高强钢板热冲压三维成形极限图的构建理论与应用研究

Hot stamping of high strength steel sheet is an effective approach to realize vehicle weight minimization for energy conservation and waste reduction. The formability of hot stamped part is generally evaluated by means of forming limit curve. However, it is difficult to describe the formability of the part with varying temperatures because the common hot stamping forming limit curves are made up of multiple isothermal forming limit curves. Moreover, the exiting forming limit diagram does not take into consideration of the impacts of phase change phenomena on the forming limits of hot stamped part. This project aims to study the material flow behavior and hot forming index during thermal deformation for the advanced high strength steel B1500HS, and establish the constitutive equation considering temperature, strain rate and phase transformation. DIC technology is used to obtain the limit strain values for high strength steel plates above the phase transition temperature. M-K model and the constitutive equation are used for setting up the ones below phase transition temperature. After that, the impacts of phase transition on hot forming limits can be studied. Based on the obtained hot forming limit data, BP neural network together with interpolation algorithm is made to establish 3D forming limit diagram. Hot stamping tool for square cup will be designed and through process tests the 3D forming limit diagram is evaluated both qualitatively and quantitatively. The objectives of the project is aims to explore how phase transition of high strength steel impacts the hot forming limit and establish the forming limit diagram suit for hot stamped part, in order to lay the foundation for applications of home-made high strength steel to modern vehicles.

高强钢板热冲压技术是实现汽车轻量化，达到节能、减排的有效途径。热冲压件的成形性通常采用成形极限进行判定，然而常规热冲压成形极限由多条等温成形极限线组成，难以描述变温过程钢板的成形性，且现有的成形极限图没有考虑相变行为对热冲压件成形性的影响。项目以B1500HS高强钢为研究对象，揭示高强钢板热变形材料流动规律、推导热成形指数，建立考虑温度、应变速率和相变行为的本构方程。采用DIC技术获取高强钢板相变温度以上的极限应变值，基于M-K理论和本构方程对材料相变温度以下的成形极限线进行构建，研究相变行为对热成形极限的影响。基于热成形极限数据，采用神经网络和插值算法构建三维成形极限图。设计盒型件热冲压模具，通过工艺试验对三维成形极限图进行定性、定量评估。本项目旨在探索高强钢相变行为对热成形极限的影响规律，建立适用于高强钢板热冲压的成形极限图，为国产高强钢在现代汽车领域的应用奠定基础。

高强钢板热冲压技术是实现汽车轻量化，达到节能、减排的有效途径。热冲压件的成形性通常采用成形极限进行判定，然而常规热冲压成形极限由多条等温成形极限线组成，难以描述变温过程中钢板的成形性，且现有的成形极限图没有考虑相变行为对热冲压件成形性的影响。项目以B1500HS高强钢为研究对象，揭示高强钢板热变形材料流动规律、推导热成形指数，建立考虑温度、应变速率和相变行为的本构方程。主要研究内容包括：基于DIC技术的高强钢板热成形极限研究；热冲压三维成形极限图的构建；典型件热冲压过程数值模拟及试验研究等。经过对本项目研究内容的深入探索，得到如下重要结果：采用DIC技术获取了高强钢板相变温度以上的成形极限曲线，基于M-K理论和本构方程对材料相变温度以下的成形极限线进行获取，同时研究了相变行为对热成形极限的影响。基于获得的热成形极限数据，采用神经网络和插值算法构建三维成形极限图；建立了描述热冲压过程的多场耦合数值模型（热、力、相、流），研究了成形参数、模具参数等对材料流动性的影响；形成了一套基于拓扑优化技术的热冲压模具设计方法，开发了类B柱典型零件热冲压模具，并搭建了流速可控、温度可测的热冲压工艺试验平台，实现对有限元模型的验证；基于三维成形极限图的概念，将成形后板料的应变点与成形极限线的距离进行量化，并将其定义为裕度，运用三维成形裕度云图有效地评价了某汽车B柱零件的热成形效果；将热冲压成形极限图进一步推广，建立了与板料厚度相关的三维成形极限图，TRB前纵梁成形性能的有效评价验证了所建立的厚度相关的三维成形极限图的可行性。本项目围绕高强钢热冲压这一主旨，开展了包括探索高强钢相变行为对热成形极限的影响规律，建立适用于高强钢板热冲压的成形极限图等基础研究，以及典型热冲压零件模具的设计和开发的应用型研究，基于研究成果，发表了4篇论文，其中SCI检索3篇，申请国家发明专利8项，授权4项，培养了研究生4名。