Investigation of the hole shape in pulsed fiber laser microdrilling of nanostructured titanium

The request of small features resulting from high productive and good quality processes has been growing in several industrial fields, such as micromechanical, microelectronic and biomedical sectors. In conjunction with this demand from industries, innovative laser sources such as pulsed fiber lasers, are becoming the answer to the machining of innovative and hard to process materials, such as the nanostructured metallic alloys. The pulsed fiber lasers indeed offer a very precise and small dimension tool able to work with high productivity and small thermal alteration, which is of fundamental importance when nanostractured alloys are machined. In this work an experimental study on percussion microdrilling of 0.7 mm thick nanostructured titanium sheets by means of a nanosecond pulsed fiber laser was performed. In particular, the entrance and exit hole quality as well as the shape of the inner hole were investigated as a function of pulse frequency and process time. The drilling time was firstly measured by means of a couple of fast infrared photodiodes. Then, the effect of the process time, immediately before and after the measured drilling time, and pulse frequency on the hole geometry was investigated. Moreover, the evolution of the machined holes as a function of the process time was discussed.