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Summary
To ensure accurate and prompt monitoring of the changes in molten metal characteristics, such as heat transfer and damped oscillation, during bead formation by arc welding with a pulsed current on the back of a thin plate, this paper describes direct detection of the changes in weldpool characteristics associated with the molten state and considers a method for overall evaluation of these characteristics.
An idea for a detection method was proposed in 1974 (Japanese Patent 876269, US Patent 3988567, and British Patent 1493524). To make the idea suitable for application in new welding systems yet to be developed, the rationality and effectiveness of the method are considered and clarified.
The depth in a partially penetrating weld can be roughly estimated through detection of the waveform and the phase difference of the change in heat radiation from the back surface due to the difference in heat transfer during welding.
The stability of back bead formation and the back bead size in a fully penetrating weld can also be estimated through detection of the waveform of the change in the heat radiation due to the damped oscillation of the molten metal on the back surface.