No abstract

High-throughput experimentation methods determine characteristic values, which are correlated with material properties by means of mathematical models. Here, an indentation method based on laser-induced shock waves is presented, which predicts the material properties, such as hardness and tensile strength, by the induced plastic deformation in the substrate material. The shock wave pushes a spherical indenter inside a substrate material. For reproducible indentations, the applied load is of importance. To compare different processes and process parameters, the measured plastic deformation is normalized by the applied load. However, eccentric irradiation leads to altered beam profiles on the surface of spherical indenters and the angle of incidence is changed. Thus, the influence of eccentric irradiation is studied with an adapted time-resolved force measurement setup to determine the required positioning tolerances. The spherical indenter is placed inside a cylindrical pressure cell to increase the laser-induced shock pressure. From the validated time-resolved force measurement method we derive that deviations from the indentation forces are acceptable, when the lateral deviation of the beam center, which depends only on the alignment of the setup, does not exceed ± 0.4 mm. A vertical displacement from the focus position between -3.0 mm and + 2.0 mm still leads to acceptable deviations from the indentation force.

Laser shock peening is a surface treatment technology, which modifies the residual stress state of metal parts. When forming thin sheet metal parts with thicknesses ≤1 mm, locally varying residual stress states are, according to the literature, the main reason for the scatter in the bent angle. Forming processes, such as bending, are often used to manufacture thin sheet metal. Thin sheets are formed in quantities of several hundreds of millions per year. Even scrap rates that are in the ppm range, caused by the scatter in the bent angle, lead to considerable manufacturing costs. To ensure a robust forming process, it is hypothesized that the laser shock peening process can reproducibly change the residual stress state in thin sheet metal parts in such a way that scatter in the bent angle can substantially be reduced. Annealed and 1 mm thick sheet metal made of X5CrNi18-10 were processed with a nanosecond pulsed fiber laser. The influence of laser peening without coating (LPwC) on the bent angle was investigated using bottom bending with a nominal bending angle of 90°. It was revealed that the standard deviation of the bent angle, i.e., the scatter, is reduced by a factor of 2 from ±0.14° down to ±0.07° compared to the initial sheet state. Hence, the possibility to use LPwC as a pretreatment to decrease the scatter in the bent angle for thin sheets is demonstrated.

Die Ultrakurzpuls (UKP)-laserbasierte Bearbeitung erlaubt die Herstellung von Netzstrukturen mit verschiedenen Transmissionsgraden. Vorteile der UKP-laserbasierten Herstellung der Netze liegen vor allem in der hohen Präzision und Bearbeitungsgeschwindigkeit. Die UKP-Laserbearbeitung ermöglicht die Herstellung von Netzen aus Aluminium in hoher Qualität, bezogen auf die Stegbreitenabweichung von < 8 µm, mit variablen Transmissionsgraden. Ultra-short pulse (USP) laser based processing enables the production of mesh structures with different degrees of transmission. The advantages of USP-based production of mesh structures are mainly the high precision and processing speed. USP laser processing enables the production of meshes of aluminum in high quality, with respect to the mesh width deviation of < 8 µm with variable transmission degrees.