JPH0565268B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention uses an AC power source as a welding power source,
This invention relates to an AC pulsed submerged arc welding method in which welding current is changed periodically.

[Prior Art] A submerged arc welding method (submerged arc welding method) is an automatic arc welding method in which granular flux is deposited on a welding member in advance, and a welding electrode is inserted into the deposited flux. It is mainly used for joining and overlaying structural members in shipbuilding, pressure vessels, steel pipes, bridges, etc.

FIG. 3 is an explanatory diagram of the planar shape of the front bead formed by the conventional submerged arc welding method.

In the figure, a groove 2 of a welding member 1a to be joined
is partially tacked with tack beads 3 in advance. Next, when main welding is performed along the groove 2 in the welding progress direction Z, a weld bead 4 having a predetermined width with respect to the groove width _GW is formed. However, in the portion of the tack bead 3, the arc is deflected by the magnetic field and the width of the weld bead 4 fluctuates. Particularly in the portion 5 just before the tacking bead 3, the arc is blown backwards and digging occurs. Furthermore, since the weld metal concentrates in the lower part of the part where the digging has occurred, the width of the front bead in this part becomes narrower, causing not only meandering of the front bead but also undercutting.

This phenomenon of digging due to deflection of the arc is unavoidable as long as the tack bead 3 exists. For this reason, in the past, when it was desired to suppress the depth of digging, a method was adopted in which the welding current was lowered to lower the heat input.

[Problems to be Solved by the Invention] However, welding using a low current significantly reduces the efficiency of welding work.

Further, when double-sided welding is performed by the conventional submerged arc welding method, surface welding is first performed at a low welding current in order to suppress the depth of digging in the vicinity of the tack bead 2. As a result, penetration is shallower and the meandering of the bead width is reduced, but
Overall, the heat input seems to be insufficient. Therefore, when back side welding is performed after front side welding, there is a problem in that it is necessary to increase the welding current to compensate for the lack of heat input in front side welding.

Note that depending on the material of the welding member, there may be a problem of thermal embrittlement and it may not be possible to increase the welding current. In such cases, normal welding current was applied to both the front and back surfaces, and no particular measures were taken to prevent digging in, as it was inevitable that the welding would occur.

Furthermore, the conventional submerged arc welding method is easily affected by fluctuations in the welding power source, and when the welding power source fluctuates, the arc becomes unstable and defects such as undercuts occur at both ends of the surface bead even in areas other than the tack bead 3. It also has

Therefore, the main object of the present invention is to propose an AC pulsed submerged arc welding method that prevents digging and undercutting and provides a stable penetration depth.

[Means for Solving the Problem] The AC pulse submerged arc welding method according to the present invention uses a commercial frequency AC main power source and an AC main power source as welding power sources when performing continuous submerged arc welding along the groove of a welding member The above problem was solved by using an auxiliary power source and superimposing the AC output from the AC auxiliary power source on and off at a frequency lower than the commercial frequency as an AC pulse current on the AC output from the AC main power source. It is something.

Note that it is desirable that the superimposed alternating current pulse current has a low frequency alternating current pulse frequency with a pulse frequency of 0.3 to 3 Hz.

[Operation] When welding is performed with a constant welding current, the molten metal melted by the welding arc solidifies while vibrating at a frequency of 0.5 to 2.0 Hz. At this time, if the welding arc fluctuates, the vibration period of the molten metal will be disturbed.

When an alternating current pulse current obtained by intermittent alternating current pulse current with a pulse frequency similar to the vibration frequency of the molten metal, preferably a low frequency alternating current pulse current with a pulse frequency of 0.3 to 3 Hz, is superimposed on the welding current, if the welding electrode becomes high, an arc The stiffness of the arc increases significantly, resulting in a stable arc.

Therefore, an arc with good directionality that is not easily affected by the presence of tack beads etc. is obtained, the vibrations of the molten metal become regular, and stable submerged arc welding can be performed.

[Examples] Examples of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an example of an apparatus configuration used in an embodiment of the present invention. The principle of the method of the present invention will be explained based on FIG. 1. The main welding power source 7 supplies voltage and current to the welding electrode 6 and the welding member 1a.
A commercial frequency AC power source is used, and an auxiliary pulse power source 8 is connected in parallel to the output side of the power source via a switch 9. This pulse auxiliary power supply 8
outputs an alternating current that is synchronized with the same voltage and frequency as the main welding power source 7, and the output from this pulse auxiliary power source 8 is regularly turned on and off at a frequency lower than the commercial frequency by a switch 9. This alternating current pulse current is changed to an alternating current pulse current by using the method shown in FIG. A control command to the switching device 9 is given by a pulse controller 10, and this pulse controller 10 is connected to a frequency setting device 11.
A control command is given to the switching device 9 based on the frequency set in , and the switching device 9 is intermittently opened and closed by the command pulse of this set frequency to change the AC output current of the pulse auxiliary power source 8 to an AC pulse current. Output. Note that 1b is a cross-sectional bead after welding. In addition, in this embodiment, the frequency setter 11
The frequency set in is a frequency lower than the commercial frequency used for the main welding power source 7, and when a command pulse is given to the switching device 9 from the pulse controller 10, the AC output current of the auxiliary power source 8 changes to a corresponding low frequency. It becomes an alternating current pulse current with a high frequency and is superimposed on the main welding current.

By superimposing the AC pulse current on the main welding current, the arc generated by the welding electrode 6 has a regular time interval from high current to low current, and
When the welding current increases, the arc column tightens, the rigidity and directivity of the arc increase significantly, and a stable arc is obtained.

FIG. 2 shows an example of waveforms of various parts when AC pulse current is superimposed by the apparatus shown in FIG. 1 above.

The waveforms of various parts when the AC pulse current is superimposed by the device shown in FIG. 1 are as shown in FIG. Waveform (B), pulse controller 8
command pulse waveform (C) given to the switch 9 from
The AC pulse current waveform (D) output from the switch 9 whose opening/closing is controlled by the pulse controller 8, and the welding electrode 6 when the AC pulse current is superimposed on the AC current from the main welding power source 7 via the switch 9. When this welding current waveform (E) flowing to the welding electrode 6 is shown in DC display, it becomes a current value change waveform (F). Note that the horizontal axis is time on the same scale. Furthermore, the AC waveforms (A), (B), (C), (D), and (E) are actually sine waves. A specific example of the welding conditions at this time is as follows.

Welding conditions: Welding speed 50cm/min Main welding power source output: 50Hz, 1000A, 38V Pulse auxiliary power source output: 50Hz, 200A, 38V Repetitive pulse frequency of AC pulse current: 0.5Hz Generally, welding is performed using only the main welding power source 7 above. If welding is performed using a conventional method that does not superimpose alternating current pulse current, the bead width will be uneven and meander, and undercuts will likely occur.

However, it has been confirmed that when welding is performed according to the method of the present invention under conditions in which an alternating current pulse current is superimposed on the welding current, a good bead without undercuts or meandering can be formed. In addition, the pulse frequency of the command pulse given from the pulse controller 10 to the switch 9 at this time is 0.5 Hz, but since the frequency of vibration of the molten metal changes depending on the magnitude of the welding current, the pulse frequency of the command pulse given to the switch 9 from the pulse controller 10 is 0.5 Hz. It is necessary to use frequencies.

Generally, when the current is large, the frequency is low because there is a large amount of weld metal, and when the current is small, the frequency is high.

According to experiments conducted by the inventors, it has been confirmed that even better results can be obtained if the alternating current pulse current is a low frequency alternating current pulse current with a pulse frequency of 0.3 to 3 Hz.

[Effects of the Invention] As explained above, the present invention generates an AC pulse current by intermittent alternating current from an AC auxiliary power source having the same commercial frequency as an AC output from an AC main power source having a commercial frequency at a frequency lower than the commercial frequency. By superimposing the welding current as As a result, the vibrations of the molten metal become regular and stable submerged arc welding can be performed. Therefore, there is an effect that a stable penetration depth can be obtained and a good bead without defects can be formed. Note that this effect is even more remarkable when the superimposed alternating current pulse current is a low frequency alternating current pulse current with a pulse frequency of 0.3 to 3 Hz.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus configuration used in an embodiment of the present invention. FIG. 2 is a chart showing waveforms of various parts according to an embodiment of the present invention. FIG. 3 is an explanatory diagram of a weld bead formed by a conventional submerged arc welding method. In the figure, 1 is the welding member, 2 is the groove, 3 is the tack bead, 4 is the weld bead, 5 is the part immediately before the tack bead 2, 6 is the welding electrode, 7 is the main welding power source, and 8 is the pulse auxiliary A power source, 9 a switch, 10 a pulse controller, and 11 a frequency setter. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. When performing continuous submerged arc welding along the groove of a welded part, a commercial frequency AC power source and an AC auxiliary power source are used as the welding power source, and the AC output from this AC main power source is . An AC pulse submerged arc welding method, characterized in that an AC pulse current obtained by intermittent AC output from the AC auxiliary power source at a frequency lower than the commercial frequency is superimposed. 2 The AC pulse current has a pulse frequency of 0.3 to 3
The alternating current pulsed submerged arc welding method according to claim 1, characterized in that the welding method is a low frequency alternating current pulsed current of Hz.