Pulsed laser spot welding is used in the manufacture of
many goods. Because weak joints can lead to product
defects, it is important to monitor and control the joint strength
precisely. This paper introduces a method to estimate the joint
strength of spot welds during the welding process. A point
infrared sensor is used to measure temporal radiation on the
top face of the spot weld. Because variable measuring conditions
affect the radiation power, a scale-free radiation feature
is extracted from the measured radiation and used as a monitoring
criterion. An artificial neural network (ANN) uses this
feature to estimate joint strength. In experiments, significant
welding parameters are varied within a controllable range,
and 640 weld parts are used for ANN learning. The correlation
coefficient between the estimated and measured strength
is more than 0.98 for learned parts. Another 180 weld parts
are used to appraise the efficiency of the learned ANN, and
the mean square error of estimation is 0.78 kgf.