机械工程英语

1、Unit 7 Metal Cutting第七章第七章 金属加工金属加工 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. (1) In USA, more than $100 billions are spent annually on machining and related operations. 机加

2、工过程的重要性可通过日常生活使用的每件产品都直接或间接经历经历这一过程的事实来强调强调。 (1)在美国，每年花在机加工及其相关作业上的费用都多于千亿美元。 (2) A large majority (above 80%) of all the machine tools used in the manufacturing industry have undergone metal cutting. (3) An estimate showed that about 10 to 15% of all the metal produced in USA was converted into chi

3、ps. (2) 用于制造业的全部机床中的大多数大多数(多于80%)都经历过金属切削。 (3) 有估计显示美国生产的所有金属中约10到15%转变成了切屑。 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. 这些事实说明了金属切削在常规制造中的重要性。因此这些事实说明了金属切削在常规制造中的重要性

4、。因此了解金属切削过程以充分利用它是重要的。了解金属切削过程以充分利用它是重要的。 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.在了解金属切削过程并运用这些知识帮助改善与金属切削有关的制造作业方面已经做了许多努力努力。 A typical cutting tool in simplified f

5、orm is shown in Fig.7.1. The important features to be observed are follows. 典型切削刀具的简化形式如图典型切削刀具的简化形式如图7.1所示。要注意所示。要注意的重要特征如下。的重要特征如下。 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 cutti

6、ng and less are the cutting forces, increasing the rake angle reduces the metal backup available at the tool rake face. 1.前角：它是被称为前倾面的刀具面与垂直机加工方向的夹角。前角越大，则切削越好且切削力越小，增加前角可以减少刀具前倾面上产生的金属阻塞阻塞。 This reduces the strength of the tool tip as well as the heat dissipation through the tool. Thus, there is a

7、maximum limit to the rake angle and this is generally of the order of 15for high speed steel tools cutting mild steel. It is possible to have rake angles at zero or negative.但这会和减少通过刀具散发散发的热量一样减少刀尖强度。因此前角有一最大限制，用高速钢刀具切削低碳钢通常为15。前角取零度或负值也是可能的。 2. Clearance angle. This is the angle between the machine

8、d 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 an

9、gle of the order of 56is used. 2. 后角：这是机加工面与被称为后侧面的刀具底面夹角。后角使刀具不产生会损坏机加工面的摩擦和增加切削力。很大的后角会削弱刀尖的强度强度，因此一般采用56的后角。 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

10、used. 对金属切削有重要影响的条件有工件材料、刀具材料、刀具几何形状、切削速度、进给率、切削深度和所用的切削液。 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 (ms-1). 切削速度v指切削刀具经过工件材料的移动速度。通常用米每秒 (ms-1)表示。 Feed rate, f, may be defined as the small relativ

11、e movement per cycle (per revolution or per stroke) of the cutting tool in a direction usually normal to the cutting speed direction. Depth of cut, d, is the normal distance between the unmachined surface and the machined surface. 进给率f可定义为每循环(每转或每行程)切削刀具在通常为垂直于切削速度方向的次要相对相对运动。 切削深度d是未加工面与已加工面之间的垂直距离

12、。 Metal cutting process is a very complex process. Fig.7.2 shows the basic material removal operation schematically. 金属切削过程是一个很复杂的过程。图7.2用图的形式显示了基本材料去除作业。 The metal in front of the tool rake face gets immediately compressed, first elastically and then plastically. This zone is traditionally called s

13、hear zone in view of fact that the material in the final form would be removed by shear from the parent metal. 在刀具前倾面前的金属直接受到压缩，首先弹性变形然后塑性变形。考虑到最终形状中的材料是通过剪切从母体金属去除的，此区域传统上称为剪切区。Chip Formation 切屑的形成切屑的形成The actual separation of the metal starts as a yielding or fracture, depending upon the cutting c

14、onditions, starting from the cutting tool tip. Then the deformed metal (called chip) flows over the tool (rake) face. 金属的实际分离分离始于屈服或断裂(视切削条件而定)，从切削刀尖开始。然后变形金属(称为切屑)流过刀具(前倾)面。 If the friction between the tool rake face and the underside of the chip (deformed material) is considerable, then the chip g

15、ets 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.如果刀具前倾面与切屑(变形金属)底面之间的摩擦摩擦相当大，那么切屑进一步变形，这也叫做二次变形。滑过刀具前倾面的切屑被提升离开刀具，切屑弯曲的结果被称为切屑卷。Plastic deformat

16、ion can be caused by yielding, in which case strained layers of material would get displaced over other layers along the slip-planes which coincide with the direction of maximum shear stress. 屈服能导致塑性变形变形，在这种情况下材料变形层沿着与最大剪应力方向一致的滑移面被其它层所取代。 A chip is variable both in size and shape in actual manufact

17、uring 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. 在实际加工过程中切屑的尺寸和形状都是变化的。对切屑的研究是金属切削最重要的事情之一。如同后面将要看到的那样，金属切削力学极大地依赖于所产生切屑的形状和尺寸。 1. Chip format

18、ion in metal cutting could be broadly categorised into three types: (Fig.7.3) (1) Discontinuous chip (2) Continuous chip (3) Continuous chip with BUE (Built up edge) 金属切削中的切屑形成可以宽泛地分成分成三个类型(图7.3)： (1)间断切屑 (2)连续切屑 (3)带切屑瘤的连续切屑 Discontinuous Chip. The segmented chip separates into short pieces, which

19、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. 间断间断切屑：分段的切屑分散成小碎片，既可能相互附着也可能不相互附着。在靠近切削面处发生金属的剧烈变形，导致在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

20、 the material, resulting in fracture and separation. With this type of chip, there is little relative movement of the chip along the tool face, Fig.7.3a.最后，横过切屑的剪切应力与材料的剪切强度相等，造成断裂和分离。生成这类切屑时，切屑沿刀具面几乎没有相对运动，见图7.3a。 Continuous chip. The continuous chip is characterized by a general flow of the separa

21、ted 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. 连续连续切屑：连续的切屑一般具有分离金属沿刀具面流动的特征特征。切屑可能有一些破裂，但在这种情况下切屑通常不会延长到足以引起断裂。 This chip is formed at the higher cutting speeds when machining ductile materials. There

22、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, Fig.7.3b.这种切屑形成于用较高切削速度机加工有延展性的有延展性的材料时。材料几乎没有粘附刀具的倾向。连续切屑通常具有良好的切削率和趋向于产生最适宜的表面光洁度，但可能成为操作的危险之源，见

23、图7.3b。Continuous with a built-up edge. This chip shows the existence of a localized, highly deformed zone of material attached or “welded” on the tool face. 带切屑瘤切屑瘤的连续切屑：这种切屑显示了粘合或“焊接”在刀具面上材料局部高度变形区的存在。 Actually, analysis of photomicrographs shows that this built-up edge is held in place by the stat

24、ic 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, Fig.7.3c.实际上，对显微照片的分析显示这种切屑瘤受到静摩擦力抑制直至它变得大到作用在它上面的外力使其移动，一些留在机加工表面上而另一些延伸到切屑的背面，见图7.3c。Cont

25、inuous with a built-up edge. This chip shows the existence of a localized, highly deformed zone of material attached or “welded” on the tool face. 带切屑瘤的连续切屑：这种切屑显示了粘合或“焊接”在刀具面上材料局部高度变形区的存在。 Actually, analysis of photomicrographs shows that this built-up edge is held in place by the static friction f

26、orce 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, Fig.7.3c.实际上，对显微照片的分析显示这种切屑瘤受到静摩擦力抑制直至它变得大到作用在它上面的外力使其移动，一些留在机加工表面上而另一些延伸到切屑的背面，见图7.3c。There are basical

27、ly 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 Fig.7.4a. The other school thinks that the actual deformation zone is a thick one with a fan shape as shown in Fig.7.4b. 在对金属去除过程的分析中主要存在两种思想

28、学派。一种思想学派认为变形区如图7.4a所示那样非常薄而平坦。另一学派则认为真实变形区象图7.4b所示那样为一厚的带有扇形的区域。Shear Zone 剪切区剪切区Though the first model (Fig.7.4a) 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,

29、the acceleration across the plane has to be infinity. 虽然第一种模型(图7.4a)从分析的角度看是方便的，但实际上是不可能存在的。这是由于未变形的材料沿着剪切面发生变形，而且越过剪切面的加速度无穷大。 Similarly the stress gradient across the shear plane has to be very large to be practical. 同样在实际运用中越过剪切面的应力梯度必须很大才行。 In the second model (Fig.7.4b) by making the shear zone

30、 over a region, the transitions in velocities and shear stresses could be realistically accounted for. 在第二种模型(图7.4b)中让剪力区分布于一个范围，速度和剪应力的转变能说明得更符合实际。The angle made by the shear plane with the cutting speed vector, is a very important parameter in metal cutting. Higher the shear angle better is the cu

31、tting performance. From a view of the Fig.7.4a, it can be observed that a higher rake angles give rise to higher shear angles. 由剪切面和切削速度矢量形成的角度在金属切削中是一个十分重要的参数。剪切角越大，切削作业越好。从图7.4a观察，可以看到较大的前角能增大剪切角。 Various cutting tool materials have been used in the industry for different applications. A number of

32、 developments have occurred in the current century. 在工业中为了不同的应用可以使用各种各样的切削刀具材料。在最近的百年里产生了许多进展。Cutting Tool Materials切削刀具材料切削刀具材料 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 mater

33、ials, let us look at the important characteristics expected of a cutting tool material.多种切削刀具材料被开发出来以满足这些方案中使用材料的多样性。讨论这些材料性能之前，先看一下作为切削刀具材料应具备哪些重要特性。 1. Higher hardness than that of the workpiece material being machined, so that it can penetrate into the work material. 2. Hot hardness, which is the

34、 ability of the material to retain its hardness at elevated temperatures in view of the high temperatures existing in the cutting zone. 1. 硬度要比被切削工件材料高，这样它才能进入工件材料。 2. 热硬度，即材料由于存在于切削区的高温而升温时仍能保持其硬度的能力。 3. Wear resistanceThe chip-tool and chip-work interfaces are exposed to such severe conditions tha

35、t adhesive and abrasion wear is very common. The cutting tool material should therefore have high abrasion resistance to improve the effective life of the tool. 3. 耐磨性切屑-刀具与切屑-工件的接触界面处于如此严酷的状态，粘附和磨损是很普遍的。因此切削刀具材料应具有高耐磨性以提高刀具的有效寿命。4. ToughnessEven though the tool is hard, it should have enough toughn

36、ess 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, e.g. milling.4. 韧性虽然刀具是坚硬的，但也应有足够的韧性以经受住冲击载荷，这些载荷来自于切削的开始或由于工件材料的缺陷而产生的作用力波动。这个要求对如铣削之类的间断切削更有

37、用。5. Low frictionThe coefficient of friction between the chip and tool should be low. This would allow for lower wear rates and better chip flow. 5. 低摩擦系数切屑与刀具间的摩擦系数应当较低。这会使磨损率较小及切屑流动更好。 6. Thermal characteristicsSince a lot of heat is generated at the cutting zone, the tool material should have hig

38、her thermal conductivity to dissipate this heat in the shortest time, otherwise the tool temperature would become high, reducing its life.6. 热特性因为大量的热产生在切削区，刀具材料应当具有较高的热传导性以在最短的时间内散发热量，否则刀具温度会升高，寿命会减少。All these characteristics may not be found in a single tool material. Improved tool materials have

39、been giving a better cutting performance. 所有这些特性不可能存在于单一刀具材料中。改进的刀具材料已经被赋予较好的切削性能。Machining operations are utilized in view of the better surface finish that could be achieved by it compared to other manufacturing operations.由于机加工能获得比其它制造作业更好的表面光洁度，所以机加工作业具有实用价值。Surface Finish表面光洁度表面光洁度 Thus it is i

40、mportant 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: 因而了解能在机加工作业中获得怎样的实际表面光洁度是重要的。给定机加工作业中的表面光洁度是两个因素共同作用的结果：(1) the ideal surface finish, which is a result of the geom

41、etry of the manufacturing process which can be determined by considering the geometry of the machining operation, and(2) the natural component, which is a result of a number of uncontrollable factors in machining, which is difficult to predict.理想的表面光洁度，是通过考虑机加工作业的几何体系所决定的制造工艺几何学的结果，和自然要素，即在机加工中一些难以预

42、测的不可控因素作用的结果。Ideal Surface Finish in Turning 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 Fig.7.5a. If the feed rate is very small, as is normal in finish turning, the surface is produced purely by the nose ra

43、dius alone as shown in Fig.7.5.车削中的理想表面光洁度 实际使用的车削刀具有一个刀尖半径取代锋利刀尖，它将表面几何形状加工为如图7.5a所示。如果进给率很小，象精车中很正常的那样，工件表面则完全是由刀尖半径单独产生的，如图7.5所示。 For the case in Fig.7.5, the surface roughness value is to be Ra=8f2/(18R3)Where: Ra is the surface roughness value R is the nose radius f is the feed rate 对图7.5这种情况，表

44、面粗糙度值为 Ra=8f2/(18R3)式中：Ra是表面粗糙度值 R是刀尖半径 f是进给率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:上述基本为几何要素，其值代表了理想情况。而实际获得的表面光洁度很大程度上还取决于下列一些因素： (1) the cutting process

45、parameter, speed, feed and depth of cut(2) the geometry of the cutting tool(3) application of cutting fluid(4) work and tool material characteristics(5) rigidity of the machine tool and the consequent vibrations.(1)切削工艺参数、速度、进给和切削深度(2)切削刀具的几何形状(3)切削液的运用(4)工件和刀具的材料特性(5)机床的刚度及其伴随发生的振动 The major influe

46、nce 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. 对表面光洁度产生主要影响的是进给率和切削速度。从上述公式可以看到，随着进给的减少，粗糙度指标会降低。 Similarly as the cutting speed increases, we have better surface finish. Thus while

47、making a choice of cutting process parameters for finish, it is desirable to have high cutting speed and small feed rates.同样随着切削速度的增大，能得到较好表面光洁度。因此在为光洁度而选择切削工艺参数时，采用较高的切削速度和较小的进给率是适当的。 Cutting Fluids 切削液 The functions of cutting fluids (which are often erroneously called coolants) are:To cool the to

48、ol and workpiece To reduce the friction 切削液(经常误称为冷却液)的功能如下：冷却刀具和工件减少摩擦To protect the work against rustingTo improve the surface finishTo prevent the formation of built-up edgeTo wash away the chips from the cutting zone保护工件不生锈改善表面光洁度防止切屑瘤的形成从切削区冲掉切屑 However, the prime function of a cutting fluid in

49、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. 然而，在金属切削作业中切削液的主要功能是控制总热量。这可通过既散发又减少所产生的热量来达到。切削液实现这些功能的机理是：

50、冷却作用和润滑作用。 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. 冷却作用：最初设想切削液仅仅是通过冷却特性来改善切削作业。这也是它曾被称为冷却液的原因。Since most of the tool wear mechanisms are thermally activated, cooling

51、the chip tool interface helps in retaining the original properties of the tool and hence prolongs its life. 由于大多数刀具的磨损机理都是由热引起的，冷却切屑刀具接触界面有助于保持刀具的原有特性，从而延长其使用寿命。 However, a reduction in the temperature of the workpiece may under certain conditions increase the shear flow stress of the workpiece, the

52、reby 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.可是工件温度的降低在特定条件下会增加工件的剪切流动应力，从而降低刀具寿命。通过一些研究已经表明实际上冷却只是改善切削作业的主要因素之一。 Lubricating action. The best improvement in cutting performance c

53、an be achieved by the lubricating action since this reduces the heat generated, thus reducing the energy input to the metal cutting operation. 润滑作用：切削作业的最大改善可通过润滑作用来达到，由于它减少了热量的产生因而减少了金属切削作业的能量输入。 However, if the cutting fluid is to be effective, it must reach the chip tool interface. But it is not

54、easy to visualize how it is accomplished in the case of a continuous turning with a single point turning tool, specially when the chip-tool contact pressure is as high as 70 MPa. 可是，如果要使切削液起作用就必须让它到达切屑刀具接触界面。但如何在采用单尖刀具连续车削的场合尤其是切屑-刀具接触压力高达70MPa时实现并非易事。 Merchant thought that minute asperities existed

55、 at the chip-tool interface and the fluid was drawn into the interface by the capillary action of the interlocking network of these surface asperities. Merchant认为：在切屑与刀具接触界面上存在微小的粗粒，切削液通过这些表面的微小粗粒组成连锁的网络的毛细管被吸入到切屑与刀具的接触界面上。Metals and Metal Alloys 金属切削金属切削机械工程专业英语教程2021-11-1131Their property Conducti

56、vityStrengthStiffnessDuctilityMagneticTheir namesIronCobaltNickelCopperAluminumChromiumGoldHomepageAll papers, both invited and contributed, will be refereed by two or three experts. After a careful refereeing process, Accepted papers will be published as a special issue of international journal Adv

57、anced Materials Research Trans Tech Publications and will be indexed in the major academic databases, including EI Compendex, Thomson ISI (ISTP), and other indexing services. The full text is online available via platform . A small amount of selected paper will be invited to submit an expanded versi

58、on of their papers for consideration of publication in the International Journal of Advanced Manufacturing Technology (all covered by SCI and EI Compendex). (In Chinese 中文) In the 21th century, there are rapid technological advancements in all the fields. Especially in the domain of manufacturing, w

59、e have entered into an exciting revolutionary period. Engineers must keep pace with new trends and constantly improve the level of research and development. Hence it needs a common platform facilitating and promoting discussion and interaction in recent development. This conference offers an opportu

60、nity to the manufacturing researchers and scientists around the world to exchange ideas, views, professional knowledge and experience in the areas of manufacturing science and technology.Publication:Some alloys, such as those based on aluminum, have low densities and are used in aerospace applicatio