Experimental investigation of the annular gradient process for circular channels using laser powder bed fusion

Laser powder bed fusion (L-PBF) technology is an appropriate scheme for producing intricate components with complex internal structures, such as the intricate flow channel networks in aircraft hydraulic manifolds. However, it is an enormous challenge to fabricate circular channels without support structures that exhibit low shape deviation and high surface quality through L-PBF. This study introduces an innovative annular gradient-forming process that divides the circular flow channel into three sections, namely the inner layer, the transition layer, and the substrate, sequentially from the inside to the outside along the radial direction. Throughout the L-PBF process, the laser energy density is incrementally increased for the inner layer, transition layer, and substrate. The research focuses on manufacturing Ti6Al4V (TC4) circular channels with a diameter of 10 mm, exploring various process parameters to achieve low surface roughness, high dimensional accuracy, and low porosity through the annular gradient process. The effectiveness of the proposed annular gradient process and its parameters is validated through the fabrication and testing of circular channels with diameters of 8 mm, 10 mm, and 12 mm. The results demonstrate that the root mean square deviation (RMS) of the horizontal circular channels using the annular gradient process is reduced by over 80%, and the surface roughness Ra is reduced by over 50%. Furthermore, the channels also have better mechanical properties.