Component-specific cushion design for stretch forming to enhance accuracy: considering space between pins in reconfigurable tools

Stretch forming with reconfigurable tooling is a flexible manufacturing process that has the potential to produce complex and customized components. A cushion (hyperelastic material) is placed between reconfigurable pinheads and sheet metal to reduce the height of dimples on formed components. Conformability between the cushion and pinhead interface is important in enhancing the accuracy of components. Among various existing cushion types, the component-specific cushion designed in earlier work improved the conformability and accuracy of components. However, considering gaps between neighboring pins after adjusting them to desired height based on component and pinhead surfaces in cushion design can further significantly enhance its effectiveness and is yet to be addressed. In the present work, an analytical model is developed by considering gaps between neighboring pins at every location to determine the conformability through a measure of global shape error (i.e., maximum geometrical deviation) for obtaining a range of base radius of scooped-out patch that further enhances accuracy. To demonstrate the effectiveness of the proposed methodology, finite element analysis of multipoint-stretch forming is performed to form a spherical shape using component-specific cushions designed with and without considering gaps between neighboring pins. Results clearly indicate that the base radius of scooped-out patch between 0.85 and 0.95 times the pinhead radius significantly improved the conformability. The accuracy and surface quality of the component formed using a component-specific cushion designed by considering gaps between neighboring pins enhanced significantly (68% local and 31% global shape errors) compared to one designed without considering gaps between them.