Hybrid Post-Processing

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Hybrid Post-Processing of Additively Manufactured (AM) Metal Surfaces

Additive manufacturing (AM) has undergone significant advancements, enabling the production of high-quality metal alloy components. This capability is becoming increasingly prominent in structural aerospace applications due to the improved material characteristics it offers. Unlike early metal AM methods, contemporary AM processes yield fully dense components with minimal porosity, often matching the properties of traditionally forged parts. Nevertheless, challenges persist with regard to achieving a satisfactory surface finish. For instance, in processes like Powder Bed Fusion (PBF), one may observe partially fused powder particles and visible deposition layers that can affect the surface finish. This rough surface finish presents difficulties in inspection and can negatively impact performance, particularly in terms of fatigue resistance and fracture toughness. While the surface finish of AM structures is indeed advancing, there is still a need for post-processing techniques such as surface machining or shot peening to enhance the surface quality. Nevertheless, achieving the desired surface finish can be challenging for internal surfaces and certain small features using these methods. 

To tackle the challenges posed by intricate AM structures, particularly the inner channels, our research group adopts a hybrid approach for post-processing AM parts. This approach combines cavitation peening and electrochemical polishing. While electrochemical polishing is a versatile and effective method for enhancing the surface quality of metals, it does have inherent limitations, such as a low material removal rate and limited impact on mechanical properties. By integrating ultrasonic cavitation peening with ECP, we have demonstrated that the synergistic effects of these two processes not only increase the rate of material removal but also enhance surface mechanical properties. For small AM parts, our current focus is on utilizing ultrasonic cavitation peening with ECP. However, our ongoing research aims to investigate the fundamental aspects of combining hydrodynamic cavitation peening with ECP as a single-step post-processing method, particularly for larger practical applications. 

SEM morphologies, a) Untreated as-built surface; b) Subjected to ultrasonic amplitude of 80 µm at a temperature of 70℃ for a duration of 60 minutes; c) Micro-dimples formed as a consequence of cavitation peening
Hybrid post-processing; (a) Electro-hydrodynamic principle; (b) Schematic diagram of the hybrid process
Surface topography, a) Untreated as-built surface; b) ECP only; c) Cavitation only; d) Hybrid process.

 

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Intensified electrohydrodynamic effect, a) Initial stage; b) Immediate transition stage, phase 1 with DC power on; c) Transition stage, phase 2 with approximately 2 seconds after when DC power is on; d) Final stage with focused cavitation peening toward the anode.

 

Publications 

J. H. Jeon*, A. Rashid, N. Panpalia, S. Melkote, “Effect of Electropolishing on Ultrasonic Cavitation in Hybrid Post-Processing of Additively Manufactured Metal Surfaces” NAMRC 52 2024, Under review, 10/2023) 

J. H. Jeon*, S. H. Ahn, S, N Melkote, “In-situ analysis of the Effect of Ultrasonic Cavitation on Electrochemical Polishing of Additively Manufactured Metal Surfaces” (Journal of Manufacturing Science and Engineering, Accepted, 01/2024) 

Wang, B., Castellana, J., and Melkote, S. N. (2021). “A hybrid post-processing method for improving the surface quality of additively manufactured metal parts.” CIRP Annals, 70(1), 175–178. 

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