Study On Precision Forming Of Spur Gear With Two Steps

Based on the current situation that the precision forming of spur gear has not yet entered the industrial stage, analyzed and summarized the main precision forming methods according to the differences in deformation approaches of tooth, and divided them into three kinds, which is "Full Long Ridge","Full Slotting" and "Open Long Ridge-Expanding Slot". A new precision forming process of spur gear with two steps was proposed and studied, which involved preform with closed die forging and final-form with splitting extrusion.The object of study is an involute cylindrical spur gear with tooth-number of12, modulus of4and rim height of30mm. According to the purposes of splitting extrusion with unfold, small collapse and less waste, focused on studying the parameter optimization design of preformed part by closed die forging. The profile features show that the edge of cross-sectional contour is half-long ridge; and diameter of split-in part is greater than diameter of split-out part at meridian plane; additionally, there is extra reserved metal to the tooth out the split-in face. Studies show that when the half-long ridge (up and down) height is between2～4mm; the preformed part does not only avoid folding, but also takes an average distribution in forming difficulty. The optimized results in parameters of meridian plane profile is as follows:at the split-in end, the tooth tip diameter is054mm, tooth root diameter is048mm; at the end, the tooth tip diameter is048mm, tooth root diameter is043mm; out of the split-in face, the height of extra reserved metal is3mm. In terms of final forming, referencing to previous studies, summarized the effect of splitting extrusion forming with changes of main parameters of splitting wedge head, including splitting angle and splitting edge angle. Feasible splitting angle ranges45°to120°, and splitting edge angle ranges30°to75°. The combination of splitting angle of60°and splitting edge angle of60°makes good comprehensive effects of split extrusion. According to forming force, splitting extrusion forming process is divided into three stages, which is split-in end forming, steady deformation and extra metal pushed out. The maximum forming force reaches at the moment of starting pushing out extra metal in the medium and final stage. The maximum stress of splitting extrusion mold happens where splitting edge contacts with the blank, which lead to edge wear, and it affects the full extent of the tip at the split-in end, the collapse and the volume of excess material pushed out.Designed and manufactured two sets of experimental mold. And carried out physical experiments in terms of preform and final-form with lead materials successfully.The results show that adding suitable preforming step before final splitting is effective to avoid folding, improve tooth tip filling at the split-in end and make up face collapse. Deformation affected zone of final-form is concentrated in tooth and a certain depth range from the bottom. The forming gear by the new process has full tooth and a clear outline. The forming force is small, easy stripping, easy action required in equipment and mold, and less waste is pushed out, witch in this instance is less than10.8%of billet. So it is suitable for precision forming large diameter and modulus gear.