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(圖6.1)是將熱塑性塑料制成最終形狀的主要工藝，并且越來越多地用于熱硬化性塑料、纖維填充合成物和人造橡膠。

???????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.

???????它是重量范圍為5g到85kg極大一類零件可選用的工藝。估計(jì)所有熱塑性塑料中有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.

???????如果考慮到新近的改進(jìn)(例如反作用注塑成型)和采用塑料替代金屬的高增長率，注塑成型在世界范圍的工業(yè)重要性很可能將繼續(xù)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.

當(dāng)前，大概所有主要處理設(shè)備的近一半是注塑成型機(jī)。1988年，美國新的注塑成型機(jī)械銷售約占全部主要聚合物機(jī)械銷售量的65%，其中包括4,600臺注塑成型設(shè)備。

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

這類機(jī)械和它們的產(chǎn)品普遍存在，對許多人來說與塑料是同義的。

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

???????往復(fù)螺旋注射成型機(jī)把壓出機(jī)和成型壓力機(jī)的功能結(jié)合起來。

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.

把熱塑性塑料樹脂的固體顆粒在壓出部分融化并增壓，迫使其高速融化并通過仔細(xì)設(shè)計(jì)的流動通道進(jìn)入冷卻模具，噴射成最終零件，然后自動再循環(huán)。

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.

這種機(jī)械是1872年Hyatt兄弟獲得專利權(quán)的融化賽璐珞的活塞型“填充機(jī)”的派生物。?1878年Hyatt兄弟開發(fā)了第一個(gè)多槽模具，但直到1938年Quillery(法國)才發(fā)明了用螺旋增塑人造橡膠并使其成型的一體化機(jī)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使用于熱塑性塑料的現(xiàn)代往復(fù)螺旋注塑成型機(jī)商業(yè)化。今天，已有超過50家制造商列入現(xiàn)代塑料制品百科全書，能為美國市場提供壓制能力從2到6,000噸的機(jī)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.

(一臺能力為10,000噸用于成型264加侖高密度聚乙烯垃圾箱的機(jī)械也已制成)。許多輔助設(shè)備、模具、儀器和控制系統(tǒng)供應(yīng)商在為聚合物工業(yè)的這一主要部分服務(wù)。

???????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.

???????注塑成型對深入研究很有價(jià)值，因?yàn)樗Y(jié)合了許多重要領(lǐng)域，如擠壓、模具設(shè)計(jì)、流變學(xué)、完備的液壓和電子控制、機(jī)器人配件、復(fù)雜產(chǎn)品的設(shè)計(jì)，當(dāng)然還有材料科學(xué)與加工工程的綜合。

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.

注塑成型工程師的目標(biāo)很簡單：在最少廢料的情況下取得最小循環(huán)時(shí)間，在有保證的情況下獲得指定產(chǎn)品性能，將由停工或其它原因產(chǎn)生的生產(chǎn)成本最小化，還有穩(wěn)定地增加專門知識和競爭力。

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.

傳統(tǒng)的注塑成型機(jī)利潤盈余據(jù)說一般是不足的；為了更多需求及更高盈余工作需要選擇一種改善利潤的確定方法，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.

???????本文將集中論述熱塑性塑料用的往復(fù)螺旋機(jī)，除了小容量機(jī)械外它已在很大程度上取代了較老的往復(fù)活塞式機(jī)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。像聚四氟乙烯之類的聚合物就不能自由流動得足以適合注塑成型。

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，例如樹脂和編織的或墊子形的玻璃纖維的混合物，由于它們的物理性質(zhì)不適合使用此工藝。一般而言，能進(jìn)入流動狀態(tài)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.

???????注塑成型的絕大多數(shù)都用于熱塑性聚合物。這類材料由具有加熱軟化、冷卻硬化甚至可重復(fù)循環(huán)能力的聚合物組成。

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.

這是由于這類材料的長鏈分子總是保持分離的實(shí)體并不相互形成化學(xué)連結(jié)。一輛由冰塊制成的模擬汽車，可以融化(即轉(zhuǎn)化為液態(tài))，倒入任何形狀的空腔，然后冷卻重新變成固體。

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.

這個(gè)特性將熱塑性材料與熱硬化性材料區(qū)分開。后者在加工過程中分離的分子鏈之間形成化學(xué)連結(jié)。在此情況下作為交聯(lián)的化學(xué)連結(jié)是硬化機(jī)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，大多數(shù)熱塑性材料具有較高的抗沖擊強(qiáng)度、耐腐蝕性以及良好流動性使其容易加工而適于復(fù)雜成型設(shè)計(jì)。熱塑性塑料通常分為兩類：即結(jié)晶質(zhì)的和非結(jié)晶質(zhì)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.

結(jié)晶質(zhì)聚合物具有規(guī)則的分子排列及明顯的熔點(diǎn)。由于規(guī)則的分子排列，結(jié)晶質(zhì)聚合物能反射大多數(shù)特定光線并一般表現(xiàn)為不透明的。

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.

它們在固化過程中收縮較大或體積減少較多。結(jié)晶質(zhì)聚合物通常多能抵御有機(jī)溶劑并具有良好的抗疲勞和磨損特性。結(jié)晶質(zhì)聚合物通常也比非結(jié)晶質(zhì)聚合物更致密并且具有更好的機(jī)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，它是可選用做高質(zhì)量透明注塑件的非結(jié)晶質(zhì)聚合物，并具有卓越的機(jī)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.

???????就本質(zhì)而言，熱塑性塑料的機(jī)械性能低于金屬，但可以通過加入玻璃纖維強(qiáng)化予以增強(qiáng)來適應(yīng)某些運(yùn)用。常用幾毫米長的短碎纖維隨機(jī)地與熱塑性樹脂混合。

??????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.

???????纖維可占材料體積的三分之一以極大改善材料的強(qiáng)度和硬度。這種加強(qiáng)的負(fù)作用通常是抗沖擊強(qiáng)度降低及磨損性增加。

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.

后者對加工過程也有影響，因?yàn)槟＞咔坏膲勖鼜牡湫偷钠胀渲慵蠹s1,000,000件減少到玻璃纖維填充樹脂零件的約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點(diǎn)或許是它們能承受的工作溫度相對較低。熱塑性塑料零件只有很少能連續(xù)運(yùn)行在250℃以上，其絕對最高工作溫度約為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.

熱塑性塑料帶載運(yùn)行溫度可從質(zhì)量上定義為熱偏差溫度。這是中心承載的該材料簡支梁達(dá)到預(yù)定偏差的溫度。

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.

其溫度值明顯取決于試驗(yàn)條件和允許偏差，因此對比較不同的聚合物而言只有試驗(yàn)數(shù)據(jù)是真正有用的。

Cycle of Operation
作業(yè)循環(huán)

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

???????往復(fù)螺旋注塑成型機(jī)被認(rèn)為由兩部分組成：一個(gè)固定注塑端和一個(gè)活動夾具端。

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.

注塑端包含壓出機(jī)，它接受小球或粒狀的固體樹脂，然后將其轉(zhuǎn)化為粘性液體或稱為融化，再強(qiáng)迫其通過連接噴嘴、中心和澆道到閘道進(jìn)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.

模具被緊緊地夾住以抵抗注塑壓力，并在熱塑性塑料的融化溫度以下很好地冷卻。當(dāng)模腔內(nèi)的零件充分冷卻，剖分模在模具分模面處打開，推出系統(tǒng)將零件推出落入下面的接收容器內(nèi)。

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.

這概述了整個(gè)循環(huán)，但省略了許多對理解此工藝所必需的很重要細(xì)節(jié)。然而通過本介紹，了解這種工藝的優(yōu)缺點(diǎn)仍是可能的。

Effects of Process Variables on Orientation ????
加工變量對方向性的影響

??????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.

???????在注塑成型時(shí)，整個(gè)填料過程始終保持成型樹脂高溫的任何加工變化都會增加松弛作用而減少方向性。下面是可以用于減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.

??較快注塑(到點(diǎn))：在填料過程中冷卻較少，因此初始固化層較薄，由于剪應(yīng)變稀少而粘性較低；能較好地流到角落；結(jié)晶度較?。凰羞@些促成表面下的方向性也較低。主要效果是閘道將較快固化。這樣使得方向性停止產(chǎn)生而松弛作用開始增加。

??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.

??較高的融化和成型溫度：融化粘性較低，更容易填充，較大松弛作用促成方向性減少。

??減少擠壓時(shí)間和壓力：過度擠壓會抑制松弛過程。

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

??減小閘道尺寸：閘道越大則固化時(shí)間越長并會使方向性增加。

???????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.

???????過高的注塑速度會引起較高的表面方向性及增加應(yīng)力破裂的敏感性。例如，要電鍍的注塑件在電鍍時(shí)會經(jīng)受酸溶液，必須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，大多數(shù)注塑件的融化前部橫向運(yùn)動部分能導(dǎo)致在主要方向性上有層理的表面下橫向方向性，產(chǎn)生需要的雙軸方向性效應(yīng)。

??????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.

???????在填充模腔時(shí)流動受到阻礙會極大地增加方向性。圍繞障礙物流動使融化前部的速度下降并產(chǎn)生較高的局部粘性而減少松弛作用。如果閘道不適當(dāng)，這也很可能發(fā)生在接近填充結(jié)束階段。

??????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.

???????注塑工必須認(rèn)識過快填充速度、不足注塑壓力、過高融化溫度和不充分?jǐn)D壓的危害性。這些危害性要與上述方向性的反向效應(yīng)相權(quán)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.

較厚零件會延遲冷卻并且增加松弛時(shí)間，趨向于導(dǎo)致較低的方向性。較厚零件也有助于減少翹曲。因此，對各種形狀、材料和工藝組合能通過經(jīng)驗(yàn)來確定最小壁厚。

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

在熱塑性塑料中較小的分子量以及較寬泛的分子量分布促成方向性減少同時(shí)降低注塑件中的內(nèi)應(yīng)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.

???????外殼厚度比受加工變量影響的方式與方向性預(yù)測一樣；也就是它能隨融化或成型溫度及模腔壓力的增加而減少。拉伸強(qiáng)度和硬度隨外殼厚度比增加而增加。因而顯微鏡檢查提供了有效研究該工藝的另一方法。

??Advantages ?優(yōu)點(diǎn)

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

??????1. 高生產(chǎn)率：例如，一張CD盤在高融體流動指數(shù)生產(chǎn)控制中只需10~12s一個(gè)循環(huán)就能生產(chǎn)出來。

???????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. 相對較少的工作內(nèi)容：一個(gè)操作者經(jīng)?？梢哉湛磧膳_以上機(jī)械，尤其是當(dāng)成品能自動卸到輸送機(jī)上時(shí)。

???????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. 零件幾乎不需要修整：例如，飛邊可以最小化并且模具能被設(shè)計(jì)成自動將澆道和閘道從零件本身分離。

???????4. 非常復(fù)雜的形狀也能成型：模具的進(jìn)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. 設(shè)計(jì)的靈活性(光潔度、顏色、插入物、材料)：通過復(fù)合注塑可以成型多于一種材料?？梢愿咝У厣a(chǎn)帶有固體外殼的泡沫型芯材料。熱硬化性塑料和纖維加強(qiáng)形狀都可以注塑成型。

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

???????6. 廢料損失最小化：澆道、閘道和廢料通?？梢灾匦卵心ァＱh(huán)熱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：現(xiàn)代微處理器控制、合適的精密模具和精心制作的液壓設(shè)備使得尺寸和重量的公差保持在0.1% 的范圍內(nèi)(但不是沒有在持續(xù)照看時(shí)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. 充分利用聚合物諸如流動能力、重量輕、透明和耐腐蝕等獨(dú)特屬性：從日常使用成型塑料產(chǎn)品的數(shù)量和種類就能明顯看到。

Disadvantages and Problems
缺點(diǎn)和問題

??????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. 較高的設(shè)備和模具投資需要較高生產(chǎn)量才合算。

??????2. 缺少專門技術(shù)和良好的預(yù)防性維修會導(dǎo)致較高的啟動和運(yùn)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. 質(zhì)量有時(shí)難以馬上確定。例如，成型后的翹曲會導(dǎo)致零件不能用，因?yàn)樵诔尚秃髱仔瞧谏踔翈讉€(gè)月尺寸變化都不能完成。

???????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. 對許多需要廣泛多樣性技能和交叉學(xué)科知識的細(xì)節(jié)必須加以注意。

???????5. 零件設(shè)計(jì)有時(shí)不能很好地適應(yīng)有效率的成型。

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

???????6. 模具設(shè)計(jì)、模具制造和調(diào)試試驗(yàn)這些先導(dǎo)工作有時(shí)要花費(fèi)很長時(shí)間。

?

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Unit 7 metals cutting

金屬切削

???????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.

???????機(jī)加工過程的重要性可通過日常生活使用的每件產(chǎn)品都直接或間接經(jīng)歷這一過程的事實(shí)來強(qiáng)調(diào)。

??????(1)在美國，每年花在機(jī)加工及其相關(guān)作業(yè)上的費(fèi)用都多于千億美元。

???????(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) 用于制造業(yè)的全部機(jī)床中的大多數(shù)(多于80%)都經(jīng)歷過金屬切削。

???????(3) 有估計(jì)顯示美國生產(chǎn)的所有金屬中約10到15%轉(zhuǎn)變成了切屑。?

??????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.

???????這些事實(shí)說明了金屬切削在常規(guī)制造中的重要性。因此了解金屬切削過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.

在了解金屬切削過程并運(yùn)用這些知識幫助改善與金屬切削有關(guān)的制造作業(yè)方面已經(jīng)做了許多努力。

????????A typical cutting tool in simplified form is shown in Fig.7.1. The important features to be observed are follows.

???????典型切削刀具的簡化形式如圖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：它是被稱為前傾面的刀具面與垂直機(jī)加工方向的夾角。前角越大，則切削越好且切削力越小，增加前角可以減少刀具前傾面上產(chǎn)生的金屬阻塞。

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.

但這會和減少通過刀具散發(fā)的熱量一樣減少刀尖強(qiáng)度。因此前角有一最大限制，用高速鋼刀具切削低碳鋼通常為15°。前角取零度或負(fù)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：這是機(jī)加工面與被稱為后側(cè)面的刀具底面夾角。后角使刀具不產(chǎn)生會損壞機(jī)加工面的摩擦和增加切削力。很大的后角會削弱刀尖的強(qiáng)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.

???????對金屬切削有重要影響的條件有工件材料、刀具材料、刀具幾何形狀、切削速度、進(jìn)給率、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指切削刀具經(jīng)過工件材料的移動速度。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.

???????進(jìn)給率f可定義為每循環(huán)(每轉(zhuǎn)或每行程)切削刀具在通常為垂直于切削速度方向的次要相對運(yùn)動。

???????切削深度d是未加工面與已加工面之間的垂直距離。

??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.

???????金屬切削過程是一個(gè)很復(fù)雜的過程。圖7.2用圖的形式顯示了基本材料去除作業(yè)。

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.

在刀具前傾面前的金屬直接受到壓縮，首先彈性變形然后塑性變形?？紤]到最終形狀中的材料是通過剪切從母體金屬去除的，此區(qū)域傳統(tǒng)上稱為剪切區(qū)。

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.

金屬的實(shí)際分離始于屈服或斷裂(視切削條件而定)，從切削刀尖開始。然后變形金屬(稱為切屑)流過刀具(前傾)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.

如果刀具前傾面與切屑(變形金屬)底面之間的摩擦相當(dāng)大，那么切屑進(jìn)一步變形，這也叫做二次變形?；^刀具前傾面的切屑被提升離開刀具，切屑彎曲的結(jié)果被稱為切屑卷。

??????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.

???????屈服能導(dǎo)致塑性變形，在這種情況下材料變形層沿著與最大剪應(yīng)力方向一致的滑移面被其它層所取代。

???????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.

???????在實(shí)際加工過程中切屑的尺寸和形狀都是變化的。對切屑的研究是金屬切削最重要的事情之一。如同后面將要看到的那樣，金屬切削力學(xué)極大地依賴于所產(chǎn)生切屑的形狀和尺寸。

?????????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)

?????????金屬切削中的切屑形成可以寬泛地分成三個(gè)類型(圖7.3)：

??????(1)間斷切屑

??????(2)連續(xù)切屑

??????(3)帶切屑瘤的連續(xù)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.

??????間斷切屑：分段的切屑分散成小碎片，既可能相互附著也可能不相互附著。在靠近切削面處發(fā)生金屬的劇烈變形，導(dǎo)致在運(yùn)動刀具前方金屬層產(chǎn)生裂縫。

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，橫過切屑的剪切應(yīng)力與材料的剪切強(qiáng)度相等，造成斷裂和分離。生成這類切屑時(shí)，切屑沿刀具面幾乎沒有相對運(yùn)動，見圖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.

???????連續(xù)切屑：連續(xù)的切屑一般具有分離金屬沿刀具面流動的特征。切屑可能有一些破裂，但在這種情況下切屑通常不會延長到足以引起斷裂。

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.

這種切屑形成于用較高切削速度機(jī)加工有延展性的材料時(shí)。材料幾乎沒有粘附刀具的傾向。連續(xù)切屑通常具有良好的切削率和趨向于產(chǎn)生最適宜的表面光潔度，但可能成為操作的危險(xiǎn)之源，見圖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.

???????帶切屑瘤的連續(xù)切屑：這種切屑顯示了粘合或“焊接”在刀具面上材料局部高度變形區(qū)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.

實(shí)際上，對顯微照片的分析顯示這種切屑瘤受到靜摩擦力抑制直至它變得大到作用在它上面的外力使其移動，一些留在機(jī)加工表面上而另一些延伸到切屑的背面，見圖7.3c。

??Shear Zone ??剪切區(qū)

???????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.

???????在對金屬去除過程的分析中主要存在兩種思想學(xué)派。一種思想學(xué)派認(rèn)為變形區(qū)如圖7.4a所示那樣非常薄而平坦。另一學(xué)派則認(rèn)為真實(shí)變形區(qū)象圖7.4b所示那樣為一厚的帶有扇形的區(qū)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.

???????雖然第一種模型(圖7.4a)從分析的角度看是方便的，但實(shí)際上是不可能存在的。這是由于未變形的材料沿著剪切面發(fā)生變形，而且越過剪切面的加速度無窮大。

Similarly the stress gradient across the shear plane has to be very large to be practical.

同樣在實(shí)際運(yùn)用中越過剪切面的應(yīng)力梯度必須很大才行。

??????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.

???????在第二種模型(圖7.4b)中讓剪力區(qū)分布于一個(gè)范圍，速度和剪應(yīng)力的轉(zhuǎn)變能說明得更符合實(shí)際。

??????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在金屬切削中是一個(gè)十分重要的參數(shù)。剪切角越大，切削作業(yè)越好。從圖7.4a觀察，可以看到較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.

???????在工業(yè)中為了不同的應(yīng)用可以使用各種各樣的切削刀具材料。在最近的百年里產(chǎn)生了許多進(jìn)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.

多種切削刀具材料被開發(fā)出來以滿足這些方案中使用材料的多樣性。討論這些材料性能之前，先看一下作為切削刀具材料應(yīng)具備哪些重要特性。

???????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，這樣它才能進(jìn)入工件材料。

???????2. 熱硬度，即材料由于存在于切削區(qū)的高溫而升溫時(shí)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-刀具與切屑-工件的接觸界面處于如此嚴(yán)酷的狀態(tài)，粘附和磨損是很普遍的。因此切削刀具材料應(yīng)具有高耐磨性以提高刀具的有效壽命。

???????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. 韌性—雖然刀具是堅(jiān)硬的，但也應(yīng)有足夠的韌性以經(jīng)受住沖擊載荷，這些載荷來自于切削的開始或由于工件材料的缺陷而產(chǎn)生的作用力波動。這個(gè)要求對如銑削之類的間斷切削更有用。

???????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. 低摩擦系數(shù)—切屑與刀具間的摩擦系數(shù)應(yīng)當(dāng)較低。這會使磨損率較小及切屑流動更好。

???????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. 熱特性—因?yàn)榇罅康臒岙a(chǎn)生在切削區(qū)，刀具材料應(yīng)當(dāng)具有較高的熱傳導(dǎo)性以在最短的時(shí)間內(nèi)散發(fā)熱量，否則刀具溫度會升高，壽命會減少。

???????All these characteristics may not be found in a single tool material. Improved tool materials have been giving a better cutting performance.

???????所有這些特性不可能存在于單一刀具材料中。改進(jìn)的刀具材料已經(jīng)被賦予較好的切削性能。

??Surface Finish ?

???表面光潔度

???????Machining operations are utilized in view of the better surface finish that could be achieved by it compared to other manufacturing operations.

???????由于機(jī)加工能獲得比其它制造作業(yè)更好的表面光潔度，所以機(jī)加工作業(yè)具有實(shí)用價(jià)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:

因而了解能在機(jī)加工作業(yè)中獲得怎樣的實(shí)際表面光潔度是重要的。給定機(jī)加工作業(yè)中的表面光潔度是兩個(gè)因素共同作用的結(jié)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)?理想的表面光潔度，是通過考慮機(jī)加工作業(yè)的幾何體系所決定的制造工藝幾何學(xué)的結(jié)果，和

(2)?自然要素，即在機(jī)加工中一些難以預(yù)測的不可控因素作用的結(jié)果。

Ideal Surface Finish in Turning

車削中的理想表面光潔度

???????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.

???????實(shí)際使用的車削刀具有一個(gè)刀尖半徑取代鋒利刀尖，它將表面幾何形狀加工為如圖7.5a所示。如果進(jìn)給率很小，象精車中很正常的那樣，工件表面則完全是由刀尖半徑單獨(dú)產(chǎn)生的，如圖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

??????對圖7.5這種情況，表面粗糙度值為

???????????????Ra=8f2/(18R√3)

式中：Ra是表面粗糙度值

???????????R是刀尖半徑

????????????f是進(jìn)給率

???????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:

???????上述基本為幾何要素，其值代表了理想情況。而實(shí)際獲得的表面光潔度很大程度上還取決于下列一些因素：

(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)切削工藝參數(shù)、速度、進(jìn)給和切削深度

(2)切削刀具的幾何形狀

(3)切削液的運(yùn)用

(4)工件和刀具的材料特性

(5)機(jī)床的剛度及其伴隨發(fā)生的振動

??????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.

???????對表面光潔度產(chǎn)生主要影響的是進(jìn)給率和切削速度。從上述公式可以看到，隨著進(jìn)給的減少，粗糙度指標(biāo)會降低。

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.

同樣隨著切削速度的增大，能得到較好表面光潔度。因此在為光潔度而選擇切削工藝參數(shù)時(shí)，采用較高的切削速度和較小的進(jìn)給率是適當(dāng)?shù)摹?/span>

??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(經(jīng)常誤稱為冷卻液)的功能如下：

??冷卻刀具和工件

??減少摩擦

??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

??保護(hù)工件不生銹

??改善表面光潔度

??防止切屑瘤的形成

??從切削區(qū)沖掉切屑

??????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，在金屬切削作業(yè)中切削液的主要功能是控制總熱量。這可通過既散發(fā)又減少所產(chǎn)生的熱量來達(dá)到。切削液實(shí)現(xiàn)這些功能的機(jī)理是：冷卻作用和潤滑作用。

???????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.

???????冷卻作用：最初設(shè)想切削液僅僅是通過冷卻特性來改善切削作業(yè)。這也是它曾被稱為冷卻液的原因。

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.

由于大多數(shù)刀具的磨損機(jī)理都是由熱引起的，冷卻切屑刀具接觸界面有助于保持刀具的原有特性，從而延長其使用壽命。

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.

可是工件溫度的降低在特定條件下會增加工件的剪切流動應(yīng)力，從而降低刀具壽命。通過一些研究已經(jīng)表明實(shí)際上冷卻只是改善切削作業(yè)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.

???????潤滑作用：切削作業(yè)的最大改善可通過潤滑作用來達(dá)到，由于它減少了熱量的產(chǎn)生因而減少了金屬切削作業(yè)的能量輸入。

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須讓它到達(dá)切屑刀具接觸界面。但如何在采用單尖刀具連續(xù)車削的場合尤其是切屑-刀具接觸壓力高達(dá)70MPa時(shí)實(shí)現(xiàn)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認(rèn)為：在切屑與刀具接觸界面上存在微小的粗粒，切削液通過這些表面的微小粗粒組成連鎖的網(wǎng)絡(luò)的毛細(xì)管被吸入到切屑與刀具的接觸界面上。

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Unit 8 Grinding

磨削

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???????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.

???????磨削是通過采用旋轉(zhuǎn)磨輪去除金屬的制造工藝。磨輪用非常大量的微型切削刃模仿銑刀進(jìn)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，磨削被認(rèn)為是一種通常用于獲得高尺寸精度和較好表面光潔度的精加工作業(yè)。磨削通過采用被稱為磨床的特殊機(jī)床能在平面、圓柱面甚至內(nèi)表面上進(jìn)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.

顯然，磨床根據(jù)結(jié)構(gòu)和功能的不同有所區(qū)別，使用何種形式的磨床主要取決于被磨削表面的幾何形狀和物理性質(zhì)。例如，圓柱面在外圓磨床上磨削。

??Type of Grinding Operations
磨削作業(yè)的類型

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：就像其名稱暗示的那樣，表面磨削和平面磨削直接有關(guān)。圖8.1表示了兩種可能的變化：臥式磨床主軸或立式磨床主軸。

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.

在第一種情況(臥式主軸)，臥式磨床通常具有安裝工件的刨床式往復(fù)工作臺。而立式主軸磨床既可以像臥式主軸磨床那樣具有刨床式工作臺也可以具有旋轉(zhuǎn)工作臺。

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.

而且在這種情況下，磨削動作是通過砂輪端面完成的(圖8.1b)，這與通過砂輪周邊磨削工件的臥式主軸磨床正好相反。

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.

圖8.1a和b同時(shí)簡述了用于估計(jì)諸如加工時(shí)間和金屬去除率之類的磨削作業(yè)不同參數(shù)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.

在平面磨削時(shí)，重的工件用夾具固定或用壓板等夾緊在磨床工作臺上，而小的工件則通常是用電磁卡盤固定的。

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. 圓柱面磨削：在圓柱面磨削中，作業(yè)時(shí)工件支撐在兩頂尖之間，砂輪轉(zhuǎn)動是導(dǎo)致回轉(zhuǎn)切削運(yùn)動的動力源，如圖8.2所示。實(shí)際上，圓柱面磨削能通過采用下列任意方法來實(shí)現(xiàn)：

(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) 橫向方法：這種方法中砂輪與工件均旋轉(zhuǎn)且采用線性縱向進(jìn)給以保證能磨削整個(gè)長度。切削深度通過改變砂輪對工件的橫向進(jìn)給來進(jìn)行調(diào)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：這種方法通過砂輪的橫向進(jìn)給完成磨削而不采用軸向進(jìn)給。正如料想的那樣，這種方法只在要磨削表面比所用砂輪寬度短時(shí)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：這種方法除了一次加工就能去除磨削余量外其它與橫向方法相同。這種方法通常在磨削較短剛性軸時(shí)推薦使用。

????????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.

???????內(nèi)表面磨削：內(nèi)表面磨削用于相對較短的孔，如圖8.3所示。工件安裝在卡盤或特殊夾具上。作業(yè)時(shí)砂輪和工件都回轉(zhuǎn)并且采用縱向進(jìn)給。

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.

通過砂輪的橫向進(jìn)給能得到任意所需的切削深度。這種方法的一個(gè)變體是行星式內(nèi)表面磨削，當(dāng)工件較重不能用卡盤固定時(shí)推薦使用。

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.

在這種情況下，砂輪不但繞自身軸線回轉(zhuǎn)，同時(shí)還繞被磨削孔的中心線旋轉(zhuǎn)。

??????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.

???????無心磨削：無心磨削用于加工圓柱形工件，工件由托板支撐，在兩輪即砂輪和調(diào)節(jié)或進(jìn)給輪之間通過去。

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.

砂輪完成實(shí)際磨削，而調(diào)節(jié)輪負(fù)責(zé)旋轉(zhuǎn)工件和產(chǎn)生縱向進(jìn)給。由于調(diào)節(jié)輪通常用橡膠粘結(jié)的磨料制成，其摩擦特性使這成為可能。

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.

正如在圖8.4中所看到的那樣，調(diào)節(jié)輪的軸與砂輪軸傾斜一個(gè)微小角度。因此調(diào)節(jié)輪的圓周速度可以分解為兩個(gè)分量，即工件回轉(zhuǎn)速度和縱向進(jìn)給。

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).

其值可由下列公式給出：

??????????V工件＝V調(diào)節(jié)輪×cosα?

??????????軸向進(jìn)給＝V調(diào)節(jié)輪×c×sinα?

式中c是考慮工件和調(diào)節(jié)輪之間滑動的恒定系數(shù)(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.

???????調(diào)節(jié)輪的速度是可控的并被用于實(shí)現(xiàn)工件任意所需的轉(zhuǎn)動速度。α角通常取1到?5°，這角度越大則縱向進(jìn)給也將越大。

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.

當(dāng)α取0°時(shí)，即砂輪和調(diào)節(jié)輪軸線平行時(shí)，則工件沒有縱向進(jìn)給。

??Grinding Wheels ?砂輪

???????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.

???????砂輪由具有相近尺寸的磨料顆粒和粘合劑組成。實(shí)際磨削作業(yè)由磨粒完成。在粘合劑中磨粒之間的孔隙使磨粒能象獨(dú)立的單刃切削刀具一樣工作。

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.

這些孔隙同時(shí)還為產(chǎn)生的切屑提供空間以防砂輪堵塞。另外孔隙幫助冷卻液容易流動，從而使在磨削作業(yè)中產(chǎn)生的熱量能有效而迅速地散發(fā)。

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

???????砂輪根據(jù)它們的形狀和尺寸、磨料的類型、磨粒的大小、粘合劑、等級(硬度)和結(jié)構(gòu)組織來分類。

???????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:

???????砂輪的形狀和尺寸：根據(jù)砂輪的用途，它們的形狀和尺寸是不同的。各種形狀如圖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、圓柱面、內(nèi)部和無心磨削的直輪。

2)用于磨削螺紋、齒輪輪齒之類的斜面或錐形輪。

3)用于圓柱面和端面磨削的直凹輪。

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)用于切斷和開槽作業(yè)的砂輪片(其厚度從0.02到0.2英寸(0.5到5毫米))。

5)用其端面進(jìn)行表面磨削的圓柱、直杯及外展杯狀砂輪。

??????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.

???????砂輪的主要尺寸有外徑D、孔徑d和厚度H。根據(jù)采用砂輪的磨削工藝，這些尺寸變化很大。

???????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).

???????磨料的類型：砂輪可以由象石英、金剛砂、剛玉之類的自然磨料制成，或者由象氧化鋁或碳化硅(也稱人造金剛砂)之類的工業(yè)制備的化學(xué)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.

當(dāng)磨削象鑄鐵類低拉伸強(qiáng)度材料時(shí)，一般采用碳化硅砂輪，而磨削合金鋼、淬火鋼等高強(qiáng)度金屬則要用氧化鋁砂輪。

???????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：正如料想的那樣，砂輪磨粒的尺寸對決定所得磨削表面的質(zhì)量起著根本的作用。

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.

磨粒越細(xì)，磨削表面越光滑。所以，粗粒砂輪用于粗加工，而細(xì)粒砂輪則用于最后精加工。

???????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.

???????粘結(jié)體的等級：粘結(jié)體的等級實(shí)際上是其抵抗將磨粒從砂輪上拉脫的指標(biāo)。一般而言，具有較硬等級的砂輪用于磨削較軟材料，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.

如果較硬等級的砂輪用于磨削較硬材料，磨鈍的磨粒將不能足夠快地脫離粘結(jié)體，這會妨礙砂輪表面的自修復(fù)，最終導(dǎo)致砂輪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.

實(shí)際上，所有砂輪的磨削性能都必須定期地通過使用硬質(zhì)合金滾輪或金剛石修整器修整而被恢復(fù)，以求很準(zhǔn)確地把砂輪加工成要求的形狀，并去除已磨鈍的磨粒。

???????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.

???????結(jié)構(gòu)組織：結(jié)構(gòu)組織與磨粒間的空隙量有關(guān)。當(dāng)磨削較軟金屬時(shí)，需要較大的空隙以便去除切屑的流動。

???????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.

???????粘合劑：磨粒可用多種不同方法粘結(jié)在一起。其中包括粘合劑、硅酸鹽、橡膠、樹脂、蟲膠和氯氧化物。然而，粘合劑是最常用的。

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

???????在實(shí)際生產(chǎn)中，為了區(qū)分砂輪采用標(biāo)準(zhǔn)標(biāo)注系統(tǒng)，通過用一特定順序?qū)⑺猩鲜鰠?shù)都表示出來。

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Unit 9 Lapping and polishing

研磨與拋光

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.

???????研磨是一種用于平面和圓柱面的精加工作業(yè)。研具，如圖9.1a所示，通常用鑄鐵、銅、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).

研磨微粒嵌入研具內(nèi)，或者可以通過液體攜帶。根據(jù)工件硬度，研磨壓力可在7kPa到140kPa(1到20psi)范圍中取。

??????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.

???????研磨有兩個(gè)主要作用。首先，它通過去除所有機(jī)加工痕跡能產(chǎn)生較好的表面光潔度。其次，它能用作獲得像活塞與氣缸之類配件間過盈配合的方法。

??????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，其實(shí)布滿著微觀峰、谷、劃痕和凹陷。幾乎沒有表面是完全平整的。研磨使表面不規(guī)則最小化，因而增加了有效接觸面積。

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.

圖9.1a上顯示了兩個(gè)表面。上面是研磨前表面可能的外觀模樣而下面則是研磨后的模樣。研磨去除了微觀峰頂從而產(chǎn)生相對平坦的平臺。整個(gè)微觀山脈范圍都需要磨去以增加有效接觸面積。

??????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.

???????研磨平面或圓柱面工件的生產(chǎn)過程是在如圖9.1b和9.1c那樣的機(jī)器上完成的。研磨也可采用特殊成型研具在諸如球形物體和透鏡之類的曲面上進(jìn)行。

Polishing ??

拋光

??????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.

???????拋光是生成平滑、有光澤表面光潔度的工藝。拋光工藝涉及兩種基本機(jī)理：?(a)精細(xì)等級磨粒去除，和(b)在拋光中通過摩擦生熱軟化并抹光表面層。

Electropolishing

電解拋光

???????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.

??????電解拋光是一種與電鍍相似的電化學(xué)工藝，但過程與電鍍正好相反。電解拋光工藝使金屬物體的微觀表面平滑和簡單化。通過電解拋光能在金屬表面得到鏡面光潔度。

???????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.

???????在電解拋光中，金屬是逐個(gè)離子地從被拋光金屬物體表面去除的。電化學(xué)和電解基本原理(Faraday定理)取代了傳統(tǒng)的機(jī)械精加工技術(shù)。

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