Experimental Investigation On Grinding-hardening With Minimum Quantity Lubrication-MQL Technology

Grinding-hardening is a hybrid process, which realizes the combination of surface heat treatment and grinding process. Grinding-hardening, which replaces the heat treatment process, can shorten the production procedure, save processing time, reduce production costs and improve production efficiency. A nd also it contributes to energy conservation and emissions reduction. Thus, compared with the traditional surface hardening process, grinding-hardening has significant economic benefits. However, due to the lack of lubrication and cooling in the grinding zone in dry grinding, the surface quality of the workpiece after grinding-hardening is poor, which restricts the performance of the parts. Therefore, minimum quantity lubrication(MQL) technology is applied to the grinding-hardening process to improve the quality of grinding surface without greatly reducing the depth of the hardened layer by efficiently lubricating and cooling grinding surface at the condition of minimum quantity grinding fluid. The main research work of this paper are as follows:(1) The gas movement in the grinding zone is simulated by FLUENT software according to the formation principle of the gas barrier layer of grinding wheel and the influence of the gas barrier layer on the penetration of grinding fluid into the grinding zone. The velocity field and pressure field of the gas movement in the grinding wedge area are obtained. The influence of nozzle direction, compressed air pressure and grinding fluid flow rate on the penetration of grinding fluid into the grinding zone are studied. And the methods to improve on the penetration of grinding fluid into the grinding zone are put forward.(2) The experiments are done under the condition of dry grinding and MQL grinding. And the grinding force, grinding temperature and surface quality of the grinding hardened workpiece under different cooling conditions are comparatively studied. The results show that compared with dry grinding,the depth of hardened layer is slightly decreased while the surface quality of workpiece can be effectively improved in MQL grinding-hardening.(3) The temperature fields of MQL grinding-hardening is simulated by ANSYS software. And the temperature fields of the workpiece in grinding-hardening process are obtained. According to the formation mechanism of hardened layer, the depth of hardened layer is predicted, which is helpful for obtaining the variation of hardened layer depth under different grinding depth and feed speed in MQL grinding.(4) The influence of MQL parameters on grinding force, harden layer depth and surface roughness are experimental studied. The results show that the influence of MQL parameters on the depth of hardened layer is not obvious. The lowest surface roughness can be obtained by positioning nozzle in the forward grinding zone. Increasing the air pressure will be helpful for reducing surface roughness. Increasing the grinding fluid flow rate will also be beneficial for reducing surface roughness.