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.     

EFFECT OF CUTTING CONDITIONS ON THE SERRATED CHIP FORMATION IN HIGH-SPEED CUTTING

Titanium alloy Ti6A14V has been widely used in many engineering fields due to its attractive specific strength and corrosion resistance. A deep understanding of the material's machinability is of primary importance. This article investigates the serrated chip formation mechanism of Ti6Al4V alloy under high-speed cutting by finite element analysis. The effect of the cutting conditions on the serrated chip formation is analyzed comprehensively. The study found that when the initial chip thickness becomes small or when the rake angle becomes large, the size of sawtooth decreases and the number of sawtooth increases. The serrated chip morphology is more sensitive to the initial chip thickness. The severe fluctuation of cutting forces is caused by the formation of sawtooth in chipping. To minimize the serrated chipping in high-speed machining, the initial chip thickness is the most important factor to consider.     

基于ABAQUS的高速切削切屑形成过程的有限元模拟

基于有限元分析软件ABAQUS的Johnson-Cook材料模型以及断裂准则模拟高速切削淬硬钢锯齿状切屑形态,并讨论刀具前角和锯齿状切屑形态对切削力的影响.研究表明仿真结果和试验结果是一致的,文中介绍的有限元模拟方法可以准确地模拟并预测高速切削淬硬钢时的切屑形成过程.     

3D FINITE ELEMENT MODELLING OF CHIP FORMATION PROCESS FOR MACHINING INCONEL 718: COMPARISON OF FE SOFTWARE PREDICTIONS

Many efforts have been focused on the development of Finite Element (FE) machining models due to growing interest in solving practical machining problems in a computational environment in industry. Most of the current models are developed under 2D orthogonal plane strain assumptions, or make use of either arbitrary damage criterion or remeshing techniques for obtaining the chip. A complete understanding of the material removal process together with its effects on the machined parts and wear behaviour of the cutting tools requires accurate 3D computational models to analyze the entire physical phenomenon in materials undergoing large elastic-plastic deformations and large temperature changes as well as high strain rates. This work presents a comparison of 3D machining models developed using commercially available FE softwares ABAQUS/Explicit^© and DEFORM?3D Machining. The work material is chosen as Inconel 718, a difficult-to-cut nickel-based alloy material. Computational results of temperature, strain and stress distributions obtained from the FE models for the effect of cutting speed are presented in comparison with results obtained from experimental tests. In addition, modified material model for Inconel 718 with flow softening is compared with the Johnson-Cook model. The predictions of forces and chip formation are improved with the modified material model.     

高速切削30CrNi3MoV淬硬钢切屑形成机理的试验研究

通过30CrNi3MoV淬硬钢的高速切削试验,观察和测量不同切削条件下切屑形态的演变过程、锯齿状切屑形成的临界切削条件、切削力.结果表明,切削速度和刀具前角是影响切屑形态和切削力的主要因素,随着切削速度的提高,在某一临界切削速度下,切屑形态由带状屑转变为锯齿状切屑,随着刀具前角由正前角逐渐变为负前角,临界切削速度明显减小,当锯齿状切屑形成时,切削力大幅度降低.使用金属切削过程中绝热剪切临界切削条件判据对锯齿状切屑形成临界切削速度预测的结果表明,锯齿状切屑形成的根本原因是主剪切区内发生周期性的绝热剪切断裂.     

Characterization of chip formation during machining 1045 steel

A deep understanding of the generation and characterization of chip formation can result for practical advices of chip type controlling in engineering applications. The chip formation is divided into the continuous chip and the serrated one in this study. The characterization of the continuous chip formation is expressed as the chip deformation and that of the serrated chip formation is expressed as the frequency of serration, the degree of segmentation, and the deformation of serrated chip. The chips of 1045 steel under different cutting speeds (100–3,600?m/min) are collected during machining. After inlay and polishing of the collected chips, the chip morphology is observed with VHX-600 ESO digital microscope. It is found that at the cutting speeds of 100–400?m/min, the chip type is continuous, at the cutting speeds of 600–2,200?m/min the chip type is serrated, and at the cutting speeds of 2,500–3,600?m/min the chip type is segmented. The quantitative relations between the characterization parameters of chip formation and the cutting speed are obtained. The chip deformation increases with the cutting speed, and the influence of the cutting speed on the shear strain rate is more sensitive than that on the shear strain during the continuous chip formation. All the characterization parameters including the shear strain rate, the frequency of serration, the degree of segmentation, and the shear strain increase with the cutting speed during the serrated chip formation. The sensitivity of influence of the cutting speed on these parameters is in the following: the shear strain rate, the degree of segmentation, the frequency of serration, and the shear strain.     

MECHANISM OF CHIP FORMATION IN HIGH-SPEED TURNING OF INCONEL 718

The mechanism of serrated chip formation during high-speed turning of Inconel 718 using PCBN cutting tools has been investigated with the aid of scanning electron microscopy and optical microscopy. A conceptual model of chip formation has been developed knowing the chip morphology. It is followed by the analysis of chip segmentation frequency and the chip forms. Further, the chip segment forms and geometry were quantitatively characterized as a function of machining parameters and the cutting edge geometry using statistical methods. The chip morphology has been correlated with the cutting forces, specific shearing energy and the resultant roughness of the machined surfaces.     

高速切削锯齿状切屑的有限元模拟

采用合理的断裂准则对高速硬切削条件下锯齿状切屑的形成进行了有限元模拟 ,并分析了切削过程中的应力场、应变场及温度场 ,探讨了锯齿状切屑的形成机理及影响因素。     

锯齿形切屑的计算机仿真

采用有限元方法仿真了不同切削速度下加工45钢的切屑形成过程。结果表明，较低切削速度下形成连续带状切屑，而高速切削时形成锯齿形切屑。通过对工件和切屑应力及温度分布的分析，探讨了锯齿形切屑的形成机理及影响因素。     

车削Inconel 625锯齿形切屑形成对颤振影响的试验研究

为研究高温合金Inconel 625车削过程中锯齿形切屑的产生对颤振的影响,本文通过有限元软件对车削刀具、机床主轴等部件进行模态仿真,获取对应的模态频率;进行不同切削参数的车削试验,采集加速度信号并进行频域分析以获取其FFT功率谱。通过超景深显微镜观察切屑形态,并计算不同切削参数下的切屑锯齿化频率。对比仿真和试验结果发现:当切屑锯齿化频率接近于车床某部件的主振频率时,产生了较大的颤振峰值,这说明锯齿形切屑的产生会诱导切削颤振发生,对切削过程稳定性产生了不利的影响。     

基于DEFORM-3D的高速车削加工仿真

DEFORM-3D是应用有限元方法(FEM)分析三维复杂加工过程的模拟工具,它不仅鲁棒性好,而且易于使用.借助于该模拟分析环境,能够对切削过程中刀具几何参数、切削条件以及加工过程中的其他因素产生的影响进行研究.应用DEFORM自带的切削仿真模型,模拟高速车削加工中工件及刀具的温度分布、切屑流动、应力、应变和切削力等.模拟结果对减少产品试验、降低开发成本、缩短开发新产品及新工艺的时间等方面都具有重大意义.DEFORM-3D对于研究刀具几何模型、切屑形成以及切削参数控制的刀具制造者和使用者来说,是一个较理想的工具.     

Simulation and analysis of serrated chip formation in cutting process of hardened steel considering ploughing-effect

A realistic finite element model considering the ploughing effect of cutting edge fillet was developed in high speed machining. Taking the hardened tool steel AISI D2 as the object of research, the cutting force and chip morphology were reasonably analyzed and compared with the actual results of cutting experiments, which verified the correctness of the model. Then, based on the model, the formation process of single serrated tooth was analyzed, while the effects of cutting heat and temperature field, material hardness and cutting speed on chip formation were explored. The research results indicate that: (1) The ploughing-effect has a great impact on the feed force, and for hardened tool steel AISI D2, the stagnation angle of 30o is more appropriate. (2) Also, stress concentration appears and shear slipping occurs along the shear plane in the process of serrated chip formation. The strain rate on the shear slipping surface is much greater than other places and the temperature gradient perpendicular to the shear plane is relatively higher. (3) The cutting force becomes larger with increasing the hardness value of workpieces, which causes the chip to more likely to produce serrated chips. (4) The fluctuation of cutting force is more significant as the cutting speed increases, which puts forward higher requirements for the tool and machine tool.     

A reliable method for predicting serrated chip formation in high-speed cutting: analysis and experimental verification

Serrated chip formation influences almost every aspect of a high-speed cutting (HSC) process. This paper aims to develop a reliable method to accurately predict such chip formation processes. To this end, a systematic finite element analysis was carried out and a series of HSC experiments were conducted on a heat treated AISI 1045 steel. It was found that the integrative use of the Johnson–Cook thermal-viscoplastic constitutive equation, Johnson–Cook damage criterion for chip separation, and the modified Zorev’s friction model can precisely predict the serrated chip formation in HSC without artificial assumptions. This advancement has removed the major barrier in the current machining investigations by numerical simulation. The present study also found that the tool rake angle has a significant effect on serrated chip formation. As the rake angle increases, the chip sawtooth degree and cutting forces decrease, but the chip segmentation frequency increases.     

FINITE ELEMENT ANALYSIS OF CHIP FORMATION IN GROOVED TOOL METAL CUTTING

Abstract

This paper presents the simulation of chip formation in grooved tool cutting using DYNA3D, 3D FEM software for dynamic nonlinear analysis that was used to simulate the orthogonal cutting problem. First, a flat-face cutting tool was employed in the simulation to verify the validity of the FEM model. Next, the same simulation techniques were used to study the effects of different groove geometries on the chip formation process in grooved tool cutting. In the first set of grooved tool simulations, the depth of the groove was constant while the width was decreased. In the second set, the width was constant and the depth was increased. By analyzing the chip flow, chip curl, chip thickness, stress and strain in the chip, the effects of different groove widths and depths on the chip formation process were then discussed.     

FEM mesh-dependence in cutting process simulations

The process simulations based on FEM techniques have been investigated for many years, some fundamental problems are still unsolved, e.g. the element size effect on the computational results. In present contribution, orthogonal cutting simulations of AISI4340 steel are considered. The major concerns are accuracy of computational results, influence of element size and effects of damage model in accommodating modeling of failure phenomenon for cutting process simulations. Numerical simulations are verified with the measured values of cutting force by considering certain case of influencing cutting parameters combination taken from literature. Element size is treated to be the most influencing constituent in the cutting process simulations. The chip morphology is related to the adiabatic assumption considered in the process simulation, the feed value and the element size. The simulation results are presented by neglecting temperature effects to show the influence of failure criterion based on plastic displacement of the numerical results. Though the chip morphology and shear band formation are most sensitive to the element size, the cutting force of process simulations is hardly influenced. The formation of saw-tooth chip in the present simulations is the result of adiabatic shear band at the tool tip and propagating towards the chip’s outer surface. The present work confirms that the effect of element size on computational results is reduced significantly if the failure criterion in the process simulation is controlled by a characteristic element length considered from the progressive damage model.     

FINITE ELEMENT ANALYSIS OF CHIP FORMATION IN GROOVED TOOL METAL CUTTING

This paper presents the simulation of chip formation in grooved tool cutting using DYNA3D, 3D FEM software for dynamic nonlinear analysis that was used to simulate the orthogonal cutting problem. First, a flat-face cutting tool was employed in the simulation to verify the validity of the FEM model. Next, the same simulation techniques were used to study the effects of different groove geometries on the chip formation process in grooved tool cutting. In the first set of grooved tool simulations, the depth of the groove was constant while the width was decreased. In the second set, the width was constant and the depth was increased. By analyzing the chip flow, chip curl, chip thickness, stress and strain in the chip, the effects of different groove widths and depths on the chip formation process were then discussed.     

数控车削刀具圆弧半径对切削过程影响的数值分析

数控车削加工中刀具的圆弧半径对切削力,切屑的断屑,切屑的形状,加工表面质量、加工变形以及已切削表面的残余应力的大小,状态,分布有着很大的影响.本文采用有限元分析方法,利用有限元增量理论,建立了二维金属切削仿真模型,分析中采用网格自适应准则,模拟了典型零件车削二维切削过程中切屑的形成,得到了加工后已加工表面的残余应力的大小,状态以及分布状况,对于工程中的实际应用具有重要的意义.     

NUMERICAL SIMULATION OF TITANIUM ALLOY DRY MACHINING WITH A STRAIN SOFTENING CONSTITUTIVE LAW

In this study, the commercial finite element software FORGE2005®, able to solve complex thermo-mechanical problems is used to model titanium alloy dry machining. One of the main machining characteristics of titanium alloys is to produce a special chip morphology named “saw-tooth chip” or serrated chip for a wide range of cutting speeds and feeds. The mechanism of saw-tooth chip formation is still not completely understood. Among the two theories about its formation, this study assumes that chip segmentation is only induced by adiabatic shear band formation and thus no material failure occurs in the primary shear zone. Based on the assumption of material strain softening, a new material law was developed. The aim of this study is to analyze the newly developed model's capacity to correctly simulate the machining process. The model validation is based on the comparison of experimental and simulated results, such as chip formation, global chip morphology, cutting forces and geometrical chip characteristics. A good correlation was found between the experimental and numerical results, especially for cutting speeds generating low tool wear.     

ANALYTICAL CHIP FORMATION MODEL OF MICRO-END-MILLING

A new analytical chip formation model is proposed for micro-end-milling operations. The model calculates an instantaneous uncut chip thickness by considering the combination of exact trochoidal trajectory of the tool tip and tool run-out, while the simplified circular trajectory and the neglected run-out create negligible change in conventional-scale chip formation models. Newton-Raphson iterative method is employed during the calculation to obtain quadratic convergence. The proposed approach allows the calculation of instantaneous uncut chip thickness to be done accurately and rapidly, and the prediction accuracy of this model is also verified by comparing the simulation results to experimental cutting forces.     

Serrated chip formation mechanism analysis for machining of titanium alloy Ti-6Al-4V based on thermal property

Based on the software ABAQUS/Explicit, a finite element (FE) model for orthogonal cutting was established. The FE model was validated by comparing the cutting forces and serrated degree of chips obtained by orthogonal cutting experiments under the cutting speeds 40, 80, 120, and 160 m/min. Based on the developed FE model, the influence of thermal conductivity on the degree of chip segmentation and the adiabatic shear localization were investigated. Furthermore, the plot contours on undeformed shape of cutting simulation was used to investigate the temperature distribution, and the high temperature zone was identified, which can help enhance the understanding of the serrated chip formation. Finally, cracks located in the adjacent segments of chips were observed. The results show that with the increase in thermal conductivity, the degree of adiabatic shear decreases. It can be concluded that the poor thermal conduction performance should be primarily responsible for the formation of serrated chips during machining Ti-6Al-4V alloy. Due to the high temperature at contact surface between cutting tool and workpiece, the increasing of cutting speed facilitates the formation of serrated chips during machining.