An ultra-narrow gap gas metal arc welding process has been developed' in order to produce the excellent welding joint with narrower softening zone at HAZ of fine-grained steel. In the ultra-narrow gap (less than 5mm gap) welding process, as the welding wire melting behavior is controlled by low frequency pulsated arc current waveform, the arc generating at the wire tip is widely oscillated in the direction of thickness.To suggest the optimum welding condition without welding defects, the track of the wire-melting tip is analyzed by FDM. And then under the welding condition, thermal cycles at HAZ are calculated by using analytical solution on thermal conduction theory.
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