Experimental study on the optimum matching of CW-nanosecond combined pulse laser drilling

A combined pulse laser (CPL) drilling method that consisted of a continuous wave (CW) laser and an assisted nanosecond laser was used for drilling the Q235B steel. The influence of the repetition rate of the nanosecond laser on the CPL drilling efficiency was analyzed. The results show that the plasma screening threshold during the CPL drilling was about ${1.40} \times {{10}^9}\,\,{\rm W}/{{\rm cm}^2}$1.40×109W/cm2. When the peak power density of the nanosecond laser exceeded the plasma screening threshold, it still could not compensate for the energy loss caused by the plasma screening, even though the high-pressure shock wave introduced by the plasma could improve the drilling efficiency. On the other hand, when the peak power density of the nanosecond laser was lower than the plasma screening threshold, it was shown that the optimum matching between the CW laser and nanosecond laser could be obtained when the repetition rate of the nanosecond laser was between 10 and 25 kHz. Finally, the results show that the CPL drilling method had a better drilling efficiency and quality than conventional millisecond laser drilling.