Fabrication of through-hole with biconically shaped cross sections by using electroforming and inert metal mask electrochemical machining

Based on the inert metal perforation plate acted as both mandrel and mask, a hybrid electrochemical fabrication process combining electroforming and mask electrochemical machining was proposed to manufacture metal through-hole arrays with double tapered openings. The feasibility of this novel hybrid process was first investigated theoretically according to developed numerical models, and then, the effect of structure parameters of the inert metal plate on profile characteristics of the through-hole being processed was numerically analyzed where optimal structure parameters were further determined. Subsequent experimental results, on the whole, agreed with those from numerical analysis. Research results showed that the profile characteristics of the shaped through-hole were significantly dependent on the structure parameters of the inert metal plate used. Smaller through-holes with a better symmetry between the opening profiles can be achieved if the inert metal plates with bigger thickness and larger hole wall angle were used. With the reduction of hole spacing in the inert metal plate, the achievable aspect ratio of the machined through-hole gradually increased, and the profile symmetry between entry and exit became better. With the increase of hole size of the patterned inert metal plate, the thickness limitation of the through-hole plates that can be achieved rose, but the minimum diameter tended to be smaller and the symmetry worsened. In addition, nonconventional inward horn-shaped profile can be shaped in the mask electrochemical machining step only when the inert metal plates having small hole spacing and hole wall angle are utilized. With a diameter deviation between the entry and the exit, 9.7 % and an expanding rate 110.1 %, favorable through-holes featuring good opening profile symmetry (88.8 %) and smooth surfaces can be machined using this hybrid process.