Thermal analysis of minimum quantity lubrication-MQL grinding process

Generally, compared to other machining processes, grinding involves high specific energy. Major fraction of this energy is changed into heat which makes harmful effect on surface quality as well as tool wear. As the name implies, MQL grinding uses a very small quantity of lubricant delivered precisely to the cutting zone. Often the quantity used is so small that no lubricant is recovered from the parts. A number of studies have shown that compared to dry grinding; MQL technique substantially enhances cutting performance in terms of increasing wheel life and improving the quality of the ground parts. However, there is not any investigation of thermal analysis in MQL grinding process. This paper presents a new method to calculate grinding temperatures and the energy partition to the workpiece during MQL grinding. Also, this model can be used for other grinding operations such as dry and conventional fluid grinding operations. To verify this model, temperature distributions were measured in the subsurface of 100Cr6 hardened steel workpieces using an embedded thermocouple during grinding with dry, MQL and conventional fluid grinding processes. In other words, to more accurately predict grinding zone temperatures and heat fluxes, refinements such as convection heat transfer coefficient of MQL/fluid in the grinding zone and incorporation of MQL/fluid-workpiece convective heat flux effects outside the grinding zone, have been made to the existing thermal model. The effects of conventional fluid parameters and MQL technique such as air pressure, oil mist flow rate, and oil droplet properties have been considered in Nusselt number to predict convection coefficient of fluid, and MQL grinding process. Using this analytical analysis procedure, the surface heat flux profile in the grinding zone as well as sub surface temperature distribution can be computed from grinding process parameters. The estimated and measured average convection heat transfer coefficient in the grinding contact zone was about 3.7×104–4.3×104 W/m2 K for fluid grinding and 900–1500 W/m2 K for MQL grinding that is in the range of measured values.

► Analytical modeling of temperature and energy partition in MQL grinding was studied.
► Convection heat transfer coefficient of MQL/fluid in the grinding zone and outside the grinding zone, have been calculated.
► The optimum MQL and grinding parameters have been determined to reduce thermal damages.