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不断提高的乘客安全标准要求的挑战。这样的趋势导致高级高强度钢（AHSS）用于制造车身部件的使用增加，所述车身部件放置在车身结构内的许多区域中。然而，高强度钢的潜在应用仍然是有限的，因为许多问题必须进行调查有关的成形性和回弹。有各种各样的策略，以尽量减少回弹的手段，工艺参数的变化，在冲压行程或通过使用额外的保持力的空白保持器。这些策略已成功应用于拉伸强度高达600 MPa的高强度钢合金的成形，并已在实践中得到成功证明。当使用这些技术来形成更强的钢材料（抗拉强度高于600 MPa）时，由于回弹和扭曲的趋势增加，所获得的结果和关于部件精度的知识并不令人满意。对于这种钢种的冷成形，到目前为止，还没有一种定义的和有效的策略或方法，可以用于回弹和扭转补偿。研究工作的动机基本上是缺乏这样的方法来减少在客车汽车的承载部件中观察到的回弹和扭转，以及找到一种制造这种钢种的回弹补偿策略。回弹补偿的方法将取决于局部应力应变状态以及侧壁卷曲和部件扭矩的大小。首先开发的方法将基于粘合剂形状的优化、硬化功能的全局和/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.