Sensor systems for real-time monitoring of laser weld quality

On-line process monitoring is beneficial for maintaining high quality products at high production rates and low cost. Off-line traditional testing of welds can be costly in terms of time, material, and productivity. Real-time nondestructive testing, however, can be just as accurate as off-line testing; yet faster, cheaper, and increase productivity, when perfected for high volume repetitive applications. In the field of real-time monitoring, various sensors have shown promise in detecting weld states. These include acoustic emission, audible sound, infrared detectors, ultraviolet detectors, electromagnetic acoustic transducers, and polyvinylidene fluoride. Nevertheless, previous work indicates that no single sensor can reliably detect the full spectrum of weld states. As a result, sensor fusion has been investigated for integrating the advantages of individual sensors. This article presents a survey of technical information that is currently available in the literature, commercial systems, and patents, for real-time (laser) weld process monitoring. The focus is on the sensors listed above, along with multiple-sensor systems: dual wavelength infrared and ultraviolet, as well as audible sound and ultraviolet detection. (C) 1999 Laser Institute of America. [S1042-346X(99)00504-5].