A comparative study on material removal rate and surface roughness during electrochemical machining of 100Cr6 steel in oxidizing and reducing electrolytic environments

Abstract

Electrochemical machining is a promising technique for creating microtextured surfaces on engineering materials due to its advantages, including a high material removal rate and superior surface finish. Electrochemical machining, however, faces challenges that hinder its precision, primarily due to the formation of a passive oxide layer on the workpiece surface. This oxide layer negatively affects both material removal rate and surface roughness (Ra), complicating the machining process. High current densities (> 20 A/cm²) can improve material removal rate, but they also increase energy consumption and worsen surface finish quality due to the intensified oxide layer formation. This dynamic creates a trade-off between increased material removal and a deteriorated surface finish. The article investigates ways to overcome these limitations by selecting appropriate electrolytic environments for the process. The study focuses on the anodic dissolution behavior of 100Cr6 steel in two distinct electrolytic solutions. The first is an oxidizing electrolyte, consisting of potassium dichromate (K₂Cr₂O₇) and sodium chloride (NaCl), which promotes oxidation. The second is a reducing electrolyte, containing copper sulfate (CuSO₄) and NaCl, which affects the electrochemical dissolution process differently by reducing the steel surface. The maximum improvement in material removal rate with the oxidizing electrolyte is observed at 22%, but simultaneously, a reduction in surface finish quality by 16.4% is noted. The reducing electrolyte offers much better overall performance, with significant improvements in both material removal rate (48.5%) and surface finish quality (21.7%). This is attributed to the reduction in oxide layer formation, which allows for a more controlled and efficient machining process. Analytical techniques like cyclic voltammetry (CV), UV–visible spectrophotometry, and field emission scanning electron microscopy (FESEM) were employed to analyze the dissolution process and visualize surface changes after machining. The results show that the oxidizing environment exposes more metal surfaces than the reducing environment, which aids in understanding and optimizing electrochemical machining processes.