Hybrid laser drilling of cooling holes by using millisecond pulsed fiber laser radiation and ultrashort pulsed laser radiation

Laser drilling is a conventional technology for drilling cooling holes into turbomachinery components such as turbine blades. The laser drilling process often causes microstructure changes and induces defects such as recast layers and cracks. These effects lead to a reduction of lifetime of the components. The defects are caused by the melt dominated drilling process by using pulse durations in the range of some 100 µm up to a few ms. A solution of this problem is the use of ultrashort pulsed laser radiation with pulse durations in the range of some 100 fs up to a few ps. Thus, thermal effects can be avoided. Unfortunately, this drilling process takes 2.5 min for one hole with a diameter of 500 µm and a length of 3 mm. Thus, the aim of this work is to combine the productive process by using ms pulsed fiber laser radiation with subsequent ablation of existing recast layers at the hole wall by using ultrashort pulsed laser radiation.