专用镗床主轴箱设计（有cad图+文献翻译+ppt）
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外语文献翻译系 别 机电工程系 专 业 机械设计制造及其自动化 Machine design theoryThe machine design is through designs the new product or improves the old product to meet the human need the application technical science. It involves the project technology each domain, mainly studies the product the size, the shape and the detailed structure basic idea, but also must study the product the personnel which in aspect the and so on manufacture, sale and use question.1对金属基复合材料的高速车削实验L. Iuliano a, L. Settineri a and A. Gatto b ,*a. Politecnico di Torino, Dipartimento di Sistemi di Produzione ed Economia dellAzienda, C. so Duca degli Abruzzi, 24-10129 Torino, Italyb. Universita di AnconaDipartimento di Meccanica, Via Brecce Bianche-60131 Ancona, Italy (Received 1 October 1997; 12 May 1998)摘 要在机加工操作中，由机械特性增加了的金属基复合材料（MMC）组成的硬磨料陶瓷元件，会引起快速磨损和刀具过早失效。本文的目的就是将高前角的硬质合金刀具和有金刚石涂层的硬质合金刀具，在对 Al2O3 Al 6061 金属基复合材料（MMC）高速加工时的特性，进行比较。关于刀具磨损和表面光洁度对切削参数的影响，尤其是切削进给量和切削速度，进行了研究。另外，涂层的高耐磨性，会使刀具寿命和切削成形机理得到提高。 （1998 年，由 Elsevier 科学有限公司出版并保留所有权利。 ）关键词：金属基复合材料（MMC） ；高速切削；刀具磨损简介使用复合材料的益处以及越来越多采用它们的原因是寻找，具有获取很多增益优势的，特性组合体。其中包括：增加强度，减少重量，更高的服务温度，耐磨性的提高及较高的弹性模量。复合材料的主要优势：在于它们的机械性能和物理性能可以根据特定的设计标准进行调整。近年来，一种被称为新一代金属基复合材料（MMC） 1,2 的材料已被开发出来，用以满足高强度和高韧性材料的需求，且能在恶劣的条件下有效地工作。这些材料的发展，始于 20 世纪 60 年代硼、石墨和芳族聚酰胺纤维复合材料的引入。对在金属基复合材料的研究中，也引出了一些硼/铝复合材料的零部2件。然而，20 世纪 70 年代早期随着聚合物基复合材料逐渐占据主导地位，有关金属基复合材料的收益便减少了。到上世纪 80 年代末，新的纤维增强材料的引进，再一次促进了金属基复合材料的发展。这些材料通常是由一种，可由任何合适的金属（铝，镁，钛的形成和一些高温合金应用最多）组成的，基质形成；且由构成陶瓷材料的连续或非连续的纤维、晶须或颗粒组成的 SiC 和 Al2O3 来增强的。这些先进的复合材料被认为是用于高温应用的良好选择。大多数的金属基复合材料含有约三分之一的钢，它们的比强度和刚度相当高 3。因为具有重量可减少量高达 25%的潜力，所以这些属性在汽车和航空航天方面的应用非常重要。此外，其高温强度保留率也是一个重要的特征，使它们适于用作汽车和飞机发动机的材料。然而，在尝试对其进行切削时，这些吸引工程设计人员的金属基复合材料（MMCs）的性能，却由于它们的高脆硬性而呈现出一个巨大的挑战。例如，由于高磨损率 4-7，用常规方法如车削、钻、铣、锯等，对硬氧化铝颗粒的氧化铝铝合金 MMC 材料加工是非常困难的。鉴于此，氧化铝被作为许多刀具的基础材料，也就不奇怪了。因此，使用这些传统的方法加工 MMCs时，往往涉及频繁及昂贵的刀具变化和因此而增多的刀补次数。所以，在车削、铣削和钻削 MMCs 时，需要使用硬质合金、金刚石或硬质氮化物涂层刀具。即使加工次数往往是那些未增强的基体材料 8-10 的两到四倍，但由于刀具磨损的增加和 MMCs 的脆性要求而需要良好的表面光洁度，就有必要减少进给速率了。图一 Al2O3 颗粒分布平行（ a）和（b）垂直于挤压方向3表 1 6061 铝基表的化学成分表 2 切削条件如果这些材料有更广泛的用途，那么金属基复合材料的加工困难就必须最小化。因此，金属基复合材料的加工，目前被认为是制造科学迫切需要关注中最有意思的领域之一。由于复合材料是相对较新的材料，所以已经建立了综合切削数据库，并引起了人们的研究兴趣 5,6,8-13。在本文中的一些调查结果的概述，包括一个用传统的车削进行高速加工的10%颗粒的 Al2O36061 T6 的铝基复合材料。几何形状相同的硬质合金刀具和有金刚石涂层的硬质合金刀具被用于测试和测量刀具的磨损和表面光洁度，试验执行时，切削速度和进给速率都在一定范围内。该芯片的扫描电镜观察，以及磨损结果的评估是在不同切削速度和进给量的切屑机理下形成的。此前，作者已报道过 13（Ti，Al）N 涂层提高刀具寿命的调查结果。然而，这些结果表明：由于要实现刀具寿命上这点优势会耗费更多成本，所以在经济上涂层是不可行的。实验装置车削试验是在一台，坚固、有刚性、由特定的滚子轴承所组成的主轴及主轴转速可达 5000 转的，数控立式车床上进行的。其主轴由一台额定功率为 80千瓦、峰值功率为 120 千瓦的直流电机连续提供动力。商用的未涂层刀具和 CVD 金刚石涂层硬质合金刀具是以三角可转位刀片的形式使用的，这些刀片典型的几何形状可用于铝合金的加工。聚晶金刚石刀4具没有被测试，是因为与未涂层硬质合金刀具相比其成本高。一般情况下，刀具的前角 ，倾角 。对 10%颗粒的 Al2O36061 T6 铝基合金进行连续切削测试，其组成见表1。图 1 显示的是分布均匀的正在增强的 Al2O3 颗粒，平行、垂直于挤压方向。经过初步试验，为避免灾难性的失败，对切削条件进行了选择。选定的切削条件见表 2。总的来说，对于每一个工具都要进行 12 次的测试加工完 150* 103 立方毫米的物体后，根据 ANSI / ASME B94 55M 标准测得的残余磨损量 VB ，所检验的刀具磨损模式都是一致的。对硬质合金刀具切削刃的磨损区域的 SEM（扫描电镜观察）照片显示，图 2 中所示的后刀面磨损的模式是统一的。表面粗糙度 Ra 是用霍梅尔 T1000 针式仪器在被加工表面测得的。测量是在四个围绕工件的空间位置间隔获得的中值及其分布。用制备金相和使用二次电子显微镜检查（SE）和背散射电子（BSE）的扫描电镜对切屑和刀具进行分析，有时也会用能谱半定量分析。图二 扫描电镜对磨损未涂层硬质合金刀具切削刃区图片，结果与讨论5对使用未涂层刀具和金刚石涂层刀具所获得的每组 VTF 参数，使用多元线性回归统计分析刀具磨损的 VB 和平均表面粗糙度 Ra 值。独立的变量包括进给量、切削速度和它们所选定的第二阶项。该模型，解释了一部分总的变异，拟合了所观察到的反应的主要因素和第二项。就该模型的意义和参数进行方差分析检验；所得的模型变异的百分比大于 80%。分析标准不允许我们排除一些变量的影响，因为他们只是指出，这些与结果的联系性很强。应该强调的是，为了预测的目的，该模型的有效性不超过由测试的独立变量的组合定义相关的样本空间。注意，实验数据排除了刀具的持续时间与切削速度符合泰勒定律的特性的初步分析。统计分析表明，数据拟合了一个二阶多项式模型。刀具的磨损图 3 和图 4 所示的是未涂层刀具和金刚石涂层刀具的磨损特性。根据以下模型，主要影响因素有：进给量、方进、方进的切削速度以及切削速度的多次进给。对无涂层的刀具，和对金刚石涂层刀具。6图三 以未涂层硬质合金刀具的切削速度和进给量为变量的后刀面磨损 VB（MM）的计算模型，星号显示实验结果已对模型进行过计算。 使用的模型：统计参数： 图四 以金刚石涂层硬质合金刀具的切削速度和进给量为变量的后刀面磨损 VB（MM）的计算模型，星号显示实验结果已对模型进行过计算。 使用的模型：统计参数：事实上，可以观察到，对于一个给定的材料去除量，最小的后刀面磨损是由一个特定的组合切削速度低和相对高的进给量获得的。另一方面，低速进给和高切削速度的组合不可取。从这两张图片的对比中可以看到，正如预期的那样，金刚石涂层工具显示了更高的耐磨性和最小的后刀面磨损是为了达到更高的切削进给和速度。图 5 所示的灰色部分，代表的参数的组合区域，仅可以安全的使用金刚石涂层刀具。7图五 灰色区域只能安全适用在金刚石涂层硬质合金刀具涂层刀具更高的耐磨性是由于与硬质合金有关的高耐磨金刚石涂层。表面光洁度表面粗糙度 Ra 值分析清楚地表明，粗糙度不依赖于位置角的 ，这是由于基体上均匀分布的 Al2O3 加固所致。通过将测量各加工实验得到的 RA 值与未涂层刀具进行加工以获得平均值Ram 进行统计分析，得到以下模型：图 6 所示的是未涂层刀具的表面粗糙度特性。切削速度-进给量两项和他们的产品没有明显的影响，因此，起主导作用的是切削速度和进给量。8图六 以切削速度和进给量为变量的，未涂层硬质合金刀具的平均表面粗糙 Ram (m) 的计算模型。星号显示实验结果已对模型进行过计算。使用的模型：统计参数：然而，用金刚石涂层刀具所加工零件时并没有显示出切削参数与表面粗糙度之间的相关性。切屑的形成采用 SE 和 BSE 处理的刀具加工后，用扫描电镜观察切屑和工件表面。时，由切屑的图像分析可观察到，基体和增强颗粒发生了脱离。这一现象，独立于切削刀具的材料，随着切削速度的增加变得更为明显（图 7） 。进给率更大时，对切削速度的影响却不是很强。 时，对切屑的下表面进行扫描电镜观察。却注意到当 、时，二者之间并无差异（图 8） 。9图七 金刚石涂层刀具加工时，产生发的切屑下表面上颗粒清晰可见：图八 金刚石涂层刀具加工时，产生的切屑下表面上，可以看到堆放的粒子：切削速度为 630 米/分钟时，已注意到一些零碎的平行流速度，随着切削速度和进给率的增加而变得更加明显。在最后的废料中，常可以在基体上观察到部分增强的颗粒。简单的解释可能是增强颗粒粘在了刀具前角和刻在切屑上的划痕，直到消失，至少部分地在切屑基体上远离刀具的前角。为了验证这一点，切屑的纵向部分被切断（图 9） 。10图九 使用未涂层刀具加工产生的切屑的纵向断面（放大 50 倍）：很明显（图 10）如 pijspanen 模型所示，由其截面图像可观察到：增强粒子倾向于在基体沿剪切平面上下沉、堆集。有足够多的粒子堆积起来以阻止另一粒子的下沉，最后一个则伸出了基体一部分。高速切削下产生的切屑，其效果更加明显。切削速度更高时产生的高温，使粒子更易于沿剪切面运输。此外，剪切面越来越不规则，下表面上可见的划痕和脊数变多。图十 增强粒子沿剪切面的扩散模型同样的特性是由切削速度增加而诱使的：剪切面之间的距离增大（如图1113） 。11图十一 时，金刚石涂层刀具加工时产生的切屑纵断面（放大 50 倍）；能够清楚地观察到粒子的堆积图十二 金刚石涂层刀具切削时，切屑的上表面的剪切面：图十三 未涂层刀具切削时，切屑的上表面的剪切面：至于对涂层的影响，可以说，加工参数不变时，用金刚石涂层刀具产生的剪切平面之间的距离是高于使用硬质合金刀具的。当用硬质合金刀具加工时，切屑的下表面更均匀且规则。这可能是由于涂层 14-16 的摩擦系数低。磨损的切削刀具12金刚石涂层的热导率约为的硬质合金的 1020 倍（10002000 W / mK和 100 W / mK） 。然而，测得沿生长方向的值却是垂直于生长方向值的两倍。这使得涂层和基板的借口处产生了高温梯度以及切屑 16上较低的温度：Al2O3硬度增强值和软基之间有一个很大的区别，所以当硬质金刚石刀具的刃口切入硬质颗粒时，这些便开始移动；而参考 9 对 PCD 刀具的描述亦有同样的效果。所观察到的切屑形成机理并不是参考 13 中作者对于一个非常不同的（Ti，Al）N 涂层刀具的描述，但由于切屑的温度较低，在此处就需要更大的局部力来移动基体上的粒子。机加工完成后，可以在金刚石涂层刀具上观察到这些局部力和热负载的影响（图 14） 。在刀具后刀面上的一个大的材料黏附区域（白色区域）很醒目；随着切削速度的增大，该区域便会延伸；随着进给率的增加，黏附区域面积开始减小。很快，下方粘着带的深色线条会变得明显，且在刀具涂层被去除部位的平行于切削刃。涂层已消失的另一面，则可以在靠近切削刃的刀具前刀面看到。必须考虑到，金刚石涂层与基体之间的附着力仍然是关键的因素，特别是在硬质合金衬底 17的情况下。图十四 机加工完成后的金刚石涂层硬质合金刀具：结语可以从试验结果中得出以下结论：（1）在形成切屑的过程中，增强的粒子沿被分割成层的变形的，切屑的剪切面堆积。因为温度升高使氧化铝粒子的移动更自由，所以随着切削速度和进给量的增加，这种现象更加明显。（2）至于涂层对切屑形成的影响：较低的摩擦系数使得剪切面之间的距离13变大 ，切屑下表面变得更均匀、规则。（3）局部应力和热负载的影响使得涂层，沿着切削刃的平行位置，被去除。（4）后刀面磨损的统计模型显示：当切削速度高达一定值时，后刀面的磨损会随着进给率的增大而降低。正如在此所陈述的，刀具上的高耐磨金刚石涂层，极大地提高了耐磨性，使其成为加工耐磨材料时的优良选择。（5）由于所展示的金刚石涂层硬质合金刀具的磨损有限，所以还需要更多的研究，以探讨其在更严酷情况下加工复合材料时的行为，尤其在材料的去除量上。致谢在此，本文的作者们希望向，在准备这份手稿时为他们提供有见地的建议和意见的，Ancona 大学的 Liliana Felloni 教授和都灵理工大学的 R. 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Composites Manufacturing, Long Beach, CA, 710 December 1987, MR87-827.8 Weinert, S., A consideration of tool wear mechanisms when machining metal matrix composites.Annals of the CIRP, 1993,42(1), 9598.9 Tomac, N. and Tonnessen, K., Machinability of particulate aluminium matrix composite. Annals of the CIRP, 1992, 41(1),5558.10 Yuan, C., Geng, L and Dong, S, Ultraprecision machining of SiCw/Al composites.Annals of the CIRP , 1993, 42(1), 107109.11 Gatto A, Ippolito R, Iuliano L, Tagliaferri V. Surface finish of metal matrix composites under high speed turning. In Veniali, F., Erta, A.(eds), ASME Proceedings of the 1994 Engineering System Design and Analysis Conference, London, 47 July, vol. 2, 1994:3542.12 Gatto A., Iuliano L., Tagliaferri V. High speed turning of metal matrix composites with tools of different material and geometry.ASME Material and Design Technology, Kssuraona, T. (ed) 29 January1 February, Houston, TX, 1995:8995.13 Iuliano L., Settineri L., Gatto A. High-speed turning of metal matrix composites with coated and uncoated carbide tools. Proceedings of the 30th ISATA Conference, Florence, 1997, Automotive Auto-mation, Croydon, 1997.14 Pulker F. Wear and Corrosion Resistant Coatings by CVD and PVD. Chichester (UK): Ellis Horwood Limited, 1990.15 Konig, W., Fritsch, R. and Kammermeier, D., New approaches to characterising the performance of coated cutting tools. Annals of the CIRP, 1992, 41(1), 4954.16 Jawahir I.S., Van Luttervelt C.A. Recent developments in chip con-trol research and application. Keynote paper in Annals of the CIRP 1994;43/1.17 Townsend, P.P., Defects in coatings. Thin Solid Films , 1990, 193/194, 342349.High-speed turning experiments on metalmatrix compositesL. Iulianoa, L. Settineriaand A. Gattob,*aPolitecnico di Torino, Dipartimento di Sistemi di Produzione ed EconomiadellAzienda, C. so Duca degli Abruzzi, 24-10129 Torino, ItalybUniversita di AnconaDipartimento di Meccanica, Via Brecce Bianche-60131 Ancona,Italy(Received 1 October 1997; 12 May 1998)The hard abrasive ceramic component which increases the mechanical characteristics of metal matrix composites(MMC) causes quick wear and premature tool failure in the machining operations. The aim of the paper is tocompare the behaviour of high rake angle carbide tools with their diamond coated versions in high-speedmachining of an Al2O3Al 6061 MMC. The influence of the cutting parameters, in particular cutting feed andspeed, on tool wear and surface finish has been investigated. The higher abrasion resistance of the coatings resultsin increased tool life performances and different chip formation mechanisms. q 1998 Published by ElsevierScience Ltd. All rights reserved.(Keywords: metal matrix composites (MMCs); high-speed machining; tool wear)INTRODUCTIONThe benefit of using composite materials, and the cause oftheir increasing adoption is to be looked for in the advantageof attaining property combinations, that can result in anumber of service benefits. Among these are: increasedstrength, decreased weight, higher service temperature,improved wear resistance and higher elastic module.The main advantage of composites lies in the taylorabilityof their mechanical and physical properties to meet specificdesign criteria.In recent years, a new generation of materials known asmetal matrix composites (MMC)1,2has been developed, inorder to satisfy the demand for a high strength andtoughness material, capable of operating effectively underadverse conditions.The development of these materials began in the 1960swith the introduction of boron, graphite and aramide fibres.Work on MMCs resulted in several boron/aluminiumMMCs parts. However, interest in MMCs diminished inthe early 1970s as polymer matrix composites became thedominant material. The introduction of new fibre reinforce-ment materials in the late 1980s encouraged once again thenew development of MMCs.These materials are generally formed by a matrix which canbe made of any suitable metal (aluminium, magnesium, titaniumand some superalloys being the most popular), reinforced withSiC or Al2O3in the form of continuous or discontinuousfibres, whiskers or particles of the ceramic material.These advanced composites are considered excellentcandidates for high temperature applications. The specificmass of most MMCs is about one third that of steel, and thespecific strength and stiffness of these materials is quite high3. These properties are important in automotive andaerospace applications because of the potential for largereductions in weightup to 25%. Furthermore, their hightemperature strength retention is also an important feature,making them suitable candidate materials for use inautomotive and aircraft-engine applications.The properties that make MMCs appealing to engineeringdesigners can, however, present a major challenge whenattempting to machine these materials because of theirbrittle behaviour and high hardness.For instance, the presence of hard Al2O3particles inAl2O3/Al-alloy MMC materials involves considerabledifficulties when machining these materials using conven-tional methods such as turning, drilling, milling and sawing,etc., due to the high wear rate47. This is not surprisinggiven that Al2O3forms the basis of many cutting-toolmaterials. Therefore, machining MMCs using these con-ventional methods often involves frequent and expensivetool changes and therefore increased job-completion times.Turning, milling and drilling of MMCs, therefore, requiresthe use of carbide, diamond or hard-nitride-coated tools.Even then machining times tend to be two to four timesgreater than those for unreinforced matrix material becauseof increased tool wear, the necessity to use reducedComposites Part A 29A (1998) 150115091359-835X/98/$ - see front matterq 1998 Published by Elsevier Science Ltd.All rights reserved.PII: S1359-835X(98)00105-51501* Corresponding author. Tel.: +39-11-5647230; fax: +39-11-5647299;e-mail: lsettineathena.polito.itfeed-rates, and the need to achieve good surface finish,which is required by the brittle behaviour of the metal-matrix composites810.The difficulties associated with the machining of MMCsmust be minimised if these materials are to be used moreextensively. Therefore, the machining of MMCs is nowconsidered to be one of the most interesting areas ofmanufacturing science requiring urgent attention. SinceMMCs are relatively new materials, comprehensivemachinability data have yet to be established and this hasaroused some research interest5,6,813.In this paper the results of some investigation are outlined,involving the high-speed machining of a 10% particulateAl2O3/6061 T6 aluminium matrix composite by conventionallathe-turning. Carbide and diamond-coated carbide tools ofthe same geometry were used for the tests and measurementsof tool wear and part-surface finish were carried out. Testswere performed over a range of cutting speeds and feed rates.SEM observations of the chips, as well as the wear resultshave enabled assessments to be made of the mechanisms ofchip formation at different cutting speeds and feeds.The authors have previously reported13the results ofinvestigations on a (Ti,Al)N coating to improve tool life.However, these results indicated that the coating would notbe economically feasible, due to the small advantage in toolduration compared with the relatively higher costs.EXPERIMENTAL SET-UPTurning tests were performed on a numerically controlledvertical lathe which has a stiff, sturdy spindle with specialpurpose roller bearings, allowing spindle speeds to reach5000 rpm. The spindle is powered by a DC motor rated80 kW in continuous duty, with a peak power of 120 kW.Commercial uncoated and CVD diamond-coated carbidetools in the form of triangular indexable inserts were used,the geometry of these inserts being typical for the machiningof aluminium alloys. Polycrystalline diamond tools were nottested due to their high cost compared with the uncoatedcarbide tools. A tool holder with a lead angle x 918 andinclination angle of l 08 was used.Tests were carried on in continuous cutting on a 10%particulate Al2O3/6061 T6 aluminium matrix alloy, whosecomposition is reported in Table 1.InFigure 1 thehomogeneous reinforcing Al2O3particle distribution isshown, parallel and perpendicular to the extrusion direction.Following preliminary tests, the cutting conditions werechosen to avoid catastrophic failure. The selected cuttingconditions are reported in Table 2. Overall, 12 tests for eachtool type were carried out.After the machining of 150 3 103mm3and verifying thatthe pattern of tool wear was uniform, the flank wear VBwasmeasured according to the ANSI/ASME B94 55M stan-dards. A SEM picture of the cutting edge area of a worncarbide tool is shown in Figure 2 to show the uniformpattern of the flank wear.High speed turning experiments on metal matrix composites: L. Iuliano et al.1502Table 1 Chemical composition of the 6061 aluminium matrixSi Fe Cu Mn Mg Cr Zn Ti Ni Al% weight 0.59 0.15 0.27 0.004 1.04 0.09 0.002 0.006 0.001 bal.Figure 1 Al2O3particle distribution parallel (a) and perpendicular (b) to the extrusion directionTable 2 Cutting conditionsInserts Uncoated carbide grade ISO KDiamond coated carbide grade ISO KRake angle (g) 208Nose radius (r) 0.4 mmMachined volume (Y) 150 3 103mm3Depth of cut (a)2mSpeed (Vt) (630, 800, 1000, 1260) m/minFeed (f) (0.03, 0.10, 0.17) mm/revCooling noneSurface roughness Rawas measured on the machinedsurfaces by a Hommel T1000 stylus instrument. Measure-ments were made in four positions spaced at v 908 aroundthe workpiece to obtain medium values and theirdistributions.Chips and tools were prepared metallographically andexamined by SEM microscope using both secondaryelectrons (SE) and backscattered electrons (BSE). EDAXsemi-quantitative analysis was also carried out.RESULTS AND DISCUSSIONThe tool wear VBand the average surface roughness Ravalues obtained for each parameter couple Vtf usinguncoated and diamond-coated tools were statisticallyanalysed using multiple linear regression. The independentvariables are feed, cutting speed and their selected secondorder terms. The models, explaining a fair percentage oftotal variation, fitted the observed responses in terms ofmain factor and second terms. The significance of themodels and the parameters were checked using varianceanalysis; the percentage of variability explained by bothmodels is greater than 80%.The analysis criteria did not allow us to exclude theeffects of some variables because they merely pinpointedwhich associations were the stronger. It should be under-lined that the validity of the models, for predictive purposes,did not exceed the relevant sample space defined by thecombination of the tested independent variables. Notice thatthe preliminary analysis of the experimental data excludedthat the behaviour of tool duration versus cutting speedagrees with Taylors law. Statistical analysis showed thedata to fit a second order polynomial model.Tool wearIn Figures 3 and 4 the wear behaviour of the uncoated anddiamond-coated tools is shown. The main affecting factorsare: feed, square feed, square cutting speed and cuttingspeed times feed, according to the following models:VB 0:33 4:63 3 f 23 3 10 83 V2t 24:74 3 f2 0:002 3 Vt3 ffor the uncoated tools, andVB 0:11 0:95 3 f 2:3 3 10 83 V2t 3:82 3 f2 0:0003 3 Vt3 ffor the diamond-coated tools.1503High speed turning experiments on metal matrix composites: L. Iuliano et al.Figure 2 SEM picture of the cutting edge area of a worn uncoated carbidetool, Vt 630 m/min, f 0.03 mm/revFigure 3 Computed model of the flank wear VB(mm) for uncoated carbide tools versus cutting speed and feed. The stars indicate the experimental resultsover which the model has been computed. Model used: VB 0:33 4:63 3 f 23 3 10 83 V2t 24:74 3 f2 0:002 3 Vt3 f . Statistical parameter: R2,Adj 0.92In fact it can be observed that, for a given removedmaterial volume, minimum flank wear is achieved with aparticular combination of low cutting speed and relativelyhigh feed. The combination of low feed and high cuttingspeed is, on the other hand, not desirable. From acomparison of the two pictures it can be noticed that thediamond-coated tools show, as expected, a much higherwear resistance and the minimum for the flank wear isachieved at higher cutting feed and speed. In Figure 5 a greyzone is shown, representing the parameters combinationarea that can be explored safely only with diamond-coatedcutting tools.The higher wear resistance of the coated tools is due tothe higher abrasion resistance of the diamond coatings withrespect to the carbide.Surface finishThe analysis of surface roughness Ravalues clearlyshows that the roughness does not depend on the positionangle v, this fact being due to the uniform distribution of theAl2O3reinforcement on the matrix.The four Ravalues measured for each of the machiningtests performed with the uncoated tools were processed toHigh speed turning experiments on metal matrix composites: L. Iuliano et al.1504Figure 4 Computed model of the flank wear VB(mm) for diamond-coated carbide tools versus cutting speed and feed. The stars indicate the experimentalresults over which the model has been computed. Model used: VB 0:11 0:95 3 f 2:3 3 10 83 V2t 3:82 3 f2 0:0003 3 Vt3 f . Statistical parameter:R2,Adj 0.91Figure 5 The feedspeed combinations falling into the grey area can only be safely explored with the diamond-coated cutting toolsobtain the average values Ramwhich were used in thestatistical analysis, which yielded the following model:Ram0:36 0:0013 3 Vt 18:40 3 fIn Figure 6 the surface roughness behaviour of the uncoatedtools is shown. Second order terms of cutting speed and feedand their product have no significant effects, therefore thedominant factors are cutting speed and feed.The parts machined with the diamond-coated tools didnot show any significant correlation between the cuttingparameters and the surface roughness.Chip formationThe tool, chip and workpiece surfaces were observed bySEM, using SE and BSE techniques.From the analysis of the chips images it can be observedthat, at f 0.03 mm/rev, a detachment between the matrixand reinforcing particles occurs. This phenomenon, inde-pendent of the cutting tool material, becomes more evidentas the cutting speed increases (Figure 7).At higher feedrates, the effect of the cutting speed is lessstrong. From the SEM observations of the lower surfaces ofchips machined at f 0.17 mm/rev, no differences can benoticed between Vt 630 m/min and Vt 1260 m/min(Figure 8).At a cutting speed of 630 m/min, some scraps parallel tothe flow speed have been noticed, which become moreevident as cutting speed and feedrate increase. At the endof the scraps, a reinforcing particle partially emergingfrom the matrix can often be observed. A simpleexplanation of this could be that the reinforcing particlesare stuck on the tool rake and engrave the scratches on thechip, until they sink, at least partially, in the chip matrix1505High speed turning experiments on metal matrix composites: L. Iuliano et al.Figure 6 Computed model of the average surface roughness Ram(mm) for uncoated carbide tools versus cutting speed and feed. The stars indicate theexperimental results over which the model has been computed. Model used: Ram0:36 0:0013 3 Vt 18:40 3 f . Statistical parameter: R2,Adj 0.83Figure 7 Lower surfaces of chips cut with the diamond-coated tools; the emerging particles are visible: (a) Vt 630 m/min, f 0.03 mm/rev; (b) Vt1260 m/min, f 0.03 mm/revandarecarriedawayfromthetoolrake.Toverifythis,some longitudinal sections of the chips have been cut andobserved (Figure 9).From the section images it is evident that the reinforcingparticles tend to sink and pile up in the matrix along theshear planes described by the Pijspanen model (Figure 10).When enough particles have piled up to prevent anotherparticle from sinking, this last one sticks out partially fromthe matrix. The effect is stronger in chips obtained at highercutting speeds. The higher temperatures developed at highercutting speeds ease the transportation of the particle alongthe shear planes. Furthermore, the shear planes becomemore irregular and the number of scratches and ridgesvisible on the lower surfaces increases.The same behaviour is induced by an increase in cuttingfeed: the distance between the shear plane grows (Figures1113).As regards the influence of the coatings, it can be saidthat, under unchanged machining parameters, withdiamond coatings, the distance between the shearplanes is higher than the one obtained using a carbidetool and that the chips lower surfaces are moreHigh speed turning experiments on metal matrix composites: L. Iuliano et al.1506Figure 8 Lower surfaces of chips cut with the diamond-coated tools; the piling-up of the particles can be seen: (a) Vt 630 m/min, f 0.17 mm/rev; (b) Vt1260 m/min, f 0.17 mm/revFigure 9 Longitudinal chip sections ( 3 50) machined with uncoated tools: (a) Vt 630 m/min, f 0.03 mm/rev; (b) Vt 1000 m/min,f 0.03 mm/revFigure 10 Model of dispersion of reinforcing particles along the shearplaneshomogeneous and regular when machined with a coatedtool. This might be explained by the lower frictioncoefficient of the coatings1416.Worn cutting toolsThe thermal conductivity of the diamond coatings isabout 1020 times higher than that of the cemented carbide(10002000 W/mK vs. 100 W/mK). However, along thegrowth direction its value is twice that measured perpendi-cularly to the growth direction. This fact promotes the hightemperature gradient at the interface between the coatingand the substrate and relatively low temperature in the chip16: there is a great difference between Al2O3reinforcementhardness value and the soft matrix one, so that when the harddiamond tool edge comes into contact with the hard1507High speed turning experiments on metal matrix composites: L. Iuliano et al.Figure 11 Longitudinal sections of chips ( 3 50) machined with diamond-coated tools at f 0.17 mm/rev: (a) Vt 630 m/min; (b) Vt 1000 m/min; (c)Vt 1260 m/min; the piling-up of the particles can be clearly observedFigure 12 Shear planes on the upper surface of chips cut with the diamond-coated tools: (a) Vt 630 m/min, f 0.03 mm/rev; (b) Vt 630 m/min,f 0.17 mm/revFigure 13 Shear planes on the upper surface of chips machined with uncoated tools: (a) Vt 630 m/min, f 0.03 mm/rev; (b) Vt 630 m/min,f 0.17particles these are moved; the same effect has beendescribed for PCD tools in Ref.9. The observed chipformation mechanism is not much different from the onedescribed by the authors in Ref.13for (Ti,Al)N coated tools,but here higher localised forces are req
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