刀具磨损和芯片形成在艰难与自航旋转工具外文文献翻译、中英文翻译、外文翻译.doc
刀具磨损和芯片形成在艰难与自航旋转工具外文文献翻译、中英文翻译、外文翻译
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附录一：刀具磨损和芯片形成在艰难与自航旋转工具 H.A. Kishawy , J. Wilcox摘要 期刊提出了一种旋转工具在加工淬火钢的性能评估。调查包括一个分析芯片的刀具磨损形态和模式。工具的影响几何形状和类型的刀具材料工具自航运动也调查了。几个测试工具材料耐磨性包括硬质合金、涂层硬质合金,和陶制品。自航涂层硬质合金工具显示优越的耐磨性。这是证明了均匀分布侧面磨损没有陨石坑穿的证据。温度的特点,在加工旋转工具生成的研究。结果表明,减少工具消除了温度扩散磨损和支配着磨损。另外,增加该工具转速改变了最高温度在chip-tool界面前沿。2002爱思唯尔的科学有限公司版权所有。关键词: 旋转工具；努力；切屑形态；刀具磨损1.介绍将代替磨削淬火钢是一种经济的方法来生成一个高质量的加工表面。在过去的几年中,有明显的工业使用干燥加工而不是兴趣淬火钢等难加工材料的磨削。作为一个例子,又干又硬把汽车差动齿轮是一个成功的工业应用这项技术。这项技术减少了加工时间和具体的削减能源,并且消除了健康和环境危害与冷却剂使用在传统加工操作。尽管大量的文学存在于硬把1 - 10,刀具磨损的控制及其对加工表面的影响的物理性质代表了主要的技术挑战。了解芯片的形成机制是至关重要的实现更好的洞察力加工过程的基础。锯片芯片形成期间观察到的硬车削和被一些研究人员感兴趣的主题(1 - 9)。几款芯片去除机制。一些研究人员解释了绝热剪切看到齿切屑形成机理的理论。然而,其他研究人员认为其裂纹扩展形态的本质。使用快速停止机制最近的研究证实,锯片芯片是由循环裂纹扩展引起的。表面的完整性产生的困难将是另一个重要的课题。控制加工诱导残余应力是广泛工业应用的一个重要方面这种技术(3、7)。努力把必需的工具材料,具有高耐磨性和忍受的能力产生的特定的切削力和高温。此外,至少三倍高硬度的工件硬度10至关重要。由于刀具磨损和塑性变形的前沿影响加工表面的质量和完整性,陶瓷和PCBN工具通常用于硬车削。尽管在早期研究(11、12)旋转工具由不同材料显示优越的耐磨性,延长刀具寿命,他们的表现在硬把只是调查使用立方氮化硼刀片旋转工具13。此外,没有尝试在公开文献模型的温度特性与旋转加工工具。本文试图评估旋转工具的切削性能,不同的材料制成的,在艰难。除了温度模型来描述这个工具的传热特点和自冷功能。2.实验的程序进行一个全面的测试过程在努力将评估旋转工具的性能。又干又硬的测试是使用10惠普执行数控车床。热处理AISI 4340钢(54-56HRC)拥有一个75或100毫米直径,和一个200毫米长度,使用。研究采用的是汽车等待和锡涂层硬质合金插入。切削速度的100年、130年和270米/分钟,进给速率为0.2毫米/转速,和深度的0.1和0.2毫米。圆形插入有一个直径25.4毫米。的刀具磨损测量在四个地点,约等距,沿着周长插入使用的一种工具制造商的显微镜。这些值然后取平均值获得刀具磨损的价值。芯片收集对不同切削条件。这些芯片然后安装在环氧树脂、地面、抛光和蚀刻使用1.5%硝酸浸蚀液的解决方案。这些芯片的横断面图为使用一个光学检查、拍照吗显微镜。光学显微镜与扫描电子显微镜(SEM)被用来分析收集到的芯片和分析工具的方式失败。该工具旋转速度用光学转速表测量。3.旋转工具的基本特征 肖在先锋工作,et al。14提出lathe-type刀具的研究形式的绕其中心旋转的磁盘。的连续旋转工具围绕其中心允许使用的整个圆周插入。由于旋转工具,提供了新鲜的尖端部分,所以一个更好的工具侧面磨损分布在整个前沿。旋转动作的工具提供了一种携带工具点的流体在高切削速度在轴颈轴承的情况下。此外,该工具提供了一个自冷功能的热量不断远离切削区。 旋转工具中发现的两种形式:驱动或自航。工具旋转动作的驱动提供的工具是一个独立的外部来源。自行式工具的旋转动作是通过工具和芯片之间的交互。驱动的工具可以正交或斜交切削速度,而自航工具需要斜前沿切割速度。的转速驱动工具独立于工艺参数。在自航工具转速是一个函数的切削速度和工件之间的角度和旋转前沿速度向量。通常,驱动旋转工具提供更多控制转速。图1显示了一个典型的加工过程设置使用一个旋转的工具和主要运动中遇到旋转工具。 在加工旋转工具,定义了三个主要的运动,即工件(Nwp)的转速,转速(Ntoot)的工具,工件和工具的进给运动(f)。由于工具的旋转运动产生的芯片是拖沿着倾斜面的工具。因此,芯片速度是远离法线方向的偏转尖端在正交的情况下加工。 Venuvinod和鲁宾斯坦15提出了一个详细的运动学分析芯片加工期间形成的旋转工具。基本实验和理论研究也提出了Armarego et al .(16、17)。其他研究人员研究了液膜的形成chip-tool接口与旋转加工时工具18。已经得出的结论是,使用旋转工具是唯一的方式提供一个连续液膜在chip-tool接口。的确,这为一个接近零摩擦铺平了道路二次变形区。12采用自行旋转工具端面铣削操作期间。旋转工具的性能均与其他常规工具和表现出优越的性能和延长刀具寿命。4.热分析的旋转工具 图2显示了三个主要变形区加工。除了主要和次要的变形区,产生的热量在穿是特别重要的80%的热流在哪里机加工表面3。为简单起见,在此只有中小变形模型区被认为是锋利的工具。的在加工的计算基于热生成分析了以前19。R1、R2和R3分区系数所产生的热量吗沿着剪切面,chip-tool接口,而穿的土地,分别。在抵达的热模型旋转工具,以下假设了:1、芯片形成发生沿薄剪切带和沿倾斜面作为刚体移动的工具。2、剪切带中所有能源消耗和摩擦chip-tool接口是转化为热能。产生的热量沿剪切带沿剪切面均匀分布。3、芯片使剪切带以恒定温度等于剪切面温度。4、沿界面的摩擦产生的热量均匀分布。5。采用干式加工的对流传热系数100 W /(K)和20C的环境温度。图1一个典型的在加工旋转工具。4.1 热模型的控制方程控制卷集成方法是应用在发展中离散方程。在使用这种方法,微分形式的起点守恒方程,综合为每个域控制卷。结果表面通量和每个控制卷卷来源组装成最后一组代数方程。守恒微分方程描述的运动能量身体内的芯片和下标的工具可以被c和t是指芯片和工具,分别t温度,材料的密度、导热系数k, cp的比热。占主剪切带产生的热量的影响,一个热源,Sc是包括在内。这些方程占能量的传导和对流在移动的质量,并在广义坐标j(e1,e2、e3)占几何芯片和工具之间的差异。4.2 Chip-tool接口图3显示了一个简化的示意图表示旋转工具模型。检查工具的特点,一维水平和3 d离散化可以盟军20。工具分为固定控制卷(1-n)。计算网格是假定为固定的热源的位置。系统建模的质量通过固定网格移动。在这样一个公式,一个稳态温度分布的网格是可能的。芯片被建模为另一个控制卷和连接到旋转工具在摩擦界面通过控制表面模型。有效的热阻,雷夫,代表了传导和对流发生在表面正常物料流的方向,除了热传导的摩擦区。 valueswr a和 Rk 指能源运输质量流和扩散,分别控制之间物质流的方向。一个已知的速度场是对控制卷在工具和芯片para-meters基于指定的过程。通过选择坐标应用表面在摩擦面(e2转换坐标),界面的表面通量守恒收益率的后:图3模型的示意图表示。图4工具材料工具旋转的影响。描述指标e2x,e2y e2z Ref。20和坐标变换的术语“ 导数” J(e2xe2ye2z)等于区域,采取行动。摩擦区域的传热控制芯片和工具材料的热性能以及携带的速度加热材料摩擦区。由于工具不断旋转,一部分冷却和加热材料搬走了的回到摩擦区可能获得更多的热量。后续开发的离散方程式(1)和(2)是使用一个有限体积离散方法21。坐标转换保留条款,允许灵活性发展方程集不同的几何图形。集成后的控制卷尺寸e1,e21,e31,高斯定理用于体积积分转换成曲面积分的对流和扩散条件。详细的分析和验证模型的提出可以在裁判发现。20。5.结果和讨论在硬车削与普通刀具最大的分力推力总是因为芯片形成主要发生在刀尖半径的工具。用一个圆形的插图更大推力组件预计由于大型图5。倾角对工具旋转的影响。有效的刀尖半径。大推力可能激发喋喋不休,因此机床的刚度建立成功的硬车削操作至关重要。在除了所需的机床刚度转动,刀具/工件的刚度与旋转工具加工系统是至关重要的成功。几个工艺参数进行测试来识别边界硬把扶轮的成功应用工具。两个切深度值0.1和0.2毫米和饲料使用0.2毫米/转速和确认作为稳定的参数测试过程在给定范围内的切削速度。图4显示了插入转速的变化与切削速度时,使用不同的工具材料。监控插入的自行式运动表明,它的速度是线性与切削速度成正比。正如所料,工具材料的类型影响工具的旋转速度。硬质合金工具展品更高的速度和插入观察是更明显的切割速度值更高。图5描述了倾角的影响在工具转速和之间的关系切割速度。观察到的线性关系是维护不同倾角的值。在任何给定的切削速度,提高倾角增加了插入转速。观察到的行为的工具转速可以表示为Vtoot和V工具旋转速度和切割速度,分别。常数C是一个函数的工具材料,(湿或chip-tool接触条件干),工具倾角和倾角的工具。理解旋转工具的冷却能力的特点的影响工具速度之间的热分区工具和芯片进行了研究。图6显示了工具之间的比例的影响热分区上的旋转速度和切割速度关系,R2。结果表明,该工具冷却特性是有效的达到一定的速度限制。图6 在热分区工具的速度的影响。这是见过R2的快速减少速度比最初时增加。增加工具旋转速度增加的热量由工具了一定的速度后,进一步增加工具的速度减少热量带走的工具。此外,正如预期的那样,所有速度比率增加切削速度增加带走的热量由芯片。临界转速比对应的时间点为一个工具的革命变得太小,不足以有效地冷却工具之前返回切削区。图7描述了工具旋转速度对温度分布的影响倾斜面的工具。增加工具转速降低了峰值温度以及散装工具温度。然而,大部分工具温度的降低更明显转速更高价值的工具。此外,峰的位置温度价值转向尖端工具旋转速度更高。减少工具电阻温度提高工具的扩散磨损,将在以下部分。验证模型的介绍和详细的分析提出了在以前的工作20。只有温度特性相关的当前工作复制支持工具性能的评估。图7 温度分布情况5.1刀具磨损碳化的SEM图像(图8(a)和(b)和涂层硬质合金(图8(c)和(d)工具后,将显示,分别。可以看到在这些照片中,侧面磨损是失败的主导模式的工具。减少峰值温度,如图7所示,解释了为什么坑穿使用旋转工具时并不占主导地位。观察工件材料存款只有当使用涂层硬质合金的切削速度270米/分钟。,没有证据表明火山口穿,通常观察到艰难的转变。应该是这里提到标准涂层和裸硬质合金工具不适合加工。除了人们所预料的严重坑穿由于高温硬车削。然而,由于插入旋转运动,一个新的部分的前沿从事切割。刀具磨损分布在整个工具的围边可以看到在这些中小企业形象。这是由于这样的事实:每个部分的圆形前沿从事切短段时间相比普通平方插入。因此一个期望的增加刀具寿命。刀具寿命的增加将更大比例的周长工具切削刃的瞬时长度,只要局部磨损率是相同的旋转和旋转工具。图8刀具磨损的模式。图9显示了一个穿比较进步的工具不同的工具材料。固定和旋转工具在相同的切削条件下使用。可以看到,性能是实现当一个改善工具旋转工具使用。陶瓷和碳化裸插入时的固定工具使用。虽然陶瓷适合加工硬的工具,该工具凿是归因于产生的高压大型插入直径(25.4毫米)。分析了亲行走的涂层硬质合金工具显示,它始于一个当使用固定工具迅速增加。然而,逐渐增加观察旋转插入。这可以的减少归因于有效的削减由于插入旋转速度。图9进步的刀具磨损对不同工具(V120米/分钟,f0.2毫米/转速,d0.1毫米)5.2切屑形态 锯片芯片通常形成于困难转向。为了理解工具旋转的影响切屑形态两组实验进行的。在这两种情况下,相同的工具材料和工具几何。第一组使用自航工具。在第二集,该工具转速受到限制(固定工具)。图10显示了在加工过程中产生的形态芯片涂层硬质合金插入。有趣的是,典型的看到齿芯片是观察到的只有当工具是固定的。当工具是免费的旋转中心,连续芯片成立。图10工具旋转切屑形态的影响这个观察是一致的在95年和270年的切削速度米/分钟。芯片的变化形态由于工具旋转观察在使用切削条件。它应该提到进一步调查正在检查工具旋转对芯片的影响下形态广泛的工艺参数。6.结论 努力把使用的试验研究自航切割工具。每-工具分析了下一次的热特性旋转工具进行了讨论。自航工具显示好耐刀具磨损与固定的工具在相同的切削条件下。更长的刀具寿命获得在加工旋转工具。这个工具穿了,只有侧面磨损。没有证据表明火山口穿的旋转工具。热分析表明,存在一个最佳转速的工具工具的温度是最低。降低刀具温度转速低于对应的工具获得在与自行加工工具。因此,建议延长刀具寿命由于圆形旋转的时间越长,尖端的工具。参考文献1k . Nakayama m . Arai t .神田硬化钢的加工特点,安。CIRP 37(1)(1988)89 - 92。2m.c肖a . Vyas芯片形成加工硬化钢,安。29-32 CIRP 42(1)(1993)。3w . Ko国家行业集团公司,a . Berktold K.F.科赫,车削和磨削,比较精度和表面完整性方面得出的,安。39-43 CIRP 42(1)(1993)。4硕士Elbestawi A.K.斯利瓦斯塔瓦,T.L. El-Wardany,模型芯片形成硬化钢加工期间,安。CIRP 45(1)(1996)71 - 76。5硕士戴维斯,y .周芯片形态、刀具磨损和切削力学在完成硬车削,安。CIRP 45(1)(1996)77 - 82。6H.A. Kishaw，硕士Elbestawi芯片形成的力学和属性在淬火钢的加工,在:国际斗牛士会议的进行,曼彻斯特,英格兰,1997年,第253 - 258页。7H.A. Kishawy,芯片形成和表面完整性的高速加工淬火钢,博士论文,麦克马斯特大学,1998年加拿大安大略省。8m.c肖a . Vyas锯齿状的芯片形成的机制在金属切削,ASNE反式。j . Manuf。科学。Eng。121(1999)163 - 172。9香港,nshoff,c阿伦特r本阿莫切割硬钢铁、安。CIRP 49(2)(2000)547 - 566。10k . Nakayama m . Arai t .神田,加工的特点硬质材料,安。CIRP 37(1)(1988)89 - 92。11陈平、高性能碳化硅whisker-reinforced的加工铝复合自航旋转工具,安。CIRP41(1)(1992)59 - 62。12H.A. Kishawy、点Shawky硕士Elbestawi,评估自行旋转工具在高速铣削:中小企业第四国际加工和磨削美国密歇根州特洛伊会议,2001年,页1 - 11。13E.J.A. Armarego A.J.R.史密斯,基本的研究驱动和自航旋转工具切割processes-I。Theoreti -卡尔调查,Int,j马赫。工具Manuf。34(6)(1994)785 - 802。14E.J.A. Armarego A.J.R.史密斯,基本的研究驱动和自航旋转工具切割processes-II。试验心理调查,Int,j马赫。工具Manuf。34(6)(1994)803 - 815。15P.K. Venuvinod,至此Lau期票Reddy,形成的液膜在旋转加工的芯片工具界面,安。CIRP 32(1)(1983)59 - 64。附录二：Tool wear and chip formation during hard turning with self-propelled rotary toolsH.A. Kishawy , J. WilcoxDepartment of Mechanical Engineering, University of New Brunswick, Fredericton, New Brunswick, Canada, E3B 5A3Received 15 February 2002; received in revised form 7 October 2002; accepted 14 October 2002AbstractThis paper presents a performance assessment of rotary tool during machining hardened steel. The investigation includes an analysis of chip morphology and modes of tool wear. The effect of tool geometry and type of cutting tool material on the tool self-propelled motion are also investigated. Several tool materials were tested for wear resistance including carbide, coated carbide, and ceramics. The self-propelled coated carbide tools showed superior wear resistance. This was demonstrated by evenly distributed flank wear with no evidence of crater wear. The characteristics of temperature generated during machining with the rotary tool are studied. It was shown that reduced tool temperature eliminates the diffusion wear and dominates the abrasion wear. Also, increasing the tool rotational speed shifted the maximum temperature at the chiptool interface towards the cutting edge.2002 Elsevier Science Ltd. All rights reserved.Keywords: Rotary tool; Hard turning; Chip morphology; Tool wear1. IntroductionTurning instead of grinding hardened steel is an economical method to generate a high quality machined surface. During the past few years, there has been significant industrial interest in using dry machining rather than grinding of hardened steel and other difficult-to-machine materials. As an example, dry hard turning of automotive differential side gears is a successful industrial application of this technology. This technology reduces both the machining time and the specific cutting energy, and eliminates the health and environmental hazards associated with coolant usage in conventional machining operations. Although a large volume of literature exists on hard turning 110, the control of the tool wear and its effect on the machined surfaces physical properties represent a major technical challenge. Understanding the chip formation mechanism is essential to achieve a better insight of the machining process fundamentals. Saw toothed chip formation is observed during hard turningand was the subject of interest by several researchers 19.Several models for the chip removal mechanism were presented. Some researchers explained the mechanism of saw toothed chip formation by the adiabatic shear theory. However, other researchers attributed the nature of its morphology to crack propagation. Recent studies using quick stop mechanism confirmed that the saw toothed chip is caused by cyclic crack propagation.The integrity of the surface produced by hard turning is another important subject. Controlling the machining induced residual stresses is an important aspect for wide spread industrial application of this technology 3,7. Hard turning required tool materials that exhibit high wear resistance and an ability to endure the specific cut-ting forces and high temperature generated. In addition, high indentation hardness of at least three times the work piece hardness is essential 10. Since tool wear and plastic deformation of the cutting edge affect the quality and integrity of the machined surface, ceramics and PCBN tools are commonly used for hard turning.rotary tools 13. In addition, there were no attempts in the open literature to model the temperature characteristics in machining with rotary tools.In this paper an attempt to evaluate the cutting performance of rotary tools, made of different materials, during hard turning is presented. In addition a temperature model is presented to describe the heat transfer characteristics and self-cooling feature of this tool.2. Experimental procedureA comprehensive testing procedure was carried out to evaluate the rotary tool performance during hard turning. Dry hard turning tests were performed using a 10 hp CNC lathe. Bars of heat-treated AISI 4340 steel (54-56 HRC) having a 75 or 100 mm diameter, and a 200 mm length, were used. The tests were conducted using car-bide and TIN coated carbide inserts. Cutting speeds of 100, 130 and 270 m/min, with a feed rate of 0.2 mm/rev, and depths of cut of 0.1 and 0.2 mm were used. Circular inserts having a diameter of 25.4 mm were used. The tool wear was measured at four locations, approximately equidistant, along the perimeter of the insert using a tool makers microscope. These values were then averaged to obtain the value of tool wear. Chips were collected for different cutting conditions. These chips were then mounted in epoxy, ground, polished, and etched using a 1.5% Nital solution. The cross-sections of these chips were examined and photographed using an optical microscope. Optical and scanning electron microscopes (SEM) were used to analyze the collected chips and to analyze the modes of tool failure. The tool spinning speed was measured using an optical tachometer.3. Essential features of rotary toolsIn a pioneer work, Shaw et al. 14 presented a study of a lathe-type cutting tool in the form of a disk that rotates around its center. The continuous spinning of the tool around its center allows for the use of the entire circumference of the insert. As a result of tool spinning, a fresh portion of the cutting edge is provided and there-fore a better distribution of tool flank wear over the entire cutting edge is expected. The spinning action of the tool provides a way for carrying the fluid to the tool point at a high cutting speed as in the case of a journal bearing. In addition, this tool offers a self-cooling feature by which the heat is continuously carried away from the cutting zone.Rotary tools are found in two forms: driven or self-propelled. The tool spinning action in the driven tool is supplied by an independent external source. In the self-propelled tool, the spinning action is achieved by the interaction between the tool and the chip. The driven tool can be either orthogonal or oblique to the cutting speed, while the self-propelled tool requires the cutting edge to be oblique to the cutting speed. The rotational speed of the driven tool is independent of the process parameters. In the self-propelled tool the rotational speed is a function of the cutting velocity and the angle between the work piece and the rotary cutting edge velocity vectors. Generally, driven rotary tools provide more control over the rotational speed. Fig. 1 shows a typical machining process set-up when a rotary tool is used and the main motions encountered in rotary tools.During machining with rotary tools, three main motions are defined, namely rotational speed of the work piece (Nwp), rotational speed of the tool (Ntoot), and the feed motion of the tool into the work piece (f). Dueto the rotary motion of the tool the produced chip is dragged along the rake face of the tool. Therefore, the chip velocity is deflected away from its normal direction to the cutting edge in the case of orthogonal machining.Venuvinod and Rubenstein 15 presented a detailed kinematics analysis of chip formation during machining with the rotary tools. Fundamental experimental and theoretical investigations were also presented by Armaregoetal. 16,17. Other researchers studied the formation of fl uid film at the chip tool interface when machining with rotary tools 18. It has been concluded that using a rotary tool is the only way to provide a continuous fluid film at the chip tool interface. Indeed, this paved the way for a near zero friction at the secondary deformation zone. More recently Kishawyetal. 12 employed a self-propelled rotary tool during face milling operation. The performance of the rotary tool was com-pared to that of other conventional tools and showed a superior performance and a prolonged tool life.4. Heat analysis of the rotary toolFig. 2 shows the three main deformation zones in machining. In addition to the primary and secondary deformation zones, the heat generated at the wear land is of particular importance where 80% of the heat flow into the machined surface 3. For simplicity, in this model only the primary and secondary deformation zones are considered where sharp tool is assumed. The heat generated during machining is calculated based on the analysis presented previously 19. R1, R2, and R3 are the partitioning coefficient of the heat generated along the shear plane, chip tool interface, and wear land, respectively. In arriving at a heat model of rotary tools, the following assumptions were employed:1. The chip formation takes place along a thin shear zone and moves as a rigid body along the rake face of the tool.All energy consumed in the shear zone and the friction at the chip tool interface isconverted into heat. The heat generated along the shear zone is along the shear plane.3. The chip leaves the shear zone at a constant temperature equal to the shear plane temperature.4. The heat generated along the friction interface is uniformly distributed.5. Dry machining is employed with a convection heat transfer coefficient of 100 W/(m2 K) and an ambient temperature of 20 C.4.1. Governing equation of the heat modelA control-volume integration approach is applied in developing the discrete equations. In using this approach, the starting point is a differential form of the conservation equations, which are integrated for each control-volume in the domain. The resulting surface fluxes and volume sources for each control-volume are assembled into the final set of algebraic equations. The differential conservation equation describing the movement of energy within the body of the chip and the tool can be described by where the subscripts c and t refer to the chip and the tool, respectively, T the temperature, r the density of the material, k the thermal conductivity, and cp is the specific heat. To account for the effect of heat generation in the primary shear zone, a heat source, Sc, is included. These equations account for both the conduction and the convection of energy in a moving mass, and are cast in the generalized coordinates j (e1, e2, e3) to account for geo-metric differences between the chip and tool.4.2. Chiptool interfaceFig. 3 shows a simplified schematic representation of the rotary tool model. For examining the characteristics of the tool, 1-D and 3-D levels of discretization can be allied 20. The tool is divided into stationary control-volumes (1 n). The computational grid is assumed to be stationary with respect to the heat source location. The mass in the system is modeled moving through the stationary grid. In such a formulation, a steady-state temperature distribution with respect to the grid is possible. The chip is modeled as another control-volume and connected to the rotary tool at the friction interface through a control surface model. The effective thermal resistance, REFF represents the conduction and convection occurring on surfaces normal to the direction of material flow, with the exception of heat conduction from the friction zone. The values WR and Refer to energy trans-port by mass flow and diffusion, respectively, between control-volumes in the direction of material flow. A known velocity field is imposed on control-volume faces in the tool and the chip based on specified process parameters.By choosing the coordinate surface along which the friction face is applied (e2 transformed coordinate), the conservation of surface flux at the interface yields theThe metrics e2x, e2y and e2z are described in Ref. 20 and the term Jacobian of the coordinate transformationJ(e2xe2y e2z) is equal to the area, Act.The heat transfer from the friction zone is controlled by the thermal properties of the chip and the tool material as well as the speed of carrying the heated material away from the friction zone. Since the tool is continuously rotating, part of the heated material is moved away for cooling and returned to the friction zone to potentially acquire more heat.For the subsequent development of the discrete equation set, Eqs. (1) and (2) are discretized using a finite-volume approach 21. The coordinate transformation terms are retained to allow for flexibility in developing equation sets for different geometries. Following integration over a control-volume of dimension e 1, e2 1, and e3 1, and the Gausss theorem is used to convert volume integrals to surface integrals for the convective and diffusive terms. Detailed analysis and validation of the model presented can be found in Ref. 20.5. Results and discussionDuring hard turning with a regular cutting tool the thrust force is always the largest force component due to the fact that chip formation takes place mainly along the tool nose radius. In using a circular inset a larger thrust force component is expected due to the large effective nose radius. Large thrust force is likely to excite chatter; therefore rigidity of machine tool is essential to establish successful hard turning operation. In addition to the needed machine tool rigidity for hard turning, the stiffness of the tool/work piece system is essential for successful machining with rotary tools. Several process parameters were tested to identify the boundaries for successful application of hard turning with the rotary tool. Two depth of cut values of 0.1 and 0.2 mm and feed of 0.2 mm/rev were used and identified as stable parameters for the testing procedure within the given range of cutting speed. Fig. 4 shows the change in the insert rotational speed with the cutting speed when using different tool materials. Monitoring the inserts self-propelled motion showed that its velocity is linearly proportional to the cutting speed. As expected, the type of tool material affects the rotational speed of the tool. The carbide tool exhibits a higher insert speed and the observation was more pronounced at higher values of the cutting speed. Fig. 5 depicts the effect of inclination angle in the relation between tool rotational speed and cutting speed. The observed linear relation was maintained for different values of the inclination angle. At any given cutting speed, an increase in the inclination angle increases the insert rotational speed. The observed behavior of the tool rotational speed can be expressed as tool rotational speed on the temperature distribution on the tool rake face. Increasing the tool rotational speed reduces the peak temperature as well as the bulk tool temperature. However, the reduction of the bulk tool temperature is more pronounced at higher value of the tool rotational speed. In addition, the position of the peak temperature value is shifted toward the cutting edge at higher tool rotational speeds. Reducing the tool temperature enhances the tool resistance to the diffusion wear, as will be seen in the following section. Validation of the model presented and detailed analysis were presented in previous work 20. Only the temperature characteristics that are relevant to the current work are reproduced to support the assessment of tool performance.ewhere Vtoot and V are the tool rotational speed and cut-ting speed, respectively. The constant C is a function of the tool material, the chip tool contact condition (wet or dry), the tool inclination angle, and the tool rake angle.To understand the characteristics of cooling abilities of the rotary tool the effect of tool speed on the heat partitioning between the tool and chip is studied. Fig. 6 shows the effect of the ratio between the tool spinning speed and the cutting speed on the heat partition coefficient, R2. The results indicate that the tool cooling feature is effective up to a certain speed limit. This is seen by the rapid reduction in R2 when the velocity ratio is initially increased. Increasing the tool spinning speed increases the amount of heat carried by the tool up to a certain speed after which further increase in the tool speed reduces the amount of the heat carried away with the tool. Also, as expected, for all speed ratios increasing the cutting speed increases the amount of heat carried away by the chip.The critical speed ratio corresponds to the point at which the time for one revolution of the tool becomes too small to effectively cool the tool prior to returning to the cutting zone. Fig. 7 depicts the influence of the5.1. Tool wearThe SEM images of both carbide (Fig. 8(a) and (b) and coated carbide (Fig. 8(c) and (d) tools after hard turning are shown, respectively. As can be seen in these images, flank wear is the dominant mode of tool failure. The reduction in the peak temperature, as shown in Fig. 7, explains why crater wear is not dominant when using rotary tools. Work piece material deposit was observed only when using coated carbide at a cutting speed of 270 m/min. There was no evidence of crater wear that is normally observed in hard turning. It should be mentioned here that standard coated and uncoated carbide tools are not suitable for hard machining. In addition one would expect a severe crater wear due to the high temperature in hard turning. However, due to the insert rotational motion, a fresh portion of the cutting edge is engaged in cutting. Tool wear distribution over the entire circumference of the tool edge can be seen in these SME images. This is due to the fact that each portion of the circular cutting edge is engaged in cutting for shorter period of time in comparison to a regular square insert. Therefore one would expect an increase in tool life. The increase in tool life would be greater by the ratio of the circumference of the tool to the instantaneous length of cutting edge, provided that localized rate of wear is the same for rotating and non-rotating tools.Fig. 9 shows a comparison of the progress of tool wear for different tool materials. Fixed and rotating tools are used under the same cutting conditions. As can be seen, an improvement in tool performance is achieved when rotary tools are used. Ceramic and uncoated carbide inserts were chipped when fixed tools are used. Although ceramic tools are suitable for hard machining, the tool chipping is attributed to the high pressure produced by a large insert diameter (25.4 mm). Analyzing the progress of coated carbide tools shows that it starts with a rapid increase when using fixed tool. However, gradual increase is observed in case of rotating insert. This can be attributed to the reduction of the effective cutting speed due to the insert rotation.5.2. Chip morphologySaw toothed chips are normally formed during hard turning. In order to understand the effect of tool spinning on the chip morphology two sets of experiments were conducted. In both cases, the same tool material and tool geometry were used. The first set was carried out using the self-propelled tool. In the second set, the tool rotational speed was restricted (fixed tool). Fig. 10 shows the morphology of the chips produced during machining with coated carbide inserts. Interestingly, the typical saw toothed chip is observed only when the tool was fixed. When the tool was free to rotate around its center, a continuous chip was formed. This observation was consistent at cutting speeds of 95 and 270 m/min. The change in the chip morphology due to the tool spinning is observed within the employed cutting conditions. It should be mentioned that further investigation is underway to examine the effect of tool spinning on the chip morphology under a wide range of the process parameters.6. ConclusionsAn experimental investigation of hard turning using self-propelled cutting tools is presented. The tool performance is analyzed and the heat characteristics of rotary tools are discussed. Self-propelled tools showed good resistance to tool wear compared with fixed tools under the same cutting conditions. Longer tool life is obtained during machining with rotary tools. The tool wear was investigated and only flank wear was observed. There was no evidence of crater wear in the rotary tools. The heat analysis showed that there is an optimum rotational speed of the tool at which the tool temperature is minimum. The lower cutting tool temperature corresponds to the tool rotational speed lower than that obtained during machining with self-propelled tool. Therefore, it is suggested that the prolonged tool life is due to the longer cutting edge in circular rotary tool.References1 K. Nakayama, M. Arai, T. Kanda, Machining characteristic of hardened steels, Ann. CIRP 37 (1) (1988) 89 92.2 M.C. Shaw, A. Vyas, Chip formation in machining of hardened steels, Ann. CIRP 42 (1) (1993) 29 32.3 W. Konig, A. Berktold, K.F. Koch, Turning versus grinding, a comparison of surface
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