Investigation into a new incremental forming process using an adjustable punch set for the manufacture of a doubly curved sheet metal

Abstract

For flexible manufacture of a doubly curved sheet metal, a new sheet metal forming process is proposed that uses a movable punch set composed of two pairs of lower support punches and one upper centre punch. The process is characterized by flexibility compared with the existing conventional processes because it does not require any complex-shaped die and the loss of material is minimized by unconstrained forming. The process involves very little thickness strain by applying the principle of bending deformation instead of stretching. In the preliminary finite element method (FEM) simulation it is found that the curvature of the formed sheet metal is determined by the distance between the supporting punches working in pairs and the forming depth of the centre punch. In the experiments using sheets of aluminium, a method with edge forming is proposed for producing sheet metal in the desired shape. The equation using process variables such as the distance between supporting punches in pairs and the forming depth of the centre punch is proposed for the prediction of curvature of the formed shape. The equation is revised by the experimental results and the FEM simulation results containing springback information. It is then shown that the radius of curvature for the formed sheet metal can be predicted by the revised equation unless a very large amount of springback occurs.