1、Unit 12 Material Forming ProcessesContentslNew Words&Expressions lText&TranslationlComplex Sentence AnalysislKey to ExercisesNew Words&Expressions lsqueeze skwi:z v.压榨,挤,挤榨lingot igt n.(冶)锭铁,工业纯铁lprofile prufailn.剖面,侧面,外形,轮廓lceramic sirmik adj.陶器的lsinter sint v.烧结loxidation ksideinn.氧化New Words&Expr
2、essions lsolidification slidifikein n.凝固llongitudinal lnditju:dinl adj.经度的,纵向的lerosive irusiv adj.侵蚀性的,腐蚀性的ldissolution dislu:n n.分解,解散lelectrolyte ilektrulait n.电解,电解液lsodium chloride sudim kl:raid 氯化钠New Words&Expressions lsodium nitrate sudim naitreit 硝酸钠lferrous fers adj.铁的,含铁的,亚铁的loxyacetylene
3、ksisetili:n adj.氧乙炔的lacetylene setili:n n.乙炔,电石气lcombustible kmbstbl adj.易燃的lplasma plzm n.等离子体,等离子区Text&TranslationlIn this text，a short description of the process examples will be given.But assembly and joining processes are not described here.l1.Forging lForging can be characterized as:mass conse
4、rving,solid state of work material(metal),and mechanical primary basic process-plastic deformation.A wide variety of forging processes are used,and Fig.12-1(a)shows the most common of these:drop forging.The metal is heated to a suitable working temperature and placed in the lower die cavity.The uppe
5、r die is then lowered so that the metal is forced to fill the cavity.Text&Translationl 1Excess material is squeezed out between the die faces at the periphery as flash,which is removed in a later trimming process.When the term forging is used,it usually means hot forging.Cold forging has several spe
6、cialized names.The material loss in forging processes is usually quite small.lNormally,forged components require some subsequent machining,since the tolerances and surfaces obtainable are not usually satisfactory for a finished product.Forging machines include drop hammers and forging presses with m
7、echanical or hydraulic drives.These machines involve simple translatory motions.Text&Translationl2.Rolling lRolling can be characterized as:mass conserving,solid state of material,mechanical primary basic process-plastic deformation.Rolling is extensively used in the manufacturing of plates,sheets,s
8、tructural beams,and so on.Fig.12-1(b)shows the rolling of plates or sheets.An ingot is produced in casting and in several stages.It is reduced in thickness,usually while hot.Since the width of the work material is kept constant,its length is increased according to the reductions.After the last hot-r
9、olling stage,a final stage is carried out cold to improve surface quality and tolerances and to increase strength.In rolling,the profiles of the rolls are designed to produce the desired geometry as needed.Text&Translationl3.Powder Compaction lPowder compaction can be characterized as:mass conservin
10、g,granular state of material,mechanical basic process-flow and plastic deformation.In this text,only compaction of metal powders is mentioned,but generally compaction of molding sand,ceramic materials,and so on,also belong to this category.Text&TranslationlIn the compaction of metal powders(Fig.12-1
11、(c)the die cavity is filled with a measured volume of powder and compacted at pressures typically around 500 N/mm2.During this pressing phase,the particles are packed together and plastically deformed.Typical densities after compaction are 80%of the density of the solid material.Because of the plast
12、ic deformation,the particles are“welded”together,giving sufficient strength to withstand handling.After compaction,the components are heat-treated-sintered-normally at 70%80%of the melting temperature of the material.The atmosphere for sintering must be controlled to prevent oxidation.The duration o
13、f the sintering process varies between 30 min and 2 h.the strength of the components after sintering can,depending on the material and the process parameters,closely approach the strength of the corresponding solid material.Text&TranslationlThe die cavity,in the closed position,corresponds to the de
14、sired geometry.Compaction machinery includes both mechanical and hydraulic presses.The production rates vary between 6 and 100 components per minute.l4.Casting lCasting can be characterized as:mass conserving,fluid state of material,mechanical basic process-filling of the die cavity.Casting is one o
15、f oldest manufacturing methods and one of the best known processes.The material is melted and poured into a die cavity corresponding to the desired geometry(Fig.12-1(d).The fluid material takes the shape of the die cavity and this geometry is finally stabilized by the solidification of the material.
16、Text&TranslationFig.12-1 Mass-conserving Processes in the Solid State of the Work Material Text&TranslationlThe stages or steps in a casting process are the making of a suitable mold,the melting of the material,the filling or pouring of the material into the cavity,and the solidification.Depending o
17、n the mold material,different properties and dimensional accuracies are obtained.Equipment used in a casting process includes furnaces,mold-making machinery,and casting machines.Text&Translationl5.Turning lTurning can be characterized as：mass reducing,solid state of work material,mechanical primary
18、basic process-fracture.The turning process,which is the best known and most widely used mass-reducing process,is employed to manufacture all types of cylindrical shapes by removing material in the form of chips from the work material with a cutting tool(Fig.12-2(a).The work material rotates and the
19、cutting tool is fed longitudinally.The cutting tool is much harder and more wear resistant than the work material.A variety of types of lathes are employed,some of which are automatic in operation.The lathes are usually powered by electric motors which,through various gears,supply the necessary torq
20、ue to the work material and provide the feed motion to the tool.Text&TranslationlA wide variety of machining operations or processes based on the same metal-cutting principle are available;among the most common are milling and drilling carried out on various machine tools.By varying the tool shape a
21、nd the pattern of relative work-tool motions,many different shapes can be produced(Fig.12-2(b)and(c).Text&Translationl6.EDM lElectrical discharge machining(EDM)can be characterized as：mass reducing,solid state of work material,thermal primary basic process-melting and evaporation(Fig.12-2(d).In EDM,
22、material is removed by the erosive action of numerous small electrical discharges(sparks)between the work material and the tool(electrode),the latter having the inverse shape of the desired geometry.Text&Translationl2Each discharge occurs when the potential difference between the work material and t
23、he tool is large enough to cause a breakdown in the fluid medium,fed into the gap between the tool and work piece under pressure,producing a conductive spark channel.The fluid medium,which is normally mineral oil or kerosene,has several functions.It serves as a dielectric fluid and coolant,maintains
24、 a uniform resistance to the flow of current,and removes the eroded material.The sparking,which occurs at rate of thousands of times per second,always occurs at the point where the gap between the tool and work piece is smallest and develops so much heat that a small amount of material is evaporated
25、 and dispersed into the fluid.The material surface has a characteristic appearance composed of numerous small craters.Text&Translationl7.ECM lElectrochemical machining(ECM)can be characterized as：mass reducing,solid state of work material,chemical primary basic process-electrolytic dissolution(Fig.1
26、2-2(e).Electrolytic dissolution of the work piece is established through an electric circuit,where the work material is made the anode,and the tool,which is approximately the inverse shape of the desired geometry,is made the cathode.The electrolytes normally used are water-based saline solutions(sod
27、ium chloride and sodium nitrate in 10%30%solutions).The voltage,which usually is in the range l5 V20 V,maintains high current densities,0.5 A/mm22 A/mm2,giving a relatively high removal rate,0.5 cm3/min1000 A6 cm3/min1000 A,depending on the work material.Text&Translationl8.Flame Cutting lFlame cutti
28、ng can be characterized as:mass reducing,solid state of work material,chemical primary basic process-combustion(Fig.12-2(f).In flame cutting,the material(a ferrous metal)is heated to a temperature where combustion by the oxygen supply can start.Theoretically,the heat liberated should be sufficient t
29、o maintain the reaction once started,but because of heat losses to the atmosphere and the material,a certain amount of heat must be supplied continuously.A torch is designed to provide heat both for starting and maintaining the reaction.Most widely used is the oxyacetylene cutting torch,where heat i
30、s created by the combustion of acetylene and oxygen.The oxygen for cutting is normally supplied through a center hole in the tip of the torch.Text&TranslationFig.12-2 Mass-reducing Processes in the Solid State of the Work Material Text&TranslationlThe flame cutting process can only by used for easil
31、y combustible materials.For other materials,cutting processes based on the thermal basic process-melting have been developed(are cutting,are plasma cutting,etc.).This is the reason cutting under both thermal and chemical basic processes.Text&Translationl本文将通过举例简单描述几种金属的切削加工工艺，不包括装配和连接工艺。l1.锻造锻造 l锻造是
32、对固态金属材料进行初步机械加工，是产生塑性成形的质量守恒的一种基本工艺方法。锻造有很多类型，如图12-1(a)所示为普通的落锤锻造：。金属加热到适合加工的温度，并放进下型腔里。上型腔与下型腔合拢，迫使金属充满型腔。多余的材料被从型腔接缝处挤出，并将被后续的清理型腔接缝工艺清除。当提到锻造术语时，通常意味热锻。冷锻有几种专门的名称。锻造工艺中损失的材料通常相当少。Text&Translationl通常，由于公差和表面粗糙度通常不能满足最终产品的需要，因此对锻造的零件要进行一些后续加工。锻造机械包括落锤和机械或水力驱动的锻压。这些机械包括简单的平移运动。l2.滚轧滚轧 l滚轧是对固态金属材料进行初
33、步机械加工，使其产生塑性变形的质量守恒的一种工艺方法。滚轧广泛应用在板材、薄板和结构桁条等制造中。如图12-1(b)所示为板材或薄板的滚轧。铸造生产出的铁锭加热后，经过几个阶段厚度上变薄。由于工件的宽度保持不变，工件的长度将随着厚度的变薄而变长。在热轧阶段之后，最终阶段是进行冷却，以提高表面质量、公差，并提高强度。滚轧工艺中，根据需要，轧辊的外形被设计生产成期望的几何形状。Text&Translation图12-1 固态下的工件材料质量不变工艺Text&Translationl3.粉末挤压粉末挤压 l粉末挤压是对粒状材料进行机械加工，使其产生塑性变形的质量守恒的一种工艺方法。在这里仅提到了金属
34、粉末挤压，但通常成型砂、陶瓷材料的挤压等也属于此加工工艺。l金属粉末挤压时，型腔充满标称体积粉末，如图12-1(c)所示施加大约500 N/mm2 的压力压紧粉末。在挤压过程中，粉末颗粒充满型腔并发生塑性变形。挤压后的典型密度是固态材料密度的80%。经过塑性变形，粉末颗粒“焊接”到一起，强度足够经受得住一般操作。挤压后，零件要以融化温度的70%80%进行一般烧结热处理。烧结用的空气一定要控制好，以防止氧化。根据材料和工艺参数，烧结过程的持续时间从30分钟到2小时不等，烧结后零件强度非常接近相应固体材料的强度。Text&Translationl闭合的型腔形状与期望得到的零件几何形状相对应。挤压机
35、械包括机械压力挤压机和水力压力挤压机两种。生产率为每分钟6100个零件。l4.铸造铸造 l铸造是将液态材料充满型腔的质量守恒的一种基础机械工艺方法。铸造是最古老的加工方法之一，同时是最广为人知的一种工艺。材料被融化，并灌入根据希望得到的几何形状制作的相应型腔(见图12-1(d)。液体材料充满型腔，随着材料凝固，零件的几何形状最终固定下来。Text&Translationl铸造工艺中的阶段或步骤包括制作适当的铸型，熔化材料，将材料充满或灌注进型腔和凝固。根据采用的不同铸型材料，可获得不同特性和尺寸精度的铸件。铸造工艺中使用的设备包括熔炉、铸型制作机械和铸造机械。Text&Translationl
36、5.车削车削 l车削是通过破裂，对固态工件进行初步的基础机械加工，质量减少的一种工艺方法。车削工艺广为人知，并且是使用最广泛的质量减少的工艺方法。车削工艺中使用切削刀具，从工件上以碎片形状切去材料(见图12-2(a)，用于生产各种类型的圆柱形工件。加工时，工件旋转，切削刀具纵向进给。切削刀具比工件更加坚硬和抗磨损。可采用不同类型的车床，有些还是自动操作的。车床通常是电动机驱动的，通过不同的齿轮系统，向工件提供必要的扭矩，使刀具进行进给动作。Text&Translationl利用相同金属切削原理，也会得到完全不同的加工操作或工艺，磨和钻就是其中最普通的一个例子，由于采用不同的加工刀具而产生完全不
37、同的两种加工操作。不同的刀具形状和相关加工刀具运动模式，可生产出许多不同的形状(见图12-2(b)和12-2(c)。Text&Translationl6.电火花加工电火花加工 l电火花加工(EDM)是通过融化和蒸发，对固态工件进行以热变化为主要基础，质量减少的一种工艺方法，如图12-2(d)所示。在电火花加工中，通过工件和工具(电极)之间许多小电火花的侵蚀动作来去除材料，工具具有希望得到的工件几何形状的反转形状。当工件和工具之间电压差异足够大时，液体介质被击穿，并在电压作用下，进入工具和工件之间的缝隙，形成传导火花的通道，这时出现了放电。流体介质通常是矿物油或煤油，它有几种功能：作为绝缘的流体
38、和散热剂，为电流维持不变的电阻，去除侵蚀的材料。电火花以每秒成千上万次的速度出现，且总是出现在工具和工件间缝隙最小的点上，产生大量的热使得少量的材料给侵蚀并散入液体中。电火花加工后的材料表面具有的特点是它由许多小弹坑组成。Text&Translation图12-2 固态下的工件材料质量减少工艺Text&Translationl7.电气化学加工电气化学加工 l电气化学加工(ECM)是通过电解分解，对固态工件进行以化学变化为主要基础、质量减少的一种工艺方法(见图12.-2(e)。工件的电解分解是通过一个电路实现的，工件作为阳极，工具作为阴极。工具具有希望得到的工件几何形状的近似反转形状。电解液通常
39、使用水基盐(氯化钠10%和硝酸钠30%)。通常使用520 V电压，可维持高的电流密度0.5 2A/mm2，相对高的移动速度0.56 cm3/min1000A，这些都根据工件来具体确定。Text&Translationl8.火焰切割火焰切割 l火焰切割是通过燃烧，对固态工件进行以化学变化为主要基础，质量减少的一种工艺方法(见图12-2)。火焰切割中，材料(含铁金属)被加热到供氧时可开始燃烧的温度。理论上，一旦开始燃烧，释放的热量应该足够维持反应，但由于热量散失到空气和材料中，因此要不断地提供一定量的热量。设计一个喷枪来提供开始和维持反应所需的热量。使用最广泛的是乙炔切削喷枪，通过燃烧乙炔和氧气产
40、生热量。切削用的氧气通常通过喷枪顶端中心的孔提供。l火焰切削工艺仅适用于易燃材料。对于其他材料，可采用通过熔化、以热变化为基础的切削工艺(切削、等离子切削等)。这是以热变化和化学变化为基础的切削工艺的前提。Complex Sentence Analysisl 1 Excess material is squeezed out between the die faces at the periphery as flash,which is removed in a later trimming process.多余的材料被从型腔接缝处挤出，并将被后续的清理型腔接缝工艺清除。l which：引导定
41、语从句，修饰excess material l as flash：如闪电一样快速l trimming process：清理缝隙的过程Complex Sentence Analysisl2 Each discharge occurs when the potential difference between the work material and the tool is large enough to cause a breakdown in the fluid medium,fed into the gap between the tool and work piece under pre
42、ssure,producing a conductive spark channel.当工件和工具之间电压差异足够大时，流体介质被击穿，并在电压作用下，进入工具和工件之间的缝隙，形成传导火花的通道，这时出现了放电。l when：引导时间状语从句l fed into：过去分词短语做状语修饰 fluid medium l producing a conductive spark channel 现在分词短语做伴随状语Key to Exercisesl.Translate the following phrases into Chinese or English.l1.材料成形工艺方法 l2.for
43、gingl3.滚轧 l4.powder compactionl5.一般烧结热处理l6.castingl7.车削 l8.electical discharge machining(EDM)l9.电气化学加工 l10.flame cuttingKey to Exercisesl.Mark the following statement with True(T)or False(F)according to the text.l1T l2.F l3.T l4.T l5.TKey to Exercisesl.Fill in the blanks with the suitable words or p
44、hrases given below.l1.be characterized asl2.A wide variety ofl3.is heated tol4.fill the cavityl5.a later trimming processl6.several specialized namesKey to Exercisesl.Translate the Chinese parts given in the brackets into English.l1.the filling or pouring of the material into the cavity,and the solidificationl2.solid state of work material fracturel3.melting and evaporationl4.electrolytic bustionlThe end!
