Study of Hole Properties in Percussion Regime with a New Analysis Method

To drill sub-millimeter holes, laser percussion drilling has been a well-established industrial process for tens years. However, inherent factors due to laser source, material properties and dynamic of the reaction are still making physical approach very difficult. Moreover conceptions on drilling are often confused with other laser applications like cutting. This paper deals with the study of the properties of holes drilled by an innovative source from Trumpf firm which ensures top hat distribution in focal plane for any laser parameters. Results are based on several post-mortem metallographic analysis. First a new and very fast hole analysis method (called DODO for Direct Observation of Drilled hOle) is described and compared to the X-ray radiography and metallographic cutting. DODO solves most of the problems of the previous methods, notably to ensure the merging the analysis plane to the drilling axe. Secondly, with the help of the DODO method we describe two drilling regimes separated by a threshold. The hole morphology (diameter, depth, profile) and the recast layer thickness are compared in each regime. We investigate this threshold as a function of pulse duration.