Signal overlap in the monitoring of laser welding

Abstract

Laser weld monitoring is usually based on the feedback from three photodiodes which are intended to provide independent information about: the thermal condition of the melt (the 'T' signal), the radiation from plume of heated gas above the melt (the 'P' signal), and the amount of reflected laser light (the 'R' signal). This work demonstrates that, in fact, the plume of hot gas above the weld pool contributes a large part of the thermal signal, which has hitherto been assumed to come only from the melt itself. It is suggested that the correlation between the 'T' and 'P' signals is so strong that a 'T-P' signal would be more useful than the raw 'T' signal in identifying the fluctuations in infra-red radiation from the melt pool.

Controlling the Electron Beam Focus Regime and Monitoring the Keyhole in Electron Beam Welding

“…The parameters of plasma are closely connected to the characteristics of the thermal action of the electron beam on welded metal, which allows operational control and studying the processes of EBW [5][6][7][8][9] . Similar works are widely reported in recent studies on laser welding [10][11][12][13][14][15] .…”

Progress and perspectives of in-situ optical monitoring in laser beam welding: Sensing, characterization and modeling

“…Photodiode sensors within UV/VIS, NIR and MIR ranges are commonly accepted in manufacturing industry due to a series of advantages of flexible configuration, simple structure and low cost. During laser overlap welding, three photodiode sensors were utilized to obtain independent information about the thermal (T-signal) condition of the molten pool, the radiation from plume (P-signal) and the back-reflected (R-signal) radiation of laser beam itself [29]. Fig.…”

Remote laser welding with in-line adaptive 3D seam tracking

“…A special place in the monitoring and control have coaxial sensor configurations where the sensor path corresponds with the laser path. Such a configuration can be seen in [25,26] where an interaction zone can be directly observed with a camera, which enables laser power control and/or correction of laser focus position. An upgrade to these systems is presented in [27] where two laser stripes are added to monitor not only the interaction zone but the pre-and post-seam positions.…”