(1. 南华大学 机械工程学院，衡阳 421001；
2. 湖南大学 汽车车身先进设计制造国家重点实验室，长沙 410082)
摘 要: 以汽车防撞梁为典型研究对象，开展型材分流模挤压试模出现的内加强筋壁厚减薄和开裂等缺陷产生机理研究，并提出挤压出模口横截面流速均匀性的精确控制方法。首先，基于任意拉格朗日-欧拉混合算法建立了型材分流模挤压稳态有限元模型。然后，基于材料流速均方差和焊合压力评价揭示型材挤压壁厚减薄和焊缝开裂的产生原因。最后，为了实现对出模口型材横截面流速的均匀控制，提出了“优化分流孔/引流槽、增添阻流块、基于Kriging近似模型和多岛遗传算法优化工作带”的分流模结构多步优化设计方法。结果表明：优化后出模口型材横截面流速均方差由23.75 mm/s减少到1.63 mm/s，型材壁厚尺寸误差小于0.1 mm。同时，型材横截面的温差大小和焊缝质量明显改善，最大温差降低27.2 ℃，焊合压力提升16.5%，焊缝基本为完全再结晶组织。
关键字: 薄壁中空型材；多孔分流模；挤压缺陷；多步优化；截面流速控制；焊缝质量
（1. School of Mechanical Engineering, University of South China, Hengyang 421001, China;
2. State Key Laboratory of Advanced Design and Manufacture for Vehicle Body, Hunan University, Changsha 410082, China）
Abstract:Taking the automobile collision beam as a typical research object, the formation mechanism of extrusion defects, such as wall thickness thinning and cracking, on internal stiffener of profile in porthole die extrusion was revealed. The method for accurately controlling the uniformity of cross-sectional velocity at die exit was proposed. Firstly, an accurate steady-state finite element model for simulating the porthole die extrusion process of profile was established based on the arbitrary Lagrangian-Eulerian formulation. Then, the formation mechanism of extrusion defects was analyzed based on the evaluation of material flow velocity standard deviation (SDV) at die exit and welding pressure. Finally, to solve the problem of the non-uniform velocity distribution, three steps of the die optimization were proposed, including optimization of portholes and drainage channels, introduction of baffle plates and optimizing the die bearings using Kriging approximation model and multi-island genetic algorithm. The results show that, after optimization, the SDV value in the cross-section of extrudate decreases from 23.75 mm/s to 1.63 mm/s. At the same time, the temperature uniformity on the cross-section of profile and seam weld quality are improved significantly. The maximum cross-sectional temperature difference is reduced by 27.2 ℃, the welding pressure is increased by 16.5%, and the grains of seam weld are basically completely recrystallized.
Key words: hollow thin-walled profile; porthole die; extrusion defects; multiple-step optimization; cross-sectional velocity control; seam weld quality
