量越高冷速率必须越慢

Normalizing and Spheroidizing正火球化

The process of normalizing consists of heating the steel about 50℉ to 100℉ (10℃~40℃) above the upper critical range and cooling in still air to room temperature正火处理包括先钢加热高界区50℉100℉(10℃~40℃)然静止空气中冷室温
This process is principally used with low and mediumcarbon steels as well as alloy steels to make the grain structure more uniform to relieve internal stresses or to achieve desired results in physical properties Most commercial steels are normalized after being rolled or cast正火低碳钢中碳钢合金钢晶粒结构更均匀释放应力获需物理特性数商业钢材轧制铸造退火
Spheroidizing is the process of producing a structure in which the cementite is in a spheroidal distribution If steel is heated slowly to a temperature just below the critical range and held there for a prolonged period of time this structure will be obtained 球化渗碳体产生成类似球状分布结构工艺果钢缓慢加热恰低界温度保持较长段时间种组织结构
The globular structure obtained gives improved machinability to the steel This treatment is particularly useful for hypereutectoid steels that must be machined获球状结构改善钢切削性处理方法必须机加工析钢特

Surface Hardening表面硬化

Carburizing渗碳

The oldest known method of producing a hard surface on steel is case hardening or carburizing Iron at temperatures close to and above its critical temperature has an affinity for carbon早硬化钢表面方法表面淬火渗碳铁高界温度时碳具亲合力
The carbon is absorbed into the metal to form a solid solution with iron and converts the outer surface into highcarbon steel The carbon is gradually diffused to the interior of the part The depth of the case depends on the time and temperature of the treatment碳吸收进金属铁形成固溶体外表面转变成高碳钢碳逐渐扩散零件部渗碳层深度取决热处理时间温度
Pack carburizing consists of placing the parts to be treated in a closed container with some carbonaceous material such as charcoal or coke It is a long process and used to produce fairly thick cases of from 003 to 016 in(076~406mm) in depth固体渗碳方法处理零件木炭焦炭含碳材料起放入密闭容器产生深度003016 英寸(076~406mm)厚硬化层较长程

Steel for carburizing is usually a lowcarbon steel of about 015 carbon that would not in itself responds appreciably to heat treatment In the course of the process the outer layer is converted into highcarbon steel with a content ranging from 09 to 12 carbon渗碳般含碳量约015身太适合热处理低碳钢处理程中外层转化含碳量0912高碳钢

A steel with varying carbon content and consequently different critical temperatures requires a special heat treatment 含碳量变化钢具界温度需特殊热处理
Because there is some grain growth in the steel during the prolonged carburizing treatment the work should be heated to the critical temperature of the core and then cooled thus refining the core structure The steel should then be reheated to a point above the transformation range of the case and quenched to produce a hard fine structure较长渗碳程中钢部会晶粒生长工件应该加热核心部分界温度冷细化核心部分组织结构然重新加热高外层转变温度淬火生成坚硬细致组织结构

The lower heattreating temperature of the case results from the fact that hypereutectoid steels are normally austenitized for hardening just above the lower critical point A third tempering treatment may be used to reduce strains恰高低界温度通常析钢奥氏体化硬化外层采较低热处理温度第三次回火处理减少应变

Carbonitriding碳氮渗

Carbonitriding sometimes known as dry cyaniding or nicarbing is a casehardening process in which the steel is held at a temperature above the critical range in a gaseous atmosphere from which it absorbs carbon and nitrogen碳氮渗时称干法氰化渗碳氮化种表面硬化工艺通钢放高界温度气体中吸收碳氮
Any carbonrich gas with ammonia can be used The wearresistant case produced ranges from 0003 to 0030 inch(008~ 076mm) in thickness An advantage of carbonitriding is that the hardenability of the case is significantly increased when nitrogen is added permitting the use of lowcost steels富碳气体加氨气生成厚度00030030英寸(008~ 076mm)耐磨外层碳氮渗优点加入氮外层淬透性极增加低价钢提供条件

Cyaniding氰化

Cyaniding or liquid carbonitriding as it is sometimes called is also a process that combines the absorption of carbon and nitrogen to obtain surface hardness in lowcarbon steels that do not respond to ordinary heat treatment 氰化时称液体碳氮渗种结合吸收碳氮获表面硬度工艺适合通常热处理低碳钢
The part to be case hardened is immersed in a bath of fused sodium cyanide salts at a temperature slightly above the Ac1 range the duration of soaking depending on the depth of the case The part is then quenched in water or oil to obtain a hard surface
需表面硬化零件浸没略高Ac1温度熔化氰化钠盐溶液中浸泡持续时间取决硬化层深度然零件水油中淬火坚硬表面
Case depths of 0005 to 0015in (013~038mm) may be readily obtained by this process Cyaniding is used principally for the treatment of small parts通样处理容易获00050015英寸(013~038mm)硬化深度氰化处理零件

Nitriding渗氮

Nitriding is somewhat similar to ordinary case hardening but it uses a different material and treatment to create the hard surface constituents 渗氮类似普通表面硬化采材料处理方法产生坚硬表面成分
In this process the metal is heated to a temperature of around 950℉(510℃) and held there for a period of time in contact with ammonia gas Nitrogen from the gas is introduced into the steel forming very hard nitrides that are finely dispersed through the surface metal种工艺中金属加热约950℉(510℃)然氨气接触段时间氨气中氮进入钢形成细微分布金属表面十分坚固氮化物

Nitrogen has greater hardening ability with certain elements than with others hence special nitriding alloy steels have been developed 氮某元素硬化力元素开发专渗氮合金钢
Aluminum in the range of 1 to 15 has proved to be especially suitable in steel in that it combines with the gas to form a very stable and hard constituent The temperature of heating ranges from 925℉ to 1050℉(495℃~565℃)钢中含铝115证明特合适氨气结合形成稳定坚固成分加热温度范围925℉1050℉ (495℃~565℃)

Liquid nitriding utilizes molten cyanide salts and as in gas nitriding the temperature is held below the transformation range Liquid nitriding adds more nitrogen and less carbon than either cyaniding or carburizing in cyanide baths 液体渗氮利熔化氰化物盐气体渗氮温度保持低转化范围液体渗氮时氰化物溶液中加入氰化渗碳较氮较少碳
Case thickness of 0001 to 0012in(003~030mm) is obtained whereas for gas nitriding the case may be as thick as 0025 in(064mm) In general the uses of the twonitriding processes are similar液体渗氮获厚度00010012英寸 (003~030mm)硬化层然气体渗氮获厚0025英寸(064mm)硬化层般言两种渗氮方法途类似

Nitriding develops extreme hardness in the surface of steel This hardness ranges from 900 to 1100 Brinell which is considerably higher than that obtained by ordinary case hardening 渗氮钢表面获远远超出正常标准硬度硬度范围9001100布氏硬度远高普通表面硬化获硬度
Nitriding steels by virtue of their alloying content are stronger than ordinary steels and respond readily to heat treatment It is recommended that these steels be machined and heattreated before nitriding because there is no scale or further work necessary after this process 渗氮钢合金例普通钢更强容易热处理建议种钢渗氮前先机加工热处理渗氮没剥落需更加工
Fortunately the interior structure and properties are not affected appreciably by the nitriding treatment and because no quenching is necessary there is little tendency to warp develop cracks or change condition in any way The surface effectively resists corrosive action of water saltwater spray alkalies crude oil and natural gas值庆幸渗氮处理点影响部结构性需淬火没产生翘曲裂缝变化条件趋势种表面效抵御水盐雾碱原油天然气腐蚀反应



UNIT 3 Casting Processes

Casting is a manufacturing process in which molten metal is poured or injected and allowed to solidify in a suitably shaped mold cavity During or after cooling the cast part is removed from the mold and then processed for delivery铸造种熔化金属倒入注入合适铸模腔中固化制造工艺冷期间冷铸件铸模中取出然加工交付
Casting processes and castmaterial technologies vary from simple to highly complex Material and process selection depends on the part’s complexity and function the product’s quality specifications and the projected cost level铸造工艺铸造材料技术简单高度复杂变化材料工艺选择取决零件复杂性功产品质量求成预算水
Castings are parts that are made close to their final dimensions by a casting process With a history dating back 6000 years the various casting processes are in a state of continuous refinement and evolution as technological advances are being made通铸造加工铸件做成接终尺寸回溯6000年历史种样铸造工艺直处着科技进步断改进发展状态

Sand Casting 砂型铸造

Sand casting is used to make large parts (typically iron but also bronze brass aluminum) Molten metal is poured into a mold cavity formed out of sand (natural or synthetic) 砂型铸造制造型零件(具代表性铁外青铜黄铜铝)熔化金属倒入型砂(天然造)做成铸模腔
The processes of sand casting are discussed in this section including patterns sprues and runners design considerations and casting allowance节讨砂型铸造工艺包括型模浇注口浇道设计考虑素铸造余量

The cavity in the sand is formed by using a pattern (an approximate duplicate of the real part) which are typically made out of wood sometimes metal The cavity is contained in an aggregate housed in a box called the flask 砂型里型腔采型模(真实零件似复制品)形成型模般木制时金属制造型腔整包含置称砂箱箱子里聚合体
Core is a sand shape inserted into the mold to produce the internal features of the part such as holes or internal passages Cores are placed in the cavity to form holes of the desired shapes Core print is the region added to the pattern core or mold that is used to locate and support the core within the mold 砂芯插入铸模砂型生成诸孔通道类部特征砂芯安放型腔里形成需形状孔洞砂芯座加型模砂芯铸模特定区域铸模部定位支撑砂芯
A riser is an extra void created in the mold to contain excessive molten material The purpose of this is to feed the molten metal to the mold cavity as the molten metal solidifies and shrinks and thereby prevents voids in the main casting口铸模部增加额外空间容纳量熔化金属目熔化金属凝固收缩时型腔里补充熔化金属防止铸件中产生孔隙

In a twopart mold which is typical of sand castings the upper half including the top half of the pattern flask and core is called cope and the lower half is called drag as shown in Fig31 The parting line or the parting surface is line or surface that separates the cope and drag 典型砂型铸造双层铸模中半部分(包括型模砂箱砂芯半部分)称型箱半部分称型箱见图31示分型线分型面分离型箱线面
The drag is first filled partially with sand and the core print the cores and the gating system are placed near the parting line The cope is then assembled to the drag and the sand is poured on the cope half covering the pattern core and the gating system首先型箱里部分填入型砂分型线处放置砂芯座砂芯浇注系统然型箱型箱装配起型砂倒入型箱盖住型模砂芯浇注系统
The sand is compacted by vibration and mechanical means Next the cope is removed from the drag and the pattern is carefully removed The object is to remove the pattern without breaking the mold cavity 型砂通振动机械方法压实接型箱撤掉型箱心翼翼取出型模目取出型模破坏型腔
This is facilitated by designing a draft a slight angular offset from the vertical to the vertical surfaces of the pattern This is usually a minimum of 15mm(0060in) whichever is greater The rougher the surface of the pattern the more the draft to be provided通设计拔模斜度—型模垂直相交表面微角度偏移量—取出型模变容易拔模斜度般15mm(0060in)型模表面越粗糙拔模斜度应越

The molten material is poured into the pouring cup which is part of the gating system that supplies the molten material to the mold cavity 熔化金属浇注杯注入型腔浇注杯浇注系统型腔提供熔化金属部分
The vertical part of the gating system connected to the pouring cup is the sprue and the horizontal portion is called the runners and finally to the multiple points where it is introduced to the mold cavity called the gates 浇注系统垂直部分浇注杯连接浇注口浇注系统水部分称浇道点熔化金属导入型腔称闸道
Additionally there are extensions to the gating system called vents that provide the path for the builtup gases and the displaced air to vent to the atmosphere外称排放口浇注系统延长段合成气体置换空气排放气提供通道

The cavity is usually made oversize to allow for the metal contraction as it cools down to room temperature This is achieved by making the pattern oversize To account for shrinking the pattern must be made oversize by these factors on the average These are linear factors and apply in each direction 型腔通常需尺寸允许金属冷室温时收缩通型模做需尺寸达解决收缩效应般言型模做需尺寸必须考虑线性素作方
These shrinkage allowances are only approximate because the exact allowance is determined by the shape and size of the casting In addition different parts of the casting might require different shrinkage allowances 收缩余量仅仅似准确余量铸件形状尺寸决定外铸件部分需收缩余量
Sand castings generally have a rough surface sometimes with surface impurities and surface variations A machining (finish) allowance is made for this type of defect砂型铸件般表面粗糙时带表面杂质表面变异采机加工(终)余量解决类缺陷

In general typical stages of sand casting operation include (as shown in Fig32) 般言砂型铸造作业典型阶段包括(图32示)：
1 Patterns are made These will be the shape used to form the cavity in the sand1 制作型模做成型砂中形成型腔形状
2 Cores may also be made at this time These cores are made of bonded sand that will be broken out of the cast part after it is complete 2 时制作砂芯砂芯粘结砂做成等铸件完成碎取出
3 Sand is mulled (mixed) thoroughly with additives such as bentonite to increase bonding and overall strength3 型砂膨润土类添加剂充分混合增强连接整体强度
4 Sand is formed about the patterns and gates runners risers vents and pouring cups are added as needed A compaction stage is typically used to ensure good coverage and solid molds 4 型砂型模周围成形根需安放闸道浇道口排放口浇注杯等通常采取压紧步骤保证良覆盖坚固铸模
Cores may also be added to make concave or internal features for the cast part Alignment pins may also be used for mating the molds later Chills may be added to cool large masses faster安放砂芯制成铸件凹形结构部特征铸模匹配定位销质量铸件需加冷物较快冷
5 The patterns are removed and the molds may be put through a baking stage to increase strength 5 取出型模铸模烘焙增加强度
6 Mold halves are mated and prepared for pouring metal6 匹配铸模做浇铸金属准备
7 Metal is preheated in a furnace or crucible until is above the liquidus temperature in a suitable range (we don’t want the metal solidifying before the pour is complete) The exact temperature may be closely controlled depending upon the application7 金属熔炉坩埚中预热高液化温度合适范围(希金属浇铸完成前凝固)确切温度根应场合严格控制
Degassing and other treatment processes may be done at this time such as removal of impurities (ie slag) Some portion of this metal may be remelted scrap from previously cast parts—10 is reasonable期间进行排气处理步骤例杂质(熔渣)加入定量原先种金属铸件废料熔化—10适
8 The metal is poured slowly but continuously into the mold until the mold is full 8 金属缓慢连续注满铸模
9 As the molten metal cools (minutes to days) the metal will shrink and the volume will decrease During this time molten metal may backflow from the molten risers to feed the part and maintain the same shape9 着熔化金属冷(分钟天)金属收缩体积减期间熔化金属口回流供零件保持形状变
10 Once the part starts to solidify small dendrites of solid material form in the part During this time metal properties are being determined and internal stresses are being generated If a part is allowed to cool slowly enough at a constant rate then the final part will be relatively homogenous and stress free10 旦零件开始凝固部形成固态金属型树枝状结晶期间金属性确定时产生应力果零件恒定速率冷足够缓慢终零件相均质释放应力
11 Once the part has completely solidified below the eutectic point it may be removed with no concern for final metal properties At this point the sand is simply broken up and the part removed At this point the surface will have a quantity of sand adhering to the surface and solid cores inside11 旦零件晶点完全凝固必担心金属性取出时简单碎砂型取出零件零件表面会量型砂粘附着部实心砂芯
12 A bulk of the remaining sand and cores can be removed by mechanically striking the part Other options are to use a vibrating table sandshot blaster hand labor etc12量剩余型砂砂芯通机械敲击零件选择采振动台喷砂喷丸机手工作业等等
13 The final part is cut off the runner gate system and is near final shape using cutters torches etc Grinding operations are used to remove any remaining bulk 13 零件刀具喷枪等切掉浇道闸道系统样接终形状磨削作业余部分
14 The part is taken down to final shape using machining operations And cleaning operations may be used to remove oxides etc14 通机加工零件切削终形状清洗作业氧化物等

Investment casting熔模铸造
Investment casting is also known as the lost wax process This process is one of the oldest manufacturing processes The Egyptians used it in the time of the Pharaohs to make gold jewelry (hence the name Investment) some 5000 years ago熔模铸造称失蜡加工古老制造工艺约5000年前法老王时代埃制造黄金饰品(名投资)
Intricate shapes can be made with high accuracy In addition metals that are hard to machine or fabricate are good candidates for this process It can be used to make parts that cannot be produced by normal manufacturing techniques such as turbine blades that have complex shapes or airplane parts that have to withstand high temperatures高精度制造复杂形状外较难机加工制作金属工艺生产般制造技术法生产零件例复杂形状涡轮叶片必须耐住高温飞机零件

The mold is made by making a pattern using wax or some other material that can be melted away This wax pattern is dipped in refractory slurry which coats the wax pattern and forms a skin This is dried and the process of dipping in the slurry and drying is repeated until a robust thickness is achieved 制作铸模型模采石蜡融化掉材料做成石蜡型模浸泡耐热浆里覆盖型模形成外壳然变干重复浸泡变干程直获足够厚度
After this the entire pattern is placed in an oven and the wax is melted away This leads to a mold that can be filled with the molten metal Because the mold is formed around a onepiece pattern (which does not have to be pulled out from the mold as in a traditional sand casting process) very intricate parts and undercuts can be made 完成整型模放烤箱里融化石蜡样做成填充熔化金属铸模种铸模环绕整块型模形成(需传统砂型铸造工艺样拔模)制作十分复杂零件浮雕
The wax pattern itself is made by duplicating using a stereo lithography or similar model—which has been fabricated using a computer solid model master石蜡型模身立体制版类似模型复制—采计算机立体模型原版制作

The materials used for the slurry are a mixture of plaster a binder and powdered silica a refractory for low temperature melts For higher temperature melts sillimanite or aluminasilicate is used as a refractory and silica is used as a binder较低熔化温度言耐热浆材料石膏作粘合剂粉末状硅石作耐温材料混合物较高熔化温度言采硅线石氧化铝硅酸盐作耐温材料水硅酸作粘合剂
Depending on the fineness of the finish desired additional coatings of sillimanite and ethyl silicate may be applied The mold thus produced can be used directly for light castings or be reinforced by placing it in a larger container and reinforcing it more slurry根需光洁度采硅线石乙烷基硅酸盐样生成铸模直接薄壁铸件通放较容器更耐热浆加强

Just before the pour the mold is preheated to about 1000℃(1832℉) to remove any residues of wax harden the binder The pour in the preheated mold also ensures that the mold will fill completely 浇铸前铸模预热约1000℃(1832℉)剩余石蜡硬化粘合剂预热铸模中浇铸保证铸模完全充满
Pouring can be done using gravity pressure or vacuum conditions Attention must be paid to mold permeability when using pressure to allow the air to escape as the pour is done浇铸采重力压力真空条件实现压力时必须注意渗透性便浇铸时空气逸出

Tolerances of 05 of length are routinely possible and as low as 015 is possible for small dimensions Castings can weigh from a few grams to 35kg (01oz to 80lb) although the normal size ranges from 200g to about 8kg(7oz to 15 lb) Normal minimum wall thicknesses are about 1mm to about 05mm(0040~ 0020 in) for alloys that can be cast easily般公差长度05尺寸低015然通常尺寸铸件重量范围200g约8kg(7oz15lb)实际克35kg (01oz to 80lb)容易铸造合金言通常壁厚约1mm05mm(0040~ 0020 in)

The types of materials that can be cast are aluminum alloys bronzes tool steels stainless steels stellite hastelloys and precious metals Parts made with investment castings often do not require any further machining because of the close tolerances that can be achieved铸造材料类型：铝合金青铜工具钢锈钢钨铬钴合金镍基合金贵金属采熔模铸造零件常常需进步加工熔模铸造达精密公差

Centrifugal Casting离心铸造

Centrifugal casting (Fig33) as a category includes centrifugal casting semicentrifugal casting and centrifuging In centrifugal casting a permanent mold is rotated about its axis at high speeds (300 to 3000rpm) as the molten metal is poured 离心铸造(图33)作种类包括离心铸造半离心铸造离心加压铸造离心铸造中永久性铸模熔化金属浇铸时较高速度(3003000rpm)绕轴线旋转
The molten metal is centrifugally thrown towards the inside mold wall where it solidifies after cooling The casting is usually a fine grain casting with a very finegrained outer diameter which is resistant to atmospheric corrosion a typical situation with pipes The inside diameter has more impurities and inclusions which can be machined away受离心力作熔化金属抛铸模壁里冷固化种铸件通常外径处晶粒非常细细晶粒铸件耐气腐蚀典型情况子径处较杂质含物机加工

Only cylindrical shapes can be produced with this process Size limits are up to 3m(10feet) diameter and 15m(50 feet) length Wall thickness can be 25mm to 125mm(01~50in) The tolerances that can be held on the OD can be as good as 25mm (01in) and on the ID can be 38mm(015in) The surface finish ranges from 25mm to 125mm(01~05in) rms(rootmeansquare)圆柱形工艺生产尺寸限制直径3m(10feet)长度15m(50feet)壁厚25mm125mm(01~50in)外径公差保持25mm(01in)径公差保持38mm(015in)表面粗糙度 效值( 均方根)范围25mm125mm(01~05in)

Typical materials that can be cast with this process are iron steel stainless steels and alloys of aluminum copper and nickel Two materials can be cast by introducing a second material during the process Typical parts made by this process are pipes boilers pressure vessels flywheels cylinder liners and other parts that are axissymmetric工艺铸造典型材料：铁钢锈钢铝铜镍合金通生产程中加入第二种材料进行两种材料铸造采种工艺制造典型零件：子锅炉压力容器飞轮汽缸衬垫轴称零件
Semicentrifugal casting The molds used can be permanent or expendable can be stacked as necessary The rotational speeds are lower than those used in centrifugal casting 半离心铸造：铸模永久性消耗性根需叠加旋转速度离心铸造低
The center axis of the part has inclusion defects as well as porosity and thus is suitable only for parts where this can be machined away This process is used for making wheels nozzles and similar parts where the axis of the part is removed by subsequent machining
零件中心轴附存缺陷孔隙仅适机加工零件种工艺制造车轮嘴类似机加工中心轴部分零件
Centrifuging Centrifuging is used for forcing metal from a central axis of the equipment into individual mold cavities that are placed on the circumference This provides a means of increasing the filling pressure within each mold and allows for reproduction of intricate details This method is often used for the pouring of investment casting pattern离心加压铸造：离心加压铸造迫金属设备中心轴进入分布圆周单独铸模型腔铸模提供种增加填充压力方法允许现复杂细节种方法常浇铸熔模铸造型模
Fullmold casting is a technique similar to investment casting but instead of wax as the expendable material polystyrene foam is used as the pattern The foam pattern is coated with a refractory material The pattern is encased in a onepiece sand mold As the metal is poured the foam vaporizes and the metal takes its place 实型铸造熔模铸造类似技术做型模消耗材料聚苯乙烯泡沫石蜡泡沫型模难熔材料覆盖型模装入整体砂模中金属浇入时泡沫材料蒸发金属取代位置
This can make complex shaped castings without any draft or flash However the pattern cost can be high due to the expendable nature of the pattern Minimum wall thicknesses are 25mm tolerances can be held to 03 on dimensions Surface finish can be held from 25μm to 25μm(01μin to 10μin) rms(rootmeansquare) 制造没拔模斜度缝脊复杂形状铸件然型模消耗特性型模成较高壁厚25mm 公差保持尺寸03 表面粗糙度效值( 均方根) 保持25μm 25μm(01μin 10μin)间
Size limits are from 400g(1lb) to several tons No draft allowance is required Typical materials that can be cast with this process are aluminum iron steel nickel alloys copper alloys Types of parts that can be made using these processes are pump housings manifolds and auto brake components重量限制400g(1lb)数吨需留拔模余量种工艺典型材料：铝铁钢镍合金铜合金采工艺制造零件类型泵壳复式接头动刹车零件



UNIT 4 Forging Processes

Introduction引言

Forging is an important hotforming process It is used in producing components of all shapes and sizes from quite small items to large units weighing several tons锻造种重热成型工艺生产种形状尺寸重量数吨零件

Forging is the process by which metal is heated and is shaped by plastic deformation by suitably applying compressive force Usually the compressive force is in the form of hammer blows using a power hammer or a press as shown in Fig41锻造程中先金属加热然施加合适压力塑性变形通常压力图41示动力锤压力机提供锤击形式出现

Hand forging tools comprise variously shaped hammers The base on which the work is supported during forging is the anvil手工锻造工具包括种形状锤子锻造中支撑工件基础铁砧

For the semimechanized forging of small to mediumsized components forging hammers powered by various means are employed The feature common to all of them is that like the hand forging hammer they utilize the energy of a falling weight to develop the pressure needed for shaping the metal 中等尺寸零件半机械化锻造言锻锤采种动力般特性言象手工锻锤样均利落重量产生金属成型需压力
Larger components are forged by means of forging presses operated by steam or compressed air or by hydraulic or electric power Largely automatic forging machines are used for the quantity production of engineering parts锻造零件蒸汽压缩空气液力电力驱动锻压机型动化锻机工程零件批量生产

A distinction may be made between opendie forging usually in the form of hammer forging and closeddie forging In hammer forging the component is shaped by hammer blows aided by relatively simple tools These may include open dies ie dies that do not completely enclose the metal to be shaped 锤锻中常开式模锻闭式模锻区锤锻中零件通锤击辅相简单工具成型中包括开式锻模完全封闭成型金属模具
One of the basic operations of hammer forging is the elongation of a piece of metal by stretching with hammer blows causing it to become thinner and longer In hand forging the workpiece is usually turned 90° after each blow in order to forge it thoroughly and prevent its lateral expansion 锤锻基操作通锤击金属伸长促变细变长手工锻造时般次锤击转90°充分锻工件防止横膨胀
The opposite of elongation is upsetting which produces compressive shortening For example the diameter of a bar can be increased by heating and hammering axially伸长相反镦粗产生压缩性缩短例棒料直径通加热轴锤击增

More important is closeddie forging very widely used for mass production in industry in which the metal is shaped by pressing between a pair of forging dies The upper die is usually attached to the ram of a forging press or a forging hammer while the lower die is stationary 更重闭式模锻工业广泛规模生产闭式模锻中金属锻模间挤压成型顶模通常附锻压机撞头锻锤底模固定
Together they form a closed die Closeddie forging can produce components of greater complexity and accuracy with a better surface finish than the more traditional methods not using closed dies The dies are made of special heatresistant and wearresistant tool steels两者合起形成闭式锻模闭式模锻生产高度复杂精确零件表面光洁度闭式锻模更传统方法闭式锻模采特殊耐热耐磨工具钢制成
A piece of hot metal sufficient to slightly overfill the die shape is placed in the bottom die and the top die is forced against it so that the metal takes the internal shape of the die 块足充填模腔稍溢出加热金属放入底模顶模加压合拢块金属便获该模腔形状
Closeddie forging is used for the rapid production of large numbers of fairly small parts and also for very large components For the latter eg modern jetaircraft components giant hydraulically operated presses are used which can develop forces of 50000 tons and more闭式模锻相零件批量快速生产零件者言例现代喷气飞机零件产生50000吨压力巨型液力锻压机

One valuable feature of forging is that it improves the strength of the metal by refining the structure and making it uniform so for heavy forgings such as marine propeller shafts an immensely powerful hydraulic press squeezes the metal with a force sometimes as great as 10000 tonnes 锻造价值特性通金属组织均匀改善强度诸船舶螺旋桨轴类重型锻件达10000吨压力庞力液压机挤压金属
Although the hydraulic forging press is a more expensive piece of equipment than a dropforge it has advantages beside those of giving greater strength and more uniform structure to large components On account of the high pressure and squeezing action it operates with less noise and vibration than a dropforge 然种液压锻机落锤锻造昂贵予零件较高强度更均匀组织外优点较高压力挤压作落锤锻造噪声振动
As ingots of steel weighing 30 tonnes or more are forged in this way manual operation is impossible and it is essential that all the manipulation of the ingot is done mechanically种情况锻钢坯重量30吨工操作钢坯操作必须机械化

Forging refines the grain structure and improves physical properties of the metal With proper design the grain flow can be oriented in the direction of principal stresses encountered in actual use 锻造细化金属晶粒组织改善物理性通适设计晶粒流动方实际时应力方致
As shown in Fig42 grain flow is the direction of the pattern that the crystals take during plastic deformation Physical properties (such as strength ductility and toughness) are much better in a forging than in the base metal which has crystals randomly oriented图42示晶粒流动方塑性变形期间结晶排列方锻件物理性(强度延展性韧性)远基础金属基础金属晶粒序排列

Forgings are consistent from piece to piece without any of the porosity voids inclusions and other defects Thus finishing operations such as machining do not expose voids because there aren’t any Also coating operations such as plating or painting are straightforward due to a good surface which needs very little preparation锻件部分连贯致没孔隙空洞杂质缺陷机加工类精加工工序会受空洞影响根存外锻件良表面电镀油漆类涂装工序简单需做准备工作

Forgings yield parts that have high strength to weight ratio thus are often used in the design of aircraft frame members 锻造生产零件具较高强度重量常飞机结构零件设计中
A forged metal can result in the following锻造金属导致列结果：
• Increase length decrease crosssection called drawing out the metal ●增加长度减横截面称延伸金属
• Decrease length increase crosssection called upsetting the metal ●减长度增加横截面称镦粗金属
• Change length change crosssection by squeezing in closed impression dies ●通封闭锻模挤压改变长度横截面
This results in favorable grain flow for strong parts导致利晶粒流零件坚固

Common Forging Processes常锻造工艺

The metal can be forged hot (above recrystallization temperatures) or cold金属热锻(高结晶温度)冷锻
Open die forgingsHand forgings Open die forgings or hand forgings are made with repeated blows in an open die where the operator manipulates the workpiece in the die The finished product is a rough approximation of the die This is what a traditional blacksmith does and is an old manufacturing process开式模锻手工锻：开式模锻手工锻操作者操工件开式锻模中反复击完成产品锻模粗糙似物传统铁匠干活较古老制造工艺
Impression die forgingsPrecision forgings Impression die forgings and precision forgings are further refinements of the blocker forgings The finished part more closely resembles the die impression压模锻精密锻：压模锻精密锻雏形模锻进步改进完成零件模膛更相似
Press forgings Press forgings use a slow squeezing action of a press to transfer a great amount of compressive force to the workpiece Unlike an opendie forging where multiple blows transfer the compressive energy to the outside of the product press forging transfers the force uniformly to the bulk of the material 压锻：压锻通压力机缓慢挤压动作巨压力传递工件开式模锻样需次击压缩量传递零件外表面压锻力均匀传递材料体
This results in uniform material properties and is necessary for large weight forgings Parts made with this process can be quite large as much as 125kg(260lb) and 3m(10 feet) long导致材料性致重量锻件言十分必采工艺生产零件重量达125kg(260lb)长度达3m(10feet)
Upset forgings Upset forging increases crosssection by compressing the length this is used in making heads on bolts and fasteners valves and other similar parts顶锻：顶锻通压缩长度增加横截面螺栓等紧固件柱塞类似零件制造头部
Roll forgings In roll forging a bar stock round or flat is placed between die rollers which reduces the crosssection and increases the length to form parts such as axles leaf springs etc This is an essential form of draw forging滚锻：滚锻时圆扁棒料放模辊间缩横截面增加长度制成诸轮轴板簧类零件轧锻基形式
Swaging Swaging—a tube or rod is forced inside a die and the diameter is reduced as the cylindrical object is fed The die hammers the diameter and causes the metal to flow inward causing the outer diameter of the tube or the rod to take the shape of the die型锻：型锻—圆圆棒强制压入锻模着圆柱形物体压入直径减锻模锤击直径金属流动导致圆圆棒外径变锻模形状
Net shapeNearnet shape forging In net shape or nearnet shape forging forging results in wastage of material in the form of material flash and subsequent machining operations as shown in Fig43 This wastage can be as high as 70 for gear blanks and even 90 in the case of aircraft structural parts 纯型似纯型锻：采纯型锻似纯型锻产生材料损耗形式飞边机加工图43示齿轮毛坯材料损耗70 飞机结构零件材料损耗甚达90
Netshape and nearnetshape processes minimize the waste by making precision dies producing parts with very little draft angle (less than 1°) These types of processes often eliminate or reduce machining 纯型锻似纯型锻工艺通制作精密模具生产拔模斜角(1°)零件材料损耗化类工艺通常省减少机加工
The processes are quite expensive in terms of tooling and the capital expenditure required Thus these processes can be only justified for current processes that are very wasteful where the material savings will pay for the significant increase in tooling costs加工角度言工艺相昂贵需资金投入工艺目前浪费生产程材料节约足补偿加工成明显增加时合理

Die Design Consideration锻模设计考虑素
• Parting surface should be along a single plane if possible else following the contour of the part The parting surface should be through the center of the part not near the upper or lower edges 果分模面应着单面着零件轮廓分模面应零件中心边缘
If the parting line cannot be on a single plane then it is good practice to use symmetry of the design to minimize the side thrust forces Any point on the parting surface should be less than 75° from the principal parting plane果分模线单面利设计称性减侧推力失种方法分模面意点分模面夹角应75°
• As in most forming processes use of undercuts should be avoided as these will make the removal of the part difficult if not impossible数成型工艺果非量避免采凹槽凹槽会零件难取出
• Generous fillets and radius should be provided to aid in material flow during the forging process Sharp corners are stressrisers in the forgings as well as make the dies weak in service 应提供倒角半径帮助材料锻造程中流动锐角会增加锻件中应力时时削弱锻模
• Ribs should not be high or narrow this makes it difficult for the material to flow加劲肋高窄会造成材料流动困难

Tolerances公差
• Dimension tolerances are usually positive and are approximately 03 of the dimension rounded off to the next higher 05mm(0020in)尺寸公差通常正约取该尺寸03圆整较05mm(0020in)
• Die wear tolerances are lateral tolerances (parallel to the parting plane) and are roughly +02 for copper alloys to +05 for aluminum and steel锻模磨损公差侧公差(行分模面)铜合金约+02 铝钢约+05
• Die closure tolerances are in the direction of opening and closing and range from 1mm(0040in) for small forgings die projection area＜150cm2(23in2) to 625mm(025in) for large forgings die projection area＞6500cm2(100in2)锻模闭合公差处开闭方范围较锻件[投影面积＜150cm2(23in2)]取1mm(0040in)较锻件[投影面积＞6500cm2(100in2)]取625mm(025in)
• Die match tolerances are to allow for shift in the upper die with respect to the lower die锻模配合公差允许模根模换
A proper lubricant is necessary for making good forgings The lubricant is useful in preventing sticking of the workpiece to the die and also acts as a thermal insulator to help reduce die wear制造良锻件必须合适润滑剂润滑剂防止工件粘住锻模作绝热体帮助减少锻模磨损



UNIT 5 Powder Metallurgy

Powder metallurgy(Fig51) uses sintering process for making various parts out of metal powder The metal powder is compacted by placing in a closed metal cavity (the die) under pressure粉末冶金(图51)采烧结工艺金属粉末制成种样零件金属粉末放封闭金属腔(模具)中压力压实
This compacted material is placed in an oven and sintered in a controlled atmosphere at high temperatures and the metal powders coalesce and form a solid A Second pressing operation repressing can be done prior to sintering to improve the compaction and the material properties压实材料置炉气压受控高温烧结金属粉末熔合形成固体烧结前进行二次挤压作业(挤压)改善压实状态材料性

Powder metallurgy is a highly developed method of manufacturing reliable ferrous and nonferrous parts Made by mixing elemental or alloy powders and compacting the mixture in a die the resultant shapes are then sintered or heated in a controlled atmosphere furnace粉末冶金种高度发达制造铁非铁零件方法通混合元素合金粉末模具中压实混合物烧结气压受控炉加热制成终形状

Material材料

The majority of the structural components produced by fixed die pressing are ironbased The powders are elemental prealloyed or partially alloyed数固定模压制结构件铁基粉末单元素预先合金部分合金
Elemental powders such as iron and copper are easy to compress to relatively high densities produce pressed compacts with adequate strength for handling during sintering but do not produce very high strength sintered parts诸铁铜类单元素粉末较容易压相密度较高生产具备足够强度压制物供烧结处理法制造出高强度烧结零件

Prealloyed powders are harder less compressible and hence require higher pressing loads to produce high density compacts However they are capable of producing high strength sintered materials预先合金粉末较硬容易压实需较高挤压力产生高密度压制物然生成高强度烧结材料

Prealloying is also used when the production of a homogeneous material from elemental powders requires very high temperatures and long sintering times The best examples are the stainless steels whose chromium and nickel contents have to be prealloyed to allow economic production by powder metallurgy果单元素粉末生产均匀材料需高温度较长烧结时间预先合金例子锈钢含铬镍成分粉末冶金必须预先合金济

Partially alloyed powders are a compromise approach Elemental powders eg iron with 2wt copper are mixed to produce an homogeneous blend which is then partially sintered to attach the copper particles to the iron particles without producing a fully diffused powder but retaining the powder form 部分合金粉末种折衷方法单元素粉末例铁2铜(重量百分) 混合均匀部分烧结铜微粒粘附铁微粒没产生充分扩散粉末保留粉末形态
In this way the compressibilities of the separate powders in the blend are maintained and the blend will not segregate during transportation and use
种方法混合物中单独粉末压缩性维持运送期间结合会分离

A similar technique is to glue the small percentage of alloying element onto the iron powder This glueing technique is successfully used to introduce carbon into the blends a technique which prevents carbon segregation and dusting producing socalled clean powders种类似技术百分合金元素粘合铁微粒种粘合技术已成功碳引入结合物种防止碳分离起尘技术生产谓清洁粉末

Powder Consolidation粉末合成

Components or articles are produced by forming a mass of powder into a shape then consolidating to form interparticle metallurgical bonds通量粉末放入模具成型零件物品然合成含微粒冶金结合物
An elevated temperature diffusion process referred to as sintering sometimes assisted by external pressure accomplishes this The material is never fully molten although there might be a small volume fraction of liquid present during the sintering process Sintering can be regarded as welding the particles present in the initial useful shape提升温度扩散工艺称烧结时辅外界压力达目然烧结程中会少量液态出现材料决全熔化烧结作微粒焊接成初始形状

As a general rule both mechanical and physical properties improve with increasing density Therefore the method selected for the fabrication of a component by powder metallurgy will depend on the level of performance required from the part Many components are adequate when produced at 85~90 of theoretical full density whist others require full density for satisfactory performance作普遍规律着密度增加机械物理性均改善选择种粉末冶金方法制作零件取决需性级许零件需理全密度85~90需全密度满足求

Some components in particular bush type bearings often made from copper and its alloys are produced with significant and controlled levels of porosity the porosity being subsequently filled with a lubricant 零件尤衬套式轴承常铜合金制作控制孔性程度意义重孔填充润滑剂
Fortunately there is a wide choice of consolidation techniques available种合成技术供选择

Cold Uniaxial Pressing冷单挤压

Elemental metal or an atomized prealloyed powder is mixed with a lubricant typically lithium stearate(075 wt) and pressed at pressures of say 600MPa (87000lbin2) in metal dies 单元素金属极颗粒预先合金粉末润滑剂(般锂硬脂酸盐重量百分075)混合然金属模具中施加压力[600MPa (87000lbin2)]挤压
Cold compaction ensures that the ascompacted or green component is dimensionally very accurate as it is moulded precisely to the size and shape of the die冷挤压保证压制未加工零件尺寸十分精确精确模具尺寸形状成型

One disadvantage of this technique is the differences in pressed density that can occur in different parts of the component due to particleparticle and die wallparticle frictional effects Typical aspressed densities for soft iron components would be 70gcc i e about 90 of theoretical density 种技术缺点微粒微粒模壁微粒间摩擦效应零件部位压实密度存差异典型软铁零件压制密度70gcc约理密度90
Compaction pressure rises significantly if higher aspressed densities are required and this practice becomes uneconomic due to higher costs for the larger presses and stronger tools to withstand the higher pressures果需较高压实密度压实压力显著提高型压力机成较高较高压力模具强度更高样合算

Cold Isostatic Pressing冷均衡挤压

Metal powders are contained in an enclosure eg a rubber membrane or a metallic can that is subjected to isostatic which is uniform in all directions external pressure As the pressure is isostatic the aspressed component is of uniform density金属粉末装入均衡受压橡胶膜金属罐受外压力方均匀压力均衡压制零件密度均匀
Irregularly shaped powder particles must be used to provide adequate green strength in the aspressed component This will then be sintered in a suitable atmosphere to yield the required product必须采规形状粉末微粒压制零件提供足够未加工强度然合适气压中烧结成需产品

Normally this technique is only used for semifabricated products such as bars billets sheet and roughly shaped components all of which require considerable secondary operations to produce the final accurately dimensioned component 通常种技术制作诸棒料坯段薄板粗糙成型零件类半成品需量进步加工生产出终尺寸精确零件
Again at economical working pressures products are not fully dense and usually need additional working such as hot extrusion hot rolling or forging to fully density the material外济工作压力产品充分致密般需增加诸热挤压热轧锻类额外工序材料达充分致密

Sintering烧结

Sintering is the process whereby powder compacts are heated so that adjacent particles fuse together thus resulting in a solid article with improved mechanical strength compared to the powder compact 烧结通粉末压制物加热邻微粒熔合起工艺生成粉末压制物机械强度更固体物
This fusing of particles results in an increase in the density of the part and hence the process is sometimes called densification There are some processes such as hot isostatic pressing which combine the compaction and sintering processes into a single step微粒熔合导致零件密度增加该工艺时称致密化工艺热均衡挤压压实烧结工艺合单步骤

After compaction the components pass through a sintering furnace This typically has two heating zones the first removes the lubricant and the second higher temperature zone allows diffusion and bonding between powder particles零件压实通烧结炉通常两加热区第润滑剂第二温度更高区域粉末微粒间扩散结合
A range of atmospheres including vacuum are used to sinter different materials depending on their chemical compositions As an example precise atmosphere control allows ironcarbon materials to be produced with specific carbon compositions and mechanical properties根材料化学成分烧结气压范围(包括真空)相例精确气压控制生产具特殊碳化物机械性铁碳材料

The density of the component can also change during sintering depending on the materials and the sintering temperature These dimensional changes can be controlled by an understanding and control of the pressing and sintering parameters根材料烧结温度零件密度烧结程中改变尺寸变化通解调节挤压烧结参数进行控制
and components can be produced with dimensions that need little or no rectification to meet the dimensional tolerances Note that in many cases all of the powder used is present in the finished product scrap losses will only occur when secondary machining operations are necessary
零件尺寸需校正满足尺寸公差注意情况粉末存制成品中废料损失仅产生需辅助机加工时

Hot Isostatic Pressing热均衡挤压

Powders are usually encapsulated in a metallic container but sometimes in glass The container is evacuated the powder outgassed to avoid contamination of the materials by any residual gas during the consolidation stage and sealedoff 粉末通常封装金属容器时装玻璃容器容器抽真空粉末抽气防止材料合成阶段密封时残留气体污染
It is then heated and subjected to isostatic pressure sufficient to plastically deform both the container and the powder加热施加均衡压力足容器粉末塑性变形

The rate of densification of the powder depends upon the yield strength of the powder at the temperatures and pressures chosen At moderate temperature the yield strength of the powder can still be high and require high pressure to produce densification in an economic time粉末致密率取决该粉末选定温度压力屈服强度中等温度粉末屈服强度然较高需较高压力济时间致密化
Typical values might be 1120℃ and 100MPa for ferrous alloys By pressing at very much higher temperatures lower pressures are required as the yield strength of the material is lower Using a glass enclosure atmospheric pressure(15psi) is used to consolidate bars and larger billets铁合金典型数值1120℃100MPa高温度材料屈服强度较低需较低压力挤压采玻璃容器气压力(15psi)合成棒料较坯段

The technique requires considerable financial investment as the pressure vessel has to withstand the internal gas pressure and allow the powder to be heated to high temperatures压力容器必须受住气压允许粉末加热较高温度种技术需相观资金投入

As with cold isostatic pressing only semifinished products are produced either for subsequent working to smaller sizes or for machining to finished dimensions工艺采冷均衡挤压样生产半成品通续加工较尺寸机加工终尺寸

Hot Forging (Powder Forging) 热锻(粉末锻造)

Cold pressed and sintered components have the great advantage of being close to final shape (nearnet shape) but are not fully dense Where densification is essential to provide adequate mechanical properties the technique of hot forging or powder forging can be used冷挤压烧结零件优点接终形状(似纯形)充分致密提供足够机械性致密化必须时采热锻粉末锻造技术

In powder forging an aspressed component is usually heated to a forging temperature significantly below the usual sintering temperature of the material and then forged in a closed die This produces a fully dense component with the shape of the forging die and appropriate mechanical properties粉末锻造中压制零件般加热远低该材料通常烧结温度锻造温度然闭模中锻造生产具锻模形状合适机械性充分致密零件

Powder forged parts generally are not as close to final size or shape as cold pressed and sintered parts These results from the allowances made for thermal expansion effects and the need for draft angles on the forging tools Further minimal machining is required but when all things are considered this route is often very costeffective粉末锻造零件通常冷挤压烧结零件样接终尺寸形状热膨胀效应设置余量锻模需拔模斜角致进步需限度机加工全面考虑种方法通常合算

Metal Injection Moulding (MIM) 金属注塑成型(MIM)

Injection moulding is very widely used to produce precisely shaped plastic components in complex dies As injection pressures are low it is possible to manufacture complex components even some with internal screw threads by the use of side cores and split tools注塑成型广泛复杂模具中生产形状精确塑料零件注塑压力较低通采侧面型芯分离工具制作复杂零件成甚带螺纹

By mixing fine typically less than 20 μm diameter spherical metal powders with thermoplastic binders metal filled plastic components can be produced with many of the features available in injection moulded plastics After injection moulding the plastic binder material is removed to leave a metal skeleton which is then sintered at high temperature细( 直径般20μm) 球形金属粉末热塑性粘合剂混合生产具数注塑成型塑料特征金属充满塑料零件注塑成型塑料粘合材料剩金属骨架然高温烧结

Dimensional control can be exercised on the assintered component as the injected density is sensibly uniform so shrinkage on sintering is also uniform烧结零件实现尺寸控制注塑密度明显均匀烧结收缩均匀
Shrinkage can be large due to both the fine particle size of the powders and the substantial proportion of polymer binder used
粉末细微粒尺寸聚合物粘合剂真实例收缩较

Features特征
• For high tolerance parts a sintering part is put back into a die and repressed In genera this makes the part more accurate with a better surface finish较公差零件烧结放回模具重新挤压般言会零件更精确时具更表面光洁度
• A part has many voids that can be impregnated One method is to use an oil bath Another method uses vacuum first then impregnation零件许供填充空间种方法采油浴种方法先抽真空然充满
• A part surface can be infiltrated with a low melting point metal to increase density strength hardness ductility and impact resistance 零件表面低熔点金属渗透增密度强度硬度延展性抗击力
• Plating heat treating and machining operations can also be used然进行电镀热处理机加工作业

Advantages优点
• Good tolerances and surface finish良公差表面光洁度
• Highly complex shapes made quickly高度复杂形状快速制作
• Can produce porous parts and hard to manufacture materials (eg cemented oxides) 制作孔零件难加工材料(粘结氧化物)

• Pores in the metal can be filled with other materialsmetals金属中气孔材料金属填充
• Surfaces can have high wear resistance表面具较高耐磨性
• Porosity can be controlled孔隙率控制
• Low waste较低损耗
• Automation is easy容易动化
• Physical properties can be controlled物理性控制
• Variation from part to part is low零件间变化较
• Hard to machine metals can be used easily难机加工金属容易
• No molten metals需熔化金属
• No need for manyany finishing operations需修整作业
• Permits high volume production of complex shapes允许加工复杂形状体积产品
• Allows nontraditional alloy combinations允许非传统合金结合
• Good control of final density终密度控制

Disadvantages缺点

• Metal powders deteriorate quickly when stored improperly果存放金属粉末质量快降低
• Fixed and setup costs are high安装调整成较高
• Part size is limited by the press and compression of the powder used零件尺寸受压力机粉末压缩限制
• Sharp corners and varying thickness can be hard to produce锐角变厚度较难加工
• Nonmoldable features are impossible to produce适合模压东西生产

UNIT 6 Injection Molding

Injection molding (Fig61) is the predominant process for fabrication of thermoplastics into finished forms and is increasingly being used for thermosetting plastics fiberfilled composites and elastomers注塑成型(图61)热塑性塑料制成终形状工艺越越热硬化性塑料纤维填充合成物造橡胶

It is the process of choice for tremendous variety of parts ranging in weight from 5g to 85kg It is estimated that 25 of all thermoplastics are injection molded 重量范围5g85kg极类零件选工艺估计热塑性塑料中25采注塑成型
If newer modifications such as reaction injection molding and the greatly increased rate of adoption of plastics as substitutes for metals are considered it is likely that the worldwide industrial importance of injection molding will continue to increase果考虑新改进(例反作注塑成型)采塑料代金属高增长率注塑成型世界范围工业重性继续增加
Currently probably close to half of all major processing units is injection molding machines In 1988 a dollar sale of new injection molding machinery in the US was approximately 65 of total major polymer machinery sales volume this included 4600 injection molding units 前概处理设备半注塑成型机1988年美国新注塑成型机械销售约占全部聚合物机械销售量65中包括4600台注塑成型设备
The machines and their products are ubiquitous and are synonymous with plastics for many people类机械产品普遍存许说塑料义

A reciprocating screw injection molding machine combines the functions of an extruder and a compressive molding press复螺旋注射成型机压出机成型压力机功结合起
It takes solid granules of thermoplastic resin melts and pressurizes them in the extruder section forces the melt at high velocity and pressure through carefully designed flow channels into a cooled mold then ejects the finished part(s) and automatically recycles 热塑性塑料树脂固体颗粒压出部分融化增压迫高速融化通仔细设计流动通道进入冷模具喷射成终零件然动循环
This machine is a descendant of the plunger type stuffing machine patented by the Hyatt brothers in 1872 to mold celluloid In 1878 the Hyatts developed the first multicavity mold but it was not until 1938 that Quillery (France) patented a machine incorporating a screw to plasticize the elastomer being molded种机械1872年Hyatt兄弟获专利权融化赛璐珞活塞型填充机派生物 1878年Hyatt兄弟开发第槽模具直1938年Quillery(法国)发明螺旋增塑造橡胶成型体化机械
In 1956 Ankerwerk Nuremberg commercialized the modern reciprocating screw injection molding machine for thermoplastics Today over 50 machine manufacturers are listed in Modern Plastics Encyclopedia offering machines to the US market ranging from 2 to 6000 tons clamping capacity 1956年Ankerwerk Nuremberg热塑性塑料现代复螺旋注塑成型机商业化天已超50家制造商列入现代塑料制品百科全书美国市场提供压制力26000吨机械
(A machine with a 10000ton capacity has been built to mold 264gallon HDPE trash containers) A host of suppliers of auxiliary equipment molds instruments and controls service this major segment of the polymer industry(台力10000吨成型264加仑高密度聚乙烯垃圾箱机械已制成)许辅助设备模具仪器控制系统供应商聚合物工业部分服务

Injection molding is particularly worthy of intensive study because it combines many areas of interest extrusion mold design rheology sophisticated hydraulic and electronic controls robotic accessories design of complex products and of course the integration of materials science and process engineering注塑成型深入研究价值结合许重领域挤压模具设计流变学完备液压电子控制机器配件复杂产品设计然材料科学加工工程综合
The objectives of injection molding engineers are simple enough to obtain minimum cycle time with minimum scrap to attain specified product performance with assurance to minimize production costs due to downtime or any other reasons and to steadily increase in expertise and competitiveness注塑成型工程师目标简单：少废料情况取循环时间保证情况获指定产品性停工原产生生产成化稳定增加专门知识竞争力
Profit margins for custom injection molders are said to be generally skimpy an established way to improve profits is to be selected for more demanding higher margin jobs that demand the highest level of efficiency and competence传统注塑成型机利润盈余说般足更需求更高盈余工作需选择种改善利润确定方法求高水效率力

This text will concentrate on the reciprocating screw machine for thermoplastics which has largely replaced the older reciprocating plunger types except for very smallcapacity machines文集中述热塑性塑料复螺旋机容量机械外已程度取代较老复活塞式机械

Injection Molding Materials注塑成型材料

It is not possible to injectionmold all polymers Some polymers like PTFE (Polytetrafluoroethylene) cannot be made to flow freely enough to make them suitable for injection molding注塑成型聚合物聚四氟乙烯类聚合物流动足适合注塑成型
Other polymers such as a mixture of resin and glass fiber in woven or mat form are unsuitable by their physical nature for use in the process In general polymers which are capable of being brought to a state of fluidity can be injectionmolded聚合物例树脂编织垫子形玻璃纤维混合物物理性质适合工艺般言进入流动状态聚合物注塑成型

The vast majority of injection molding is applied to thermoplastic polymers This class of materials consists of polymers which always remain capable of being softened by heat and of hardening on cooling even after repeated cycling 注塑成型绝数热塑性聚合物类材料具加热软化冷硬化甚重复循环力聚合物组成
This is because the longchain molecules of the material always remain as separate entities and do not form chemical bonds to one another An analogy car be made to a block of ice that can be softened (ie turned back to liquid) poured into any shape cavity and then cooled to become a solid again 类材料长链分子总保持分离实体相互形成化学连结辆冰块制成模拟汽车融化(转化液态)倒入形状空腔然冷重新变成固体
This property differentiates thermoplastic materials from thermosetting ones In the latter type of polymer chemical bonds are formed between the separate molecule chains during processing In this case the chemical bonding referred to as cross linking is the hardening mechanism特性热塑性材料热硬化性材料区分开者加工程中分离分子链间形成化学连结情况作交联化学连结硬化机制

In general most of the thermoplastic materials offer high impact strength corrosion resistance and easy processing with good flow characteristics for molding complex designs Thermoplastics are generally divided into two classes namely crystalline and amorphous 般言数热塑性材料具较高抗击强度耐腐蚀性良流动性容易加工适复杂成型设计热塑性塑料通常分两类：结晶质非结晶质
Crystalline polymers have an ordered molecular arrangement with a sharp melting point Due to the ordered arrangement at molecules the crystalline polymers reflect most incidents light and generally appear opaque 结晶质聚合物具规分子排列明显熔点规分子排列结晶质聚合物反射数特定光线般表现透明
They also undergo a high shrinkage or reduction in volume during solidification Crystalline polymers usually are more resistant to organic solvents and have good fatigue and wearresistant properties Crystalline polymers also generally are denser and have better mechanical properties than amorphous polymers 固化程中收缩较体积减少较结晶质聚合物通常抵御机溶剂具良抗疲劳磨损特性结晶质聚合物通常非结晶质聚合物更致密具更机械性
The main exception to this rule is polycarbonate which is the amorphous polymer of choice for high quality transparent moldings and has excellent mechanical properties中例外聚碳酸酯选做高质量透明注塑件非结晶质聚合物具卓越机械性

The mechanical properties of thermoplastics while substantially lower than those of metals can be enhanced for some applications through the addition of glass fiber reinforcement This takes the form of shortchopped fibers a few millimeters in length which are randomly mixed with the thermoplastic resin质言热塑性塑料机械性低金属通加入玻璃纤维强化予增强适应某运常毫米长短碎纤维机热塑性树脂混合

The fibers can occupy up to one third of the material volume to considerably improve the material strength and stiffness The negative effect of this reinforcement is usually a decrease in impact strength and an increase in abrasiveness 纤维占材料体积三分极改善材料强度硬度种加强负作通常抗击强度降低磨损性增加
The latter also has an effect on processing since the life of the mold cavity is typically reduced from about 1000000 parts for plain resin parts to about 300000 for glassfilled parts者加工程影响模具腔寿命典型普通树脂零件约1000000件减少玻璃纤维填充树脂零件约300000件

Perhaps the main weakness of injectionmolded parts is the relatively low service temperatures to which they can be subjected Thermoplastic components can only rarely be operated continuously above 250℃ with an absolute upper service temperature of about 400℃ 注塑成型零件缺点许承受工作温度相较低热塑性塑料零件少连续运行250℃绝高工作温度约400℃

The temperature at which a thermoplastic can be operated under load can be defined qualitatively by the heat deflection temperature This is the temperature at which a simply supported beam specimen of the material with a centrally applied load reaches a predefined deflection
热塑性塑料带载运行温度质量定义热偏差温度中心承载该材料简支梁达预定偏差温度
The temperature value obviously depends upon the conditions of the test and the allowed deflection and for this reason the test values are only really useful for comparing different polymers温度值明显取决试验条件允许偏差较聚合物言试验数真正

Cycle of Operation作业循环

The reciprocating screw injection molding machine is considered as consisting of two halves a fixed injection side and a movable clamp side螺旋注塑成型机认两部分组成：固定注塑端活动夹具端
The injection side contains the extruder that receives solid resin in pellet or granular form and converts it into a viscous liquid or melt that can be forced through the connecting nozzle spine and runners to the gates that lead into the mold cavities 注塑端包含压出机接受球粒状固体树脂然转化粘性液体称融化强迫通连接喷嘴中心浇道闸道进入模具腔
The mold is tightly clamped against injection pressure and is cooled well below the melt temperature of the thermoplastic When the parts in the cavities have cooled sufficiently the mold halves are opened at the mold parting plane and the parts ejected by a knockout system drop into a receiving bin below 模具紧紧夹住抵抗注塑压力热塑性塑料融化温度冷模腔零件充分冷剖分模模具分模面处开推出系统零件推出落入面接收容器
This summarizes the overall cycle but leaves out much vital detail that is necessary for understanding the process However with this introduction it is possible to understand the advantages and disadvantages of the process概述整循环省略许理解工艺必需重细节然通介绍解种工艺优缺点

Effects of Process Variables on Orientation加工变量方性影响

In injection molding any variation in processing that keeps the molding resin hot throughout filling allows increased relaxation and therefore decreased orientation Some of the steps that can be taken to reduce orientation are as follows注塑成型时整填料程始终保持成型树脂高温加工变化会增加松弛作减少方性面减少方性干措施
• Faster injection (up to a point) less cooling during filling hence a thinner initial frozen layer lower viscosity due to shear thinning better flow to corners and less crystallinity all favor lower subsurface orientation The primary effect is that the gate will freeze more quickly At that point orientation stops and relaxation starts较快注塑(点)：填料程中冷较少初始固化层较薄剪应变稀少粘性较低较流角落结晶度较促成表面方性较低效果闸道较快固化样方性停止产生松弛作开始增加
• Higher melt and mold temperatures lower melt viscosity easier filling and greater relaxation favor reduced orientation 较高融化成型温度：融化粘性较低更容易填充较松弛作促成方性减少
• Reduced packing time and pressure overpacking inhibits relaxation processes减少挤压时间压力：度挤压会抑制松弛程
• Reduced gate size larger gates take longer to freeze off and permit increased orientation 减闸道尺寸：闸道越固化时间越长会方性增加

Excessively high injection speed can cause high surface orientation and increase susceptibility to stress cracking For example moldings that are to be electroplated and will be subject to acid solutions during plating must be made using very slow injection speeds to minimize surface orientation 高注塑速度会引起较高表面方性增加应力破裂敏感性例电镀注塑件电镀时会受酸溶液必须采低注塑速度制造表面方性化
On the other hand the transverse motion component of the melt front in most moldings can cause transverse subsurface orientation superimposed on the primary orientation giving a desirable biaxial orientation effect方面数注塑件融化前部横运动部分导致方性层理表面横方性产生需双轴方性效应

Orientation can be seriously increased by obstructions to flow during filling of the cavity Flow around an obstruction causes a decrease in melt front speed and leads to high local viscosity and reduced relaxation This is also likely to occur near the end of the filling phase if gating is inadequate填充模腔时流动受阻碍会极增加方性围绕障碍物流动融化前部速度降产生较高局部粘性减少松弛作果闸道适发生接填充结束阶段

The molder must recognize the dangers of excessive fill speed insufficient injection pressure excessive melt temperature and inadequate packing These dangers are weighed against the opposing effects on orientation discussed above注塑工必须认识快填充速度足注塑压力高融化温度充分挤压危害性危害性述方性反效应相权衡
Thicker parts delay cooling and increase relaxation time and tend to result in lower orientation Thicker parts also tend to warp less Therefore a minimum wall thickness can be established by experience for various shapes materials and process combinations 较厚零件会延迟冷增加松弛时间趋导致较低方性较厚零件助减少翘曲种形状材料工艺组合通验确定壁厚
Lower molecular weight and broader molecular weight distribution in thermoplastics favor lower orientation and reduced internal stress in moldings热塑性塑料中较分子量较宽泛分子量分布促成方性减少时降低注塑件中应力

The skin thickness ratio is affected by process variables in the same way as one would predict for the orientation that is it decreases as the melt or mold temperatures and cavity pressure increases Tensile strength and stiffness increase as skin thickness ratio increases Microscopic examination thus provides another way of studying the process efficiently外壳厚度受加工变量影响方式方性预测样融化成型温度模腔压力增加减少拉伸强度硬度外壳厚度增加增加显微镜检查提供效研究该工艺方法

Advantages优点

1 High production rates For example a CD disk can be produced with a 10~12s cycle in high melt flow index PC1 高生产率：例张CD盘高融体流动指数生产控制中需10~12s循环生产出
2 Relatively low labor content One operator can frequently take care of two or more machines particularly the moldings are unloaded automatically onto conveyors2 相较少工作容：操作者常两台机械尤成品动卸输送机时
3 Parts require little or no finishing For example flash can be minimized and molds can be arranged to automatically separate runners and gates from the part itself 3 零件需修整：例飞边化模具设计成动浇道闸道零件身分离
4 Very complex shapes can be formed Advances in mold tooling are largely responsible4 非常复杂形状成型：模具进步程度
5 Flexibility of design (finishes colors inserts materials) More than one material can be molded through coinjection Foam core materials with solid skins are efficiently produced Thermosetting plastics and fiberreinforced shapes are injection molded5 设计灵活性(光洁度颜色插入物材料)：通复合注塑成型种材料高效生产带固体外壳泡沫型芯材料热硬化性塑料纤维加强形状注塑成型
6 Minimum scrap loss Runners gates and scrap can usually be reground Recycled thermoplastics can be injection molded6 废料损失化：浇道闸道废料通常重新研磨循环热塑性塑料注塑成型
7 Close tolerances are obtainable Modern microprocessor controls fitted to precision molds and elaborate hydraulics facilitate tolerances in the 01 range on dimensions and weights (but not without a high level of operational skills in constant attendance)7 接公差：现代微处理器控制合适精密模具精心制作液压设备尺寸重量公差保持01 范围(没持续时高水操作技)
8 Makes best use of the unique attributes of polymers such as flow ability light weight transparency and corrosion resistance This is evident from the number and variety of molded plastic products in everyday use8 充分利聚合物诸流动力重量轻透明耐腐蚀等独特属性：日常成型塑料产品数量种类明显

Disadvantages and Problems缺点问题
1 High investment in equipment and tools requires high production volumes 1 较高设备模具投资需较高生产量合算
2 Lack of expertise and good preventive maintenance can cause high startup and running costs2 缺少专门技术良预防性维修会导致较高启动运行成
3 Quality is sometimes difficult to determine immediately For example postmold warpage may render parts unusable because of dimensional changes that are not completed for weeks or months after molding3 质量时难马确定例成型翘曲会导致零件成型星期甚月尺寸变化完成
4 Attention is required on many details requiring a wide variety of skills and crossdisciplinary knowledge 4 许需广泛样性技交叉学科知识细节必须加注意
5 Part design sometimes is not well suited to efficient molding5 零件设计时适应效率成型
6 Lead time for mold design mold manufacture and debugging trials is sometimes very long6 模具设计模具制造调试试验先导工作时花费长时间



UNIT 7 Metal Cutting

The importance of machining processes can be emphasised by the fact that every product we use in our daily life has undergone this process either directly or indirectly 机加工程重性通日常生活件产品直接间接历程事实强调
(1) In USA more than 100 billions are spent annually on machining and related operations(1)美国年花机加工相关作业费千亿美元
(2) A large majority (above 80) of all the machine tools used in the manufacturing industry have undergone metal cutting (2) 制造业全部机床中数(80)历金属切削
(3) An estimate showed that about 10 to 15 of all the metal produced in USA was converted into chips(3) 估计显示美国生产金属中约1015转变成切屑

These facts show the importance of metal cutting in general manufacturing It is therefore important to understand the metal cutting process in order to make the best use of it 事实说明金属切削常规制造中重性解金属切削程充分利重
A number of attempts have been made in understanding the metal cutting process and using this knowledge to help improve manufacturing operations which involved metal cutting解金属切削程运知识帮助改善金属切削关制造作业方面已做许努力

A typical cutting tool in simplified form is shown in Fig71 The important features to be observed are follows典型切削刀具简化形式图71示注意重特征
1 Rake angle It is the angle between the face of the tool called the rake face and the normal to the machining direction Higher the rake angle better is the cutting and less are the cutting forces increasing the rake angle reduces the metal backup available at the tool rake face 1前角：称前倾面刀具面垂直机加工方夹角前角越切削越切削力越增加前角减少刀具前倾面产生金属阻塞
This reduces the strength of the tool tip as well as the heat dissipation through the tool Thus there is a maximum limit to the rake angle and this is generally of the order of 15°for high speed steel tools cutting mild steel It is possible to have rake angles at zero or negative会减少通刀具散发热量样减少刀尖强度前角限制高速钢刀具切削低碳钢通常15°前角取零度负值
2 Clearance angle This is the angle between the machined surface and the underside of the tool called the flank face The clearance angle is provided such that the tool will not rub the machined surface thus spoiling the surface and increasing the cutting forces A very large clearance angle reduces the strength of the tool tip and hence normally an angle of the order of 5~6°is used2 角：机加工面称侧面刀具底面夹角角刀具产生会损坏机加工面摩擦增加切削力角会削弱刀尖强度般采5~6°角

The conditions which have an important influence on metal cutting are work material cutting tool material cutting tool geometry cutting speed feed rate depth of cut and cutting fluid used金属切削重影响条件工件材料刀具材料刀具形状切削速度进率切削深度切削液

The cutting speed v is the speed with which the cutting tool moves through the work material This is generally expressed in metres per second (ms1)
切削速度v指切削刀具工件材料移动速度通常米秒 (ms1)表示

Feed rate f may be defined as the small relative movement per cycle (per revolution or per stroke) of the cutting tool in a direction usually normal to the cutting speed direction 进率f定义循环(转行程)切削刀具通常垂直切削速度方次相运动

Depth of cut d is the normal distance between the unmachined surface and the machined surface切削深度d未加工面已加工面间垂直距离

Chip Formation切屑形成

Metal cutting process is a very complex process Fig72 shows the basic material removal operation schematically金属切削程复杂程图72图形式显示基材料作业
The metal in front of the tool rake face gets immediately compressed first elastically and then plastically This zone is traditionally called shear zone in view of fact that the material in the final form would be removed by shear from the parent metal 刀具前倾面前金属直接受压缩首先弹性变形然塑性变形考虑终形状中材料通剪切母体金属区域传统称剪切区
The actual separation of the metal starts as a yielding or fracture depending upon the cutting conditions starting from the cutting tool tip Then the deformed metal (called chip) flows over the tool (rake) face 金属实际分离始屈服断裂(视切削条件定)切削刀尖开始然变形金属(称切屑)流刀具(前倾)面
If the friction between the tool rake face and the underside of the chip (deformed material) is considerable then the chip gets further deformed which is termed as secondary deformation The chip after sliding over the tool rake face is lifted away from the tool and the resultant curvature of the chip is termed as chip curl果刀具前倾面切屑(变形金属)底面间摩擦相切屑进步变形做二次变形滑刀具前倾面切屑提升离开刀具切屑弯曲结果称切屑卷

Plastic deformation can be caused by yielding in which case strained layers of material would get displaced over other layers along the slipplanes which coincide with the direction of maximum shear stress屈服导致塑性变形种情况材料变形层着剪应力方致滑移面层取代

A chip is variable both in size and shape in actual manufacturing practice Study of chips is one of the most important things in metal cutting As would be seen later the mechanics of metal cutting are greatly dependent on the shape and size of the chips produced实际加工程中切屑尺寸形状变化切屑研究金属切削重事情面样金属切削力学极赖产生切屑形状尺寸
Chip formation in metal cutting could be broadly categorised into three types (Fig73) 金属切削中切屑形成宽泛分成三类型(图73)：
(1) Discontinuous chip(1)间断切屑
(2) Continuous chip(2)连续切屑
(3) Continuous chip with BUE (Built up edge)(3)带切屑瘤连续切屑
Discontinuous Chip The segmented chip separates into short pieces which may or may not adhere to each other Severe distortion of the metal occurs adjacent to the face resulting in a crack that runs ahead of the tool 间断切屑：分段切屑分散成碎片相互附着相互附着切削面处发生金属剧烈变形导致运动刀具前方金属层产生裂缝
Eventually the shear stress across the chip becomes equal to the shear strength of the material resulting in fracture and separation With this type of chip there is little relative movement of the chip along the tool face Fig73a横切屑剪切应力材料剪切强度相等造成断裂分离生成类切屑时切屑刀具面没相运动见图73a
Continuous chip The continuous chip is characterized by a general flow of the separated metal along the tool face There may be some cracking of the chip but in this case it usually does not extend far enough to cause fracture连续切屑：连续切屑般具分离金属刀具面流动特征切屑破裂种情况切屑通常会延长足引起断裂
This chip is formed at the higher cutting speeds when machining ductile materials There is little tendency for the material to adhere to the tool The continuous chip usually shows a good cutting ratio and tends to produce the optimum surface finish but it may become an operating hazard Fig73b种切屑形成较高切削速度机加工延展性材料时材料没粘附刀具倾连续切屑通常具良切削率趋产生适宜表面光洁度成操作危险源见图73b

Continuous with a builtup edge This chip shows the existence of a localized highly deformed zone of material attached or welded on the tool face 带切屑瘤连续切屑：种切屑显示粘合焊接刀具面材料局部高度变形区存
Actually analysis of photomicrographs shows that this builtup edge is held in place by the static friction force until it becomes so large that the external forces acting on it cause it to dislodge with some of it remaining on the machined surface and the rest passing off on the back side of the chip Fig73c实际显微片分析显示种切屑瘤受静摩擦力抑制直变作面外力移动留机加工表面延伸切屑背面见图73c

Shear Zone剪切区

There are basically two schools of thought in the analysis of the metal removal process One school of thought is that the deformation zone is very thin and planar as shown in Fig74a The other school thinks that the actual deformation zone is a thick one with a fan shape as shown in Fig74b金属程分析中存两种思想学派种思想学派认变形区图74a示样非常薄坦学派认真实变形区象图74b示样厚带扇形区域

Though the first model (Fig74a) is convenient from the point of analysis physically it is impossible to exist This is because for the transition from undeformed material to deform to take place along a thin plane the acceleration across the plane has to be infinity 然第种模型(图74a)分析角度方便实际存未变形材料着剪切面发生变形越剪切面加速度穷
Similarly the stress gradient across the shear plane has to be very large to be practical 样实际运中越剪切面应力梯度必须行

In the second model (Fig74b) by making the shear zone over a region the transitions in velocities and shear stresses could be realistically accounted for第二种模型(图74b)中剪力区分布范围速度剪应力转变说明更符合实际

The angle made by the shear plane with the cutting speed vector Φ is a very important parameter in metal cutting Higher the shear angle better is the cutting performance From a view of the Fig74a it can be observed that a higher rake angles give rise to higher shear angles剪切面切削速度矢量形成角度Φ金属切削中十分重 参数剪切角越切削作业越图74a 观察较前角增剪切角

Cutting Tool Materials切削刀具材料

Various cutting tool materials have been used in the industry for different applications A number of developments have occurred in the current century工业中应种样切削刀具材料百年里产生许进展
A large variety of cutting tool materials has been developed to cater to the variety of materials used in these programmes Before we discuss the properties of these materials let us look at the important characteristics expected of a cutting tool material
种切削刀具材料开发出满足方案中材料样性讨材料性前先作切削刀具材料应具备重特性
1 Higher hardness than that of the workpiece material being machined so that it can penetrate into the work material 1 硬度切削工件材料高样进入工件材料
2 Hot hardness which is the ability of the material to retain its hardness at elevated temperatures in view of the high temperatures existing in the cutting zone2 热硬度材料存切削区高温升温时保持硬度力
3 Wear resistance—The chiptool and chipwork interfaces are exposed to such severe conditions that adhesive and abrasion wear is very common The cutting tool material should therefore have high abrasion resistance to improve the effective life of the tool3 耐磨性—切屑刀具切屑工件接触界面处严酷状态粘附磨损普遍切削刀具材料应具高耐磨性提高刀具效寿命
4 Toughness—Even though the tool is hard it should have enough toughness to withstand the impact loads that come in the beginning of cut or force fluctuations due to imperfections in the work material This requirement is going to be more useful for the interrupted cutting eg milling4 韧性—然刀具坚硬应足够韧性受住击载荷载荷切削开始工件材料缺陷产生作力波动求铣削类间断切削更
5 Low friction—The coefficient of friction between the chip and tool should be low This would allow for lower wear rates and better chip flow5 低摩擦系数—切屑刀具间摩擦系数应较低会磨损率较切屑流动更
6 Thermal characteristics—Since a lot of heat is generated at the cutting zone the tool material should have higher thermal conductivity to dissipate this heat in the shortest time otherwise the tool temperature would become high reducing its life6 热特性—量热产生切削区刀具材料应具较高热传导性短时间散发热量否刀具温度会升高寿命会减少
All these characteristics may not be found in a single tool material Improved tool materials have been giving a better cutting performance特性存单刀具材料中改进刀具材料已赋予较切削性

Surface Finish 表面光洁度

Machining operations are utilized in view of the better surface finish that could be achieved by it compared to other manufacturing operations机加工获制造作业更表面光洁度机加工作业具实价值
Thus it is important to know what would be the effective surface finish that can be achieved in a machining operation The surface finish in a given machining operation is a result of two factors解机加工作业中获样实际表面光洁度重定机加工作业中表面光洁度两素作结果：
(1) the ideal surface finish which is a result of the geometry of the manufacturing process which can be determined by considering the geometry of the machining operation and理想表面光洁度通考虑机加工作业体系决定制造工艺学结果
(2) the natural component which is a result of a number of uncontrollable factors in machining which is difficult to predict 然素机加工中难预测控素作结果

Ideal Surface Finish in Turning车削中理想表面光洁度

The actual turning tool used would have a nose radius in place of the sharp tool point which modifies the surface geometry as shown in Fig75a If the feed rate is very small as is normal in finish turning the surface is produced purely by the nose radius alone as shown in Fig75实际车削刀具刀尖半径取代锋利刀尖表面形状加工图75a示果进率象精车中正常样工件表面完全刀尖半径单独产生图75示

For the case in Fig75 the surface roughness value is to be图75种情况表面粗糙度值
Ra8f2(18R√3) Ra8f2(18R√3)
Where Ra is the surface roughness value
R is the nose radius
f is the feed rate
式中：Ra表面粗糙度值R刀尖半径f进率

The above are essentially geometric factors and the values represent an ideal situation The actual surface finish obtained depends to a great extent upon a number of factors such as述基素值代表理想情况实际获表面光洁度程度取决列素：
(1) the cutting process parameter speed feed and depth of cut(1)切削工艺参数速度进切削深度
(2) the geometry of the cutting tool(2)切削刀具形状
(3) application of cutting fluid(3)切削液运
(4) work and tool material characteristics(4)工件刀具材料特性
(5) rigidity of the machine tool and the consequent vibrations (5)机床刚度伴发生振动

The major influence on surface finish is exerted by the feed rate and cutting speed As the feed decreases from the above equations we can see that the roughness index decreases 表面光洁度产生影响进率切削速度述公式着进减少粗糙度指标会降低
Similarly as the cutting speed increases we have better surface finish Thus while making a choice of cutting process parameters for finish it is desirable to have high cutting speed and small feed rates样着切削速度增较表面光洁度光洁度选择切削工艺参数时采较高切削速度较进率适

Cutting Fluids 切削液

The functions of cutting fluids (which are often erroneously called coolants) are 切削液(常误称冷液)功：
• To cool the tool and workpiece冷刀具工件
• To reduce the friction减少摩擦
• To protect the work against rusting保护工件生锈
• To improve the surface finish改善表面光洁度
• To prevent the formation of builtup edge防止切屑瘤形成
• To wash away the chips from the cutting zone切削区掉切屑

However the prime function of a cutting fluid in a metal cutting operation is to control the total heat This can be done by dissipating the heat generated as well as reducing it The mechanisms by which a cutting fluid performs these functions are cooling action and lubricating action然金属切削作业中切削液功控制总热量通散发减少产生热量达切削液实现功机理：冷作润滑作

Cooling action Originally it was assumed that cutting fluid improves the cutting performance by its cooling properties alone That is why the name coolant was given to it 冷作：初设想切削液仅仅通冷特性改善切削作业称冷液原
Since most of the tool wear mechanisms are thermally activated cooling the chip tool interface helps in retaining the original properties of the tool and hence prolongs its life 数刀具磨损机理热引起冷切屑刀具接触界面助保持刀具原特性延长寿命
However a reduction in the temperature of the workpiece may under certain conditions increase the shear flow stress of the workpiece thereby decreasing tool life It has been shown through a number of investigations that cooling in fact is one of the major factors in improving the cutting performance工件温度降低特定条件会增加工件剪切流动应力降低刀具寿命通研究已表明实际冷改善切削作业素
Lubricating action The best improvement in cutting performance can be achieved by the lubricating action since this reduces the heat generated thus reducing the energy input to the metal cutting operation 润滑作：切削作业改善通润滑作达减少热量产生减少金属切削作业量输入
However if the cutting fluid is to be effective it must reach the chip tool interface But it is not easy to visualize how it is accomplished in the case of a continuous turning with a single point turning tool specially when the chiptool contact pressure is as high as 70 MPa 果切削液起作必须达切屑刀具接触界面采单尖刀具连续车削场合尤切屑刀具接触压力高达70MPa时实现非易事
Merchant thought that minute asperities existed at the chiptool interface and the fluid was drawn into the interface by the capillary action of the interlocking network of these surface asperities Merchant认：切屑刀具接触界面存微粗粒切削液通表面微粗粒组成连锁网络毛细吸入切屑刀具接触界面



UNIT 8 Grinding

Grinding is a manufacturing process that involves the removal of metal by employing a rotating abrasive wheel The latter simulates a milling cutter with an extremely large number of miniature cutting edges 磨削通采旋转磨轮金属制造工艺磨轮非常量微型切削刃模仿铣刀进行切削
Generally grinding is considered to be a finishing process that is usually used for obtaining highdimensional accuracy and better surface finish Grinding can be performed on flat cylindrical or even internal surfaces by employing specialized machine tools which are referred to as grinding machines般言磨削认种通常获高尺寸精度较表面光洁度精加工作业磨削通采称磨床特殊机床面圆柱面甚表面进行
Obviously grinding machines differ in construction as well as capabilities and the type to be employed is determined mainly by the geometrical shape and nature of the surface to be ground eg cylindrical surfaces are ground on cylindrical grinding machines显然磨床根结构功区种形式磨床取决磨削表面形状物理性质例圆柱面外圆磨床磨削

Type of Grinding Operations磨削作业类型

1 Surface grinding As the name surface grinding suggests this operation involves grinding of flat or plane surfaces Fig81 indicates the two possible variations either a horizontal or vertical machine spindle1 表面磨削：名称暗示样表面磨削面磨削直接关图81表示两种变化：卧式磨床轴立式磨床轴
In the first case (horizontal spindle) the machine usually has a planertype reciprocating table on which the workpiece is held However grinding machines with vertical spindles can have either a planer type table like that of the horizontalspindle machine or a rotating worktable第种情况(卧式轴)卧式磨床通常具安装工件刨床式复工作台立式轴磨床卧式轴磨床样具刨床式工作台具旋转工作台
Also the grinding action in this case is achieved by the end face of the grinding wheel (Fig81b) contrary to the case of horizontalspindle machines where the workpieces ground by the periphery of the grinding wheel 种情况磨削动作通砂轮端面完成(图81b)通砂轮周边磨削工件卧式轴磨床正相反
Fig81a and b also indicate the equations to be used for estimating the different parameters of the grinding operation such as the machining time and the rate of metal removal图81ab时简述估计诸加工时间金属率类磨削作业参数方程式
During the surfacegrinding operations heavy workpieces are either held in fixtures or clamped on the machine table by strap clamps and the like whereas smaller workpieces are usually held by magnetic chucks面磨削时重工件夹具固定压板等夹紧磨床工作台工件通常电磁卡盘固定
2 Cylindrical grinding In cylindrical grinding the workpiece is held between centers during the grinding operation and the wheel rotation is the source and cause for the rotary cutting motion as shown in Fig82 In fact cylindrical grinding can be carried out by employing any of the following methods2 圆柱面磨削：圆柱面磨削中作业时工件支撑两顶尖间砂轮转动导致回转切削运动动力源图82示实际圆柱面磨削通采列意方法实现：
(1) The transverse method in which both the grinding wheel and the workpiece rotate and longitudinal linear feed is applied to enable grinding of the whole length The depth of cut is adjusted by the cross feed of the grinding wheel into the workpiece(1) 横方法：种方法中砂轮工件均旋转采线性进保证磨削整长度切削深度通改变砂轮工件横进进行调整
(2) The plungecut method in which grinding is achieved through the cross feed of the grinding wheel and no axial feed is applied As you can see this method can be applied only when the surface to be ground is shorter than the width of the grinding wheel used(2) 插入切削方法：种方法通砂轮横进完成磨削采轴进正料想样种方法磨削表面砂轮宽度短时
(3) The fulldepth method which is similar to the transverse method except that the grinding allowance is removed in a single pass This method is usually recommended when grinding short rigid shafts(3) 全深度方法：种方法次加工磨削余量外横方法相种方法通常磨削较短刚性轴时推荐

Internal grinding Internal grinding is employed for grinding relatively short holes as shown in Fig83 The workpiece is held in a chuck or a special fixture Both the grinding wheel and the workpiece rotate during the operation and feed is applied in the longitudinal direction表面磨削：表面磨削相较短孔图83示工件安装卡盘特殊夹具作业时砂轮工件回转采进
Any desired depth of cut can be obtained by the cross feed of the grinding wheel A variation from this type is planetary internal grinding which is recommended for heavy workpieces that cannot be held in chucks 通砂轮横进意需切削深度种方法变体行星式表面磨削工件较重卡盘固定时推荐
In that case the grinding wheel not only spins around its own axis but also rotates around the centerline of the hole that is being ground种情况砂轮绕身轴线回转时绕磨削孔中心线旋转
Centerless grinding Centerless grinding involves passing a cylindrical workpiece which is supported by a rest blade between two wheels ie the grinding wheel and the regulating or feed wheel 心磨削：心磨削加工圆柱形工件工件托板支撑两轮砂轮调节进轮间通
The grinding wheel does the actual grinding while the regulating wheel is responsible for rotating the workpiece as well as generating the longitudinal feed This is possible because of the frictional characteristics of that wheel which is usually made of rubberbonded abrasive砂轮完成实际磨削调节轮负责旋转工件产生进调节轮通常橡胶粘结磨料制成摩擦特性成
As can be seen in Fig84 the axis of the regulating wheel is tilted at a slight angle with the axis of the grinding wheel Consequently the peripheral velocity of the regulating wheel can be resolved into two components namely workpiece rotational speed and longitudinal feed 正图84中样调节轮轴砂轮轴倾斜微角度调节轮圆周速度分解两分量工件回转速度进
These can be given by the following equations 值列公式出：
Vworkpiece＝Vregulating wheel×cosα
Axial feed ＝Vregulating wheel×c×sinα
Where c is a constant coefficient to account for the slip between the workpiece and the regulating wheel (c094~098)
V工件 ＝V调节轮×cosα
轴进 ＝V调节轮×c×sinα
式中c考虑工件调节轮间 滑动 恒定 系数(c094~098)

The velocity of the regulating wheel is controllable and is used to achieve any desired rotational speed of the workpiece The angleαis usually taken from 1°to 5°and the larger the angle the larger the longitudinal feed would be 调节轮速度控 实现 工件意需转动速度α角通常取1 5° 角度越进越
Whenαis taken as 0° ie the two axes of the grinding and regulating wheels are parallel there is no longitudinal feed of the workpieceα取0° 时砂轮调节轮轴线行时工件没进

Grinding Wheels砂轮

Grinding wheels are composed of abrasive grains having similar size and a binder The actual grinding process is performed by the abrasive grains Pores between the grains within the binder enable the grains to act as separate singlepoint cutting tools砂轮具相尺寸磨料颗粒粘合剂组成实际磨削作业磨粒完成粘合剂中磨粒间孔隙磨粒象独立单刃切削刀具样工作
These pores also provide space for the generated chips thus preventing the wheel from clogging In addition pores assist the easy flow of coolants to enable efficient and prompt removal of the heat generated during the grinding process孔隙时产生切屑提供空间防砂轮堵塞外孔隙帮助冷液容易流动磨削作业中产生热量效迅速散发

Grinding wheels are identified based on their shape and size kind of abrasive grain size binder grade (hardness) and structure砂轮根形状尺寸磨料类型磨粒粘合剂等级(硬度)结构组织分类
Shape and size of grinding wheels Grinding wheels differ in shape and size depending upon the purpose for which they are to be used Various shapes are shown in Fig85 and include the following types砂轮形状尺寸：根砂轮途形状尺寸种形状图85示中包括：
1)Straight wheels used for surface cylindrical internal and centerless grinding
2)Bevelledface or tapered wheels used for grinding threads gear teeth and the like
3)Straight recessed wheels for cylindrical grinding and facing
1)表面圆柱面部心磨削直轮
2)磨削螺纹齿轮轮齿类斜面锥形轮
3)圆柱面端面磨削直凹轮
4)Abrasive disks for cutoff and slotting operations (thickness 002 up to 02in (05 to 5mm))
5)Cylinders straight cups and flaring cups are used for surface grinding with the end face of the wheel
4)切断开槽作业砂轮片(厚度00202英寸(055毫米))
5)端面进行表面磨削圆柱直杯外展杯状砂轮
The main dimensions of a grinding wheel are the outside diameter D the bore diameter d and the height H These dimensions vary widely depending upon the grinding process for which the wheel is to be used砂轮尺寸外径D孔径d厚度H根采砂轮磨削工艺尺寸变化
Kind of abrasive Grinding wheels can be made of natural abrasives such as quartz emery and corundum or of industrially prepared chemical compounds such as aluminum oxide or silicon carbide (known as carborundum) 磨料类型：砂轮象石英金刚砂刚玉类然磨料制成者象氧化铝碳化硅(称造金刚砂)类工业制备化学化合物制成
Generally silicon carbide grinding wheels are used when grinding lowtensilestrength materials like cast iron whereas aluminum oxide wheels are employed for grinding highstrength metals such as alloy steel hardened steel and the like磨削象铸铁类低拉伸强度材料时般采碳化硅砂轮磨削合金钢淬火钢等高强度金属氧化铝砂轮
Grain size of abrasive used As you may expect the grain size of the abrasive particles of the wheel plays a fundamental role in determining the quality of ground surface obtained 磨粒尺寸：正料想样砂轮磨粒尺寸决定磨削表面质量起着根作
The finer the grains the smoother the ground surface is Therefore coarsegrained grinding wheels are used for roughing operations whereas finegrained wheels are employed in final finishing operations
磨粒越细磨削表面越光滑粗粒砂轮粗加工细粒砂轮精加工
The grade of the bond The grade of the bond is actually an indication of the resistance of the bond to pulling off the abrasive grains from the grinding wheel Generally wheels having hard grades are used for grinding soft materials and vice versa 粘结体等级：粘结体等级实际抵抗磨粒砂轮拉脱指标般言具较硬等级砂轮磨削较软材料反然
If a hardgrade wheel were to be used for grinding a hard material the dull grains would not be pulled off from the bond quickly enough thus impeding the selfdressing process of the surface of the wheel and finally resulting in clogging of the wheel and burns on the ground surface
果较硬等级砂轮磨削较硬材料磨钝磨粒足够快脱离粘结体会妨碍砂轮表面修复终导致砂轮堵塞磨表面留灼斑
In fact the cutting properties of all grinding wheels must be restored periodically by dressing with a cemented carbide roller or a diamond tool to give the wheel the exact desired shape and remove all worn abrasive grains实际砂轮磨削性必须定期通硬质合金滚轮金刚石修整器修整恢复求准确砂轮加工成求形状已磨钝磨粒
Structure Structure refers to the amount of void space between the abrasive grains When grinding softer metals larger void space are needed to facilitate the flow of the removed chips结构组织：结构组织磨粒间空隙量关磨削较软金属时需较空隙便切屑流动
The binder Abrasive particles are bonded together in many different ways These include bond silicate rubber resinoid shellac and oxychloride Nevertheless the bond is the most commonly used one粘合剂：磨粒种方法粘结起中包括粘合剂硅酸盐橡胶树脂虫胶氯氧化物然粘合剂常

In fact the standard marking system is employed for distinguishing grinding wheels by providing all the preceding parameters in a specific sequence实际生产中区分砂轮采标准标注系统通特定序述参数表示出



UNIT 9 Lapping Polishing

Lapping 研磨

Lapping is a finishing operation used on flat and cylindrical surfaces The lap shown in Fig91a is usually made of cast iron copper leather or cloth研磨种面圆柱面精加工作业研具图91a示通常铸铁铜皮革布制成
The abrasive particles are embedded in the lap or they may be carried through slurry Depending on the hardness of the workpiece lapping pressures range from 7kPa to 140kPa (1 to 20 psi)研磨微粒嵌入研具者通液体携带根工件硬度研磨压力7kPa140kPa(120psi)范围中取

Lapping has two main functions Firstly it produces a superior surface finish with all machining marks being removed from the surface Secondly it is used as a method of obtaining very close fits between mating parts such as pistons and cylinders研磨两作首先通机加工痕迹产生较表面光洁度次作获活塞气缸类配件间盈配合方法

The lapped workpiece surface may look smooth but it is actually filled with microscopic peaks valleys scratches and pits Few surfaces are perfectly flat Lapping minimizes the surface irregularities thereby increasing the available contact area 研磨工件表面似滑实布满着微观峰谷划痕凹陷没表面完全整研磨表面规化增加效接触面积
The drawing in Fig91a shows two surfaces The upper one is how a surface might look before lapping and the lower one after lapping Lapping removes the microscopic mountain tops and produces relatively flat plateaus Entire microscopic mountain ranges may need to be ground down in order to increase the available contact area图91a显示两表面面研磨前表面外观模样面研磨模样研磨微观峰顶产生相坦台整微观山脉范围需磨增加效接触面积

Production lapping on flat or cylindrical pieces is done on machines such as those shown in Fig91b and 91c Lapping is also done on curved surfaces such as spherical objects and lenses using specially shaped laps研磨面圆柱面工件生产程图91b91c样机器完成研磨采特殊成型研具诸球形物体透镜类曲面进行

Polishing 抛光

Polishing is a process that produces a smooth lustrous surface finish Two basic mechanisms are involved in the polishing process (a) finescale abrasive removal and (b) softening and smearing of surface layers by frictional heating during polishing抛光生成滑光泽表面光洁度工艺抛光工艺涉两种基机理： (a)精细等级磨粒(b)抛光中通摩擦生热软化抹光表面层

Electropolishing电解抛光

Electropolishing is an electrochemical process similar to but the reverse of electroplating The electropolishing process smoothes and streamlines the microscopic surface of a metal object Mirrorlike finishes can be obtained on metal surfaces by electropolishing电解抛光种电镀相似电化学工艺程电镀正相反电解抛光工艺金属物体微观表面滑简单化通电解抛光金属表面镜面光洁度

In electropolishing the metal is removed ion by ion from the surface of the metal object being polished Electrochemistry and the fundamental principles of electrolysis (Faraday’s Law) replace traditional mechanical finishing techniques 电解抛光中金属逐离子抛光金属物体表面电化学电解基原理(Faraday定理)取代传统机械精加工技术
In basic terms the object to be electropolished is immersed in an electrolyte and subjected to a direct electrical current The object is maintained anodic with the cathodic connection being made to a nearby metal conductor基术语说电解抛光物体浸没电解液中通直流电该物体阳极阴极连接附金属导体

Smoothness of the metal surface is one of the primary and most advantageous effects of electropolishing During the process a film of varying thickness covers the surface of the metal This film is thickest over micro depressions and thinnest over micro projections 金属表面滑电解抛光优势效应程中变化着厚度膜覆盖金属表面该膜微观凹陷处厚微观凸出处薄
Electrical resistance is at a minimum wherever the film is thinnest resulting in the greatest rate of metallic dissolution Electropolishing selectively removes microscopic high points or peaks faster than the rate of attack on the corresponding microdepressions or valleys 电阻膜薄处导致金属分解率电解抛光选择性微观高点峰 快相应微观凹陷处谷侵蚀速率
Stock is removed as metallic salt Metal removal under certain circumstances is controllable and can be held to 00001 to 00025 mm原材料金属盐形式特定环境金属控保持00001 00025mm范围

Chemical Mechanical Polishing化学机械抛光

Chemical mechanical polishing is becoming an increasingly important step in the fabrication of multilevel integrated circuits Chemical mechanical polishing refers to polishing by abundant slurry that interacts both chemically and mechanically with the surface being polished化学机械抛光正层集成电路制造领域成日益重步骤化学机械抛光指量抛光液抛光表面产生化学机械作抛光
During the chemical mechanical polishing process a rotating wafer is pressed face down onto a rotating resilient polishing pad while polishing slurry containing abrasive particles and chemical reagents flows in between the wafer and the pad化学机械抛光程中旋转晶片面压旋转回弹力抛光衬垫时含研磨微粒化学反应物抛光液流晶片衬垫间
The combined action of polishing pad abrasive particles and chemical reagents results in material removal and polishing of the wafer surface Chemical mechanical polishing creates flat damagefree on a variety of brittle materials and it is used extensively on silicon wafers in the manufacture of integrated circuits抛光衬垫研磨微粒化学反应物作导致晶片表面材料抛光化学机械抛光种易碎材料整受损害集成电路制造中广泛硅晶片

Chemical mechanical polishing is a complicated multiphase process It mainly includes the following two dynamics First the active component in polishing slurry reacts with the atoms of the wafer and the process is chemical reaction step with oxidationreductive reaction 化学机械抛光种复杂相工艺包括列两动态程：第抛光液中活性成分晶片原子发生反应带氧化原反应化学反应步骤
The second step is the process of desorption that is to say the resultants gradually separate from the wafer surface and new surface is exposed to polishing slurry If chemical reactive rate is smaller the total removal rate of the wafer is also small furthermore the surface degree of finish is not good第二步解吸附程反应产物逐渐晶片表面分离新表面暴露抛光液果化学反应速率较晶片总率较表面光洁程度够
On the contrary even if chemical reaction is very rapid but desorption is very slow the total removal rate is not good Because resultants connot separate from the wafer surface the active component in the polishing slurry cannot expose and react with the atoms on the new surface which holds up chemical reaction 相反化学反应快解吸附慢总率够反应产物晶片表面分离抛光液中活性成分暴露新表面原子起反应会抑制化学反应
The balance and compositive effects of two steps decide the total removal rate and its surface degree of finish两步骤衡合成效应决定总率表面光洁程度
UNIT 10 surface engineering

The processes of surface engineering or surface treatments tailor the surfaces of engineering materials to (1) control friction and wear (2) improve corrosion resistance (3) change physical property eg conductivity resistivity and reflection (4) alter dimension (5) vary appearance eg color and roughness (6) reduce cost 进行表面工程表面处理目：(1)控制摩擦磨损(2)改善抗腐蚀性(3)改变物理性例传导率电阻系数反射率(4)修改尺寸(5)变更外观例颜色粗糙程度(6)降低成
Common surface treatments can be divided into two major categories treatments that cover the surfaces and treatments that alter the surfaces通常表面处理分两类型：覆盖表面处理改变表面处理

Covering the Surface覆盖表面

The treatments that cover the surfaces include organic coatings and inorganic coatings 覆盖表面处理包括机涂层机涂层
The inorganic coatings perform electroplatings conversion coatings thermal sprayings hot dippings furnace fusings or coat thin films glass ceramics on the surfaces of the materials机涂层电镀转化层热喷涂热浸渍熔炉熔融材料表面涂薄膜玻璃陶瓷

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath电镀种电镀槽通电流金属沉淀基体电化学程

Usually there is an anode (positively charged electrode) which is the source of the material to be deposited the electrochemistry which is the medium through which metal ions are exchanged and transferred to the substrate to be coated and a cathode (negatively charged electrode) which is the substrate to be coated通常阳极(正电极)沉淀材料源电化学反应金属离子交换迁移覆盖基体中间程阴极(负电极)覆盖基体

Plating is done in a plating bath which is usually a nonmetallic tank (usually plastic) The tank is filled with electrolyte which has the metal to be plated in ionic form电镀通常非金属容器(般塑料)电镀槽中进行该容器装满含离子态镀金属电解液

The anode is connected to the positive terminal of the power supply The anode is usually the metal to be plated (assuming that the metal will corrode in the electrolyte) For ease of operation the metal is in the form of nuggets and placed in an inert metal basket made out noncorroding metal (such as titanium or stainless steel)阳极电源正极相连阳极通常镀金属(假定该金属电解液中腐蚀)操作容易该金属呈固体块形式置抗腐蚀金属(钛锈钢)制成惰性金属筐

The cathode is the workpiece the substrate to be plated This is connected to the negative terminal of the power supply The power supply is well regulated to minimize ripples as well to deliver a steady predictable current under varying loads such as those found in plating tanks阴极工件镀基体连接电源负极调节电源波动化载荷变化情况(电镀容器中样)提供稳定预知电流

As the current is applied positive metal ions from the solution are attracted to the negatively charged cathode and deposit on the cathode As a replenishment for these deposited ions the metal from the anode is dissolved and goes into the solution and balances the ionic potential旦通电流溶液正金属离子吸引带负电阴极沉淀作沉淀离子补充阳极金属溶解进入溶液衡离子势

Thermal spraying process Thermal spraying metal coatings are depositions of metal which has been melted immediately prior to projection onto the substrate The metals used and the application systems used vary but most applications result in thin coatings applied to surfaces requiring improvement to their corrosion or abrasion resistance properties热喷涂工艺：热喷涂金属涂层金属熔化立投射基体形成金属沉积层金属应系统变化数应求改善抗腐蚀耐磨性表面涂薄层

Thermal spray is a generic term for a broad class of related processes in which molten droplets of metals ceramics glasses andor polymers are sprayed onto a surface to produce a coating to form a freestanding nearnetshape or to create an engineered material with unique properties热喷涂类相关工艺通术语喷涂表面产生涂层熔化滴金属陶瓷玻璃聚合物形成独立似纯形产生具独特性设计材料

In principle any material with a stable molten phase can be thermally sprayed and a wide range of pure and composite materials are routinely sprayed for both research and industrial applications Deposition rates are very high in comparison to alternative coating technologies 体稳定熔化状态材料热喷涂范围宽阔纯净合成材料般喷涂研究工业目沉积率供选择涂层技术较高
Deposit thickness of 01 to 1mm is common and thickness greater than 1cm can be achieved with some materials
沉淀厚度普遍011mm某材料沉淀厚度达1cm

The process for application of thermal spray metal is relatively simple and consists of the following stages 热喷涂金属应工艺相简单列阶段组成：
(1) Melting the metal at the gun (1)喷枪熔化金属
(2) Spraying the liquid metal onto the prepared substrate by means of compressed air(2)通压缩空气液态金属喷涂准备基体
(3) Molten particles are projected onto the cleaned substrate (3)熔化微粒投射清洁基体
There are two main types of wire application available today namely arc spray and gas spray现两种金属丝应类型选电弧喷涂气体喷涂

ARC—A pair of wires are electrically energized so that an arc is struck across the tips when brought together through a pistol Compressed air is blown across the arc to atomise and propel the autofed metal wire particles onto the prepared workpiece电弧喷涂—金属丝通手持喷枪连起时通电横末端划燃电弧压缩空气吹电弧雾化驱动送料金属丝微粒准备工件

GAS—In combustion flame spraying the continuously moving wire is passed through a pistol melted by a conical jet of burning gas The molten wire tip enters the cone atomises and is propelled onto the substrate气体喷涂—连续移动金属丝燃烧火焰喷射中通手持喷枪燃烧气体锥形喷嘴熔化熔化金属丝顶端进入锥体雾化驱基体

ThinFilm Coatings Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) are two most common types of thinfilm coating methods薄膜涂层：物理蒸发沉淀(PVD)化学蒸发沉淀(CVD)两种常见薄膜涂层方法类型

PVD coatings involve atombyatom moleculebymolecule or ion deposition of various materials on solid substrates in vacuum systems物理蒸发沉淀涂层涉真空装置种样材料原子紧原子分子紧分子离子沉淀固态基体

Thermal evaporation uses the atomic cloud formed by the evaporation of the coating metal in a vacuum environment to coat all the surfaces in the line of sight between the substrate and the target It is often used in producing thin 05μm decorative shiny coatings on plastic parts热蒸发利涂层金属真空环境中蒸发形成微粒子雾基体靶材间见范围表面覆盖塑料零件生成较薄(05μm) 装饰性光泽涂层时常常

The thin coating however is fragile and not good for wear applications The thermal evaporation process can also coat a very thick 1mm layer of heatresistant materials such as MCrAIY—a metal chromium aluminum and yttrium alloys on jet engine parts然种薄涂层易碎适合磨损场合热蒸发工艺喷气发动机零件覆盖厚(1mm)耐热材料涂层例MCrAIY—种金属铬铝钇合金

Sputtering applies hightechnology coatings such as ceramics metal alloys organic and inorganic compounds by connecting the workpiece and the substance to a highvoltage DC power supply in an argon vacuum system反应溅射法通氩真空设备中连接工件具特定成分材料高压直流电应诸陶瓷金属合金机机化合物类高技术涂层
The plasma is established between the substrate (workpiece) and the target (donor) and transposes the sputtered off target atoms to the surface of the substrate等离子区形成基体(工件)靶材(原料物质)间溅射靶材原子转移基体表面
When the substrate is nonconductive eg polymer a radiofrequency (RF) sputtering is used instead Sputtering can produce thin less than 3μm (120μin) hard thinfilm coatings eg titanium nitride (TIN) which is harder than the hardest metal 果基体导电例聚合物采射频(RF) 溅射代反应溅射法生成较薄( 3μm(120μin)) 坚硬薄膜涂层硬金属硬氮化钛(TIN)
Sputtering is now widely applied on cutting tools forming tools injection molding tools and common tools such as punches and dies to increase wear resistance and service life现反应溅射法已广泛应切削刀具成型工具注射模具诸头模类通器具增强耐磨性寿命

CVD is capable of producing thick dense ductile and good adhesive coatings on metals and nonmetals such as glass and plastic Contrasting to the PVD coating in the line of sight the CVD can coat all surfaces of the substrate化学蒸发沉淀金属玻璃塑料类非金属生成较厚致密延伸性带良粘性涂层物理蒸发沉淀见范围化学蒸发沉淀基体表面覆盖

Conventional CVD coating process requires a metal compound that will volatilize at a fairly low temperature and decompose to a metal when it contacts with the substrate at higher temperature常规化学蒸发沉淀涂层工艺需种容易相低温度挥发较高温度基体接触时分解成纯金属金属化合物
The most well known example of CVD is the nickel carbonyl (NiCO4) coating as thick as 25mm (01in) on glass windows and containers to make them explosion or shatter resistant熟知化学蒸发沉淀例子玻璃窗容器镀厚25mm(01in)羰基镍(NiCO4)涂层抵抗爆裂破碎

Diamond CVD coating process is introduced to increase the surface hardness of cutting tools However the process is done at the temperatures higher than 700℃ (1300℉) which will soften most tool steel 增加切削刀具表面硬度引入钻石化学蒸发沉淀涂层工艺工艺高700℃(1300℉)温度实现温度会软化数工具钢
Thus the application of diamond CVD is limited to materials which will not soften at this temperature such as cemented carbides
钻石化学蒸发沉淀应受材料限制求材料温度软化例硬质合金

PlasmaAssisted CVD coating process can be performed at lower temperature than diamond CVD coatings This CVD process is used to apply diamond coatings or silicon carbide barrier coatings on plastic films and semiconductors including the state of the art 025μm semiconductors等离子体辅助化学蒸发沉淀涂层工艺钻石化学蒸发沉淀涂层低温度操作种化学蒸发沉淀塑料膜半导体( 包括工025μm 半导体情况) 覆盖钻石涂层碳化硅隔离涂层

Altering the Surfaces改变表面

The treatments that alter the surfaces include hardening treatments highenergy processes and special treatments改变表面处理包括淬火处理高加工特殊处理

Highenergy processes are relatively new surface treatment methods They can alter the properties of surfaces without changing the dimension of the surface Common highenergy processes including electron beam treatment ion implantation and laser beam treatment are briefly discussed as follows高加工相较新表面处理方法改变表面尺寸情况改变表面性通高加工包括电子束处理离子注入激光束处理简讨：
Electron beam treatment Electron beam treatment alters the surface properties by rapid heating—using electron beam and rapid cooling—in the order of 106℃see in a very shallow region 100μm near the surface This technique can also be used in hardfacing to produce surface alloys电子束处理： 电子束处理表面浅(100μm) 区域通电子束快速加热106℃ 秒 等级 快速冷改变表面性种技术表面硬化产生 表面合金
Ion implantation Ion implantation uses electron beam or plasma to impinge gas atoms to ions with sufficient energy and embed these ions into atomic lattice of the substrate accelerated by magnetic coils in a vacuum chamber The mismatch between ion implant and the surface of a metal creates atomic defects that harden the surface离子注入：离子注入采电子束等离子体通真空室磁性线圈加速足够量气体原子撞击离子离子嵌入基体原子点阵中离子注入金属表面间错配产生硬化表面原子瑕疵
Laser beam treatment Similar to electron beam treatment laser beam treatment alters the surface properties by rapid heating and rapid cooling in a very shallow region near the surface It can also be used in hardfacing to produce surface alloys激光束处理：电子束处理类似激光束处理通表面浅区域快速加热快速冷改变表面性表面硬化产生表面合金

The results of highenergy processes are not well known or very well controlled But the preliminary results look promising Further development is needed in highenergy processes especially in implant dosages and treatment methods高加工结果充分解控制初步结果前途高加工需进步开发特注入剂量处理方法



UNIT11 Lathe and Turning

The Lathe and Its Construction车床结构

A lathe is a machine tool used primarily for producing surfaces of revolution and flat edges车床生成旋转表面整边缘机床
Based on their purpose construction number of tools that can simultaneously be mounted and degree of automation lathesor more accurately lathetype machine tools can be classified as follows根目结构时安装刀具数量动化程度车床— 更确切说车床类机床分成类：
(1)Engine lathes(1)普通车床
(2)Toolroom lathes(2)万车床
(3)Turret lathes(3)转塔车床
(4)Vertical turning and boring mills (4)立式车床
(5)Automatic lathes(5)动车床
(6)Specialpurpose lathes(6)特殊车床

In spite of that diversity of lathetype machine tools they all have common features with respect to construction and principle of operation These features can best be illustrated by considering the commonly used representative type the engine lathe Following is a description of each of the main elements of an engine lathe which is shown in Fig111然车床类机床种样结构操作原理具特性特性通普通车床常代表性类型说明面关图111示普通车床部分描述

Lathe bed The lathe bed is the main frame involving a horizontal beam on two vertical supports It is usually made of grey or nodular cast iron to damp vibrations and is made by casting 车床床身：车床床身包含两垂直支柱水横梁骨架减振般灰铸铁球墨铸铁铸造成
It has guideways to allow the carriage to slide easily lengthwise The height of the lathe bed should be appropriate to enable the technician to do his or her job easily and comfortably面拖板轻易滑动导轨车床床身高度应适技师容易舒适工作

Headstock The headstock is fixed at the left hand side of the lathe bed and includes the spindle whose axis is parallel to the guideways (the slide surface of the bed) The spindle is driven through the gearbox which is housed within the headstock 轴箱：轴箱固定车床床身左侧包括轴线行导轨轴轴通装轴箱齿轮箱驱动
The function of the gearbox is to provide a number of different spindle speeds (usually 6 up to 18 speeds) Some modern lathes have headstocks with infinitely variable spindle speeds which employ frictional electrical or hydraulic drives
齿轮箱功轴提供干速度(通常618速)现代车床具采摩擦电力液压驱动级调速轴箱
The spindle is always hollow i e it has a through hole extending lengthwise Bar stocks can be fed through that hole if continuous production is adopted 轴中空通孔果采取连续生产棒料通孔进
Also that hole has a tapered surface to allow mounting a plain lathe center The outer surface of the spindle is threaded to allow mounting of a chuck a face plate or the like时孔锥形表面安装普通车床顶尖轴外表面螺纹安装卡盘花盘类似装置

Tailstock The tailstock assembly consists basically of three parts its lower base an intermediate part and the quill The lower base is a casting that can slide on the lathe bed along the guideways and it has a clamping device to enable locking the entire tailstock at any desired location depending upon the length of the workpiece 尾架：尾架总成基包括三部分底座尾架体套筒轴底座车床床身导轨滑动铸件定位装置整尾架根工件长度锁定需位置
The intermediate part is a casting that can be moved transversely to enable alignment of the axis of the tailstock with that of the headstock The third part the quill is a hardened steel tube which can be moved longitudinally in and out of the intermediate part as required 尾架体横运动铸件调整尾架轴线轴箱轴线成直线第三部分套筒轴淬硬钢根需尾架体中进出移动
This is achieved through the use of a handwheel and a screw around which a nut fixed to the quill is engaged The hole in the open side of the quill is tapered to enable mounting of lathe centers or other tools like twist drills or boring bars The quill can be locked at any point along its travel path by means of a clamping device通手轮螺杆达螺杆啮合固接套筒轴螺母套筒轴开口端孔锥形安装车床顶尖诸麻花钻镗杆类工具套筒轴通定位装置着移动路径锁定点

The carriage The main function of the carriage is mounting of the cutting tools and generating longitudinal andor cross feeds It is actually an Hshaped block that slides on the lathe bed between the headstock and tailstock while being guided by the Vshaped guideways of the bed 拖板：拖板功安装刀具产生横进实际车床床身V形导轨引导车床床身轴箱尾架间滑动H形滑块
The carriage can be moved either manually or mechanically by means of the apron and either the feed rod or the lead screw拖板手动者通溜板箱光杆(进杆)丝杆(引导螺杆)机动
When cutting screw threads power is provided to the gearbox of the apron by the lead screw In all other turning operations it is the feed rod that drives the carriage The lead screw goes through a pair of half nuts which are fixed to the rear of the apron切削螺旋时动力通丝杆提供溜板箱齿轮箱余车削作业中光杆驱动拖板丝杆穿固定溜板箱部剖分螺母

When actuating a certain lever the half nuts are clamped together and engage with the rotating lead screw as a single nut which is fed together with the carriage along the bed When the lever is disengaged the half nuts are released and the carriage stops开动特定操作杆时剖分螺母夹起作单螺母旋转丝杆啮合带动拖板着床身提供进操作杆脱离时剖分螺母释放时拖板停止运动
On the other hand when the feed rod is used it supplies power to the apron through a worm gear The latter is keyed to the feed rod and travels with the apron along the feed rod which has a keyway extending to cover its whole length方面光杆时通蜗轮溜板箱提供动力 蜗轮键连接光杆溜板箱起光杆运动光杆全长范围开键槽
A modern lathe usually has a quickchange gearbox located under the headstock and driven from the spindle through a train of gears It is connected to both the feed rod and the lead screw and enables selecting a variety of feeds easily and rapidly by simply shifting the appropriate levers 现代车床般轴箱装备快速变换齿轮箱通系列齿轮轴驱动光杆丝杆连接容易快速通简单转换适操作杆选择种进
The quickchange gearbox is employed in plain turning facing and thread cutting operations Since that gearbox is linked to the spindle the distance that the apron (and the cuttingtool) travels for each revolution of the spindle can be controlled and is referred to as the feed快速变换齿轮箱普通车削端面切削螺旋切削作业中种齿轮箱轴相连轴转圈溜板箱(切削刀具)运动距离控制距离认进

Lathe Cutting Tools车床切削刀具

The shape and geometry of the lathe tools depend upon the purpose for which they are employed车床刀具形状参数取决目
Turning tools can be classified into two main groups namely external cutting tools and internal cutting tools Each of these two groups include the following types of tools车削刀具分两组外部切削刀具部切削刀具两组中组包括类型刀具：

Turning tools Turning tools can be either finishing or rough turning tools Rough turning tools have small nose radii and are employed when deep cuts are made 车削刀具：车削刀具精车刀具粗车刀具粗车刀具刀尖半径较深切削
On the other hand finishing tools have larger nose radii and are used for obtaining the final required dimensions with good surface finish by making slight depths of cut Rough turning tools can be righthand or lefthand types depending upon the direction of feed They can have straight bent or offset shanks精车刀具刀尖半径较通微量进刀深度获具较表面光洁度终需尺寸粗车刀具进方右手型左手型直弯偏置刀杆

Facing tools Facing tools are employed in facing operations for machining plane side or end surfaces There are tools for machining lefthandside surfaces and tools for righthandside surfaces Those side surfaces are generated through the use of the cross feed contrary to turning operations where the usual longitudinal feed is used 端面刀具：端面刀具端面作业中加工板侧面端部表面加工左右侧表面分般采进车削作业相反侧表面通采横进产生

Cutoff tools Cutoff tools which are sometimes called parting tools serve to separate the workpiece into parts andor machine external annular grooves切断刀具：切断刀具时称分割刀具工件分割成干部分加工外部环形槽

Threadcutting tools Threadcutting tools have either triangular square or trapezoidal cutting edges depending upon the cross section of the desired thread Also the plane angles of these tools must always be identical to those of the thread forms 螺纹切削刀具：螺纹切削刀具根需螺纹横截面三角形矩形梯形切削刃时刀具面角必须始终螺纹形状面角保持致
Threadcutting tools have straight shanks for external thread cutting and are of the bentshank type when cutting internal threads
车外螺纹螺纹切削刀具直刀杆车螺纹螺纹切削刀具弯刀杆

Form tools Form tools have edges especially manufactured to take a certain form which is opposite to the desired shape of the machined workpiece成形刀具：成形刀具专门制成特定形状刀刃种刀刃形状加工工件需外形正相反

An HSS tool is usually made in the form of a single piece contrary to cemented carbides or ceramic which are made in the form of tips The latter are brazed or mechanically fastened to steel shanks．高速钢刀具通常单件形式制造硬质合金陶瓷刀具刀尖形式制造者铜焊机械方法固定钢质刀杆
Fig112 indicates an arrangement of this latter type which includes the carbide tip the chip breaker the pad the clamping screw (with a washer and a nut) and the shank图112示机械式固定布置方式包括硬质合金刀尖断屑槽衬垫卡装螺杆(带垫圈螺母)刀杆
As the name suggests the function of the chip breaker is to break long chips every now and then thus preventing the formation of very long twisted ribbons that may cause problems during the machining operation 顾名思义断屑槽功时折断长切屑防形成长会机加工操作中引起问题缠绕切屑条
The carbide tips (or ceramic tips) can have different shapes depending upon the machining operations for which they are to be employed The tips can either be solid or with a central through hole depending on whether brazing or mechanical clamping is employed for mounting the tip on the shank 硬质合金刀尖(陶瓷刀尖)根采机加工操作形状根刀尖装配刀杆通铜焊机械卡装刀尖实心带中心通孔

Lathe Operations车床操作

In the following section we discuss the various machining operations that can be performed on a conventional engine lathe面节中讨传统普通车床进行种机加工作业
It must be borne in mind however that modern computerized numerically controlled lathes have more capabilities and can do other operations such as contouring for example Following are conventional lathe operations然必须记住现代计算机数控车床具更功进行操作例仿型面传统车床操作

Cylindrical turning Cylindrical turning is the simplest and the most common of all lathe operations A single full turn of the workpiece generates a circle whose center falls on the lathe axis this motion is then reproduced numerous times as a result of the axial feed motion of the tool 圆柱面车削：圆柱面车削车床操作中简单普通工件旋转整圈产生圆心落车床轴圆刀具轴进运动种动作重复许次
The resulting machining marks are therefore a helix having a very small pitch which is equal to the feed Consequently the machined surface is always cylindrical产生机加工痕迹条具节距螺旋线该节距等进机加工表面始终圆柱形
The axial feed is provided by the carriage or the compound rest either manually or automatically whereas the depth of cut is controlled by the cross slide轴进通拖板复式刀架手动动提供然切削深度横滑板控制
In roughing cuts it is recommended that large depths of cuts (up to 025in or 6mm depending upon the workpiece material) and smaller feeds would be used On the other hand very fine feeds smaller depths of cut (less than 005in or 04mm) and high cutting speeds are preferred for finishing cuts粗车中推荐较切削深度(根工件材料达025英寸6毫米)较进方面精车采进较切削深度(005英寸04毫米)较高切削速度

Facing The result of a facing operation is a flat surface that is either the whole end surface of the workpiece or an annular intermediate surface like a shoulder During a facing operation feed is provided by the cross slide whereas the depth of cut is controlled by the carriage or compound rest 端面车削：端面车削操作结果工件整端部表面者轴肩类中间环形表面加工整端面车削操作中进横滑板提供切削深度通拖板复式刀架控制
Facing can be carried out either from the periphery inward or from the center of the workpiece outward It is obvious that the machining marks in both cases take the form of a spiral 端面车削外表面切削工件中心外切削明显两种情况机加工痕迹螺线形式
Usually it is preferred to clamp the carriage during a facing operation since the cutting force tends to push the tool (and of course the whole carriage) away from the workpiece In most facing operations the workpiece is held in a chuck or on a face plate通常端面车削作业时惯采夹住拖板切削力倾刀具(然包括整拖板)推离工件数端面车削作业中工件支撑卡盘花盘

Groove cutting In cutoff and groovecutting operations only cross feed of the tool is employed The cutoff and grooving tools which were previously discussed are employed开槽：切断开槽操作中刀具横进采前面已讨切断开槽刀具

Boring and internal turning Boring and internal turning are performed on the internal surfaces by a boring bar or suitable internal cutting tools If the initial workpiece is solid a drilling operation must be performed first The drilling tool is held in the tailstock and the latter is then fed against the workpiece镗孔部车削：镗孔部车削通镗杆合适部切削刀具表面进行果初始工件实心必须首先进行钻孔作业钻孔刀具安装尾架然着工件进

Taper turning Taper turning is achieved by driving the tool in a direction that is not parallel to the lathe axis but inclined to it with an angle that is equal to the desired angle of the taper Following are the different methods used in taperturning practice锥面车削：锥面车削通着车床轴行倾斜成等锥面需角度方进刀实现面实际锥面车削中采方法：
(1) Rotating the disc of the compound rest with an angle equal to half the apex angle of the cone Feed is manually provided by cranking the handle of the compound rest This method is recommended for taper turning of external and internal surfaces when the taper angle is relatively large(1) 复式刀架盘旋转等圆锥体顶角半角度通摇动复式刀架操柄手动提供进锥角相较时切削外锥面锥面推荐种方法
(2) Employing special form tools for external very short conical surfaces The width of the workpiece must be slightly smaller than that of the tool and the workpiece is usually held in a chuck or clamped on a face plate In this case only the cross feed is used during the machining process and the carriage is clamped to the machine bed(2) 短外锥面采特殊成型刀具工件宽度必须略刀具宽度工件通常卡盘支撑夹紧花盘种情况机加工作业时横进拖板夹紧床身
(3) Offsetting the tailstock center This method is employed for external taper turning of long workpieces that are required to have small taper angles (less than 8°) The workpiece is mounted between the two centers then the tailstock center is shifted a distance S in the direction normal to the lathe axis(3)偏移尾架顶尖需较锥角(8°) 较长工件外锥面车削采种方法工件安装两顶尖间然尾架顶尖垂直车床轴方移动距离S
(4) Using the taperturning attachment This method is used for turning very long workpieces when the length is larger than the whole stroke of the compound rest The procedure followed in such cases involves complete disengagement of the cross slide from the carriage which is then guided by the taperturning attachment(4) 采锥面车削附加装置种方法车削长工件长度复式刀架整行程种场合遵循步骤横滑板完全脱离拖板然通锥面车削附加装置进行引导
During this process the automatic axial feed can be used as usual This method is recommended for very long workpieces with a small cone angle ie 8°through 10°作业中常动轴进具较锥角(8°10°)长工件推荐采种方法

Thread cutting When performing thread cutting the axial feed must be kept at a constant rate which is dependent upon the rotational speed (rpm) of the workpiece The relationship between both is determined primarily by the desired pitch of the thread to be cut螺纹切削：螺纹切削作业时轴进必须保持恒定速率取决工件转速(rpm)两者间关系基切削螺纹需节距决定
As previously mentioned the axial feed is automatically generated when cutting a thread by means of the lead screw which drives the carriage When the lead screw rotates a single revolution the carriage travels a distance equal to the pitch of the lead screw 前述驱动拖板丝杆切削螺纹时轴进动产生丝杆旋转圈拖板行进等丝杆节距段距离
Consequently if the rotational speed of the lead screw is equal to that of the spindle (ie that of the workpiece) the pitch of the resulting cut thread is exactly equal to that of the lead screw 果丝杆旋转速度等心轴转速(工件转速)生成切削螺纹节距正等丝杆节距
The pitch of the resulting thread being cut therefore always depends upon the ratio of the rotational speeds of the lead screw and the spindle Pitch of the lead screw Desired pitch of workpiecerpm of the workpiecerpm of lead screwspindletocarriage gearing ratio
切削生成螺纹节距总取决丝杆心轴转速：丝杆节距工件需节距工件转速丝杆转速心轴拖板传动
This equation is useful in determining the kinematic linkage between the lathe spindle and the lead screw and enables proper selection of the gear train between them公式决定车床心轴丝杆间运动学关系时提供正确挑选间轮系方法
In thread cutting operations the workpiece can either be held in the chuck or mounted between the two lathe centers for relatively long workpieces The form of the tool used must exactly coincide with the profile of the thread to be cut ie triangular tools must be used for triangular threads and so on螺纹切削作业中工件支撑卡盘中相较长工件安装两车床顶尖间刀具外形必须正切削螺纹轮廓致三角形刀具必须三角形螺纹等等

Knurling Knurling is mainly a forming operation in which no chips are produced It involves pressing two hardened rolls with rough filelike surfaces against the rotating workpiece to cause plastic deformation of the workpiece metal滚花：滚花种产生切屑成型操作两带粗锉式表面淬火滚轮压旋转工件工件金属产生塑性变形
Knurling is carried out to produce rough cylindrical (or conical) surfaces which are usually used as handles Sometimes surfaces are knurled just for the sake of decoration there are different types of patterns of knurls from which to choose滚花生成粗糙圆柱(圆锥)面通常作手柄时表面滚花装饰滚花图案类型供选择

Cutting Speeds and Feed切削速度进

The cutting speed which is usually given in surface feet per minute (SFM) is the number of feet traveled in the circumferential direction by a given point on the surface (being cut) of the workpiece in 1 minute切削速度通常分钟表面英尺出分钟工件(切削)表面定点圆周方行进英尺数
The relationship between the surface speed and rpm can be given by the following equation SFMπDN
Where
Dthe diameter of the workpiece in feet
Nthe rpm
表面速度转速间关系式出：
SFMπDN
式中
D 英尺表示工件直径
N 转速

The surface cutting speed is dependant primarily upon the material being machined as well as the material of the cutting tool and can be obtained from handbooks information provided by cutting tool manufacturers and the like 表面切削速度切削材料切削刀具材料决定手册切削刀具生产商提供资料类似东西查取
Generally the SFM is taken as 100 when machining coldrolled or mild steel as 50 when machining tougher metals and as 200 when machining softer materials For aluminum the SFM is usually taken as 400 or above There are also other variables that affect the optimal value of the surface cutting speed 般言SFM机加工冷轧低碳钢时取100机加工较坚韧金属时取50机加工较软材料时取200铝言SFM通常取400存变量影响表面切削速度佳值
These include the tool geometry the type of lubricant or coolant the feed and the depth of cut As soon as the cutting speed is decided upon the rotational speed (rpm) of the spindle can be obtained as follows
NSFM(πD) 中包括刀具形状润滑剂冷液类型进切削深度切削速度旦确定心轴转速(rpm) 式：
NSFM(πD)

The selection of a suitable feed depends upon many factors such as the required surface finish the depth of cut and the geometry of the tool used Finer feeds produce better surface finish whereas higher feeds reduce the machining time during which the tool is in direct contact with the workpiece合适进选择取决许素例需表面光洁度切削深度刀具形状进越生成光洁度越刀具工件直接接触时进越减少机加工时间
Therefore it is generally recommended to use high feeds for roughing operations and finer feeds for finishing operations Again recommended values for feeds which can be taken as guidelines are found in handbooks and in information booklets provided by cutting tool manufacturers粗车般推荐较进精车较进者作指导方针进推荐值手册切削刀具生产商提供资料册子找



UNIT 12 Drilling and Milling

Drilling and Drills钻削钻头

Drilling involves producing through or blind holes in a workpiece by forcing a tool which rotates around its axis against the workpiece钻削通迫绕身轴线旋转切削刀具进入工件生成通孔盲孔
Consequently the range of cutting from that axis of rotation is equal to the radius of the required hole In practice two symmetrical cutting edges that rotate about the same axis are employed旋转轴线开始切削范围等需孔半径实际两条围绕相轴线旋转称切削刃

Drilling operations can be carried out by using either hand drills or drilling machines The latter differ in size and construction Nevertheless the tool always rotates around its axis while the workpiece is kept firmly fixed This is contrary to drilling on a lathe钻削作业采手钻采钻床实现钻床尺寸结构差然始终切削刀具围绕身轴线旋转工件稳固定位形式正车床钻孔相反

Cutting Tool for Drilling Operation钻削作业切削刀具

In drilling operations a cylindrical rotaryend cutting tool called a drill is employed The drill can have either one or more cutting edges and corresponding flutes which can be straight or helical钻削作业中称钻头圆柱形回转端切削刀具钻头条条直螺旋状切削刃相应出屑槽
The function of the flutes is to provide outlet passages for the chips generated during the drilling operation and also to allow lubricants and coolants to reach the cutting edges and the surface being machined Following is a survey of the commonly used drills出屑槽功钻削作业中产生切屑提供排出通道允许润滑剂冷液达切削刃正加工表面面常钻头概述

Twist drill The twist drill is the most common type of drill It has two cutting edges and two helical flutes that continue over the length of the drill body as shown in Fig121 The drill also consists of a neck and a shank that can be either straight or tapered 麻花钻：麻花钻常钻头类型两条切削刃两条钻头体全长连续螺旋状出屑槽图121示麻花钻包括钻颈钻柄钻柄直锥形
In the latter case the shank is fitted by the wedge action into the tapered socket of the spindle and has a tang which goes into a slot in the spindle socket thus acting as a solid means for transmitting rotation 锥形钻柄通楔入动作安装轴锥形轴孔中钻柄柄舌插入轴轴孔中插槽作传递转动方法
On the other hand straightshank drills are held in a drill chuck that is in turn fitted into the spindle socket in the same way as tapered shank drills方面直柄钻头钻头卡盘夹住接钻头卡盘象锥形钻柄钻头样安装轴轴孔
As can be seen in Fig121 the two cutting edges are referred to as the lips and are connected together by a wedge which is a chisellike edge The twist drill also has two margins which enable proper guidance and locating of the drill while it is in operation 图121示两条切削刃钻唇通凿子状边缘楔形体连起麻花钻两条导边作业中钻头正确导定位
The tool point angle (TPA) is formed by the two lips and is chosen based on the properties of the material to be cut The usual TPA for commercial drills is 118° which is appropriate for drilling lowcarbon steels and cast irons两条钻唇形成钻顶角根钻削材料性选取商品化钻头钻顶角般118°适钻削低碳钢铸铁
For harder and tougher metals such as hardened steel brass and bronze larger TPAs (130°or 140°) give better performance The helix angle of the flutes of the commonly used twist drills ranges between 24°and 30° When drilling copper or soft plastics higher values for the helix angle are recommended (between 35°and 45°)更硬更韧金属诸淬火钢黄铜青铜更钻顶角(130°140°)更效果麻花钻常出屑槽螺旋角范围24° 30°钻削紫铜软塑料时推荐采更螺旋角(35°45°)
Twist drills are usually made of highspeed steel although carbidetipped drills are also available The sizes of twist drills used in industrial practice range from 001 up to 325 in (i e 025 up to 80 mm)然硬质合金刀尖钻头麻花钻般高速钢制成工业实际中麻花钻尺寸范围001325英寸(02580毫米)

Core drills A core drill consists of the chamfer body neck and shank as shown in Fig122 This type of drill may have either three or four flutes and equal number of margins which ensure superior guidance thus resulting in high machining accuracy 空心钻：空心钻包括斜面钻头体钻颈钻柄图122示类钻头三条四条出屑槽相数量保证良导导边样加工高精度
It can also be seen in Fig122 that a core drill has flat end The chamfer can have three or four cutting edges or lips and the lip angle may vary between 90°and 120° 图122中样空心钻具坦端部斜面三四条切削刃钻唇钻唇角90°120°间变化
Core drills are employed for enlarging previously made holes and not for originating holes This type of drill is characterized by greater productivity high machining accuracy and superior quality of the drilled surfaces 空心钻扩已孔孔类钻头具较生产率高加工精度优良钻削表面质量特性

Gun drills Gun drills are used for drilling deep holes All gun drills are straightfluted and each has a single cutting edge A hole in the body acts as a conduit to transmit coolant under considerable pressure to the tip of the drill深孔钻：深孔钻钻深孔深孔钻直出屑槽均单切削刃钻头体中孔作导相压力冷液传送钻头顶端
There are two kinds of gun drills namely the centercut gun drill used for drilling blind holes and the trepanning drill The latter has a cylindrical groove at its center thus generating a solid core which guides the tool as it proceeds during the drilling operation深孔钻两种类型钻盲孔中心切削深孔钻套孔钻者中心圆柱形沟槽样生成整体芯钻孔作业程中引导钻头

Spade drills Spade drills are used for drilling large holes of 35 in(90mm) or more Their design results in a marked saving in cost of the tool as well as a tangible reduction in its weight which facilitates its handling Moreover this type of drill is easy to grind扁钻：扁钻钻削35英寸(90毫米)更孔设计钻头成明显节省重量切实减轻重量轻操作更方便外种钻头容易磨利

Milling and Milling Cutter铣削铣刀

Milling is a machining process that is carried out by means of a multiedge rotating tool known as a milling cutter铣削采称铣刀刃旋转刀具完成机加工作业
In this process metal removal is achieved through combining the rotary motion of the milling cutter and linear motions of the workpiece simultaneously Milling operations are employed in producing flat contoured and helical surfaces as well as for thread and gearcutting operation工艺中金属通铣刀旋转运动工件直线运动组合实现铣削作业生成面轮廓面螺旋面切削螺纹齿轮

Each of the cutting edges of a milling cutter acts as an individual singlepoint cutter when it engages with the workpiece metal Therefore each of those cutting edges has appropriate rake and relief angles 铣刀切削工件金属时铣刀条切削刃象单独单刃刀具样作条切削刃适前角
Since only a few of the cutting edges are engaged with the workpiece at a time heavy cuts can be taken without adversely affecting the tool life In fact the permissible cutting speeds and feeds for milling are three to four times higher than those for turning or drilling 时间部分切削刃切削工件刀具寿命没利影响情况承担重型切削事实铣削允许切削速度进车削钻削高三四倍
Moreover the quality of the surfaces machined by milling is generally superior to the quality of surfaces machined by turning shaping or drilling外铣削加工表面质量通常优车削刨削钻削加工表面质量

A wide variety of milling cutters is available in industry This together with the fact that a milling machine is a very versatile machine tool makes the milling machine the backbone of a machining workshop工业采铣刀类型众连铣床极通机床事实铣床成机加工车间支柱

As far as the direction of cutter rotation and workpiece feed are concerned milling is performed by either of the following two methods涉铣刀转动方工件进铣削通列两种方法进行

Up milling (conventional milling) In up milling the workpiece is fed against the direction of cutter rotation as shown in Fig123a As we can see in that figure the depth of cut (and consequently the load) gradually increases on the successively engaged cutting edges 逆铣(传统铣削)：逆铣中工件逆着铣刀转动方进图123a示图中样切削深度(作结果载荷)着切削刃持续进入切削逐渐增加
Therefore the machining process involves no impact loading thus ensuring smoother operation of the machine tool and longer tool life The quality of the machined surface obtained by up milling is not very high Nevertheless up milling is commonly used in industry especially for rough cuts
种工艺没击载荷保证机床较稳运行较长寿命通逆铣机加工表面质量高然逆铣常工业尤粗切削时

Down milling (climb milling) As can be seen in Fig123b in down milling the cutter rotation coincides with the direction of feed at the contact point between the tool and the workpiece It can also be seen that the maximum depth of cut is achieved directly as the cutter engages with the workpiece 铣(铣削)：图123b中样铣时刀具工件间接触点铣刀旋转进方致刀具进入工件切削时直接达切削深度
This results in a kind of impact or sudden loading Therefore this method cannot be used unless the milling machine is equipped with a backlash eliminator on the feed screw The advantages of this method include higher quality of the machined surface and easier clamping of workpieces since the cutting forces act downward会导致种击突然加载种方法铣床进螺栓配备间隙消器时采种方法优点包括机加工表面质量较高工件切削力作较容易夹紧

Types of Milling Cutters铣刀类型

There is a wide variety of milling cutter shapes Each of them is designed to perform effectively a specific milling operation铣刀形状类型中种效进行特定铣削作业设计
Generally a milling cutter can be described as a multiedge cutting tool having the shape of a solid of revolution with the cutting teeth arranged either on the periphery or on an end face or on both Following is a quick survey of the commonly used types of milling cutters通常铣刀描述具旋转实体形状切削齿安装周边两端面刃切削刀具面常铣刀类型快速综览

Plain milling cutter A plain milling cutter is a diskshaped cutting tool that may have either straight or helical teeth as shown in Fig124a This type is always mounted on horizontal milling machines and is used for machining flat surfaces面铣刀：面铣刀种盘状切削刀具具直齿螺旋齿图124a示类铣刀总安装卧式铣床机加工面
Face milling cutter A face milling cutter is also used for machining flat surfaces It is bolted at the end of a short arbor which is in turn mounted on a vertical milling machine Fig124b indicates a milling cutter of this type端面铣刀：端面铣刀机加工面螺栓固定短刀杆端部短刀杆次安装立式铣床图124b显示类铣刀
Plain metal slitting saw cutter Fig124c indicates a plain metal slitting saw cutter we can see that it actually involves a very thin plain milling cutter面金属开槽锯刃铣刀：图124c显示种面金属开槽锯刃铣刀实种薄面铣刀
Side milling cutter A side milling cutter is used for cutting slots grooves and splines As shown in Fig124d it is quite similar to the plain milling cutter the difference being that this type has teeth on the sides As is the case with the plain cutter the cutting teeth can be straight or helical侧铣刀：侧铣刀切削狭槽凹槽花键槽正图124d示面铣刀十分相似差类铣刀齿侧面象面铣刀情况样切削齿直螺旋
Angle milling cutter An angle milling cutter is employed in cutting dovetail grooves ratchet wheels and the like Fig124e indicates a milling cutter of this type倾斜铣刀：倾斜铣刀切削燕尾槽棘轮类图124e显示类铣刀
Tslot cutter As shown in Fig124f a Tslot cutter involves a plain milling cutter with an integral shaft normal to it As the name suggests this type is used for milling TslotsT型槽铣刀：图124f示T型槽铣刀包括面铣刀根垂直整体轴正名字表明类铣刀铣削T型槽
End mill cutter End mill cutters find common applications in cutting slots grooves flutes splines pocketing work and the like Fig124g indicates an end mill cutter The latter is always mounted on a vertical milling machine and can have two or four flutes which may be either straight or helical端面铣刀：端面铣刀切削狭槽凹槽长凹槽花键槽凹状工件类时均发现普遍应图124g端面铣刀总安装立式铣床具两四条直螺旋长凹槽
Form milling cutter The teeth of a form milling cutter have a certain shape which is identical to the section of the metal to be removed during the milling operation Examples of this type include gear cutters gear hobs convex and concave cutters and the like From milling cutters are mounted on horizontal milling machines成形铣刀：成形铣刀齿具特定形状形状铣削时切削部分金属形状致类铣刀例子包括齿轮铣刀齿轮滚刀凸形凹形铣刀等等成形铣刀安装卧式铣床

Materials of Milling Cutters铣刀材料
The commonly used milling cutters are made of highspeed steel which is generally adequate for most jobs 普通铣刀高速钢制造般数工作已足够Milling cutters tipped with sintered carbides or cast nonferrous alloys as cutting teeth are usually employed for mass production where heavier cuts andor high cutting speeds are required规模生产言需重型切削高切削速度铣刀顶端常装烧结碳化物色金属碳合金作切削齿



UNIT 13 Jigs and Fixtures

Introduction 导言

It has already been stated that the workpiece must be located relative to the cutting tool and be secured in that position After the workpiece has been marked out it is still necessary to position it with respect to the machine movements and to clamp it in that position before machining is started已说明工件必须相切削刀具定位确保位工件划线必相切削运动定位机加工开始前装夹位

When several identical workpieces are to be produced the need to mark out each part is eliminated by the use of jigs and fixtures but if a casting or forging is involved a trial workpiece is marked out to ensure that the workpiece can be produced from it and to ensure that ribs cores etc have not become misplaced加工干样工件时钻模夹具必工件划线铸件锻件言需取试验工件划线保证加工会加强肋型芯等放错位置

Jigs and fixtures are alike in that they both incorporate devices to ensure that the workpiece is correctly located and clamped but they differ in that jigs incorporate means of tool guiding during the actual cutting operation and fixtures do not 钻模夹具相似点保证工件正确定位夹紧装置相结合钻模实际切削作业中刀具导方法相结合夹具
In practice the only cutting tools that can be guided while actually cutting are drills reamers and similar cutters and so jigs are associated with drilling operations and fixtures with all other operations Fixtures may incorporate means of setting the cutting tools relative to the location system实际真实切削中导切削刀具钻头铰刀类似刀具钻模钻削作业夹具余作业夹具切削刀具相定位系统装夹方法结合起

The advantages of jigs and fixtures can be summarised as follows
1)Marking out and other measuring and setting out methods are eliminated
2)Unskilled workers may proceed confidently and quickly in knowledge that the workpiece can be positioned correctly and the tools guided or set
钻模夹具优点纳：
1)省划线测量放样程序
2)知道工件正确定位刀具恰导装夹情况熟练工信快速操作
3)the assembly of parts is facilitated since all components will be identical within small limits and trying and filing of work is eliminated
4)The parts will be interchangeable and if the product sold over a wide area the problem of spare parts will be simplified
3)零件较极限范围相省掉工件试装’锉削零件装配方便
4)零件具互换性样果产品较范围销售话备件问题简单化

Bolt holes often have 15mm or even 30mm clearance for the bolt and the reader may doubt the necessity of making precision jigs for such work It must be remembered that the jigs once made will be used on many components and the extra cost of an accurately made jig is spread over a large output 螺栓孔常螺栓留出15毫米甚30毫米间隙读者会怀疑样工作制造精密钻模必性记住种钻模旦造许零部件精确制造钻模额外成分摊量产品
Furthermore it is surprising how small errors accumulate in a mechanism during its assembly When a clearance is specified it is better to ensure its observance rather than to allow careless marking out and machining to encroach upon it．外样做装配机械装置时累积误差令惊讶确定间隙时保证惯求便划线机加工超出正常界限

1) The location of workpiece Fig131 represents a body that is completely free in space In this condition it has six degrees of freedom Consider these freedoms with respect to the three mutually perpendicular axes XX YY and ZZ 1) 工件定位：图131表示空间完全物体种情况具六度相三根互相垂直坐标轴XXYYZZ考虑度
The body can move along any of these axes it therefore has three freedoms of translation It can also rotate about any of the three axes it therefore has three freedoms of rotation The total number of freedoms is six When work is located as many of these freedoms as possible must be eliminated to ensure that the operation is performed with the required accuracy 物体三根坐标轴意根移动样具三移度围绕三根坐标轴意根回转样具三旋转度总度数目六工件定位时必须消度保证作业求精度进行
Accuracy is ensured by machining suitable location features as early as possible and using them for all location unless other considerations mean that other location features must be used If it is necessary the new location features must be machined as a result of location from the former location features非必采外定位素考虑精度通早加工合适定位素采进行定位保证果必话新定位素必须作先前定位素定位结果加工

2) The clamping of the workpiece The clamping system must be such that the workpiece is held against the cutting forces and the clamping forces must not be so great as to cause the workpiece to become distorted or damaged 2) 工件装夹：装夹系统必须工件着切削力夹持装夹力引起工件变形损坏
The workpiece must be supported beneath the point of clamping to ensure that the forces are taken by the main frame of the jig or fixture and on to the machine table and bed When jigs and fixtures are designed the clamping system is designed to ensure that the correct clamping force is applied and that the clamps can be operated quickly but with safety 工件必须装夹点支撑保证力钻模夹具框架承受传递机器台床身设计钻模夹具时时设计装夹系统保证提供恰装夹力装夹操作快速安全

Definition of a Drill Jig钻模定义

A drill jig is a device for ensuring that a hole to be drilled tapped or reamed in a workpiece will be machined in the proper place钻模种确保工件正确位置进行钻孔攻丝铰孔加工装置
Basically it consists of a clamping device to hold the part in position under hardenedsteel bushings through which the drill passes during the drilling operation The drill is guided by the bushings 基淬硬钢衬套零件夹持位夹持装置组成钻孔作业中钻头穿衬套通导
If the workpiece is of simple construction the jig may be clamped on the workpiece In most cases however the workpiece is held by the jig and the jig is arranged so that the workpiece can be quickly inserted and as quickly removed after the machining operation is performed果工件结构较简单钻模夹持工件然数情况工件钻模夹持钻模设计成工件迅速装入加工样快取出

Jigs make it possible to drill ream and tap holes at much greater speeds and with greater accuracy than when the holes are produced by conventional hand methods Another advantage is that skilled workers are not required when jigs are used Responsibility for the accuracy of hole location is taken from the operator and given to the jig相常规手工方法加工孔钻模钻孔铰孔攻丝速度快精度更高成优点采钻模时需熟练工保证孔定位精度责操作者身转移钻模

The term jig should be used only for devices employed while drilling reaming or tapping holes It is not fastened to the machine on which it is used and may be moved around on the table of the drilling machine to bring each bushing directly under the drill Jigs physically limit and control the path of the cutting tool钻模术语服务钻孔铰孔攻丝装置固定钻床钻床工作台处移动衬套直接位钻头钻模形限制控制钻削刀具路径

If the operation includes machining operations like milling planing shaping turning etc the term fixture should be used A fixture holds the work during machining operations but does not contain special arrangements for guiding the cutting tool as drill jigs do果作业包括象铣削刨削成型车削等机加工应采夹具术语夹具机加工作业时夹持工件象钻模样包含引导切削刀具特殊布置

Typical Jigs and Fixtures典型钻模夹具

Typical drill jig Figure 132 illustrates a drilling jig for drilling four holes in the flange of a workpiece that has been completed except for the four holes典型钻模：图132示某工件法兰钻四孔钻模该工件四孔外已全部完成
The workpiece has an accurately machined bore and is located from the bore and the end face from a cylindrical post There is no need to control the rotational position about the axis of the bore because up to the time when the holes are drilled it is symmetrical about that axis 工件精确机加工孔通圆柱体采该孔工件端面定位直钻孔时工件称孔轴线没必控制围绕孔轴线回转位置
The four bushes used to control the drill are held in the drill plate which with the hand nut is used to clamp the workpiece against the base of the fixture四控制钻头衬套装钻板里连手拧螺母起着夹具基座夹持工件

Typical milling fixture Figure 133 illustrates a simple milling fixture for milling the slot in the otherwise completed workpiece shown The workpiece is located from two of the four holes in its base and from the underside of the base 典型铣削夹具：图133示图示工序完成工件铣槽简单铣削夹具工件采基座四孔中两孔基座底面定位
The workpiece is clamped in position and cutter is located against the setting block which provides setting or cutter position and depth of cut 工件夹持位铣刀着提供安装铣刀位置切削深度安装台定位
The fixture must be positioned relative to the machine table this is done by engaging the two tenons at the bottom of the fixture in the slot in the machine table The fixture is secured to the machine table with Tbolts also engaging in the slots in the table (Fig133)夹具必须相铣床工作台定位通夹具底部两凸榫插入工作台槽中实现夹具T型螺栓固定铣床工作台时工作台槽接合(图133)



UNIT 14 Limit and Tolerances

Dimensioning 标注尺寸

The design of a machine includes many factors other than those of determining the loads and stresses and selecting the proper materials机械设计计算载荷应力选择合适材料外包括许素
Before construction or manufacture can begin it is necessary to have complete assembly and detail drawings to convey all necessary information to the shop men The designer frequently is called upon to check the drawings before they are sent to the shop Much experience and familiarity with manufacturing processes are needed before one can become conversant with all phases of production drawings建造制造开始前完成装配图零件图必信息传达车间工必须送车间前设计者常常召集检查图纸精通生产图纸情况前需许验熟悉制造工艺

Drawings should be carefully checked to see that the dimensioning is done in a manner that will be most convenient and understandable to the production departments It is obvious that a drawing should be made in such a way that it has one and only one interpretation图纸必须仔细检查尺寸否生产部门方便易懂方式标注明显图纸应该唯解释
In particular shop personnel should not be required to make trigonometric or other involved calculations before the production machines can be set up尤求车间工生产机械安排前进行三角复杂计算

Dimensioning is an involved subject and long experience is required for its mastery尺寸标注项复杂工作掌握需丰富验

Tolerances must be placed on the dimensions of a drawing to limit the permissible variations in size because it is impossible to manufacture a part exactly to a given dimension 零件加工正定尺寸图纸尺寸必须加公差限制允许变化
Although small tolerances give higher quality work and a better operating mechanism the cost of manufacture increases rapidly as the tolerances are reduced as indicated by the typical curve of Fig141 It is therefore important that the tolerances be specified at the largest values that the operating or functional considerations permit然较公差较高加工质量较操作机构着公差减制造成会迅速增加图141典型曲线示公差定操作功考虑允许值重

Tolerances may be either unilateral or bilateral In unilateral dimensioning one tolerance is zero and all the variations are given by the other tolerance In bilateral dimensioning a mean dimension is used which extends to the midpoint of the tolerance zone with equal plus and minus variations extending each way from this dimension公差单双单标注公差零变化公差定双标注采均尺寸公差带中点该尺寸双扩展相等正负变化范围

The development of production processes for largevolume manufacture at low cost has been largely dependent upon interchangeability of component parts Thus the designer must determine both the proper tolerances for the individual parts and the correct amount of clearance or interference to permit assembly with the mating parts 规模低成制造生产工艺发展程度取决组成零件互换性设计者必须确定单零件合适公差配合零件装配允许正确间隙盈量
The manner of placing tolerances on drawings depends somewhat on the kind of product or type of manufacturing process If the tolerance on a dimension is not specifically stated the drawing should contain a blanket note which gives the value of the tolerance for such dimensions图纸标注公差方法相程度赖产品性质制造工艺类型果尺寸公差没特注明图纸应该包含出尺寸公差值普遍适注释
However some companies do not use blanket notes on the supposition that if each dimension is considered individually wider tolerances than those called for in the note could probably be specified In any event it is very important that a drawing be free from ambiguities and be subject only to a single interpretation然公司采普遍适注释假定尺寸单独考虑会规定出注释中求更宽公差情况图纸模棱两服单解释十分重

Dimension and Tolerance尺寸公差

In dimensioning a drawing the numbers placed in the dimension lines represent dimension that are only approximate and do not represent any degree of accuracy unless so stated by the designer图纸标注尺寸时非设计者意标明注尺寸线数字代表尺寸仅仅似代表精度等级

To specify a degree of accuracy it is necessary to add tolerance figures to the dimension Tolerance is the amount of variation permitted in the part or the total variation allowed in a given dimension 详细标明精度等级必尺寸增加公差数字公差零件允许变动量定尺寸允许总变动
A shaft might have a nominal size of 25in(635mm) but for practical reasons this figure could not be maintained in manufacturing without great cost Hence a certain tolerance would be added and if a variation of±0003in(±008mm) could be permitted the dimension would be stated 2500±0003(635±008mm)根轴名义尺寸25in(635mm)实际原成制造中保持数字增加确定公差果允许±0003in(±008mm)变化尺寸表达2500±0003(635±008mm)

Dimensions given close tolerances mean that the part must fit properly with some other part Both must be given tolerances in keeping with the allowance desired the manufacturing processes available and the minimum cost of production and assembly that will maximize profit 具紧密公差尺寸表示该零件必须恰某零件配合采制造工艺利润化生产装配成求定公差保持需允差
Generally speaking the cost of a part goes up as the tolerance is decreased If a part has several or more surfaces to be machined the cost can be excessive when little deviation is allowed from the nominal size般言零件成着公差减升果零件干较表面机加工允许偏离名义尺寸成会超正常合理界限

Allowance which is sometimes confused with tolerance has an altogether different meaning It is the minimum clearance space intended between mating parts and represents the condition of tightest permissible fit 允差时会公差混淆具完全含义配合零件间预期间隙空间代表着允许紧配合条件
If a shaft size 14980003 is to fit a hole of size 1500+0003 the minimum size hole is 1500 and the maximum size shaft is 1498 Thus the allowance is 0002 and the maximum clearance is 0008 as based on the minimum shaft size and maximum hole dimension 果根尺寸14980003轴尺寸1500+0003孔配合孔尺寸1500轴尺寸1498样允差0002轴尺寸孔尺寸形成间隙0008

Tolerances may be either unilateral or bilateral Unilateral tolerance means that any variation is made in only one direction from the nominal or basic dimension Referring to the previous example the hole is dimensioned 1500+0003 which represents a unilateral tolerance 公差单双单公差意味着变动名义基尺寸出发方变动引前例孔尺寸标注1500+0003表示单公差
If the dimensions were given as 1500±0003 the tolerance would be bilateral that is it would vary both over and under the nominal dimension The unilateral system permits changing the tolerance while still retaining the same allowance or type of fit 果尺寸标1500±0003双公差名义尺寸变化单体系允许然保留相允差配合类型情况改变公差
With the bilateral system this is not possible without also changing the nominal size dimension of one or both of the two mating parts In mass production where mating parts must be interchangeable unilateral tolerances are customary To have an interference or force fit between mating parts the tolerances must be such as to create a zero or negative allowance双体系时改变两配合零件名义尺寸情况做规模生产中配合零件必须互换单公差常遇配合零件间具盈强制配合公差必须产生零负允差

Tolerances Limits and Fits公差极限配合

The drawing must be a true and complete statement of the designer’s requirements expressed in such a way that the part is convenient to manufacture图纸必须方便制造零件方式设计者求真实完整表达出
Every dimension necessary to define the product must be stated once only and not repeated in different views Dimensions relating to one particular feature such as the position and size of a hole should where possible appear on the same view描述产品需尺寸须标注次必视图中重复关特性尺寸诸孔位置果应出现视图

There should be no more dimensions than are absolutely necessary and no feature should be located by more than one dimension in any direction绝需尺寸外应该更尺寸意方尺寸标注特性求
It may be necessary occasionally to give an auxiliary dimension for reference possibly for inspection When this is so the dimension should be enclosed in a bracket and marked for reference Such dimensions are not governed by general tolerances偶尔检查必须出供参考辅助尺寸种情况尺寸应该括号括起便参考样尺寸受通公差控制

Dimensions that affect the function of the part should always be specified and not left as the sum or difference of other dimensions 影响零件功尺寸总应该标注留作尺寸差
If this is not done the total permissible variation on that dimension will form the sum or difference of the other dimensions and their tolerances and this will result in these tolerances having to be made unnecessarily tight The overall dimension should always appear果样尺寸允许总变化形成尺寸公差差会导致公差定紧总尺寸般应该标注

All dimensions must be governed by the general tolerance on the drawing unless otherwise stated Usually such a tolerance will be governed by the magnitude of the dimension Specific tolerances must always be stated on dimensions affecting function or interchangeability非行说明尺寸必须受图通公差控制般样公差受尺寸量值控制影响功互换性尺寸必须标注专门公差

A system of tolerances is necessary to allow for the variations in accuracy that are bound to occur during manufacture and still provide for interchangeability and correct function of the part允许制造程中必然会发生精度变化提供零件互换性正确功公差系统必需

A tolerance is the difference in a dimension in order to allow for unavoidable imperfections in workmanship The tolerance range will depend on the accuracy of the manufacturing organisation the machining process and the magnitude of the dimension 公差允许工艺避免缺陷存尺寸公差范围取决制造机构精度机加工程尺寸量值
The greater the tolerance range the cheaper the manufacturing process A bilateral tolerance is one where the tolerance range is disposed on both sides of the nominal dimension A unilateral tolerance is one where the tolerance zone is on one side only of the nominal dimension in which case the nominal dimension may form one of the limits 公差范围越制造程成越低双公差公称尺寸两侧公差带公差单公差仅公称尺寸侧公差带公差种情况公称尺寸成两极限中

Limits are the extreme dimensions of the tolerance zone For example nominal dimension极限公差带极限尺寸例公称尺寸
30mm tolerance limits30毫米 公差 极限

Fits depend on the relationship between the tolerance zones of two mating parts and may be broadly classified into a clearance fit with positive allowance a transition fit where the allowance may be either positive or negative (clearance or interference) an interference fit where the allowance is always negative配合取决两配合零件公差带间关系概括分具正允差间隙配合允差正负渡配合总负允差盈配合

Type of Limits and Fits极限配合类型

The ISO System of Limits and Fits widely used in a number of leading metric countries is considerably more complex than the ANSI system采公制国家中广泛ISO极限配合系统ANSI极限配合系统复杂

In this system each part has a basic size Each limit of size of a part high and low is defined by its deviation from the basic size the magnitude and sign being obtained by subtracting the basic size from the limit in question The difference between the two limits of size of a part is called the tolerance an absolute amount without sign系统中零件基尺寸零件尺寸极限通基尺寸偏差定义量值符号正讨极限减基尺寸零件尺寸两极限差称公差没符号绝量值

There are three classes of fits 1) clearance fits 2) transition fits (the assembly may have either clearance or interference) and 3) interference fits存三种配合：1)间隙配合2)渡配合(装配间隙盈)3)盈配合

Either a shaftbasis system or a holebasis system may be used For any given basic size a range of tolerances and deviations may be specified with respect to the line of zero deviation called the zero line 基轴制基孔制均采定基尺寸公差范围偏差相称零线零偏差线确定
The tolerance is a function of the basic size and is designated by a number symbol called the grade—thus the tolerance grade公差基尺寸函数 通称等级数字符号标明—公差等级
The position of the tolerance with respect to the zero line also a function of the basic size—is indicated by a letter symbol (or two letters) a capital letter for holes and a lowercase letter for shafts Thus the specification for a hole and shaft having a basic size of 45 mm might be 45H8g7公差相零线位置样基尺寸函数通两字母符号表达写字母表示孔写字母表示轴样基尺寸45毫米孔轴配合规格45H8g7

Twenty standard grades of tolerances are provided called IT01 IT0 IT1~18 providing numerical values for each nominal diameter in arbitrary steps up to 500mm (for example 0~3 3~6
6~10 400~500 mm)
ISO规定二十种标准公差等级称IT01IT0IT1~18直500毫米强行分段(例0~33~66~10 400~500毫米)中公称直径提供具体数值
The value of the tolerance unit i for grades 5~16 is5～16级言公差单位i值式计算
Where i is in microns and D in millimeters里i单位微米D单位毫米

Standard shaft and hole deviations similarly are provided by sets of formulas however for practical application both tolerances and deviations are provided in three sets of rather complex tables 标准轴孔偏差样干公式提供然实际应公差偏差三张相复杂表格中规定
Additional tables give the values for basic sizes above 500 mm and for Commonly Used Shafts and Holes in two categories—General Purpose and Fine Mechanisms and Horology基尺寸500毫米般途精密机械钟表两类中常轴孔言附加表格出数值


特种加工工艺（ⅠⅡ）

Ⅰ：年高强度高硬度耐火材料需求增新加工工艺技术进步明显日益重材料说传统工艺磨削外适效率生产率极低说许新工艺难加工材料专门开发方法反加工常材料复杂结构
加工方法入特种加工者说非传统加工
超声加工电子束加工等离子射流加工激光加工等特种加工工艺代表外包括化学蚀刻工艺化学蚀刻方法样做形状复杂材料柔软工件航空铝合金
电加工工艺
利电流放电材料工艺统称电加工电加工工艺省传统加工工艺中量形式转换损失掉部分加工日趋广泛应硬材料合金时产生重加工力磨损
电加工加工刀具必加工材料硬切削率材料硬度关明显优势
时电加工象基条求必须导电条限制非常重
电加工工艺根应求三种方发展成三类通放电工作电火花加工机（EDM）通产生高频连续电火花侵蚀工件材料外两种工艺电化学加工电磨削电解方式材料基电解工艺变体电火花加工相工作机理特征
电火花加工
众周知电火花侵蚀作两久前发现电火花加工实现首先直流电火花阳极腐蚀作更强刀具损失减切削率加非常重第二腐蚀效率液体中高空气中必须指出电火花延续长会退化成动弧加工非常利
电火花电路必须具备素特征图151示工件电极间缝中充加压循环绝缘液者整体浸入液槽中加工重否电极会粘满阳极泥脏污电极工件间缝宽仅千分英寸伺服机构通控制进量保证
电火花加工工件机械性质关必考虑工件强度硬度结构什形状做切削力零放电区温度华氏千度绝缘液快速循环防发生冶金反应
电化学加工
电化学加工指电解方式材料时候电磨削类中
电化学加工电镀激励程刚相反
电解液扮演载流体角色电极工件缝隙间迅速流动液体金属离子作阳极工件体走迅速流动镀作阳极电极获加工腔电极外形拓印通改进种工艺车表面加工砌缝锯模压印工艺中电极作切削工具
成形电极工具般铜黄铜青铜锈钢制成电解液导电性非常优秀机盐溶液氯化钠硝酸钠水溶液电极中通道量流5V~25V直流电源营造15A~8Amm电流密度活化表面
电化学加工般高强度材料做形状复杂表面航空工业中涡轮叶片喷气引擎部件喷口等制锻模模腔开孔等
电化学工艺产生杂质表面实际甚做杂会工件发生热变质没切削力作工件变形样没电极磨损适合产生复杂外形加工难加工材料
电磨削电化学工艺变体工具电极包括转动研磨轮般金属粘结金刚石制成导电电解液注研磨轮工件间会研磨轮带动着工件移动磨粒轮工件间定值间隙研磨轮阴极工件阳极接入直流电源
超声加工
超声加工（UCM）通高频振荡工作头研磨液材料超声指频率高耳听频率限声音般指高16kHz频率
超声设备略图图153示变频器产生20~30kHz振幅002mm波通软材料制成称刀架连接物传刀具刀具终期腔非常均合
振动刀具工件施压连续进研磨浆拍加工区域研磨浆般调30浓度研磨粒振动头推加工面力达研磨粒重十五万倍工件砸出坑工件易碎许样坑会迅速许材料
材料伺服机构推动振动头进工件振动头间定宽缝终振动头形状压入工件形成腔
超声加工切率相低唯济易碎材料制复杂形腔办法刀具直触工件超声加工易碎件应


激光束加工
激光束加工相干光源光束加工种受激辐射增强光称激光特定条件某频率光会激发原子中电子产生入射光子频率相位完全相光子激光产生应加工根条件
激光重性质方致光束发散1~2毫弧度激光力营造高量密度环境切割典型量密度约15~150MWcm量较高时直接固体材料汽化掉已激光标记机
图161示激光钻孔设备激光束藉透镜帮助工件附聚集激光脉该材料液化汽化汽化部分迅速膨胀液化部分炸开成许微液滴四溅开未飞走部分孔壁凝固制0125~125mm长径达100细长孔
激光束加工广泛应种金属非金属陶瓷复合材料做孔等切削激光加工较清洁复合材料普通加工方式容易产生磨粒激光加工成种前景吸引革命性加工方式
孔径0005mm长径达50：1深孔已激光制作济孔径般0025mm激光金属切削厚度达32mm激光束加工电气动化工业中应日趋广泛例油泵吸油孔联轴器润滑孔采激光加工波音747飞机引擎初级增压涡轮叶片冷孔激光制做激光加工幅降低消耗电火花加工间产生竞争
激光孔锥度圆度佳125mm孔量分散般难加工激光切割激光钻孔应范围更广泛激光切割营造高速气流中进行样迅速金属切割区域移走
激光束：
<1>焊接
<2>形局部热处理针金属陶瓷表面机械性耐磨性质
<3>标记例字母数字码等标记墨水蚀刻子印针尖笔滚筒等然激光方式相昂贵考虑精度高生产率高柔性高易实现动化远程控制激光标记雕刻应日益广泛
电子束加工
电子束加工工作介质高速电子敲击工件表面发热图16250kV~200kV电压电子加速光速50~80应激光束加工相似电子束加工须真空环境中进行应较激光少工件尺寸须限定真空仓尺寸
俟电子束触工件电子动化热量涉种机理电子束究竟穿透工件尚知晓知工件表面电子压力表面张力熔化熔化部分迅速射出汽化电子束加工许中金属实施精度非常高加工表面质量更佳切割缝热切割更窄种设备需特训练员电子束金属碰撞会产生伤害性紫外线
射水流加工
手伸入风水流会感觉产生推力液体动量变化带实际液气工作介质液力加工原理射水流加工切削修整
射水流材料锯出条缝实水压达400MPa强压力已达1400Mpa射水流直径005mm~1mm间射水流切割机工作图163示包括塑料纤维橡胶木材纸张皮革绝缘绝热材料砖复合材料等
根材料切深25mm（英寸）更汽车乙烯树脂挡泥板车身嵌板轴机器引导射水流切开射水流仅高效清洁食品工业中食物分割切片
射水流加工优点：
切削方开始须底孔
产生热量
产生工件歪曲偏斜适合柔韧制造系统
工件实际太受水作潮湿切屑毛刺均少种环境友型加工工艺
磨粒射水流加工
磨粒射水流加工中水流包含磨粒碳化硅刚玉等材料率较普通射水流加工高种厚度金属非金属先进复合材料做普通切割分层切割
种工艺特适加工热稳定材料生热方法加工加强塑料走刀速度达75mmmin(25英寸分)切割金属时慢适合生产率求处记载较质量产生孔径约3mm孔深25mm左右轴机器导引水刀立体部件直接切尺寸现代化磨粒射流加工中液流研磨性系统动控制喷嘴通红宝石蓝宝石硬质合金基复合材料等延长寿命
光化学加工
光化学加工称光蚀刻应摄影术感光耐蚀术配合湿法化学腐蚀工件特定区域材料种工艺尤适合生产形状复杂薄片状工件
1986年Allen开发出工艺步骤图164示首先印制需图样光具胶片玻片等然金属薄片做化学清洁剂敷感光胶相胶片样强光曝光会成溶物质感光胶干湿两类湿式时工件须浸涂感光胶晾干干式时干胶片必须助热压力附金属片
须图样通曝光转印感光胶产生足够光强频率曝光灯胶片洗留溶部分附着金属片
采氯化 氯化铜盐酸标准混合配制蚀刻液蚀未覆盖部分做出工件
光化学加工装潢图案生产中应日益广泛制作标志标签等时标徽说明号码等字符性质标记入设计中蚀刻折痕便板件折成盒状等形态




计算机技术
引子
计算机辅助设计制造核心数字式计算机计算机身具高运算速度存储容量力进行图处理实时控制复杂说耗时重工作熟悉计算机辅助设计制造必须先解数字式计算机概念技术
现代化计算机预定程序完成数学运算逻辑运算数处理计算机体硬件式样程序软件
般计算机硬件分
中央处理器（CPU）
存储器
输入输出单元
三部分关系图11示中央处理器般认两部分：控制单元算术逻辑单元控制单元协调部分运行通输入输出部分理计算机外部数吞吐协调计算机部分间信号传输控制单元功算术逻辑单元执行数运算逻辑处理包括加减根程序作较存储器计算机储存单元数字存存储器中容易输送算数逻辑单元输入输出单元处理输入输出单元提供计算机外部交流数渠道通信通读数器印机接口设施等外设完成通输入输出单元电脑连接外部存储器磁带磁盘等
软件包括放存外存中程序指令计算机种功组织起完成务计算机处执行指令迅速准确存储器容想改写十分容易载入程序数字式计算机许场合
考虑实际应需计算机执行程序数基形态：数计算机中电信号电高低表现种形式称二进制更熟悉十进制更量软件语言作机器二进制代码间桥梁
中央处理器
中央处理器理系统组件工作数作算术逻辑操作完成功中央处理器包括：
控制单元
算术逻辑单元
控制单元根程序指令协调操作包括接收进入数安排处理时机控制单元指导算术逻辑单元工作算术逻辑单元发送数字告应数字作处理存结果处控制单元功存储存储器中系列指令称执行程序
算术逻辑单元执行加法减法较等操作作二进制数逻辑单元特殊条件改变程序执行序编辑隐藏计算数等
控制单元逻辑运算单元均寄存器完成工作寄存器容量接受保持转移数存储器寄存器包含二进制电容保存数字位位数决定计算机吞吐字长早期微机字长4型科学计算机字长达64
计算机编程语言
二进制数系代表意十进制数字母简单符号数指令二进制码形式送计算机执行时电脑二进制码序列作电脑操作指导完成加减载入载出等工作二进制码指令序决定计算机根程序数进行运算处理等操作
机器听懂二进制指令称机器码幸难阅读书写样码机器码方便编程工作更高级语言说相易学计算机程序三档：
机器码
汇编语言
面程（高级）语言
机器码汇编语言：
计算机二进制机器码条指令包含操作码操作数操作数存储器址设备址直接数字机器码编程中存储器址程序数编制整程序中查特定数程序步外程序员必须熟悉特定计算机系统机器码指令写法机宜写机器码工作冗长乏味繁琐耗时减轻写机器码工作符号语句发展出记英文样指令代二进制指令提高编程速度包含助记指令语言称汇编语言
汇编语言视低级语言程序员须非常熟知编程计算机低级语言非常高效执行快捷程序员想编写较程序计算机执行种务非常明显困难执行前汇编语言转换成机器码汇编程序转换汇编程序汇编语言程序必转换工作生成两文件机器码版程序编译单编译单显示汇编语言程序编译应法包含原汇编语言程序错误
高级语言
汇编语言面机器码高级语言正相反面程执行程序具体机器影响降机程序彼机需改
高级语言采英文式陈述应传统数学符号高级语言语句相条机器码指令
高级语言处程序员必特解机器码程序写成英文式规解题高级语言付诸执行前汇编语言样必须转机器码工作称编译器程序完成高级语言编程序转换低级语言机器码程序中存叙述错误拼错单词会根程序列出
高级语言许种常BASICCOBOLFORTRANAPLRPGPL1PASCAL
计算机接口 CRT 阴极射线示波器
计算机必须够外界交换信息数处理系统中信息交换种输入输出设备完成读卡器印机阴极控制面板等计算机辅助制造场合计算机环境仅包括外设包括制造工艺作程控制系统计算机必须加工中读取重变量做出必响应保障工艺接检视计算机程控制系统重组成部分
加工程数
指加工程计算机间必须交流数分成三类
连续模拟信号
离散二进制数信号
脉数信号
连续模拟数时间连续变量代表生产循环中已间断表示值定范围模拟信号包括例温度压力流量速度等时间连续函数范围取值穷种实际取值密度测试装备力决定分辨差值少
离散二进制数两取值例启动停止开启关闭开关马达阀灯等工况均二进制位表示数字电路中二进制码般合适电表示典型取值+5V接
脉量包含系列脉发生器生成脉电信号驱动步进电机脉量固定脉序列量取决该序列包含脉数目序列中脉计数数字数代表反数码信息转换成具定量脉序列
系统程数转换
述三数必须计算机接受监视程输入数必须进入计算机控制程输出数必须计算机生成转换送生产系统六类计算机——程接口负责前面述三类信号间转换
模数转换
触电输入
脉计数
数模转换
触电输出
脉发生器
模数转换包括实数值转相应数位值程包含许步骤涉列硬件：
传感器测实际量流量温度进度等转化值应电信号例热电偶温度转电压差例子
信号调整器机电噪声传感器输出信号
路复设备：程监视设备接模数转换器程规律抽样送转换器
输入信号做幅度调整适应模数转换器工作范围
模数转换器输入实数值处理等数位信号
数字计算机输入输出区域模数转换器中接受数极限较器般接输入输出区模数转换器间免超出限界信号干扰中央处理器正常工作
触点输入接口系列指示行程开关钮等二进制式量简单触点离散实际量计算机间媒介定期扫描状态预编值作较
数字式传感器属电测设备采集稳定点脉序列脉计数器脉序列转换数字信号信道中传递
三种设备理电脑送程数
数模转换器计算机生成数位信号转伪模拟信号样称呼计算机设置限数字信号取值法生成真正模拟信号穷取值
触点输出接口触点输入接口差系列开闭触点计算机输出量点亮指示灯报警甚控制切削油泵
脉发生器常作计算机输出转脉序列装置驱动说步进电机样东西
计算机网络结构
网络介绍：
计算机网络指处计算机间实际连接1964年首次出现发展已历数阶段：机系统局域网城域网广域网网络计算已称类史工程成通讯线数字服务信息享等计算机网络万机械工程中包含网络化制造虚拟制造柔性制造系统灵活制造
网络结构
计算机网络仅许计算机许终端信息线交换中心量实现功技术装备构造穷种变网络安排分干基类时称拓扑形态基拓扑形态图12示
点点结构中两设备间架设条通讯线路般说台计算机作终端外设连接起设备总数种方式相简便结构中量处理设备时点点连接数目复杂程度均急剧升系统造价涨网络结构种方式避免造价高点点结构显易见优势条线路断掉连接保持连接断
星型网络包括中央计算机相连周边设备中央计算机称机周边设备称隶属机机隶属机分派务作隶属机间交换器星型结构缺点旦机崩溃整网络会失效
分支结构中计算机设备起连根电缆条总线支信道系列局限性时刻仅允许设备互相通信线路享造成
环形结构中台计算机连通讯线路线路终连成环形般说台机子理计算机间通讯传台机信息实际送网络中台机子收件解读址接收讯息
树形结构中机连许处次级位置计算机台次级机连台次级机机次级机间传递信息指令均十分便捷简单缺点两意设备间连接简单
网络协议国际标准系统结构
网络中计算机间连接通信某种颁布规识称网络协议网络协议作实现秩序通信接收普通协议通讯控制协议互联网协议（TCPIP）网络系统模型阐述中国际标准组织颁布阐述协议分七层次层称呼功系统模型结构图13示
物理层次：物质媒介保证信号正确设备送彼处
数链层次：通校订证实反馈物理连接转数链
网络层次：通分类组合解决数源送目问题
传送层次：提供点点传输服务
时段层次：组织机间通讯步
提交层次：数信息提交高层户
应层次：具体申请提供访问网络环境方式
互联网应发展
世网络互联网广域虚拟网种（TCPIP）协议全球千万台计算机连成巨网络网络中台计算机址应超越区国家陆界限组成收新新闻消息享快捷服务虚拟网怕身处遥远偏僻方练互联网计算机设备越越互联网提供服务信息越越时互联网成许国家超级信息高速公路计划基础互联网发展快应万维网集中文图声音种媒体文件供享超链接导航着电信技术迅速发展互联网正义越越快速度发展成类文明缺组成

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