Robust Springback Optimisation of DP600 Steels for U-Channel Forming

Automobile companies have increased the use of high strength dual phase steels as an alternative to aluminium and magnesium alloys due to their light weight, low cost and durability. Due to their high tensile strength, however, dual phase steels have a tendency to springback more than other structural steels in a forming operation. In addition, variations in material properties and manufacturing process parameters cause springback variation over different manufactured parts. Therefore, it is an important task to reduce the magnitude of springback as well as its variation within to produce robust and cost-effective parts. This paper investigates minimization of the magnitude and variation of springback of DP600 steels in U-channel forming within a robust optimisation framework. The computational cost is reduced by utilizing metamodels for prediction of the springback and its variation during optimisation. Three different allowable sheet thinning levels are considered in solving robust optimisation problem and it is found that as the allowable thinning increases the die radius reduces thereby the magnitude and variation of springback reduces. Finally, a sensitivity analysis is performed and the yield stress is found to be the most important random variable.