Grindability of titanium alloy using cryogenic nanolubricant minimum quantity lubrication

The defect suppression of titanium alloy disturbed by low thermal conductivity is an urgent problem in grinding. The existing green manufacturing processes such as Nanolubricant minimum quantity lubrication (NMQL) and cryogenic air cooling are unsatisfactory due to insufficient cooling or lubrication performance. Cryogenic NMQL (CNMQL) is a new approach that utilizes the heat transfer capacity of cryogenic air and antiwear/antifriction performance of nanolubricant. However, the lack of grindability analysis and in-depth mechanism explanation limits the optimization and application of CNMQL. In this research, the calculation formulas for the Energy ratio coefficient of the cooling medium (Rm) and Defect ratio (Dr) of workpiece surface were established to evaluate Ti-6Al-4V grindability based on other common parameters, including force, temperature, surface roughness, workpiece and debris morphology. Results show that the lowest grinding force (tangential force is 46.8 N, normal force is 61.4 N), grinding peak temperature (151.2 °C), and surface roughness value (Ra = 0.468 μm) are obtained by CNMQL, compared with NMQL and cryogenic air cooling. The Rm in CNMQL is 36.4 %, which is 68.5 % higher than that of NMQL. The Dr value under CNMQL is 2.67 %, which is 84.5 % lower than cryogenic air cooling and 69.2 % lower than NMQL. Cryogenic nanolubricant displays excellent grinding performance due to its higher viscosity and shows significant improvement of convective heat transfer capacity. The critical cutting depth and plastic accumulation are significantly reduced therefore resulting in fewer surface defects.