Hole taper control in laser percussion drilling using statistical modelling

The present work investigates the effect of six controllable variables on hole taper in laser percussion drilling. The six independent variables are peak power, pulse width, pulse frequency, number of pulses, gas pressure and focal plane position. Response surface method (RSM) along with experimental design and regression techniques were used to statistically analyse the process. A half scale Central Composite Design (CCD) was selected for planning the experiments. For each variable five levels were considered and each experiment was repeated five times to analyse the process as accurate as possible. The drilling experiments were performed on mild steel sheets, with a thickness of 2.5 mm. The hole taper was considered as a process characteristic and was modelled in terms of the six independent variables. Modelling was performed through linear multiple regression. By variance analysis (ANOVA) the significant variables on the taper model were found at 1% and 7% levels of significance. It was found that pulse width, peak power and number of pulses have significant effects on the hole taper. However, pulse frequency has no effect on the hole taper. Also, there are some interaction effects between independent variables which have significant effects on the hole taper.