Optimization of asymmetric tooth root generated with protuberance hob

Abstract

The Direct Gear Design method optimizes various parameters and elements of gear tooth geometry to achieve the required gear drive performance. One such critical element of the tooth profile is the root fillet. Previous publications had considered asymmetric tooth root fillet optimization assuming that the tooth involute flanks and root fillets are processed (machined) simultaneously. However, there are many applications that require high gear tooth flank accuracy and high load capacity in combination with minimized gear production cost. In order to satisfy these requirements, the tooth involute flanks and root fillets are processed separately. A gear blank is machined by a topping protuberance hob that finalizes the root fillet, tooth tip diameter and chamfers, leaving stock for the tooth flank grinding. Then, after the gear’s heat treatment (carburizing + case hardening) and in some cases shot peening of the tooth root, the tooth flanks are processed using highly productive generating grinding, removing the grinding stock. As a result, the full residual stress developed by case hardening is retained. This fabrication sequence is most typical for automotive transmission gears.