Study and optimization of recast layer thickness and surface quality in laser trepan drilling of ZTA

Zirconia-toughened alumina (ZTA) has promising characteristics to be used for combustion chambers, pump, heat exchanger, armor, bearings, cutting tool inserts, aerospace, and nuclear parts. But it has limited applications due to its adverse machining characteristics. Laser machining has been proven to machine difficult-to-cut-materials with certain limitations. Being thermal energy-based advanced machining process, laser machining develops extreme thermal stresses and causes melting/vaporization. Therefore, ceramic samples are preheated at high temperature before applying laser machining. Control of laser machining quality without preheating of ZTA samples is a difficult task. The present paper investigates the laser trepan drilling (laser hole cutting) of 6.0-mm thick ZTA without preheating with the aim to optimize recast layer thickness, microcrack width on hole surface, and surface roughness. The optimal solution is determined by using a genetic algorithm. The results show an average improvement of approximately 15% in the above characteristics, considered simultaneously. The surface microcrack widths have been reduced much below than earlier claimed in laser processing of ceramics by other researchers. Mathematical relationship between input and output parameters has been developed and validated. The effect of process parameters on quality characteristics has also been discussed, scientifically.