Effects of minimum quantity lubrication (MQL) usage on machinability in turning of AISI 4140 material

Using cutting fluids is a common method in manufacturing processes to extend the tool life, improve surface quality and dimensional accuracy. Cutting fluids also facilitate chip breaking and chip transfer. However, excessive use of cutting fluids damages environment and human health and it also significantly increases the total production cost. Thus, it is necessary to identify alternative methods to conventional cutting fluids. By applying techniques such as minimum quantity lubrication (MQL), consumption of cutting fluids and production costs can be reduced. MQL method enhances the cutting tool life and surface quality by cooling cutting tool and workpiece in cutting area and it also helps temperature decrease in the cutting area by moving away chips through its compressed air property. In this study, it is aimed to examine the effects of MQL usage on machinability in turning of material AISI 4140. Therefore, machining and tool wear experiments were performed on different machining conditions and cutting parameters. The machining conditions were determined as dry machining, wet machining and three different MQL flow rates and machinability criteria were evaluated in terms of cutting forces, tool wear and surface roughness. Four different cutting speeds (75, 100, 125, 150 m/min), three different feeds (0.16, 0.25, 0.5 mm/rev) and constant depth of cut (2.5 mm) were used as cutting parameters in machining experiments while constant cutting speed (125 m/min), feed (0.16 mm/rev) and depth of cut (2.5 mm) were used in tool wear experiments. As a result of the experiments, it was determined that the MQL application generally reduced the main cutting forces according to the dry and wet machining and the increase in MQL flow rate had a positive effect on the main cutting forces to a certain level. It was seen that the lowest values in surface roughness were generally obtained by MQL application and there was no regular trend in surface roughness values according to MQL flow rate increase. It was determined that the average flank wear of the cutting tool decreased with MQL application in comparison to dry and conventional wet machining and positively affected by MQL flow rate increase. It was also seen that the main cutting force and surface roughness increased with the feed and generally decreased with the cutting speed in all machining conditions.