Imperfections in narrow gap multi-layer welding - Potential causes and countermeasures

• Published in: Optics and lasers in engineering 2020-06, Vol.129, p.106011, Article 106011
• Main Authors: Näsström, Jonas, Brueckner, Frank, Kaplan, Alexander F.H.
• Format: Article
• Language: English
• Subjects: Cavities; High-speed imaging; Laser welding; Manufacturing Systems Engineering; Narrow gap; Narrow gap multi-layer welding (NGMLW); Porosity; Produktionsutveckling
• ISSN: 0143-8166; 1873-0302; 1873-0302
• DOI: 10.1016/j.optlaseng.2020.106011

•Cavities in Narrow Gap Multi-layer Welding most often formed close to the gap edges•The filler wire can block the laser beam which can limit wetting during welding•High Speed Imaging can be used for wire tracking and manual process evaluation•Single pixel row footage at 1 kHz frame rate show potential for closed loop control Narrow Gap Multi-Layer Welding (NGMLW) using a laser as the main heat source and metal wire for material addition has been a growing topic of interest in the last decade. This is in part due to its potential for joining much thicker sheets of steel than what is usually considered possible when using autogenous laser welding. The process has shown great potential but improvements can still be made, e.g. through increased process control to decrease welding imperfections. Using closed-loop control, where the process is continuously monitored and regulated automatically, can help to account for variations during manufacturing. However, achieving functional closed loop control can be challenging due to limitations in data gathering and processing speeds. Important initial steps include identifying what data can be useful and how frequently this data has to be recorded. Too much data takes too long to process while too little causes risks of missing important details. In this study, 20 mm thick X80 pipeline steel sheets are joined together using this multi-layer approach; the samples are examined using 3D scanning and Computed Tomography (CT) analysis and the process is observed using High-Speed Imaging (HSI). The quality of the welded joint and welding imperfections are discussed and potential points of formation are identified. Suggestions on how to mitigate imperfections to improve the quality of the welded joint are presented, including the potential to use camera imaging for closed-loop process control and additional industrial uses of the HSI footage.