Modeling the Forces Exerted on the Tool-Electrode During Spark Assisted Chemical Engraving Constant Velocity Feed-Drilling

Spark Assisted Chemical Engraving (SACE) is an interesting technology for micro-machining several types of non-conductive materials like glass, quartz, polymers and some ceramics. The process takes place in an electrochemical cell with two electrodes immersed in an electrolyte. The electrolytic solution is typically sodium hydroxide (30%wt NaOH) or potassium hydroxide (KOH). The cathode is used as tool and the anode as counter-electrode. When the applied voltage is higher than a critical value (typically around 30V, depending on the electrolyte and tool-electrode geometry) bubbles grow so dense on the electrode surface that they coalesce into a gas film. Electrical discharges occur between the electrode and the electrolyte. Machining begins consequently if the electrode is placed close enough to the surface to be machined (typically 25μm for glass). In the present paper, the forces exerted on the tool-electrode during constant velocity feed drilling is investigated experimentally and a model is proposed. The setup is composed of a machine head mounted on XYZ precision linear stage holding the tool-electrode. The machining head further incorporates a force sensor which is able to monitor, during drilling operation, the force exerted on the tool-electrode based on the zero displacement measurement principle.