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.
