Laser micro-drilling process: experimental investigation, modeling based on RSM-BBD tool and multi-criteria optimization

The laser micro-drilling (LMD) process is one of the nontraditional machining processes most widely used for producing micro-holes, complicated shapes, and geometries. The quality of all types of LMDs is judged on the dimensions and geometry of the created micro-holes. But this quality still needs optimization and qualification, particularly in its relationship with the used setting laser parameters. In this work, a new drilling strategy has been employed to produce high quality of LMDs. Moreover, this work presents important attempt to investigate the effect of the process parameters namely laser power, laser scanning speed, and laser repetition on the LMDs quality which can be presented by dimensions of micro-holes including drilling depth, entrance diameter of the hole, the width of the heat effect zone, and taper angle. A set of experiments based on a Design of Experiments (DoE) has been implemented on a polymer plate of a mineral reinforced Poly-Phthalimide (PPA) with glass fiber. A nanosecond Nd:YAG laser used in the LMD process. A mathematical response surface methodology founded on Box-Behnken experimental design (RSM-BBD) technique is utilized to perform modeling task which was used also for optimization task. The experimental results show that the laser power has the highest impact on both drilling depth, entrance diameter, and HAZ width, whereas the scanning speed has the highest effect on the taper angle. The results of the RSM-BBD model were compared with the experimental data showing good agreement. The average percentage errors were 7.4%, 6.55%, 4.18, and 2.27% for the depth of drilling, the taper angle, HAZ, and entrance diameter, respectively.