Induction Heat Treatment Study Of Hub Bearing Flange Inner Ring

The use of third-generation automobile hub bearing unit, which has been widely used in the passenger car industry, has effectively improved the operational stability of the bearing and saved a large amount of time in complete vehicle assembly. The heat treatment quality of the flange inner ring can directly affect the usability and reliability of the entire hub bearing unit.This paper designs a hardening inductor for the flange inner ring of the third-generation hub bearing by analyzing the induction heat treatment technology requirements of the flange inner ring of the hub bearing and basic structure of its inductor. The design mainly includes induction coil size design, design of the clearance between induction coil and workpiece, and magnetizer selection.Effects of different induction heat treatment parameters on hardening depth and microstructure of the third generation hub bearing flange inner ring were investigated. Results show that macroscopic profile expands obviously and the depth of hardening zone increases with the increasing of input energy during induction heat treatment; The normal microstructure in surface and sub-surface layer consists of fine needle martensite and lath martensite, while the too high input energy results in the surface over-heating and formation of thick needle martensite, even over-burning. The normal microstructure in transition zone consists of fine needle martensite, a small amount of ferrite and troostite, but too low input energy cause the presence of a large amount of troostite and the increasing fraction of retained ferrite. Base on the present work, the optimum induction heat treatment process parameters is recommended, including the quenching power of 180 KW, and heating time of 5.4s. Base on tempering hardness value under different power parameter, the optimum induction tempering process parameters is recommended, the tempering power of 8.5KW.Through normality tests and process capability analysises on bolt hole positions before and after the heat treatment with Minitab analysis software, the impact of the induction heat treatment on the deformation of the third generation hub bearing flange inner ring were investigated. Results show that the maximum impact of the induction heat treatment on the bolt hole position is determined to be within 0.085 mm, which can be regarded as the design basis for the position tolerance requirement of the bolt hole before the heat treatment. The correlation analysis method is adopted to carry out the deformation analysis on the flange and spigot based on paired T tests, results show that changes in bolt hole positions are mainly due to flange deformation.