Effect of Process Parameters on the Roughness and Wetting Characteristics of SS304 Surfaces Using Electrolytic and Plasma Electrolytic Polishing Techniques
K. Sushil, Vyom Sharma, Shikhar Krishn Jha, C. Chandraprakash, J. Ramkumar
Abstract
Metallic parts manufactured by conventional machining and additive manufacturing techniques possess poor surface quality and require post-processing operations before their end-use. Many methods exist for the post-processing of parts with free-form surfaces. In this study, two of the most used polishing techniques, electrolytic polishing (EP) and plasma electrolytic polishing (PeP), were investigated to understand the morphology of the resultant surface after both techniques. Pilot experiments suggested that an aqueous solution of ammonium sulphate is the most effective electrolyte for both the polishing techniques in terms of the lowest achievable value of average surface roughness ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>a</mml:mi> </mml:mrow> </mml:msub> </mml:math> ). A systematic investigation of the electrolyte concentration, applied voltage, and polishing time revealed an identical dependence on all these process parameters: First, a decrease and then an increase in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>a</mml:mi> </mml:mrow> </mml:msub> <mml:mo>.</mml:mo> </mml:math> A minimum <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>a</mml:mi> </mml:mrow> </mml:msub> </mml:math> of 0.63 μ m and 0.49 μ m were achieved with EP and PeP, respectively. Samples polished by PeP possess high gloss with negligible changes to the shape and form of the samples. Furthermore, static contact angle measurements with water revealed that surfaces treated with PeP showed higher hydrophilicity compared to those polished with EP. This can be attributed to the lower <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>a</mml:mi> </mml:mrow> </mml:msub> </mml:math> value achieved with PeP.