780MPa超高强钢扭力梁内高压成形研究

Hydroforming of an Automotive Torsion Beam with 780 MPa Advanced High Strength Steel

目的为了适应载荷和安装空间及轻量化的要求,轿车扭力梁正趋于设计成空心封闭变截面高强钢结构,但高强钢成形存在着回弹大、成形精度低等缺点。方法针对这一问题,采用数值模拟和实验的方法,开展了780 MPa超高强钢扭力梁内高压成形研究,重点研究了预制坯形状对扭力梁内高压成形的影响,并采用响应面模型,优化了预制坯,获得了最优的预制坯形状。在此基础上,研究了加载路径对扭力梁内高压成形过程的影响。结果当扭力梁预成形压下量为62.2 mm,下模引导角为29.2°时,得到了最优的预制坯形状。后续内高压成形过程中,支撑压力过小或补料量过大,在试件端部引起起皱缺陷;支撑压力过大或者补料量过小,补料主要集中于端部,对大膨胀量区域影响较小;当采用补料量为8%的加载路径时,可以有效改善壁厚的分布,避免起皱缺陷。结论合理的预制坯形状能够有效避免超高强钢扭力梁内高压成形过程中的飞边缺陷,而加载路径控制是扭力梁内高压成形过程中避免起皱缺陷和过度减薄,提高成形极限和零件成形精度的重要途径。

Torsion beam is popular to be designed into a hollow closed section of high strength steel structure to satisfy the requirements of the load,installation space and the lightweight.However,there are springback,forming accuracy and other shortcomings during the forming of the advanced high strength steel.In this paper,a 780 MPa advanced high strength steel torsion beam was investigated using numerical simulation and experimental method.The effect of preform shape on hydroforming was mainly focused and the preform shape was optimized using a response surface model and the optimal preform shape was obtained.On the basis of this,the effect of loading path on hydroforming process of torsion beam was studied.The results show that the optimal preform shape of the torsion beam can be obtained when the press displacement is 62.2 mm and the guidance angle of lower die is 29.2 degrees.During hydroforming process,if the support pressure is too small or axial feeding is too large,wrinkling defect will occur.While the support pressure is too large or axial feeding is too small,feeding mainly concentrated in the end and less affected on expansion regions.When the axial feeding is 8%,it can effectively improve the wall thickness dis-tribution and avoid wrinkling defects.It can be known that the appropriate preform shape can effectively avoid flashing defects when hydroforming of a high strength steel torsion beam.At the same time,the control of loading paths is an effective way to avoid wrinkling and severe thinning and improve forming limit and forming precision.