The machining gap during constant velocity-feed glass micro-drilling by Spark Assisted Chemical Engraving

Spark Assisted Chemical Engraving (SACE) is one among several technologies used to micro-drill glass. So far, two strategies are used in SACE: gravity-feed and constant velocity-feed drilling. Contrary to gravity-feed, constant velocity-feed drilling is less studied. The last presents several advantages from the technological point of view, the major one being that machining can be conducted with no contact between the tool and the glass work-piece if a gap between both surfaces can be maintained. In this paper a methodology to measure the gap between the tool and work-piece is presented.The gap is measured for different machining conditions that allow varying the local flushing and heating. It is found that both factors affect the gap which is estimated to be in the order of 5–10 μm for typical SACE machining conditions. A model that estimates the machining gap is proposed based on the process understanding brought throughout this work. Further, it is found that the bottom hole surface texture is affected by the electrolyte flow within the machining gap.