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).     

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。     

MODELING OF WHITE AND DARK LAYER FORMATION IN HARD MACHINING OF AISI 52100 BEARING STEEL

In machining of hardened materials, maintaining surface integrity is one of the most critical requirements. Often, the major indicators of surface integrity of machined parts are surface roughness and residual stresses. However, the material microstructure also changes on the surface of machined hardened steels and this must be taken into account for process modeling. Therefore, in order for manufacturers to maximize their gains from utilizing hard finish turning, accurate predictive models for surface integrity are needed, which are capable of predicting both white and dark layer formation as a function of the machining conditions. In this paper, a detailed approach to develop such a finite element (FE) model is presented. In particular, a hardness-based flow stress model was implemented in the FE code and an empirical model was developed for describing the phase transformations that create white and dark layers in AISI 52100 steel. An iterative procedure was utilized for calibrating the proposed empirical model for the microstructural changes associated with white and dark layers in AISI 52100 steel. Finally, the proposed FE model was validated by comparing the predicted results with the experimental evidence found in the published literature.     

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。     

放电成型加工中的单晶硅材料去除率建模分析与实验研究

在半导体材料放电加工可行性的基础上,分析了影响材料去除率的几个主要因素,其中包括空载电压、峰值电流、脉冲宽度以及脉冲间隔。采用中心组合设计实验,考察峰值电流、脉冲宽度、脉冲间隔这3个因素对单晶Si放电加工的材料去除率的影响,建立了单晶Si放电加工的材料去除率的响应模型,进行响应面分析。方差分析结果表明模型具有很好的拟合程度和适应性。采用满意度函数(DFA)确定了单晶Si放电加工的最佳工艺参数,当峰值电流取18.5A、脉冲宽度取358.62μs、脉冲间隔取20μs时,满意度为0.912,此时材料去除率的最优值为76.26 mm~3/min。用所确定的最佳工艺参数在电火花成型机床上重复多次实验,测得P型单晶硅的平均MRR为73.86 mm~3/min。模型预测结果与最佳工艺参数下的实验结果平均相对误差为3.2%,验证实验表明该模型能实现相应的半导体材料放电加工过程的材料去除率预测。     

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.     

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.     

基于遗传算法的超精密切削表面粗糙度预测模型参数辨识及切削用量优化

建立易于分析各切削用量对粗糙度影响关系的表面粗糙度预测模型和最优的切削用量组合,是超精密切削加工技术的不断发展的需要。针对最小二乘法和传统优化方法的不足,提出了将遗传算法用于超精密切削表面粗糙度预测模型的参数辨识,并用于求解最优切削用量,给出了金刚石刀具超精密切削铝合金的表面粗糙度预测数学模型和切削用量优化结果,进行了遗传算法和常规优化算法的比较,结果表明遗传算法较最小二乘法和传统的优化方法更适合于粗糙度预测模型的参数辨识及保证切削用量的最优。     

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.     

垂直管内气固两相流数值模拟计算--颗粒动力学理论方法

基于气固两相流体动力学模型、颗粒动力学理论的颗粒脉动动能模型（ＫＴＧＦ）和气体湍流动能模型（ＳＧＳ）,对气固两相垂直上升流动进行数值计算,模拟计算结果得到了与试验研究所揭示的环—核流动结构。模拟计算与Ｍｉｌｌｅｒ和Ｇｉｄａｓｐｏｗ （１９９２）试验结果进行了比较,颗粒相浓度、速度和颗粒相动力粘性系数分布与试验值基本吻合     

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。     

SURFACE FINISH AND TOOL WEAR CHARACTERIZATION IN HARD TURNING USING A MATHEMATICAL CUTTING TOOL REPRESENTATION

The development of a general 3D model for a corner-radiused, chamfered, edge-honed cutting worn tool is elaborated. The surface of the cutting tool was constructed using one angular scalar specifying location on the corner radius and leading/trailing edges and another non-dimensional scalar for specifying location on the relief, edge-hone, chamfer and tool-top. Then, for given geometric parameters and cutting conditions, the angular extremities of contact on the corner radius and leading/trailing edges was obtained and validated. The kinematic surface finish on the workpiece surface including the Brammertz and sideflow effects was then simulated in typical hard turning. The model was expanded to allow wiper edges and flank wear. A simplified crater wear model was adopted for continuous hard turning to allow virtual cross-sectioning. Accurate estimation of flank and crater wear volume was also enabled. The model results for the fresh tool agreed with well-known trends from 2D modeling. Preliminary results indicate that there exists a geometric basis for higher R_a and R_t for a worn tool. The Brammertz effect simulation, though not in agreement with the data of Knuefermann (2003 Knuefermann , M.M.W. ( 2003 ) Machining surfaces of optical quality by hard turning, School of Applied Sciences, Cranfield University, Cranfield, Bedfordshire, UK . [Google Scholar]) corroborated the modification proposed therein.     

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。     

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.     

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。     

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.