Enhancement of Accuracy in Multi-Point Stretch Forming: Cushion Stretching

Abstract

Multi-point stretch forming (MPSF) is one of the flexible manufacturing processes that uses the reconfigurable tools to produce the three-dimensional sheet metal components. An elastic cushion is placed between the tools and sheet surfaces to avoid direct contact and reduce the dimples as well as wrinkles. The cushion is also known to play an important role as it directly affects the component surface characteristics (accuracy and quality) and thickness strain distribution. An attempt made to apply stretching on the cushion resulted in enhancement of accuracy. In the present work, an analytical methodology is proposed to predict the initial thickness of cushion and stretching load necessary to apply on the cushion. FEA of MPSF of the spherical geometry is carried out with and without application of stretching load on the cushion. Results indicate that effective stress and strain distributions are more uniform when the stretching is applied to cushion thickness in certain range. Proposed methodology can be effectively used to determine initial cushion thickness before stretch and stretch load necessary to achieve chosen final cushion thickness to enhance the accuracy of sheet metal components formed using MPSF.