Finite Element Analysis of the Effect of rake angle on residual Stress

Finite Element Analysis of the Effect of rake angle on residual Stress, Strain and Temperature in Orthogonal Cutting Process

Abstract - The service life of the parts produced by machining and, in particular as regards its fatigue life are not only related to the surface condition of the part, but also to the residual stress profile induced during machining, which was influenced by the geometrical conditions of the cutting tool. For this reason a 2D finite element simulation of orthogonal metal cutting process is made through the explicit finite element code ABAQUS in order to investigate the effects rake angle of cutting tool on temperature, plastic strain fields, chip morphology and residual stress within a workpiece are predicted by using explicit dynamic Arbitrary Lagrangian Eulerian (ALE) technique.

The Johnson-Cook material and damage model are utilized to simulate the plastic behavior and chip formation during the cutting process. The simulation results are compared with experiments measurements, which were obtained from the literature.

Get quality help now

Bella Hamilton

Verified writer

Proficient in: Chemistry

5 (234)

“ Very organized ,I enjoyed and Loved every bit of our professional interaction ”

+84 relevant experts are online

Hire writer

A reasonable agreement was obtained.

Introduction

The Material removal process is one of the most important mechanical parts development processes in the industry. Different types of cutting configurations exist and are applied (orthogonal, oblique, three-dimensional). When machining at high speeds, many parameters are involved and have an influence on the quality of the part to be produced, such as cutting speed, chip thickness, and feed rate, as well as the geometric characteristics of the tool. Many studies and experiments were performed in the early 1940s, and since then, considerable effort has been made in order to develop models capable of correctly predicting the cutting operations.

Analytical models of orthogonal metal cutting have been developed by early researchers [1-4]. In recent years, FEM based numerical models has been extensively employed for cutting process simulations due to their potential to provide predictions in various process variables such as cutting forces, the stresses, strains and temperatures in the workpiece and in the tool, which can help to optimize cutting processes and tool design, reduce costs and increase productivity[5-11].

The main advantage of using numerical models is to limit the number of tests, and therefore the cost of an experimental process. The models allow studying the influence of various conditions and gometries of cutting without having to carry out a large number of tests. for this reason and because of the complexity of 3D modeling, a simplified 2D finite element model based on plane strain assumption was performed in the present study to model orthogonal cutting process of AISI 316L steel based on the Arbitrary Lagrangian Eulerian (ALE) formulation. The numerical simulations are carried out using the finite element software package ABAQUS and investigated to predict the influence of the rake angle on the temperature and stress distributions, chip morphology and residual stress profile in the orthogonal machining process.

Finite Element Modeling

In this paper, as part of cutting modeling, we chose to adopt the Lagrangian-Eulerian Arbitrary formulation (A.L.E.), often used by researchers [7, 8, 9], and rather adapted to the 2D stationary cutting modelization. In addition, this approach minimizes the distortion of the mesh often encountered during the simulation. Fig. 1 shows the geometry and boundary condition of the proposed numerical model. The plane strain condition is assumed for the deformations in the orthogonal cutting process simulation which was developed with Abaqus/Explicit software. The workpiece and a cutting tool are meshed with, respectively, 11256 and 702 isoparametric four-node plan strain thermo-mechanical coupled quadrilateral continuum elements, with reduced integration and automatic hourglass control (CPE4RT). In order to accurately predict the strain and stress fields and chip morphology, a finer mesh are used in the area where the machining will take place in the workpiece and round the tool edge in which high stress gradients occur.

The workpiece material was fixed in x and y directions, the cutting speed of 400 m/min is applied to the tool in the x direction. The depth of cut has been set to 0.2 mm, the rake angle change from -9° to 15°, the clearance angle is 7°, the cutting tool edge radius is 20 ?m and the initial temperature was assumed to be 20 °C. The physical properties of the workpiece (AISI 316L) and the cutting tool materials (Kennametal K313) were obtained from [12] and they are summarized in Table I.

Johnson-Cook Constitutive Model

The Johnson-Cook plasticity model [12] is widely used to describe the material behavior at large strains and high strain rates. The model is expressed by the equivalent plastic flow stress as shown in Eq. (1).

?_e "= " [A+B(?_e^P )^n ][1+C ln((? ?_e^p)/? ?_0 ) ][1-((T-T_r)/(T_m-T_r ))^m ]

where ?_e is the equivalent plastic flow stress, ?_e^P and ? ?_e^p are respectively the equivalent plastic strain and the equivalent plastic strain rate, ? ?_0 is the reference strain rate (1s-1), Tm and Tr are the melting and the room temperature, respectively. A is the yield stress, B is the strain hardening coefficient, n is the strain hardening exponent, C is the strain rate sensitivity factor, m is thermal softening. The Johnson Cook parameters which are adopted from [13] are presented in Table II.

The most realistic description of frictional normal and shear stress at chip/tool interface has been proposed by Zorev friction model [17]. As illustrated in Fig. 2, two zones exist in the contact zones between the chip and the tool rake face, named the sliding region and the sticking region. The sliding zone obeys the Coulomb friction model while in the second so-called "sticking zone" near the tip of the tool where the frictional stress (?f) is assumed to be equal to the shear strength of the machined material (tcrit). The whole contact zone of chip and the tool rake face can be described by the modified Coulomb friction model which has been used in many previous publications in metal cutting simulations [18, 19, 6, and 20] as follow: ?_(f )= ??_n when ??_n