With the development of science and technology and to improve the degree of specialization, many companies are increasing product yield. Manual cutting, cutting methods used semi-automatic cutting can not satisfy their production requirements.

CNC profile cutting machine appears not only can easily cut a variety of shapes of the workpiece, is more suitable for mass production, but also especially suitable for field work and for play, medium and small plants.

The purpose of the mechanical design is starting from the needs of the community; creative design of new machinery has a specific function or improve the mechanical properties of the original, in order to meet people's needs in life and production among.

Through this graduation design issues, the general method of mechanical design mastery, training perfect design ideas, exercise to analyze problems, problem-solving skills, especially methods and techniques to master the overall design and components designed for. Integrated use of mechanical design and principles and other relevant expertise to analyze and solve problems in life and work, so that theory with practice, to further consolidate their acquired knowledge.

Keywords: design； production； profile cutting

1绪论1

1.1 仿形切割机的概况1

1.2仿形切割机的特点与简介1

2仿形切割机设计参数的确定2

2.1总体方案的确定3

2.2.1机械传动部分的计算的选用与选型3

3仿形切割机各个设计计部分的算4

3.1 机架的选材及设计4

3.1.1 机架设计的准则4

3.1.2机架的分类4

3.1.3力的基本类型4

3.2机架的材料及制造方法6

3.2.1立柱的选择7

3.2.2轴的设计8

3.2.3精确的校核该轴的疲劳强度9

3.2.4轴的支撑座的设计10

3.2.5机臂结构的设计10

3.2.6对本设计的机臂进行强度校核12

3.3割炬12

3.3.1管道的设计13

4结论15

参考文献16

致谢17

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基臂A0.jpg

轴承端盖A2.jpg

主轴A1.jpg

装配图A0.jpg

内容简介：: 中国地质大学（北京）长城学院本科毕业设计（论文）任务书学生姓名陈东辉班级机制五班专业机械设计制造及其自动化导师姓名杨运强职称教授单位中国地质大学（北京）工程学院毕业设计（论文）题目仿行数控切割系统设计毕业设计（论文）主要内容和要求：仿形切割机是按照工件的形状制成样板,使割炬按照样板的形状轨迹运行而进行自动切割的一种高效切割工具,由于采用样板仿形,可以很方便地切割各种形状的工件,特别适用于批量生产各种不规则形状和内外同心的各种形状的工件。这种机器特别适宜于野外工作，同时也适宜于大、中、小型工厂使用。请设计一款仿形切割机，主要指标如下：（1）切割厚度：8-60mm；（2）切割速度：50-750mm/min；（3）切割圆直径：600mm（CG2-150A型为直径1800mm）；（4）切割最大正方尺寸：500500mm；（5）切割长方形尺寸：400900mm，450750mm；（6）切割直线长度：1200mm；（7）输入电压：AC220V/50Hz；（8）电动机:ZYT261/A5，DC110V24W,3600r/min.设计该款仿行切割机机械传动部分，完成方案规划，设计计算，图纸绘制。毕业设计（论文）主要参考资料：1 徐铭，琚海，经济型数控雕刻机的控制系统研究J，制造技术与机床，2012（9）：74-81.2 李绍林，低成本数控微雕机控制系统研究开发D.济南：山东大学，20123 王金娥等，机电一体化课程设计指导书M，北京大学出版社，2012.毕业设计（论文）应完成的主要工作：1、了解本课题的研究意义，调研本课题国内外烟具情况及存在的问题；写出调研报告。2、记性课题方案的规划和详细设计，完成全部设计。3、撰写设计计算说明书，要求正文字数不少于5000字，且打印输出并装订、格式一律参照“中国地质大学毕业论文（设计）撰写规范”要求，提交毕业设计Word文档电子版并打印；4、提交AutoCAD图纸电子版并打印图纸。毕业设计（论文）进度安排：序号毕业设计（论文）各阶段内容时间安排备注1查阅资料，准备开题20141215201501042总体方案的分析、比较、论证及确定20150215201503153机械系统设计20150315201504054数控系统设计20150405201504255整理归纳，准备答辩2015042520150510课题信息：课题性质：设计论文课题来源：教学科研生产其它发出任务书日期：指导教师签名：年月日教研室意见：教研室主任签名：年月日学生签名：中国地质大学长城学院本科毕业设计外文文献翻译系别工程技术系学生姓名陈东辉专业机械设计制造及其自动化学号 05211523 指导教师杨运强职称教授 2015年 4 月 20日金属正交切削中的残余应力和压力摘要在平面变形情况下，有限元法用于模仿和分析正交金属切削过程。在剩余应力和张力领域完成制件与对焦。采用了各种建模。沿工具芯片界面摩擦相互作用，建模与改良库仑摩擦法。基于临界应力准则的节点释放技术建立芯片分离模型。在与温度相关的材料属性和工具的范围内，确定是前角和摩擦系数的值。实验发现通过热冷却，取决于这些参数的范围可以增加残余水平应力，倾角和磨擦系数的影响，并且是非线性的。比较预测残余应力与文献中的实验观测结果。关键词：有限限元模拟金属正交切削残余应力1.导言金属正交切削，非线性复杂耦合的热机械进程的加工操作。应变和主剪切带中的高应变率和相应芯片与工具之间的联系，沿辅助剪切区域复杂性的摩擦。除上述以外，工作形成的切屑和工具之间的摩擦引起产热。在金属切削加工的副产品中，出现残余应力与新增压力，会影响已加工表面的完整性，缩短机械组件蠕变疲劳寿命。因此，审慎评估工件残余应力与应变的区域是必要的，针对机械零件在蠕变疲劳载荷条件下过早失效，要对切削过程的进行优化与维护。在过去60 年中，已经进行了大量的金属切削研究工作，Theearliest和 Piispanen 开发了金属切削力学分析模型。这些模型被称为剪角模型，它们都提供剪角、倾角和磨擦系数的实证关系。这些模型还可用于估计部件、应力和平面应变条件下的金属切削加工过程中的能源消耗。在这以后制订了更复杂的剪角模型，以包括各种设计参数的影响。Lee李和 Shaffer 提出一种基于滑移线场理论，其中假定刚性完美塑料材料切削和直剪切平面的剪角模型。kudo通过引入曲线的剪切平面来考虑控制曲线的切片和直线工具之间的接触，修改滑移线模型。帕尔默.奥克斯利和奥克斯利认为是在粘塑性条件和工件硬化及应变率效应。duke等人研究芯片和工具之间的界面摩擦的安置，触发器和分析局部加热的金属切削加工的影响。有限元方法已经广泛的应用于各种金属切削技术的研究。有限元方法的多功能性使得它考虑到工件大变形、应变率效应、工具芯片接触和摩擦，局部加热和温度的影响、不同边界和加载条件，和其他现象遇到的金属切削加工问题。Usui和 Shirakashi 开发的金属切削加工模型是早期有限元模型之一。基于经验数据，他们假定无关变形的材料和工具提示在芯片分离几何的标准。岩田等人提议低速金属切削的有限元模型，其中假定塑料为材料和包括该工具与芯片之间的摩擦的影响（但忽略温度影响）。Strenkowski 和卡罗尔，用基于在工件中有效的塑性应变芯片分离准则，更新了的拉格朗日制订的代码 NIKE2D 有限元。Komvopoulos 和 Erpenbeck 研究的各向同性的应变硬化和 strainrate研究的敏感性视为理想弹塑性材料和材料。有限元分析基于耦合热弹塑性大变形本构模型和雇用芯片分离的应变能量密度标准。田和杨上在正交的金属切削过程，基于最优理论和欧拉参考系统中的一个极限分析定理进行有限元研究。施和杨进行了两个有限元正交金属切削研究实验。通用有限元代码的正交金属切削研究和调查的摩擦影响和工具的形变场数量分布的倾角。已经比较了这些研究与文献中的实验数据和新的测试及其作者所取得的成果。以上讨论的分析与数值提供了很好的金属切削过程的理解与模拟的研究。尤其是，这些研究涉及大应变和应变率、稳态反应、摩擦和局部加热的影响和芯片分离标准等问题。但是，已进行的多计算工作，以了解有关机械加工零件的表面完整性的问题。已知残余应力会使表面完整性产生影响。Henriksen 为了解在加工表面的各种切削条件下的钢和铸铁零件中的残余应力进行一系列的测试。他在报告说残余应力可能高达 689.48 MPa 。他还强调了在韧性材料（如碳钢）。通常拉伸和压缩的脆性材料（铁等）。由于各种原因已归入在工件中的残余应力的原因。刘和拉什观察到工件表面的机械变形诱导残余应力。科诺中南工业大学和 Tonsoff 等人发现残余应力是依赖的切削速度，残余应力对工件材料的硬度有重大影响。表明在金属切削中的摩擦也有助于形成的残余应力。确定了机械加工零件，如评价显微硬度、表面完整性的各种方法 x 射线衍射，和层去除偏转技术。日本早稻田大学柿野，发现残余应力均与加工中的切削力和温度分布有关，提出了早期预测模型的残余应力。在另一种分析模型中，连接残余应力和工件最脆弱部位。施和杨进行了机械加工的工件残余应力分布的联合实验，计算研究。最近，刘和郭用有限元方法来评价在工件的残余应力。他们还观察到进行第二次下调时在切割面上残余应力幅度降低了。虽然现有的资料为机械加工部件的残余应力的研究提供了重要的见解，但是残余应变分布，从每个阶段的切割冷却过程中工具耙角影响的等问题，仍然没有得到充分的理解。为此，这项调查的目的是要了解工具界面摩擦和工具耙角度对形成和分布的残余应力和应变的机械加工零件是如何影响的，并划分切割冷却过程分为四个阶段并调查的每个阶段的用处。有限元方法用于模拟正交金属切削的过程，通过使用 ABAQUS 的通用代码中的几个高级的建模选项，制定了仿真程序。采用最新的拉格朗日制订适合大应变变形。假定平面应变条件。包括电源过压粘塑性本构模型与应变率效应。沿工具芯片界面摩擦接触已遵守修改库仑摩擦定律。在绝热加热条件下，对可塑性和摩擦所致的局部加热升温。基于应力的芯片分离建模标准把工件的芯片分离，被认为是依赖于温度的物质属性。这项研究提供了详细的博览会的不同阶段后切割、应力、应变场演化和形成的残余应力和工件的成品表面附近的金相。2.有限元模型描述图 1 显示了金属正交切削过程，是其中一个连续的芯片正在从工件切削刀具相对于工件匀速移动的原理图。在芯片分离和对待摩擦的交互工具-芯片-工件系统中，定义了三个相关关系。如图 1 所示。接触面1的切割路径，两个接触表面由两组节点（每个面上一个）粘合在一起并用配对。当达到芯片分离标准，工具提示的联系节点距离，使该工具以增量方式推进。作为工具的联系节点对材料成形芯片的内面，将移动到所接触面2的定义区域，和那些形成成品的工件表面将移动到接触面3，如图 1 所示。虽然有接触面2的芯片和工具的前刀面之间的摩擦相互作用，接触面3 只用于维护工具提示新切工件表面的接触。因为相比与平面维度的工件，被刀具切削的材料层的厚度通常是非常薄，声称是平面应变条件。由于其与芯片和工件的高刚度、切割工具作为刚体理想化，建模的弹性材料与人工高杨氏模量（2.1 1015 MPa 在此研究中使用的值）。本节的其余部分描述了一些实施这项研究进行的金属切削模拟计算要点。2.1.摩擦界面沿 toolchip 界面的接触摩擦的影响，通过修改库仑摩擦法（在 ABAQUS 中可用的选项）建立模型，。它指出在一个联系点的相对运动将发生是否应用抗剪应力 t 相切的联系人界面到达下面定义的 tc 的临界摩擦剪应力。（1）其中 p 是接触点处的正常压力、 n 是摩擦系数，t是阈值，剪应力。它指出，当t设置为无穷大时，常规的库仑摩擦法收回。在此研究中，工件材料是 AISI 4340 钢，这是略高于材料的屈服应力在简单剪切。图1 金属切割与相关部分2.2.能量耗散和局部加热在金属切削过程中，在芯片和工件的塑料工作和沿 toolchip 摩擦工作接口局部加热造成的能量耗散。在高速切削，产生的热量已没有时间传导和由此产生的温度上升通常被视为工件自身承受。绝热加热条件下，局部温度升高，Tp，诱导塑料工作在时间间隔 t，可以写为（2） J，相当于热转换因子，c 比热、密度，r 和塑料工作的百分比转化为热能的 hp （通常，85%hp 95%； hp = 90%在此研究中 16,35)。（3）其中 t 是接触点处的剪应力、 s 是滑动速度，J，c 和 r 是界定的智商系数 hf 代表摩擦工作转化为热量，这作为这项研究的 1.0 的小数部分。沿工具芯片接口，产生的总热量的一半（50%）假定走进芯片和另一半到工具。2.3.芯片分离在金属切削加工仿真中，沿切削工具前小区域的应力和变形区域，芯片分离切割平面，满足某些芯片分离的判据。值得注意的是研究表明芯片的几何形状和应力应变场的分布不影响。在本研究中，用于控制芯片分离的临界应力，按照这一标准，在一定距离的工具提示之前到达一个关键的组合芯片分离时发生应力状态。数学上，可以作为下面给定的应力索引（4）沿切割的路径，剪切力和正常组件应力，工具提示指定距离处的应力状态。如图 1 所示是失去压力下纯材料的拉伸和剪切加载条件下切削。芯片分离发生时应力指数 f 达到工具提示前一个元素长度 (在这项研究的约 50.8 m) 的值。对于AISI 4340材料钢，临界压力也就是948 MPa 和 548 MPa （基于 von Mises 屈服的关系）。2.4.材料模型工件是 AISI 4340材料钢在粘塑性本构模型建模。（5）在一定电压下进行适合高应变率应用程序（如高速金属切削）。标准的常量值用于其他物理属性（比热 c = 502.0 J/动量K 和大规模密度 r = 7800 kg/m3)。在金属切削加工过程中产生的巨大热量将改变工件材料的材料特性。因此，依赖于温度的材料属性 (例如弹性常数、初始屈服应力和热膨胀系数）。2.5.有限元网格和边界条件图 2 显示了有限元离散化整个几何模型的工件-芯片-工具系统。芯片层由倾斜的元素组成，它们从工件中分离，在交互的工具切割时，防止过度失真的元素。约 64 的倾角的倾斜元素与切削方向。该芯片切割的起始位置，一层芯片的右端是最初分隔从工件，以便顺利和快速过渡到稳定状态。左端，芯片层三角部分维持以使网格生成更简单和不可望对稳态仿真结果的影响。此网格设计是有效和原拟由 Strenkowski 和卡罗尔，并已经通过其他研究人员的可肯定图 2 所示的有限元网格由 1160个四节点平面应变元素与 1308个节点组成。在预期大变形芯片中，网格的芯片图层是比工件更精细。具体而言，芯片层，其中有 254 m 的高度（切削深度），分为十个二类油层的元素。该工件区域，其中有 2540年 m 的长度和高度 889 m，分为 11 层，但每个有 50 个元素在切削方向。它被发现 50 个元素是使用频谱-评价的有限元模拟，在切割工具到达左结尾之前以达到稳定状态。下方的切割路径元素的顶部五层细是维度 50.8 m 50.8 微米，这些是比工件网格的下半部分中的那些小方形内容与离散化。图2 金属切割网格层工件边界条件的指定方式如下：因为下半部分中的工件材料可望接受很小的变形，工件的底部边界被认为具有零位移。由于工件是足够长，在实现（忽略任何瞬变影响的开头和末尾的切割模拟）稳态解的切割方向，左、右两端的工件边界和切削方向被限制。为了保持耙角度和刚性切割工具的间隙角，鉴于该工具是基长度407 m，高度 762 m 的平行四边形的形状。它由 60 大小相等平面应变元素组成。虽然该工具是在切割过程中与恒速负 x 方向移动，该工具的上边缘是始终限制在 y 方向在整个切割过程中。在此研究中，n 的恒定的切削速度 = 2.54 m/s (为 152.4 米/分钟）。 Residual stresses and strains in orthogonal metal cuttingC. Shet, X. DengDepartment of Mechanical Engineering, University of South Carolina, Columbia, SC 29208, USAReceived 7 August 2002; received in revised form 29 October 2002; accepted 3 January 2003AbstractThe nite element method is used to simulate and analyze the orthogonal metal cutting process under plane strain conditions,with focus on the residual stress and strain elds in the nished workpiece. Various modeling options have been employed. Thefrictional interaction along the tool-chip interface is modeled with a modied Coulomb friction law. Chip separation is modeledby the nodal release technique based on a critical stress criterion. Temperature-dependent material properties and a range of toolrake angle and friction coefcient values are considered. It is found that while thermal cooling increases the residual stress level,the effects of the rake angle and the friction coefcient are nonlinear and depend on the range of these parameters. The predictedresidual stress results compare well with experimental observations available in the literature.2003 Elsevier Science Ltd. All rights reserved.Keywords: Finite element simulation; Orthogonal metal cutting; Residual stress1. Introduction Machiningoperations such as orthogonal metal cut- ting are complex nonlinear and coupled thermomechan- ical processes. The complexities are due to large strain and high strain-rate in the primary shear zone and due to the contact and friction between the chip and tool along the secondary shear zone. In addition to the above, complexities are also caused by local heat generation through the conversion of plastic work in the chip during chip formation and the frictional work between the tool and chip. An undesired byproduct of the metal cutting process is the creation of residual stresses and strains in the freshly cut workpiece, which is known to affect theintegrity of the newly nished surface, including short-ened creep and fatigue lives of the machined componentunder service loads. Hence a careful assessment of theresidual stress and strain elds in the workpiece is neces-sary for optimizing the cutting process and for safe-guarding against the premature failure of machined partsunder creep and fatigue loading conditions.A signicant amount of metal-cutting research workhas been carried out in the past 60 years. Amongst theearliest work were analytical models developed by Mer-chant 1,2 and Piispanen 3 on the mechanics of metalcutting. These models are known as the shear-anglemodels in that they provide empirical relations betweenthe shear angle, the rake angle and the coefcient offriction. These models can also be used to estimateforces, stresses, strains, and energy consumption in themetal cutting process under plane strain conditions.More sophisticated shear-angle models were laterdeveloped to include the effect of various design para-meters. Lee and Shaffer 4 proposed a shear-anglemodel based on the slip-line eld theory, which assumesa rigid-perfectly plastic material behavior and a straightshear plane. Kudo 5 modied the slip-line model byintroducing a curved shear plane to account for the con-trolled contact between curved chip and straight toolface. Palmer and Oxley 6 and Oxley et al. 7 con-sidered viscoplastic conditions and included work hard-ening and strain-rate effects. Doyle et al. 8 studied theeffect of interfacial friction between the chip and thetool. Trigger and Chao 9 analyzed the effect of localheating in metal cutting.Among the various numerical techniques for studyingmetal cutting, the nite element method has been widelyapplied. The versatility of the nite element methodallows it to take into account large deformation, strainrate effect, tool-chip contact and friction, local heating and temperature effect, different boundary and loading conditions, and other phenomena encountered in metal cutting problems. Usui and Shirakashi 10 developedone of the early nite element models for metal cuttingbased on empirical data. They assumed a rate-inde-pendent deformation behavior for the material and a geo-metric criterion for chip separation in front of tool tip.Iwata et al. 11 proposed a FEM model for low-speedmetal cutting, which assumed rigid-plastic behavior forthe material and included the effect of friction betweenthe tool and the chip (but ignored the temperature effect).Strenkowski and Carroll 12 used the general-purposenite element code NIKE2D with the updated Lagrang-ian formulation. They used a chip separation criterionbased on the effective plastic strain in the workpiece.Carroll and Strenkowski 13, and Strenkowski andMoon 14 also developed nite element models basedon the Eulerian formulation. Komvopoulos and Erpen-beck 15 considered elastic-perfectly plastic materialsand materials with isotropic strain hardening and strain-rate sensitivity. The nite element analysis by Lin andLin 16 was based on a coupled thermo-elastic-plasticconstitutive model with large deformation and employeda strain energy density criterion for chip separation.Tyan and Yang 17 conducted a nite element study onthe orthogonal metal cutting process based on a limitanalysis theorem in the context of an optimal theory andthe Eulerian reference system. Shih and Yang 18 andShih 19,20,21 carried out both experimental and niteelement studies on orthogonal metal cutting. Morerecently, Shet and Deng 22 and Shi et al. 23 studiedorthogonal metal cutting using a general-purpose niteelement code and investigated the effect of friction andtool rake angle on the distribution of thermomechanicaleld quantities. These studies have been compared withexperimental data in the literature and with new testresults obtained by their collaborators (see Deng andShet 24 and Zehnder et al. 25).The analytical and numerical studies discussed above have provided a good understanding of the metal cuttingprocess. In particular, these studies have covered issuessuch as large strains and strain rates, the steady-stateresponse, the effect of friction and local heating and thechip separation criteria. It appears, however, that notmuch computational work has been carried out to under-stand issues relevant to the surface integrity ofmachined partsResidual stresses are known to cause poor surface integrity. Henriksen 26 conducted a series of tests to understand residual stresses in the machined surface of steel and cast iron parts under various cutting conditions. He reported that residual stresses could be as high as 689.48 MPa (100 ksi). He also found that residual stresses were usually tensile in ductile materials (e.g. carbon steel) and compressive in brittle materials (e.g. cast iron). Various reasons have been attributed to the cause of residual stresses in the workpiece. Liu and Bar- ash 27 observed that the mechanical deformation of the workpiece surface induced residual stresses. Kono et al. 28 and Tonsoff et al. 29 revealed that residual stresses are dependent on the cutting speed. Matsumoto et al. 30 and Wu and Matsumoto 31 observed that the hardness of the workpiece material has a signicant inuence on the residual stress eld. Konig et al. 32 showed that friction in metal cutting also contributes to the formation of residual stresses. Field et al. 33 reviewed various methods for determining the surface integrity of machined parts, such as micro-hardness evaluation, X-ray diffraction, and layer removal-deec- tion techniques.An early analytical model for predicting residual stresses was proposed by Okushima and Kakino 34, in which residual stresses were related to the cutting force and temperature distribution during machining. In another analytical model (Wu and Matsumoto 31) a connection was made between residual stresses and the hardness of the workpiece. Shih and Yang 18 conduc- ted a combined experimental/computational study of the distribution of residual stresses in a machined workpiece. More recently, Liu and Guo 35 used the nite element method to evaluate residual stresses in a workpiece. They also observed that the magnitude of residual stress reduces when a second cut is made on the cut surface.While existing studies on residual stresses in machined parts have provided important insights, issues such as residual strain distributions, the effect of tool rake angle, the level of contribution from each stage of the cutting-cooling process, are still not well understood. To this end, the objective of this investigation is to understand how the tool-chip interfacial friction and the tool rake angle affect the formation and distribution of residual stresses and strains in machined parts, and div- ide the cutting-cooling process into four stages and investigate the contribution of each stage. The nite element method is used to simulate the orthogonal metal cutting process. A simulation procedure has been developed through the use of several advanced modeling options in the general-purpose code ABAQUS 36. An updated Lagrangian formulation suitable for large strain deformations is employed. Plane strain conditions are assumed. Strain-rate effects are included with an over- stress viscoplastic constitutive model. Frictional contact along the tool-chip interface is made to obey a Modied Coulomb Friction Law. Adiabatic heating conditions are used to account for temperature rise due to local heating induced by plasticity and friction. Chip separation from the workpiece is modeled using a stress-based chip sep- aration criterion. Temperature-dependent material properties are considered. This study provides a detailed exposition of stress and strain eld evolution at different stages after cutting, and of the formation of residual stresses and strains near the nished surface of the work- piece.2. Finite element model description Fig. 1 shows a schematic diagram of the orthogonal metal cutting process, in which a continuous chip is being taken off from the workpiece by a cutting tool that is moving relative to the workpiece with a constant velo- city In order to model chip separation and treat frictional interactions in the tool-chip-workpiece system, three contact pairs are dened, as shown in Fig. 1. Contact Pair 1 denes the cutting path, where the two contact surfaces are represented by two sets of nodes (one on each surface) that are paired and bonded together. When the chip separation criterion is satised, the contact node pair immediately ahead of the tool tip is separated, enabling the tool to advance incrementally. As the tool breaks the contact node pairs, materials forming the chips inner face will move into the region dened by Contact Pair 2, and those forming the nished work-piece surface will move into the region of Contact Pair 3, as illustrated in Fig. 1. While Contact Pair 2 models the frictional interaction between the chip and tools rake face, Contact Pair 3 is used only to maintain tool tip contact with the newly cut surface of the workpiece. Because the thickness of the layer of material being removed by the cutting tool is usually very thin com-pared to the out-of-plane dimension of the workpiece,the plane strain condition is claimed. Due to its highstiffness relative to the chip and workpiece, the cuttingtool is idealized as a rigid body and is modeled as anelastic material with an articially high Youngs modu-lus (a value of 2.1 1015 MPa is used in this study).The rest of this section describes some of the keycomputational elements implemented in this study inorder to carry out the metal cutting simulations.2.1. Interfacial frictionTo model the effect of contact friction along the tool-chip interface, a Modied Coulomb Friction Law (anoption available in ABAQUS) is adopted. It states thatrelative motion at a contact point will occur if theapplied shear stresst tangent to the contact interfacereaches the critical frictional shear stresstc dened below t c min( np,t th) (1) where p is the normal pressure at the contact point, n is the coefcient of friction, and t th is a threshold shear stress value. It is noted that, when t th is set to innity, the conventional Coulomb Friction Law is recovered. In this study, the workpiece material is AISI 4340 steel and t th is taken to be 549 MPa, which is slightly higher than the materials yield stress in simple shear.2.2. Energy dissipation and local heatingIn a metal cutting process local heating arises because of energy dissipation due to plastic work in the chip and workpiece and due to the frictional work along the tool- chip interface. In high-speed cutting, the heat generated has no time for conduction and the resulting temperature rise is usually considered to take place locally. Under the above adiabatic-heating conditions, the local temperature rise, T p, induced by plastic work in a time interval t, can be written as where s e is the effective stress, e p the effective plastic strain rate, J the equivalent heat conversion factor, c the specic heat, r the mass density, and图1 金属切割与相关部分Similarly, the local temperature rise T f caused by friction in a time interval t can be determined from2.3. Chip separation In metal cutting simulations, chip separation along the cutting plane takes place when the stress and defor- mation states in a small region ahead of the tool tip satisfy a certain chip separation criterion. It is worth not- ing that the study by Huang and Black, 37 has shown that the geometry of the chip and the distribution of stress and strain elds are not very much inuenced by the use of a particular chip separation criterion. In the present study, a critical stress criterion is used to govern chip separation. According to this criterion, chip separ- ation occurs when the stress state at a certain distance ahead of the tool tip reaches a critical combination. Mathematically, this critical stress criterion can be writ- ten in terms of a stress index parameter f as given below where s n = max(s2,0)where t and sn are the shear andnormal stress components of the stress state at a specieddistance in front of the tool tip along the cutting path,as shown in Fig. 1, andsf and tf are the failure stressesof the material under pure tensile and shear loading con-ditions, respectively. Chip separation occurs when thestress index f reaches the value of 1.0 at one elementlength (approximately 50.8m in this study) ahead ofthe tool tip. For the material AISI 4340 steel, the failurestresses are taken to besf= 948 MPa and tf = sf / 3=548 MPa (based on the von Mises yielding relationship).2.4. Material modelThe workpiece material considered is AISI 4340 steeland is modeled with a viscoplastic constitutive model ofthe over-stress power law typefors s0where ep is the effective plastic strain rate, sis the current ow stress,s0 is the initial yield stress,and D and m are material parameters (following Komvopoulos and Erpenbeck 15, D = 2.21 105s 1, m =2.87). This rate-dependent power law is highly suitablefor high strain-rate applications (such as high-speedmetal cutting). Standard constant values are used forother physical properties (specic heat c= 502.0 J/kgKand the mass densityr= 7800 kg/m3). The enormousheat generated during the metal cutting process willlocally alter the material properties of the workpiecematerial. Hence, temperature-dependent material proper-ties (e.g. elastic constants, initial yield stress, and ther-mal expansion coefcient) are used (see Shet and Deng22 and shi et al. 23).2.5. Finite element mesh and boundary conditionsFig. 2 shows the nite element discretization of theentire geometry model of the workpiece-chip-tool sys-tem. The chip layer consists of tilted elements to preventthe excessive distortion of the elements when they separ-ate from workpiece and interact with the tools rake face. The angle of inclination of the tilted elements with the cutting direction is about 64 . At the right end o

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