Study of Behavior of EC Discharges during PMMA Machining by ECDM Process
Authors: Arab Julfekar , Chen Shih-Chi 
Published: December 2024

Poly (methyl methacrylate)-PMMA material is an essential and useful material for the majority of microfluidic devices. The superior properties of PMMA, namely, optical transparency, biocompatibility and chemical inertness make the PMMA a worthy candidate for microfluidic devices. Micro-holes are one of the significant micro-features used in microfluidic devices fabricated in PMMA material. The various techniques of PMMA machining includes laser machining, hot embossing, injection molding, and mechanical cutting. Nevertheless, the usage of such processes is limited due to limitations such as higher cost, processing difficulties and machining quality. In recent times, the electrochemical discharge machining (ECDM) process has emerged as a efficient process for machining electrically non-conductive material such as glass, alumina etc. The present work is an attempt to perform micromachining in PMMA using the ECDM process. The primary mechanism of material removal in ECDM process consists of exhaustive and elevated temperature heating of the PMMA material due to the electrochemical (EC) discharges occurring at tool electrode tip in the EC region that leads to melting as well as vaporization of the material. Furthermore, the increment in the local machining region temperature enhances the rate of chemical etching which produces the smoother sidewalls of the microfeatures. The work material-PMMA, stainless steel tool electrode is kept in the close vicinity of each other in an electrochemical cell which also includes aqueous KOH electrolyte with counter ring electrode. The micro-hole quality factors such as size, depth, circularity etc. depend on the heat energy produced by EC discharges. Hence, the behavior of EC discharges greatly affects the machining process and micro-hole quality and it’s study is critical in order to achieve the micro-holes of appropriate quality for different microfluidic applications. The heat energy(q) generated, and EC discharges behavior depends majorly on the applied voltage (Va) and mean EC discharge current (Id). EC discharge behavior was evaluated by analyzing the Id values, the discharge frequency (f) with the help of current-time graphs which show the current peak stabilities and uniformities. Moreover, the stable and unstable EC discharge zones were also identified using the electrolysis current, discharge current and Va values recorded during the actual machining. The Va values up to 26 V indicated the instability region of EC discharges. The current peaks recorded for 26 V indicated the non-uniformity resulting in the micro-holes with inferior quality (higher size, lower depth, less circularity). The Va values greater than 28 V showed a higher stability as well as uniformity of EC discharges. Based on the outcome of the experimental results, superior quality micro-holes of varied sizes have been fabricated and characterized. The appropriate quality micro-holes of average opening size of ~181±5 µm with average depth of ~142± µm were achieved at the optimal range of Va i.e. 28 V to 30 V.

Figure 1