Key Technologies Research of Cold Rotary Forging Finishing for Hypoid Gear Wheel

Author:Dang Yu Gong

Supervisor:deng xiao zhong


Degree Year:2017





Hypoid gears are widely used as main reduction gears in the automobile drive axle.At present the traditional machining method of hypoid gears is face milling,and this forming method leads to some deficiencies such as low bending fatigue strength of tooth root,poor fatigue resistance of tooth surface,high removal rate of material and low production efficiency.The deficiencies of face milling can be overcome by using near-net shaping precision forging process for hypoid gear,but due to the complexity of hypoid gear shape and the big forming difficulty,big tonnage forging equipments are required and the precision of teeth is low.At present in order to guarantee tooth profile accuracy,hypoid gear after precision forging still need to broaching or grinding finishing,so compact metal fibre of workpiece surface after forging will be cut off,thus it can not reach the effect of anti-fatigue manufacture.In order to meet the requirements of anti-fatigue manufacturing,this paper aim at the deficiencies such as die structure for the technology of traditional cold rotary forging is complex,tooth surface defects and stress concentration are easy to produce,and the author put forward a special cold rotary forging technology to finish machining the forging gear.Systematic explorations and researches are carried out by using numerical simulations and experiments,and the main research contents are as follows:Based on the formate theory,the author put forward a special cold rotary forging technology for driven wheel of hypoid gear.On the basis of constructing coordinate system for cold rotary forging technology,equation of the die is deduced from equation of the virtual grinding wheel.According to the rule of addendum and dedendum not interfere in the process of gear meshing,the maximum radius of dedendum transition curve for the driven wheel is determined.Interference of the die and virtual grinding wheel is checked to ensure the accuracy of rotary forging.The method adopts single tooth rotary forging means and greatly simplifies die structure.Based on the basic theory of elastoplastic and thermal coupling finite element,geometric grid model and material model are analyzed,and then boundary condition and process parameters are reasonable set,and the cold rotary forging finite element model can be established.Through numerical simulation of forming process,the paper reveals the change rule of contact area between the workpiece and die,metal flow velocity field,temperature field,stress field,rotary forging force,rotary forging torque and microstructure.Simulation results further prove the local load properties of this rotary forging,and materials can keep good plasticity in difficult forming area,and metal grain eventually can be drawn into fibrous tissue,and thus mechanical properties are improved greatly.Using method of single factor and orthogonal experiment respectively,the influences of process parameters on experimental index are studied by means of numerical simulation,and the trend curve of forming force change with process parameters is matched,and the optimal process parameters are get,and regression analysis and correlation test of the results is conducted.Through the research of die failure modes,die life prediction model is built based on the theory of local stress strain.Using single factor method,the influence law of process parameters on die life is studied through numerical simulation,and the optimal process parameters are get to improve the die life.According to the results of finite element numerical simulation,springback tooth surface is rebuilt,and then the size and distributio of springback error is detected.By springback error of reference point on tooth surface,the elastic recovery law of workpiece along tooth height and length is get.The comprehensive compensation method is adopted to correct springback error of the die,and according to the correction algorithm,springback error iteration compensation system is constructed.LTCA analysis for the cold rotary forging gear is carried out to verify feasibility of the correction algorithm.Based on the above research,using revised die,the author carrie out processing experiment in cold rotary forging machine,and measurement results of the gear show that machining precision can reach level 7.Metallographic analysis is carried out for the experimental gear,and the results show that after cold rotary forging metal fiber of the gear has not been cut off and in the function of rotary forging stress metal grain eventually can be drawn into fibrous tissue,and the hardness has been significantly improved,and all this prove that the method of cold rotary forging can improve mechanical properties remarkably.