On-line laser weld sensing for quality control

This paper describes the development of a simple device for the online detection of the quality of laser welding using a slightly modified laser processing nozzle. When a high power laser beam is focussed onto a workpiece, metal vapor and ionized plasma is usually generated. The plasma consists of positively charged ions and negative electrons. Their uneven distribution above the melt pool causes a potential differences in the space along the beam axis between the laser processing nozzle and workpiece if the nozzle is insulated from the workpiece. By the measurement of this naturally produced electrical signal the laser weld quality can be monitored during processing. The parameters that the sensor can detect include the depth of penetration, holes, craters, humping, mis-tracking, keyhole formation and end notches. This new sensing device has the advantages of very small in size, robust, coaxial, good signal to noise ratio and economic compared with other techniques. It would be very suitable for multi-axis processing with robot guided moving beam system as well as other types of laser material processing systems.This paper describes the development of a simple device for the online detection of the quality of laser welding using a slightly modified laser processing nozzle. When a high power laser beam is focussed onto a workpiece, metal vapor and ionized plasma is usually generated. The plasma consists of positively charged ions and negative electrons. Their uneven distribution above the melt pool causes a potential differences in the space along the beam axis between the laser processing nozzle and workpiece if the nozzle is insulated from the workpiece. By the measurement of this naturally produced electrical signal the laser weld quality can be monitored during processing. The parameters that the sensor can detect include the depth of penetration, holes, craters, humping, mis-tracking, keyhole formation and end notches. This new sensing device has the advantages of very small in size, robust, coaxial, good signal to noise ratio and economic compared with other techniques. It would be very suitable for multi-ax...