Improved Tool development Process for novel SCS Technology for Aluminium Sheet Metal

Today’s stretch forming technologies mainly are used for production of large and flat parts made of sheet metal mainly for the aircraft industry (wing fabrication) and for shipbuilding. Because of the high investment costs and high process time, the use of such conventional stretch forming technologies is not qualified for production of car body panels. However, benefits of present stretch forming methods such as improvement of the mechanical properties of these parts today makes stretch forming technologies attractive for automotive industry. For this very reason a new technology for stretch forming of sheet metals (Short-Cycle-Stretch forming SCS) has been developed at the Institute for Metal Forming Technology (IFU) at Universitaet Stuttgart [1]. The SCS technology combines a plane pre-stretching and subsequent deep drawing operation for production of small car body panels with high demands concerning surface quality. SCS technology is based on a low cost tool which is used in a single action deep drawing press with short process cycles [2]. Former investigations have shown the tremendous potentials of the SCS technology by using typical mild steel alloys for car body panels. Conducted investigations about theoretical achievable effective strain in the stretched region included experimental validation which approved an effective strain value of φ≈0.09 in the stretched region of the specimen [3]. In order to fulfil increasing environmental regulations, the automotive industry focuses on reducing car body’s weight by using lightweight materials such as aluminium or high strength steel. SCS technology offers the possibility of producing car body panels with high surface quality at a minimum of investment costs. Therefore it is necessary to verify SCS technology for new lightweight sheet metal materials as described in [3]. Because of the material properties of high strength steel it does not make sense to investigate such materials for their use with SCS technology regarding the denting resistance and the part stiffness. However, aluminium is due to lower material properties predestinated for a pre-stretching process to increase such properties. The SCS technology offers a huge potential for pre-stretching aluminium blanks and to produce parts with significant better part quality with regard to part stiffness and dent resistance.