Effect of Die Geometry on Residual Stress at Surface of Drawn Bar

Abstract

Recently, bars for office automation and automobile industry have been required to achieve high fatigue strength. Generally, tensile residual stress is generated at the surface layer of a drawn bar after the drawing process. The tensile residual stress at the surface layer reduces fatigue strength. Therefore, decreasing in tensile residual stress is required. In this study, the effects of approach geometry and bearing length on the residual stress were investigated. Next, the residual stress of the bar drawn using a new die, which had a protrusion in the bearing area, was investigated. Consequently, the effective approach geometry for decreasing tensile residual stress was determined. Tensile residual stress decreased with increasing bearing length. Additionally, it was clarified that the compressive residual stress is generated during drawing with a protrusion die.

Residual Stress Control in Drawn Bar and Wire by Heating-Cooling-Drawing Process

“…However, due to inhomogeneous deformation during this process, tensile residual stress is generated in the surface layer of the bar and compressive residual stress is generated in its center. 1) The residual stresses in the bar or wire cause deformation during secondary processing and heat treatment, and the tensile residual stresses in the surface layer reduces the fatigue strength. Therefore, it is necessary to reduce the residual stress to suppress deformation, and to add compressive residual stress to the surface layer to improve fatigue strength.…”

“…3) Kajino et al clarified the effects of the die approach shape, bearing length, and protrusion into the bearing area on the residual stress. 1) Kuntani et al clarified the effect of the die half angle, bearing length, die transition radius, friction coefficient, and area reduction on the residual stress by finite element analysis (FEA). 4) However, these studies did not achieve a strong compressive residual stress in the surface layer.…”