The effects of the flow rate and speed of lubricoolant jets on heat transfer in the contact zone when grinding a nitrided steel

In this paper, the influence of lubrication parameters, such as flowrate and jet velocity, on the cutting fluid efficiency are studied. A foil/workpiece thermocouple and an inverse matching method are used to observe changes in the heat partition ratio, the heat flux absorbed into the fluid, the convection heat transfer coefficient (CHCT) and the maximum temperature in the contact area. Low jet velocity and flowrate tend to decrease the cutting fluid efficiency however excessive flowrate or jet speed in grinding are useless and do not lead to an extra decrease in the temperature of the grinding zone. The "burn out" phenomenon is also studied and the temperature at which it occurs is compared to the autoignition point of the cutting fluid. When burn occurs, the fluid no longer lubricates or cools the contact area. It allows an increase in the temperature in the grinding zone which may damage the microstructure of the workpiece, and produce distortions and cracks.