Abstract: In an effort to look for a diagnostic signals for in-line monitoring during laser welding of aluminum alloy, a pyroelectric detector was used to record the reflected laser radiation from the weld pool when a CO$- 2$/ laser welds aluminum alloy sheets. The signals were processed with a fast-Fourier transform (FFT). From the FFT spectrum strong components of the reflected laser radiation in the low frequency range were found to be a strong function of laser welding variables. When the laser intensity is kept constant, a minimum signal is found at a particular welding speed. At speeds of either slower or faster than that particular speed, the signals increase up to a factor of 3 or more. No corresponding components were noticed in the photodiode signals. Analysis of the weldments indicates that optimum welding is produced around this specific speed.!4
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