基于修正滑移线场模型的倒棱刀具切削力预测

基于材料塑性滑移理论与刀具刃前材料流动状态分析,提出了一种考虑倒棱刀具负前角切削过程下的材料滞流区（死区）和预剪区的修正滑移线场模型,并给出了材料流动剪切应力和刃前切削几何参数的迭代求解方法,揭示了倒棱刃口几何形状与滑移线场几何参数之间的变化规律。将此模型应用于倒棱刀具切削过程,得到了适用于倒棱刀具正交切削力的预测方法。采用有限元仿真和切削试验相结合的方法对所提出的滑移线场模型和切削力预测方法分别进行了验证,模型预测结果与仿真结果和试验测量结果对比误差均在10%以内。研究结果为研究倒棱几何形状对工件材料流动特性和刀具切削性能的影响提供了参考。     

A New Slip-Line Field Modeling of Orthogonal Machining with a Rounded-Edge Worn Cutting Tool

In this study, a new slip-line field model and its associated hodograph for orthogonal cutting with a rounded-edge worn cutting tool are developed using Dewhurst and Collins's matrix technique. The new model considers the existence of dead metal zone in front of the rounded-edge worn cutting tool. The ploughing force and friction force occurred due to flank wear land, chip up-curl radius, chip thickness, primary shear zone thickness and length of bottom side of the dead metal zone are obtained by solving the model depending on the experimental resultant force data. The effects of flank wear rate, cutting edge radius, uncut chip thickness, cutting speed and rake angle on these outputs are specified.     

高速硬态切削温度场和切削力动态变化的数值模拟

基于大型有限元软件ABAQUS仿真平台,建立了高速加工的有限元模型。该模型采用Johnson—Cook（JC）模型作为工件材料模型,采用JC破裂模型作为工件材料失效准则,刀-屑接触摩擦采用可自动识别滑动摩擦区和黏结摩擦区的修正库仑定律,并采用任意拉格朗日一欧拉方法实现切屑和工件的自动分离。通过有限元方法对AISI4340（40CrNiMoA）淬硬钢高速直角切削过程进行了数值模拟。通过改变刀具前角的大小,对高速硬态切削过程中刀具的温度场及切削力的动态变化进行了研究,探讨了它们各自的变化规律,研究结果有助于优化高速切削工艺,研究刀具磨损机理和建立高速切削数据库。     

Slip-line solution for orthogonal cutting with a chip breaker and flank wear

A slip-line field model for orthogonal cutting with chip breaker and flank wear has been developed. For a worn tool, this slip-line field includes a primary deformation zone with finite thickness; two secondary shear zones, one along the rake face and the other along the flank face; a predeformation zone; a curled chip; and a flank force system. It is shown that the cutting geometry is completely determined by specifying the rake angle, tool-chip interface friction and the chip breaker constraint. The chip radius of curvature, chip thickness, and the stresses and velocities within the plastic region are readily computed. Grid deformation patterns, calculated with the velocity field determined, demonstrate that the predicted effects of changes in frictional conditions at the tool-chip interface and of the rake angle on chip formation are in accord with experimental observations. The calculated normal stress distribution at the tool-chip interface is in general agreement with previously reported experimental measurements. The model proposed predicts a linear relationship between flank wear and cutting force components. The results also show that non-zero strains occur at and below the machined surface when machining with a worn tool. Severity and depth of deformation below the machined surface increases with increasing flank wear. Forces acting on the chip breaker surface are found to be small and suggest that chip control for automated machining may be feasible with other means.     

有限元数值模拟技术在轴类零件切削中的应用

建立了合理的材料本构、接触模型和摩擦模型,基于合理的切屑分离准则,建立了正交切削过程有限元力学模型,应用DEFORM软件实现了正交切削过程数值模拟。研究了不同转速、不同刀具前角和不同刀刃钝圆半径下的正交切削过程,分析了切削过程中应力、应变和切削力的变化特性,获得了轴类零件加工过程中应力、应变、切削力的变化规律。     

考虑后刀面磨损条件下的正交切削模型分析

在试验研究基础上进行了有后刀面磨损的正交切削模型分析。经过正交切削试验及理论分析,发现后刀面磨损无论是定性上还是定量上都不影响刀具基本切削或剪切过程,即不改变剪切角和摩擦角,但是在磨损区的摩擦力及整个切削力都会增加。充分利用剪切区分析理论,确定了剪切区的切削力、后刀面磨擦力和后刀面磨损量的对应关系,从而建立了在后刀面磨损情况下的切削力模型。     

COMBINED EFFECTS OF FLANK AND CRATER WEAR ON CUTTING FORCE MODELING IN ORTHOGONAL MACHINING—PART II: BAYESIAN APPROACH-BASED MODEL VALIDATION

Flank and crater wear are the primary tool wear patterns during the progressive tool wear in metal cutting. Cutting forces may increase or decrease, depending on the combined contribution from the flank and/or crater wear. A two-dimensional (2D) slip-line field based analytical model has been proposed to model the force contributions from both the flank and crater wear. To validate the proposed force model, the Bayesian linear regression is implemented with credible intervals to evaluate the force model performance in orthogonal cutting of CK45 steels. In this study, the proposed analytical worn tool force model-based predictions fall well within the 75% credible intervals determined by the Bayesian approach, implying a satisfactory modeling capability of the proposed model. Based on the parametric study using the proposed force model, it is found that cutting forces decrease with the increasing crater wear depth but increase with the increasing flank wear length. Also, the predicted cutting forces are affected noticeably by the friction coefficients along the rake and flank faces and the ratio of crater sticking region to sliding region, and better knowledge of such friction coefficients and ratio is expected to further improve worn tool force modeling accuracy. Compared with the finite element approach, the proposed analytical approach is efficient and easy to extend to three-dimensional worn tool cutting configurations.     

Numerical experiments on the influence of material and other variables on plane strain continuous chip formation in metal machining

Finite element simulations of metal machining chip formation have been carried out with model materials that have been given a range of thermal softening and strain hardening behaviours. For materials that are approximately perfectly plastic, predictions of slip-line field theory regarding the dependence of chip/tool normal contact stress distribution on the combination of shear plane angle, friction angle and tool rake angle are reproduced. But it has not proved possible to generate the full range of non-unique fields predicted by slip-line theory. The introduction of strain hardening causes chips to thicken but with deviations at high hardening rates from the behaviour proposed by Oxley. These observations are generally in agreement with previously published physical test data. A study of the effect of increasing the cutting edge radius confirms the important effect of that, particularly on tool thrust forces. By continually comparing the results to expectations from more simple modelling, and asking the question ‘Is that expected?’, a general problem of creating a friction law applicable to both plastically flowing high stress conditions and to more lightly loaded elastic conditions has been recognised and is the subject of continuing work.     

A NEW MECHANISTIC MODEL FOR PREDICTING WORN TOOL CUTTING FORCES

An enhanced model for predicting worn tool cutting forces in metal cutting without the need for any worn tool calibration tests is presented in this paper. The new model utilizes a previously developed slip-line field approach in conjunction with a mechanistic force model to predict the shear flow stress and shear angle for a range of cutting conditions with only a minimal number of sharp tool calibration tests. The shear flow stress and shear angle values are then used as inputs into a worn tool force model to predict the cutting forces due to tool flank wear. Predictions of worn tool cutting forces from the new model have been compared to experimental data from both a steel and a ductile iron workpiece. Ductile iron tests are significant because previous shear flow stress and shear angle models require chip measurements which cannot be made with the chips produced by iron workpieces. Model predictions are also compared to literature data obtained using an aluminum workpiece. An excellent comparison between the model predictions and the experimental data is found for all of the materials considered.     

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.     

Prediction model and simulation of cutting force in turning hard-brittle materials

The removal mechanism of hard-brittle material was studied in this paper. The shear strain and specific shear work of brittle material cutting were analyzed. The cutting force model of hard-brittle material was developed based on the fracture mechanics. Johnson-Cook model was modified and applied to finite element simulation of hard-brittle material cutting. The cutting force of machinable ceramics was predicted by BP neural network. The turning experiments of machinable ceramics were carried out. The influence of processing parameters on cutting force was investigated. The results show that the modified constitutive model well reflects the fracture removal process of brittle material. The simulation results are in well agreement with experimental data and theoretical data. The effects of cutting depth and feed speed on cutting force are larger than those of cutting speed and tool cutting edge angle.     

Application of a comprehensive dynamic cutting force model to orthogonal wave-generating processes

The dynamics of a cutting process are very complex in nature. They involve not only the changes of plastic state in the intensive shear zone of the chip formation process but also the elastic behaviour of work material surrounding the plastic deformation zone, especially in the vicinity of the tool nose region. As an extension to the previous developments in formulating the shear angle oscillation in dynamic cutting (D. W. Wu, Development of dynamic shear angle model for wave-generating processes based on work-hardening slip-line field theory. Int. J. Mech. Sci. 29, 407–424, 1987; D. W. Wu, Governing equations of the shear angle oscillation in dynamic orthogonal cutting. Trans. ASME J. of Engng for Indust. 108, 280, 1986), a comprehensive dynamic cutting force model has been developed from the mechanics of the cutting process by taking into account the equilibrium of forces in the primary and secondary plastic deformation zones and the redistribution of the contact stress inside the workpiece in the vicinity of the tool nose region.The model has been tested through a computer simulation for orthogonal wave-generating processes. By reference to existing experimental evidence, the theoretical predictions show generally good agreement with the test results.     

An experimental investigation of oblique cutting mechanics

In this study, an experimental investigation of oblique cutting process is presented for titanium alloy Ti-6Al-4V, AISI 4340, and Al 7075. Important process parameters such as shear angle, friction angle, shear stress, and chip flow angle are analyzed. Transformation of the data from the orthogonal cutting test results to oblique cutting process is applied, and the results are compared with actual oblique cutting tests. Effects of hone radius on cutting forces and flank contact length are also investigated. It is observed that the shear angle, friction angle, and shear stress in oblique cutting have the same trend with the ones obtained from the orthogonal cutting tests. The transformed oblique force coefficients from orthogonal tests have about 10% discrepancy in the feed and tangential directions. For the chip flow angle, the predictions based on kinematic and force balance results yield better results than Stabler's chip flow law. Finally, it is shown that the method of oblique transformation applied on the orthogonal cutting data yields more accurate results using the predicted chip flow angles compared to the ones obtained by the Stabler's rule.     

基于有限元法分析超精密切削中的摩擦问题

基于更新的拉格朗日公式,建立了热-机械耦合的平面应变大变形正交切削模型.根据此模型,对金刚石车削过程中的摩擦问题进行了仿真研究.对两种摩擦模型仿真所得的切削力与实验数据进行了比较,验证了前刀面上的摩擦状态应是粘结-滑移摩擦同时存在,并研究了刀具摩擦系数各向异性对超精密切削中切屑变形、切削力、剪切角的影响.     

基于ABAQUS的30CrMnSiA合金钢切削仿真研究

基于有限元分析软件ABAQUS开展了30Cr Mn Si A合金钢正交切削有限元仿真研究,分析了该材料切削过程中塑性变形区分布及内应力分布。通过调整刀具前角及主轴转速分别研究了刀具前角和主轴转速对切削力的影响规律,得到刀具最佳前角为13°,临界主轴转速为2000r/min。     

基于AdvantEdge的斜角车削仿真实验确定刀屑摩擦因数的方法

当使用AdvantEdge软件进行切削仿真实验时,刀屑摩擦因数对仿真结果的影响明显,但现有有限元软件未提供刀屑摩擦因数数据库。为建立一种基于AdvantEdge的斜角车削仿真实验的刀屑摩擦因数确定方法,首先提出基于斜角车削的摩擦力计算方法,然后建立AdvantEdge三维斜角车削仿真模型,设定不同切削速度、切削深度、进给量及摩擦因数,通过AdvantEdge仿真正交试验,获得刀屑摩擦因数的经验计算公式。为验证刀屑摩擦因数经验计算公式的正确性,设定不同切削速度和切削深度及进给量的斜角车削正交试验,获得切削力数据,并基于摩擦因数经验计算公式求得对应刀屑摩擦因数。利用求得的摩擦因数数据修改AdvantEdge中刀屑摩擦因数参数,进行残余应力切削仿真实验。仿真实验获得的残余应力与实际切削实验获得的残余应力相比,误差在10%以内,证明提出的刀屑摩擦因数确定方法是正确的。     

切削工艺参数对切屑形状的影响及其有限元分析

以刚塑性有限元理论为基础,采用有限元仿真技术,对金属正交切削过程中切屑成形进行了模拟仿真,得到了不同的刀具前角和摩擦条件对切屑形状的影响规律。对二维切削过程进行加工实验,结果表明切削模拟结果与实际加工情况比较吻合,可以为实际加工提供参数选择的依据。     

基于正交切削的有限元仿真建模技术

利用Deform2D有限元分析软件建立了金属正交切削过程的仿真模型。通过正交切削试验,对仿真结果进行了验证和比较,并分析了摩擦系数对仿真结果中切屑形状、切削力等的影响。     

An explicit finite element model to study the influence of rake angle and friction during orthogonal metal cutting

A fundamental understanding of the tribology aspects of machining processes is essential for increasing the dimensional accuracy and surface integrity of finished products. To this end, the present investigation simulates an orthogonal metal cutting using an explicit finite element code, LS-DYNA. In the simulations, a rigid cutting tool of variable rake angle was moved at different velocities against an aluminum workpiece. A damage material model was utilized for the workpiece to capture the chip separation behavior and the simultaneous breakage of the chip into multiple fragments. The friction factor at the cutting tool–workpiece interface was varied through a contact model to predict cutting forces and dynamic chip formation. Overall, the results showed that the explicit finite element is a powerful tool for simulating metal cutting and discontinuous chip formation. The separation of the chip from the workpiece was accurately predicted. Numerical results found that rake angle and friction factor have a significantly influence on the discontinuous chip formation process, chip morphology, chip size, and cutting forces when compared to the cutting velocity during metal cutting. The model was validated against the experimental and numerical results obtained in the literature, and a good agreement with the current numerical results was found.     

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.