Real-time monitoring of laser beam welding using infrared weld emissions

Abstract

A nonintrusive, solid-state device has been developed to monitor in real time the infrared emissions during laser welding. The weld monitor output is an analog signal ͑100-1000 mV͒ that depends on the beam power and weld characteristics. The dc level of this signal is related to weld penetration, while ac portions of the output can be correlated with surface irregularities and part misalignment or contamination. Changes in dc behavior are also noted for both full and deep penetration welds. Full penetration welds are signified by an abrupt reduction in the weld monitor output. Bead-on-plate welds were made on steel, aluminum, and magnesium with both a cw CO 2 laser and a pulsed Nd:YAG laser to explore the relationships between the weld characteristics and the weld monitor output.

Nondestructive evaluation and real-time monitoring of laser surface hardening

“…The characteristic optical and acoustic signals associated with the laser materials process, particularly with laser welding, are well understood. Researchers have implemented various forms of process monitoring to collect the signals and correlate them with variations in weld quality (Leong, 1997;Sanders et al, 1998;Chen et al, 1991). Leong integrated an infrared emission detector into the beam delivery optics to monitor the infrared weld signal (Leong, 1997 and Leong tested in detail the infrared weld monitor technique as a welding process monitor and correlated the simple analog output with weld penetration, weld surface quality, and surface contamination with product scrap rate minimized .…”

Sensor Monitoring during Tack Welding of Aerospace Components

“…In [10] a device was developed for real-time monitoring of infrared emissions during laser welding. Many other sensor monitoring techniques have been implemented since in order to provide real-time welding process control and assure high quality weldments [11].…”

Quality assessment in laser welding: a critical review

“…From the findings, a more general theoretical description of the links, between the welding process, the defect mechanism, and the generated signal, was also described. On the other hand, the studies in [61] and [62] described a monitoring system developed only on the basis of infrared signals. The primary infrared signal collected by the weld monitor was linearly related to the penetration depth in partial penetration welds.…”