Shaping of Helical Gear by Two-Step Cold Extrusion

Abstract

The authors previously proposed a two-step cold extrusion method for shaping spur gears. This method was applied to shape helical gears in this study. A specially designed die was used for shaping helical gears in two steps. The specifications of the gears examined were as follows: module m = 1.5, number of teeth Z = 18, helix angle β = 20°. The material used for the experiment was low-carbon S15C steel. Workpieces with different inner diameters were formed to examine the effect of a reduction in cross-sectional area. To examine the effect of reductions in area, extrusion was carried out in three ways: 1) using a mandrel whose diameter is equal to the inner diameter of the workpiece; 2) using a mandrel whose diameter is smaller than the inner diameter of the workpiece; and 3) using no mandrel. Helical gears with complete teeth were formed in almost all the shaping conditions examined, even when the reduction in area was as low as 7% and punch pressure was relatively low.