Structural Analysis And Research On Integral Extrusion Forming Of Heavy Truck Driving Axle Housing

With the rapid development of automobile industry, automobile emission pollution is increasingly serious and the lightweight of automobile has a great significance on energysaving and emission-reduction. As important components of heavy truck transmission system, the mechanical strength, stiffness, and fatigue property of drive axle housing and half-shaft sleeve have a large influence on vehicle performance. Therefore, studies on lightweight design and new forming technology of them are helpful to reducing cost, improving production efficiency and product quality.Casting and stamping-welding processes are two methods in manufacturing drive axle housing at present. The axle housing produced by casting has a larger mass which doesn’t meet the requirement of lightweight. Also, the former method can easily produce casting defects and higher rejection rates. The latter also has several drawbacks, such as low material utilization, complex process, high requirements of equipment and welding quality. Welding defects seriously affect the quality of stamping-welding axle housing. Integral extrusion forming method of axle housing is presented in this paper, which regards axle housing ontology and half-shaft sleeves as a whole, to avoid the welding between them, to reduce costs, and to improve the productivity. This method uses circular tube as the billet, whose ends are extruded in advance to form the half-shaft parts. Then, the unshaped circular tube was pushed into a square tube and a pre-manufactured hole was made in the middle of it to form the axle housing ontology by means of mechanical expanding process. The specific research contents and conclusions are as follows:(1) Static analyses were carried out in typical working conditions of integral drive axle housing to get the stress nephogram. The results showed that the strength of axle housing met all working conditions and had a space for optimization. The optimization focused on the thickness of axle housing ontology with half-shaft parts’ thickness unchanged, the optimized thickness of the axle housing is 13 mm.Through modal analysis in a free state of axle housing after optimization, the natural frequency and vibration mode were obtained. The optimized axle housing performed well in all working conditions and didn’t cause any resonance with ground excitation.(2) An extrusion process of half-shaft parts within different temperature section was proposed. The half-shaft is a kind of circular tube part with several steps in different thickness. Considering the local larger thickness at the steps of the half-shaft parts, simple process by reducing the diameter process couldn’t meet the strength requirements. Therefore, the flow of metal can be controlled by the principle of metal’s plasticity changing with different temperature of 500 oC and 700 oC to thicken the local zone of the half-shaft.(3) Undeformed circular tube was pushed into a square tube, and was processed into the axle housing ontology by mechanical expanding. The forming process and stress variation during three processes: expanding without core-die, expanding with core-die and reshaping were explored through numerical simulation. The temperature and axial force have great influence on forming effect, they are 1050 oC, 80 kN in expanding without coredie and 60 kN with core-die process. The local thinning phenomenon was improved by changing the fillet radius of axle housing ontology which changed from R200 mm to R100 mm and local thickened to 19 mm.(4) The desired moulds to form axle housing ontology were designed and processed, then some necessary process tests were carried out in the factory. Finally, the integral driving axle housing were manufactured successfully and the thickness of thinning area was 11 mm at least. In the bench test of the driving axle assembly, the vertical bending strength stiffness met the requirements, and the fatigue life was more than 1.2 million times.