On processing strategy to minimize defects while drilling borosilicate glass with microwave energy

Abstract

Application of microwave energy at 2.45 GHz frequency has the potential to provide thermal energy-based alternative solution to drilling of glass in the sub-millimeter domain. In this process, the concentrated microwave energy around a concentrator (tool) is utilized to melt or ablate the target material from the workpiece. The present study discusses the effect of parameters like tool shape, tool immersion depth, feed rate, and machining gap on the quality of hole in terms of thermal damage, overcut, and amount of material removed while drilling borosilicate glass using a graphite concentrator. It was found that the concentrator with a conical tip performs better compared to the concentrator with cylindrical tip due to concentration of thermal energy at the tip. Further, it was observed that the thermal damage, overcut, and amount of material removed decrease with the increase in immersion depth and feed rate. A machining gap (~ 300 μm) between the concentrator tip and the workpiece is essential as it facilitates flushing the glass residue from the machining zone. Effective flushing also reduces thermal damage and roundness error around the hole drilled. However, overcut and amount of material removed increases with increase in the machining gap due to increased plasma zone area and interaction time between plasma and the workpiece. The results of heat-affected zone obtained from this research were significantly less compared to that in published results. The approach was found to be promising while drilling borosilicate glass, though further study will be needed to improve precision.