外文翻譯--材料去除機(jī)制新材料的精密加工

揚(yáng)州大學(xué)機(jī)械工程學(xué)院 畢業(yè)設(shè)計(jì)（論文）外文資料翻譯 教 科 部： 機(jī)械電子工程系 專 業(yè)： 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 姓 名： 學(xué) 號(hào)： 外 文 出 處： Material removal mechanisms in precision machining of newmaterials 指導(dǎo)老師評(píng)語 簽 名： 年 月 日 翻譯原文 Material removal mechanisms in precision machining of newmaterials Abstract Modern-day products are characterised by high-precision components. A wide range of materials, includingmetals and their alloys, ceramics, glasses and semiconductors, are finished to a given geometry, finish,accuracy and surface integrity to meet the service requirements. For advanced technology systems, demandsfor higher fabrication precision are complicated by the use of brittle materials. For efficient and economicalmachining of these materials, an understanding of the material removal mechanism is essential. This paperfocuses on the different material removal mechanisms involved in machining of brittle materials. 2001Published by Elsevier Science Ltd. Keywords: Brittle； Defects； Ductility； Material removal； Precision machining 1. Introduction Ultra-precision machining technology has been developed over recent years for the manufactureof cost-effective and quality-assured precision parts for several industrial applications such aslasers, optics, semiconductors, aerospace and automobile applications. Precision manufacturingdeals with the realisation of products with high shape accuracy and surface quality. The accuracymay be at the nanometric level. Several machining techniques can be mentioned here like diamondturning, grinding, lapping, polishing, honing, ion and electron-beam machining, laser machining,etc. Efficient overviews of the processes are given in Refs. 1 3. Ultra-precision machining technology has been highly developed since the 1980s mainlybecause of its high accuracy and high productivity in the manufacturing of optical, mechanicaland electronic components for industrial use. For many advanced technology systems, higherfabrication precision is complicated by the use of brittle materials. The past decade has seen atremendous resurgence in the use of ceramics in structural applications. The excellent thermal,chemical and wear resistance of these materials can be realised because of recent improvementsin the overall strength and uniformity of advanced ceramics 4. Ceramic materials have been widely adapted as functional materials as well as structuralmaterials in various industrial fields and their application to precision parts is also increasing 5. However, the high dimensional accuracy and good surface quality required for precision parts arenot necessarily obtained by the conventional forming and sintering process of ceramic powders.Thus precision finishing of the ceramics after forming and sintering is recognised as a key technologyto precision ceramic parts 6. The quantity of ceramic material to be removed by the finishing process must be very small,so that microcracks do not remain on the finished surface. Abrasive processes such as grindingor lapping with diamond abrasives have generally been adopted for precision finishing of ceramics79. However, it is expected that better surface integrity and higher production rates can berealised by cutting processes. Compared with other processes, cutting is also advantageous inmachining complex shapes.Brittle materials can be divided into three groups: amorphous glasses, hard crystals andadvanced ceramics. Advanced ceramics are a modern development. They are made from fineporous particles that are formed, consolidated and thermally treated under precisely controlledconditions. Use of these materials enables development of high-technology devices and systemsthat simply could not be produced otherwise 10. The same statement could be made about theuse of certain crystalline materials (e.g., semiconductors) and advanced high-temperature glasses. 2. Ductile regime machining Improvements in machining tolerances have enabled researchers to expose the ductile materialremoval of brittle materials. Under certain controlled conditions, it is possible to machine brittlematerials like ceramics using single- or multi-point diamond tools so that material is removed byplastic flow, leaving a crack-free surface (Fig. 4). This process is called ductile regime machining. Ductile regime machining follows from the fact that all materials will deform plastically if thescale of deformation is very small. Another way of viewing the ductile regime machining problemis that described by Miyashita 17, as shown in Fig. 5. The material removal rates for grindingand polishing are compared and there is a gap in which neither technique has been utilised. Thisregion can be termed the micro-grinding gap since the region lies in between grinding and polishing.This gap is important because it represents the threshold between ductile and brittle grindingregimes for a wide range of materials like ceramics, glasses and semiconductors. 2.1. Principle of ductile regime machining The transition from brittle to ductile mode during machining of brittle materials is described in terms of the energy balance between strain energy and surface energy 18. Localised fracturesproduced during application of load are of interest in machining of brittle materials. Machiningis an indentation process during which indentation cracks are generated, and these cracks play animportant role in ductile regime machining 19. A critical penetration depth dc for fracture initiation is described as follows 20 where Kc is the fracture toughness, H is the hardness, E is the elastic modulus and b is a constantwhich depends on tool geometry. Fig. 6 shows a projection of the tool perpendicular to the cuttingdirection. According to the energy balance concept, fracture damage will initiate at the effectivecutting depth and will propagate to an average depth yc. If the damage does not continue belowthe cut surface plane, ductile regime conditions are achieved. The cross-feed f determines theposition of dc along the tool nose. Larger values of f move dc closer to the tool centreline.Another interpretation of ductile transition phenomena is based on cleavage fracture due to thepresence of defects 21. The critical values of a cleavage and plastic deformation are affectedby the density of defects/dislocations in the work material. Since the density of defects is not solarge in brittle materials, the critical value of fracture depends on the size of the stress field. Fig 7 shows a model of chip removal with size effects. When the uncut chip thickness is small, thesize of the critical stress field is small to avoid cleavage. Consequently a transition in the chip 2.2. Material removal mechanisms in ductile regime machining Machining generates a useful surface by intimate contact of two mating surfaces, namely the workpiece and abrasive tool. However, the micromechanisms of material removal differ from material to material depending upon the microstructure of both workpiece and tool material. Generally, during high-precision machining of brittle materials, tools having large negative rake angles are used (as high as -30). The negative rake angle provides the required hydrostatic pressure for enabling plastic deformation of the work material beneath the tool radius. During conventional machining with a single-point tool, the rake angle will be positive or close to 0.With positive rake angle, the cutting force will generally be twice the thrust force. Hence the deformation ahead of the tool will be in a concentrated shear plane or in a narrow plane as shown in Fig. 8. During the grinding process, it is generally agreed that the tool will have a large negative rake angle and also that the cutting force is about half of the thrust force Fig. 8(b). In ultraprecision machining of brittle materials at depths of cut smaller than the tool edge radius, the tool presents a large negative rake angle and the radius of the tool edge acts as an indenter as shown in Fig. 8(c). This represents indentation sliding of a blunt indenter across the workpiece surface. This is similar to a situation where the tool is rigidly supported and cuts the workpiece under a stress such that no median vents are generated but the material below the tool is plastically deformed due to large hydrostatic pressure as in Fig. 8(d). 3. Material removal in glass and ceramics The ductile grinding of optical glass is considered as the most perfect adaptation of a machining method to the material 22. Glass is an inorganic material supercooled from the molten state to the solid state without crystallising. Glasses are non-crystalline (or amorphous) and respond intermediate between a liquid and a solid； i.e., at room temperature they behave in a brittle manner 1838 P.S. Sreejith, B.K.A. N個(gè) goi / International Journal of Machine Tools & Manufacture 41 (2001) 18311843 but above the glass transition temperature in a viscous manner. The high brittleness of glass is due to the irregular arrangement of atoms. In crystalline materials like metals, the atoms have a fixed arrangement and regularity described by Miller indices, whereas glass structure does not show any definite orientation 23. The unique physical and mechanical properties of ceramics such as hardness and strength,chemical inertness and high wear resistance have contributed to their increased application in mechanical and electrical components. The advanced ceramics for structural and wear applications include alumina (Al2O3), silicon nitride (Si3N4), silicon carbide (SiC), zirconia (ZrO2) and SiAlON. The nature of atomic bonding determines the hardness of the material as well as the Youngs modulus. For ductile metallic-bonded materials the ratio E/H is about 250, while for covalentbonded brittle materials the ratio is about 20. The ratio will lie in between these values for ionicbonded materials. Low density and low mobility of dislocations are the reasons for the high hardness of some of brittle materials. 4. Gentle grinding There is an alternative hypothesis called “gentle” machining wherein it is believed that plastic deformation is not involved exclusively in the material removal 26. According to this theory, since the mode of deformation (plastic/brittle) depends on the state of the stress and not on the magnitude of the stress, it is difficult to assume that the mode of deformation will change by merely changing the depth of cut keeping all other parameters constant. Investigations have shown that, in order for brittle materials to deform in a ductile manner, considerable hydrostatic stress and/or temperature are required. Reducing the depth of cut will merely decrease the stress without changing the stress state. Therefore this theory suggests that the superior quality of the surface produced at lower depth of cut is due to the above effect and not necessarily to plastic deformation. At smaller depths of cut, microcracks may be formed but they may not propagate to form larger cracks. Hence grinding at extremely small depth of cut can be called gentle grinding rather than ductile grinding. 翻 譯 材料去除機(jī)制新材料的精密加工 注 : Sreejith *,B.K.A. Ngoi 學(xué)校的機(jī)械和生產(chǎn)工程、南洋理工大學(xué)、新加坡南洋大道 639798 年 文摘 現(xiàn)代產(chǎn)品的特點(diǎn)是高精度的零部件。廣泛的材料 ,螢火蟲 -荷蘭國際集團(tuán)金屬及其合金、陶瓷、眼鏡和半導(dǎo)體 ,完成給定的幾何形狀 ,完成 ,精度和表面完整性 ,以滿足服務(wù)需求。先進(jìn)技術(shù)系統(tǒng)的要求制造精度高是復(fù)雜的脆性材料的使用。有效的和經(jīng)濟(jì)的這些材料的加工 ,材料去除機(jī)理的 理解是至關(guān)重要的。摘要側(cè)重于不同的材料去除機(jī)制參與脆性材料的加工。 2001 年 由愛思唯爾的科學(xué)有限公司出版。 介紹 超精密加工技術(shù)是近年來開發(fā)生產(chǎn)成本效益和有質(zhì)量保證的精密零件等工業(yè)應(yīng)用激光、光學(xué)、半導(dǎo)體、航空航天和汽車應(yīng)用。精密制造處理產(chǎn)品的認(rèn)識(shí)高形狀精度和表面質(zhì)量的準(zhǔn)確性可能的水平。這里提到一些加工技術(shù)可以像鉆石車削、磨削、研磨、拋光、珩磨、離子和電子束加工 ,激光加工等。有效參過程給出的概述。 1 - 3。 超精密加工技術(shù)自 1980 年代以來一直高度發(fā)達(dá)的主要 因?yàn)樗母邷?zhǔn)確性和高生產(chǎn)率生產(chǎn)的光學(xué) ,機(jī)械和 電子元件工業(yè)使用。許多先進(jìn)的技術(shù)系統(tǒng) ,制造精度高使用復(fù)雜的脆性材料。過去的十年已經(jīng)取得了一個(gè)巨大的復(fù)興在結(jié)構(gòu)陶瓷的使用應(yīng)用程序。優(yōu)秀的熱、化學(xué)和耐磨性可以意識(shí)到 ,因?yàn)樽罱@些材料的先進(jìn)陶瓷的整體強(qiáng)度和均勻性的改善 4。 陶瓷材料廣泛適應(yīng)功能材料和結(jié)構(gòu)材料在各種工業(yè)領(lǐng)域及其應(yīng)用精密零件也增加 5 然而 ,所需的尺寸精度高 ,表面質(zhì)量好精密零件不一定是通過傳統(tǒng)的形成和陶瓷粉末的燒結(jié)過程。因此精密加工成形和燒結(jié)后陶瓷的認(rèn)可作為一個(gè)關(guān)鍵技術(shù) 認(rèn)識(shí)精密陶瓷部件 6。 陶瓷材料的數(shù)量要?jiǎng)h除的后整理工序必須非常小 ,因 此 ,微裂隙不停留在加工表面。研磨過程 ,如磨或與金剛石磨料研磨一般都采用精密加工陶瓷 7。然而 ,預(yù)計(jì)更好的表面質(zhì)量和更高的生產(chǎn)速度可以實(shí)現(xiàn)切削過程。與其他進(jìn)程相比 ,切削在加工復(fù)雜形狀也是有利的。 脆性材料可分為三組 :非晶眼鏡 ,水晶和先進(jìn)陶瓷。先進(jìn)陶瓷是現(xiàn)代發(fā)展。他們是由細(xì)小的多孔顆粒的形成 ,鞏固和精確控制條件下熱處理。使用這些材料使發(fā)展的高科技設(shè)備和系統(tǒng) ,否則根本不可能產(chǎn)生 10。相同的語句可能會(huì)對(duì)某些晶體材料的使用 (如。、半導(dǎo)體 )和先進(jìn)的高溫眼鏡。 1.自由磨料加工 自由研磨加工 (FAM)是一個(gè)加工過程 ,利用磨料如鉆石、碳化硅、碳化硼、氧化鋁切削和完成。磨料的家人通常是與液體混合漿。這泥漿之間放置一個(gè)硬 (60 - 62 Rc)旋轉(zhuǎn)的車輪 ,稱為研磨塊 ,和工件。研磨塊通常是淬火鋼做的。過程的原理圖所示 (圖 1)。在家人不要研磨塊中嵌入磨料粒子 ,因此加工過程有點(diǎn)類似三體磨損。如果研磨塊是由柔軟的材料如銅或錫 ,然后有機(jī)會(huì)磨料粒子將會(huì)嵌入到塊中。在這里加工過程可以被認(rèn)為是三體和雙體穿。這將對(duì)應(yīng)線研磨和拋光過程。流暢的加工表面得到軟研磨塊時(shí)采用的表面的平面度。難研磨塊給一個(gè)表面平面度比軟塊 11。 脆性材料的材料去除 機(jī)理在家人非常不同于韌性材料由于材料特性和結(jié)構(gòu)的差異。在加工韌性材料 ,材料去除之前相當(dāng)大的塑性變形發(fā)生。這些塑料品種的表層和次表層的導(dǎo)致裂紋成核和傳播。這將最終導(dǎo)致材料去除。延性材料的材料去除機(jī)制形容 microcutting 和磨損機(jī)制 ,提出 Rabinowicz12和塞繆爾 13。 注 :Sreejith B.K.A. Ngoi /國際期刊的機(jī)床和制造 41(2001)1831 2001。 自由研磨加工的原理圖 形容 microcutting 和磨損機(jī)制 ,提出 Rabinowicz12和塞繆爾 13。 觀察骨折在脆性固體研磨確認(rèn)事實(shí)中扮演一個(gè)重要的角色在韌性材料去除除了政權(quán)加工 (14 - 16)。陶瓷加工表面的微觀觀察 FAM 揭示材料去除的骨折。圖 2 顯示了 Ni-Zn 鐵氧體和鈉鈣玻璃表面加工后被家人拋光光學(xué)質(zhì)量。粗糙的表面受到家人加工碳化硅 (SiC)勇氣 (62.9m)2。 Ni-Zn 鐵氧體表面顯示區(qū)域的橫向開裂 ,壓碎區(qū)和塑料劃痕。這些劃痕的性質(zhì)和骨折熊相似 thesliding 壓痕在硬脆性固體 ,indenters 鋒利 ,如圖 3 所示。拋光的鈉鈣玻璃表面也顯示了類似的功能。這里的差別是 ,在的情況下玻璃表面壓痕的 特征更特點(diǎn)大幅 indenters 比滑動(dòng)壓痕如 Ni-Zn 鐵氧體的表面。相似類型的骨折由 Imanaka14,格蘭姆斯 15et al。 圖 2 高度拋光的表面擦傷的顯微圖自由研磨加工。 1834 注 :Sreejith B.K.A. Ngoi /國際期刊的機(jī)床和制造 41(2001)1831 2001 圖 3。 顯微圖表面劃傷的滑動(dòng)維氏壓痕在正常負(fù)載 100 g。 2.韌性政權(quán)加工 提高加工公差使研究人員公開脆性材料的塑性材料去除。在一定控制條件下 ,可以使用單一機(jī)器脆性材料如陶瓷 刪除或多點(diǎn)金剛 石工具 ,材料塑性流動(dòng) ,留下 crack-free 表面 (圖 4)。這個(gè)過程稱為韌性政權(quán)加工。韌性政權(quán)加工之前 ,所有材料將變形可塑性如果變形非常小的規(guī)模。另一種方式查看韌性政權(quán)的加工問題是被 Miyashita17,如圖 5 所示。研磨的材料移除率和拋光比較 ,無論是技術(shù)利用的差距。這地區(qū)可以稱為該地區(qū)以來 micro-grinding 差距在于研磨和波爾 -愿。這種差距是很重要的 ,因?yàn)樗砹隧g性和脆性磨 之間的閾值荷蘭國際集團(tuán)政權(quán)為范圍廣泛的材料如陶瓷、眼鏡和半導(dǎo)體。 圖 4 韌性的機(jī)理或剪切模式脆性材料的磨削。 另外 ,B.K.A. Sreejith Ngoi /國際期刊的機(jī)床和制造 41(2001)1831 - 2001 3.1 韌性機(jī)制原理加工 從脆性過渡到韌性模式在脆性材料的加工中描述應(yīng)變能之間的能量平衡和表面能 18。局部的斷裂過程中產(chǎn)生感興趣的應(yīng)用程序負(fù)載在脆性材料的加工。加工是一個(gè)壓痕過程中產(chǎn)生壓痕裂紋 ,這些裂紋韌性政權(quán)加工起著重要的作用19。 臨界穿透深度 dc 斷裂開始描述如下 (20) 其中 kc 是斷裂韌性， H 是硬度， E 是彈性模量和 B 是一個(gè)常數(shù)這取決于刀具的幾何形狀。圖 6 顯示 了一個(gè) 工具垂直 線與 切 割方向 的關(guān)系 。 圖 5 可實(shí)現(xiàn)的材料移除率磨齒加工。 1836 注 :Sreejith B.K.A. Ngoi /國際期刊的機(jī)床和制造 41(2001)1831 2001 圖 6 垂直于切削方向投影的工具。 根據(jù)能量平衡的概念，斷裂損傷，將 增大有效 切削深度，并以平均深度 yc 擴(kuò)展 。如果 在加工 面下?lián)p害不繼續(xù)， 塑 性 加工 條件可以 實(shí)現(xiàn) 。 f 決定 dc 所在 刀尖 的位置 。一個(gè)較大的 F 值 使 dc 接近 于刀具的中心線。塑 性過渡現(xiàn)象另外的解釋，是 建立在 因應(yīng)存在缺陷 而產(chǎn)生 斷裂 的基礎(chǔ)之上 21 。在工作的材料中 疲勞斷裂 和塑性變 形 是 由缺陷 /脫位的 多少?zèng)Q定的 。 在 脆性材料 中 于的缺陷并非如此大， 疲勞 斷裂取決于應(yīng)力場(chǎng)的大小。 材料去除與刀具尺寸的關(guān)系 。未切割 材料厚度 小，臨界應(yīng)力是小， 可以避免斷裂。 因此 在材料去 除過程中，由脆性向 塑 性 變化取決 于未切割 材料厚度。 3.2 塑 性 材料一般加工 材料去除 原理 加工 生成一個(gè)有用的表面 需要 兩個(gè)交配接觸表面即工件和磨具。不過，微觀的材料去除不同于物質(zhì)材料 去除后者 取決于工件和刀具材料 的 微觀結(jié)構(gòu)。 一般而言，在高精密加工脆性材料 中 工具 使用 過大的負(fù)面角度（高達(dá) -30 ） 。負(fù)前角提供所需的壓力使工作