超高强汽车车身结构件辊－冲复合成形基础及应用研究

AHSS (Advanced High Strength Steels) have been the most important lightweight materials for automotive structural parts in recent years, but their high strength　property not only poses great challenge to their forming processes, but also brings much difficulty to residual stress/strain control in forming, which aggravates the so called delayed fracture of AHSS during their usage. There are some formidable problems in either stamping or roll forming process when forming high strength automotive structural components, such as high forming forces, severe dies wear, large redundant deformation, unsatisfactory product dimension accuracy, etc. A new hybrid forming process, like the chain-die forming, was proposed by combining roll forming and stamping, aiming at overcoming those forming defects in roll forming or stamping processes, and improving product accuracy. The key point of this project is to clarify and control the deformation behaviors of AHSS in the new forming mode for achieving a better forming quality for AHSS automobile structural parts. Correspondingly, the following work will be researched. The elastic-plastic deformation　behaviors of AHSS sheets will be studied and a constitutive model that can describe both Bauschinger effect and nonlinear elasticity of AHSS will be established. The influence of strain path change and bending effect on forming limit of AHSS sheets will be studied, and a deformation path and control strategy will be put forward. Then the forming process design methodology of roll-stamping will be established. The typical characteristic parts for automobile beam-type structural parts will be designed. The finite element model of the hybrid forming process of those characteristic parts will be built and the influence of processing parameters on the geometrical accuracy and quality of the formed products will be investigated, through which process design standards for those parts will be developed. Finally, the forming machine will be developed, and the roll forming-stamping hybrid forming experimental platform will be established. Finally, a typical automobile structural part will be formed by using the roll-stamping technology. The project will make great contribution to the development of AHSS forming technologies in terms of low residual stress/strain, and stimulate application of AHSS.

先进高强度钢板是最主要的车身轻量化材料。其高强度不仅给成形加工带来严峻挑战，而且使得成形残余应力应变控制困难从而加剧延迟断裂等服役缺陷。先进高强钢汽车结构件冲压成形载荷高、模具磨损严重，而辊弯成形冗余变形控制难、产品精度不易保证。以链模成形为代表的辊－冲复合成形技术，通过将辊弯与冲压相结合的渐近成形方式，在实现高强度构件高精度与低残余应力成形方面有很好前景。本项目对高强度车身结构件辊－冲复合成形技术开展基础与应用。研究先进高强钢板变形行为规律，建立描述包辛格效应、非线性弹性等特性的材料本构模型；研究辊弯－冲压耦合模式下的变形路径设计与协调方法，形成辊－冲复合成形工艺设计方法；设计车身梁类结构特征件，研究工艺参数对成形质量的影响规律，建立工艺设计标准；构建辊－冲复合成形实验平台，应用于典型车身梁类结构件的成形。项目旨在为超高强车身结构件低应力成形技术的发展做出重要探索,促进先进高强钢的应用。

先进高强度钢板是当前最主要的车身轻量化材料。辊－冲复合成形是一种将辊弯与冲压相结合的新型板材成形技术，通过增大等效轧辊直径增加变形区长度，减小板材边缘冗余变形，同时有效缩短成形流程；采用分段模具实现纵向的渐近成形，有利于解决先进高强钢冲压成形的高载荷和模具磨损严重问题。.项目以超高强车身结构件的辊冲成形为对象，对先进高强钢板的变形行为与材料模型、辊－冲复合变形机理、典型特征结构的成形极限与工艺设计准则、成形实验平台构建、车身结构件成形试制等关键问题开展了基础和应用研究。通过开展先进高强钢板拉伸、循环压缩－拉伸、加载－卸载－再加载等材料实验，研究板材的屈服与硬化特性，卸载/再加载的非线性弹性变形行为。建立各向异性屈服准则、混合硬化和非线性弹性模型，建立准确描述先进高强钢板变形行为的材料模型，为准确预示辊－冲复合成形过程与样件残余应力建立基础。基于典型车身梁类结构件进行特征提取与归类，包括多种变高度、变宽度特征，以帽形件为基础载体，形成典型结构件，并选取重要特征描述参数。建立辊－冲复合成形过程的有限元模型，计算典型特征件的成形过程，分析特征件几何参数对成形质量的影响规律，预测成形缺陷。完成了辊－冲复合成形误差分析、弯曲角分析、纵向应变分析、过渡面分析等，为辊－冲复合成形性能综合优化提供工艺设计方法及理论基础。.完成了辊－冲复合成形试验平台的搭建，开发了典型特征件与车身梁类结构件的辊冲成形模具。完成了帽形件标准试验、变截面特征件及典型车身梁类结构件辊－冲复合成形实验，对产品成形应变、残余应力、成形质量等进行检测与评估，并验证模拟计算结果。实现了典型车身结构件的辊－冲复合成形试制，丰富和发展了先进高强钢板的先进成形加工技术，促进先进高强钢板的应用。