A computer numerically controlled dieless incremental forming of a sheet metal

Abstract

In a previous paper a new incremental tube-forming method was proposed in which forming is carried out by a series of movements of a hemispherical head tool without using any die or mandrel that corresponds to the product shape. This paper aims to develop a similiar method that can form flat metal sheets into three-dimensional shapes without using dedicated dies. For this purpose, very simple and compact tooling is devised and put on the bed of a numerically controlled (NC) machine tool. It can be controlled with an NC program, which is made by commercial CAD/CAM (computer aided design/manufacture) systems. The method is broadly applicable to any product where the outer surface is convex, and is examined for the forming of an aluminium sheet into cones and pyramids having an arbitrary number of sides with a half-apex angle with a minimum of 10°. Sharp edges between adjacent sides of the pyramid are easily formed. The ratio of the wall thickness of the product to that of the original sheet corresponds with the sine of the half-apex angle of the pyramid, and the sine law in shear spinning holds. The outer surfaces of the products have a glossy appearance due to ironing by the tool.