Tool type and hole diameter influence in deep ultrasonic drilling of micro-holes in glass

Brittle materials such as ceramics, glasses and oxide single crystals find increasing applications in advanced micro-engineering products. Machining small features in such materials represents a manufacturing challenge. Ultrasonic drilling constitutes a promising technique for realizing simple micro-holes of high diameter-to-depth ratio. The process involves impacting abrasive particles in suspension in a liquid slurry between tool and work piece. Among the process performance criteria, the drilling time (productivity) is one of the most important quantities to evaluate the suitability of the process for industrial applications. This paper summarizes recent results pertaining to the ultrasonic micro-drilling process obtained with a semi-industrial 3-axis machine. The work piece is vibrated at 40 kHz frequency with an amplitude of several micrometers. A voice-coil actuator and a control loop based on the drilling force impose the tool feed. In addition, the tool is rotated at a prescribed speed to improve the drilling speed as well as the hole geometry. Typically, a WC wire serves as tool to bore 100 mu m and 200 mu m diameter micro-holes of 300 to 1,000 mu m depth in glass and ruby. The abrasive slurry contains B4C particles of 1 mu m to 5 mu m diameter in various concentrations. This paper discusses, on the basis of the experimental results for glass deep hole micro-machining, the influence of the hole diameter (100 or 200 mu m), and the type of tool (wire or drill). The use of drills help to keep a higher mean drilling speed while the cylindrical wire tools provide a higher speed (twice) in the first 20% of the drilling depth. This study shows that the drilling speed in glass deep mu icro-drilling is depending on depth and type of tool used. (C) 2013 The Authors. Published by Elsevier B.V.