Successive Forming of Multi-thickness Plates by Using Wedge-shaped Tool

Abstract A new forming process has been studied for manufacturing sheet metal blanks with multi-thickness profiles, referred to as “tailor-formed blanks”. The thickness variations will be effective in achieving load-optimized profiles, which further reduce weight of structural parts in automotive, aerospace, electronics metal components and etc. Unlike tailor-welded blanks, these tailor-formed blanks offer smooth and continuous thickness transitions, preferable for subsequent forming operations. In this new process, a multi-thickness plate is formed from a uniform thickness plate by a successive forming operation using a wedge-shaped tool and flat tool. The wedge-shaped tool features three different zones – knifing, spreading and sizing zone with two key defining parameters – forming angle (α) and spreading angle (β). These three zones progressively cause metal to flow transversely creating a distinct thinner portion of predefined width and transition walls in the plate. The thin portion in the workpiece can then be extended to the plate’s full length by the successive forming under a relatively small forming force in each forming step. This paper discusses the basic concept of this new forming process, tool design, deformation characteristics, and process limits through experimental and numerical studies. It was found that inner crack and edge crack were the dominant defects in this forming method. Based on the experimental results, forming process windows were established, describing relationships between the defects, workpiece thickness reduction and feed rate. The numerical study showed effects of the forming angle (α) and spreading angle (β) on maximum damage value induced and forming load. The tailor-formed blanks of 50mm by 500mm were successfully fabricated from three kinds of aluminum alloy, i.e. Al5052, Al6061 and Al7075 of 2-4 mm thickness with maximum thickness reduction of 35%-45%. Subsequently, the aluminum tailor-formed blanks were stamped to produce lightweight part demonstrators with thickness variations.