The mechanics of multi-point sandwich forming

Multi-point sandwich forming (MPSF) is a sheet metal forming process of recent innovation, in which a reconfigurable bottom die and a rubber top die are used. Also, a reusable die sheet is placed on the pins of the reconfigurable die to form a continuous surface. Because a simple press may be used and the cost of altering the tooling to make a new part shape is small, MPSF is a suitable method for forming small-batch quantities of a particular part. However, the basic deformation mechanics of MPSF have not yet been investigated and thus the best configuration of tool components to make a given part shape has to be determined by trial and error, which detracts from the low-cost aspect of the process. Therefore, in this paper, the results of investigation of the effect of workpiece and tool component dimensions and workpiece properties on the characteristics of the formed part shapes are presented. To enable the effect of tool and process parameters to be revealed more readily, plane strain deformation is used and a cylindrically shaped die surface was chosen for the bottom die. Three kinds of metal sheet and two kinds of rubber were used in the experiments. Experimental results show that for the die sheet, forming force increases and dimple size reduces with increase in the thickness of the sheet. Dimples occur on the surface of 1 mm LF21 aluminum sheet workpieces, however no dimples are formed on 2-mm-thick Q235B and ST12 steel sheet workpieces. The stiffness of the interpolator has an effect on the final shape accuracy. Also, the forming force of the workpiece reduces and shape accuracy increases, when lubrication is used in the surfaces of a workpiece.