JPH0464794B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to the control of bipolar arc welding in which the polarity of a DC voltage applied between a consumable electrode and a base material is switched to repeat positive and reverse polarity. It is about the method.

[Prior Art] In consumable electrode type arc welding, in which welding is performed by generating an arc between the welding wire (consumable electrode) and the base metal while supplying the welding wire (consumable electrode) at a constant speed, normally the base metal side is negative and the welding wire side is negative. Reverse polarity welding is performed by applying a positive DC voltage.

This reverse polarity welding has the advantage that the heat input to the base metal is large, so the amount of penetration is large, and it is easy to obtain a flat bead. There is a drawback that burn-through phenomenon tends to occur.

On the other hand, positive polarity welding, in which a DC voltage is applied so that the base metal side is positive and the welding wire side is negative, is effective for burn-through because the amount of heat input to the base metal is small, but it can cause poor penetration. The bead tends to have a convex shape. Therefore, the scope of application of positive polarity single welding is narrow.

Therefore, the present inventor filed a patent application No. 62-289445.
No. (Japanese Unexamined Patent Publication No. 1-133678) and patent application No. 1982-
In the invention of No. 289446 (Japanese Patent Application No. 1-133679), positive polarity and reverse polarity are alternately repeated, and the polarity ratio is arbitrarily varied to suit various joint shapes, thereby demonstrating the characteristics of bipolarity. The practical application of an AC welding method that can be used is being considered.

[Problems to be Solved by the Invention] However, in this type of AC welding method, workability problems such as instability of the arc and increase in spatter occur, and high-speed welding causes an increase in large spatter. However, there are problems such as the stabbing phenomenon and the occurrence of thin and constricted parts of the beat, making it impossible to fully utilize the features of bipolar welding.

By the way, in positive polarity welding, which is one of the two polarity welding types, the arc tends to rise above the wire tip more easily than in reverse polarity welding, so the range of appropriate welding conditions is narrower, and large particles of spatter may occur. It has the property of being easy to occur. From this point of view, although the arc stabilization method known as the positive pulse shot arc method disclosed in Japanese Patent Application No. 56-109171 and the positive polarity arc welding device disclosed in Japanese Patent Application Laid-open No. 58-38666 have been proposed, Although either method is effective in stabilizing the arc in positive polarity single welding, it is not effective in AC welding.

In order to solve the above-mentioned problems, the present invention aims to eliminate the poor workability caused by polarity switching, and suppresses the burning of the consumable electrode (welding wire) and the abnormal growth of droplets during polarity switching. As a result, by preventing a decrease in the number of short circuits, the present invention provides a control method for bipolar arc welding that stabilizes the AC arc and enables high-speed welding, thereby maximizing the benefits of AC welding. The purpose is to

[Means for Solving the Problems] In order to achieve the above object, the bipolar arc welding control method of the present invention changes the polarity of the DC voltage applied between the consumable electrode and the base material from reverse polarity to positive polarity. When switching to , the set value of at least one of the welding current and the welding voltage is lowered for a predetermined period at least one of immediately before and after the switching.

[Function] In the bipolar arc welding control method of the present invention described above, when switching the polarity of the DC voltage applied between the consumable electrode and the base material from reverse polarity to positive polarity, the polarity of At least one of the welding current and welding voltage is lowered for a predetermined period at least on one side, so that after the polarity is reversed, a current that is high for positive polarity welding does not flow suddenly, and a current suitable for positive polarity welding is maintained immediately after the polarity reversal. value of welding current will begin to flow. Therefore, burning out of the consumable electrode (welding wire) and abnormal growth of droplets are suppressed, a decrease in the number of short circuits is prevented, and poor workability caused by polarity switching is eliminated.

[Embodiments of the Invention] Hereinafter, a method for controlling bipolar arc welding as an embodiment of the present invention will be explained with reference to the drawings.
Fig. 1 is an overall configuration diagram showing a control device for bipolar arc welding to which this method is applied. In Fig. 1, 1 is a DC power supply, 2 is a power transistor.
An inverter circuit consisting of Tr ₁ to _{Tr 4} , 3 is a welding wire (consumable electrode), 4 is an arc, 5 is a base material,
Reference numeral 6 denotes a wire feed motor for supplying the welding wire 3 from the wire reel 7 to the welding area at a constant speed, 8 a reactor in the welding current supply path, 9 a current detector for detecting the welding current, and 10 the welding wire 3 and base material 5
This is a voltage detector that detects the welding voltage between the
Further, 11 is a transistor driver that outputs on/off signals for the power transistors Tr ₁ to _{Tr 4} in the inverter circuit 2, 12 is a polarity switching control circuit, 13 is a circuit for setting energization time for positive polarity and reverse polarity, and 14 is a polarity ratio. 15 is a voltage reduction control circuit, 16 is a current reduction control circuit, 17 is a wire feed speed setting device, and 18 is an output control circuit for controlling the output of the DC power supply 1.

Next, the operation of the above-mentioned control device will be explained.

The energization time setting circuit 13 includes a polarity ratio setting device 14
Take in the ratio setting value explained in , and set the energization times T _SP and T _RP for positive polarity and reverse polarity. Then, the polarity switching control circuit 12 receives the energization times T _SP and T _RP set by the energization time setting circuit 13, performs time integration, and sets the polarity to High level during the reverse polarity period and Low level during the positive polarity period. A signal is output to the transistor driver 11. The transistor driver 11 turns on and turns on the power transistors Tr ₁ and Tr ₄ when the polarity signal is at a high level.
While Tr ₂ and Tr ₃ are turned off, when the polarity signal is at a low level, Tr ₁ and Tr ₄ are turned off and Tr ₂ and Tr ₃ are turned on. Here, the power transistor Tr ₁ ,
When Tr ₄ is on and Tr ₂ and Tr ₃ are off, the current from the DC power supply 1 flows from the welding wire 3 to the base metal 5 side, and reverse polarity welding is performed, while the power transistors Tr ₁ and Tr ₄ are off. , Tr ₂ and Tr ₃ are on, the current from the DC power supply 1 flows from the base metal 5 to the welding wire 3 side, and positive polarity welding is performed.

By the way, when switching the polarity during arc generation, as shown in the example of the welding voltage and welding current waveforms in Figures 5a and b, if the polarity is reversed to positive polarity during arc generation, the polarity will be reversed until then. A current that is approximately the same value as the current that was flowing flows through the positive polarity arc [see section A in Figure 5b]. For this reason, a high current flows rapidly for positive polarity, so droplets already formed with opposite polarity are pushed upwards and more solution is formed. Although the current returns to normal after several milliseconds, the arc period inevitably increases and the solution continues to grow.

On the other hand, if a short circuit occurs while the solution is still growing, the temperature of the droplet during the short circuit transition will drop, the viscosity of the droplet will increase, and the short circuit transition will be prevented, and it will take time to constrict the droplet. In some cases, the so-called stubbing phenomenon occurs in which unmelted welding wire plunges into the molten pool, and the bead becomes thinner or breaks at that portion.

In this way, the arc generation period and the short circuit period are extended, which reduces the number of short circuits or increases the fluctuation in the number of short circuits, leading to deterioration of workability. Furthermore, when the droplets grow large, the spatter immediately before the short circuit becomes larger or increases in size.

Therefore, in this embodiment, the current reduction control circuit 16 takes in the polarity signal from the polarity switching control circuit 12, integrates the time of reverse polarity welding, and adjusts the current reduction timing based on the preset current reduction time. and outputs a current reduction start command signal, a preset reduction current target value (a value lower than the normal welding current value in reverse polarity), and a current reduction waveform to the output control circuit 18, and At the time of polarity switching to positive polarity, a signal for canceling the current lowering operation is output to the output control circuit 18.

Furthermore, the voltage reduction control circuit 15 outputs a voltage reduction start signal and a preset initial voltage value at the time of switching to the output control circuit 18 at the time of polarity switching from reverse polarity to positive polarity, and also outputs a voltage reduction start signal and a preset initial voltage value at switching to the output control circuit 18.
While integrating the time of positive polarity welding by taking in the polarity signal from the A control circuit 18 that outputs a voltage rising waveform to return to the level
Output to.

The output control circuit 18 includes a current detector 9,
Voltage detector 10 and wire feed speed setting device 17
While receiving signals from the DC power source 1, the output of the DC power source 1 is controlled so that the welding voltage and welding current follow the outputs from the voltage reduction control circuit 15 and the current reduction control circuit 16.

Note that the drop time, target value, and waveform of welding voltage and welding current may be fixed in advance based on experimental results, or, for example, may be set as a function of wire feeding speed or switching frequency, or as a function of time after arc recurrence. Voltage reduction control circuit 15 and current reduction control circuit 16
It may also be set to automatically control.

By using a device having the configuration and operation described above, when switching the polarity of the DC voltage applied between the welding wire 3 and the base metal 5 from reverse polarity to positive polarity, prior to this switching, The current reduction control circuit 16 controls the set value of the welding current in reverse polarity.
_I0 is set lower than the normal welding current value, so that when switching to positive polarity, the output control circuit 18
The output of the DC power supply 1 is controlled by this, and the welding current at the time of switching to positive polarity becomes low.

That is, as shown in Fig. 2b, a predetermined time before the switching from reverse polarity to positive polarity, the current starts to be lowered from the previous current value as a preparatory step for positive polarity welding [Fig. 2b [Refer to Part B ₂ ], so that the welding current I ₁ immediately after polarity reversal is a current value that does not promote the increase of droplets, that is, approximately the same current value that should flow during normal positive polarity welding [Part 2]. [See section C in Figure 2b] The DC power supply 1 controls the output.

Note that instead of lowering the current set value immediately before polarity reversal, a voltage reduction control circuit (not shown) may perform control to lower the voltage set value, or
Control may be performed to simultaneously lower the current set value and voltage set value [B ₁ and B ₂ in Figures 2 a and b.
reference〕.

On the other hand, as in this embodiment, by setting the welding voltage setting value lower than the original setting value by the voltage reduction control circuit 15 for a predetermined period of time from the time when the polarity is switched from the reverse polarity to the positive polarity. The same effect can be obtained even if the current is set low, and the current or both may be set low instead of the voltage [Figure 3 a, b
See Parts C and D]. A more preferable control method is
The above-mentioned output reduction control is performed immediately before and after the polarity switching (see FIGS. 4a and 4b).

Now, the experimental results obtained by actually using the apparatus shown in FIG. 1 and performing welding based on various waveform controls are shown below.

When current reduction control is performed before switching In a horizontal lap joint with a base metal plate thickness of 1.2 mm and a gap of 0.4 mm, welding wire diameter is 1.2 mm, shielding gas CO ₂ , wire feeding speed is 4 m/min, and welding speed
When welding was performed at 0.8 m/min, polarity ratio (positive polarity ratio) of 60%, and switching frequency of 50Hz, it was found that without waveform control, the droplets grew large, the arc became unstable, and spatter occurred frequently. Poor workability occurred. Number of short circuits at this time: 15
It was as low as ~25 times/second. However, if we perform waveform control to reduce the current before switching [Fig. 2 b]
Refer to Part _B ], the growth of droplets is suppressed and the number of short circuits is also reduced.
It became around 60 times/second, and the arc became stable.

When voltage drop control is performed after switching In a horizontal lap joint with a base metal plate thickness of 1.2 mm and a gap of 0.4 mm, welding wire diameter is 1.2 mm, shielding gas CO ₂ , wire feeding speed is 6 m/min, welding speed
When welding was performed at 1.2 m/min, polarity ratio of 50%, and switching frequency of 100 Hz, if waveform control was not performed, the droplets grew large, the arc became unstable, and spatter occurred frequently, resulting in poor workability. In addition to this, a thin constriction appeared on the bead. The number of short circuits at this time was about 20 times/second. However, when the waveform of the voltage drop was controlled after switching [see section D in Figure 3a], droplet growth was suppressed and the number of short circuits decreased to 50 times/second, the arm became stable, and the bead also became continuous. A product with good appearance was obtained.

When current drop control is performed before switching and voltage drop control is performed after switching In a horizontal lap joint with base metal plate thickness 1.6 mm and gap 0.5 mm, welding wire diameter 1.2 mm, shielding gas CO ₂ , wire feed speed 9.5 m/min, welding speed 1.5m/min, polarization ratio 70%, switching frequency 300Hz
When welding was carried out in the welding process, it was found that if waveform control was not performed, the droplets would grow abnormally large, the arc would become unstable, large spatters would occur frequently, the weld bead would be interrupted or constricted, and even stubbing could occur. A phenomenon has occurred. The number of short circuits at this time was about 10 times/second. However, when waveform control is performed to reduce the current before switching and to reduce the voltage after switching (see section B 2 of Figure _2b and section D of Figure 3a), droplet growth is suppressed and the number of short circuits also increases from 40 to 40.
45 times/second, the arc was stabilized and large spatter was reduced. And, it was possible to obtain a continuous and stable bead.

The above welding example describes CO ₂ AC arc welding using solid wire, but it can also be applied to Ar-CO ₂ mixed gas shield AC welding, non-gas shield AC welding using composite wire, etc. .

[Effects of the Invention] As detailed above, according to the bipolar arc welding control method of the present invention, when switching the polarity of the DC voltage applied between the consumable electrode and the base material from reverse polarity to positive polarity, Since the set value of at least one of the welding current and welding voltage is lowered for a predetermined period of time immediately before and after switching, the burning of the consumable electrode and abnormal growth of droplets are suppressed during polarity switching. As a result, the number of short circuits is reduced and irregularity is prevented, and AC arc stabilization and high-speed welding are achieved. This eliminates workability problems caused by polarity switching.
The effect of maximizing the benefits of AC welding can be obtained.

[Brief explanation of the drawing]

1 and 2 show a control method for bipolar arc welding as an embodiment of the present invention, and FIG. 1 is an overall configuration diagram showing a control device for bipolar arc welding to which this method is applied; Figure 2 a, b, Figure 3 a, b
4a and 4b are graphs showing the voltage and current waveforms when waveform control is performed by the device of the above embodiment, and FIGS. 5a and 5b are graphs showing the voltage and current waveforms when conventional waveform control is performed, respectively 3 is a graph showing voltage waveforms and current waveforms when 1...DC power supply, 2...Inverter circuit, 3...
...Welding wire (consumable electrode), 4... Arc, 5...
... Base material, 6 ... Wire feed motor, 7 ... Wire reel, 8 ... Reactor, 9 ... Current detector,
10... Voltage detector, 11... Transistor driver, 12... Polarity switching control circuit, 13... Energization time setting circuit, 14... Polarity ratio setting device, 15...
... Voltage reduction control circuit, 16 ... Current reduction control circuit, 17 ... Wire feed speed setting device, 18 ... Output control circuit, Tr ₁ to Tr ₄ ... Power transistor.

Claims (1)

[Claims] 1. In a control method for bipolar arc welding in which the polarity of the DC voltage applied between the consumable electrode and the base metal is alternately repeated during arc generation, the DC voltage applied between the consumable electrode and the base metal is bipolar arc welding, characterized in that when switching the polarity from reverse polarity to positive polarity, the set value of at least one of the welding current or welding voltage is lowered for a predetermined period at least one of immediately before and after the switching. Control method.