Development of three-dimensional finite element model to calculate the turning processing parameters in turning operations
Graphical abstract
Introduction
Recently, performing metal turning processes based on the finite element method (FEM) in a computer environment is very significant in terms of both reducing the higher costs brought by experimental method and time efficiency. Considering the metal cutting processes analytically, they are very complicated problems to solve. This complexity is due to the nonlinear nature of the problem. In particular, in some cases, analytical or experimental methods may remain inadequate to determine the temperature distribution in deformation area. In such cases, FEM emerges as an alternative solution. However, correct load and boundary conditions should be identified in order to get good results from the method. Otherwise, undesirable results may occur. Therefore, the friction coefficient and heat transfer coefficient between the components and material models must be entered correctly.
In the literature, there are a few studies to determine the heat transfer in thermal analyses carried out by using FEM. Kang et al. [1] tried to get the right coefficients of convection and contact heat transfer for finite element analysis in the process of hot forming process. Abukhshim et al. [2] showed the essential requirements to model high speed metal processing based on available machining models. Between these requirements, they estimated the thermal formation. In a study carried out by Basiaga et al. [3], they assumed that the heat generated in the cutting process in the unit of time is equal to the total cutting power. Yen et al. [4] used some estimations to calculate the heat transfer in an orthogonal cutting simulation model. Yvonnet et al. [5], in a typical orthogonal cutting process, introduced an innovative approach depending an inverse procedure to identify both the heat flux flow in the tool throughout the rake face and the heat transfer coefficient between the environment and the tool. Değirmenci and Dirikolu [6] on the other hand, tried to determine the coefficient of convective heat transfer which is needed for the finite element thermo mechanic analysis of firing a barrel. Ceretti et al. [7] presented a new procedure to determine the global heat transfer coefficient in orthogonal cutting. Ulutan et al. [8] estimated the three dimensional (3D) heat areas on chips, work piece and tool in the process of machining operations using finite difference method based on numerical model.
As well as these studies, studies about cutting power and energy consumption in the process of machining and the friction coefficient at the tool–chip interface were conducted by some researchers. Kara and Li [9] presented an empirical model to characterize the relationship between energy consumption and process variables for material removal processes. The methodology tested and validated using turning and milling machine tools. Rodrigues and Coelho [10] presented specific cutting energy measurements as a function of the cutting speed and tool cutting edge geometry. Bayoumi et al. [11] investigated to model specific cutting energy, torque and power for milling operations in a closed form mechanistic approach. Özel and Altan [12] presented a methodology to determine simultaneously the flow stress at high deformation rates and temperatures that are encountered in the cutting zone, and the friction at the chip–tool interface. In another study carried out by Özel [13], is to address the friction-modeling problem and its influence upon the finite element (FE) simulations of orthogonal cutting. Özel and Zeren [14] developed a methodology to determine flow stress at the machining regimes and friction characteristics at the tool–chip interface from the results of orthogonal cutting tests.
The turning process has been investigated experimentally and numerically over AISI 1045 materials, which are very frequently used in the industry. In particular, no software has been developed yet that can calculate the heat transfer coefficient, mechanical power and coefficient of friction at the tool and chip interface, which are very important inputs for solution of the turning processes performed in a computer environment based on FEM. In this study, a 3D FEM model has been created by developing software and an analytic model that can calculate the required mechanical power and the friction coefficient at the tool–chip interface as well as heat transfer mechanisms and coefficients between cutting tool, work piece and environment for using in finite element (FE) simulations of the turning processes. A comparison was also made for temperature, main cutting force and thrust force obtained from experimental and numerical analyses.
Section snippets
Material
In this study, AISI 1045 samples are used for turning processes. AISI 1045 material was selected to be used in the study, because it is among the most commonly used materials in the manufacturing industry. WC-quality CCGT120404 K313 Kennametal cutting insert was used as the cutting tool.
Turning processes
Turning processes were performed on a CNC turning lathe that has a capacity of 10 kW by using AISI 1045 samples prepared in dimensions of Ø50 × 100 mm. The chip and clearance angles of the cutting inserts are 10°.
Thermal model of turning process
Turning process is widely used in machining operations. During turning process, the work piece rotates on its own axis while the cutting tool moves forward in the feed direction at a constant speed. Fig. 1 shows a simple turning process.
A number of forces occur for machining in the turning process. These forces are presented in Fig. 2 in accordance with orthogonal cutting theory. The free body diagram of a chip that moves along the shear plane is shown in figure. This free body diagram is
Development of software
Software was developed using Visual Basic 6.0 program as seen Fig. A1. The software calculates the shear energy and the friction energy and the heat transfer coefficients which are essential for machining in the turning simulations. As in analytic equations above, with the change in cutting parameters, the shear energy, the friction energy and the heat transfer coefficients change. As calculating these for every each parameter separately may cause user error, this software was developed. In
Computer aided finite element model
In this study, to calculate the mechanical power, the heat transfer coefficients and the friction coefficient at the tool–chip interface essential for the numeric simulations of metal turning processes, turning processes was performed by finite element based software, DEFORM-3D. 3D model of the cutting tool used in simulations, was created using Reverse Engineering (RE) method. 3D model of the work piece was modeled by using Geometry Primitive of DEFORM-3D software.
Results
At the end of the study, the temperatures of the work piece and cutting tool, the main cutting force and thrust force, values were acquired with experimental and FEM. These values were compared with the results of the FEM simulations as shown in Fig. 9. As result of, the main cutting force and thrust force values decrease with increasing of cutting speed (Fig. 9a and b). In contrast, temperature values of cutting tool and workpiece increase with increasing of cutting speed (Fig. 9c and d). As
Conclusions
In this study, an analytic model and software was developed for calculating mechanical energy, the heat transfer coefficients, and the friction coefficient at the tool–chip interface for machining in numerical simulations of turning processes. Computer aided numerical simulation of the turning process was also performed using DEFORM-3D software. It can be said that the 3D FEM model gives reasonable results with experimental results in view of temperature, main cutting force, thrust force, shear
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