Appearance of measured signals with changes in basic welding conditions: Features of monitoring methods for laser welding and their application (2)

Summary

The authors are engaged in a research programme intended to clarify the behaviour of laser-induced plasma during laser welding and to establish its applicability in monitoring laser welding parameters.

This paper describes the appearance of the measured signals in response to changes in the basic welding conditions. The main results obtained are as follows:

1. The average amplitude (V_amp) of both the spectrum emission intensity and plasma potential is far better correlated with the penetration depth than the average output (V_ave).

2. The good correlation found between the average amplitude and spectrum emission is due to the fact that a strong effect is exerted by any change in the configuration of metal plasma fluctuation due to the effects of the penetration shape, such as the keyhole and molten pool shape. This also suggests the need for consideration to be given, regarding the signal output changes that occur in response to laser power changes, to the correlation factors of the spectrum emission intensity and laser power as the source of energy for plasma formation.

3. V_amp of the measured signals of the spectrum emission and plasma potential can be applied as monitoring parameters for the process speed and process power in laser welding.