By: Yinzhou Yan

Laser drilling is commonly acknowledged as a hole fabricating technique especially for hard and brittle materials like advanced ceramics. Unfortunately, laser drilled hole are inherently associated with spatter deposition due to the incomplete expulsion of molten ejection from the hole, which enlarges the hole diameter and resolidifies on the workpiece surface around the hole periphery. This defect is more evident in laser percussion drilling thick ceramics that has a high melting boiling point. It causes a low quality of drilled hole and needs a long pre-cutting path in laser cutting to avoid spatter depositing on the cutting path. In our current study, the behaviors of debris and hole diameter in CO2 laser percussion drilling of 95 % alumina ceramic sheets (4.4 mm thick) under different processing parameters were investigated to figure out the effect of main energetic processing parameters on these behaviors. The corresponding processing parameters include laser peck power, pulse duty cycle, pulse repetition frequency and piercing time. The change trend curves of debris and hole diameter with the related parameters were plotted respectively. The combined effects of these parameters were also studied in our work, such as the co-action of peak power and pulse duty cycle, the co-action of peak power and piercing time, the co-action of pulse repetition frequency and piercing time, the co-action of pulse duty cycle and piercing time, and the co-action of pulse duty cycle, pulse repetition frequency and piercing time. The potential mechanism of individual parameter affected on material removal during laser percussion drilling was also discussed based on the experimental result.

The obtained result shows that (1) Laser peak power affected vaporization rate. (2) Pulse duty cycle influenced melt rate. (3) Pulse frequency affected valid heating efficiency in workpiece. Higher pulse frequency caused the debris and hole diameter decreased, and resulted in more symmetrical spatter deposition which contributed to the perfect circularity of the drilled holes. (4) Piercing time influenced drilled depth before entire beam break-through. With increasing peak power, pulse duty cycle or pulse frequency, the piercing time for a complete through-hole could be shorten. (5) On the process qualities (debris and hole diameter), peak power and pulse duty cycle had significant effects, pulse frequency had a lower effect, while piercing time had the lowest effect. Comparatively, peak power had a more significant effect than pulse duty cycle on spatter formation.

From our research, the effects of different processing parameters on quality of laser drilled hole in alumina ceramics were observed. The processing parameters could be further optimized to achieve less debris and finer hole drilling by some basic conclusions from our work. The possibility of controlling debris and hole diameter also leads to numerous benefits especially during closely spaced array laser drilling or short per-cutting path laser cutting for efficiency improvements. Moreover, the method referred in the work is also suitable for studying other materials drilled by laser, which could help technicians optimize processing parameters more effectively.

The above brief overview was extracted from its original abstract and paper presented at The International Congress on Applications of Lasers & Electro-Optics (ICALEO) in Orlando, FL. To order a copy of the complete proceedings from this conference click here