| Automobile axle housing should have enough strength, enough stiffness and light weight as the safety and functional part of motor vehicle. The sink-bulging craft is a new technology and its advantages of no any welding, higher strength, stiffness and material utilization had been discovered by experimentation. However, at present the rules of material strain-hardening is not clear; the increase in intensity and stiffness has not been analyzed quantificationally or proved systematically, say nothing of supplying the theoretic basis to optimum design.A low-volume pilot production of sinking process, which is a master operation in the hydroforming process for automobile axle housing, is done in this paper. Then the sinked tubes' compression test is carried out in order to find the rule of material hardening occurred in sinking process, which discloses that the yield stress increase by 78.0%, the hardening in first sinking amounts to 86.6% of the total;The strength and vertical bend stiffness of automobile axle housing are calculated and analyzed and the distribution of stress and strain is given when load is 0.75 ton.The relationship between material-harden and fatigue life of hydrobulging axle housing is analyzed quantitatively based on the modified stress-life curve when load is 0.75 ton: the fatigue life increased by 96.9 times when material strength increased to 1.78 times, the failing stress increased by 57.7% with same fatigue life and the carrying power increased by 33.3% when fatigue life is 800,000 times.This paper perfects the sink-bulging craft, provides theoretical foundation for optimum design, and offers sound references for its real production.
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