New methodology of springback compensation for Advanced High Strength Steels based on geometrical modifications

如今，汽车行业面临着越来越多的环境法规以及对乘客安全标准要求的不断提高的挑战。这种趋势导致越来越多地使用先进的高强度钢(AHSS)来制造车身部件，这些部件被放置在车身结构的许多区域。然而，高强度钢的潜在应用仍然受到限制，因为需要研究许多与成形性和回弹相关的问题。有各种策略可以通过在冲压行程期间改变工艺参数或通过由压边机施加额外的保持力来减少回弹。这些策略已成功地应用于高强度钢合金的成形，其抗拉强度可达600 Mpa，并在实践中得到成功验证。当使用这些技术成形更坚固的钢材料(抗拉强度高于600兆帕)时，由于回弹和扭转的趋势增加，所取得的结果和在部件精度方面的应用知识并不令人满意。到目前为止，对于此类钢种的冷成形，缺乏一种明确而有效的回弹和扭转补偿策略或方法。研究工作的动机基本上是缺乏这样的方法来减少客车承载部件中观察到的回弹和扭转，以及为制造此类钢种找到复杂的补偿策略。回弹补偿的方法将取决于局部应力-应变状态以及部件的侧壁卷曲和扭矩的大小。首先开发的方法将基于粘结剂形状的优化、硬化函数的全局和/或局部应用、部件识别区域中的特殊压痕以及部件半径的反击目标的形状细节。

Nowadays, the automotive industry is challenged by increasing environmental regulations as well as continuously enhancement of the standard requirements regarding to passengers safety. Such tendencies lead to increased use of advanced high strength steels (AHSS) for manufacturing of car body components which are placed in many areas within car body structure. However, the potential application of high strength steels is still limited since many issues have to be investigated related to formability and springback.There are various strategies to minimize springback by means of process parameter variation during the press stroke or by use of additional retention forces by the blank holder. These strategies were already applied successfully in the forming of high-strength steel alloys up to 600 MPa tensile strength, and have proven successfully in practice. When using these techniques for forming of more stronger steel materials (tensile strength higher than 600 MPa), results achieved and knowledge applied with respect to component accuracy are not satisfactory due to the increased tendency towards springback and twisting. For cold forming of such steel grades until now a defined and valid strategy or method that can be used for springback and twisting compensation is missing.The motivation of the research work basically stands for lack of such methodology to reduce springback and torsion observed in load carrying components of passenger cars, as well as to find a sophisticating compensation strategy for manufacturing such steel grades. The methodology for springback compensation will be dependent on local stress-strain state as well as on magnitude of sidewall curl and torsion moment of the component. The method to be developed first will be based on optimization of binder shapes, on global and/or local application of hardening functions, on special indentations in identified areas of component as well as on details in shape for counter striking objectives of component radii.