负前角刀具切削加工机理的有限元仿真分析

利用有限元仿真方法对-80°-0°刀具负前角时切削过程进行二维正交切削仿真试验,研究了负前角刀具切削加工过程和切屑产生的必要条件以及不同刀具负前角下切削力分量的主导作用和相互影响规律。结果表明:负前角切削过程中首先产生刀尖点处的集中变形点a;随着切削进行,产生自由端面上的集中变形点b;集中变形点a、b相向扩展,形成集中剪切滑移带,进而产生切屑;负前角切削加工中,存在临界负前角使切削加工不产生切屑;随着负前角绝对值增大,加工所需的切削力也随之急剧增大,越来越难产生切屑。     

304不锈钢超声辅助切削研究

通过霍普金森杆试验确定304不锈钢的本构模型,在ANSYS软件中建立工件和刀具模型,设置切削加工参数和超声参数,进行超声辅助车削仿真试验得到相应切削力,并与理论模型进行比对,确定仿真试验的正确性。分析仿真数据,利用单因素分析法研究超声辅助切削过程中超声振幅、切削速度、切削深度和进给量对切削力的影响。结果表明:在相同切削参数下,相比于传统车削,超声辅助切削304不锈钢可有效降低切削力;随着超声振幅的增大,切削力先变小后变大;超声振幅A=23μm时,切削力最小。在给定的车削加工参数范围内、保证加工效率和工件质量的前提下,超声辅助车削304不锈钢最优车削加工参数为:超声振幅A=23μm,切削速度v_c=21m/min,切削深度a_p=0.1mm,进给量f=0.08mm/r。     

氧化锆陶瓷车削中刀具表面微织构参数对切削性能的影响

利用飞秒激光加工技术在硬质合金车刀后刀面加工出不同宽度和间距的沟槽型表面织构。通过氧化锆陶瓷材料干切削试验,研究织构化刀具磨损机理,分析织构参数对切削力和刀具磨损量的影响规律。实验结果表明：具有合理参数的后刀面织构化刀具能够明显降低切削力,减少刀具磨损。沟槽型织构通过储存切屑、稳定黏结物和对已加工表面上硬质点的二次切削作用,降低刀具后刀面的黏着磨损和磨粒磨损。织构的二次切削作用会导致切削力增大,与织构的减摩作用共同影响切削力。     

刀具角度对316H不锈钢切削力的影响仿真研究

316H不锈钢在切削加工中的切削力较大，其中主切削力对于工件表面质量和加工稳定性起着关键作用。由于刀具角度对切削力有很大的影响，因此建立了仿真加工316H不锈钢切削力的模型，运用正交实验方法仿真研究了刀具角度对主切削力的影响，并通过极差分析和方差分析相结合的方法研究了刀具主要角度与主切削力之间的关系。研究表明，主切削力与刀具前角呈负相关；与刀具刃倾角呈正相关，但是变化幅度很小；随着主偏角增大，呈现先减小后增大的变化趋势。     

弧齿锥齿轮铣齿加工三维应力仿真及分析

根据弧齿锥齿轮轮坯、刀盘及机床调整参数,建立了弧齿锥齿轮的三维加工模型。研究了金属切削加工有限元分析中所涉及的刀屑界面摩擦模型、刀屑接触定义、切屑分离准则等相关关键技术。建立了弧齿锥齿轮铣齿加工过程的有限元模型,通过ABAQUS软件仿真模拟出了不同工艺参数和刀具参数下的铣齿加工过程,得到了切削层形态及应力分布结果。研究结果表明:刀具前角增大,切削层变形减小,主切削力减小;切削速度增大,主切削力减小;刀具的合理前角应取为20°,切削速度应根据实际情况取较大值。同时也为选取和研究弧齿锥齿轮加工工艺参数提供了一套有效的方法。     

304不锈钢切削加工温度分布建模与分析

为了研究304不锈钢在切削加工中的温度分布情况,根据非等分剪切区模型和Waldorf的刀具磨损力模型,分别计算了主剪切面上的剪切力和刀具后刀面磨损带作用下的切削力,通过热源法建立了直角切削中工件加工表面及次表面的温度分布解析模型,预测出了304不锈钢工件在不同切削条件下加工表面和次表面的温度分布情况,预测的结果与有限元软件仿真结果基本一致。建立的模型仅需要输入工件材料属性参数和切削条件就能预测出工件加工表面及次表面的温度分布。     

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。     

刀具材料及角度对7075-T6铝合金切削力的影响仿真

为了提高7075-T6铝合金的切削效率,采用单因素试验法基于ABAQUS软件分析不同刀具材料及刀具几何参数对切削力的影响。试验结果表明：使用YG8刀具切削加工7075-T6铝合金时受到的切削力最小;随着刀具前角的不断增大,切削力显著降低;随着刀具后角的不断增大,水平切削力的下降相对较缓,但垂直切削力显著降低。     

应用经济型数控车床研究不锈钢车削力和加工质量

应用经济型数控车床加工SUS304不锈钢,研究切削过程中刀具各个方向受力以及零件加工表面的粗糙度分布趋势。采用单因素试验方法设计车削力试验,并记录加工过程中的切削力以及对应参数下获得的零件表面粗糙度。研究发现,不锈钢切削时,切削力和粗糙度都随着主轴转速增加而略有增大,随着进给量和切削增加而明显增大,并且切削力和粗糙度之间存在弱负相关关系,两个指标都与材料去除率呈正比例变化。     

微织构刀具织构参数优化仿真研究

高温镍基合金在切削加工过程中,较大的切削力会产生较高的切削温度,造成刀具磨损严重、加工表面质量差等加工难题。在刀具前刀面加工区域,设计微观织构(微织构)可以改善切削加工中刀-屑接触面的摩擦润滑状态,从而改善刀具的切削性能。采用有限元仿真软件对正弦型微织构刀具进行切削镍基合金的仿真实验,通过正交实验研究正弦型微织构刀具的织构刃边距、织构宽度、织构间距、正弦曲线幅值和周期长度5个织构参数对刀具切削性能的影响,并优化了正弦型微织构刀具的织构参数。结果表明:正弦型微织构刀具的主切削力降低程度与织构参数密切相关,且织构参数对主切削力大小的影响程度依次为:织构刃边距织构间距织构宽度正弦曲线幅值周期长度。优化后得到的刀具切削力、切削温度和断屑能力优于优化前无微织构刀具。     

Optimizing the geometric parameters of chamfered edge for rough machining Fe–Cr–Ni stainless steel

Geometry of cutting edge has great influence on performance and reliability of modern precision cutting tools. In this study, two-dimensional finite element model of orthogonal cutting of Fe–Cr–Ni stainless steel has been built to optimize the geometric parameters of chamfered edge. A method to measure the chip curl radius has been proposed. The effect of cutting edge geometric parameters on tool stress and chip curl radius has been analyzed. Then, the chamfered edge parameters have been optimized based on numerical simulation results. It finds that, keeping the equal material removal rate, the optimal geometric parameters of chamfered edge for rough machining Fe–Cr–Ni stainless steel are that the rake angle is from 16° to 17°, and the chamfer length is from 60 to 70 μm. Small (large) rake angle combined with small (large) chamfer length is more reasonable to reduce the tool stress. When the length of land is approximately equal to undeformed chip thickness and the rake angle is larger than 15°, the chip curl radius is minimal. The groove type with large radio of width to depth should be used in the chip breaking based on the optimization results.     

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。     

A numeric investigation of friction behaviors along tool/chip interface in nanometric machining of a single crystal copper structure

The interaction between the tool rake face and the chip is critical to chip morphology, cutting forces, surface quality, and other phenomena in machining. A large body of existing literature on nanometric machining or nano-scratching only considers the overall friction behavior by simply regarding the total force along tool movement direction as the friction force, which is not suitable for describing the intriguing friction phenomena along the tool/chip interface. In this study, the molecular dynamic (MD) simulation is used to model the nanometric machining process of single crystal copper with diamond tools. The effects of three factors, namely, tool rake angle, depth of cut, and tool travel distance, are considered. The simulation results reveal that the normal force and friction force distributions along tool/chip interface for all cases investigated are similarly shaped. It is found that the normal force consistently increases along the entire tool/chip interface when a more negative rake angle tool is used. However, the friction force increases as the rake angle becomes more negative only in the contact area close to the tool tip, and it reverses the trend in the middle of tool/chip interface. Meanwhile, the increase of depth of cut overall increases the normal force along the tool/chip interface, but the friction force does not necessarily increase. Also, the progress of tool into the work material does not change the patterns of normal force, friction force, or friction coefficient distributions to a great extent. More importantly, it is discovered that the traditional sliding model with a constant friction coefficient can be used to approximate the later section of friction distributions. However, no friction model for traditional machining is appropriate to describe the first section of friction distributions obtained from the MD simulation.     

A SLIPLINE FIELD ANALYSIS OF FREE-CHIP ORTHOGONAL MACHINING WITH ADHESION FRICTION AT RAKE FACE

The paper presents slipline field solutions for metal machining assuming adhesion friction at the chip-tool interface. The field is of “indirect” type and is analyzed by the matrix method suggested by Dewhurst, Dewhurst and Collins. The range of validity of the proposed solutions is examined from the consideration of overstressing of rigid vertices in the assumed rigid regions. Rake angle and rake friction are found to be the most important variables that influence the deformation process in machining. Variation of cutting forces, chip thickness ratio, chip curvature and contact length with rake angle and friction parameters is investigated. It is observed that cutting and thrust forces and cutting ratio decrease as rake angle increases but increase as coefficient of friction increases. However, tool-chip contact length decreases as rake angle increases. As a result the average normal and shear stresses on the tool face increases as rake angle increases though, the cutting and thrust forces decrease. Results indicate that friction coefficient cannot be uniquely determined by the rake angle alone, but may have a range of allowable values for a particular value of rake angle. The theoretical results are compared with experimental data available in literature and also with those obtained by the authors from orthogonal cutting tests.     

A SLIPLINE FIELD ANALYSIS OF FREE-CHIP ORTHOGONAL MACHINING WITH ADHESION FRICTION AT RAKE FACE

The paper presents slipline field solutions for metal machining assuming adhesion friction at the chip-tool interface. The field is of “indirect” type and is analyzed by the matrix method suggested by Dewhurst, Dewhurst and Collins. The range of validity of the proposed solutions is examined from the consideration of overstressing of rigid vertices in the assumed rigid regions. Rake angle and rake friction are found to be the most important variables that influence the deformation process in machining. Variation of cutting forces, chip thickness ratio, chip curvature and contact length with rake angle and friction parameters is investigated. It is observed that cutting and thrust forces and cutting ratio decrease as rake angle increases but increase as coefficient of friction increases. However, tool-chip contact length decreases as rake angle increases. As a result the average normal and shear stresses on the tool face increases as rake angle increases though, the cutting and thrust forces decrease. Results indicate that friction coefficient cannot be uniquely determined by the rake angle alone, but may have a range of allowable values for a particular value of rake angle. The theoretical results are compared with experimental data available in literature and also with those obtained by the authors from orthogonal cutting tests.     

带减摩槽刀片在加工不锈钢中的应用

通过分析不锈钢切削加工过程中切屑与刀具前刀面之间的摩擦情况,提出减少切屑与刀具前刀面的接触面积能降低切屑与刀具之间的摩擦阻力,从而减小主切削力。据此,设计了两种带减摩槽的三维槽型刀片,并通过切削试验、切削力检测验证了减摩槽能有效减小主切削力并改善刀片槽型断屑性能的结论。     

Thermoviscoplastic modelling of oblique cutting: forces and chip flow predictions

A modelling of oblique cutting for viscoplastic materials is presented. The thermomechanical properties and the inertia effects are accounted for to describe the material flow in the primary shear zone. At the tool–chip interface, a temperature-dependent friction law is introduced to take account of the extreme conditions of pressure, velocities and temperature encountered during machining. The chip flow angle is calculated by assuming that the friction force is collinear to the chip flow direction on the tool rake face. Due to the temperature dependence of the friction law at the tool–chip interface, the chip flow angle predicted by the model, is affected by the cutting speed, the undeformed chip thickness, the normal rake angle, the edge inclination angle and the thermomechanical behavior of the work material. This dependence and the trends predicted by the present approach are confirmed by experimental observations. Effects of cutting conditions on the cutting forces are also presented and compared to experiments.     

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.     

Thermomechanical approach for the modeling of oblique machining with a single cutting edge

This article aims to predict performances of oblique machining with a single cutting edge. A thermomechanical approach for the modeling of oblique cutting with a single cutting edge is proposed. A good agreement was found between predicted and experimental data. New rules were established to determine experimentally the average friction coefficient and chip flow angle at the rake face. The computation algorithm permits to predict all thermomechanical parameters such as cutting forces, cutting temperatures, and chip geometry. Besides, all predicted oblique machining parameters are mainly controlled by the Po-criterion, which is defined as the ratio of tool–chip contact length to uncut chip thickness.     

An experimental study of edge radius effect on cutting single crystal silicon

According to the hypothesis of ductile machining, brittle materials undergo a transition from brittle to ductile mode once a critical undeformed chip thickness is reached. Below this threshold, the energy required to propagate cracks is believed to be larger than the energy required for plastic deformation, so that plastic deformation is the predominant mechanism of material removal in machining these materials in this mode. An experimental study is conducted using diamond cutting for machining single crystal silicon. Analysis of the machined surfaces under a scanning electron microscope (SEM) and an atomic force microscope (AFM) identifies the brittle region and the ductile region. The study shows that the effect of the cutting edge radius possesses a critical importance in the cutting operation. Experimental results of taper cutting show a substantial difference in surface topography with diamond cutting tools of 0° rake angle and an extreme negative rake angle. Cutting with a diamond cutting tool of 0° rake angle could be in a ductile mode if the undeformed chip thickness is less than a critical value, while a ductile mode cutting using the latter tool could not be found in various undeformed chip thicknesses.