Realization and first time operation of a high-power laser-water-jet system

Micromachining industry successfully uses the advantageous properties of laser-water-jets (LWJ), e.g. high depth of field, cooling and cleaning effect of water as well as high kerf parallelism. Until now short-pulsed laser sources with average powers of few 100 W are the main beam sources used in laser-water-jets applications. In machining, the comparably low average powers limit processing speeds, especially when high material thicknesses are present.
The objective of ongoing research at Fraunhofer IPT is to expand the range of possible applications for laser-water-jets to macro laser processing by using a continuous-wave fiber laser source with a maximum average power of 30 kW. Using high laser power within a macro-water-jet enables a significant increase in processing speeds while maintaining the above-mentioned beneficial properties of laser-water-jets. In a previous publication, using up to 2 kW laser power of an infrared fiber laser coupled in a laser-water-jet generated by an industrial micro machining system, the need for a dedicated high-power laser system, capable of dealing with thermo-optical and thermo-mechanical issues, was identified.
For the first time a laser head for the generation a laser-water-jet for macro machining has been designed, built and tested in a new high-power laser test rig with active laser safety at Fraunhofer IPT. In order to increase the transmittable laser power the internal water supply was up-scaled to high flow rates and specialized high power optics as well as suitable cooling strategies were developed to ensure increased thermal stability. Using a 30 kW fiber laser the new
machining head is tested and its thermal stability is investigated. The effects of system stability on the water-jet properties are studied in order to identify further system improvement. Finally, possible applications for using the new technology are outlined and first processing trials are performed.