专业英语28-33.doc

28. Machining FundamentalsVocabulary:machining mE5Fi:niN 加工universally ju:ni5v:sEli 一般的; 普遍的; 普通的form fC:m 形状, 形态workpiece 5wE:kpi:s 工件chip tFip 碎片，屑片portable 5pC:tEbl 手提(式)的, 便携式的raw rC: 未加工的available E5veilEbl 可用到的, 可利用的exterior eks5tiEriE 外部的, 表面的desire di5zaiE 期望, 希望logically 5lRdVikEli 论理上, 逻辑上finish 5finiF (表面)粗糙度deformation 7di:fC:5meiFEn 变形internal in5tE:nl 内(部)的Text:Machining as a shape-producing method is the most universally used and the most important of all manufacturing processes. Machining is a shape-producing process in which a power-driven device causes material to be removed in chip form. Most machining is done with equipment that supports both the workpiece and cutting tool although in some cases portable equipment is used with unsupported workpiece.Low setup cost for small quantities. Machining has two applications in manufacturing. For casting, forging, and pressworking, each specific shape to be produced, even one part, nearly always has a high tooling cost. The shapes that may be produced by welding depend to a large degree on the shapes of raw material that are available. By making use of generally high cost equipment but without special tooling, it is possible, by machining, to start with nearly any form of raw material, so long as the exterior dimensions are great enough, and produce any desired shape from any material. Therefore, machining is usually the preferred method for producing one or a few parts, even when the design of the part would logically lead to casting, forging or pressworking if a high quantity were to be produced.Close accuracies, good finishes. The second application for machining is based on the high accuracies and surface finishes possible. Many of the parts machined in low quantities would be produced with lower but acceptable tolerances if produced in high quantities by some other process.On the other hand, many parts are given their general shapes by some high quantity deformation process and machined only on selected surfaces where high accuracies are needed. Internal threads, for example, are seldom produced by any means other than machining and small holes in pressworked parts may be machined following the pressworking operations.29. Basic Machining VariablesVocabulary:adequately 5Adikwitli 足够地geometry dVi5Cmitri 表面形状；几何学appropriate E5prEuprit 恰当的tough tQf 坚强的, 坚韧的character 5kAriktE (事物的)特性, 性质express iks5pres 表达magnitude 5mAnitju:d 大小, 数量, 巨大, 广大reciprocate ri5siprEkeit 往复运动stroke strEuk 行程inversely 5in5vE:sli 相反地, 倒转地otherwise 5QTEwaiz 另外的, 其他方面的similar 5similE 相似的rectilinear 5rektE5lini:E 直线的rough 5rQf 粗糙的, 粗略的, 大致的Text:The basic tool-work relationship in cutting is adequately described by means of four factors: tool geometry, cutting speed, feed, and depth of cut.The cutting tool must be made of an appropriate material; it must be strong, tough, hard, and wear resistant. The tools geometry, characterized by planes and angles, must be correct for each cutting operation.Cutting speed is the rate at which the work surface passes by the cutting edge. It may be expressed in feet per minute. For efficient machining the cutting speed must be of a magnitude appropriate to the particular work-tool combination. In general, the harder the work material, the slower the speed.Feed is the rate at which the cutting tool advances into the workpiece. Where the workpiece or the tool rotates, feed is measured in inches per revolution. When the tool or the work reciprocates, feed is measured in inches per stroke. Generally, feed varies inversely with cutting speed for otherwise similar conditions.The depth of cut, measured inches, is the distance the tool is set into the work. It is the width of the chip in turning or the thickness of the chip in a rectilinear cut. In roughing operations, the depth of cut can be larger than for finishing operations.30. The Effect of Changes in Cutting Parameters on Cutting TemperaturesVocabulary:generate 5dVenE7reit 产生primary 5praimEri 第一位的, 主要的deformation 7di:fC:5meiFEn 变形zone zEun 地域，区域distribution 7distri5bju:FEn 散布，分步throughout Wru(:)5aut 遍及，贯穿typical 5tipikEl 典型的isotherm 5aisEuWE:m 等温线gradient 5reidiEnt 梯度, 倾斜度, 坡度adjacent E5dVeisEnt 邻近的, 接近的virtually 5v:tjJEli 事实上, 实质上convert kEn5vE:t 使转变, 转换rake reik angle前角constant 5kCnstEnt 不变的, 持续的tend tend 趋向, 往往是scale skeil 刻度，衡量，比例proportion prE5pC:FEn 比例, 均衡parameter pE5rAmitE 参数, 参量consequently 5kRnsikwEntli 从而, 因此wear wiE 磨损assess E5ses 估定, 评定accurate 5Akjurit 正确的, 精确的yield ji:ld 出产, 生长, 生产detail 5di:teil 细节, 详情metallographic mi7tAlE5rAfik 金相学的measurement 5meVEmEnt 测量法, 度量range reindV 范围microscopy mai5krEJskEpi 显微镜方法tempering 5tempEriN 回火martensitic 9mB:tinzitik 马氏体的matrix 5meitriks 结构，矩阵元素turning tool 车刀twist twist drill麻花钻Text:In metal cutting operations, heat is generated in the primary and secondly deformation zones and this results in a complex temperature distribution throughout the tool, workpiece and chip. A typical set of isotherms is shown in figure where it can be seen that, as could be expected, there is a very large temperature gradient throughout the width of the chip as the workpiece material is sheared in primary deformation and there is a further large temperature in the chip adjacent to the faces as the chip is sheared in secondary deformation. This leads to a maximum cutting temperature a short distance up the face from the cutting edge and a small distance into the chip.Since virtually all the work done in metal cutting is converted into heat, it could be expected that factors which increase the power consumed per unit volume of metal removed will increase the cutting temperature. Thus an increase in the rake angle, all other parameters remaining constant, will reduce the power per unit volume of metal removed and the cutting temperatures will reduce. When considering increase in undeformed chip thickness and cutting speed, the situation is more complex. An increase in undeformed chip thickness tends to be a scale effect where the amounts of heat which pass to the workpiece, the tool and chip remain in fixed proportions and the changes in cutting temperature tend to be small. Increase in cutting speed, however, reduce the amount of heat which passes into the workpiece and this increase the temperature rise of the chip in primary deformation. Further, the secondary deformation zone tends to be smaller and this has the effect of increasing the temperatures in this zone. Other changes in cutting parameters have virtually no effect on the power consumed per unit volume of metal removed and consequently have virtually no effect on the cutting temperatures. Since it has been shown that even small changes in cutting temperature have a significant effect on tool wear rate, it is appropriate to indicate how cutting temperatures can be assessed from cutting data.The most direct and accurate method for measuring temperatures in high-speed-steel cutting tools is that of Wright & Trent which also yields detailed information on temperature distributions in high-speed-steel cutting tools. The technique is based on the metallographic examination of sectioned high-speed-steel tools which relates microstructural changes to thermal history.Trent has described measurements of cutting temperatures and temperature distributions for high-speed-steel tools when machining a wide range of workpiece materials. This technique has been further developed by using scanning electron microscopy to study fine-scale microstructural changes arising from over tempering of the tempered martensitic matrix of various high-speed-steels. This technique has also been used to study temperature distributions in both high-speed-steel single point turning tools and twist drills.31. Types of Tool WearVocabulary:discount 5diskaunt 忽视，不考虑brittle 5britl 易碎的, 脆弱的fracture 5frAktFE 破裂flank wear后刀面磨损minor cutting edge 副切削刃responsible ris5pCnsEbl 有责任的, 负责的bulk bQlk 大小, 大批, 大多数oversize 5EuvE5saiz 超差的abrasive E5breisiv 研磨的seizure 5si:VE 卡住，捕捉localize 5lEJkElaiz 局部化pit 5pit 凹陷，凹坑crater5kreitE wear 前刀面磨损、月牙洼磨损refer ri5fE: 提交, 谈及, 归诸于respect ris5pekt 某方面severe si5viE 严重的, 严峻的criterion krai5tiEriEn 标准, 准据, 规范significantly si5nifikEntli 重大地，重要地pronounced prE5naunst 显著的, 断然的, 明确的introduce 7intrE5dju:s 传入, 引进previous 5pri:vjEs 在前的, 早先的scale skeil 薄片occasionally E5keiVEnEli 有时候, 偶而property 5prCpEti 特性relatively 5relEtivli 相对地notchnCtF wear 条纹状磨损progressive prE5resiv 渐进的，前进的eventually i5ventjJEli 最后, 终于dramatically drEmAtikEli 戏剧地, 引人注目地catastrophically 9kAtEstrCfik 悲惨的, 灾难的capable 5keipEbl 有能力的, 能干的scrap skrAp 废弃carbide 5kB:baid 硬质合金onset 5Cnset 开始non-uniform 5nCn5ju:nifC:m 不一致的, 不均匀的meaningful 5mi:niNful 有意义的Text:Discounting brittle fracture and edge chipping, which have already been dealt with, tool wear is basically of three types. Flank wear, crater wear, and notch wear. Flank wear occurs on both the major and the minor cutting edges. On the major cutting edge, which is responsible for bulk metal removal, this results in increased cutting forces and higher temperatures which if unchecked can lead to vibration of the tool and workpiece and a condition where efficient cutting can no longer take place. On the minor cutting edge, which determines work-piece size and surface finish, flank wear can result in an oversized product which has poor surface finish. Under most practical cutting conditions, the tool will fail due to major flank wear before the minor flank wear is sufficiently large to result in the manufacture of an unacceptable component.Because of the stress distribution on the tool face, the frictional stress in the region of sliding contact between the chip and the face is at a maximum at the start of the sliding contact region and is zero at the end. Thus abrasive wear takes place in this region with more wear taking place adjacent to the seizure region than adjacent to the point at which the chip lose contact with the face. This results in localized pitting of tool face some distance up the face which is usually refered to as cratering and which normally has a section in the form of a circular arc. In many respects and for practical cutting conditions, crater wear is a less severe form of wear than flank wear and consequently flank wear is a more common tool failure criterion. However, since various authors have shown that the temperature on the face increases more rapidly with increasing cutting speed than the temperature on the flank, and since the rate of wear of any type is significantly affected by changes in temperature, crater wear usually occurs at high cutting speeds.At the end of the major flank wear land where the tool is in contact with the uncut workpiece surface, it is common for the flank wear to be more pronounced than along the rest of the wear land. This is because of localized effects such as a hardened layer on the uncut surface caused by work hardening introduced by a previous cut, an oxide scale, and localized high temperatures resulting form the edge effect. This localized wear is usually referred to as notch wear and occasionally is very severe. Although the presence of the notch will not significantly affect the cutting properties of the tool, the notch is often relatively deep and if cutting were to continue there would be a good chance that the tool would fracture.If any form of progressive wear allowed to continue, eventually the wear rate would increase dramatically and the tool would fail catastrophically, i.e. the tool would be no longer capable of cutting and, at best, the workpiece would be scrapped whilst, at worst, damage would be caused to the machine tool. For carbide cutting tools and for all types of wear, the tool is said to have reached the end of its useful life long before the onset of catastrophic failure. For high-speed-steel cutting tools, however, where the wear tends to be non-uniform it has been found that the most meaningful and reproducible results can be obtained when the wear is allowed to continue to the onset of catastrophic failure even though, of course, in practice a cutting time far less than that to failure would be used.The onset of catastrophic failure is characterized by one of several phenomena, the most common being a sudden increase in cutting force, the presence of burnished rings on the workpiece, and a significant increase in the noise level.32. Mechanism of Surface Finish ProductionVocabulary:mechanism 5mekEnizEm 方法、机理contribute kEn5tribju:t 贡献axially AksiEli 向轴的方向revolution 7revE5lu:FEn 旋转perpendicularly 7pE:pEn5dikjulEli 垂直地, 直立地cusp kQsp 尖头, 尖端replicate5replikit 复制unstable 5Qn5steibl 不稳定的degradation 7derE5deiFEn 降级adverse 5AdvE:s 不利的, 敌对的, 相反的uneven 5Qni:vEn 不平坦的, 不均匀的noticeable 5nEutisEbl 显而易见的, 值得注意的ductile 5dQktail 易延展的, 柔软的clamp 5klAmp 夹住, 夹紧rigidity ri5dViditi 刚性instability 7instE5biliti 不稳定(性)steady 5stedi 稳定的,amplitude 5Amplitju:d 振幅chatter 5tFAtE 颤动helical 5helikEl 螺旋状的undulation QndjJ5leiF(E)n 波动transient 5trAnziEnt 短暂的, 瞬时的swarf swC:f 金属屑brittle 5britl 易碎的, 脆弱的evident 5evidEnt 明显的, 显然的impinge im5pindV 撞击built-up edge积屑瘤inevitably in5evitEbli 不可避免地, 必然地unattractive 7QnE5trAktiv 不引人注意的，令人厌恶relief angle后角clearance angle 副后角recommend rekE5mend 推荐, 介绍marked mB:kt 显著的Text:There are basically five mechanisms which contribute to the production of a surface which have been machined. These are:(1) The basic geometry of the cutting process. In, for example, single point turning, the tool will advance a constant distance axially per revolution of the workpiece and the resultant surface will have on it, when views perpendicularly to the direction of tool feed motion, a series of cusps which will have a basic form which replicates the shape of the tool in cut.(2) The efficiency of the cutting operation. It has already been mentioned that cutting with unstable built-up-edges will produce a surface which contains hard built-up-edge fragments which will result in a degradation of the surface finish. It can also be demonstrated that cutting under adverse conditions such as apply when using large feeds, small rake angles and low cutting speeds, besides producing conditions which lead to unstable built-up-edge production, the cutting process itself can become unstable and instead of continuous shear occurring in the shear zone, tearing takes place, discontinuous chips of uneven thickness are produced, and the resultant surface is poor. This situation is particularly noticeable when machining very ductile materials such as copper and aluminum.(3) The stability of the machine tool.Under some combinations of cutting conditions: workpiece size, method of clamping, and cutting tool rigidity relative to the machine tool structure, instability can be set up in the tool which causes it to vibrate. Under some conditions, this vibration will reach and maintain a steady amplitude whilst under other conditions the vibration will built up and unless cutting is stopped, considerable damage to both the cutting tool and workpiece may occur. This phenomenon is known as chatter and in axial turning is characterized by long pitch helical bands on the workpiece surface and short pitch undulations on the transient machined surface.(4) The effectiveness of removing swarfIn discontinuous chip production machining, such as milling or turning of brittle materials, it is expected that the chip (swarf) will leave the cutting zone either under gravity or with the assistance of a jet of cutting fluid and that they will not influence the cut surface in any way. However, when continuous chip production is evident, unless steps are taken to control the swarf, it is likely that it will impinge on the cut surface and mark it. Inevitably, this marking besides looking unattractive, often results in a poorer surface finishing.(5) The effective clearance angle on the cutting tool. For certain geometries of minor cutting edge, relief and clearance angles it is possible to cut on the major cutting edge and burnish on the minor cutting edge. This can produce a good surface finish but, of course, it is strictly a combination of metal cutting and metal forming and is not to be recommended as a practical cutting method. However, due to cutting tool wear, these conditions occasionally arise and lead to a marked change in the surface characteristics.33. Limits and TolerancesVocabulary:interchangeable intE5tFeindVEb(E)l 可互换的variation 7vZEri5eiFEn 变更, 偏差impractical im5prAktikEl 不切实际的tolerance 5tClErEns 公差permissible pE5misEbl 可允许的derive di5raiv 起源unilateral 5ju:ni5lAtErEl 单方面, 单边的dimension di5menFEn 尺寸nominal 5nCminl 名义上的seriously 5siEriEsli 严重地bilateral bai5lAtErEl 有两面的, 双边的plus plQs 正的, 加的minus 5mainEs 负的, 减的split split 分开Text:Machine parts are manufactured, so they are interch