Unit11FundamentalsofMaterialForming机电专业英语图文课件.ppt

Unit 11 Fundamentals of Material FormingContentslNew Words & Expressions lText & TranslationlComplex Sentence AnalysislKey to ExercisesNew Words & Expressions lsynonymously [si'nɔniməsli] adv. 同义地lcohesion [kəu'hi:ʒən] n. 结合，凝聚，（物理）内聚力结合lsubassembly [sʌbə'sembli] n. 部件，组件limpregnate [im'pregneit] v. 使充满，使怀孕；注入，灌输ladj.充满的，怀孕的lgalvanise ['gælvənaiz] v .& n. 电镀lfoil [fɔil] n. 箔，金属薄片，烘托，衬托；v. 贴箔于……，衬托，阻止lsubstrate ['sʌbstreit] n. (=substratum) 底层，下层，（地）底土层，基础New Words & Expressions ldeliberately [di'libəritli] adv. 有目的地，故意地lmetallurgy [me'tælədʒi] n. 冶金, 冶金学，冶金术lmacroscopically [͵mækrə'skɔpikəli] adv. 宏观上lrecovery [ri'kʌvəri] n. 回复lrecrystallization [ri'kristəlaizeiʃən] n. 再结晶ltangled ['tæŋgld] adj. 紊乱的；复杂的ldislocation [͵dislə'keiʃən] n. 位错lpolygonized subgrain structure 多边形亚晶结构lgrain growth 晶粒生长Text & Translationl1. Material Forming Processes as a System lThe term material forming refers to a group of manufacturing methods by which the given shape of a workpiece (a solid body) is converted to another shape without change in the mass or composition of the material of the workpiece. lClassification of manufacturing processes: Material forming is used synonymously with deformation or deforming and comprises the methods in group II of the manufacturing process classification shown below. The manufacturing processes are divided into six main groups. Text & TranslationlGroup I—Primary forming. Original creation of a shape from the molten or gaseous state or from solid particles of undefined shape，that is，creating cohesion between particles of the material. lGroup II—Deforming. Converting a given shape of a solid body to another shape without change in mass or material composition，that is，maintaining cohesion. Text & TranslationlGroup III—Separating. Machining or removal of material，that is，destroying cohesion. lGroup IV—Joining. Uniting of individual workpieces to form filling subassemblies，filling and impregnating of workpieces，and so on，that is，increasing cohesion between several workpieces. lGroup V—Coating. Application of thin layers to a workpiece，for example，galvanizing，painting，coating with plastic foils，that is，creating cohesion between substrate and coating. Text & TranslationlGroup VI—Changing the material propertie. Deliberately changing the properties of the workpiece in order to achieve optimum characteristics at a particular point in the manufacturing process.[1]These methods include changing the orientation of micro-particles as well as their introduction and removal，such as by diffusion，that is，rearranging，adding，or removing particles. lIn manufacturing technology，particularly in groups I to IV，we are continually faced with the problem of how to manufacture most economically a particular technical product，with specific tolerance requirements，surface structure，and material properties. Text & Translationl2. Principles of Plastic Forming lPlasticity theory is the foundation for the numerical treatment of metal forming processes. Materials science and metallurgy can explain the origins of the plastic state of metallic bodies and its dependence on various parameters，such as process speed，prior history，temperature. The essentially older plasticity theory deals with the calculation of stresses，forces，and deformation. Text & TranslationlPlasticity theory is rather based on macroscopically observed phenomena，in other words，on the properties of materials which can be observed and measured directly in deformation processes，such as the tension and compression tests. This leads to the following simple description of the plastic state. Text & Translationl[2]Plasticity is the capacity of a material to change its shape permanently under the action of forces when the corresponding stress state reaches a material-dependent critical magnitude called yield strength or initial flow stress. As seen from the results of the tension test，when the stress is below the yield strength, the deformation disappears upon unloading：the material behaves elastically. If the stress exceeds the yield strength，permanent deformation will be formed. Upon unloading，the workpiece has a form that is different from its initial one. It is then said to have been plastically or permanently deformed，or，if a definite final shape was sought，it has been (trans) formed. Materials which behave in an elastic-plastic manner can，after having been permanently deformed，again be loaded until the flow stress is reached without additional permanent deformation setting in. This increase in the flow stress as a result of prior deformation is called strain hardening or work hardening. Text & TranslationlWork hardening can be balanced by the dynamic softing processes of recovery and recrystallization. lThe original cold-worked microstructure is composed of deformed grains containing a large number of tangled dislocations. When we first heat the metal，the additional thermal energy permits the dislocation to move and form the boundaries of a polygonized subgrain structure. The dislocation density，however，is virtually unchanged. This low temperature treatment removes the residual stresses due to cold working without causing a change in dislocation density is called recovery. Text & TranslationlWhen a cold worked metallic material is heated above a certain temperature (recrystallization temperature)，rapid recovery eliminates the residual stresses and produce the polygonized dislocation structure. New small grains then nucleate at the cell boundaries of the polygonized structure，eliminating most of the dislocations. Because the number of dislocations is greatly reduced，the recrystallized metal has low strength and high ductility. The process of formation of new grains by heat treating a cold-worked material is known as recrystallization. Recrystallization may be followed by grain growth if the temperature is sufficiently high. Text & Translationl1.材料成形工艺体系材料成形工艺体系l材料成形指的是将固体材料工件的原有形状变成另外一种形状而不改变工件材料的质量和化学成分的一系列制造工艺方法的总称。

l制造工艺的分类：材料“成形”常常与下面的制造工艺分类的第II组方法中的“变形”通用机械制造工艺可以分为下面6大主要类别Text & Translationl第I 类——最初的成形即将材料由熔融态、气态或未定形的固态颗粒制成一定的形状，也就是将材料的粒子牢固地聚合起来l第II 类——变形将固体材料由一种给定的形状转变为另外的一种形状而不改变原来的成分和质量，即保持聚合状态l第Ⅲ类——分离切削加工或材料的去除，即分离Text & Translationl第Ⅳ类——连接将单个的工件连接到一起以形成大的零部件、工件等，即使分散的工件连接起来，增加工件间的聚合力l第Ⅴ类—涂覆在工件表面涂覆薄层，如电镀、刷油漆、喷塑等，即要使材料的基体与涂覆层间产生聚合力Text & Translationl第Ⅵ类—材料属性的变化有目的地改变材料的性能以在加工处理过程中获得某些方面的最优性能这些方法包括改变微粒的取向，以及通过扩散产生或消除这些微粒，即重排、增加或减少微粒l在制造工艺特别是Ⅰ至Ⅳ类工艺中，我们总是要面对在兼顾保证满足公差、表面构造及材料性能的前提下如何最经济地制造好一个特定的科技产品的问题。

Text & Translationl2.塑性成形原理塑性成形原理 l塑性理论是金属成形工艺方法数学处理的基础材料科学及冶金学可以解释金属固体塑性状态的本质及其各影响参数，如成形速度、前期工艺历史及温度等但早期的塑性理论主要进行应力、力及变形的计算l塑性理论是基于宏观上所观察到的现象建立起来的，换句话说，就是以材料在变形过程中如拉伸及压缩试验中所能观察到或测试出的性能为基础的这就引出了下面关于塑性状态的简单定义Text & Translationl塑性是材料在外力(应力状态达到了该材料的临界值，即屈服强度或初始流变应力时) 的作用下永久地改变其形状的能力正如我们在拉伸试验中可看到的那样，当应力低于屈服强度时，载荷去除后变形将自行回复：此时，材料的变形为弹性行为如果应力增加到高于屈服极限，则会产生永久变形，卸载后，工件变成了与原来不同的新的形状此时，我们就说材料发生了塑性变形或永久变形，或者最终变成了一定的形状，就可以说材料成形了具有弹塑性行为的材料在产生了永久变形后再次承载时，在达到流变应力前不会再发生塑性变形这种由于前面的变形导致流变应力增大的现象称为形变硬化或加工硬化Text & Translationl加工硬化现象可以通过回复和再结晶的动态软化过程消除。

l产生了加工硬化的显微结构由含有大量复杂的位错变形的晶粒组成，当将这种金属加热时，热能会促使位错运动并形成多边形亚晶粒的边界但是位错密度不会变小这种在较低温度下加硬化以消除残余应力而没有改变位错密度的过程称为回复Text & Translationl当把产生了加工硬化的金属材料加热到某一温度(再结晶温度)以上时，快速的回复将进一步消除残余应力并形成多边形的位错结构新的细小的晶粒在多边形晶粒的晶界处形成核，同时大多数位错被消除由于位错数量大大减少，所以再结晶金属的强度下降而塑性增大这种通过加热产生加工硬化的材料以形成新晶粒的过程叫做再结晶再结晶时如加热温度太高，将会引起晶粒变大 Complex Sentence Analysisl [1] These methods include changing the orientation of micro-particles as well as their introduction and removal，such as by diffusion，that is，rearranging，adding，or removing particles.这些方法包括改变微粒的取向，以及通过扩散产生或消除这些微粒，即重排、增加或消除微粒。

l① that is 即，也就是说l② rearranging：重排Complex Sentence Analysisl[2] Plasticity is the capacity of a material to change its shape permanently under the action of forces when the corresponding stress state reaches a material-dependent critical magnitude called yield strength or initial flow stress. 塑性是材料在外力(应力状态达到了该材料的临界值，即屈服强度或初始流变应力时) 的作用下永久地改变其形状的能力 l① under the action of：在……作用下l② critical magnitude ：临界值Key to ExerciseslⅠⅠ. Translate the following phrases into Chinese or English.l1. 材料成型l2. classification of manufacturing progressesl3. 材料属性l4. surface structurel5. 塑性成型原理l6. process speedl7. 形变硬化l8. polygonized subgrain structure l9.位错密度l10.grain growthKey to ExerciseslⅡⅡ. Mark the following statement with True (T) or False (F) according to the text.l1．Tl2. F l3. Tl4. T l5. FKey to ExerciseslⅢⅢ. Fill in the blanks with the suitable words or phrases given below.l1. As seen froml2. below the yield strengthl3. is different froml4. It is then said tol5. in an elastic-plastic mannerl6. as a result ofKey to ExerciseslⅣⅣ.Translate the Chinese parts given in the brackets into English.l1. how to manufacture most economically a particular technical productl2. changing the orientation of micro-particlesl3. balanced by the dynamic softing processes of recovery and recrystallization. l4. without causing a change in dislocation densityl5. if the temperature is sufficiently highlThe end!。