Investigation of optical sensor approaches for real-time monitoring during fibre laser welding

Laser beam welding can be a high productivity joining process, offering significant benefits over conventional welding methods. However, the need for real-time monitoring of laser welding processes is important to provide information on the possible presence of imperfections formed during welding and guarantee quality assurance in production. Laser process monitoring methods are based on the recording of physical phenomena occurring during the laser-material interaction. This paper has investigated an established optical-based monitoring method, using photodiodes responsive to either visible or near-infrared emissions, to correlate the photodiode signals with different types of weld features, imperfections and/or process anomalies. These have included occurrence of internal porosity, changes in penetration depth and beam to joint alignment, deliberate changes in laser power and intentionally poor joint preparation, cleanliness or fit-up. Also, a new type of commercially available process monitoring approach was investigated, based on laser interferometry, to measure keyhole depth. The results of both approaches have confirmed which types of weld features, imperfections and/or process anomalies are most sensitive to these monitoring techniques, with potential to then implement these findings in to a future multisensor solution for real-time process control.