Setup of a UV emission measurement system for manual laser beam welding processes and execution of extensive quantitative measurements for the user’s risk assessement

Status:

completed 09/2021

Aims:

The aim of the research project was to determine and evaluate information on the extent of emission of potentially hazardous incoherent ultraviolet and visible secondary radiation (UV and VIS), including the spectral characteristics, from the process zones of laser-beam welding processes. Due to the high specific hazard potential, the focus was on hand-guided or hand-positioned laser material processing. In general, however, the results obtained are also relevant for automated laser beam welding processes, provided that persons are present in the working area. The results serve to improve the currently deficient data situation and provide a basis for carrying out risk assessments by the operators of the laser equipment. Finally, the introduction of the results into standardization is to be initiated in the near future.

Activities/Methods:

In the course of the work carried out, the selection of the measurement system was first verified with a calibrated deuterium beam source on a typical laser-beam welding process. The development of a compact measuring-system head enabled the congruent and simultaneous measurement of the secondary radiation emitted from the process zone in the spectral ranges UV-A, UV-B and UV-C (180 and 400 nm) as well as VIS (300 and 700 nm), so that an evaluation could be made with regard to the relevant exposure-limit values according to Directive 2006/25/EC. In systematic parameter studies on blind welds, the influence of the material, the laser-beam source and the welding parameters on the intensity and spatial distribution of the secondary radiation emission was evaluated. The measurement results were related to the exposure limits. To verify the results on the blind welds, three real laser- beam welding processes were simulated experimentally. Based on the data obtained, recommendations for the protection of operators from secondary radiation were developed.

Results:

With the laser systems used, UV secondary radiation exposure values critical for the skin and cornea are observed in a similar order of magnitude. At a short distance from the laser process zone, the relevant exposure limit H_eff is in some cases reached after less than one minute, especially in the case of titanium. This is highly relevant for ensuring occupational safety in hand-held or hand-positioned laser beam welding, because the hands of the operating personnel must be very close to the process zone. Accordingly, lightproof work gloves must be worn. Protection of the hands against emitted laser radiation should not be ignored. It is also urgently recommended to cover the skin, especially on the arms, which are still relatively close to the process zone, with lightproof clothing. For the eyes, the potential exposure of the retina to blue light emitted from the welding process zone has proven to be more relevant compared to the exposure of the lens to emitted UV radiation, which can be explained by the fact that the spectral maximum of the secondary radiation is shifted out of the UV range into the VIS range. Depending on the material being processed and the distance from the process zone, the exposure limit E_B may also be reached in less than one minute. Obviously, the processing of titanium is particularly critical. In general, the operating personnel must wear suitable laser safety goggles during the operation of a hand-held laser device to protect their eyes against the laser radiation released from the process zone. Care must be taken to ensure that these goggles also meet the requirements for protection against UV radiation and, above all, visible light. The safety goggles must therefore be darkened in a similar way to welding safety goggles, although not as much, in order to reduce the transmission over a wide spectral range.

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