Three-dimensional Complex Tooth Profile Generated by Surface Rolling of Sintered Steel Helical Gears using Special CNC form Rolling Machine

The surface rolling process of sintered steel helical gears was optimized by using a newly developed CNC form rolling machine of two-roller dies transverse type equipped with a tooth lead correction function. Powder metallurgy test gears with a module of 3.0, tooth number of 20, pressure angle of 20°, helix angle of 20° and face width of 23 mm were machined from 0.5Ni-1.0Mo high-density (7.50 Mg/m3) sintered steel packs via the single-press single-sinter (1P1S) route. The modified tooth profile of the dies and the reciprocating rolling schedule were optimized empirically through trial and error. The experimental results revealed the feasibility of the new special rolling machine to obtain high-precision helical gears with a regular involute tooth profile corresponding to DIN 5 and a crowned lead by using a die having an unmodified lead profile. The surface densification state was almost uniform in the tooth lead direction, and a fully densified flank layer was observed from the surface down to a depth of approximately 0.5 mm.