The mechanism of anisotropic micro-milling properties in additively manufactured Ti-6Al-4V alloy

Selective Laser Melting (SLM) technology offers great flexibility in manufacturing complex parts. However, secondary processing of selective laser melted (SLMed) parts is essential due to the poor surface morphology. This study investigated the influence of microstructural anisotropy in SLMed Ti-6Al-4V alloy on micro-milling performance. The orthogonal milling tests were conducted on the top, front, and side surfaces of specimens. Parameters including cutting force, chip morphology, burr morphology, surface quality, microhardness, and microstructure were evaluated to represent the anisotropy. The experimental findings demonstrated that the tool's orientation relative to the columnar grains influenced the slip strain modes and the density of grain boundaries in the shear band, thereby determining the correlation of the cutting force with the machined surface and feed direction. The variations in grain boundary density in different machining regions caused plastic anisotropy, which affects chip morphology, burr formation, and machined surface roughness. This research could provide valuable insights for manufacturers in selecting appropriate machining methods for precision processing.