Assessment of steel shields for protection against laser radiation

Abstract

High-power laser processing shows increasing importance in the manufacturing industry. Solid-state lasers provide optical powers of several kilowatts in continuous-wave mode with power densities of more than 1 MW/mm2, thus helping to achieve economically relevant processing speeds. However, to minimize health risks due to intense laser radiation, sophisticated safety concepts are required. An essential part of these concepts is the laser-process housing, which typically consists of metallic walls as passive shielding against laser radiation. The standard EN 60825-4 defines requirements and testing conditions for these shielding materials. Here, it is considered that the material durability depends not only on the laser irradiance on the material surface but also on the laser-spot size, which is attributed to hindered heat conduction at the spot edge due to heat accumulation occurring at larger spot sizes. However, this behavior has not been fully understood. In this work, a simplified finite-element modeling approach based on the heat equation is used to simulate the dependence of the material durability on the laser-spot size for 2 mm thick structural steel, a typical shielding material in industry. The calculated times to reach the material-melting temperature are compared with the measured material lifetimes upon laser irradiation. It is shown that the presented finite-element modeling can reproduce the general size dependence of the material durability. Thus, this analysis to calculate the times up to the material-melting start can be used to derive lower limits of the material lifetimes under defined irradiation conditions, suitable for designing the shielding sufficiently.

Change of dominant material properties in laserperforation process with high-energy lasers up to 120kilowatt

“…In this paper we present the results of laser penetration experiments with up to 120 kW laser power on aluminium and steel samples. The extended power range compared to previous reports 16,20,25 yields that the longer penetration times of aluminium compared to steel no longer apply at high laser powers. We show, that at roughly 80 kW the perforation times do interchange with shorter times for aluminium above this value.…”

“…Because large spot sizes require much higher laser powers, while maintaining similar intensities to those typically used for small spot sizes, large spot size applications could not be developed until the advent of such powerful lasers. As a result, there are only a few reports on applications using large spot sizes in the centimetre range [8][9][10][11][12][13][14][15][16][17][18][19][20] .…”

“…Higher intensities, due to smaller spot sizes, concentrate the energy on a smaller area. This means that a smaller amount of material has to be melted for the perforation, which reduces the perforation times 16,25 . However, reducing the spot size does not always reduce the perforation time.…”