Machinability improvement during high-speed end-milling of Inconel 718 alloy

“This thesis presents the results of the experimental investigation of the effects of machining parameters (spindle speed and feedrate) and cooling strategies [Minimum Quantity Lubrication (MQL), Cryogenic Liquid Nitrogen (LN2), and combined (MQL+LN2)] on cutting force components, cutting temperature, tool wear and surface roughness during high-speed slot end-milling of Inconel 718 alloy. In addition, a comparative evaluation of the three cooling strategies was conducted for cutting force components, surface roughness and residual stresses. All end-milling experiments were conducted on a Cincinnati Milacron Vertical Machining center (VMC), using a 0.5 inch (12.7 mm) diameter, 0.03 inch (0.762 mm) corner radius four-flute uncoated carbide end-mill. A one-third fractional factorial design of experiments was constructed (nine experimental runs) and used in analyzing all experimental results. Cutting force components were acquired using a Kistler type 9272 4-component dynamometer, which was connected to an amplifier and a junction box. Cutting temperature was measured using a 0.125 inch (3.175 mm) diameter ungrounded k-type thermocouple, while tool wear was investigated indirectly by analyzing the maximum cutting force components of the last two passes (19 and 20). Surface roughness and residual stresses were measured using a profilometer and X-ray diffraction respectively. The results showed that high spindle speed (750 rpm) and medium feed rate (2 ipm) gave the lowest cutting force components, while low spindle speed (250 rpm) gave the lowest cutting temperature and tool wear. Furthermore, a low spindle speed (250 rpm) and feed rate (1 ipm) gave the least surface roughness, while MQL cooling strategy induced the highest compressive stresses”--Abstract, page iv