The residual stress state in meso- and micro-milling processes with a ball-end mill in Ti-6Al-4V titanium alloy

An experimental investigation and comparative analysis of the residual stress state between micro- and meso-milling processes with a ball-end mill on the Ti-6Al-4V titanium alloy were carried out. A methodology to study the characteristic kinematics of a five-axis machining process in a three-axis vertical machining centre was proposed. The study considers the chip formation process according to the lead and tilt angles of the tool axis concerning the normal vector of the surface. When using the up-milling cutting strategy, the defect of smeared/adhered material to the surface occurs in both the micro- and meso-milling levels, associated with the build-up edge and build-up layer phenomenon. The residual stress tensor of the surface was obtained through the X-ray diffraction technique. The down-milling cutting strategy produced the best surface finish and higher compressive residual stresses. The experiments showed higher compressive residual stresses in the feed direction than in the cross-feed direction. The micro-milling process produced higher compressive residual stresses than those observed in the meso-milling process.