Abstract
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.
Highlights
Laser welding offers significant advantages in aerospace manufacture, for both engines and airframes
In safety-critical applications such as aerospace manufacture it is vital that every weld can be assured to be free of defects, and an on-line process monitoring system is part of the necessary quality assurance process
The tested configurations show that the focus control system is able to adjust the focus by 10 mm over a distance of 100 mm for Inconel and titanium
Summary
Laser welding offers significant advantages in aerospace manufacture, for both engines and airframes. In safety-critical applications such as aerospace manufacture it is vital that every weld can be assured to be free of defects, and an on-line process monitoring system is part of the necessary quality assurance process. On-line sensing offers the possibility of process control, reducing the requirement for rework. Several techniques have been developed for process monitoring and control of laser welding. A small number of optical-based process monitoring. The main drawback of such systems is that such off-axis measurement requires good optical access to the workpiece and necessitates some intrusion into the process. Alternative techniques based on the on-axis detection of process-generated radiation through the focusing optics and the delivery optical fiber system have been reported. One technique exploits the chromatic aberrations in the optical elements, such that
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