Using statistical experimental methods, we developed a manufacturing process for drilling through holes in 99.6% polished alumina (Al2O3). The goal of this project was to take an existing process and identify the key process variables that most significantly affect the final product. The main factors that led to an improvement in hole quality were table speed, assist gas air flow, and the distance between the workpiece and the nozzle that supplied the coaxial air flow.
The process was established after a six-factor, two-level, full-factorial design of experiments that yielded 64 individual runs with 5 replicates for each run. The responses that we used to characterize the process were maximum topside diameter, minimum backside diameter, and backside chip-out size. Quantitative measurements were taken for each of the through holes using a video caliper system, and the data was analyzed using a commercially available design of experiments software package. The laser we used was a slow flow, 150 watt, CO2 laser equipped with a CNC controller that controlled both the X-Y table and the laser pulsing parameters. For the beam delivery system we used a ZnSe aspheric focusing lens coaxially with high-pressure air as the assist gas.
The final process is superior to the one it replaced as measured by the capability indexes Cp and Cpk. The responses we monitored for process capability were the topside diameter and backside diameter of the through holes.