Hydro-mechanical Forming Process Combined with Multi-directional Local Loading for Special-shaped Exhaust Pipes

In order to solve the manufacturing problems of the integrated exhaust pipes with special shapes in one kind of passenger car, the whole hydro-mechanical forming processes combined with multi-directional local loading of 4 series stainless steel tubes were carried out. Based on Dynaform software, the finite elements models of rotary bending and hydro-mechanical forming were established, and the evolution law of the wall thickness distribution of the tubes was monitored to optimize the forming parameters and develop experimental verification. The results show that the initial tube diameter has a significant effect on the wall thickness distribution of the hydro-mechanical formed tubes, and the initial tube diameter of 54 mm may meet the process requirements. In the longitudinal hydro-mechanical forming stages, the local loading to the tubes may be achieved by the convex ribs of the upper dies. And in the horizontal hydro-mechanical forming stages, the internal pressure of 48 MPa may avoid the occurrence of cracks, material folding and other defects. In addition, the hydro-mechanical forming combined with local loading may significantly change the stress and strain states of the tubes. The wall thickness of the tubes in the deformation zones shows an increasing trend. The maximum thinning rate of the tubes is reduced from 27.43% to 24.65%, while the maximum thinning rate of the final parts is as 28.05%. The simulation and experimental results are basically consistent and the maximum deviation is only 2.89%. © 2020, China Mechanical Engineering Magazine Office. All right reserved.