Real Time Optical Spectral Monitoring of Laser Welding Plumes

摘要

Real time monitoring and control of laser welding performance will be a key technology leading to the widespread acceptance of laser welding by industry. Optical emission from the weld plume is a rich source of information about the behaviour of the weld keyhole, and various methods have been developed to observe and extract information from the plume light. Compact, optical fibre delivered spectrometers now provide the ability to monitor the emission spectrum of the plume in real time, and probe specific spatial regions of the plume. This allows one to measure plume temperature, and observe the relative concentrations of alloy elements in real time. Plume temperature and species concentrations may be used to diagnose transient weld conditions, which may lead to a weld fault such as a blowout or loss of coupling. Other weld fault initiators, such as excess seam gap, and metal surface or assist gas contamination, also produce characteristic spectral markers. Spectral monitoring may be used directly on the production floor to detect these conditions, or spectral monitoring may be used to identify a process signature which can be detected by a simpler, dedicated device. Applications involving the welding of steel, zinc coated steel, and aluminum will be discussed.