Study on the Surface Quality of Overhanging Holes Fabricated by Additive/Subtractive Hybrid Manufacturing for Ti6Al4V Alloy

Abstract

Additive/subtractive hybrid manufacturing (ASHM) based on laser powder bed fusion (LPBF) enables to achieve high precision and good surface quality of complex structures such as small holes with overhanging features. However, the rapid heating and cooling rates during the ASHM results in sinkage at the alternating interface of additive manufacturing and subtractive milling, which degrades the surface quality of the components. This study employs shielding height at the alternating interface to solve this problem and improve the surface quality. The effect of internal diameters and shielding heights on the surface quality were studied experimentally for overhanging holes fabricated by ASHM of Ti6Al4V. The results show that the Ti6Al4V samples prepared by LPBF possessed high density and uniformly distributed microstructure. For overhanging holes without shielding height, the largest depth value of sinkage and surface roughness were obtained, indicating a worse surface quality; when the shielding height was increased to 0.5 mm, the smallest sinkage value and surface roughness were obtained, indicating a better surface quality. With the same shielding height, the overhanging holes with different diameters had a similar surface roughness. This study reveals that an appropriate shielding height can improve the surface quality, which provides guidance to the improvement of the surface quality for complex structures in ASHM.