Sensing and control system of process quality in CO 2 laser deep-penetration welding

Abstract

A sensing and control system of process quality in C02 laser deep penetration welding has been developed, including plasma photo sensor (PS) and plasma charge sensor (PCS), signal processing circuit, personal computer, and optimization and control software. By using the information of plasma radiation and plasma charge, the focusing lens is adjusted to the optimum focal point position (at which the maximum penetration can be achieved ) and closed-loop control is realized to assure the focal point position and penetration depth constant. In laser welding of the workpiece aslant placed with larger angle, the variation offocal point position is less than 0.2mm and the fluctuation ofpenetration depth is less than 0.05mm. The control system has been preliminarily applied in laser precision welding of 2.5m long zircaloy fuel channel used in nuclear heat-supply reactor.

Real-time implementation of a time-frequency analysis scheme

“…piece. By using these emissions, it is possible to evaluate laser process quality, and in particular to find out the relationship between emission characteristics and weld quality characteristics [6] [9] [7] [2].…”

Review of techniques for on-line monitoring and inspection of laser welding

“…The work, which was untaken by Chen et al [15], Farson et al [16] and Hugel et al [17], also showed that detecting the plasma/plume signal or the reflected laser using optical detectors is a kind of simple and effective way to real time monitor the welding process.…”

<title>Monitoring of process stability in underwater Nd:YAG laser beam welding with optical sensor</title>

“…In general, there are two methods to detect the plasma and the reflected laser signal, with photodiode viewing from the side of keyhole or coaxial to the laser beam [10] . As for selection of photodiode, three wavebands of diode were used, ultraviolet sensor for plasma induced in CO2 laser welding [14] , visible light for plasma detecting in both CO2 and Nd:YAG laser welding [8,9,11] , and infrared sensor for both CO2 and Nd:YAG laser welding [10,11,15] . The relation between detected signal and welding parameters, for example, focal position, has been obtained good results and been used in application [8,9] .…”

“…As for selection of photodiode, three wavebands of diode were used, ultraviolet sensor for plasma induced in CO2 laser welding [14] , visible light for plasma detecting in both CO2 and Nd:YAG laser welding [8,9,11] , and infrared sensor for both CO2 and Nd:YAG laser welding [10,11,15] . The relation between detected signal and welding parameters, for example, focal position, has been obtained good results and been used in application [8,9] . The other research including the detecting of burnout or pin and humping defects by using photo sensors was also reported [13] .…”

“…For deep penetration laser welding, detecting of plume signal and reflected laser by using optical sensor is a simple and effective way to real-time monitor welding process [8][9][10][11][12][13][14][15] . In general, there are two methods to detect the plasma and the reflected laser signal, with photodiode viewing from the side of keyhole or coaxial to the laser beam [10] .…”