Evolution of surface quality in micromilling Ti-6Al-4V alloy with increasing machined length

Micromilling is a subtractive manufacturing process that presents challenges due to scale effects and rapid tool wear. To understand the evolution of surface quality when increasing the machined length during the micromilling process, this study assessed the surface roughness, topography, and defects of slots micromilled on Ti-6Al-4V. For the experiments, 1 mm diameter flat end mills were employed, and the cutting parameters were varied using a full factorial design. Subsequently, the surface texture field parameter S_a was assessed every 20 mm, up until the machining length of 260 mm. The analysed results led to the conclusion that, for the adopted set of parameters and the machining length of up to 260 mm, surface roughness was not significantly correlated to the machined length in the micromilling process of Ti-6Al-4V, as the Pearson coefficient, obtained from the correlation analysis, was -0.052. However, the surface roughness was mainly influenced by feed rate (Pearson coefficient of 0.82), with higher feed rates leading to roug surfaces (up to S_a = 0.4 μm) duhere to the tool load increase that causes wider feed marks on the surface. Regarding the feed marks, they were affected by the tool rotational frequency due to system vibration. Additionally, surface defects of adhered material, smearing, tearing and side flow were observed. For lower feeds, material adhesion was the main type of defect observed, while higher feed rates favoured the side flow phenomenon.