An efficient approach to springback compensation for ultra high strength steel structural components for the automotive field

The use of High Strength Steel (HSS) and Ultra High Strength Steel (UHSS) offers high lightweighting potentiality for car body structural components. The large amount of springback after forming is currently limiting the impact of such steel grades, because of the large effort to be spent for tool design and tolerance satisfaction, requiring longer try-out phases and increased development costs. One of the most promising ways to enlarge the use of UHSS is the definition of robust and efficient methodologies able to evaluate the springback phenomenon and to compensate it by means of appropriate tool shape modifications, for example during the design phase of the stamping tools. This paper presents an approach for the evaluation of springback phenomena and its reduction by die shape modification for HSS and UHSS. The approach is based on the use of reliable constitutive equations for springback prediction and on an innovative method for springback compensation, in which the number of degree of freedom in the iterative optimization problem is reduced by an appropriate selection of the base functions used to interpolate the springback deviations. The approach guarantees improved and usable results, specifically High and Ultra High Strength Steel. The feasibility of the approach is demonstrated by means of an industrial example.