Combined pulsed laser drilling of metal by continuous wave laser and nanosecond pulse train

In this paper, a new form of combined pulsed laser (CPL) consisting of continuous wave (CW) laser and nanosecond (ns) pulse train was proposed for drilling Q235B steel without high-pressure gas jet. The average power of CW laser ranged from 100 to 700 W, while the average power of the ns laser was fixed at 12 W. The experiments were carried out to study the influence of the average CW laser power on the drilling efficiency and quality of CPL. The results show that there were two completely different matching mechanisms between the CW laser and ns pulse train. Firstly, during the CPL drilling with the 100-200 W CW laser, the ns pulse train could be used to timely and periodically eject the central part of the molten metal, leaving a recast layer with a thickness of up to 200 μm. In addition, for the CPL drilling with the 550 W CW laser, a little part of molten metal was continuously ejected by the ns pulse train, and all of the remaining molten metal could be removed by the boiling of molten metal, thus leaving a recast layer with thickness less than 10 μm. The new CPL presented in this paper has an important guiding significance for improving the quality and making full use of the high efficiency of CW laser drilling.