复杂环境下汽车冲压件回弹的准确计算分析

Sheet metal stamping is a widely applied plastic forming technology. Numerical simulation has been used to aid stamping process design, die engineering and problem solving. However, with further and deeper application, the limitations of the current simulation technology surfaced up, namely, it cannot accurately or even correctly calculate the springback under complex stamping environment. The proposed project aims to build an accurate large plastic deformation computational mechanics model for sheet metal contacting with and sliding over small die radius, to build a stamping simulation model with substructures, and to develop a seamless multi-step automatic switching scheme between dynamic explicit algorithm and static implicit algorithm during springback calculation. These methods will help accurately simulate the less than 0.3 mm surface distortion problem, and calculate the springback of large drawn panels with drawbead and the springback of flanging over tight die radius. Simulation of stamping and springback under complex environment involves many aspects of computational mechanics. These aspects reflect the common fundamental scientific problem facing simulation of manufacturing processes. An effective solution to this problem will help advance the application of computational mechanics into manufacturing, and help establish scientific foundation for the core technology of the forthcoming new round industrial revolution, i.e. digital and intelligent manufacturing processes. For stamping alone, accurate simulaiton of springback relates domestic eight billion yuan annual cost for die manufacturing and product quality. So this project has an important economic value besides scientific significancy.

金属板材冲压成形是应用十分广泛的一种塑性成形技术，冲压成形的数值仿真已被广泛使用，但随着仿真在工程应用中进一步深入，现有技术的局限性开始暴露出来，不能准确计算复杂环境下冲压件的回弹。本项目旨在揭示当前有限元法不能准确模拟三种复杂环境下冲压成形及回弹的原因，并通过构建准确模拟金属板材接触小圆角模具表面并滑动的大塑性变形计算力学模型、构建含有子结构的冲压仿真有限元模型、以及计算回弹过程中动力显式算法与静力隐式算法多步骤自动切换等手段，来准确模拟0.3 mm以下的轻微表面塌陷问题、含拉延筋大冲压件的拉延回弹问题、以及小模具圆角的翻边回弹问题。复杂环境下冲压成形及回弹的数值模拟涉及到诸多计算力学难题，这些问题是数值模拟制造过程的共性基础科学问题，有效解决此类问题有助于推进计算力学在制造领域中的应用，为实现新一轮工业革命里的核心技术，即制造业的数字化智能化，奠定科学基础。

金属板材冲压成形是应用十分广泛的一种塑性成形技术，冲压成形的数值仿真已经在汽车制造领域被广泛使用，但随着仿真在工程应用中进一步深入，现有技术的局限性开始暴露出来，不能准确计算复杂环境下冲压件的回弹。本项目旨在揭示当前有限元法不能准确模拟三种复杂环境下冲压成形及回弹的原因，并通过构建准确模拟金属板材接触小圆角模具表面并滑动的大塑性变形计算力学模型、构建含有子结构的冲压仿真有限元模型、以及计算回弹过程中动力显式算法与静力隐式算法多步骤自动切换等手段，来准确模拟 0.3 mm 以下的轻微表面塌陷问题、含拉延筋大冲压件的拉延回弹问题、以及小模具圆角的翻边回弹问题。设计制造了小圆角翻遍模具、可切换拉延筋U型冲压模具、圆头型冲压模具、楔型镶块驱动式双向拉伸模具、表面微缺陷冲压模具，在实验室进行了大量冲压实验和数值仿真，并参与了江淮汽车瑞丰S5后地板的模具设计及模具调试，发现回弹预测值对厚向积分点个数以及壳单元方程公式并不是很敏感；对于小圆角翻边来说，1000mm/s 的冲压速度能提高仿真可靠性、回弹预测的准确性；固体单元比壳单元能更准确计算小圆角翻边的应力应变分布，进而得到精度更高的回弹预测值；回弹预测值对网格密度也比较敏感，网格粗糙将导致回弹预测反向；采用力控制压边圈的回弹结果比采用等料厚压边间隙的回弹结果更接近实际值；采用能够描述包星格效应的随动硬化模型以提高后地板回弹计算的精度，采用等料厚压边间隙的位移控制压边圈或是采用力控制压边圈，均能正确计算后地板的拉延回弹方向；计算时应采用全料片进行分析计算，设置对称的边界条件虽然可以减少计算时间，但是对成形和回弹结果的影响较大。复杂环境下冲压成形及回弹的数值模拟涉及到诸多计算力学难题，这些问题是数值模拟制造过程的共性 基础科学问题，有效解决此类问题有助于推进计算力学在制造领域中的应用，为制造业的数字化智、能化奠定科学基础。