Preliminary Study On Precision Forming Of Spur Internal Gear

Spur of internal gear(hereinafter referred to as internal gear) is part of typical mechanical transmissions, which requires high dimensional accuracy and good strength. The work piece made by traditional cutting has poor property because the fibers are destroyed, both existing low material utilization rate and high cost issues. Using precision shaping approach is an effective way to solve those problems. According to the existing forging, extrusion, spinning and other internal gear precision forming technology research. This paper proposes a new process of precision forming of ring blanks "pre-split + reverse split" two steps splitting extrusion forming process of internal gear.In this study, we take a kind of internal gear with tooth-number of 18, modulus of 3 and rim height of 30 mm as the research object. Using work piece with inner diameter of 52 mm, outer diameter of 80 mm, height of 30 mm to conduct the 3D modeling, numerical simulation and optimization, physical experiments mold making work, ultimately, we get qualified Lead pieces through the experiments. The main work of the study is preformed mold optimization, the summary of numerical simulation experiments law and the results comparison between physical experiments with numerical simulation.The study shows: When using punch with both splitting angle and splitting edge angle 60° to split ring blank with inner diameter of 52 mm, outer diameter of 80 mm, folding detect can be avoid if φ≤80o, h0≥3.4 mm. But one step splitting extrusion cann’t avoid the collapse of the end face and it also cause tooth tip unfull, meanwhile, to decrease the forming force, we adopt a two-step molding process.To avoid those defects, we determined performing circumferential outline is light dentate shaped, the split-out part has a certain height uplift, and the radial diameter is smaller than split-in part. Simulation and optimization of preformed main parameters: at the split-in end, the tooth tip diameter is ?47.6, tooth root diameter is ?50.6; Simulation and optimization of preformed main parameters: at the split-in part, the tooth tip diameter is ?47.6, tooth root diameter is ?50.6;at the split-out part, the tooth tip diameter is ?51.6, tooth root diameter is ?59.6; the reserve height of the end face of the metal is 5 mm, the radial reserve width is 6 mm, the shaped end split height of preform punch is 8 mm, the splitting angle 80o.Processing physical experiment mold and conduct experiment according to the best simulation results: casting Lead then turning to get required work piece; during the preform phase, the punch downstream and the work piece is splitted, the split-out part begin to form uplift profile, and the split-in part forms profile which is between the blank and the tooth profile, the qualified performs formed when the split-in height is 39 mm; make the preform reverse placed on the final mold, the qualified internal gear formed when the punch penetrate the die.The results show that, one step split extrusion of internal gear can avoid folding when the mold structure parameters is reasonable, but the collapse angle defect of the end face can’t be removed, and the tooth tip can’t be filled full. Those defects can be solved when adding split extrusion preforming, moreover, it can lower forming force. The forming internal gear has full tooth and a clear outline. The two step s splitting extrusion process has the superiority of small forming force, simple mold, simple equipment action, etc. And it offers the potential for large modulus and multi-teeth precision forming.