Theory And Experimental Study On Spur Gear Manufactured By The Forced Throughfeed Rolling Process

Rolling process is an advanced chipless maching method due to its advantages of high machining efficiency,less material consumption,excellent surface quality and service performance.During the rolling process,one or more of the rolling tools is used to drive the workpiece to rotate together and extrude the metal material of the workpiece surface radially or axially.Then,the material subjected to forming forces begins to plastic flow and forms the workpieces having specific size and shape.Also,it conforms to the production idea of efficiency,precision and green in the modern gear manufacturing industry.Based on the analysis of free divide-tooth and forming accuracy,a new technology of manufacuturing cylindrical spur gear by using speed-controlled forced divide-tooth for throughfeed rolling is proposed in this thesis.And then the forming principle,divide-tooth error,material flow,tooth growth of formed workpiece,design method of rolling tools,design and manufacturing of machine and accuracy of formed workpiece are investigated,which provides theoretical basis and support for the high efficiency and precision manufacuturing of spur gear.The main research is as follows:(1)Analysis of divide-tooth error in the gear free throughfeed rolling process,including the deduction of accurate divide-tooth condition in the gear free throughfeed rolling process;the mathematical models of contact ratio,initial phase of rolling tools,initial diameter of workpiece and pitch error are established,and the proposed pitch error models are veried by the theoretical analysis,Finite Element Simulation(FES)and rolling experiement.In order to keep the universality of the rolling tools and minimize the impact of the factors mentioned-above on the divide-tooth error,a cylindrical spur gear forced throughfeed rolling process is proposed in the thesis.(2)Material flow under split-extrusion-rolling recombination action is studied.The prediction models of the radial and circumferential material flow as well as the material flow on the tooth surface are constructed,and the material flow is evaluated by the relative sliding distance.The flow velocity and displacement of the formed workpiece material in the axial,radial and circumferential direction are analyzed by using the Point-tracking in DEFORM-3D,and the root cause and location of the forming defects are found.The blanks are sliced to thin pieces and the grid pattern(GP)is utilized to track the trajectory of flowing materials,which provides the basis for the subsequent size calculation of the workpiece and the design of the rolling tools.Moreover,the effect of material flow on the microstructure is also studied.(3)Study on the crest defect formation and growth mechanism of the workpiece.Growth coefficient of the workpiece with considering the effective top circle is modeled to investigate the influences of the number of teeth of the formed workpiece,addendum coefficient,tip clearance coefficient,module,tooth width,root fillet,pressue angle and end-bulge on the initial dimension of the workpiece.Then the influences of the number of teeth on the workpiece,module,pressue angle and material on the top circle of the formed workpiece is analyzed by simulation software,and the growth coefficient of the formed teeth at different conditions are given.Finally,the validity of the proposed model is verified by the experiments,and it can provide a new method for determining the initial dimension of the workpiece.(4)Geometric design and experimental study of the rolling tools are finished,it includes structural determination of the rolling tools based on the characteristic of gear throughfeed rolling process,modeling of cone angle of the entrance section,tooth depth of the correction section and addendum coefficients of the correction and exit section as well as effect of geometric parameters of rolling tools on rolling process.Obtaining mechanical properties of the cold working die steel DC53 through the room temperature tensile test.The proposed geometric design method of rolling tools is also verifed by the manufactured rolling tools,which provides a tool for the related experiments.(5)An experimental machine for cylindrical gear roll-forming is developed and accuracy of the formed workpiece is analyzed.The mechanical structures(workpiece clamping,phase adjustment and synchronous rotation of rolling tools)and principle of hydraulic system are designed and then the accuracy of the workpiece(20CrMnTi)formed by the experimental machine is detected and analyzed.The results show that the single pitch error,total profile error and profile error are IT7;the tooth profile slope error and radial runout are IT8;the total cumulative pitch error is IT9,and the length variation of common normal is IT10.