Surface finishing of additively manufactured IN718 lattices by electrochemical machining

Abstract

Metal additive manufacturing offers design freedom, but high surface roughness can limit key properties such as fatigue and pressure drop. Machining all over is a common strategy to mitigate surface roughness, which unfortunately becomes technically and economically prohibitive in the case of significant geometric complexity, e.g., an internal lattice structure. In this paper, a strategy for finishing the surfaces of lattices using the commercial electrochemical machining (ECM) process COOLPULSE is proposed and demonstrated. Inconel 718 lattice coupons and complementing cathode tooling were designed and manufactured via laser powder bed fusion (LPBF). The tooling featured prongs to reach into the core of the lattice coupon in order to establish proximity between cathode and lattice surface (workpiece) as well as ports to allow electrolyte circulation in and around the lattice coupon. Both features extended the electrochemically active region into the core of the workpiece. Inspection of the processed lattice specimens revealed that a significant amount of material was removed from internal surfaces with accompanying improvement in roughness. Depth profiling indicated that the improvement of lattice surface state extended well into the core of the specimen without diminishment, in contrast to an external-only blasting process.