Analysis of tool wear in micromilling Ti6Al4V and its impact on generated surface integrity

Tool wear is one of the dominant factors that impacts the surface integrity of machined materials. Understanding the impact of tool wear on surface integrity is crucial in micromilling, due to the size of the features being machined and the cutting tools. Therefore, this work aims to analyse the impact of tool wear on surface integrity during the micromilling of Ti6Al4V. In this context, microslots were manufactured on a Ti6Al4V workpiece using both coated and uncoated 1 mm flat end mills at constant cutting parameters with varying cutting lengths in order to analyse the progression of tool wear with machined length and its impact on surface integrity. The microtools were investigated using both Scanning Electron Microscope (SEM) and infinite focus optical imaging (Alicona) to determine the tool wear evolution. Surface integrity was assessed by analysing surface roughness areal parameters, surface microscope images, and subsurface microstructure and microhardness perpendicular to the cutting direction. The results show that surface quality was not affected by the evolution of tool wear, with surface topography, including surface roughness parameters, remaining within a similar range until the catastrophic failure of the tool. Analysis of the machined surface revealed small chips adhered to it, which affected the surface texture height measurements, leading to a predominance of atypical peaks on the surface. Subsurface analysis of the machined material showed that the microstructure and microhardness remained consistent with the bulk material characteristics, indicating no evidence of severe plastic deformation in the machined subsurface. However, once the tool failed and began rubbing against the workpiece surface, swept grains due to material dragging and heat-affected zones were observed in the subsurface microstructure. Swept grains, caused by material extrusion, were also observed in the microstructure of the top burr formation regions throughout the experiments. From the tool wear morphology analyses, adhesive wear was the main wear mode observed, with abrasion, built-up edge formation and heat-affected zones also being observed in the tools.