On the use of the current signal in spark assisted chemical engraving for micromachining process control

Spark-Assisted Chemical Engraving (SACE) is a hybrid manufacturing process used to micromachine glass and other hard-to-machine materials. A tool-electrode, integrated in an electrochemical cell, is used to generate sparks and locally heat the workpiece surface, which enables material removal through thermally-promoted etching by an alkaline electrolytic solution. A challenge in SACE machining is the precise in-situ monitoring of material removal for process control; (electro)mechanical solutions exist, however they are complex to realize, hence limiting the use of the SACE process for precision glass machining in industry and academia. The present study introduces novel, quantitative and practical methods of obtaining process information by measuring the current flowing through the electrodes for both workpiece surface referencing by probing and SACE machining feedback and control strategies. During workpiece surface probing operations, a spike in the average current signal was observed at a repeatable tool height with respect to the workpiece, which can be used to accurately and repeatably measure the machining gap in a probing operation. Furthermore, three distinct current modes were identified and related to a different gas film state during machining of microchannels, paving the way for active control of gas film stability through monitoring of the current signal.