(1. 南華大學 機械工程學院，衡陽 421001；
2. 湖南大學 汽車車身先進設計制造國家重點實驗室，長沙 410082)
摘 要: 以汽車防撞梁為典型研究對象，開展型材分流模擠壓試模出現(xiàn)的內(nèi)加強筋壁厚減薄和開裂等缺陷產(chǎn)生機理研究，并提出擠壓出模口橫截面流速均勻性的精確控制方法。首先，基于任意拉格朗日-歐拉混合算法建立了型材分流模擠壓穩(wěn)態(tài)有限元模型。然后，基于材料流速均方差和焊合壓力評價揭示型材擠壓壁厚減薄和焊縫開裂的產(chǎn)生原因。最后，為了實現(xiàn)對出模口型材橫截面流速的均勻控制，提出了“優(yōu)化分流孔/引流槽、增添阻流塊、基于Kriging近似模型和多島遺傳算法優(yōu)化工作帶”的分流模結(jié)構(gòu)多步優(yōu)化設計方法。結(jié)果表明：優(yōu)化后出模口型材橫截面流速均方差由23.75 mm/s減少到1.63 mm/s，型材壁厚尺寸誤差小于0.1 mm。同時，型材橫截面的溫差大小和焊縫質(zhì)量明顯改善，最大溫差降低27.2 ℃，焊合壓力提升16.5%，焊縫基本為完全再結(jié)晶組織。
關(guān)鍵字: 薄壁中空型材；多孔分流模；擠壓缺陷；多步優(yōu)化；截面流速控制；焊縫質(zhì)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
