Investigation of forming accuracy in multipoint forming with composite elastic pads

Abstract

Defects in the form of dimples, straight edges, and wrinkles can easily appear when a multipoint die is used to directly form sheet metal. The main methods currently used to address this issue are to add polyurethane elastic pads between the punch units and the blank or to use a blank holder device. However, the use of polyurethane elastic pads or a blank holder device may reduce the accuracy of the formed die surface or the material utilization ratio, respectively. To improve the outcome, a composite elastic pad for multipoint forming is proposed. Taking a spherical surface of radius R400 as the target surface, numerical simulations and forming experiments using three different forming conditions, namely, without any cushion, with polyurethane elastic pads, and with composite steel pads, were conducted using the finite element analysis software Abaqus and a YAM-200 multipoint forming press, which was independently developed by the Jilin University. The results show that compared with the forming conditions without any cushion and with polyurethane elastic pads, when the proposed composite steel pads are used in multipoint forming, the forming accuracy is effectively improved, and defects in the form of dimples, straight edges, and wrinkles are effectively suppressed. Further research revealed that varying the thickness of polyurethane sheet A or polyurethane sheet B in the composite elastic pad design will result in different effects on forming accuracy and quality improvement. When the thicknesses of polyurethane board A and polyurethane board B are 5 mm and 10 mm, respectively, the forming effect is the best. Compared with forming without a cushion, the maximum error and average error of the formed parts are reduced by 68.3% and 66.1%, respectively.