Influence of minimum quantity of lubrication (MQL) when turning hardened SAE 1045 steel: a comparison with dry machining

Minimum quantity of lubrication (MQL) is an efficient practice in machining of soft materials. Its application during machining of hard materials has not yet been completely explored in scientific research. This work evaluates the wear process of PCBN cutting tools, as well as machining forces, workpiece surface roughness and white layer depth, chip morphology, and chip microstructure in hard turning of induction hardened SAE1045 steel using MQL and compared to dry machining. Results demonstrated that for all the experiments (MQL and dry machining), the abrasive wear was the prevailing mechanism, where the tool wear modes were flank wear and crater wear. Notch wear was observed on both at the end of contact in the secondary cutting edge and at the end of the depth of cut. Secondary notch wear affects the white layer formation and increases the workpiece surface roughness. After a certain period along the cutting time, a reduction in the roughness with an increase in the average flank wear was also observed when using MQL. The use of MQL, despite reducing the average flank wear, increased the notch wear at the secondary cutting edge, and consequently increased the surface roughness. In regard to crater wear, the MQL reduced its occurrence. MQL provided better results than dry machining concerning the machining forces, as well as reduced the white layer occurrence.