PULSED ARC WELDING METHOD

Abstract

Disclosed is a pulsed arc welding method using a pulse current of alternately repeating first and second pulses as a weld current, wherein the first pulse and the second pulse have a pulse waveform of a different pulse peak current level and a different pulse width, respectively, and the following conditions are satisfied: peak current of the first pulse (Ip1)=300 to 700A; peak period (Tp1)=0.3 to 5.0 ms; base current Ib1=30 to 200A, base period (Tb1)=0.3 to 10 ms; peak current of the second pulse (Ip2)=200 to 600A; peak period (Tp2)=1.0 to 15 ms; base current (Ib2)=30 to 200A; and base period (Tb2)=3.0 to 20 ms. In this manner, the consumable electrode arc welding using carbon dioxide gas alone or a mixed gas made mainly of carbon dioxide gas as a shield gas can benefit from stabilized welding arc, improved regularity of droplet transfer, and significantly reduced generation rates of spatters and fumes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 is a waveform diagram showing a pulse current used in a pulsed arc welding method of the present invention;

FIG. 2 is a diagram showing a relation between pulse current and a weld transfer unit;

FIG. 3 is a waveform diagram showing a pulse waveform having an upward slope and a downward slope;

FIGS. 4A and 4B are a perspective view and a schematic cross-sectional view showing how spatter is collected;

FIG. 5 is a graph showing a relation between a wire feed rate and a spatter generation rate; and

FIG. 6 is a graph showing a relation between a wire feed rate and a fume generation rate.

Claims

1. A pulsed arc welding method using carbon dioxide gas alone or a mixed gas made mainly of carbon dioxide gas as a shield gas and using a pulse current of alternately repeating first and second pulses as a weld current, wherein the first pulse and the second pulse have a pulse waveform of a different pulse peak current level and a different pulse width, respectively, and the following conditions are satisfied: peak current (Ip1) of the first pulse=300 to 700A; peak period (Tp1) of the first pulse=0.3 to 5.0 ms; base current (Ib1) of the first pulse =30 to 200A, base period (Tb1) of the first pulse=0.3 to 10 ms; peak current (Ip2) of the second pulse=200 to 600A; peak period (Tp2) of the second pulse=1.0 to 15 ms; base current (Ib2) of the second pulse=30 to 200A; and base period (Tb2) of the second pulse=3.0 to 20 ms, in which, when Ip1>Ip2, one pulse-one droplet transfer is maintained, and a distance between a contact chip and a base metal is varied, at least one of the parameters selected from a group consisting of Ip2, Ib2, Tp2, and Tb2 is adjusted so as to control an arc length at a given level, within a range that one pulse-one droplet transfer is not violated.

2. The method according to claim 1, wherein proper Ip2, Tp2, and Ib2 are preset by wire feed rates, and at least one of the parameters selected from a group consisting of Ip2, Tp2, and Ib2 is adjusted so as to ensure that Tb2 falls within a range of 3.0 to 20 ms according to an increase of the wire feed rate.

3. The method according to claim 1, wherein a slope is formed about a time axis in order to make a smooth variation with respect to a rise and fall of the first pulse; a slope is formed about a time axis in order to make a smooth variation with respect to a rise of the second pulse; and Tup1 and T p2 are preferably not longer than 3 ms, and Tdown is preferably not longer than 6 ms, in which Tup1 denotes an upward slope period of the first pulse, Tdown denotes a downward slope period of the first pulse, and Tup2 denotes an upward slope period of the second pulse.

4. The method according to claim 1, wherein the release of a droplet is detected during the first pulse peak period (Tp1) or during the subsequent first pulse downward slope period (Tdown) and, at the same time, a welding current is immediately changed, even during the first pulse peak period (Tp1) or during the first downward slope period (Tdown), to a predetermined current level lower than the first pulse base current (Ib1) or lower than the current during detection.

5. The method according to claim 1, wherein a high frequency pulse of a pulse frequency in a range of 500 to 2000 Hz is superposed on a welding current in one of the periods or in at least two periods among (Tp1, Tp1, Tdown, and Tb1), or (Tup2, Tp2, and Tb2).

6. The method according to claim 1 utilizing a consumable electrode wire which contains not more than 0.1 wt % of C, 0.20 to 1.0 wt % of Si, 0.5 to 2.0 wt % of Mn, and 0.05 to 0.40 wt % in total of Ti+Al+Zr, with the balance being Fe and inevitable impurities.

7. The method according to claim 6, wherein the consumable electrode wire is not plated with copper on the wire surfaces.