Formation Mechanism of Surface Integrity Anisotropism after Milling Laser-Deposition-Manufactured Titanium Alloy

The special characteristics of the laser deposition manufacturing (LDM) process for forming titanium alloys (Ti6Al4V) lead to significant anisotropy in the mechanical properties of the alloy. The existence of anisotropy leads to different processing efficiency and processing performance in different processing directions. In this study, the cutting force, cutting temperature, and surface integrity of the additive titanium alloy machined by LDM at five angles of 0, 22.5, 45, 67.5, and 90° to the deposition direction were comparatively studied. Tensile properties, cutting force, cutting temperature, surface topography, surface roughness, and work hardening were used as evaluation indicators to observe the surface layer of the material after end milling under the same milling parameters. The results showed that the smallest grain size at the machining angle of 22.5° resulted in slightly higher cutting forces, cutting temperatures, and surface roughness than the other four groups. Meanwhile, large surface defects such as scratches and plowing were observed on the surface of the specimens at 22.5°, with a higher degree of machining hardening and deeper hardening layer depth. It proves that the anisotropy of the additive titanium alloy itself will have a greater impact on the cutting force, cutting temperature and surface integrity during its machining.