Flexibility improvement in two-point incremental forming by implementing multi-point die

Abstract

Among various incremental forming methods, two-point incremental forming (TPIF) is superior to single-point incremental forming (SPIF), but nonetheless, its flexibility is lower than SPIF. In this paper, in order to increase the flexibility of TPIF to form parts with free-form surfaces from an aluminum sheet, a supporting structure together with a reconfigurable multi-point die is implemented. The flexibility of TPIF process using the multi-point die is experimentally and numerically studied by forming a set of components comprising a hemisphere and free-form surfaces such as a scaled-down bulbous bow of a ship hull. The results showed that the proposed multi-point die has a high ability and flexibility in manufacturing of various symmetric and asymmetric components with different dimensions and geometries. In this regard, TPIF of a hemisphere using the rigid and presented flexible dies is experimentally and numerically compared. The results showed that the part formed using the multi-point die has an acceptable accuracy, but for improving the surface quality, the use of a rubber pad between pins and the aluminum sheet is inevitable. The effect of three different types of rubber and the influence of a polyurethane pad with three different hardness values on the thickness distribution and the dimensional accuracy were numerically studied. The results showed that the rubber type does not affect the minimum thickness, and the hemisphere produced using the natural and polyurethane rubbers has the highest and lowest dimensional accuracy, respectively. It was numerically shown that by increasing the hardness of the rubber pad, the minimum thickness and the dimensional accuracy are improved.