断虹霁雨

 

Lesson 1 Tool Materials

New words and expressions:

1. evaluation  n.评价，估价，鉴定，计算	2. satisfactory  a.满意的，符合要求的
3. availability  n.存在，具备，有效性，利用率	4. category  n.种类，范畴，类型
5. epoxy  a.环氧的	6. thermal a.热量的，由热造成的n.上升暖气流
7. toughness  n.韧性，韧度，塑性，刚度	8. brittle  a.脆的，易碎的，易损坏的
9. malleability  n.可锻性，延展性，韧性	10. modulus  n.模量，模数，系数
11. standpoint  n.观点，立场	12. sufficient  a.充分的，足够的
13. strength  n.力量，强度	14. dimensional  a.尺寸的，量纲的
15. stability  n.稳定性，安定度	16. metallurgical  a.冶金（学）的
17. porosity  v.多孔（性），孔隙度，疏松（度）	18. segregation  n.分离，分开，隔离，偏析
19. impurity  n.杂质	20. macroscopic  a.宏观的，肉眼可见的
21. microscopic  a.显微镜的，微观的，微小的	22. inspection  n.检查，调查，参观，视察
23. blade  n.刀口，刀片，叶片，刀身	24. carbide  n.碳化物，电石，碳化钙
25. composition  n.组成，合成，构成，组织	26. in some cases 有时，在有些情况下
27. (be) subjected to 曾受到，使受到	28. epoxy resins 环氧树脂

Text:

The specific material selected for a particular tool is normally determined by the mechanical properties necessary for the proper operation of the tool. These materials should be selected only after a careful study and evaluation of the function and requirements of the proposed tool. IN most applications, more than one type of material will be satisfactory, and a final choice will normally be governed by material availability and economic considerations.

The principal materials used for tools can be divided into three major categories: ferrous materials, nonferrous materials, and nonmetallic materials. Ferrous tool materials have iron as a base metal and include tool steel, alloy steel, carbon steel, and cast iron. Nonferrous materials have a base metal other than iron and include aluminum, magnesium, zinc, lead, bismuth, copper, and a variety of alloys. Nonmetallic materials are those materials such as woods, plastics, rubbers, epoxy resins, ceramics, and diamonds that do not have a metallic base. To properly select a tool material, there are several physical and mechanical properties you should understand to determine how the materials you select will affect the function and operation of the tool①.

Physical and mechanical properties are those characteristics of a material which control how the material will react under certain conditions. Physical properties are those properties which are natural in the material and cannot be permanently altered without changing the material itself. These properties include: weight, color, thermal and electrical conductivity, rate of thermal expansion, and melting point. The mechanical properties of a material are those properties which can be permanently altered by thermal or mechanical treatment. These properties include strength, hardness, wear resistance, toughness, brittleness, plasticity, ductility, malleability, and modulus of elasticity.

From a use standpoint, tool steel are utilized in working and shaping basic materials such as metals, plastics, and wood into desired forms. From a composition standpoint, tool steels are carbon alloy steels which are capable of being hardened and tempered. Some desirable properties of tool steels are high wear resistance and hardness, good heat resistance, and sufficient strength to work the materials. In some cases, dimensional stability may be very important. Tool steels also must be economical to use and be capable of being formed or machined into the desired shape for the tool.

Since the property requirements are so special, tool steels are usually melted in electric furnaces using careful metallurgical quality control. A great effort is made to keep porosity, segregation, impurities, and nonmetallic inclusions to as low a level as possible②. Tool steels are subjected to careful macroscopic and microscopic inspection to ensure that they meet strict “tool steel” specifications.

Although tool steels are a relatively small percentage of total steel production, they have a strategic position in that they are used in the production of other steel products and engineering materials. Some applications of tool steels include drills, deepdrawing dies, shear blades, punches, extrusion dies, and cutting tool.

For some application, especially where extremely high-speed cutting is important, other tool materials such as sintered carbide products are a more economical alternative to tool steels. The exceptional tool performance of sintered carbides results from their very high hardness and high compressive strength. Other tool materials are being used more and more often industrially.

Notes:

[1]     To properly select a tool material, there are several physical and mechanical properties you should      understand to determine how the materials you select will affect the function and operation of the tool. 为了选择工具材料，我们应当掌握材料的一些物理性能和力学性能，以便确定所先材料对工具的功能和操作会有何影响。不定式to properly select a tool material放在句首作目的状语；you select为定语从句修饰紧在前面的the materials。

[2]     A great effort is made to keep porosity, segregation, impurities, and nonmetallic inclusions to as low a level as possible.（对于工具钢的冶炼），要最大限度地使钢中的气孔、偏析、杂质以及非金属夹杂物等含量尽可能地低一些。这里的a great effort is made是make a great effort的被动形式，意为“尽一切力量”。

Practice:

Translate one paragraph of the reading materials on page 4-5.

Homework:

Answer the questions on page 1.

 

 

 

 

 

Lesson 2 Heat Treating of Tool Steels

New words and expressions:

1. alteration  n.改变，变更	2. nature  n.本性，性质，自然界
3. distribution  n.分配，分布	4. constituent  n.成分，分量，要素；a.组成的
5. grain  n.谷物，晶粒，粒度；v.（使）结晶	6. strain vt.应变，张力，变形，弯曲
7. annealing  n.退火，韧化，缓冷	8. corrosion  n.腐蚀，侵蚀，锈，铁锈
9. magnetic  a.磁的，磁化的，有吸引力的	10. customarily  ad.通常，习惯上
11. spheroidizing  n.球化处理	12. coarsen  vt.使粗，粗化；vi.变粗
13. homogeneous  a.同种的，同性的，均匀的	14. globular  a.球状的，有小球的，世界范围的
15. elevate  vt.抬起，举起，使升高	16. appreciable  a.可估计的，明显的，可观的
17. cyanide  n.氰化物	18. carburize  vt.渗碳
19. grain size  晶粒尺寸	20. cold working  冷加工
21. internal stress内应力	22. corrosion resistance  耐腐蚀
23. heat resistance  耐热	24. magnetic property  磁性能
25. (be) referred to  把…归因于，参考，认为…	26. critical range 临界范围

Text:

The purpose of heat treatment is to control the properties of a metal or alloy through the alteration of the structure of the metal or alloy by heating it and controlled cooling determines not only the nature and distribution of the microconstituents, which in turn determine the properties, but also the grain size.

Heat treating should improve the alloy or metal for the service intended. Some of the various purposes of heat treating are as follows:

1.       To remove strains after cold working.

2.       To remove internal stresses such as those produced by drawing, bending, or welding.

3.       To increase the hardness of the material.

4.       To improve machinability.

5.       To improve the cutting capabilities of tools.

6.       To increase wear-resisting properties.

7.       To soften the material, as in annealing.

8.       To improve or change properties of a material such as corrosion resistance, heat resistance, magnetic properties, or others as required.

Treatment of Ferrous Materials. Iron is the major constituent in the steels used in tooling, to which carbon is added in order that the steel may harden. Alloys are put into steel to enable it to develop properties by plain steel, such as the ability to harden in oil or air, increased wear resistance, higher toughness, and greater safety in hardening.

含铁金属材料的热处理，铁是用于工具制造钢材的主要成份，在铁中加入碳以使钢材变硬，合金元素加入钢中能得到不搀合金元素钢不具有的性能，如能使钢材在空气或油中进行淬火，提高钢材的耐磨性，增大材料的韧性及在淬火时更安全。

Heat treatment of ferrous materials involves several important operation which are customarily referred to under various headings, such as normalizing, spheroidizing, stress relieving, annealing, hardening, tempering, and case hardening.

含铁材料的热处理包含几个重要操作，常常被冠以如下这些称谓，例如正火、球化、应力消除、退火、淬火、回火和表面硬化。

Normalizing involves heating the material to a temperature of about 100-200F(55-100 ℃) above the critical rang and cooling in still air. This is about 100F(55 ℃) over the regular hardening temperature.

正火包括将材料加热到临界温度范围以上，大约为55-100℃左右，然后在空气中冷却。该温度约为55℃，高于正常的淬火温度。

The purpose of normalizing is usually to refine grain structures that have been coarsened in forging. With most of the medium-carbon forging steels, alloyed and unalloyed, normalizing is highly recommended after forging and before machining to produce more homogeneous structures, and in most cases, improved machinability.

正火的目的通常是为了细化锻造过程中被粗化的晶粒。对于大多数中碳锻造钢，合金钢及非合金钢，在其锻造后强烈推荐正火热处理工艺，此种热处理工艺使机加工前的材料产生更均匀的结构，并且大大多情况下对材料机加工性能有所改善。

High-alloy air-hardened steels are never normalized, since to do would cause them to harden and defeat the primary purpose.

高合金空气硬化钢从不进行正火，因为对此种材料进行正火将导致材料变硬并导致淬火的主要目的失败。

Spheroidizing is a form of annealing which, in the process of heating and cooling steel, produces a rounded or globular form of carbide ----the hard constituent in steel.

球化是退火的一种，此工艺中加热与冷却钢材，钢材内部产生圆形或球状碳化粒子，碳化粒子是钢材的硬质部分。

Tool steels are normally spheroidized to improve machinability. This is accomplished by heating to a temperature to 1380-1400’F (749-760℃) for carbon steels and higher for many alloy tool steels, holding at heat one to four hours , and cooling slowly in the furnace .

工具钢通常进行球化处理工艺以改善机加工性能。这一工艺对碳钢来说是加热到749-760℃（对许多合金钢要更高一点），保持温度1-4小时，然后在炉内慢慢冷却。

Stress Relieving . This is a method of relieving the internal stresses set up in steel during forming, cold working , and cooling after welding or machining . It is the simplest heat treatment and is accomplished merely by heating to 1200-1350’F(649-732℃) followed by air or furnace cooling .

应力消除:这是一种消除钢材在成型过程中产生的内应力的方法，材料在冷作加工、焊接或机加工后冷却产生的内应力。这是一种最简单的热处理工艺，它仅是过将材料加热到649-732℃接着在空气中冷却或在炉内冷却来完成。

Large dies are usually roughed out ,then stress-relieved and finish-machined . This will minimize change of shape not only during machining but during subsequent heat treating as well . Welded sections will also have locked-in stresses owing to a combination of differential heating and cooling cycles as well as to changes in cross section. Such stresses will cause considerable movement in machining operations .

大型模具通常是做一个毛坯，然后消除内应力，再进行精加工。这样不断是在机加工期间而且在随后的热处理期间都最少改变模具的形状。焊接区也同样存在内应力，因为焊接联接区受到的加热与冷却时间不同以及焊接断面受热与冷却的情况也发生了变化。这些内应力会导致零件机加工时产生明显的变形。

Annealing .The process of annealing consists of heating the steel to an elevated temperature for a definite period of time and, usually, cooling it slowly .Annealing is done to produce homogenization and to establish normal equilibrium conditions , with corresponding characteristic properties.

退火，退火工艺通常是在确定的时间内加热工件升至某一温度，再进行缓慢冷却。退火使工件性能均匀一致并且建立正常的平衡条件，从而获得相应的性能。

Tool steel is generally purchased in the annealed condition . Sometimes it is necessary to rework a tool that had been hardened, and the tool must then be annealed . For this type of anneal, the steel is heated slightly above its critical range and then cooled very slowly .

购回的工具钢一般是已经退火了，有时需要对已经淬火的工具钢进行重新加工，此时工具钢必须进行退火。对于这种类型的退火，钢材加热稍高于临界温度然后进行非常缓慢的冷却。

Hardening .This is the process of heating to a temperature above the critical range , and cooling rapidly enough through the critical range to appreciably harden the steel .

淬火，该工艺是加热工件到临界温度以上，然后以足够快的速度进行冷却通过临界温度区域以使工件明显硬化。

Tempering .This is the process of heating quenched and hardened steels and alloys to some temperature blow the lower critical temperature to reduce internal stresses set-up in hardening .

回火，回火是加热骤冷并硬化钢材与合金，加热的温度是在最低临界温度以下以降低硬化过程中产生的内应力。

Case Hardening . The addition of carbon to the surface of steel parts and the subsequent hardening operations are important phase in heat treating. The process may involve the use of molten sodium cyanide mixtures, pack carburizing with activated solid material such as charcoal or coke , gas or oil carburizing , and dry cyaniding .

表面硬化，将碳渗加到零件表面，接下来的硬化操作是热处理的重要阶段。这个过程包括使用熔融氰化钠混合物，用活性固体材料如木炭、焦炭，或者用能够提供碳原子的气体、油类的干的氰化物填满渗碳介质。

Practice:

Translate one paragraph of the reading materials on page 9-10.

Homework:

Answer the questions on page 7.

Lesson 3 Cutting Tool Design

New words and expressions:

1. framework  n.骨架，构架，框架，结构	2. buttery  a.黄油状的，涂有黄油的
3. handle  n.柄；vt. 管理，应付；vi.易于触摸	4. distinction  n.差别，区别，特征，特性
5. diversity  n.参差，不同，多样性，发散	6. match  n.比赛，匹配；vt.配得上；vi.相符合
7. geometry  n.几何学，几何形状，几何图	8. trial  n.试验，偿试； a.试验性的，试制的
9. comparison  n.比较，对照，比喻	10. literature  n. 文学，文献，著作，文学作品
11. interaction  n.相互作用，相互影响（制约）	12. govern  vt.统治，管理； vi. 统治，管理
13. signature  n. 签名，署名，用法说明	14. nomenclature  n. 名称，术语同，命名法
15. alpha  n. 希腊字母，最初，开始	16. numeric  a. 数字的，数值的；n.数，分数
17. significant  a. 有意义的，重大的，重要的	18. nose  n. 头部，机头，管口，喷嘴
19. identification  n. 辩别，鉴别，识别	20. trial and error 反复试验
21. theoretical framework 理论框架	22. on the basis of  在…基础上，根据
23. to a great extent  很大程度上	24. (be) governed by  取决于，以…为转移

Text:

Physics of metal-cutting provide the theoretical framework by which we must examine all other elements of cutting tool design. We have workpiece materials from a very soft, buttery consistency to very hard and shear resistant. Each of the workpiece materials must be handled by itself; the amount of broad information that is applicable to each workpiece. Not only is there a vast diversity of workpiece materials, but there is also a variety of shapes of tools and tool compositions.

The tool designer must match the many variables to provide the best possible cutting geometry. There was a day when trial and error was normal for this decision, but today, with the ever-increasing variety of tools, trial and error is for too expensive.

The designer must develop expertise in applying data and making comparisons on the basis of the experience of other. For example: tool manufacturers and material salesmen will have figures their companies have developed. The figures are meant to be guidelines; however, a careful examination of the literature available will provide an excellent place from which to start, and be much cheaper than trial and error.

Material removal by machining involves interaction of five elements: the cutting tool, the toolholding and guiding device, the workholder, the workpiece, and the machine. The cutting tool may have a single cutting edge or may have many cutting edges. It may be designed for linear or rotary motion. The geometry of the cutting tool depends upon its intended function. The toolholding device may or may not be used for guiding or locating. Toolholder selection is governed by tool design and intended function.

The physical composition of the workpiece greatly influences the selection of the machining method, the tool composition and geometry, and the rate of material removal①. The intended shape of the workpiece influences the selection of the machining method and the choice of linear or rotary tool travel. The composition an geometry of the workpiece to a great extent determines the workholder requirements. Workholder selection also depends upon forces produced by the tool on the workpiece. Tool guidance may be incorporated into the workholding function.

Successful design of tools for the material removal processes requires, above all, a complete understanding of cutting tool function and geometry. This knowledge will enable the designer to specify the correct tool for a given task. The tool, in turn, will govern the selection of toolholding and guidance methods. Tool forces govern selection of the workholding device. Although the process involves interaction of the five elements, everything begins with and is based on what happens at the point of contact between the workpiece and the cutting tool.

The primary method of imparting form and dimension to a workpiece is the removal of material by the use of edged cutting tools. An oversize mass is literally carved to its intended shape. The removal of material from a workpiece is termed generation of form by machining, or simply machining.

Form and dimension may also be achieved by a number of alternative processes such as hot or cold extrusion, sand casting, die casting, and precision casting. Sheet metal can be formed or drawn by the application of pressure. In addition to machining, metal removal can be accomplished by chemical or electrical methods. A great variety of wokpieces may be produced without resorting to a machining operation. Economic considerations, however, usually dictate form generation by machining, either as the complete process or in conjunction with another process.

Cutting tools are designed with sharp edges to minimize rubbing contact between the tool and workpiece. Variations in the shape of cutting tool influence tool life, surface finish of the workpiece, and the amount of force required to shear a chip from the parent metal. The various angles on a tool compose what is often termed the tool geometry. The tool signature or nomenclature is a sequence of alpha and numeric characters representing the various angles, significant dimension, special features, and the size of the nose radius②. This method of identification has been standardized by the American National Standards Institute for carbide and for high speed steel, and is illustrated in Figure 3-1, together with the elements that make up the tool signature.

Notes:

[1]     The physical composition of the workpiece greatly influences the selection of the machining method, the tool composition and geometry, and the rate of material removal.实际工件的组成极大地影响着对加工方法、刀具组成与几何形状以及切削速度的选择。此句两处用到composition这个词，其意思是指工件和刀具的“组成部分”。

[2]     The tool signature or nomenclature is a sequence of alpha and numeric characters representing the various angles, significant dimension, special features, and the size of the nose radius.刀具的命名以希腊字母“α”和一些数字构成的一个有序排列，其中的数字代表着一些刀具的角度、重要尺寸、特殊性能以及刀头半径的大小。句中的representing引导的分词短语作后置定语，用来修饰a sequence of alpha and numeric characters.

Practice:

Translate one paragraph of the reading materials on page 14-16.

Homework:

Answer the questions on page 13.

 Lesson 4 Workholding Principles

New words and expressions:

1. workholder  n. 工件夹紧装置	2. grip  n.紧握，柄；v.紧握，控制
3. chuck  n.夹头，夹盘；vt.夹紧，卡紧	4. pneumatic  a.空气的，气动的；n.气胎
5. pliers  n.钳，手钳，老虎钳	6. tong  n. 钳，夹子vt. 用钳夹住
7. serration  n.锯齿形，成锯齿形	8. slippage  n.滑动，打滑，空转，下降
9. vise  a.虎钳；vt.钳住，夹紧	10. jaw  n.虎钳牙，夹片，口部
11. attachment  n.连接物，附件	12. depict  vt.描写，描述，描绘
13. wrench  n.拧，扳钳，扳手；v.拧，扳紧	14. unison  n. 一致，统一
15. firmness  n.坚固，固定，稳定	16. abrupt  a. 突然的，陡峭的
17. thrust  v.锰推，冲，延伸；n.拉力，牵引力	18. torque  n. 转矩，扭矩，扭转
19. except for  除了，只有	20. in contact with  和…接触着
21. tool-holder 刀夹，刀杆，刀柄	22. tool-holding  刀具夹紧
23. attachment screw  止动螺钉

Text:

The term workholder include all devices that hold, grip,or chuck a workpiece to perform a manufacturing operation. The holding force may be applied mechanically, electrically, hydraulically, or pneumatically. This section considers workholders used in material-removing operations. Workholding is one of the most important elements of machining processes.

Figure 4-1 illustrates almost all the basic elements that are present in a material-removing operation intended to shape a workpiece. The right hand is the toolholder, the left hand is the workholder, the knife is the cutting g tool, and the piece of wood is the workpiece. Both hands combine their motion to shape the piece of wood by removing material in the form of chips. The body of the person whose hands are shown may be considered a machine that imparts power, motion, position, and control to the elements shown. Except for the elements of force multiplication, these basic elements may be found in all of the forms of manufacturing setups where toolholders hand workholders are used.

Figure 4-2 shows a pair of pliers or tongs used to hold a rod on which a point has to ground or filed. This simple workholder illustrates the element of force multiplication by a lever action, and also shows serrations on the parts contacting the rod to increase resistance against slippage.

Figure 4-3 shows a widely used workholder, the screw-operated vise. The screw pushes the movable jaw and multiplies the applied force. The vise remains locked by the self-locking characteristic of the screw, provides means of attachment to a machine, and permits precise placement of the work①.

A vise with a number of refinements often used in workholders is depicted in Figure 4-4. The main holding force is supplied by hy6draulic power, the screw being used only to bring the jaws in contact with a workpiece. The jaws may be replaceable inserts profiled to locate and fit a specific workpiece as shown. Other, more complicated jaw forms are used to match more complicated workpieces.

Another large group0 of workholders are the chucks. They are attached to a variety of machine tools and are used to hold a workpiece during turning, boring, drilling, grinding, and other rotary operations. Any types of chucks are available. Some are tightened manually with a wrench, others are power operated by air or hydraulic means or by electric motors. On some chucks, each jaw is individually advanced and tightened, while others have all jaws advance in unison. Figure 4-5 shows a workpiece clamped in a four-jaw independent chuck. The drill, which is removing material from the workpiece is clamped in a universal chuck.

Purpose and Function of Workholders. A workholder must position or locate a workpiece in a definite relation to the cutting tool and must withstand holding and cutting forces while maintaining that precise location. A workholder is made up of several elements, each performing a certain function. The locating elements position the workpiece; the structure, or tool body, withstands the forces; brackets attach the workholder to the machine;; and clamps, screws, and jaws app;y holding forces. Elements may have manual or power activation. All functions must be performed with the required firmness of holding, accuracy of positioning, and with a high degree of safety for the operator and the equipment.

The design or selection of a workholder is governed by many factors, the first being the physical characteristics of the workpiece. The workholder must be strong enough to support the workpiece without deflection. The workholder material must be carefully selected with the workpiece in mind so that neither will be damaged by abrupt contact, e.g., damage to a soft copper workpiece by hard steel jaws②.

Cutting forces imposed by machining operations vary in magnitude and direction. A drilling operation induces torque, while a shaping operation causes straight-line thrust. The workholder must support the workpiece in opposition to the cutting forces and will generally be designed for a specific machining operation.

Many workholders are used in industry that are not used on material removing operations. Workholders may be used for the inspection of workpieces, assembly, welding, and so on. There may be very little difference in their basic design and their appearance. Quite often a standard commercial design may be used in one application for a turning operation and for the same or another workpiece in an inspection operation.

Notes:

[1]     The vise remains locked by the self-locking characteristic of the screw, provides means of attachment to a machine, and permits precise placement of the work. 虎钳是由螺旋的自锁特性来保持锁紧的，它提供了一个使其它部件附着到机床上的一种手段，从而确保加工时的精确定位。句中remains,provides, permits为并列谓语，进一步说明虎钳的作用。

[2]     The workholder material must be carefully selected with the workpiece in mind so that neither will be damaged by abrupt contact, e.g., damage to a soft copper workpiece by hard steel jaws.在考虑工件材料的前提下，必须细心选择制造工件夹紧装置的材料，只有这样才不会引起接触性破坏，例如：若选用硬的钢质虎钳口，就会引起比较软的铜质工件材料受到破坏。句中so that neither will be damaged by abrupt contact为目的状语从句。

Practice:

Translate one paragraph of the reading materials on page 21-22.

Homework:

Answer the questions on page 19.

 Lesson 5 Jig and Fixture Design

New words and expressions:

1. jig  n. 夹具，模具，规尺，机架	2. hold  v. n.拿，握，支持，夹住
3. locate  v. 设置，安排，定位，确定位置	4. tap  n. 丝锥，螺丝攻，塞子
5. reamer  n. 扩孔锥，铰刀，铰床	6. countersink  n. 埋头孔，锥口孔； v.钻孔
7. counterbore  n. 扩孔，锪孔	8. chamfer  n. 槽，斜面，圆角，倒角
9. pilot  n. 领航员，定料销，导向器	10. bush  n. 衬套，轴瓦；vt.加衬套于
11. spot  n. 点，污点；vt.定点，定位	12. precise  a. 正确的，精确的，精密的
13. benefit  n. 利益，好处；vt.有益于…	14. compile  vt.编纂，编辑，编译程序
15. predetermine  vt. 预定	16. fixture  n. 夹具，夹紧装置，型架，固定
17. align  v. 匹配，排列成一行，定位，校直	18. gang  n. 一组，一队；v.定位，校直
19. bandsaw  n. 带锯，带锯机	20. slot  n. 切口，裂口，槽沟；vt.开槽于
21. share  n. 一份，股份；vt.均分，分配	22. versus  prep. …对…，与…比较，依…转移
23. warrant  n. 证明，理由，根据；vt.保证	24. slotter  n. 插床，侧床，立刨床
25. spindle  n. 轴，主轴，杆，蜗杆	26. by far 非常，大大，最
27. apply to 致力于，适用于	28. (be) aware of 知道，意识到，认识

Text:

Jigs are workholders which are designed to hold, locate，and support a workpiece while guiding the cutting tool throughout its cutting cycle. Jigs can be divided into two general classifications: drill jigs and boring jigs. Of these, drill jigs are, by far, the most common. Drill jigs are generally used for drilling, tapping, and reaming, but may also be used for countersinking, counterboring, chamfering, and spotfacing, Boring jigs, on the other hand, are normally used exclusively for boring holes to a precise, predetermined size. The basic design of both classes of jigs is essentially the same. The only major difference is that boring jigs are normally fitted with a pilot bushing or bearing to support the outer end of the boring bar during the machining operation.

In designing any jig, there are numerous considerations that must be addressed. Although several of these points, such as locating, supporting, and clamping, have already been covered, they are included in this section because they apply to jig design. Since all jigs have a similar construction, the points covered for one type of jig normally apply to the other types as well. Jig design and selection begins with an analysis of the workpiece and the manufacturing operation to be performed.

One of the first considerations in the design of any workholder is the relative balance between the cost of the tool and the expected benefits of using the tool for production①. All workholders should save more in production costs than the tool costs to design and construct. In many instances, tool designers may have to complete detailed estimates to justify the cost of special tooling. This involves a close look at the part drawing, process specifications and other related documents.

Typically, the complexity of the part, location and number of holes, required accuracy, and the number of parts to be made are all points which must be considered to determine if the cost of a particular jig is warranted. Once the tool designer is satisfied that the cost of special tooling is justified, the remaining data required to produce a suitable workholder is complied and analyzed.

Fixtures are workholders which are designed to hold, locate, and support the workpiece during the machining cycle. Unlike jigs, fixtures do not guide the cutting tool, but rather provide a means to reference and align the cutting tool to the workpiece. Fixtures are normally classified by the machine with which they are designed to be used. A sub-classification is sometimes added to further specify the fixture classification. This sub-classification identifies the specific type of machining operation the fixture is intended to perform. For example: a fixture used with a milling machine is called a milling fixture, however, if the operation it is to perform is gang milling, it may also be called a gang-milling fixture. Likewise, a bandsawing fixture designed for slotting operations may also be referred to as a bandsaw-slotting fixture.

The similarity between jigs and fixtures normally ends with the design of the tool body. For the most part, fixtures are designed to withstand much greater stresses and tool forces than jigs, and are always securely clamped to the machine②. Fore these reasons, the designer must always be aware of proper locating, supporting, and clamping methods when fixturing any part.

In designing any fixture, there are several considerations in addition to the part which must be addressed to complete a successful design. Cost, production capabilities, production processing and tool longevity are some of the points which must share attention with the workpiece when a fixture is designed.

As with all tooling, the first consideration in fixture design is the cost versus the benefit. The production quantity, rate, or accuracy must warrant the added expense of special tooling. In addition, the fixture must pay for itself with savings derived from its use in as short a time as possible.

Notes:

[1]     One of the first considerations in the design of any workholder is the relative balance between the cost of the tool and the expected benefits of using the tool for production. 在设计工件夹持位置时，首先要考虑的问题是制造该工具的成本和使用该工具进行生产所希望产生的效益两者之间应保持相对平衡。单个分词expected作名词benefits的前置定语；动名词短语using the tool for production作介词of的宾语。

[2]     For the most part, fixtures are designed to withstand much greater stresses and tool forces than jigs, and are always securely clamped to the machine. 就绝大多数而言，fixtures(夹紧装置)在设计上比jigs(夹具)能够承受更大的应力，并且总能可靠地将工件夹紧到机床上。介词短语for the most part在这里相当于in most cases, 可译为“在绝大部分情况下”。

Practice:

Translate one paragraph of the reading materials on page 26-29.

Homework:

Answer the questions on page 24.

 

Lesson 6 Press Types

New words and expressions:

1. interval  n. 间隔，空间，周期	2. bolster  n. 垫枕，垫木；vt.支撑，垫
3. reciprocate  vt. 使往复运动，互换，互给	4. ram  n. 压头，柱塞，滑枕；vt.撞击，冲击
5. slide  vi.滑，溜vt.使滑入n.滑动滑块，冲头	6. flywheel  n. 飞轮，惯性轮，整速轮
7. hydraulic  a. 水力（学）的，液压的	8. incline  vt. 倾斜，偏向；n.斜坡，斜面
9. gap  n. 裂口，缺口，间隙；vt.使成缺口	10. disposal  n. 安排，排列，处理，配置
11. stock  n. 杠杆，钻柄，台，座；vt.装把手	12. stroke  n. 打击，冲程，行程
13. shut  vt. 关闭，封闭，关上	14. knock  vt.打击，碰撞；n. 敲打
15. eject  vt. 顶出，抛出，排斥	16. cushion  n.垫子，气垫；vt. 使减少振动
17. accessory  n.附件，附属设备；a. 附加的	18. notch  n. 切口，切痕；v.开缺口，冲缺口
19. prototype  n. 原型，模型，样机，样品	20. injury  n. 损害，伤害
21. triple  a. 三倍的，三重的，三联的	22. knuckle  n.万向接头，指节，肘节
23. coining  n. 压印加工，压花，立体挤压	24. crank  n. 曲柄，曲轴，手柄，弯曲
25. oscillate  vi. 波动，振动	26. deformation 形变，畸变，失真
27. rectangular  a.长方形的，矩形的，成直角的	28. reverse  v.颠倒，反转，倒退；n.反向
29. strict  a. 严格的，精确的，严密的	30. compliance  n. 答应，服从，可塑性，柔量
31. result in 结果形成，导致	32. a series of 一系列，许多
33. (be) comprised of  包括在…内	34. triple screw 三头螺旋，三纹螺旋
35. prototype workpiece  样件

Text:

Characteristic of the press working process is the application of large forces by press tools for a short time interval, which results in the cutting(shearing) or deformation of the work material.

A pressworking operation, generally completed by a single application of pressure, often results in the production of a finished part in less than one second.

Pressworking forces are set up, guided, and controlled in a machine referred to as a press.

Power Presses. Essentially, a press is comprised of a frame, a bed or bolster plate, and a reciprocating member called a ram or slide which exerts force upon work material through special tools mounted on the ram and bed.

Energy stored in the rotating flywheel of a mechanical press(or supplied by a hydraulic system in a hydraulic press) is transferred to the ram for its linear movements.

Press Types. An open-back inclinable (OBI) press (Figure 6-1), also called a gap-frame press, has a C-shaped frame which allows access to its working space (between the bed and the ram). The frame can be inclined at an angle to the base, allowing for the disposal of finished parts by gravity. The open back allows the feeding and unloading of stock, workpieces, and finished parts through it from front to back.

Major components of a press are as follows:

1. Press Bed. A rectangular part of the frame, generally open in its center,which supports a bolster plate.

2. Bolster Plate. A flat steel plate, from 2 to 5"(51-127mm) thick, upon which press press tools and accessories are mounted. Bolsters having standard dimensions and openings are available from press manufacturers.

3. Ram or Slide. The upper press member that moves through a stroke a distance depending upon the size and design of the press. The position of the ram, but not its stroke, can be adjusted.

The distance from the top of the bed(or bolster)to the bottom of the slide, with its stroke down and adjustment up, is the shut height of a press①.

4. Knockout. A mechanism operating on the upstroke of a press, which ejects workpieces or blanks from a press tool.

5. Cushion. A press accessory located beneath or within a bolster for producing an upward motion and force; it is actuated by air, oil, rubber, or springs or a combination of mechanisms.

A straight side press of conventional design has columns (up rights) at the ends of the bed, usually with windows (square or rectangular openings) to allow the feeding and unloading of stock, workpieces, and finished parts.

With special applications, this type of press also can be used for feeding from front to back (Figure 6-2).

A press brake is essentially the same as a gap-frame press except for its long bed from 6 to 20 feet (1.8-6m) or more. It is used basically for various bending operation on large sheet metal parts. It can also be used with a series of separate sets of press tools to do light piercing, notching, and forming. This allows parts of a complex design to be accurately made without a high-cost press tool by simply breaking the complex part down into several simple operations. This type of operation is used on low-run or prototype parts. The tooling cost is usually very low, but the labor cost is high as the parts are manually transferred and located in each station. The operator must follow good safety practices at all times to avoid injury.

A hydraulic press is used basically for forming operations and slower operation cycle time than most mechanical presses. The advantages of hydraulic presses are that the working pressure, stroke, and speed of the ram are adjustable (Figure 6-3).

A double –action press is used for large, or deep drawing operations on sheet metal parts. This type of press has an outer ram (blank holder) and a second inner ram (punch holder). During the operating cycle, the blank folder contacts the material first and applies pressure to allow the punch holder to properly draw the part.

A triple-action press has the same inner and outer ram as the double-action press, but a third ram in the press bed moves up allowing a reverse draw to be made in one press cycle②. The triple-action press is not widely used.

A knuckle press is used for coining operations. The design of the drive allows for very high pressures at the bottom of the ram stroke. This type uses a crank, which moves a joint consisting of two levers that oscillate to and from dead center and results in a short, powerful movement of slide with slow travel near the bottom of the stroke.

These are the basic press types used in industry, although there are many more types with special applications.

Press operator safety must be a primary concern for everyone in the press area. While working under the ram the press control must be locked in the off position and safety blocks placed under the ram to prevent it from coasting down. While the press is running, the use of proper guards and safety procedures must always be followed.

Press safety under OHSA (Occupational Health and Safety Act) is law. Strict compliance to the regulations are required.

Notes:

[1]     The distance from the top of the bed(or bolster)to the bottom of the slide, with its stroke down and adjustment up, is the shut height of a press. 从工作台（或垫板）的上表面到滑块的下表面之间的距离（可以上、下调节），称为压力机的闭合高度。句中介词短语from the top of the bed (or bolster) to the bottom of the slide属于“from…to…”，可译为“从…到…”，这个介词短语作后置定语，修饰the distance。

[2]     A triple-action press has the same inner and outer ram as the double-action press, but a third ram in the press bed moves up allowing a reverse draw to be made in one press cycle.三动式压力机具有和双动式压力机相同的内、外滑块。此外，三动压力机工作缸还有另一个滑块，它可向上运动，从而在一个冲压循环中允许反向拉伸。句中短语the same inner and outer ram as the double-action press属于the same…as…这种结构；inner and outer ram译为内、外滑块。原文中的“a third”主要侧重于“another(另一个)”的意思，而不强调次序。

Practice:

Translate one paragraph of the reading materials on page 34-35.

Homework:

Answer the questions on page 32.

 Lesson 7 The Injection-molding Machine

New words and expressions:

1. compound  vt.混合，复合n.化合物，混合物	2. powder  n. 粉末，粉剂；v.磨成粉，粉化
3. granular  a. 粒状的	4. hopper  n. 漏斗，给料斗
5. metering  n. 测量，计量，记录，统计	6. reciprocate  v. 使机件往复运动，互换
7. barrel  n.圆筒，桶，圆柱体；vt.把…装桶	8. polymerize  v. 使聚合
9. sketch  n.草图，设计图；v. 画草图，草拟	10. squirt  v.喷湿，喷出；n. 喷射器
11. cram  n.填塞，压碎；vt. 塞入，塞满	12. withdraw  v. 撤回，缩回，拉开
13. spurt  v. n. 喷出，迸出	14. trip  n.往返，行程，脱开，切断；v. 解扣
15. activate  vt. 使活动，开动，对…起作用	16. optimum  a. 最佳条件，最佳状况，最佳值
17.foam  vt. 泡沫，泡沫材料；v.（使）起泡沫	18. (be) based on  以…作为…的根据
19. (be) capable of  能…的，易…的

Text:

The greatest quantity of plastic parts are made by injection molding. The process consists of feeding a plastic compound in powdered or granular form from a hopper through metering and melting stages and then injecting it into a mold①. After a brief cooling period, the mold is opened and the solidified part ejected. In most cases, it is ready for immediate use.

Several methods are used to force or inject the melted plastic into the mold. The most commonly used system in the larger machines is the in-line reciprocating screw, as shown in Figure 7-1.

The screw acts as a combination injection and plasticizing unit. As the plastic is fed to the rotating screw, it passes through three zones as shown: feed, compression, and metering. After the feed zone, the screw-flight depth is gradually reduced, forcing the plastic to compress. The work is converted to heat by shearing the plastic, making it a semifluid mass. In the metering zone, additional heat is applied by conduction from the barrel surface. As the chamber in front of the screw becomes filled, it forces the screw back, tripping a limit switch that activates a hydraulic cylinder that forces the screw forward and injects the fluid plastic into the closed mold②. An antiflowback valve prevents plastic under pressure from escaping back into the screw flights.

The clamping force that a machine is capable of exerting is part of the size designation and is measured in tons. A rule-of-thumb can be used to determine the tonnage required for a particular job. It is based on two tons of clamp force per square inch of projected area. If the flow pattern is difficult and the parts are thin, this may have to go to three or four tons.

Many reciprocating-screw machines are capable of handing thermosetting plastic materials. Previously these materials were handled by compression or transfer molding. Thermosetting materials cure or polymerize in the mold and are ejected hot in the range of 375℃～410℃. Thermoplastic parts must be allowed to cool in the mold in order to remove them without distortion. Thus thermosetting cycles can be faster. Of course the mold must be heated rather than chilled, as with thermoplastics.

 

Figure 7-1 (a) The injection-molding machine  (b) The reciprocating-screw injection system

Ways of injection molding plastic material are sketched in Figure 7-2. The oldest is the single-stage plunger method. When the plunger is drawn back, raw material falls from the hopper into the chamber. The plunger is driven forward to force the material through the heating cylinder where it is softened and squirted under pressure into the mold. The single-stage reciprocating screw system has become more popular because it prepares the material more thoroughly for the mold and is generally faster. As the screw turns, it is pushed backward and crams the charge from the hopper into the heating cylinder. When enough material has been prepared, the screw stops turning and is driven forward as a plunger to ram the charge into the dir. In a two-stage system, the material is plasticized in one cylinder, and a definite amount transferred by a plunger or screw into a shot chamber from which a plunger injects it into the mold.

An injection molding machine heats to soften, molds, and cools to harden a thermoplastic material. Operating-temperature is generally between 150°C and 380°C (300°F and 700°F) with full pressure usually over 35 and up to 350 MPa (5000 to 50000 psi). The mold is water cooled. The molded piece and sprue are withdrawn from the injection side and ejected from the other side when the mold is opened. The mold is then closed and clamped to start another cycle. Thermosetting plastics can be injection molded but have to be polymerized and molded before they set in the machine. This may be done in a reciprocating screw machine where one charge at a time is brought to curing temperature. By another method, sometimes called jet molding, performs are charged one at a time into a single-stage plunger machine.

Machines are available for molding sandwich parts. One cylinder and plunger injects a measured amount of skin material into the die, and then a second cylinder squirts the filler inside the mass. Finally, a final spurt from the first cylinder clears the core material from the sprue. The aim is to produce composites with optimum properties. Either case or core may be foamed.

Notes

[1]     The process consists of feeding a plastic compound in powdered or granular form from a hopper through metering and melting stages and then injecting it into a mold.注塑成型的工艺过程包括：首先把料斗中的粉状或粒状的塑料混合物依次输送到定量区和熔化区，然后再注射到模具型腔中。句中consist of 意为：由……组成，由and连接的三个动名词短语作of的宾语。

[2]     As the chamber in front of the screw becomes filled, it forces the screw back, tripping a limit switch that activates a hydraulic cylinder that forces the screw forward and injects the fluid plastic into the closed mold.当熔体充满螺杆前部区域时，螺杆在熔体压力的作用下后退，触动限位开关使液压缸工作，在液压力的作用下推动螺杆向前运动，将熔融塑料注射到闭合的模具型腔中。句中as引导的时间状语从句，that activates a hydraulic cylinder that forces the screw forward and injects the fluid plastic into the closed mold为限制性定语从句修饰a limit switch，that forces the screw forward and injects the fluid plastic into the closed mold修饰a hydraulic cylinder。

Practice:

Translate one paragraph of the reading materials on page 40-43.

Homework:

Answer the questions on page 38.

 Lesson 8 Blanking Technique

New words and expressions:

1. terminology  n. 术语；专门名词	2. frequent  a. 频繁的；屡次的；vt.常去，常到
3. encounter  vt. 遭遇，碰见；vi.偶遇；n. 遭遇	4. stress  n. 压力，紧迫，应力；vt.受应力
5. fracture  a.vt. 断口，断面，断裂	6. beyond  prep. 在…那边，远于，迟于
7. stretch  n.;vi.;n.伸展，展开，加宽	8. emboss  vt. 拷花，压纹；在…上浮雕图案
9. correspond  vi. 相当，对应，符合	10. penetration  n. 渗透，穿透，穿透能力
11. edge  n. 刃，刀口，边缘; vi.使锐利	12. clearance  n. 清除，消除
13. eventual  a. 最后的，结局的，万一的	14. separation  n. 分离，分类，间隔
15. stock  n. 树干，托柄，台，座	16. contour  n. 轮廓，外型
17. summation  n. 总结，总和	18. undesirable  a. 不希望的，不合乎需要的
19. deflection  n. 偏转，偏移，偏差	20. misalignment  n. 未对准
21. symmetrical  a. 对称的	22. perimeter  n. 圆周，周长
23. gravity  n. 重力，严重性	24. axis  n. 轴，轴线
25. mate  n. 同事，联接	26. appearance  n.出现，显露，外表
27. optimum  n.最佳条件	28. schematic  a. 图解的，纲要的
29. respective  a.各自的，各个的	30. pronounced  a.显著的，明确的
31. burr  n.毛刺，毛边	32. formula  n.公式，准则，方案
33. pad  n.衬垫，衬套，垫片	34. ultimate strength 极限强度
35. (be) subjected to 使受到，使遭遇	36. tensile and compressive stresses 拉和压应力
37. elastic limit 弹性极限	38. plastic deformation 塑性变形
39. cross-sectional area 横截面积	40. in many cases 在许多方面
41. spring-loaded stripper   弹簧加载卸料板

Text:

Cutting (shearing ) operations

In the following discussion, certain die terminology will be used frequently, Figure 8-1 presents the terms most commonly encountered.

Shear Action in Die Cutting Operations

The cutting of metal between die components is a shearing process in which the metal is stressed in shear between two cutting edges to the point of fracture, or beyond its ultimate strength.

The metal is subjected to both tensile and compressive stresses (Figure 8-2); stretching beyond the elastic limit occurs, then plastic deformation, reduction in area, and finally, fracturing starts through cleavage planes in the reduced area and becomes complete.

The fundamental steps in shearing or cutting are shown in Figure 8-3. The pressure applied by the punch on the metal tends to deform it into the die opening. When the elastic limit is exceeded by further loading, a portion of the metal will be forced into the die opening in the form of an embossed pad on the lower face of the material. A corresponding depression results on the upper face, as indicted at Figure 8-3a. As the load is further increased, the punch will penetrate the metal to a certain depth and force an equal portion of metal thickness into the die , as indicated at Figure 8-3b. This penetration occurs before fracturing starts and reduces the cross-sectional area of metal through which the cut is being made. Fracture will start in the reduced area at both upper and lower cutting edges, as indicated at Figure 8-3c. If the clearance is suitable for the material being cut, these fractures will spread toward each other and eventually meet, causing complete separation①. Further travel of the punch will carry the cut portion through the stock and into the die opening.

Center of Pressure

If the contour to be blanked is irregularly shaped, the summation of shearing forces on one side of the center of the ram may greatly exceed the forces on the other side. Such irregularity results in a bending moment in the press ram, and undesirable deflections and misalignment. It is therefore necessary to find a point about which the summation of shearing forces will be symmetrical. This point is called the center of pressure, and is the center of gravity of the line that is the perimeter of the blank. It is not the center of gravity of the area.

The press tool will be designed so that the center of pressure will be on the axis of the press ram when the tool is mounted in the press.

Clearances

Clearance is the space between the mating members of a die set. Proper Clearances between cutting edges enable the fractures to meet. The fractured portion of the sheared edge will have a clean appearance. For optimum finish of a cut edge, proper clearance is necessary and is a function of the type, thickness, and temper of the work material. Clearance, penetration, and fracture are shown schematically in Figure 8-4. In Figure 8-5, characteristics of the cut edge on stock and blank, with normal clearance, are shown schematically. The upper corner of the cut edge of the stock and the lower corner of the blank will have a radius where the punch and die edges, respectively, make contact with the material. This radiusing is due to the plastic deformation taking place, and will be more pronounced when cutting soft metals②. Excessive clearance will cause a large radius at these corners, as well as a burr on opposite corners.

Cutting Forces

The force required to cut the work material can be calculated by using the following formulas:

   (for contours)

   (for round holes)

Stripping Forces

The force required to strip the work material off punches can be calculated by using the following formulas:

        (for contours)

        (for round holes)

P—Cutting force in pounds;

TN—Cutting force in tons;

Ps—Stripping force in pounds;

TNS—Stripping force in tons;

S—Shear strength in pounds per square inch;

L—Length of cut in inches;

T—Thickness of material in inches;

D—Diameter in inches.

Press Tonnage

This is a total of forces required to cut and form the part with a 30% safety factor added. In many cases, you will have to add stripping force if stripping is being done with a spring-loaded stripper, because the press has to compress the springs while cutting the material. Likewise, any spring pressure for forming, draw pads, and the like, will have to be added.

The force needed to punch a 2″(50.8mm) dia, hole in 1/8″(3.18mm) thick SAE1020 steel having a shear strength of 60000psi (413.7N/mm2).

Notes:

[1]     If the clearance is suitable for the material being cut, these fractures will spread toward each other and eventually meet, causing complete separation. 对于所需要剪切的材料，若间隙适当时，这些断口将相互扩展最终相遇，从而引起材料完全分离。原文主句中有两个谓语动词，一个是spread，另一个是meet，它们共用一个主语，即these fractures。分词短语causing complete separation用作状语，表示结果，汉译为“从而使材料完全分离”。注意：在科技文章中，分词短语作状语时，一般都用“，”把它与句子的其它部分分开。

[2]     This radiusing is due to the plastic deformation taking place, and will be more pronounced when cutting soft metals. 这个圆角半径是由于材料发生塑性变形而引起的，并且在总裁比较软的金属材料时圆角半径就会更明显。句中的duo to意为“由于…原因”，分词短语taking place是deformation的后置定语。

Practice:

Translate one paragraph of the reading materials on page 49-53.

Homework:

Answer the questions on page 47.

 

 

 

Lesson 9 Piercing and Blanking Die Design

New words and expressions:

1. stroke  n. 打，冲程	2. actuate  v. 开动，激励，驱使
3. terminology  n. 术语，专门名词	4. pin  n. 针，钉，栓，销
5. post  n. 拄，杆	6. bush  n. 衬套，轴瓦
7. assembly  n. 集合，装配	8. commercial  a. 工业用的，工厂的
9. available  a. 可用的，有效的	10. cling  v. 粘住，依附
11. clarity  n. 透明	12. insert  v. 插入；n.金属型芯
13. sleeve  n. 套筒	14. encircle  v. 包围，环绕
15. incorporate  v. 结合，合并	16. nest  n. 定位孔，窝，巢
17. invert  v. 倒置，相反	18. secure  a. 安全的，牢固的
19. bolster  n. 垫枕，支撑	20. necessitate  v. 需要
21. draft  n. 草稿，草图	22. intricate  a. 错综的，复杂的
23. rod  n. 棒，杆，连杆，拉杆	24. collar  n. 领，垫圈，法兰盘
25. slug  n. 弹丸，金属小块，嵌条，冷料	26. disposal  n.配置，安排
27. shedder  n.卸件装置，推料机	28. dowel  n.木钉，安装销钉
29. a single-station piercing die	30. guide pins 导向销
31. lower shoe; upper shoe 下模座，上模座	32. spring-loaded strippers 弹簧加载卸料板
33. instead of 代替，而不	34. inverted blanking die  倒置落料模
35. knockout bar 打料杆

Text:

A complete press tool for cutting two holds in work material at one stroke of the press, as classified and standardized by a large manufacturer as a single-station piercing die is shown in Figure 9-1.

Any complete press tool, consisting of a pair (or a combination of pairs) of mating members for producing pressworked parts, including all supporting and actuating elements of the tool, is a die. Pressworking terminology commonly defines the female part of any complete press tool as a die.

The guide pins, or posts, are mounted in the lower shoe. The upper shoe contains bushings which slide on the guide pins. The assembly of the lower and upper shoes with guide pins and bushings is a die set. Die sets in many sizes and designs are commercially available. The guide pins shown in Figures 9-2 and 9-3 guide the stripper in its vertical travel. For clarity, the guide pins are not shown in Figure 9-3.

A punch holder mounted to the upper shoe holds two round punches (male members of the die) which are guided by bushings inserted n the stripper①. A sleeve, or quill, encloses one punch to prevent its buckling under pressure from the ram of the press. After penetration of the work material, the two punches enter the die bushings for a slight distance.

The female member, or die, consists of two die bushings inserted in the die block. Since this press tool punches holes to the diameters required , the diameters of the die bushings are larger than those of the punches by the amount of clearance.

Since the work material stock or workpiece can cling to a punch on the upstroke, it may be necessary to strip the material from the punch. Spring-loaded strippers hold the work material against the die block until the punches are withdrawn from the punched holes. A workpiece to be pierced is commonly held and located in a nest composed of flat plates shaped to encircle the outside part contours. Stock is positioned in dies by pins, blocks, or other types of stops for locating before the downstroke of the ram.

Blanking Die Design

The design of a small blanking die shown in Figure 9-2 is the same as that of the piercing die of Figure 9-1 except that a die replaces the die bushings and the two piercing punches are replaced by one blanking punch. A stock stop is incorporated instead of nest plates. This is a drop-through design since the finished blanks drop through the die, the lower shoe, and the press bolster.

Large blanks are commonly produced by an inverted blanking die in which the die is mounted to the upper shoe with the punch secured to the bottom shoe. The passing of a large blank through the bolster is often impractical passing of a large blank through the bolster is often impractical but its size may necessitate sectional die design.

Draft, or angular clearance in an inverted die is unnecessary because the blank does not pass through it. For ease of construction, regrinding, and strength the cutting edges of each section should not include points and intricate contours. Sections 1 and 2 of the die of Figure 9-4 were laid out to include the entire semicirculare contour, with straight contours included in the other six sections.

The spring –loaded stripper is mounted on the lower shoe; it travels upward in stripping the stock from the punch fastened to the lower shoe. Stripper bolts hold and guide the stripper in its travel.

On the upstroke of the ram, the upper end of the knockout rod strikes an arm on the press frame, which forces the lower end of the rod downward, through the die, and ejects the finished blank from the die cavity. A stop collar retains the rods and limits their travel.

Compound Die Design

A compound die performs only cutting operations (usually blanking and piercing) which are completed during a single press stroke. A characteristic of compound dies is the inverted position of the blanking die and blanking punch which also functions as the piercing die. As shown in Figure 9-5, the die is fastened to the upper shoe and the blanking punch having a tapered hole in it and in the lower shoe for slug disposal is mounted on the lower shoe.

On the upstroke of the press slide, the knock out rod of the press strikes the ejector plate, forcing the ejector tie rod and shedder downward, thus pushing the finished work piece out of the blanking die②.

Four special shoulder screws (stripper bolts), commercially available, guide the stripper in its travel and retain it against the preload of its springs.

The blanking die as well as the punch pad is screwed and doweled to the upper shoe.

A spring-loaded shedder pin incorporated in the shedder is depressed when the shedder pushes the blanked part from the die. On this upstroke of the ram the shedder pin breaks the oil seal between the surface of the blanked part and shedder, allowing the part to fall out of the blanking die.

Figure 9-5  A blanking and piercing compound die

Notes:

[1]     A punch holder mounted to the upper shoe holds two round punches (male members of the die) which are guided by bushings inserted n the stripper.安装在上模座上的凸模固定装置固定两个圆形凸模（模具中的突出部分），这两个圆形凸模通过插入在卸料板上的模套进行导向。句中分词短语mounted to the upper shoe作后置定语，它修饰的是主语a punch holder，这里mount意为“安装”；另一个分词短语inserted in the stripper也是作后置定语，它修饰的是bushings, insert意为“插入”；由which引导出的定语从句修饰two round punches。

[2]     On the upstroke of the press slide, the knock out rod of the press strikes the ejector plate, forcing the ejector tie rod and shedder downward, thus pushing the finished work piece out of the blanking die.在压力机滑块的上行程中，压力机的打料杆碰到打料环，作用在打料杆上的力使卸料装置下移，这样就会将成品件从落料凹模中推出。句中的forcing the knockout rods and shedder downward和pushing the finished workpiece out of the blanking die均为分词短语作状语的情况，它们均用“，”与句子其它部分分开。

Practice:

Translate one paragraph of the reading materials on page 59-64.

Homework:

Answer the questions on page 57.

 

 

Lesson 10 Bending Dies

New words and expressions:

1. strain  vt. 拉紧，伸张	2. lie  v.保持…状态，位于
3. neutral  a. 中立的，中性的	4. lengthwise  ad. 纵长的
5. inner  a. 内部的	6. illustrate  vt. 图解，插图
7. crack  vt. 弄裂，敲碎	8. wedge  a. 楔块
9. obtuse  a.钝角的	10. acute  a. 锐角的
11. knurl  n. 节，压纹	12. vee  n. V字型物
13. creep  vi. 爬，蔓延	14. cantilever  n. 悬臂，交叉支架
15. clamp  n. 夹钳	16. contact  n. 接触，联系
17. metric  a. 公制的	18. release  n. 释放装置，排气装置
19. portion  n. 部分	20. customarily  ad. 照例，习惯上
21. relieve  vt. 援救，减轻，缓和，解除	22. friction  n. 摩擦
23. flat sheet or strip metal n. 平钢板或金属带材	24. lie in  n. 在于
25. neutral plane  n. 中性面	26. take place 发生
27. inner surface 内表面	28. outer surface 外表面
29. ultimate tensile strength 极限抗拉强度	30. elastic stress 弹性应力
31. spring-back angle 回弹角

Text:

Bending is the uniform straining of material, usually flat sheet or strip metal, around a straight axis which lies in the neutral plane and normal to the lengthwise direction of the sheet or strip. Metal flow takes place within the plastic range of the metal, so that the bend retains a permanent set after removal of the applied stress①. The inner surface of a bend is in compression; the outer surface is in tension. A pure bending action does not reproduce the exact shape of the punch and die in the metal; such a reproduction is one of forming. The neutral axis is the plane area in bent metal where all strains are zero.

Bend Radii. Minimum bend radii vary for different metals; generally, different annealed metals can be bent to a radius equal to the thickness of the metal without cracking or weakening.

Bend Allowances. Since bent metal is longer after bending, its increased length, generally of concern to the product designer, may also have to be considered by the die designer if the length tolerance of the bent part is critical. The length of bent metal may be calculated from the equation:

Where  B—bend allowance, in (mm) (along neutral axis);

       A—bend angle, deg;

       Ri—inside radius of bend, in (mm);

       t—metal thickness, in (mm);

       K—0.33 when Ri is less than 2t and is 0.50 when Ri is more than 2t.

Bending Methods. Two bending methods are commonly made use of in press tools. Metal sheet or strip, supported by a V block, is forced by a wedge-shaped punched into the block. This method, termed V bending, produces a bend having an included angle which may be acute, obtuse, or of 90°C. Friction between a spring- loaded knurled pin in the vee of a die and the part will prevent or reduce side creep of the part during its bending②.

Edge bending is cantilever loading of a beam. The bending punch 1 forces the metal against the supporting die 2. The bend axis is parallel to the edge of the die. The workpiece is clamped to the die block by a spring-loaded pad 3 before the punch contacts the workpiece to prevent its movement during downward travel of the punch.

Bending Force. The force required for V bending is as follows:

Where  P—bending force, tons (for metric usage, multiply number of tons by 8.896 to obtain kilonewtons);

K—die opening factor:1.20 for a die opening of 16 times metal thickness, 1.33 for an opening of eight times metal thickness;

L—length of part, in;

W—width of V or U die,in;

t—metal thickness,in;

For U bending pressures will be approximately twice those required for V bending; edge bending requires about one-half those needed for V bending.

Springback. After bending pressure on metal is released, the elastic stresses also are released, which causes metal movement resulting in a decrease in the bend angle(as well as an increase in the included angel between the bent portions)③. Such a metal movement, termed springback, vairies in steel from 0.5°to 5°, depending upon its hardness, phosphor bronze may spring back from 10°to 15°.

V-bending dies customarily compensate for springback with V blocks and wedge-shaped punches having included angle somewhat less than that required in the part. The part is bent through a greater angle than that required but it springs back to the desired angle.

Parts produced in other types of bending dies are also overbent through an angle equal to the spring-back angel with an undercut or relieved punch.

Notes:

[1]     Metal flow takes place within the plastic range of the metal, so that the bend retains a permanent set after removal of the applied stress. 由于弯曲金属的流动是发生在金属的塑性变形范围内，因此当所施加的外力去除后将会保留一个永久性的弯曲变形。句中的介词短语within the plastic range of the metal意为在金属的塑性变形范围内；so that引导出的是一个状语从句，它表示结果；单个分词applied作stress的定语，意为“外加的”。

[2]     Friction between a spring- loaded knurled pin in the vee of a die and the part will prevent or reduce side creep of the part during its bending. 在V字形模具内，弹簧加载压销和零件之间的摩擦将会防止或减小零件期间的边缘位移。Between的一般用法为between A and B,本句中between后面的两个关键词为：一个是pin，另一个是part；在pin前有两个分词，一个是spring-loaded，另一个是knurled，二者都是pin的前置定语。

[3]     After bending pressure on metal is released, the elastic stresses also are released, which causes metal movement resulting in a decrease in the bend angle(as well as an increase in the included angel between the bent portions).当作用在金属上的弯曲力去除后，弹性应力也就随即消失，这样引起金属的移动，从而导致弯曲角的减小（也即弯曲部件间的包角增大）。句子中由which引导的从句是一个非限定性定语从句，它对整个主句the elastic stresses also are released作进一步说明，其中关系代词which在定语从句中作主语，由于which代替了整个主句，所以从句的谓语用causes这一形式。句中有一分词短语resulting in a decrease in the bend angled在定语从句中作状语，表示结果，可译为“从而导致弯曲角的减小”。

Practice:

Translate one paragraph of the reading materials on page 69-71.

Homework:

Answer the questions on page 66.