Study On The Key Technology Of Precision Die Forging For High Strength Al-alloy Parts In Car

Along with the energy and the environment problems increasingly outstanding, and people's increasing requests for safety, reliability and comfortable to car, each big car manufactory makes efforts to improve the car structure design and look for new lighter material to light the car's weight, and continuously improve and adopt new advanced manufacturing technology to raise the quality of product. With a series of good performance, such as the small density, high strength ratio and rigidity ratio, good resistance to impact, corrosion and wear, high recycle etc., the aluminum alloy is thought to be the optimum materials for lighter cars. In recent years, the ratio of the aluminum alloy parts in entire car is incressing constantly, and has a very big development potential to increase.In the paper, the development and existing problems in the plastic forming technology of high strength aluminum alloy at home and abroad were summarized firstly. Based on the research of the precision die forging 7075 Al-alloy multi-layer cylinder parts and silumin SC100-T6 piston tails, a series of works have been done. The flow control forming process of the key parts in car airbags and hot die forging process of piston tails were successfully developed, adopting the plastic forming theory, FEM and experiment together.The structure and features of the key parts of the gas generator in car airbags were analyzed, and consequently two schemes of closed backward extrusion were designed. The judgment terms which the metal reaches the location of the mould cavity at the last were put forward, and the force calculating model and formula of forming force were established. The distributions of the effective stress, effective strain, velocity, and the relation between the load and the stroke were analyzed based on rigid-plastic finite element analysis, and two design schemes were presented. According to the theoretical study and result of FEM, the backward extrusion die was designed and the experiments were done successfully, and the qualified forging parts were carried out finally.Traditionally, die-cast process is applied for silumin Al-alloy parts. Due to continuously enhancement of car's performance, these components are requested to be manufactured using plastic forming process. In order to realize this target, the compression behavior of SC100-T6 aluminum alloy was studied under the circumatance of different deformation temperature and deformation strain ratio using the Gleeble 1500 thermal stress-strain simulator. The constitutive relationship of this kind of Al-alloy was established using the least squares fit method.According to the structure and features of the piston tails part, two preforging billets were designed. The two forming schemes were simulated using thermal coupled rigig-viscoplastic finite element. With analysis and compare of the distributes of the effective stress, effective strain , velocity and temperature in the two simulation process, the conclusion was achieved that the"V"type preforging workpiece was a better design which was advantage of final forming. According to the theoretical study and FEM result, the preforging die, final die, and cutting die were designed, and the experiments have been done successfully. At last, the microstructure of SC100-T6 was analyzed, concluding that the silicon block which separates out in solidifying process of SC100-T6 alloy was broken up in the plastic forming process and scattered inα?Al uniformly. The result shows that plastic forming enhance the general mechanical behavior of the parts.The water burst experiments have been done successfully for the cold precision parts of gas generator in ShanXi Auto Parts Co.Ltd in TaiYuan city, which shows that the technical indexes reach the U.S. national standard. And this achievement has been in the lists of industry development projects of WenZhou Science and Technology Bureau in 2005. The quality of precision forging of piston tails has exceeded Japanese products, and the Japanese company has been signed a multitudinous supply contract with WenLing LiHua instrument factory, which is the client of this achievement. These show that the two achievements have reached the practical level and will produce remarkable technical and economic benefit soon after.