Research On The Parameter Optimization And Die Wear & Fatigue About Pre-Forging Formation Process Of J11 Steering Knuckle

With the rapid development of automobile industry,the demand of high-precision,high-quality and high-performance forgings exceeds the supply.As a key forging between car-front-axle and car-front-wheel,car steering knuckles play an important role in smooth running and sensitive steering.The complex class of J11steering knuckle is S4,which is relatively difficult to shape up.Meanwhile,the lifespan of hot forging die is an important factor to ensure the surface quality and dimensional accuracy of steering knuckles,the die wear failure and the thermal-mechanical fatigue can directly affect the life-span of hot forging die,and further affect the quality of the steering knuckle.Numerical simulation of steering knuckle pre-forging and the study of die failure factors are of great significance to the improvement of the surface quality of steering knuckle and longer tool life.Firstly,J11 steering knuckle was taken as the research object,the variation regularity（the metal flow rule and the field of stress,strain,temperature）of pre-forging process of steering knuckle was simulated with the finite element software of Deform-3D,it investigated the influence of single factor on the forming process of J11 steering knuckle.The results show that the blank was full of the cavity of the die,and there were no defects such as content-napped and folding.When the upper die running speed was 100mm/s,the lower die initial hardness was 50HRC,the lower die pre-heating temperature was 260℃and the billet initial temperature was1200℃,the pre-forging part has high surface quality due to its uniform stress.Secondly,aiming at the wear failure of J11 steering knuckle,the variation regularity of the wear depth of the lower die was deeply studied,the influence of single factor on the wear depth of the lower die was investigated.In this paper,in order to improved the steering knuckle quality and extend the die life,taked the upper die running speed,lower die pre-heating temperature,billet initial temperature as examining factors,taked the maximum wear depth of the lower die and the steering knuckle forming process（forming load,effective stress）as examining index,SPSS software was used to complete the four factors in three levels with L₉（3⁴）orthogonal test as well as multi-objective optimization.The results show that when the upper die running speed was 100mm/s,the lower die initial hardness was 55HRC,the blank initial temperature was 1400℃,and the lower die pre-heating temperature was 260℃,it can not only improve the surface quality of the steering knuckle,improve the structure performance,but also reduced the wear depth of the die and extend the life of the die.Finally,aiming at the thermal mechanical fatigue failure of J11 steering knuckle,to study the variation regularity of demolding temperature field and the effective stress field,an orthogonal experiment was designed to explore the effect of the uncontrollable factors（rate of strain,friction factor,coefficient of heat transfer）on the maximum effective stress and highest temperature of the die.The results show that the convex horn around the die was easy to produce stress concentration,cause die easily thermal mechanical fatigue,the proposed thermal mechanical fatigue life model provide theoretical reference for the optimization of die design and the estimation of die fatigue life.The forging technology,thermal-force coupled finite element theory,the Archard wear theory,plastic forming CAE technology and die design CAD technology are integrated through this research,it helps to improve the structural performance of steering knuckle and longer tool life,the progeny of the research can provide reference for the selection of technological parameters of the same type steering knuckle.