The effect of hybrid cooling/lubrication techniques on surface roughness and cutting temperature in turning of AISI 2507 super duplex stainless steel

In this study, the effects of cutting parameters on cutting temperature and surface roughness were investigated in turning of AISI 2507 duplex stainless steel under different cooling/lubrication conditions. The experiments were carried out under three different cooling lubrication conditions (MQL, Cryo and Cryo+MQL), three different cutting speeds (80, 120 and 160 m/min) and three different feed rates (0.16-0.20 and 0.24 mm/rev). In turning experiments, PVD TiCN coated carbide cutting tools (CNMG 120408 ML) were used. Vegetable based cutting oil was used as cutting oil in the MQL system and liquid nitrogen (LN2) was used in the cryogenic cooling system. The experiments were carried out according to Taguchi orthogonal L27 experimental design and signal-to-noise ratios (S/N) were used to evaluate the data obtained from the experiments. Variance analysis (ANOVA) was used to determine the effect levels of the factors. In addition, multiple regression analysis was performed to obtain estimation equations. As a result of the experimental study, the lowest surface roughness value was obtained under the Cryo+MQL cooling lubrication condition, cutting speed of 160 m/min and feed rate of 0.16 mm/rev. The lowest cutting temperature was obtained at Cryo+MQL cooling lubrication condition, cutting speed of 80 m/min and feed rate of 0.16 mm/rev. Combining the superior lubrication of MQL with the superior cooling of cryogenic cooling has been shown to have a significant effect on improved surface quality (surface roughness and topography) and reduced cutting temperature. According to the ANOVA results, the most effective parameter was the feed rate with 81.54% contribution rate on surface roughness and cooling/lubrication method with 91.30% contribution rate in tool life. As a result of multiple regression analysis, determination coefficients of the obtained equations were determined as 0.9551 and 0.9875 for surface roughness and shear temperature, respectively.