外文翻译--材料去除机制新材料的精密加工

扬州大学机械工程学院 毕业设计（论文）外文资料翻译 教 科 部： 机械电子工程系 专 业： 机械设计制造及其自动化 姓 名： 学 号： 外 文 出 处： Material removal mechanisms in precision machining of newmaterials 指导老师评语 签 名： 年 月 日 翻译原文 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个 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 译 材料去除机制新材料的精密加工 注 : Sreejith *,B.K.A. Ngoi 学校的机械和生产工程、南洋理工大学、新加坡南洋大道 639798 年 文摘 现代产品的特点是高精度的零部件。广泛的材料 ,萤火虫 -荷兰国际集团金属及其合金、陶瓷、眼镜和半导体 ,完成给定的几何形状 ,完成 ,精度和表面完整性 ,以满足服务需求。先进技术系统的要求制造精度高是复杂的脆性材料的使用。有效的和经济的这些材料的加工 ,材料去除机理的 理解是至关重要的。摘要侧重于不同的材料去除机制参与脆性材料的加工。 2001 年 由爱思唯尔的科学有限公司出版。 介绍 超精密加工技术是近年来开发生产成本效益和有质量保证的精密零件等工业应用激光、光学、半导体、航空航天和汽车应用。精密制造处理产品的认识高形状精度和表面质量的准确性可能的水平。这里提到一些加工技术可以像钻石车削、磨削、研磨、抛光、珩磨、离子和电子束加工 ,激光加工等。有效参过程给出的概述。 1 - 3。 超精密加工技术自 1980 年代以来一直高度发达的主要 因为它的高准确性和高生产率生产的光学 ,机械和 电子元件工业使用。许多先进的技术系统 ,制造精度高使用复杂的脆性材料。过去的十年已经取得了一个巨大的复兴在结构陶瓷的使用应用程序。优秀的热、化学和耐磨性可以意识到 ,因为最近这些材料的先进陶瓷的整体强度和均匀性的改善 4。 陶瓷材料广泛适应功能材料和结构材料在各种工业领域及其应用精密零件也增加 5 然而 ,所需的尺寸精度高 ,表面质量好精密零件不一定是通过传统的形成和陶瓷粉末的烧结过程。因此精密加工成形和烧结后陶瓷的认可作为一个关键技术 认识精密陶瓷部件 6。 陶瓷材料的数量要删除的后整理工序必须非常小 ,因 此 ,微裂隙不停留在加工表面。研磨过程 ,如磨或与金刚石磨料研磨一般都采用精密加工陶瓷 7。然而 ,预计更好的表面质量和更高的生产速度可以实现切削过程。与其他进程相比 ,切削在加工复杂形状也是有利的。 脆性材料可分为三组 :非晶眼镜 ,水晶和先进陶瓷。先进陶瓷是现代发展。他们是由细小的多孔颗粒的形成 ,巩固和精确控制条件下热处理。使用这些材料使发展的高科技设备和系统 ,否则根本不可能产生 10。相同的语句可能会对某些晶体材料的使用 (如。、半导体 )和先进的高温眼镜。 1.自由磨料加工 自由研磨加工 (FAM)是一个加工过程 ,利用磨料如钻石、碳化硅、碳化硼、氧化铝切削和完成。磨料的家人通常是与液体混合浆。这泥浆之间放置一个硬 (60 - 62 Rc)旋转的车轮 ,称为研磨块 ,和工件。研磨块通常是淬火钢做的。过程的原理图所示 (图 1)。在家人不要研磨块中嵌入磨料粒子 ,因此加工过程有点类似三体磨损。如果研磨块是由柔软的材料如铜或锡 ,然后有机会磨料粒子将会嵌入到块中。在这里加工过程可以被认为是三体和双体穿。这将对应线研磨和抛光过程。流畅的加工表面得到软研磨块时采用的表面的平面度。难研磨块给一个表面平面度比软块 11。 脆性材料的材料去除 机理在家人非常不同于韧性材料由于材料特性和结构的差异。在加工韧性材料 ,材料去除之前相当大的塑性变形发生。这些塑料品种的表层和次表层的导致裂纹成核和传播。这将最终导致材料去除。延性材料的材料去除机制形容 microcutting 和磨损机制 ,提出 Rabinowicz12和塞缪尔 13。 注 :Sreejith B.K.A. Ngoi /国际期刊的机床和制造 41(2001)1831 2001。 自由研磨加工的原理图 形容 microcutting 和磨损机制 ,提出 Rabinowicz12和塞缪尔 13。 观察骨折在脆性固体研磨确认事实中扮演一个重要的角色在韧性材料去除除了政权加工 (14 - 16)。陶瓷加工表面的微观观察 FAM 揭示材料去除的骨折。图 2 显示了 Ni-Zn 铁氧体和钠钙玻璃表面加工后被家人抛光光学质量。粗糙的表面受到家人加工碳化硅 (SiC)勇气 (62.9m)2。 Ni-Zn 铁氧体表面显示区域的横向开裂 ,压碎区和塑料划痕。这些划痕的性质和骨折熊相似 thesliding 压痕在硬脆性固体 ,indenters 锋利 ,如图 3 所示。抛光的钠钙玻璃表面也显示了类似的功能。这里的差别是 ,在的情况下玻璃表面压痕的 特征更特点大幅 indenters 比滑动压痕如 Ni-Zn 铁氧体的表面。相似类型的骨折由 Imanaka14,格兰姆斯 15et al。 图 2 高度抛光的表面擦伤的显微图自由研磨加工。 1834 注 :Sreejith B.K.A. Ngoi /国际期刊的机床和制造 41(2001)1831 2001 图 3。 显微图表面划伤的滑动维氏压痕在正常负载 100 g。 2.韧性政权加工 提高加工公差使研究人员公开脆性材料的塑性材料去除。在一定控制条件下 ,可以使用单一机器脆性材料如陶瓷 删除或多点金刚 石工具 ,材料塑性流动 ,留下 crack-free 表面 (图 4)。这个过程称为韧性政权加工。韧性政权加工之前 ,所有材料将变形可塑性如果变形非常小的规模。另一种方式查看韧性政权的加工问题是被 Miyashita17,如图 5 所示。研磨的材料移除率和抛光比较 ,无论是技术利用的差距。这地区可以称为该地区以来 micro-grinding 差距在于研磨和波尔 -愿。这种差距是很重要的 ,因为它代表了韧性和脆性磨 之间的阈值荷兰国际集团政权为范围广泛的材料如陶瓷、眼镜和半导体。 图 4 韧性的机理或剪切模式脆性材料的磨削。 另外 ,B.K.A. Sreejith Ngoi /国际期刊的机床和制造 41(2001)1831 - 2001 3.1 韧性机制原理加工 从脆性过渡到韧性模式在脆性材料的加工中描述应变能之间的能量平衡和表面能 18。局部的断裂过程中产生感兴趣的应用程序负载在脆性材料的加工。加工是一个压痕过程中产生压痕裂纹 ,这些裂纹韧性政权加工起着重要的作用19。 临界穿透深度 dc 断裂开始描述如下 (20) 其中 kc 是断裂韧性， H 是硬度， E 是弹性模量和 B 是一个常数这取决于刀具的几何形状。图 6 显示 了一个 工具垂直 线与 切 割方向 的关系 。 图 5 可实现的材料移除率磨齿加工。 1836 注 :Sreejith B.K.A. Ngoi /国际期刊的机床和制造 41(2001)1831 2001 图 6 垂直于切削方向投影的工具。 根据能量平衡的概念，断裂损伤，将 增大有效 切削深度，并以平均深度 yc 扩展 。如果 在加工 面下损害不继续， 塑 性 加工 条件可以 实现 。 f 决定 dc 所在 刀尖 的位置 。一个较大的 F 值 使 dc 接近 于刀具的中心线。塑 性过渡现象另外的解释，是 建立在 因应存在缺陷 而产生 断裂 的基础之上 21 。在工作的材料中 疲劳断裂 和塑性变 形 是 由缺陷 /脱位的 多少决定的 。 在 脆性材料 中 于的缺陷并非如此大， 疲劳 断裂取决于应力场的大小。 材料去除与刀具尺寸的关系 。未切割 材料厚度 小，临界应力是小， 可以避免断裂。 因此 在材料去 除过程中，由脆性向 塑 性 变化取决 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 生成一个有用的表面 需要 两个交配接触表面即工件和磨具。不过，微观的材料去除不同于物质材料 去除后者 取决于工件和刀具材料 的 微观结构。 一般而言，在高精密加工脆性材料 中 工具 使用 过大的负面角度（高达 -30 ） 。负前角提供所需的压力使工作