Ball spin forming for flexible and partial diameter reduction of tubes

Abstract: This paper proposed a new ball spin forming equipment, which can form a reduced diameter section on halfway of tube. The effects of forming process parameters on the surface integrity and deformation characteristics of the product were investigated. The proposed method can reduce the diameter in the middle portion of the tube, and maximum diameter reduction ratio was over 10% in one pass. When the feed pitch of the ball die was more than 2.0 mm/rev, spiral marks remained on the surface of tube. Torsional deformation, axial elongation and an increase in thickness appeared in the tube during forming process. All of them were affected by the feed pitch and feed direction of ball die, while they were not affected by the rotation speed of tube. By sending the ball die towards the fixed part of tube or by increasing the feed pitch, torsional deformation and elongation decreased, and the amount of thickening increased. When the tube was pressed perpendicularly to the axis without axial feed, a diameter reduction ratio of 21.1% was achieved without defects using a ball diameter of 15.9 mm. The polygonization of tube was suppressed by reducing the pushing pitch. The ball spin forming has a high advantage in flexible diameter reduction processing on the halfway of the tube for producing different diameter tubes.