Analysis of residual stress and cutting force in end milling of Inconel 718 using conventional flood cooling and minimum quantity lubrication

Due to its excellent mechanical strength and corrosion resistance at high temperatures, Inconel 718 alloy has several applications in the aerospace and nuclear industries. This austenitic material promotes rapid hardening by self-hardening during machining, and its low thermal conductivity leads to high temperature in the cutting zone. As heat increases, cutting tool wear accelerates, compromising the final quality of the machined workpiece. These factors lead to Inconel 718’s difficult machinability and influence the presence of surface residual stresses due to thermal and mechanical loads during machining. To address a knowledge gap pertaining to Inconel 718 end milling, this study conducts a series of experiments to gather a set of important results. The optimum cutting speed is calculated by high-efficiency range analysis using the conventional flood method; then, this calculated speed was adopted in the minimum quantity lubrication (MQL) experiments, and the results of the two methods were compared. For the same cutting conditions, the cutting fluid method did not influence the cutting force and surface hardness results, which remained constant along the cutting length. In the MQL application mode, the flow rate influenced tool wear, which was greater than for the flood mode throughout the cutting length. The flood method resulted in improved residual stresses in the longitudinal and transverse directions when compared with MQL, obtaining compressive residual stresses for longer cutting lengths. Surface roughness values were similar for the two lubrication methods up to 50 mm, from which the flood method values increase. Based on the results, the flood mode was found to be the preferred method for milling Inconel 718.