An exploration of friction models for the chip–tool interface using an Arbitrary Lagrangian–Eulerian finite element model

A better understanding of friction modeling is required in order to produce more realistic finite element models of machining processes to support the goals of longer tool life and better surface quality. In this work an attempt has been made to explore and evaluate various friction models used in numerical metal cutting simulations. A finite element model, based on the ALE approach, was developed for orthogonal machining and used to study the conditions prevailing at the chip–tool interface for hardened steel. The ALE approach does not require any chip separation criteria and enables an approximate initial chip shape to smoothly evolve into a reasonable chip shape, while maintaining excellent mesh properties. The results, for a wide range of feed values, were obtained using different friction models and are compared to previously published experimental findings. A reasonable agreement was obtained between the measured and predicted forces with some discrepancy between the cutting and feed force depending on the friction model: if agreement with the cutting forces was good, then the feed force was underestimated; if the feed force agreed well, then the cutting force was overestimated. In all cases the chip thickness was well estimated but the chip–tool contact length was underestimated.     

Numerical simulation for abrasive water jet machining based on ALE algorithm

In dealing with fluid impact and large deformation problems by traditional Lagrange grid, calculation failure often happens due to grid distortion. An abrasive water jet machining model is created to simulate the whole stage by software LS-DYNA from the jet into the nozzle to the workpiece material removal process using ALE (Arbitrary Lagrange–Euler) algorithm. The mesh for the abrasive and water is based on the ALE formulation, while the target mesh applies the Lagrange formulation. The effect of jet penetration is implemented by coupling the grids of ALE and Lagrange. The jet traverse speed is achieved by definition of the movement of ALE grid to reduce the mesh domain. The abrasive constitutive equations are also presented in this paper. The uniform mixture for abrasive and water is achieved by definition of volume percentage of the two materials in the initial ALE elements. Simulation results give the relationships between processing parameters and the cutting depth. The good agreement between simulation results and experimental data verifies the correctness of the simulation.     

FINITE ELEMENT MODELING OF OBLIQUE MACHINING USING AN ARBITRARY LAGRANGIAN–EULERIAN FORMULATION

A 3D finite element model (FEM) of the oblique chip formation process was proposed in Abaqus/Explicit? (v6.5) using an Arbitrary Lagrangian Eulerian (ALE) formulation. The sensitivity of the obtained results to variations of tool geometry angles, tool-chip friction, and cutting conditions was analyzed. Experimental tests were carried out on AISI-4140 steel using uncoated cemented carbide tools under oblique cutting conditions for validation of the FEM results, and a good qualitative agreement between them was obtained. The analysis highlighted the need for a proper identification of the friction on the tool-chip interface for the accurate reproduction of the chip formation process by means of finite element modeling.     

基于不同刀具前角金属直角切削的数值模拟

基于大变形一大应变理论、增量理论以及更新拉格朗日算法,建立二维弹塑性金属直角切削有限元模型;采用几何分离准则(距离准则)判断材料的分离,并自动对畸变网格进行重划分;通过用不同的刀具前角对金属直角切削过程进行数值模拟,分析总结结果,得出直角切削过程中在不同切削前角时切削力、刀具与工件的温度、应力应变的分布情况,为选用刀具形状、提高切削表面质量提供了理论依据。     

A slip-line approach to the machining with rounded-edge tool

In this paper, a new slip-line model approach for modeling the orthogonal cutting process with rounded-edge tools and its associated hodograph are proposed. This model consists of eight regions, which include a dead region in front of the rake face of tool. Dewhurst and Collins’s matrix technique for numerically solving the slip-line problem is employed in the mathematical formulation of the new model. The experimental results show that a small dead region is seen in front of the rake face of tool during cutting with a rounded-edge cutting tool. The unknown slip-line angle pair was solved depending on the force data obtained experimentally and variation of the subregions with cutting edge radius was determined. Cutting force, thrust force, and dead zone grow as cutting edge radius increases in cutting edge-radiused tools.     

Investigations on the effects of friction modeling in finite element simulation of machining

Accurately predicting the physical cutting process variables, e.g. temperature, velocity, strain and stress fields, plays a pivotal role for predictive process engineering for machining processes. These predicted field variables, however, are highly influenced by workpiece constitutive material model (i.e. flow stress), thermo-mechanical properties and contact friction law at the tool-chip-workpiece interfaces. This paper aims to investigate effects of friction modeling at the tool-chip-workpiece interfaces on chip formation process in predicting forces, temperatures and other field variables such as normal stress and shear stress on the tool by using advanced finite element (FE) simulation techniques.For this purpose, two distinct FE models with Arbitrary Lagrangian Eulerian (ALE) fully coupled thermal-stress analyses are employed to study not only the effects of FE modeling with different ALE techniques but also to investigate the influence of limiting shear stress at the tool-chip contact on frictional conditions, which was never done before. A detailed friction modeling at the tool-chip and tool-work interfaces is also carried by coupling sticking and sliding frictions. Experiments and simulations have been performed for machining of AISI 4340 steel using tungsten carbide tooling and the simulation results under increasing limit shear stress have been compared to experiments. The influence of limiting shear stress on the tool-chip contact friction was explored and validity of friction modeling approaches was examined. The results presented in this work not only provide a clear understanding of friction in FEM modeling of machining but also advance the process knowledge in machining.     

基于ALE方法的AZ31B镁合金微铣削有限元仿真

基于任意拉格朗日—欧拉(ALE)法,以AZ31B镁合金为研究对象,采用考虑应变梯度理论修正的Johnson-Cook本构模型作为描述力学性能的材料模型,使用ALE自适应网格技术有效克服仿真过程中网格畸变过大的问题,运用ABAQUS/Explicit对微铣削加工过程进行非线性弹塑性有限元模拟,分析切削过程中的应力应变以及温度分布,探究微细加工过程中的尺度效应和最小切削厚度,为实际加工参数的选择提供参考。     

正交切削高强耐磨铝青铜的有限元分析

采用热力耦合、平面应变、连续带状切屑的切削模型模拟了高强耐磨铝青铜的正交切削加工过程。采用增量步移动刀具的方法,结合有限元分析软件Marc的网格重划分功能,模拟了刀具从初始切入到切削力和切削温度达到稳态的切削加工过程,获得了不同切削深度和切削速度下的切屑形态、温度、应力、应变和应变速率的分布。并将模拟计算得到的切削力和切削温度与试验结果进行了比较,两者具有较好的一致性。     

金属正交切削加工过程的有限元分析

运用大型通用有限元程序对金属正交切削加工过程进行非线性弹塑性有限元模拟分析，得到不同刀具前角在加工过程中对切屑形状、应力分布、应变分布、残余应力及残余变形的影响，得出刀具前角值与剪切角的关系。计算验证了一些实验结果，结论可供工程应用参考。     

A study of acoustic emission generated during orthogonal metal cutting—1: Energy analysis

The application of acoustic emission (AE) sensing in metal cutting process monitoring requires a knowledge of the signal dependence on the variables encountered in the process and an understanding of the source mechanisms responsible for AE generation. In this paper, we study the dependence of the AE signal energy on orthogonal machining variables such as cutting velocity, uncut chip thickness and the chip-tool contact length. Controlled contact length tools were used in orthogonal machining of tubular 6061-T6 aluminum, at varying cutting velocities and feed rates (the feed rate in this case is equal to the uncut chip thickness). The root mean square (RMS) value of the AE signal was found to be linearly proportional to the cutting velocity. Based on this observation, the damping of dislocation motions is proposed as a possible AE source mechanism at the high strain rates encountered in metal cutting. The validity of the dislocation damping based model for AE generation is supported by experimental results and observations.     

涂层刀具前后刀面摩擦下界面应力分析

基于任意拉格朗日欧拉方法(ALE)建立金属正交切削加工的热力耦合的有限元模型,获得不同速度下切削稳定时涂层刀具前后刀面的接触应力、剪应力以及温度场。通过对涂层刀具施加已获得的刀具表面的应力场和温度场,分析了不同速度下摩擦分界点变化的规律以及对涂层基体界面应力的影响。结果表明,随着速度的增大,摩擦分界点逐渐有向前刀面移动的趋势,表明磨损的方式开始从后刀面磨损向前刀面月牙湾磨损转变,这与切削试验结果一致。同时随着速度的增大,涂层界面应力突变更加显著,表明高速条件下涂层更容易破坏,且速度越高,前刀面涂层破坏的几率越大。     

Analytical prediction of cutting forces in orthogonal cutting using unequal division shear-zone model

This paper presents an analytical method based on the unequal division shear-zone model to study the machining predictive theory. The proposed model only requires workpiece material properties and cutting conditions to predict the cutting forces during the orthogonal cutting process. In the shear zone, the material constitutive relationship is described by Johnson?CCook model, and the material characteristics such as strain rate sensitivity, strain hardening, and thermal softening are considered. The chip formation is supposed to occur mainly by shearing within the primary shear zone. The governing equations of chip flow through the primary shear zone are established by introducing a piecewise power law distribution assumption of the shear strain rate. The cutting forces are calculated for different machining conditions and flow stress data. Prediction results were compared with the orthogonal cutting test data from the available literature and found in reasonable agreement. In addition, an analysis of the deviation from experimental data for the proposed model is performed, the effects of cutting parameters and tool geometry were investigated.     

金属切削过程的三维显式动力分析

利用非线性有限元程序LS-DYNA,对低碳钢直角自由切削过程进行三维显式动力分析.模型采用单点积分Lagrange算法的三维显式实体单元solid164,以各向同性应变率相关分段线性塑性材料本构模拟切削层材料,以面-面固连断开接触算法模拟切屑与工件母体的分离过程,以同时考虑滑动摩擦与粘结摩擦的模型模拟切屑与前刀面的接触关系.显式分析结果预测低碳钢切削过程中切削力的大小,切削力分析值与已有实验值相比误差为0.6%;模拟出切屑变形过程中金属晶粒的剪切滑移和流动现象;获得切屑的变形形态及切屑中压力及应力应变的分布情况.     

基于ABAQUS的金属切削过程模拟

基于ABAQUS系统强大的大变形分析功能,对A6061铝合金材料的正交切削过程进行了有限元模拟分析.讨论了切削过程中切削层内部应变场和工件中残余应力的分布,分析了不同参数对切削力、残余应力的影响.模拟结果与切削试验数据相互吻合.     

Numerical study the flow stress in the machining process

In the machining process, the workpiece is under severe plastic deformation with large strain, high strain rate, and temperature. It is necessary to know the flow stress of workpiece material in such condition to better understand the mechanism of chip formation, tool wear and damage, etc. In this study, a Split Hopkinson Pressure Bar (SHPB) with synchronically assembled heating system was employed to study the flow stress similar to the deformation condition in the machining process. A phenomenological constitutive model was proposed by the regression analysis of the experimental results. Furthermore, orthogonal metal cutting processes were carried out by the finite element method (FEM). The cutting force predicted by the FEM showed good agreement with the experimental results, which confirmed that the proposed constitutive model can give an accurate estimate of the flow stress in the machining process.     

Modeling of residual stresses in milling

A model to predict residual stresses produced from milling is presented. It uses process conditions as inputs and predicts surface and subsurface residual stress profiles due to milling. The model formulation incorporates cutting force and cutting temperature predictions and utilizes those parameters to define the thermomechanical loading experienced by the workpiece. Model predictions are compared with published experimental data for both cutting forces and residual stress profiles. The results show that the model performs well in predicting residual stress trends for various milling conditions. Residual stress magnitudes as well as profiles are well predicted with the modeling approach.     

基于ABAQUS/Explicit的AZ31b镁合金微铣削三维仿真研究

传统铣削仿真往往基于宏观建模而忽略了切削刃钝圆半径,对于微切削过程中出现的尺度效应以及最小切削厚度等特有现象无法进行准确描述,与实际加工差距较大。本文利用有限元软件ABQUS/Explicit对AZ31b镁合金材料微铣削过程进行三维变切削厚度仿真,采用ALE自适应技术控制网格畸变过大问题,进而获得了反映尺度效应的微铣削模型,并研究了主轴转速、铣削深度、每齿进给量对于铣削力的相关影响。     

Finite element modeling the influence of edge roundness on the stress and temperature fields induced by high-speed machining

High-speed machining (HSM) may produce parts at high production rates with substantially higher fatigue strengths and increased subsurface micro-hardness and plastic deformation, mostly due to the ploughing of the round cutting tool edge associated with induced stresses, and can have far more superior surface properties than surfaces generated by grinding and polishing. Cutting edge roundness may induce stress and temperature fields on the machined subsurface and influence the finished surface properties, as well as tool life. In this paper, a finite element method (FEM) modeling approach with arbitrary Lagrangian Eulerian (ALE) fully coupled thermal-stress analysis is employed. In order to realistically simulate HSM using edge design tools, an FEM model for orthogonal cutting is designed, and solution techniques such as adaptive meshing and explicit dynamics are performed. A detailed friction modeling at the tool–chip and tool–work interfaces is also carried out. Work material flow around the round edge cutting tool is successfully simulated without implementing a chip separation criterion and without the use of a remeshing scheme. The FEM modeling of the stresses and the resultant surface properties induced by round edge cutting tools is performed for the HSM of AISI 4340 steel. Once FEM simulations are complete for different edge radii and depths of cut, the tool is unloaded and the stresses are relieved. Predicted stress fields are compared with experimentally measured residual stresses obtained from the literature. The results indicate that the round edge design tools influence the stress and temperature fields greatly. An optimization scheme can be developed to identify the most desirable edge design by using the finite element analysis (FEA) scheme presented in this work.     

金属切削加工热弹塑性大变形有限元理论及关键技术研究

基于有限变形理论、虚功原理和更新的拉格朗日公式建立了热弹塑性本构方程，导出了热弹塑性大变形耦合控制方程。对切削加工有限元模拟中的关键技术，如材料模型，工件和切屑的分离、断裂准则，刀具、切屑间的接触摩擦模型以及切削热进行了探讨，针对这些关键技术建立了正交切削加工铝合金7050T7451有限元模型，对切屑形态、切削力、切削温度以及应力场和应变场等物理量的分布进行了有效预测。     

SERRATED CHIP PREDICTION IN FINITE ELEMENT MODELING OF THE CHIP FORMATION PROCESS

A 2D Finite Element Model set up using the Arbitrary Lagrangian Eulerian (A.L.E) formulation proposed in Abaqus/Explicit (v6.4) is employed to predict serrated chip formation during cutting process. No artificial criterion is employed to create the chip or to initiate serrated chip formation. The sensitivity of serrated chip prediction to numerical and process parameters is analyzed in this paper. Experimental tests in orthogonal cutting conditions on machining of AISI-4140 with coated and uncoated cemented-carbide inserts were carried out to validate numerical results. They showed significant influence of cutting speed and rake angle on the serrated chip phenomena. The comparison between numerical and experimental results showed a good qualitative agreement and underlined the outstanding influence of the element dimensions employed in Finite Element Modeling (F.E.M.) tests.