Wrinkling Behaviour of Engineering Fabrics in Diaphragm-Assisted Deep Drawing

Wrinkling during diaphragm forming of engineering fabrics compromises structural integrity and surface quality. This study investigates two strategies—diaphragm pre-tensioning and fabric inter-ply lubrication—to mitigate wrinkle formation. A pre-tensioning (PT) blank holder was designed and evaluated through deep-draw experiments supported by finite element analysis (FEA). Results show that pre-tensioning (50% strain) significantly reduces wrinkle severity compared to a conventional blank holder. The PT blank-holder creates initial equi-biaxial strain consistent with analytical and FEA predictions. Resin inter-ply lubrication also decreased wrinkling and reduced forming force by approximately 70%, primarily by lowering inter-ply friction. However, pre-tensioning proved more effective overall. These findings demonstrate the potential of diaphragm pre-tensioning for improving forming quality and provide a foundation for advanced multi-step thermoforming processes.