Multi-point sandwich forming of a spherical sector with tool-shape compensation

The need for a cost-effective means of rapid, small-batch quality parts manufacture is greater than ever in the sheet metal industry. A new reconfigurable multi-point forming process, multi-point sandwich forming (MPSF), has been conceived and investigated as a possibly useful method to fulfill this need. This process is different from to conventional multi-point forming, in that a re-usable die sheet is used, a large distance between pins exists in the reconfigurable die and the upper die is made of polyurethane. In the work described in this paper, the performance of a multi-pin die with pins in circular array and an adjustable blank holder is investigated. This die is suitable to form work-pieces with rotational symmetry. Also, a die shape optimization design method using inverse displacement compensation is presented. Experimental and simulation results from forming a spherical shell sector, with a diameter of 380 mm show this method is feasible and effective. The results also show the blank holder can reduce/eliminate dimples that sometimes arise in the work-piece and the deformation of the interpolator during the forming process can induce a shape error in the formed work-piece.