Effect of lubricated CO2 on grinding of AISI 4140 steel

Abstract

This paper explores the potential of using lubricated liquid carbon dioxide (LCO₂) in grinding processes. Cooling and lubrication are critical in grinding, with conventional flood cooling effectively reducing temperatures and improving surface integrity. However, conventional fluids often contain petroleum-based substances, posing a challenge to fossil-free production. A novel approach involves the use of premixed LCO₂ and oil via single-channel minimum quantity lubrication (MQL), which has shown promise in machining with geometrically defined cutting edges but is under-researched in grinding.To fill this gap, we conducted an experimental study on the grindability of AISI 4140 steel, evaluating different cooling/lubrication methods and their effects on surface roughness, residual stresses, microhardness, grinding forces and specific energy. The results indicate that LCO₂ + MQL can achieve surface roughness and microhardness comparable to conventional flood cooling, especially for less aggressive finish grinding. However, higher tensile stresses in rough grinding suggest that cooling may be inadequate. Optimisation of nozzle design, orientation and flow rate can improve cooling efficiency and reduce residual tensile stresses. This study shows that LCO₂ + MQL is a viable, sustainable alternative to conventional flood cooling, capable of maintaining the required surface integrity in grinding operations.