Creating Helical Tool Paths for Single Point Incremental Forming

Single point incremental forming (SPIF) is a relatively new sheet forming process. A sheet is clamped in a rig and formed incrementally using a rotating single point tool in the form of a rod with a spherical end. The process is often performed on a CNC milling machine and the tool movement is programed using CAM software intended for surface milling. Often the function called profile milling or contour milling is applied. Using this milling function the tool only has a continuous feed rate in two directions X and Y, which is the plane of the undeformed sheet. The feed in the vertical Z direction is done in the same angular position in the XY plane along a line down the side of the work piece. This causes a scarring of the side and also results in a peak in the axial force when the tool is moved down. The present paper offers a solution to this problem. A dedicated program uses the coordinates from the profile milling code and converts them into a helical tool path with continuous feed in all three directions. Using the helical tool path the scarring is removed, the part is otherwise unchanged and a major disadvantage of using milling software for SPIF is removed. The solution is demonstrated by SPIF of three different geometries: a pyramid, a cone and a complex part.