Synchrone Qualitäts- und Produktivitätssteigerung beim Laserstrahlbohren
Dietrich, Jens; Poprawe, Reinhart (Thesis advisor)
Aachen : Publikationsserver der RWTH Aachen University (2013)
Dissertation / PhD Thesis
The simultaneous production of holes with high quality and high productivity by melt dominated laser drilling is not possible. The quality is poor due to recast and oxide layers attached to hole walls with up to several hundred micrometers. Cracks in the recast and oxide layer can propagate into the base material. Spillings around the hole entrance and ripples at the hole exit, poor circularity and cylindricity as well as a small reproducibility have an influence on the quality of holes. To increase the quality and productivity for laser drilling two strategies are applied:1. By the development of a new process gas strategy the recast and oxide layer as well as the length and frequency of cracks are to be decreased. For this purpose, fundamental process gas investigations are carried out to identify and quantify the effects on productivity and quality. The sort and pressure of the process gas, the distance between nozzle and workpiece, and the diameter of the nozzle are varied. Based on the results a new process gas strategy is implemented by using the process gases argon and oxygen after each other to drill one hole. By this the regimes with high quality and productivity of each process gas are used. The temporal combination of the process gases lead to a reduction of the drilling time by up to 33% and of the recast and oxide layer thickness by 66%.2. New laser sources (diode pumped fiber lasers) differ from conventional flash lamp pumped laser sources regarding temporal and local intensity distribution e.g. smaller beam parameter product or rectangular pulse shape. The influence of the temporal and local intensity distribution on quality and productivity is investigated. By using a fiber laser the reproducibility, cylindricity , circularity of the hole entrance as well as the productivity is improved. Both strategies lead to a synchronous quality and productivity enhancement which can be used for drilling holes for industrial purposes.