Optimization of superalloy Inconel 718 micro-milling process by combined Taguchi and multi-criteria decision making method

Micro-cutting of Inconel 718 superalloys is very difficult due to its mechanical and chemical properties. It must be carried out under controlled and sustainable machining conditions to achieve adequate surface quality and dimensional accuracy. In this study, micromilling of channels is performed with a combination of different depth of cut and feed per tooth values combinations, and under MQL lubrication conditions. A relatively high cutting speed of 40 m/min, and micromilling tool with diameter 0.6 mm and extra-long neck, is used. The cutting force, channel depth deviation, surface roughness, and burr formation are analyzed as process performance outputs. There is concluded that the cutting force, channel depth deviation and burr formation increased with the increase of cutting parameters. Increasing of the cutting parameters had a different effect on the surface roughness. ANOVA showed that depth of cut is most significant parameter to cutting force in x-direction (parameter influence PI = 65.5%), burr height (with PI = 61.5%), and channel depth deviation (PI = 67.5%). Feed per tooth is most significant parameter to surface roughness also (with PI = 74.6%), and cutting force in z-direction (PI = 56.3%). Optimal cutting parameters was concluded by combined Taguchi and TOPSIS method, which converts a single-objective optimization problem into a multi-objective optimization problem. As optimal cutting parameters were found depth of cut of a_p = 0.010 mm and feed per tooth of f_z = 0.008 mm/tooth. These parameters resulted in a channel depth deviation of 0.41 μm, a burr formation height of 6 μm, and surface roughness arithmetic mean of 0.24 μm. Analysis is shown that both varied micromilling parameters are statistically significant on closeness coefficient, and feed per tooth has the greatest influence on the response PI = 52.3%, followed by depth of cut PI = 37.1%.