Application of Central Composite Design for Optimization of Two-Stage Forming Process Using Ultra-thin Ferritic Stainless Steel

Two-stage forming process for manufacturing micro-channels of bipolar plate as a component of a proton exchange membrane fuel cell was optimized. The sheet materials were ultra-thin ferritic stainless steel (FSS) sheets with thicknesses of 0.1 and 0.075 mm. For the successful micro-channel forming in the two-stage forming approach, three process variables during the first stage were selected: punch radius, die radius, and forming depth. In this study, the effect of the three process variables on the formability of ultra-thin FSSs was investigated by finite element (FE) simulations, experiments, and central composite design (CCD) method. The optimum forming process designed by the CCD showed good agreement with those by experiments and FE simulations. The newly adopted optimization tool, CCD, was found to be very useful for optimization of process parameters in the multi-step sheet metal forming processes.