The Key Technology On Precision Forming Process By Continuous Cold Extrusion And Cold Finishing Of Spur Gears On Camion

Spur gear is one of the most commonly transmission parts in automobile and machinery industry,and it has large market demand,generally being manufactured by cutting process.With the development of precision plastic forming technology,more and more spur gears are manufactured by the near net shape forming method.After forming,the tooth surface is bright and clean,metal streamline is continuous,the carrying capacity is high.Thus the precision plastic forming technology of spur gear has a widely application prospect.With the development of mould manufacturing technology and application of new mould material,precision plastic forming technology of spur gear with large module and wide tooth is increasingly used in industrial production,but its unstable forming quality and low forming accuracy still exist.Therefore,how to improve the forming quality and forming accuracy of spur gears is the key to precision plastic forming process.In this paper,spur gear in camion reducer was studied,and a new forming method of spur gear was put forward,that was "compound forming process of cold extrusion and cold finishing ".The key technology of the compound forming process were studied comprehensively and systematically,such as multi-objective optimization of cold extrusion process parameters for spur gear,the choice of cold finishing method and finishing amount for cold extrusion gear with large modulus,optimization design of cold extrusion combined die for spur gear.The main research works of this paper are as follows:(1)The problem of poor forming quality and forming accuracy was analyzed with the original process,it was concluded that the main reasons are insufficient back pressure and elastic recovery.Based on the analysis results,a new compound forming process of cold extrusion and cold finishing was proposed.(2)The influence of cold extrusion process parameters on forming quality was analyzed by using FEM,the response surface method(RSM)combined with finite element method(FEM)were used for the multi-objective optimization of cold extrusion process parameter.By analyzing the optimization graphs in the variable space,the optimal process parameters were obtained.Error analysis and production practice had proved that the optimized process parameters could effectively improve the forming quality and lower forming load.(3)Based on the measurement of extruded gear,the influence of different finishing ways and finishing amount on metal flow and forming accuracy on cold finishing of gears were analyzed by using FEM,then a reasonable way of cold finishing and finishing amount were determined.Finishing only on tooth surface and finishing amount of 0.15 mm were applied on process experiment,the results showed that the magnitude of tooth profile accuracy increased from 8 to 7 and the magnitude of gear direction precision increased from 10 to 8 after cold finishing,it was concluded that the accuracy of cold extruded gear could be improved significantly by finishing only on tooth surface.(4)Experimental design combined with numerical simulation were adopt,the Kriging model of maximum effective stress and structure parameters of the combined die was built.The particle swarm optimization was used to find the optimal structure size of combined die in the variable space,the optimal die diameter ratio and interference coefficient were obtained.The overall size of optimized combined die was only 68.75% of the one by the experience method,the size of the combined die decreased effectively,the mould material was saved.The actual production with the optimal combined die showed that the service life of die was about 150000,the service life remained unchanged compared with the die designed by the experience method.(5)Production practice of the compound forming process of cold extrusion and cold finishing showed that the minimum of addendum circle diameter of top and bottom were 74.40 mm and 73.86 mm respectively,both of them met the requirements of machining.The convex amount of bottom of gear end-face was about 2mm;the concave amount of top of gear end-face was about 2mm.The allowance of gear end-face maching was reduced.The experimental results indicated that the total deviation of tooth profile was 12.2mm,magnitude of tooth profile accuracy was 6 and the total deviation of spiral was 26.6mm,magnitude of gear direction precision stabilize in 8.Therefore,the compound forming process could produce the spur gears with large modulus and its magnitude achieved the 8th clss.