This paper describes a real time laser weld monitoring system based on detection of laser weld optical emissions in the UV, visible and IR wavelength ranges. These three signals are examined using chromatic analysis, and threshold tests are applied to various chromatic parameters to identify unacceptable weld quality.
Classical chromatic analysis is the quantitative description of a color in terms of the amounts of “primary” colors that must be mixed to produce the desired color. For laser welding analysis, we extend this concept to consider UV, visible, and near IR wavelengths. The weld “color” is determined by the proportion of UV, visible, and IR light observed in the weld emission. Trichromatic coordinates can be defined as follows:
X = IR/(UV + Visible + IR),
Y = Visible/(UV + Visible + IR),
Z = UV/(UV + Visible + IR)
Any two of these values can be used to quantify the “color” of the weld. By plotting, for example, X versus Y as the weld proceeds with time, any changes in weld “color” may be observed. A stable welding process produces near constant trichromatic values. Any significant change (transient or long term) in the trichromatic coordinates indicates an anomaly in the weld.