Unit 6 Injection molding

注塑模具

      Injection molding (Fig.6.1) is the predominant process for fabrication of  thermoplastics into finished forms, and is increasingly being used for thermosetting plastics, fiber-filled composites, and elastomers.

       注塑成型(图6.1)是将热塑性塑料制成最终形状的主要工艺，并且越来越多地用于热硬化性塑料、纤维填充合成物和人造橡胶。

       It is the process of choice for tremendous variety of parts ranging in weight from 5g to 85kg. It is estimated that 25% of all thermoplastics are injection molded.

       它是重量范围为5g到85kg极大一类零件可选用的工艺。估计所有热塑性塑料中有25%是采用注塑成型的。

If newer modifications, such as reaction injection molding, and the greatly increased rate of adoption of plastics as substitutes for metals are considered, it is likely that the worldwide industrial importance of injection molding will continue to increase.

       如果考虑到新近的改进(例如反作用注塑成型)和采用塑料替代金属的高增长率，注塑成型在世界范围的工业重要性很可能将继续增加。

Currently, probably close to half of all major processing units is injection molding machines. In 1988, a dollar sale of new injection molding machinery in the U.S. was approximately 65% of total major polymer machinery sales volume; this included 4,600 injection molding units.

当前，大概所有主要处理设备的近一半是注塑成型机。1988年，美国新的注塑成型机械销售约占全部主要聚合物机械销售量的65%，其中包括4,600台注塑成型设备。

The machines and their products are ubiquitous and are synonymous with plastics for many people.

这类机械和它们的产品普遍存在，对许多人来说与塑料是同义的。

        A reciprocating screw injection molding machine combines the functions of an extruder and a compressive molding press.

       往复螺旋注射成型机把压出机和成型压力机的功能结合起来。

It takes solid granules of thermoplastic resin, melts and pressurizes them in the extruder section, forces the melt at high velocity and pressure through carefully designed flow channels into a cooled mold, then ejects the finished part(s), and automatically recycles.

把热塑性塑料树脂的固体颗粒在压出部分融化并增压，迫使其高速融化并通过仔细设计的流动通道进入冷却模具，喷射成最终零件，然后自动再循环。

This machine is a descendant of the plunger type “stuffing machine” patented by the Hyatt brothers in 1872 to mold celluloid. In 1878, the Hyatts developed the first multicavity mold, but it was not until 1938 that Quillery (France) patented a machine incorporating a screw to plasticize the elastomer being molded.

这种机械是1872年Hyatt兄弟获得专利权的融化赛璐珞的活塞型“填充机”的派生物。 1878年Hyatt兄弟开发了第一个多槽模具，但直到1938年Quillery(法国)才发明了用螺旋增塑人造橡胶并使其成型的一体化机械。

In 1956, Ankerwerk Nuremberg commercialized the modern reciprocating screw injection molding machine for thermoplastics. Today, over 50 machine manufacturers are listed in Modern Plastics Encyclopedia, offering machines to the U.S. market ranging from 2 to 6,000 tons clamping capacity.

1956年，Ankerwerk Nuremberg使用于热塑性塑料的现代往复螺旋注塑成型机商业化。今天，已有超过50家制造商列入现代塑料制品百科全书，能为美国市场提供压制能力从2到6,000吨的机械。

(A machine with a 10,000-ton capacity has been built to mold 264-gallon HDPE trash containers.) A host of suppliers of  auxiliary equipment, molds, instruments, and controls service this major segment of the polymer industry.

(一台能力为10,000吨用于成型264加仑高密度聚乙烯垃圾箱的机械也已制成)。许多辅助设备、模具、仪器和控制系统供应商在为聚合物工业的这一主要部分服务。

       Injection molding is particularly worthy of intensive study because it combines many areas of interest extrusion, mold design, rheology, sophisticated hydraulic and electronic controls, robotic accessories, design of  complex products, and, of course, the integration of materials science and process engineering.

       注塑成型对深入研究很有价值，因为它结合了许多重要领域，如挤压、模具设计、流变学、完备的液压和电子控制、机器人配件、复杂产品的设计，当然还有材料科学与加工工程的综合。

The objectives of injection molding engineers are simple enough: to obtain minimum cycle time with minimum scrap, to attain specified product performance with assurance, to minimize production costs due to downtime or any other reasons, and to steadily increase in expertise and competitiveness.

注塑成型工程师的目标很简单：在最少废料的情况下取得最小循环时间，在有保证的情况下获得指定产品性能，将由停工或其它原因产生的生产成本最小化，还有稳定地增加专门知识和竞争力。

Profit margins for custom injection molders are said to be generally skimpy; an established way to improve profits is to be selected for more demanding, higher margin jobs that demand the highest level of efficiency and competence.

传统的注塑成型机利润盈余据说一般是不足的；为了更多需求及更高盈余工作需要选择一种改善利润的确定方法，它要求最高水平的效率和能力。

       This text will concentrate on the  reciprocating screw machine for  thermoplastics, which has largely replaced the older reciprocating plunger types except for very small-capacity machines.

       本文将集中论述热塑性塑料用的往复螺旋机，除了小容量机械外它已在很大程度上取代了较老的往复活塞式机械。

• Injection Molding Materials
注塑成型材料

       It is not possible to injection-mold all polymers. Some polymers like PTFE (Poly-tetra-fluoro-ethylene), cannot be made to flow freely enough to make them suitable for injection molding.

       要注塑成型所有聚合物是不可能的。像聚四氟乙烯之类的聚合物就不能自由流动得足以适合注塑成型。

Other polymers, such as a mixture of resin and glass fiber in woven or mat form, are  unsuitable by their physical nature for use in the process. In general, polymers which are capable of being brought to a state of fluidity can be injection-molded.

其它聚合物，例如树脂和编织的或垫子形的玻璃纤维的混合物，由于它们的物理性质不适合使用此工艺。一般而言，能进入流动状态的聚合物都可以注塑成型。

         The vast majority of injection molding is applied to thermoplastic polymers. This class of materials consists of polymers which always remain capable of being softened by heat and of hardening on cooling, even after repeated cycling.

       注塑成型的绝大多数都用于热塑性聚合物。这类材料由具有加热软化、冷却硬化甚至可重复循环能力的聚合物组成。

This is because the long-chain molecules of the material always remain as separate  entities and do not form chemical bonds to one  another.  An analogy car, be made to a block of ice that can be softened (i.e. turned back to liquid), poured into any  shape cavity, and then cooled to become a solid again.

这是由于这类材料的长链分子总是保持分离的实体并不相互形成化学连结。一辆由冰块制成的模拟汽车，可以融化(即转化为液态)，倒入任何形状的空腔，然后冷却重新变成固体。

This property differentiates thermoplastic materials from thermosetting ones. In the latter type of polymer, chemical bonds are formed between the separate molecule chains during processing. In this case the chemical bonding referred to as cross linking is the hardening mechanism.

这个特性将热塑性材料与热硬化性材料区分开。后者在加工过程中分离的分子链之间形成化学连结。在此情况下作为交联的化学连结是硬化机制。

        In general, most of the thermoplastic materials offer high impact strength, corrosion resistance, and easy processing with good flow characteristics for molding complex designs. Thermoplastics are generally divided into two classes: namely crystalline and amorphous.

       一般而言，大多数热塑性材料具有较高的抗冲击强度、耐腐蚀性以及良好流动性使其容易加工而适于复杂成型设计。热塑性塑料通常分为两类：即结晶质的和非结晶质的。

Crystalline polymers have an ordered molecular arrangement, with a sharp melting point. Due to the ordered arrangement at molecules, the crystalline  polymers reflect most incidents light and generally appear opaque.

结晶质聚合物具有规则的分子排列及明显的熔点。由于规则的分子排列，结晶质聚合物能反射大多数特定光线并一般表现为不透明的。

They also undergo a high shrinkage or reduction in volume during solidification. Crystalline polymers usually are more resistant to organic solvents and have good fatigue and wear-resistant properties. Crystalline polymers also generally are denser and have better mechanical properties than amorphous polymers.

它们在固化过程中收缩较大或体积减少较多。结晶质聚合物通常多能抵御有机溶剂并具有良好的抗疲劳和磨损特性。结晶质聚合物通常也比非结晶质聚合物更致密并且具有更好的机械性能。

The main exception to this rule is polycarbonate, which is the amorphous polymer of choice for high quality transparent moldings, and has excellent mechanical properties.

其中主要例外是聚碳酸酯，它是可选用做高质量透明注塑件的非结晶质聚合物，并具有卓越的机械性能。

       The mechanical properties of thermoplastics, while substantially lower than those of metals, can be enhanced for some applications through the addition of glass fiber reinforcement. This takes the form of short-chopped fibers, a few  millimeters in length, which are randomly  mixed with the thermoplastic resin.

       就本质而言，热塑性塑料的机械性能低于金属，但可以通过加入玻璃纤维强化予以增强来适应某些运用。常用几毫米长的短碎纤维随机地与热塑性树脂混合。

      The fibers can occupy up to one third of the material volume to considerably improve the material strength and stiffness. The negative effect of this reinforcement is usually a decrease in impact strength and an increase in abrasiveness.

       纤维可占材料体积的三分之一以极大改善材料的强度和硬度。这种加强的负作用通常是抗冲击强度降低及磨损性增加。

The latter also has an effect on processing since the life of the mold cavity is typically reduced from about 1,000,000 parts for plain resin parts to about 300,000 for glass-filled parts.

后者对加工过程也有影响，因为模具腔的寿命从典型的普通树脂零件大约1,000,000件减少到玻璃纤维填充树脂零件的约300,000件。

       Perhaps the main weakness of injection-molded parts is the relatively low service temperatures to which they can be subjected. Thermoplastic components can only rarely be operated continuously above 250℃, with an absolute upper service temperature of about 400℃.

       注塑成型零件的主要缺点或许是它们能承受的工作温度相对较低。热塑性塑料零件只有很少能连续运行在250℃以上，其绝对最高工作温度约为400℃。

The temperature at which a thermoplastic can be operated under load can be defined qualitatively by the heat deflection temperature. This is the temperature at which a simply supported beam specimen of the material, with a centrally applied load, reaches a predefined deflection.

热塑性塑料带载运行温度可从质量上定义为热偏差温度。这是中心承载的该材料简支梁达到预定偏差的温度。

The temperature value obviously depends upon the conditions of the test and the allowed deflection and for this reason, the test values are only really useful for comparing different polymers.

其温度值明显取决于试验条件和允许偏差，因此对比较不同的聚合物而言只有试验数据是真正有用的。

Cycle of Operation
作业循环

      The reciprocating screw injection molding machine is considered as  consisting of two halves: a fixed injection side, and a movable clamp side.

       往复螺旋注塑成型机被认为由两部分组成：一个固定注塑端和一个活动夹具端。

The injection side contains the extruder that receives solid resin in pellet or granular form and converts it into a viscous liquid or melt that can be forced through the  connecting nozzle, spine, and runners to the gates that lead into the mold cavities.

注塑端包含压出机，它接受小球或粒状的固体树脂，然后将其转化为粘性液体或称为融化，再强迫其通过连接喷嘴、中心和浇道到闸道进入模具腔。

The mold is tightly clamped against injection pressure and is cooled well below the melt temperature of the thermoplastic. When the parts in the cavities have cooled sufficiently the mold halves are opened at the mold parting plane and the parts ejected by a knockout system drop into a receiving bin below.

模具被紧紧地夹住以抵抗注塑压力，并在热塑性塑料的融化温度以下很好地冷却。当模腔内的零件充分冷却，剖分模在模具分模面处打开，推出系统将零件推出落入下面的接收容器内。

This summarizes the overall cycle, but leaves out much vital detail that is necessary for understanding the process. However, with this introduction, it is possible to understand the advantages and disadvantages of the process.

这概述了整个循环，但省略了许多对理解此工艺所必需的很重要细节。然而通过本介绍，了解这种工艺的优缺点仍是可能的。

Effects of Process Variables on Orientation     
加工变量对方向性的影响

      In injection molding, any variation in processing that keeps the molding resin hot throughout filling allows increased  relaxation and, therefore, decreased  orientation. Some of the steps that can be taken to reduce orientation are as follows.

       在注塑成型时，整个填料过程始终保持成型树脂高温的任何加工变化都会增加松弛作用而减少方向性。下面是可以用于减少方向性的若干措施。

• Faster injection (up to a point): less  cooling during filling, hence a thinner initial  frozen layer, lower viscosity due to shear  thinning; better flow to corners; and less   crystallinity all favor lower subsurface orientation. The primary effect is that the gate will freeze more quickly. At that point, orientation stops and relaxation starts.

• 较快注塑(到点)：在填料过程中冷却较少，因此初始固化层较薄，由于剪应变稀少而粘性较低；能较好地流到角落；结晶度较小；所有这些促成表面下的方向性也较低。主要效果是闸道将较快固化。这样使得方向性停止产生而松弛作用开始增加。

• Higher melt and mold temperatures: lower  melt viscosity, easier filling, and greater relaxation favor reduced orientation.

• Reduced packing time and pressure: overpacking inhibits relaxation processes.

• 较高的融化和成型温度：融化粘性较低，更容易填充，较大松弛作用促成方向性减少。

• 减少挤压时间和压力：过度挤压会抑制松弛过程。

• Reduced gate size: larger gates take longer to freeze off and permit increased orientation.

• 减小闸道尺寸：闸道越大则固化时间越长并会使方向性增加。

       Excessively high injection speed can cause high surface orientation and increase susceptibility to stress cracking. For example, moldings that are to be electroplated, and will be subject to acid solutions during plating, must be made using very slow injection speeds to  minimize surface orientation.

       过高的注塑速度会引起较高的表面方向性及增加应力破裂的敏感性。例如，要电镀的注塑件在电镀时会经受酸溶液，必须采用很低的注塑速度制造以使表面方向性最小化。

On the other hand, the transverse motion component of the melt front in most moldings can cause transverse subsurface orientation superimposed on the primary orientation, giving a desirable biaxial orientation effect.

另一方面，大多数注塑件的融化前部横向运动部分能导致在主要方向性上有层理的表面下横向方向性，产生需要的双轴方向性效应。

      Orientation can be seriously increased by obstructions to flow during filling of the cavity. Flow around an obstruction causes a decrease in melt front speed and leads to high local viscosity and reduced relaxation. This is also likely to occur near the end of the filling phase if gating is inadequate.

       在填充模腔时流动受到阻碍会极大地增加方向性。围绕障碍物流动使融化前部的速度下降并产生较高的局部粘性而减少松弛作用。如果闸道不适当，这也很可能发生在接近填充结束阶段。

      The molder must recognize the dangers of excessive fill speed, insufficient injection pressure, excessive melt temperature, and inadequate packing. These dangers are weighed against the opposing effects on orientation discussed above.

       注塑工必须认识过快填充速度、不足注塑压力、过高融化温度和不充分挤压的危害性。这些危害性要与上述方向性的反向效应相权衡。

Thicker parts delay cooling and increase relaxation time and tend to result in lower orientation. Thicker parts also tend to warp less. Therefore, a minimum wall thickness can be established by experience for  various shapes, materials, and process  combinations.

较厚零件会延迟冷却并且增加松弛时间，趋向于导致较低的方向性。较厚零件也有助于减少翘曲。因此，对各种形状、材料和工艺组合能通过经验来确定最小壁厚。

Lower molecular weight and broader molecular weight distribution in thermoplastics favor lower orientation and reduced internal stress in moldings.

在热塑性塑料中较小的分子量以及较宽泛的分子量分布促成方向性减少同时降低注塑件中的内应力。

      The skin thickness ratio is affected by process variables in the same way as one would predict for the orientation; that is, it decreases as the melt or mold temperatures and cavity pressure increases. Tensile strength and stiffness increase as skin thickness ratio increases. Microscopic examination thus provides another way of studying the process efficiently.

       外壳厚度比受加工变量影响的方式与方向性预测一样；也就是它能随融化或成型温度及模腔压力的增加而减少。拉伸强度和硬度随外壳厚度比增加而增加。因而显微镜检查提供了有效研究该工艺的另一方法。

• Advantages  优点

      1. High production rates. For example, a CD disk can be produced with a 10~12s cycle in high melt flow index PC.

      1. 高生产率：例如，一张CD盘在高融体流动指数生产控制中只需10~12s一个循环就能生产出来。

       2. Relatively low labor content. One operator can frequently take care of two or more machines, particularly the moldings  are unloaded automatically onto  conveyors.

       2. 相对较少的工作内容：一个操作者经常可以照看两台以上机械，尤其是当成品能自动卸到输送机上时。

       3. Parts require little or no finishing. For example, flash can be minimized and molds can be arranged to automatically separate runners and gates from the part itself.

       4. Very complex shapes can be formed. Advances in mold tooling are largely responsible.

       3. 零件几乎不需要修整：例如，飞边可以最小化并且模具能被设计成自动将浇道和闸道从零件本身分离。

       4. 非常复杂的形状也能成型：模具的进步很大程度上是可靠的。

       5. Flexibility of design (finishes, colors,  inserts, materials). More than one  material can be molded through co-injection. Foam core materials with solid skins are efficiently produced. Thermosetting plastics and fiber-reinforced shapes are injection molded.

       5. 设计的灵活性(光洁度、颜色、插入物、材料)：通过复合注塑可以成型多于一种材料。可以高效地生产带有固体外壳的泡沫型芯材料。热硬化性塑料和纤维加强形状都可以注塑成型。

       6. Minimum scrap loss. Runners, gates, and scrap can usually be reground. Recycled thermoplastics can be injection molded.

       6. 废料损失最小化：浇道、闸道和废料通常可以重新研磨。循环热塑性塑料可以注塑成型。

        7. Close tolerances are obtainable. Modern microprocessor controls, fitted to precision molds, and elaborate hydraulics, facilitate tolerances in the 0.1% range on  dimensions and weights (but not without a high level of operational skills in constant attendance).

        7. 能得到接近的公差：现代微处理器控制、合适的精密模具和精心制作的液压设备使得尺寸和重量的公差保持在0.1% 的范围内(但不是没有在持续照看时的高水平操作技能)。

      8. Makes best use of the unique attributes of polymers, such as flow ability, light weight, transparency, and corrosion resistance. This is evident from the number and variety of molded plastic products in everyday use.

      8. 充分利用聚合物诸如流动能力、重量轻、透明和耐腐蚀等独特属性：从日常使用成型塑料产品的数量和种类就能明显看到。

Disadvantages and Problems
缺点和问题

      1. High investment in equipment and tools requires high production volumes.

      2. Lack of expertise and good preventive maintenance can cause high startup and running costs.

      1. 较高的设备和模具投资需要较高生产量才合算。

      2. 缺少专门技术和良好的预防性维修会导致较高的启动和运行成本。

      3. Quality is sometimes difficult to  determine immediately. For example, post-mold warpage may render parts unusable because of dimensional changes that are not completed for weeks or months after molding.

       3. 质量有时难以马上确定。例如，成型后的翘曲会导致零件不能用，因为在成型后几星期甚至几个月尺寸变化都不能完成。

       4. Attention is required on many details requiring a wide variety of skills and cross-disciplinary knowledge.

       5. Part design sometimes is not well suited to efficient molding.

       4. 对许多需要广泛多样性技能和交叉学科知识的细节必须加以注意。

       5. 零件设计有时不能很好地适应有效率的成型。

       6. Lead time for mold design, mold  manufacture and debugging trials is  sometimes very long.

       6. 模具设计、模具制造和调试试验这些先导工作有时要花费很长时间。

 

 

Unit 7 metals cutting

金属切削

       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这一过程的事实来强调。

      (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 chips.

       (2) 用于制造业的全部机床中的大多数(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。

        A typical cutting tool in simplified form 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7.1所示。要注意的重要特征如下。

      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 cutting 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。

This reduces the strength of the tool tip as well as the heat dissipation through the tool. Thus, there is a maximum limit to the rake angle and this is generally of the order of 15°for 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 machined 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 angle of the order of 5~6°is 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，因此一般采用5~6°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 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  relative 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运动。

       切削深度d是未加工面与已加工面之间的垂直距离。

• Chip Formation  切屑的形成

       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 shear 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。

The actual separation of the metal starts as a yielding or fracture, depending upon the cutting conditions, 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 gets 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 deformation 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，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 manufacturing 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。

         Chip formation 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 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 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 separated 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.

       连续切屑：连续的切屑一般具有分离金属沿刀具面流动的特征。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 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 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。

• Shear Zone   剪切区

       There are basically 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。

     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, 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 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, Φ is a very important parameter in metal cutting. Higher the shear angle better is the cutting 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Φ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。

• Cutting Tool Materials
切削刀具材料

       Various cutting tool materials have been used in the industry for different applications. A number of 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。

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 materials, 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 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 resistance—The chip-tool and chip-work interfaces are exposed to such severe conditions that 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. Toughness—Even though the tool is hard, it should have enough toughness 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用。

       5. Low friction—The 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 characteristics—Since a lot of heat is generated at the cutting zone, the tool material should have higher 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 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。

• Surface Finish  

•  表面光洁度

       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。

Thus it is important 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 geometry 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.

(1) 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

(2) 自然要素，即在机加工中一些难以预测的不可控因素作用的结果。

Ideal Surface Finish in Turning

车削中的理想表面光洁度

       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 radius alone as shown in Fig.7.5.

       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/(18R√3)

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，表面粗糙度值为

               Ra=8f2/(18R√3)

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 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 influence 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 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 tool 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 rusting

• To improve the surface finish

• To prevent the formation of built-up edge

• To 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 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：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 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, thereby 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 can 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 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 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。

 

 

 

 

 

 

 

 

 

 

 

 

 

Unit 8 Grinding

磨削

 

       Grinding is a manufacturing process that involves the removal of metal by employing a rotating abrasive wheel. The latter simulates a milling cutter with an extremely large number of miniature cutting edges.

       磨削是通过采用旋转磨轮去除金属的制造工艺。磨轮用非常大量的微型切削刃模仿铣刀进行切削。

Generally, grinding is considered to be a finishing process that is usually used for obtaining high-dimensional accuracy and  better surface finish. Grinding can be performed on flat, cylindrical, or even  internal surfaces by employing specialized  machine tools, which are referred to as grinding machines.

一般而言，磨削被认为是一种通常用于获得高尺寸精度和较好表面光洁度的精加工作业。磨削通过采用被称为磨床的特殊机床能在平面、圆柱面甚至内表面上进行。

Obviously, grinding machines differ in construction as well as capabilities, and the type to be employed is determined mainly by the geometrical shape and nature of the surface to be ground, e.g., cylindrical surfaces are ground on cylindrical grinding machines.

显然，磨床根据结构和功能的不同有所区别，使用何种形式的磨床主要取决于被磨削表面的几何形状和物理性质。例如，圆柱面在外圆磨床上磨削。

• Type of Grinding Operations
磨削作业的类型

1. Surface grinding. As the name surface grinding suggests, this operation involves grinding of flat or plane surfaces. Fig.8.1 indicates the two possible variations, either a horizontal or vertical machine spindle.

1. 表面磨削：就像其名称暗示的那样，表面磨削和平面磨削直接有关。图8.1表示了两种可能的变化：卧式磨床主轴或立式磨床主轴。

In the first case (horizontal spindle), the machine usually has a planer-type reciprocating table on which the workpiece is held. However, grinding machines with vertical spindles can have either a planer type table like that of the horizontal-spindle machine or a rotating worktable.

在第一种情况(卧式主轴)，卧式磨床通常具有安装工件的刨床式往复工作台。而立式主轴磨床既可以像卧式主轴磨床那样具有刨床式工作台也可以具有旋转工作台。

Also, the grinding action in this case is achieved by the end face of the grinding wheel (Fig.8.1b), contrary to the case of horizontal-spindle machines, where the workpieces ground by the periphery of the grinding wheel.

而且在这种情况下，磨削动作是通过砂轮端面完成的(图8.1b)，这与通过砂轮周边磨削工件的卧式主轴磨床正好相反。

Fig.8.1a and b also indicate the equations to be used for estimating the different parameters of the grinding operation, such as the machining time and the rate of metal removal.

图8.1a和b同时简述了用于估计诸如加工时间和金属去除率之类的磨削作业不同参数的方程式。

During the surface-grinding operations, heavy workpieces are either held in fixtures or clamped on the machine table by strap clamps and the like, whereas smaller workpieces are usually held by magnetic chucks.

在平面磨削时，重的工件用夹具固定或用压板等夹紧在磨床工作台上，而小的工件则通常是用电磁卡盘固定的。

2. Cylindrical grinding. In cylindrical grinding, the workpiece is held between centers during the grinding operation, and the wheel rotation is the source and cause for the rotary cutting motion, as shown in Fig.8.2. In fact, cylindrical grinding can be carried out by employing any of the following methods:

2. 圆柱面磨削：在圆柱面磨削中，作业时工件支撑在两顶尖之间，砂轮转动是导致回转切削运动的动力源，如图8.2所示。实际上，圆柱面磨削能通过采用下列任意方法来实现：

(1) The transverse method, in which both the grinding wheel and the workpiece rotate and longitudinal linear feed is applied to enable grinding of the whole length. The depth of cut is adjusted by the cross feed of the grinding wheel into the workpiece.

(1) 横向方法：这种方法中砂轮与工件均旋转且采用线性纵向进给以保证能磨削整个长度。切削深度通过改变砂轮对工件的横向进给来进行调整。

(2) The plunge-cut method, in which grinding is achieved through the cross feed of the grinding wheel and no axial feed is applied. As you can see, this method can be applied only when the surface to be ground is shorter than the width of the grinding wheel used.

(2) 插入-切削方法：这种方法通过砂轮的横向进给完成磨削而不采用轴向进给。正如料想的那样，这种方法只在要磨削表面比所用砂轮宽度短时才使用。

(3) The full-depth method, which is similar to the transverse method except that the grinding allowance is removed in a single pass. This method is usually recommended when grinding short rigid shafts.

(3) 全深度方法：这种方法除了一次加工就能去除磨削余量外其它与横向方法相同。这种方法通常在磨削较短刚性轴时推荐使用。

        Internal grinding. Internal grinding is employed for grinding relatively short holes, as shown in Fig.8.3. The workpiece is held in a chuck or a special fixture. Both the grinding wheel and the workpiece rotate during the operation and feed is applied in the longitudinal direction.

       内表面磨削：内表面磨削用于相对较短的孔，如图8.3所示。工件安装在卡盘或特殊夹具上。作业时砂轮和工件都回转并且采用纵向进给。

Any desired depth of cut can be obtained by the cross feed of the grinding wheel. A variation from this type is planetary internal grinding, which is recommended for heavy workpieces that cannot be held in chucks.

通过砂轮的横向进给能得到任意所需的切削深度。这种方法的一个变体是行星式内表面磨削，当工件较重不能用卡盘固定时推荐使用。

In that case, the grinding wheel not only spins around its own axis but also rotates around the centerline of the hole that is being ground.

在这种情况下，砂轮不但绕自身轴线回转，同时还绕被磨削孔的中心线旋转。

      Centerless grinding. Centerless grinding involves passing a cylindrical workpiece, which is supported by a rest blade, between two wheels, i.e., the grinding wheel and the regulating or feed wheel.

       无心磨削：无心磨削用于加工圆柱形工件，工件由托板支撑，在两轮即砂轮和调节或进给轮之间通过去。

The grinding wheel does the actual grinding, while the regulating wheel is responsible for rotating the workpiece as well as generating the longitudinal feed. This is possible because of the frictional characteristics of that wheel, which is usually made of rubber-bonded abrasive.

砂轮完成实际磨削，而调节轮负责旋转工件和产生纵向进给。由于调节轮通常用橡胶粘结的磨料制成，其摩擦特性使这成为可能。

As can be seen in Fig.8.4, the axis of the regulating wheel is tilted at a slight angle with the axis of the grinding wheel. Consequently, the peripheral velocity of the regulating wheel can be resolved into two components, namely, workpiece rotational speed and longitudinal feed.

正如在图8.4中所看到的那样，调节轮的轴与砂轮轴倾斜一个微小角度。因此调节轮的圆周速度可以分解为两个分量，即工件回转速度和纵向进给。

These can be given by the following  equations:

          Vworkpiece＝Vregulating wheel×cosα 

          Axial feed＝Vregulating wheel×c×sinα 

Where c is a constant coefficient to account for the slip between the workpiece and the regulating wheel (c=0.94~0.98).

其值可由下列公式给出：

          V工件＝V调节轮×cosα 

          轴向进给＝V调节轮×c×sinα 

式中c是考虑工件和调节轮之间滑动的恒定系数(c=0.94~0.98)。 

      The velocity of the regulating wheel is controllable and is used to achieve any desired rotational speed of the workpiece. The angleαis usually taken from 1°to 5°and the larger the angle, the larger the longitudinal feed would be.

       调节轮的速度是可控的并被用于实现工件任意所需的转动速度。α角通常取1到 5°，这角度越大则纵向进给也将越大。

Whenαis taken as 0°, i.e., the two axes of the grinding and regulating wheels are parallel, there is no longitudinal feed of the  workpiece.

当α取0°时，即砂轮和调节轮轴线平行时，则工件没有纵向进给。

• Grinding Wheels  砂轮

       Grinding wheels are composed of abrasive grains having similar size and a binder. The actual grinding process is performed by the abrasive grains. Pores between the grains within the binder enable the grains to act as separate single-point cutting tools.

       砂轮由具有相近尺寸的磨料颗粒和粘合剂组成。实际磨削作业由磨粒完成。在粘合剂中磨粒之间的孔隙使磨粒能象独立的单刃切削刀具一样工作。

These pores also provide space for the generated chips, thus preventing the wheel from clogging. In addition, pores assist the easy flow of coolants to enable efficient and prompt removal of the heat generated during the grinding process.

这些孔隙同时还为产生的切屑提供空间以防砂轮堵塞。另外孔隙帮助冷却液容易流动，从而使在磨削作业中产生的热量能有效而迅速地散发。

      Grinding wheels are identified based on their shape and size, kind of abrasive, grain size, binder, grade (hardness), and structure.

       砂轮根据它们的形状和尺寸、磨料的类型、磨粒的大小、粘合剂、等级(硬度)和结构组织来分类。

       Shape and size of grinding wheels. Grinding wheels differ in shape and size, depending upon the purpose for which they are to be used. Various shapes are shown in Fig.8.5 and include the following types:

       砂轮的形状和尺寸：根据砂轮的用途，它们的形状和尺寸是不同的。各种形状如图8.5所示，其中包括：

1)Straight wheels used for surface, cylindrical, internal, and centerless grinding.

2)Bevelled-face or tapered wheels used for grinding threads, gear teeth, and the like.

3)Straight recessed wheels for cylindrical grinding and facing.

1)用于表面、圆柱面、内部和无心磨削的直轮。

2)用于磨削螺纹、齿轮轮齿之类的斜面或锥形轮。

3)用于圆柱面和端面磨削的直凹轮。

4)Abrasive disks for cutoff and slotting operations. (thickness 0.02 up to 0.2in. (0.5 to 5mm)).

5)Cylinders, straight cups, and flaring cups are used for surface grinding with the end face of the wheel.

4)用于切断和开槽作业的砂轮片(其厚度从0.02到0.2英寸(0.5到5毫米))。

5)用其端面进行表面磨削的圆柱、直杯及外展杯状砂轮。

      The main dimensions of a grinding wheel are the outside diameter D, the bore diameter d, and the height H. These dimensions vary widely, depending upon the grinding process for which the wheel is to be used.

       砂轮的主要尺寸有外径D、孔径d和厚度H。根据采用砂轮的磨削工艺，这些尺寸变化很大。

       Kind of abrasive. Grinding wheels can be made of natural abrasives such as quartz, emery, and corundum or of industrially prepared chemical compounds such as aluminum oxide or silicon carbide (known as carborundum).

       磨料的类型：砂轮可以由象石英、金刚砂、刚玉之类的自然磨料制成，或者由象氧化铝或碳化硅(也称人造金刚砂)之类的工业制备的化学化合物制成。

Generally, silicon carbide grinding wheels are used when grinding low-tensile-strength materials like cast iron, whereas aluminum oxide wheels are employed for grinding high-strength metals such as alloy steel, hardened steel, and the like.

当磨削象铸铁类低拉伸强度材料时，一般采用碳化硅砂轮，而磨削合金钢、淬火钢等高强度金属则要用氧化铝砂轮。

       Grain size of abrasive used. As you may expect, the grain size of the abrasive particles of the wheel plays a fundamental role in determining the quality of ground surface obtained.

       所用磨粒的尺寸：正如料想的那样，砂轮磨粒的尺寸对决定所得磨削表面的质量起着根本的作用。

The finer the grains, the smoother the ground surface is. Therefore, coarse-grained grinding wheels are used for roughing operations, whereas fine-grained wheels are employed in final finishing operations.

磨粒越细，磨削表面越光滑。所以，粗粒砂轮用于粗加工，而细粒砂轮则用于最后精加工。

       The grade of the bond. The grade of the bond is actually an indication of the resistance of the bond to pulling off the abrasive grains from the grinding wheel. Generally, wheels having hard grades are used for grinding soft materials and vice versa.

       粘结体的等级：粘结体的等级实际上是其抵抗将磨粒从砂轮上拉脱的指标。一般而言，具有较硬等级的砂轮用于磨削较软材料，反之亦然。

If a hard-grade wheel were to be used for grinding a hard material, the dull grains would not be pulled off from the bond quickly enough, thus impeding the self-dressing process of the surface of the wheel and finally resulting in clogging of the wheel and burns on the ground surface.

如果较硬等级的砂轮用于磨削较硬材料，磨钝的磨粒将不能足够快地脱离粘结体，这会妨碍砂轮表面的自修复，最终导致砂轮的堵塞并在被磨表面留下灼斑。

In fact, the cutting properties of all grinding wheels must be restored periodically by dressing with a cemented carbide roller or a diamond tool to give the wheel the exact desired shape and remove all worn abrasive grains.

实际上，所有砂轮的磨削性能都必须定期地通过使用硬质合金滚轮或金刚石修整器修整而被恢复，以求很准确地把砂轮加工成要求的形状，并去除已磨钝的磨粒。

       Structure. Structure refers to the amount of void space between the abrasive grains. When grinding softer metals, larger void space are needed to facilitate the flow of the removed chips.

       结构组织：结构组织与磨粒间的空隙量有关。当磨削较软金属时，需要较大的空隙以便去除切屑的流动。

       The binder. Abrasive particles are bonded together in many different ways. These include bond, silicate, rubber, resinoid, shellac, and oxychloride. Nevertheless, the bond is the most commonly used one.

       粘合剂：磨粒可用多种不同方法粘结在一起。其中包括粘合剂、硅酸盐、橡胶、树脂、虫胶和氯氧化物。然而，粘合剂是最常用的。

      In fact, the standard marking system is employed for distinguishing grinding wheels, by providing all the preceding parameters in a specific sequence.

       在实际生产中，为了区分砂轮采用标准标注系统，通过用一特定顺序将所有上述参数都表示出来。

 

 

Unit 9 Lapping and polishing

研磨与抛光

Lapping  研磨

      Lapping is a finishing operation used on flat and cylindrical surfaces. The lap, shown in Fig.9.1a, is usually made of cast  iron, copper, leather, or cloth.

       研磨是一种用于平面和圆柱面的精加工作业。研具，如图9.1a所示，通常用铸铁、铜、皮革或布制成。

The abrasive particles are embedded in the lap, or they may be carried through slurry. Depending on the hardness of the workpiece, lapping pressures range from 7kPa to 140kPa (1 to 20 psi).

研磨微粒嵌入研具内，或者可以通过液体携带。根据工件硬度，研磨压力可在7kPa到140kPa(1到20psi)范围中取。

      Lapping has two main functions. Firstly, it produces a superior surface finish with all machining marks being removed from the surface. Secondly, it is used as a method of obtaining very close fits between mating parts such as pistons and cylinders.

       研磨有两个主要作用。首先，它通过去除所有机加工痕迹能产生较好的表面光洁度。其次，它能用作获得像活塞与气缸之类配件间过盈配合的方法。

      The lapped workpiece surface may look smooth but it is actually filled with microscopic peaks, valleys, scratches and pits. Few surfaces are perfectly flat. Lapping minimizes the surface irregularities, thereby increasing the available contact area.

       研磨后的工件表面可能看似平滑，其实布满着微观峰、谷、划痕和凹陷。几乎没有表面是完全平整的。研磨使表面不规则最小化，因而增加了有效接触面积。

The drawing in Fig.9.1a shows two surfaces. The upper one is how a surface might look before lapping and the lower one after lapping. Lapping removes the microscopic mountain tops and produces relatively flat plateaus. Entire microscopic mountain ranges may need to be ground down in order to increase the available contact area.

图9.1a上显示了两个表面。上面是研磨前表面可能的外观模样而下面则是研磨后的模样。研磨去除了微观峰顶从而产生相对平坦的平台。整个微观山脉范围都需要磨去以增加有效接触面积。

      Production lapping on flat or cylindrical pieces is done on machines such as those shown in Fig.9.1b and 9.1c. Lapping is also done on curved surfaces, such as spherical objects and lenses, using specially shaped laps.

       研磨平面或圆柱面工件的生产过程是在如图9.1b和9.1c那样的机器上完成的。研磨也可采用特殊成型研具在诸如球形物体和透镜之类的曲面上进行。

Polishing   

抛光

      Polishing is a process that produces a smooth, lustrous surface finish. Two basic mechanisms are involved in the polishing process: (a) fine-scale abrasive removal, and (b) softening and smearing of surface layers by frictional heating during polishing.

       抛光是生成平滑、有光泽表面光洁度的工艺。抛光工艺涉及两种基本机理： (a)精细等级磨粒去除，和(b)在抛光中通过摩擦生热软化并抹光表面层。

Electropolishing

电解抛光

       Electropolishing is an electrochemical process similar to, but the reverse of, electroplating. The electropolishing process smoothes and streamlines the microscopic surface of a metal object. Mirror-like finishes can be obtained on metal surfaces by electropolishing.

      电解抛光是一种与电镀相似的电化学工艺，但过程与电镀正好相反。电解抛光工艺使金属物体的微观表面平滑和简单化。通过电解抛光能在金属表面得到镜面光洁度。

       In electropolishing, the metal is removed ion by ion from the surface of the metal object being polished. Electrochemistry and the fundamental  principles of electrolysis (Faraday’s Law) replace traditional mechanical finishing techniques.

       在电解抛光中，金属是逐个离子地从被抛光金属物体表面去除的。电化学和电解基本原理(Faraday定理)取代了传统的机械精加工技术。