Sequentielle Ultrakurzpuls-Laserbearbeitung zur effizienten Oberflächentexturierung

  • Sequential ultrashort pulse laser processing for efficient surface texturing

Brenner, Andreas; Häfner, Constantin (Thesis advisor); Bergs, Thomas (Thesis advisor)

1. Auflage. - Aachen : Apprimus Verlag (2021)
Book, Dissertation / PhD Thesis

In: Ergebnisse aus der Lasertechnik
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2021

Abstract

Laser structuring is becoming increasingly important in the tool and mold making industry. In addition to design structures (e.g. leather grain), the production of microstructures for surface functionalization represents a particular challenge. For example, structured surfaces contribute to increasing the efficiency of LED-based lighting systems or to modifying the wetting properties to create self-cleaning surfaces. In terms of this surface textures influence the optical and haptic properties that are increasingly becoming a quality feature. The automotive and consumer goods industries in particular offer a wide range of applications for structured surfaces, which can usually be produced by replication. The currently used production processes for tool texturing such as photochemical etching or laser texturing using nanosecond lasers are limited in their precision and flexibility. Ultrashort pulse lasers (USP) with pulse durations in the femtosecond to picosecond range offer the possibility of surface functionalization with highest precision and surface quality. Due to the mainly vaporization-dominated ablation, debris and melt-induced protrusions can be avoided in contrast to nanosecond lasers. The main drawback is the limited productivity with ablation rates of a few mm³/min. Accordingly, this thesis investigates the sequential use of ultrashort pulse laser sources for efficient surface texturing with increased productivity. In a first step, the possibility to increase productivity by using pulse bursts and reducing the pulse duration from 10 ps to 2 ps is investigated. It can be shown that the same efficiency can be achieved as with nanosecond lasers while increasing the surface quality by a factor of 4. In the next step, the process of USP cleaning is investigated, which is used to remove the oxide layer created during the productive laser ablation. The investigation of high quality USP ablation proves that the surface roughness can be reduced during ablation. The final process, USP polishing, enables a final smoothing of the roughness peaks by remelting a thin surface layer. This technology can also be used to selectively create specific gloss effects.The photonic USP process chain presented here, consisting of the four individual processes USP productive, USP cleaning, USP quality and USP polishing, achieves time savings of up to 59% compared to an industrially established nanosecond process, while at the same time reducing surface roughness by 92%. The component production can be carried out in one machinery without time-consuming set-up or reclamping.

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