Shaping of Spur Gear by Two-Step Cold Extrusionunder Condition of Low Reduction in Area

The authors previously proposed the two-step cold extrusion method to shape a gear. Namely, a specially designed die, to shape a gear in two steps, is used without reducing the outer diameter of the cylindrical workpiece. This method allows complete shaping of a gear even for a solid workpiece with no hollow region. The solid workpiece results in the lowest reduction in area, and no experiment with a lower reduction in area is possible. This research is aimed at shaping a gear by a method in which a mandrel is not used and radial inward flow of the workpiece material to achieve a low reduction in area is possible. The specifications of the spur gear examined were as follows: module 1.25, number of teeth 18. The workpiece material is low-carbon S15C steel, selected as a model material for carburized quenching. The inner diameter of the workpiece was varied to investigate the effect of the reduction in area. As a result, under all shaping conditions, a gear with complete teeth could be shaped successfully at a low punch pressure even with a low reduction in area of 6%.