Experimental investigation and multi-objective optimization of Nd:YAG laser micro-channeling process of zirconia dental ceramic

Basem M. A. Abdo (King Saud University)

CHALLENGE - In biomedical applications, micro-channels are one of the important features and are often fabricated by laser ablation process. However, laser-processed micro-channels exhibit crucial issues of heat-affected zone (HAZ), dimensional errors, and poor surface quality.

SOLUTION -  This study investigates the influence of key laser process parameters on the dimensional accuracy and the surface quality of the micro-channels fabricated on zirconia dental material. A full factorial based on design of experiment (DOE) methodology was adopted for carrying out experiments in a pulsed Nd:YAG laser micro-milling. The process parameters considered during machining were laser scanning speed, pulse frequency, and pulse intensity with four levels for each parameters resulting into 64 individual experiments.  Channel dimensional accuracy (depth error, top width error and taper angle), surface roughness (Ra), and HAZ were considered as the performance criteria for the present study. The experimental results show that the scanning speed and the pulse intensity and their interaction have the most influential effects on the depth error and HAZ. Moreover, it was found that the pulse intensity controls Ra, and the top width error is mainly affected by the scanning speed. The pulse frequency has the main effect on the channel taper angle, while its effects on other responses are negligible. The modeFRONTIER multiobjective genetic algorithm (MOGA-II) was employed to determine the optimal parametric conditions for minimizing the ablated depth errors and HAZ while putting the constraints on the minimum acceptable levels of the surface roughness, top width error, and taper angle. The optimized solutions were obtained at the moderate levels of scanning speed and pulse intensities and low levels of pulse frequencies.

BENEFITS -  Multi-objective optimization is successfully carried out by the MOGA-II algorithms, and the optimized solutions are consistent with the ANOVA results. However, laser micro-milling is a complicated process, and it is not easy to find the proper combination of process parameters to achieve different quality outputs.