Investigation of material failure in micro-stamping of metallic bipolar plates

Micro-stamping is a promising process for the low-cost manufacture of micro-channels from thin metal sheet for fuel cell bipolar plates. Most previous studies numerically analysed micro-stamping processes by assuming a perfect tool profile and position. In this work, thin 316 L stainless steel sheet is stamped with a micro-stamping tool to produce micro-channels and the initiation of fracture is experimentally investigated. Severe material thinning and fracture were observed in locations where the sheet contacts the tool and related to tool misalignment and profile inaccuracies that only could be identified with a 3D profilometer and an optical microscope. A 2D finite element model of the process was then developed and showed that, to accurately represent material thinning and forming limits in the micro-stamping of the stainless steel sheet, the scanned tool profile shape and position need to be accounted for. Comparison with the experimental Forming Limit Diagram (FLD) suggests that in the stamping of micro-channels from thin stainless steel sheet, material failure is governed by the development of a neck and therefore can be successfully assessed by the FLD.