Optimization Of Heat Treatment Process On Automotive Transmission Second Output Flange

Hardening and Tempering Heat Treatment is a composite process of high temperature tempering after quenching for steel parts,mainly as a preparatory or final heat treatment for medium carbon steel or medium carbon alloy steel.Isothermal normalising is an isothermal stage added to the normal normalising process,it has the advantage of more uniform metallurgical organisation and less deformation.45 steel has the advantages of mature technology and low price,and is widely used in the machinery industry.However,its tempering heat treatment has the deficiencies of long cycle,poor machinability,and high cost.An auto parts enterprise production of automotive transmission second shaft output flange,using 45 steel tempering heat treatment,the process has a long heat treatment cycle,short tool life,induction quenching bore deformation and other problems,resulting in high production costs.This paper proposes to use a shorter cycle time and lower cost isothermal normalizing process instead of quenching process to achieve the enterprise’s goal of improving efficiency and reducing costs,and to provide a reference for similar products.Firstly,the theory related to phase transformation of solid metals is described and the parameter requirements of phase transformation,CCT/TTT for heat treatment of 45 steel materials are obtained by JMatPro analysis software.The controlling equations for the transient temperature field and the analytical solutions for the zero-dimensional temperature field of the test bar under the third type boundary conditions are analyzed and obtained by calculations.Afterwards,the heat treatment process simulation curves for isothermal normalization and tempering of the test bar were obtained by ANSYS transient temperature field simulation analysis and compared with the analytical solution for isothermal normalization of the test bar,the maximum discrepancy between the two was 2.63%.At the same time,the simulation curve of the heat treatment process of isothermal normalization and tempering of flanges was obtained,the results showed that the isothermal normalization process can shorten the process time by 38.97% compared with the tempering process.Secondly,the isothermal normalizing and tempering heat treatment simulation process was verified through experiments,the hardness,metallurgical organization and one-way tensile tests were carried out.The effect of heat treatment on the surface quality of flange machining and tool life was analyzed through comparative turning,grinding and drilling experiments.The induction quenching process of the flange was compared and optimized.By adjusting the gap between the induction heater and the flange,the depth of the hardened layer was reduced and the deformation of the flange inner bore was reduced.The experimental results show that:(1)the cutting surface quality of the flange meets the requirements after isothermal normalization,and the tool life of the drill is 1.6 times that of the tempering heat treatment.(2)When the gap between the induction heater and the flange is increased from4.00 mm to 5.00 mm,the depth of the hardened layer is reduced from 2.50 mm to 1.75 mm,while the deformation of the inner bore is reduced from 0.036 mm to 0.016 mm to meet the process requirements.And the cubic polynomial of the hardened layer depth was obtained by MATLAB fitting,which can realize the prediction of the hardened layer depth.Finally,the strength analysis of the finished isothermal normalized heat-treated flange is carried out,the theoretical analysis of the overall flange strength,internal spline compressive stress,bending stress,tooth root maximum shear stress and the corresponding safety factors are calculated,and the formula for calculating the internal spline maximum shear stress is derived based on the existing formula for calculating the external spline tooth root maximum shear stress.Based on the Archard wear theory,the theoretical calculation of the surface wear of the flange and oil seal mating was carried out,and the formulae for calculating the surface wear of the flange in each gear were obtained.The flange was then subjected to a static simulation and a durability test bench test.The results show that the maximum deviation of7.89% between the theoretical calculation and the simulation results of the stresses and safety factors meet the requirements.