Quality assurance of industrial spot welding with a pulsed Nd:YAG-laser

Abstract

The Philips company produces approx. 10 billion spot welds every year applying pulsed Nd:YAG-lasers. The failure rate of most processes amounts to only few ppm (parts per million). The quality of these laser welding processes is assured by SPC (statistical process control) with spot check destructive tests. Introducing an in-process quality assurance system called laser welding monitor LWM900 by Jurca Optoelektronik GmbH, destructive tests will be avoided because every single laser pulse is monitored and evaluated.An examplary application of this real-time monitoring system is in the production line of electron guns for TV and PC-monitors. The laser welding monitor detects independent key characteristics (such as temperature, plasma luminosity, reflected laser power) and computes the probability that a significant welding failure (such as lack of laser power (>10%), gap between sheets in overlap welding (>50μm), etc.) has happened. The probability is calculated by comparing the detected signals with a stored reference previously determined in a teach process. If the failure probability reaches the 100%-level, an alarm signal is generated and the handling system automatically separates the faulty part. In the presentation the operability of the system which is applied for the first time in spot welding is shown as well as its integration concept in the existing quality assurance plan of the Philips production plant.The Philips company produces approx. 10 billion spot welds every year applying pulsed Nd:YAG-lasers. The failure rate of most processes amounts to only few ppm (parts per million). The quality of these laser welding processes is assured by SPC (statistical process control) with spot check destructive tests. Introducing an in-process quality assurance system called laser welding monitor LWM900 by Jurca Optoelektronik GmbH, destructive tests will be avoided because every single laser pulse is monitored and evaluated.An examplary application of this real-time monitoring system is in the production line of electron guns for TV and PC-monitors. The laser welding monitor detects independent key characteristics (such as temperature, plasma luminosity, reflected laser power) and computes the probability that a significant welding failure (such as lack of laser power (>10%), gap between sheets in overlap welding (>50μm), etc.) has happened. The probability is calculated by comparing the detected signals with a sto...