Analysis of stamping performances of dual phase steels: a multi-objective approach to reduce springback and thinning failure

The industrial interest on light weight components has contributed in the last years to a significant research effort on new materials able to guarantee high mechanical properties, good formability and reasonable costs together with reduced weights when compared to traditional mild steels. Among such materials advanced high strength steels (AHSS) such as transformations induced plasticity (TRIP) and dual phase (DP), and light weight alloys proved their usefulness in stamping of automotive components. As AHSS are concerned, one of the main drawbacks is related to springback occurrence. Many aspects have to be taken into account when springback reduction is investigated: material behavior issues, process conditions, numerical simulations parameters calibration, geometrical aspects and so on. Moreover, springback minimization problems are typically multi-objective ones because springback reduction may conflict with other goals in stamping design such as thinning reduction. In this paper, such problem was investigated through integration between numerical simulations, Response Surface Methodology and Pareto optimal solutions search techniques. The design of a U-channel stamping operation was investigated utilizing two different dual phase steel grades: DP 1000 and DP 600. An explicit/forming-implicit/ springback approach was utilized for the numerical simulations. Friction conditions and blank holder force were optimized as design variables in order to accomplish two different objectives: reduce excessive thinning and avoid excessive geometrical distortions due to springback occurrence.