机械设计制造及其自动化专业英语-Unit-02-Selection-of-Construction-Materials分解课件.ppt--（课件中不含音视频）

1、word availability 可用性 veilbiliti fabrication 制造 fbrikein forgeability 可锻性 f:dblt nickle 鎳 nikl chromium 铬 kroumjm vanadium 钒 vneidim discernible 可辨别得出的；可看出的 disnbl ductility 延(展)性；韧性 dktiliti cracking 开裂；裂纹 krkiSelection of Construction Materials1word Work-harden 加工硬化；冷作硬化 anneal 退火 ni:l warp 翘曲；变形

2、w:rp preheat 预热 prihit microstructure 显微结构 makrostrkt mislead 使误解；误导 msli:d ream 铰孔 rim arbitrary 任意的 :rbitrri Selection of Construction Materials2Selection of Construction Materials There is not a great difference between“this”steel and“that”steel;all are very similar in mechanical properties.在钢之间没

3、有太大的区别；所有的钢在机械性能方面都是近似的。3Selection of Construction Materials Selection must be made on factors such as hardenability,price,and availability,and not with the idea that“this”steel can do something no other can do because it contains 2 percent instead of 1 percent of a certain alloying element,or becau

4、se it has a mysterious mistiris name.它们的选取标准是诸如脆硬性，价格，和可用性等。不仅仅是因为这种钢含有2的合金元素另一种钢含有1而使前者具有了后者没有的某些能力，或者是某种钢具有神奇的名字。4Selection of Construction Materials A tremendous range of properties is available in any steel after heat treatment;this is particularly true of alloy steels.经过热处理后，任何一种钢都具有大范围的特性；这种性质

5、同样在合金钢中存在。5Considerations in fabrication The properties of the final part(hardness,strength,and machinability),rather than properties required by forging,govern the selection of material.最后零件的特性（硬度、强度和可加工性）而不是锻造特性决定了材料的选择。6Considerations in fabrication The properties required for forging have very l

6、ittle relation to the final properties of the material;therefore,not much can be done to improve its forgeability.可锻性与材料的最后特性联系不大；因此，提高金属的可锻造性价值不大。Higher-carbon steel is difficult to forge.Large grain size is best if subsequent heat treatment will refine the grain size.高碳钢很难锻造。如果后续的热处理会细化晶粒尺寸，那么大的晶粒

7、尺寸是最好的。7Considerations in fabrication Low-carbon,nickel-chromium steels are just about as plastic at high temperature under a single 520-ftlb(1 ftlb=1.35582J)blow as plain steels of similar carbon content.Nickel decreases forgeability of medium-carbon steels,but has little effect on low-carbon steel

8、s.在高温下低碳，镍铬合金钢在受到520-ftlb的冲击下表现出与相同碳含量普通钢几乎同样的塑性。镍减少了中碳钢的可锻性，但对低碳钢影响不大。8Considerations in fabrication Chromium seems to harden steel at forging temperatures,but vanadium has no discernible effect;neither has the method of manufacture any effect on high-carbon steel.铬在锻造温度下时使钢硬化，但钒没有明显的效果；两种加工方法对高碳钢没

9、有影响。9Formability The cold-formability of steel is a function of its tensile strength combined with ductility.The tensile strength and yield point must not be high or too much work will be required in bending;likewise,the steel must have sufficient ductility to flow to the required shape without crac

10、king.钢的冷成形是它的拉伸强度和延展性相结合的结果。拉伸强度和屈服点不能太高否则在发生弯曲时需要做很多工作；相似地，钢应该有高延展性，使其在没断裂的情况下成形。10Formability The force required depends on the yield point,because deformation starts in the plastic range above the yield point of steel.Work-hardening also occurs here,progressively stiffening the metal and causing

11、difficulty,particularly in the low-carbon steels.加工力的大小取决于屈服点，因为钢在屈服点之上才开始变形。与此同时，加工硬化也同时发生，金属变得越来越硬，增加加工难度，尤其在低碳钢中容易发生。11Formability It is quite interesting in this connection to discover that deep draws can sometimes be made in one rapid operation that could not possibly be done leisurely leli in

12、two or three.在这方面，相当有趣的是你将发现有时可通过一次快速加载完成大拉伸，但以缓慢的方式两三次加载却不能实现。12Formability If a draw is half made and then stopped,it may be necessary to anneal before proceeding,that is,if the piece is given time to work-harden.This may not be a scientific statement,but it is actually what seems to happen.如果拉伸进行

13、了一半就停止了，那么在再加工之前应先退火，也就是说，如果工件已经有时间被加工硬化。这不是一种科学的叙述方法，但确实是发生了。13Internal stresses Cold forming is done above the yield point in the work-hardening range,so internal stresses can be built up easily.Evidence of this is the springback as the work leaves the forming operation and the warpage in any subs

14、equent heat treatment.在高于屈服点的加工硬化区进行冷加工很容易产生内应力。例如工件停止成型加工后会发生回弹，在随后的热处理后，工件会发生翘曲。14Internal stresses Even a simple washer might,by virtue of the internal stresses resulting from punching and then flattening,warp severely during heat treating.即使是一个简单的垫圈，由于打孔和随后的平整加工中产生内应力，也会在热处理中呈现严重的翘曲。15Internal s

15、tresses When doubt exists as to whether internal stresses will cause warpage,a piece can be checked by heating it to about 1100 and then letting it cool.当是否内应力会引起翘曲的怀疑存在时，可以通过将工件加工至1100 然后进行冷却来验证。16Internal stresses If there are internal stresses,the piece is likely to deform.Pieces that will warp s

16、everely while being heated have been seen,yet the heat-treater was expected to put them through and bring them out better than they were in the first place.如果存在内应力，工件会发生变形。经过热处理的工件像我们看到的那样会发生严重的翘曲，但是我们仍然希望工件被扔到热处理炉中被处理，这样好过它存在内应力的状态。17Welding The maximum carbon content of plain carbon steel safe for

17、 welding without preheating or subsequent heat treatment is 0.3%.higher-carbon steel is welded every day,but only with proper preheating.不需要预热或之后进行热处理就能安全焊接的最高碳含量为0.3。高碳钢通过合适的预热通常也可焊接。18Welding There are two important factors:the amount of heats that is put in;the rate at which it is removed.Welding

18、 at a slower rate puts in more heat and heats a large volume of metal,so the cooling rate due to loss of heat to the base metal is decreased.A preheat will do the same thing.有两点值得注意：吸收热量的多少；热量移除速度。低速焊接带来了更多的热量，这对金属的大量体积进行了加热，由于基体金属热损失的减少因此冷却速度降低。预热可以取得与之相当的效果。19Welding For example,SAE 4,150 steel,pr

19、eheated to 600 or 800 ,can be welded readily.When the flame or arc is taken away from the weld,the cooling rate is not so great,owing to the higher temperature of the surrounding metal and slower cooling results.Even the most rapid air-hardening steels are weldable if preheated and welded at a slow

20、rate.例如当SAE 4,150钢被预热至600 或800 时可以很好的焊接。由于周围金属的较高温度，当焊接弧移开焊接点后，冷却速度不会太快，产生了低速冷却的结果。即使是冷作硬化速度最快的金属也可以通过预热和慢速焊接达到良好的焊接效果。20Machinability Machinability means several things.To production men it generally means being able to remove metal at the fastest rate,leave the best possible finish,and obtain the

21、longest possible tool life.Machinability applies to the tool-work combination.可加工性意味着几件事情。对于加工者来说，它意味着可以快速的移除金属，取得最好的加工效果，得到最长的刀具寿命。可加工性是刀具和零件的结合。21Machinability It is not determined by hardness alone,but by the toughness,microstructure,chemical composition,and tendency of a metal to harden under co

22、ld work.In the misleading expression“too hard to machine”,the word“hard”is usually meant to be synonymous with“difficult”.加工性不仅仅只由硬度决定，它还由韧性，微观结构，化学成分和在冷加工下金属所呈现的硬化特性所决定。在容易混淆的表示“难加工”中，“hard”与“difficult”同义。22Machinability Many times a material is actually too soft to machine readily.Softness and tou

23、ghness may cause the metal to tear and flow ahead of the cutting tool rather than cut cleanly.Metal that are inherently soft and tough are sometimes alloyed to improve their machinability at some sacrifice in ductility.Examples are use of lead in brass and of sulfur in steel.许多时候，因为材料过软而难于稳定加工。材料柔软性

24、和韧性能够产生金属撕裂，使金属在完成切削前流动至刀具前端。本质上柔软而坚韧的金属往往会被加入合金从而牺牲它的延展性来提高加工性能。如黄铜中加入铅钢中加入硫磺。23Machinability Machinability is a term used to indicate the relative ease with which a material can be machined by sharp cutting tools in operations such as turning,drilling,milling,broaching,and reaming.机械加工性能是在指对工件材料使用

25、刀具进行诸如车、钻、铣、拉削、铰加工时的难易程度。24Machinability In the machining of metal,the metal being cut,the cutting tool,the coolant,the process and type of machine tool,and the cutting conditions all influence the results.By changing any one of these factors,different results will be obtained.在对金属进行加工时，被切削的金属，切削刀具，

26、冷却液，使用的机床的制程与种类，切削条件均影响着切削效果。改变任何一种均会产生不同的切削效果。25Machinability The criterion upon which the ratings listed are based is the relative volume of various materials that may be removed by turning under fixed conditions to produce an arbitrary fixed amount of tool wear.切削效果等级评定的标准是：车削时在固定的切削条件下产生一定量的刀具磨损时，被加工试件相应的材料去除量。2627