Experimental observation and simulation of keyhole dynamics during laser drilling

Direct observation and simulation of keyhole dynamics is the key to the study of laser drilling. In this study, the author used a piece of transparent material GG17 glass to perform a direct observation of the dynamics in laser drilling. This technique enabled us to analyze the developmental process of elongated keyhole formation and the flow characteristics of the vapor and molten materials in the keyhole. Subsequently, the various features associated with laser drilling velocity and depth and the influence of laser power and defocus distance on the drilling velocity were investigated in experiments. In addition, to simulate the process of material vaporization removal during laser drilling process, a finite element model was established for laser drilling with Gaussian heating. To compensate for the multiple reflection of the laser on the keyhole wall and the energy loss during the drilling process, a convergence function, a coordination function and a factor function were introduced at the same time to model the changes of the laser energy and its intensity distribution as it reached the keyhole bottom.

► In order to observe dynamic laser drilling process, the special GG17 glass was used.
► During the drilling simulation, the laser heat source was re-treated by a simple way.
► In laser drilling experiment, the keyhole with special features was observed clearly.
► Two distinct mechanisms of the material removal process were analyzed.
► The effects of laser power and defocus distance on drilling speed and depth were studied in detail.