Characteristics of Millisecond Fibre Laser Drilling of Alumina Ceramics

Laser drilling of metals and alloys is a well-established process widely utilised in industries such as aerospace, medical, and automotive. However, the laser drilling of ceramics, particularly alumina of thickness greater than 5 mm, remains a significant challenge. This difficulty arises from alumina’s high melting temperature, brittleness that leads to cracking, and its low absorption of standard fibre laser wavelength. This study investigates laser trepanning drilling of 6 mm thick alumina, focusing on understanding the material removal characteristics and the influence of key process parameters on hole geometry and thermal damages. The effects of pulse energy, frequency, assist gas composition, and trepanning speed were systematically examined. A minimum specific energy requirement of 80 J/mm was established for through-hole formation, while crack initiation occurred beyond 640 J/mm. Among various assist gases tested, oxygen demonstrated superior performance with minimal taper despite no reactive fusion. Optimal drilling performance can be achieved by balancing pulse energy (for hole geometry stability and minimal thermal affected zone), frequency (for controlled thermal effects), and trepanning speed (for minimal taper and reduced thermal affected zone).