ANALYSIS: LASER SAFETY
“Our R&D team identified a material that could offer the required mechanical, heat and laser protection while also being lightweight”
Handheld laser welding can be used to achieve fast, high-quality welds of both similar and dissimilar materials in spatially challenging environments
laser safety standards evolve however, this will continue to remain the case.
A simpler, combined solution is needed
As a specialist in both welding and laser safety, Kentek is uniquely placed to approach the problem of designing, testing and certifying a simpler ‘combined’ solution in the hope that the published standards eventually catch up. In doing this we are, of
course, considering both welding and laser hazards. Any welding helmet or face
shield must protect the user from sparks and mechanical hazards, however the eyes and skin are also at serious risk from the harmful radiant energy produced by all welding processes. Therefore, in the case of the eyes, the window fitted to the welding helmet must block out the harmful UV and infrared light. In addition, the window must
have the necessary ‘Shade’ value to attenuate the visible light to a safe level for the user. The higher the Shade value, the darker the filter, meaning a particularly high Shade value can obscure a welder’s view of the workpiece. Therefore, a balance must be achieved between safety and visibility to achieve the optimal Shade value for each welding application.
The minimum safe Shade
value that is required for conventional welding (MIG, TIG, ARC, Plasma etc.) is based upon a number of factors, such as the arc current and the materials being welded. It is usually in the range of Shade 8
46 Electro Optics February 2024
to Shade 12, but can sometimes be higher. However, the arc created during handheld laser welding is not as bright, which presents the opportunity to use a lower shade value and grant users a better view of the workpiece. Such has now been requested by experienced welders who have adopted this new application: they are asking for filters between the range of Shade 3 and Shade 5. Therefore in developing an optimal, combined safety solution for handheld laser welding, a filter offering the desired shade value while also blocking all present harmful laser radiation must also be used. We must therefore also consider some of the unique hazards that are presented by laser welding. Unlike conventional, remote laser applications, it is very common – and almost routine – practice in handheld welding for the user to move themselves closer to the workpiece – often as close as 100-200mm to the focal point of the laser where the welding is taking place! In addition, during the laser welding of metallic substrates, it is common for a large percentage of the incoming energy to be reflected by the molten metal surface, which forms an exceptional reflector.
Creating the ideal handheld laser welding helmet After a full analysis of the application by Kentek’s R&D department, it was identified that a filter offering D LB9 at 1,070nm was required to provide the appropriate protection from the laser
radiation present during handheld laser welding. Such protection is offered by our MULTIWAVE coated laser filter, which is typically fitted to laser protective eyewear and offers a unique coating with hundreds of layers, produced over a span of days in a special chamber. The coating is harder than the glass it is created on and, during production, can be adjusted to block specific wavelengths (narrow notch) as well as bands of wavelengths (range blocking). To address the unique demands presented by handheld laser welding, our R&D team set about developing a new flat MULTIWAVE filter that not only blocks wavelengths in the IR and UV, but also allows all visible wavelengths to transmit/ pass through. This filter was then laminated to the Shade 3 and Shade 5 specifications requested by experienced welders, and was then independently tested. Having been certified to D LB9 @ 1,070nm, our R&D team moved onto fitting the newly developed safety window into an appropriate welding helmet. As with all handheld welding applications, due to the user wearing the helmet for extended periods of time, it needs to be light. Most current welding helmets are
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made of polycarbonate, ABS or carbon fibre, which are not only light but also provide the mechanical and heat protection that is required in conventional handheld welding applications. However, after laser damage
testing, it was found that they were very poor at laser blocking and, as well as allowing a surprising amount of IR transmission, simply melted very quickly with the scattered energy of a high-power multi- kW laser.
And so our R&D team set about identifying alternative materials that could offer the required mechanical, heat and laser protection while also being lightweight. After testing many candidates across a range of scenarios, they identified a thermoset plastic that delivers each of these characteristics. Using this material, a helmet
was manufactured and the new safety window fitted. Following further testing and certification, the LaserWELD Laser Welding Helmet was born: and this is now available on Kentek’s website with both Shade 3 (model C900W3) and Shade 5 (model C900W5) windows.
Standards must still catch up Despite both of Kenek’s newly developed helmets being fully capable of protecting the eyes and face from laser radiation during handheld laser welding, in order to conform with the current safety standards, both will still need to be worn with a set of protective laser safety eyewear. Until the safety standards are amended, this will remain the case. EO
Handheld laser welding systems offer simple, flexible and cost-effective joining solutions, however must be treated as a Class-4 laser product and thus used in a way that protects the user from harm (as has not been done here...)
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