Electrochemical finishing of complex curved internal channels fabricated by metal additive manufacturing using a segmented multi-link cathode

Abstract The polishing of curved internal channels in metal additive manufacturing remains exceedingly challenging, primarily constrained by the limitations of cathode structures and the intricate geometry of internal channels. To address this issue, an electrochemical finishing method with a segmented multi-link cathode is proposed for the polishing of curved holes fabricated via selective laser melting. Simulation results of stress and offset amount show that the segmented multi-link cathode in the curved hole enables flexible bend to adapt to the channel’s contour. Moreover, the integration of the nylon brush facilitates the alignment of the center of the segmented multi-link cathode with that of the curved hole. Compared with the maximum offset amount of 0.21 mm at the center of the monolithic twisted cathode, the center of the segmented multi-link cathode exhibits negligible deviation. Current density distribution simulations further confirm that a uniform side gap ensures a homogeneous current density distribution during the electrochemical finishing. This uniformity mitigates the occurrence of non-uniform material removal problems, such as overcut polishing and undercut polishing. Consequently, a curved hole with a diameter of 2 mm, a length of 60 mm and a curvature radius of 120 mm is successfully polished. The average surface roughness Ra is reduced from 11.36 μm to 1.59 μm, while the average roundness is improved from 0.138 mm (achieved via conventional electropolishing with monolithic twisted cathode) to 0.011 mm using the proposed method. Furthermore, the proposed method enables the finishing of spiral internal channel with variable curvature radius and reciprocal internal channel with small curvature radius. The average surface roughness Ra of the spiral and reciprocal internal channel are remarkably reduced from 11.80 μm and 11.36 μm to 2.57 μm and 2.80 μm respectively. Such a result cannot be attained using conventional electropolishing, thereby validating the superiority of the proposed method.