We describe a closed-loop control system ensuring full penetration in welding by controlling the focus position and power of a 4-kW Nd:YAG laser. A focus position monitoring system was developed based on the chromatic aberration of the focusing optics. With the laser power control system we can determine the degree of penetration by analyzing the keyhole image intensity profile. We demonstrate performance in bead-on-plate welding of Inconel 718 and titanium. The focus control system maintained a focal position on tilted and nonflat workpieces, and the penetration monitoring technique successfully controlled the laser power to maintain the full-penetration regime in the presence of linear and step changes of thickness. Finally we discuss the performances and the limits of the systems when applied to a realistic complex aerospace component.
© 2005 Optical Society of America
(040.0040) Detectors : Detectors
(060.2370) Fiber optics and optical communications : Fiber optics sensors
(100.2960) Image processing : Image analysis
(140.3390) Lasers and laser optics : Laser materials processing
Fabrice Bardin, Adolfo Cobo, Jose M. Lopez-Higuera, Olivier Collin, Pascal Aubry, Thierry Dubois, Mats Högström, Per Nylen, Peter Jonsson, Julian D. C. Jones, and Duncan P. Hand, "Closed-loop power and focus control of laser welding for full-penetration monitoring," Appl. Opt. 44, 13-21 (2005)