FEM-SIM-OF-R-STRESSES-IN-MACHINING-TITANIUM.pdf - Finite Element Modeling and Simulation of Residual Stresses Cutting Forces and Temperature in


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Finite Element Modeling and Simulation of Residual Stresses, Cutting Forces and Temperature in Orthogonal Machining of Titanium Alloy. A. Chukwujekwu Okafor * , A. Oteka and S. Aramalla Laboratory for Industrial Automation and Flexible Manufacturing Department of Mechanical and Aerospace Engineering University of Missouri-Rolla, Rolla MO 65409-0050, USA ABSTRACT Structural defects and the stresses to which the structure is exposed affect the life of the structure. These stresses arises from a combination of operational and manufacturing processes, the later hereafter is referred to as residual stresses. However, the correlation of residual stresses with machining parameters is not well understood, especially for high speed machining of titanium. This paper presents the results of finite element modeling, simulation and prediction of residual stresses and cutting forces in orthogonal turning of TI- 6Al-4V titanium work piece used in aerospace manufacturing. Finite element modeling and simulation were performed using Third Wave Systems AdvantEdge software. The effect of speed at constant feed and rake angle were investigated. The residual stress prediction as a function of speed and depth from the workpiece surface are presented. Tool temperature, power, cutting and feed forces are also presented. The results show that residual stresses are predominantly tensile on the surface and predominantly compressive below the surface, and both decrease with increase in cutting speed and depth below the workpiece surface. The main cutting and feed forces increases with length of cut until it reaches a steady state. Tool temperature follows the same pattern as the main cutting force. 1 INTRODUCTION The demand for better surface quality has lead to the study of residual stresses on machined structures. Residual stresses in machined surface result from temperature gradients at the surface and the plastic deformation involved in surface formation, and changes in the microstructure. Residual stresses in a machined surface are vital element in determining surface integrity. Machined structures for the aircraft require high fatigue strength and high resistance to corrosion. The effects of residual stress can be either beneficial or detrimental, depending upon the magnitude, sign or distribution of stress with respect to the load–induced stresses. Studies have shown that surfaces of machined structure has tensile residual stresses which can lead to microcrack formation at the machined surface and reduce the fatigue strength of the components part [1-2]. The presence of residual stress affects stress corrosion cracking of a machined component. Residual stresses can be reduced by reducing plastic deformation, frictional heating, and temperature gradients at the tool-workpiece, which could be done by reducing cutting speed, applying flood cooling, and avoiding the use of dull tools. Excellent fatigue performance is reported when high compressive residual surface stresses are combined with smooth defect free surface. The
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