Minimum quantity lubrication grinding using nanofluids.

摘要

This research develops a new grinding temperature measurement method and a finite difference method (FDM) based grinding thermal model to study the application of nanofluids for minimum quantity lubrication (MQL) grinding. The formulation of nanofluids including Al2O3 and multi-wall carbon nanotubes is explored, and the thermal properties of nanofluids are characterized. High thermal conductivity enhancement of 61% is observed for ZnO nanofluids at 15 vol%. However, there is no significant difference between the nanofluids and the base fluids in terms of convective heat transfer. MQL grinding of cast iron using water- and oil-based nanofluids is investigated. Experimental results show that G-ratio can be significantly improved with high concentration Al2O3 nanofluids. However, water-based nanofluids are not able to provide superior cooling. Oil-based MoS2 nanofluids can significantly reduce grinding forces, increase G-ratio, and improve overall grinding performances. A new thermocouple fixating method, which is easy to install and can provide direct measurement of the surface temperature, is developed for grinding temperature measurement. For shallow-cut grinding of cast iron using aluminum oxide wheels, the energy partition, which is defined as the ratio of the energy entering the workpiece, is estimated as 84% for dry grinding, 84% for MQL grinding, but only 24% for wet grinding. Much lower energy partition, 68% for dry grinding, 54% for MQL grinding, and 13% for wet grinding, is achieved by using vitrified CBN wheels. The insufficient cooling problem of MQL grinding can be improved by using vitrified CBN wheels, which makes MQL grinding feasible in the high volume production. A grinding thermal model based on the FDM has been developed to investigate the transient heat transfer and temperature distributions in the workpiece with finite dimension and various cooling conditions. Investigation of cooling effects reveals that the grinding zone is the most critical cooling region. The FDM is further applied to investigate the convective cooling in grinding. The estimated average convection heat transfer coefficient in the grinding contact zone is about 4.2x105 W/m2-K for wet grinding and 2.5x104 W/m2-K for MQL grinding, while the estimated convection coefficient in the trailing edge is much lower.