Design And Optimization Of The Precision Roll Forging And Die Forging On A Front Axle By The Numerical Simulation Method

The front axle is an axle-like part, which is characterized by symmetrical construction, complex shape and variational cross section along the length direction. The cross sections of the spring seats and I-beam are narrow and deep. It is an important component of automobile which carries 70% weight of the vehicle, when the vehicle stops suddenly. So there are strict requirements for strength, stiffness and fatigue life of front axle, due to the heavy load it bears. During the decade, the heavy truck's demand grows greatly with the development of the express way and that of the infrastructure of the China western development. From 2002 to 2009, the production of the heavy truck increases from 417 thousand to 4 million, and the supply is not adequate to the demand due to the limit of the manufactureing capacity of the front axle in heavy truck.The process in which the billet is blanked by roll forging, and then entirely forged to the final dimensions by die forging is suitable for the forming of the front axle, however, its application is limited by the high requirement for the capacity of the equipment, huge investment and long cycle of the manufacturing line construction. In the 1990s, a combined forming process of precision forming roll-forging and die-forging for front axle was proposed in China. In this process, 60% to 80% of the I-beam can be formed in the roll-forging process, which significantly reduces the forming loads of the die-forging and the investment for die-forging equipment. Therefore, the process is suitable to mass production of front-axles. However, the factors such as forward slip, inhomogeneous deformation, width, construction of the groove, etc, have effects on the forming quality of the part in the roll-forging process. To a great extent, the design of forming roll-forging process and the die depends on the experience of the designer, for there is no enough guidance. Therefore, the productive results can not agree with the predicted one, which calls for process debugging to solve the problem. Whereas, the repetitious modification of the roll-forging die results in the long debugging cycle (more than 3 months) and the quality of the final part is conducted with repair welding and polishing. The parts studied in this paper have a high requirement for quality without operation of repair welding and polishing, which has cost 4 years for a company to debug the roll-forging process. The repeated modification for the dies decreased the precision and the dies were ruined. Problems of a front axle of heavy truck in the roll-forging process and die-forging process are studied in this paper. Firstly, based on numerous data in the prophase process debugging, the finite element models of the roll-forging process and die-forging process are conducted in DEFORM, by analysing the effects of the rotational speed of the roll-forging machine, billet temperature and the surface friction coefficient of the dies on the forming quality of the part. Then, the mechanism of defects in prophase process and the effect of the parameters on the forming quality are studied by analysing the simulation results. Thirdly, on the basis of the analysis, the process of the roll-forging is optimized and the constructions of die are redesigned. In addition, a novel die construction of side roll-forging is proposed. The defects are eliminated in the numerical simulation results. The results of the pilot production with the optimized process and the die construction shows that the stability of the roll-forging process is realized and the finial products without defects are approached. In addition, the material utilization rate reaches 88%. This numerical simulation aided design method can reduce the modification of mould as well as the development cycle, increase the accuracy of the forming roll-forging process and mould design and improve the quality of the final products. What's more, it also reduces production cost and increases material utilization rate. Therefore, it can rapidly response to the requirement of the market. The finite element models of the roll-forging process and die-forging process can also be used for the similar products. This study offers knowledge for the forming of front axles.