[材料绿色成形技术]异形排气管多向局部加载液力成形工艺

针对某乘用车异形排气管整体制造的难题，开展4系列不锈钢管材包括多向局部加载液力成形新方法的全流程液力成形工艺研究。基于Dynaform有限元模拟软件，建立绕弯成形及液力成形的有限元模型，监测管材壁厚分布的演化规律，进而优化成形工艺参数，开展实验验证。研究结果表明：初始管材直径对液力成形管材壁厚分布影响显著，初始管材直径为54 mm时能很好地满足工艺要求；在纵向加载液力成形阶段，可通过在上模具设计凸筋来实现对管材的局部加载成形，而在横向加载液力成形阶段，内压为48 MPa时可避免管材破裂、折叠等缺陷的产生；此外，局部加载液力成形可导致管材的应力应变状态发生明显改变，变形区管材的壁厚呈现增大趋势，最大减薄率由27.43%降至24.65%，最终零件的最大减薄率为28.05%。实验结果与模拟结果基本吻合，最大偏差值仅为2.89%。

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%.