PHENOMENOLOGICAL ANALYSIS OF MATERIAL SIDE FLOW IN HARD TURNING: CAUSES,MODELING, AND ELIMINATION

ABSTRACT

Material side flow causes surface damage that has been observed and partly investigated over a period of several years. This paper presents a phenomenological analysis of material side flow in hard turning. First, material side flow is identified, characterized, and its causes classified. Then, the dependence of the material side flow on different process parameters is analyzed using the results of a comprehensive experimental investigation. Tool nose radius, tool wear, and feed are considered as the primary factors that initiate the occurrence of material side flow in finish turning of hardened steel. A new concept for modeling material side flow is then proposed. This model predicts the minimum chip thickness that allows the workpiece material in the vicinity of cutting to plastically flow at the side of the tool, instead of shearing. The value of the minimum chip thickness affects the size of material side flow on the feed marks. Based on the results obtained from the model, the feed and tool nose radius that eliminates/minimizes material side flow in hard turning are specified.     

FORCES AND TEMPERATURES IN HARD TURNING

In precision machining, due to the recent developments in cutting tools, machine tool structural rigidity and improved CNC controllers, hard turning is an emerging process as an alternative to some of the grinding processes by providing reductions in costs and cycle-times. In industrial environments, hard turning is established for geometry features of parts with low to medium requirements on part quality. Better understanding of cutting forces, stresses and temperature fields, temperature gradients created during the machining are very critical for achieving highest quality products and high productivity in feasible cycle times. To enlarge the capability profile of the hard turning process, this paper introduces prediction models of mechanical and thermal loads during turning of 51CrV4 with hardness of 68 HRC by a CBN tool. The shear flow stress, shear and friction angles are determined from the orthogonal cutting tests. Cutting force coefficients are determined from orthogonal to oblique transformations. Cutting forces, temperature field for the chip and tool are predicted and compared with experimental measurements. The experimental temperature measurements are conducted by the advanced hardware device FIRE-1 (Fiberoptic Ratio Pyrometer).     

PREDICTIVE MODELING OF MACHINING PERFORMANCE IN TURNING OPERATIONS

Recent definitions of machining performance have been based on technological machining performance measures such as cutting forces, tool-life/tool-wear, chip-form/chip breakability, surface roughness, etc. However, modeling work on these performance measures has so far been characterized by isolated treatment of each of these measures. The modeling approach followed by the machining research group at the University of Kentucky aims for an integrated predictive modeling methodology for the major technological machining performance measures. Extensive use of analytical, experimental, numerical, and Al-based approaches is made in the development of these predictive models. This paper presents the outline of this modeling effort and reports the progress made to date in implementing it.     

车削过程中工件的振动力学建模与分析

针对车削过程中工件受轴向移动三维切削力的动态作用,建立车削轴的振动力学模型,其中考虑被加工轴的直径和质量变化的影响。用Matlab软件对振动模型的运动方程进行数值求解,得到在不同车削条件下直径和质量随时间变化的轴的振动响应。计算结果表明,车削加工中工件直径和质量变化对工件的振动响应影响较大,载荷移动速度影响工件的振动幅度,该模型更符合实际车削轴加工过程的情况。     

物流网络设计建模与求解算法研究

研究了制造系统中物流网络设计问题,构建了一个带固定费用的容量受限的网络设计模型,提出了一种求解该问题的基于拉格朗日启发式算法的增强型分枝定界方法。通过大量的试验测试,结果表明该算法能有效地解决大型的具有NP-hard特性的网络设计问题。     

模具曲面抛光时表面去除的建模与试验研究

提出用表面去除廓形来描述模具表面在垂直于抛光轨迹方向的抛光去除量。在假设抛光工具与模具自由曲面的接触服从椭圆赫兹接触的前提下,利用提出的抛光去除系数推导了表面去除廓形的理论方程。仿真和试验结果揭示了抛光表面去除的规律,验证了表面去除廓形的理论模型。     

MODELING TOOL STRESSES AND TEMPERATURE EVALUATION IN TURNING USING FINITE ELEMENT METHOD

The proposed approach to model stresses in cutting tools leading to evaluation of tool temperature distribution, and to eventually model the combined thermo-elastic stress state, is primarily intended for the development of efficient cutting tools rather than process control. The highlights of the approach are the semianalytical modeling of the tool-chip and tool-work contract stresses and friction, incorporation of the role of the secondary shear effects (albeit empirical) and the use of finite element method (FEM)-based estimation of the elastic (2-D) stress field. The contact stress information is used subsequently to model the temperature distribution in the tool. This approach was successfully evaluated in the case of single point turning tools using results from the experimentally measured temperature field in the tool based on the Binder Phase Transformation (BPT) technique. The temperature distribution in the tool for both dry and wet conditions as predicted by the FEM approach agreed quite well, in general, with experimentally obtained isotherms. Deviations in the observed results in the vicinity of the flank region appears to be related to the simplifications used in modeling the contact stresses therein.     

MODELING TOOL STRESSES AND TEMPERATURE EVALUATION IN TURNING USING FINITE ELEMENT METHOD

ABSTRACT

The proposed approach to model stresses in cutting tools leading to evaluation of tool temperature distribution, and to eventually model the combined thermo-elastic stress state, is primarily intended for the development of efficient cutting tools rather than process control. The highlights of the approach are the semianalytical modeling of the tool-chip and tool-work contract stresses and friction, incorporation of the role of the secondary shear effects (albeit empirical) and the use of finite element method (FEM)-based estimation of the elastic (2-D) stress field. The contact stress information is used subsequently to model the temperature distribution in the tool. This approach was successfully evaluated in the case of single point turning tools using results from the experimentally measured temperature field in the tool based on the Binder Phase Transformation (BPT) technique. The temperature distribution in the tool for both dry and wet conditions as predicted by the FEM approach agreed quite well, in general, with experimentally obtained isotherms. Deviations in the observed results in the vicinity of the flank region appears to be related to the simplifications used in modeling the contact stresses therein.     

管道类连续系统可靠性分析与建模

以管道--典型的连续系统为背景,研究以失效概率评估为目的的连续系统的离散化问题.首先,探讨连续系统中"元件"的定义、划分及其物理意义,研究元件的强度分布与元件划分之间的依赖性.继而,考察系统强度分布与由不同的元件划分得出的元件强度分布之间的关系,分析系统失效概率与元件失效概率之间的关系,以及不同尺度的元件划分对系统失效概率模型的影响.最后,建立元件间的失效相关性模型和相应的系统失效概率模型,展示连续系统失效概率与元件数量(或系统尺度)之间的极限关系和典型连续系统失效概率的有界性.     

硬齿面刮削加工的关键技术分析

阐述了硬齿面刮削技术,并综合分析了机床、齿坯、刀具、夹具及切削参数等因素对这种加工方式的影响。     

ANALYSIS AND CONTROL OF THE ACTUATOR ROCKING MODE IN A HARD DISK DRIVE

The recording head in a hard disk drive (HDD) is supported by an actuator assembly which is being controlled by a servo system. Structural resonance modes in the actuator impact the performance of the servo system. The actuator rocking mode has been identified as a major contributor to seek settling and hence, affects the servo stability. This paper presents the effect of actuator structure, skew angle and magnetic flux on the actuator rocking mode. A model to show the effect of the actuator rocking mode on the head motion was constructed to study the interaction with the control plant. The analysis was then verified with experiments. Excellent correlation was established between the experimental result and the theoretical model. Although the rocking mode cannot be eliminated, methods to suppress it are proposed based on the findings.     

软硬交替多层膜应力应变响应的分析

为了对软硬交替多层表面膜在磨粒作用下的应力应变响应、膜层界面剥离和裂纹的产生及扩展的影响等有一个定量和全面的了解,从而为多层表面膜的结构设计提供理论基础,采用大变形弹塑性有限元法对高速钢基体上的ＴｉＮ／Ｔｉ／ＴｉＮ／Ｔｉ…多层膜在法向压痕作用下的力学行为进行了模拟和分析。为了研究膜层数和膜厚的影响,对从单层到１６层的不同膜层体系进行了计算。通过对膜层的变形、最大应力随膜层数的变化、界面切应力分布和表面张应力分布等的分析得出了这些参数的分布及其随载荷和膜层数的变化规律。这些结果将为多层膜的结构优化设计提供定量的依据。     

不同过程参数对搅拌摩擦焊接中材料流动以及残余应力分布的影响

通过有限元法建立了搅拌摩擦焊接的二维模型,并研究了不同工艺参数下搅拌摩擦焊接过程中材料的流动以及残余应力的分布。在搅拌摩擦焊接过程中,切向流动构成了材料流动的主要形式,并且材料流动最为剧烈的区域发生在后退侧。在材料的切向流动中,材料的流动方向不是单一的,可能会形成漩涡。搅拌头平移速度和转速的增加,都能使材料在后退侧的流动变得更为剧烈,但是在材料流动速度较小的区域,参数的改变对材料流动的影响很小。纵向残余应力的最大值始终发生在热影响区的边界,并且纵向残余应力在靠近焊缝中心线的附近一般为正值,而在靠近焊接构件边界的地方,残余应力则表现为负值。纵向残余应力的最大值随着搅拌头平移速度的增加而有所增加,但是搅拌头转速的变化对纵向残余应力的分布影响不大。     

MODELING AND SIMULATION OF WORKPIECE TEMPERATURE IN GRINDING BY FINITE ELEMENT ANALYSIS

The quality of ground workpieces is largely determined by the accuracy of dimensions and geometry, and by the surface finish. The thermal stress to which workpieces are subjected during the grinding process, characterized by the temperatures that develop, plays a major role as far as the economical fulfillment of high-quality requirements is concerned. Too high thermal stresses have a deleterious effect on the workpiece, leading to changes in specific service characteristics. This paper predominantly concerns experiments to determine the temperature when grinding cemented carbides. In this context, the temperature fields developing in the workpiece were examined for different grinding conditions, both on the basis of experiments and calculations by means of finite element analysis (FEA). The simulations show a rise in surface temperatures in the workpiece from the run-in to the run-out phase of the grinding process. The analysis indicates that the-grinding process gives rise to an inho-mogeneous distribution of the material properties of the workpiece, along the grinding direction.     

车削加工磁流变减振装置设计及磁路分析

为有效抑制外圆车削加工中的颤振,研制了基于挤压模式的外圆车刀磁流变减振装置。在结构设计的基础上,根据减振装置的工作特性及电磁学理论,对直接影响磁流变材料特性进而影响减振效果的磁路进行了理论计算;利用有限元软件Ansoft Maxwell对不同材料、结构参数下减振装置内的磁感应强度进行了三维磁场仿真分析,总结了各主要参数对磁感应强度的影响规律,确定了外圆车刀磁流变减振装置的各主要设计参数,并获得了较理想的磁感应强度。研究为磁流变减振装置的参数优化设计奠定了基础。     

滑片式空气压缩机压力和功率的分析与试验

对滑片式空气压缩机工作时的压力状态和功率组成进行分析研究,并通过与应用压力温度传感器和电流表的检测方法得到的试验数据进行比较来验证研究结果。在理论分析中,压力平衡状态被分成6个主要部分,功率组成分成4个主要部分,对每部分的压力和功率过程进行分析,建立理论计算模型,分别求解得到各个部分的参数:为验证理论分析的有效性,对两种不同类型压缩机在正常工作条件下的内部工作状态进行测试;将计算结果与试验数据进行比较后的结果表明,两者有较好的一致性,因此研究结果可用来预测滑片式压缩机的工作状态。     

冲击载荷作用下磁流变阻尼器的建模与分析

以某12．7 mm机枪的磁流变(MR)后坐阻尼器为研究对象,基于Herschel-Bulkley本构模型,建立了该MR后坐阻尼器的轴对称一维层流模型。运用ANSYS软件,对该阻尼器的MR阀进行了磁场有限元分析,求得了环状间隙间MR流体的磁通密度。将MR流体流动模型和MR阀有限元结果相结合,建立了不同磁场作用下阻尼力随活塞速度的变化规律,利用这些规律对该阻尼器的落锤撞击试验和实弹射击试验进行了数值仿真。理论与试验结果的对比指出,在低磁场作用的情况下,理论与试验结果具有较好的一致性。     

NUMERICAL ANALYSIS OF GASEOUS FLOW IN MICRO-CHANNELS

The algorithm of gaseous flow in bi-dimensional micro-channels is set up and the corre sponding program based on micro-flow theory is presented. Gaseous flow in micro-channels is numerically analyzed and the pressure drop along the duct as well as the velocity profile in the micro-channels is obtained. The numerical results agreed well with the experimental results in the references. Moreover, the effects of Kn, σv and Re on the velocity profiles are analyzed. It is found that for Kn>0.001, with increasing Kn number, the slip velocity on the wall boundary increases; the tangential momentum coefficient σv affects the slip velocity greatly. The slip velocity increases with decreasing σv In the slip flow regime and for low Re numbers, the slip velocity is little influenced by the Re number.     

毛细管电渗流微泵的流体动力学的数值仿真

利用电渗流(EOF:Electroosmotic flow)机理制作出的微泵,以其体积小、噪声低、易于控制和结构简单等优点,在药物输送、生化合成及微机电系统(MEMS)中得到了广泛的应用。以实现CPU的温度控制为目标,对电渗流泵的控制及速度、压力间的关系进行了分析。应用无网格法(Meshless/meshfree)对Laplace方程、Poisson-Boltzmann方程、Navier-Stokes方程进行数值求解。数学模型不仅可以仿真几何形状简单的直管内微流体的驱动过程,也可以仿真几何形状复杂、ζ电势较大条件下的微流体的流动情况,为电渗流泵的设计提供了仿真模型。主要讨论通过改变外加垂直电势和ζ电势,实现对电渗流泵的控制以及电渗流泵所能承受的背压问题。     

基于实验分析的机床结构有限元建模及其应用研究

针对一台数控弧齿锥齿轮铣齿机,进行机床整机的有限元动态和静态分析,测量机床静刚度,进行模态实验测试及分析.结合有限元模态分析结果,依据重要的实验模态和机床静刚度修正导轨结合部有限元模型参数.对机床整机结构进行改进,通过有限元分析计算,改进后整机结构动、静刚度明显提高.为确定机床导轨结合部模型参数提供一种研究思路与方法.