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.
Efficient air flow control plays a crucial role for the reliability of remote laser beam welding applications.Local air flows are helpful to suppress unfavorable interactions between laser radiation and welding fumes as a result of absorption and/or scattering effects. On the other hand, local and additional global flows have to be applied for emission control to protect optical components and workpieces from contamination and to avoid harmful air pollution of the atmosphere. However, the appropriate design of complex air flow systems under the additional condition of preferably low overall gas consumption is still a challenging task because a high number of decisive factors and a multitude of possible interactions complicate the pure empirical selection and positioning of suitable flow components and the adjustment of the numerous control parameters. This paper presents the results of a combined and complementary approach of experimental and theoretical investigations to meet these challenges. The experimental work was focused on the aspects of interaction mechanisms between the laser beam and the welding fume. Besides the characterization of process emissions some of the requirements of stable remote processing with maximum penetration depth are revealed. In contrast, the theoretical work describes a general methodology on how to support the optimization of the cabin air flow by means of Computational Fluid Dynamics (CFD) models in combination with Design-of-Experiments (DoE) approaches.
In the case of serious accidents, severely injured persons may be trapped inside damaged vehicles and thus must be rescued quickly. Typically, structural parts containing high-strength steels or fiber-reinforced plastics must be cut to generate rescue openings. Hence, mechanical rescue systems like hydraulic shears may reach their performance limits. Therefore, a mobile laser cutting device for rescuers has been developed, being suitable for harsh outdoor conditions and providing optimized robustness, handleability, and weight. A crucial aspect is the requirement of laser safety for all persons involved. Here, the description of the first version of a demonstration system consisting of a mobile laser cutting device for complex rescue operations is presented.
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