A Preliminary Research On Precision Forming For Spur/Helical Internal Gear With One Step

Compared with the gear cutting process,the forged gears have the advantages of higher material utilization,higher productivity,better metal fiber streamline,higher bending strength of gear teeth,and so on,but the research on precision forming of internal gears is not deep enough.Based on precision forming of spur gears by the added die cavity,a new precision forming with expansion die cavity for spur/helical internal gear is studied in this paper.In order to improve the flashless die forging,the key point of the new technology is to set the expansion die cavity at the bottom corner of the toothed mandrel,so that the upper corner is filled well when the upsetting is finished,and the most area of tooth shape is basically completed,but the bulge is only formed in expansion die cavity under the bottom corner.This is due to the addition of an expanded die cavity in the lower corner,which makes it difficult to fill the local surface of the workpiece as a free surface,thus reducing the deformation force.On the other hand,although the lower corner is not regular in shape,it reserves a suitable volume to return to the dentate cavity during the the stage of ejection.At the stage of ejection,the effect of constrained shaping is produced by the inclined side wall of the expansion die cavity,which makes the bulge at bottom corner backflow smoothly to the cavity of the concave die,so as to finish the filling of the bottom corner of the internal gear.In this paper,the spur/helical internal gear with modulus of 3 mm,tooth number of 18,tooth width of 25 mm and helix angle of 15°are taken as the research object.The DEFORM-3D finite element software is used to simulate the forming process of the new technology.To analyze the forming quality and forming force of the spur internal gears under five different expansion die cavities,and obtained the optimal expansion die cavity.And then,on this basis,the influence of the geometric parameters(the expansion angle?,the dimension b in the tooth width direction,and the dimension h in the tooth height direction)is further analyzed.The simulation results show that when the values of?(b or h)increased,the upsetting forming force decreased,and the ejection force rose accordingly.When the values of?,b,h are selected 8~o-14~o,(1/4~1/2)B,(1/4~1/2)H,respectively,the better forming quality is obtained.The result of orthogonal optimization test shows that under the premise of ensuring the forming quality of internal gear,smaller?and h values can be taken,and b value can be increased appropriately.The forming quality,forming force,equivalent stress and metal flow rule of internal gear are analyzed in this paper.The results show that the forming force of upsetting is about 70%lower than that of the flashless die forging process,while the filling quality of corner area can be improved significantly.In addition,the precision forming with expansion die cavity of helical internal gear is studied in this paper.The simulation results show that the forming force of upsetting can be reduced by about55%,and the forming force of ejecting is less than 10%.Finally,a physical simulation experiment is carried out to test the precision forming with expansion die cavity for spur internal gear with a ring blank made of lead.The experimental results are in good agreement with the numerical simulation results,which further proves the feasibility of the new process and the accuracy of the numerical simulation.