A new strategy to optimize variable blank holder force towards improving the forming limits of aluminum sheet metal forming

The lower formability of aluminum alloy sheet greatly limits its application in reducing weight of stamping parts. This paper proposes a new strategy to optimize the variable blank holder force (BHF) and determine the drawing limit under the constant and variable BHF. The optimization strategy is based on the analysis of BHF formability window and integrated into FEM code to obtain time and spatial optimal BHF that applies on segmental binders. And then a stepped rectangular box of 60 mm drawing height with 10 segmental binders is adopted to validate the optimization strategy. The constant BHF experiment and the derived trajectory of optimal BHF are verified on a multipoint variable BHF hydraulic press and the experiment results correspond well with those of FEM optimization. This new BHF optimization strategy helps to determine time and spatial optimal BHF profiles simultaneity in a single round of FEM simulation, which makes it an effective method.