Study On Mechanism And Experiment Of Electric Resistance Heating Grind-hardening

Grind-hardening, as a highly integrated process, not only makes good use of grinding heat, but also replaces the processes of heat treatment, cleaning and transport, which will shorten the process chain, increase the manufacturing efficiency and reduce the pollution. Thus, the research of grind-hardening is of great importance. In view of low harden layer depth and the tensile residual stress or small compressive residual stress distribution in grind-hardening layer, the electric resistance heating grind-hardening is proposed to improve the harden layer depth and the surface residual stress distribution. This paper mainly focuses on the following aspects:Firstly, the impact of preheating temperature on the harden layer depth is quantitatively analyzed based on energy conservation, and the relationship between heating temperature and heating current is studied, which are helpful to explain the feasibility of electric resistance heating grind-hardening. Then, the scheme of experiment platform is designed, and the associated equipment is designed and selected. When the set-up has been put up, the heating speed is studied by an experiment.Secondly, the experiment scheme is designed and the electric resistance heating grind-hardening experiment has been done on 40 Cr steel. The influences of preheating temperature on grinding force and surface quality(including surface roughness, surface topography, harden layer depth and micro-hardness, residual stress on machined surface) are analyzed. The results show that the grinding force slightly decreases, while the harden layer depth obviously increases as the rising of preheating temperature. And the micro-hardness of the harder layer in preheating grind-hardening is lower than that of dry grinding. Moreover, the surface residual stress changes from tensile residual stress to compressive residual stress. What’s more, the influences of preheating temperature and grinding depth on harden layer depth are compared. The results show that the electric resistance heating grind-hardening can get deeper harden layer depth by using small grinding depth, which can lead to less wear of the grinding wheel and less supply of the spindle power.Finally, based on the energy conservation and heat transfer theory, the total energy and subsurface temperature of workpiece are calculated, and the workpiece temperature field is simulated. The calculated results show that the total energy and the subsurface temperature are increased with the rising of the heating temperature. At the same time, the simulation analysis shows that the surface temperature and subsurface temperature all increase while the temperature gradient decreases. Thus, with the compensation of preheating energy, the harden layer depth is increased, and the surface residual stress is also improved.