15. Investigations on the Influence of Size Effect on Surface Characteristics During Micro-End Milling of Inconel 718

Micro-end milling is one of the widely used micromachining techniques in industries and research organizations to produce microfeatures having complex 3D shapes with high flexibility and high material removal rate. The analysis of areal surface roughness, surface defect, and microhardness are important for understanding the surface characteristics of the machined surface. This paper focused on the analysis of areal surface roughness, surface defect, and microhardness during micro-end milling on Inconel 718. Inconel 718, a nickel-based superalloy, was used as the workpiece material due to the superior properties such as high hardness, high strength to weight ratio, resistance to high-temperature loading, and corrosion resistance. Areal surface roughness and microhardness were taken as responses to understand their variations with feed per tooth at a constant depth of cut and speed. The feed per tooth is selected by giving importance to both inside and outside the size effect zone. It was observed that the areal surface roughness shows a decreasing trend initially at lower feed per tooth and then it shows an increasing trend outside the size effect region. The minimum value of areal surface roughness (Sa) was found to be in the range of 3 µm, which is the cutting edge radius of the tool. Inside the size effect zone, severe strain hardening was observed. Size effect in microhardness was also found. Inside the size effect region, the microhardness increases with feed per tooth and outside size effect region microhardness shows a decreasing trend.