보론강을 적용한 차량용 휠 너트의 냉간단조 금형설계에 관한 연구

Abstract

Abstract

Boron steel (51B20) was cold forged using by new designed dies to apply for automotive aluminum wheel nut. The formability and mechanical properties of boron steel were compared with carbon steel(SM45C) which has been used up to date for wheel nut material. The formability was analysed on the dies designed with various types of punch nose by FEM. The metal flow and compressive stress on the dies during cold forging were investigated and compared each other. The forging process with the new designed die showed the improved metal flow as well as a reduced forging load which resulted in the significant increase of the die life. It could be recommended that the carbon steel for automotive wheel nut material could be substituted by the boron steel(51B20). In order to increase the lifetime of cold forging die, insert rings are generally used. Insert ring and shrunk ring of the flange upsetting die were additionally designed for the cold forging of an automotive wheel nut in this study. The Stress distribution occurring in the die during forging was simulated by using a commercial finite element analyzing program. The effects of the fitting interference and inclined angle of the insert ring have been investigated on the compressive stress of the die inside. The simulated data were compared with the real lifetime of the forging die. The maximum compressive stress acting on the edge of a forging die should have the most effective influence on the die lifetime, from which could develop the die design with the longest lifetime. The design of the most optimal forging die with the longest lifetime make it possible by analyzing the maximum inner pressure and principal stress between shrink ring and insert ring.