Abstract
In the pulsed MAG welding with highly precise periodic drop transfer, welding current was analyzed by FFT (Fast Fourier Transform). By this analysis peculiar frequency of the molten pool was detected by resonance phenomena with the base plate vibration and it was confirmed that peculiar frequency falls according to growth of the molten pool. Furthermore natural frequency was detected at natural welding state that is without vibration of the base plate and confirmed by resonance method with the base plate vibration. To amplify natural vibration of the molten pool, drop transfer pulse was modulated consisting of regular pulse peak current and higher pulse peak current. The higher pulse peak current makes arc pressure change and molten pool is pushed down in the period of higher pulse. Because short circuit is apt to occur at the time that the molten pool is at the top of front side, so it is effective for amplify the molten pool oscillation that higher pulse phase begins at this time instantaneously or somewhat later. According this way higher peak was gained at peculiar frequency by FFT analysis. It means that amplify of the molten pool oscillation was successful. Appropriate period of higher pulse for maintain stable oscillation is from about 1/4 to 1/2 of the oscillation cycle.
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