JPH01215468A - Method for controlling bipolar arc welding - Google Patents

Abstract

PURPOSE:To stabilize an AC arc and to perform welding at a high speed by reducing a welding current or the welding voltage for a prescribed period of time right before or right after a changeover at the time of changing over the polarity of the DC voltage impressed between a consumable electrode and base metal from the reversed polarity to the straight polarity. CONSTITUTION:At the time of changing over the polarity of the DC voltage impressed between the consumable electrode 3 and the base metal 5 from the reversed polarity to the straight polarity while an arc 4 being generated, a high current is carried suddenly to the straight polarity and an arc generating period of time and short-circuit period of time are extended. As a result, a decrease of the number of short circuits or an increase of its change takes place and deterioration of workability or an increase of a large-sized spatter right before the short circuit is caused. As a result, while a current decrease control circuit 16 executes the time integration of the reversed polarity welding by a polar signal from a polarity changeover control circuit 12, it determines the current decrease timing based on the set current decrease time and outputs a current decrease starting command signal, a set decrease current target value and a decrease current waveform to an output control circuit 18. By this method, when the changeover is executed to the straight polarity, the output of a DC power source 1 is controlled by the circuit 15 and the welding current at the time of changing over decreases.

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. However, when the base metal is a thin plate and the joint accuracy is poor and the gap becomes large, 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 previously applied for patent application No. 62-2894.
In the inventions of No. 45 and Japanese Patent Application No. 62-329432, positive polarity and reverse polarity are alternately repeated, and the polarity ratio is arbitrarily varied to suit various joint shapes, thereby exhibiting the characteristics of bipolarity. The practical application of an AC welding method that can achieve this is being considered.

[Problems to be Solved by the Invention] However, in this type of AC welding method, workability problems such as unstable arc and increased spatter occur, and high-speed welding also increases large spatter. However, there are problems such as the occurrence of stabbing phenomena and thin bead constrictions, and the advantages of bipolar welding cannot be fully demonstrated.

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, arc stabilization methods such as the positive polarity pulsed short arc method shown in JP-A-56-109171 have been proposed, but none of them are effective in stabilizing the arc of positive polarity single welding. AC welding has no effect.

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, we provide 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, At least one of the welding current and welding voltage is lowered for a predetermined period in at least one of them, so that after the polarity reversal, a current that is high for positive polarity welding does not flow suddenly, and the current value suitable for positive polarity welding is maintained immediately after the polarity reversal. Welding current starts to flow. Therefore, burning out of the consumable electrode (welding wire) and abnormal growth of droplets are suppressed, a reduction in the number of short circuits is prevented, and poor workability caused by polarity switching is eliminated.

[Embodiments of the Invention] A control method for bipolar arc welding as an embodiment of the present invention will be explained below with reference to one drawing. 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 an inverter circuit composed of power transistors Tr1 to Tr4, 3 is a welding wire (consumable electrode), 4 is an arc,
5 is a base material, 6 is a wire feed motor for feeding the welding wire 3 from the wire reel 7 to the welding area at a constant speed, 8 is a glue handle in the welding current supply path, 9 is a current detector for detecting the welding current, 1o is a voltage detector that detects the welding voltage between the welding wire 3 and the base material 5.

Further, 11 is a transistor driver that outputs on/off signals to the power transistors Tr1 to Tr4 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 setting circuit. 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 8-force control circuit for controlling the output of the DC power source 1.

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

The energization time setting circuit 13 takes in the ratio setting value set by the polarity ratio setting device 14 and sets the energization time TSPy TRP for positive polarity and reverse polarity. Then, the polarity switching control circuit 12 receives the energization time TSP+TRP set by the energization time setting circuit 13 and performs time integration,
High level during reverse polarity period, Low during positive polarity period
A level polarity signal is output to the transistor driver 11. The transistor driver 11 has a polarity signal of High
When the power transistor Tr1. Tr4
is turned on and Tr2., Tr2. Turn on Tr3. Here, power transistor Tr engineering.

When Tr4 is on and Tr, , Tr3 are off, the current from the DC power supply l flows from the welding wire 3 to the base metal 5 side,
While reverse polarity welding is performed, the power transistor Tr
1. Tr4 is off, Tr2. When Tr is 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, the third
An example of the welding voltage and welding current waveforms in Figures (a) and (b) shows that when the polarity is reversed to positive polarity while an arc is occurring, a current that is almost the same value as the current flowing with the opposite polarity until then will flow. Flows in the positive polarity arc [see part A in Figure 3 (b)]
. For this reason, a high current flows rapidly for positive polarity, and the droplets already formed with the opposite polarity are pushed upwards and more droplets are formed. After that, the current returned to normal after several m5ec, but the arcing period was inevitably extended.

The droplet continues to grow.

On the other hand, if a short circuit occurs while the droplet continues to grow large, the temperature of the droplet during the short-circuit transition decreases, the viscosity of the droplet increases, and the short-circuit transition is hindered, and it takes time to constrict the droplet. In some cases, a so-called stubbing phenomenon occurs in which unmelted welding wire plunges into the molten pool, or the bead becomes thinner or breaks at that portion.

In this way, the arc generation period and the short circuit period are extended, so the number of short circuits decreases and the fluctuations in the number of short circuits increase, 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 voltage increase waveform is output to the output control circuit 18 so as to return to the level.

The output control circuit 18 receives signals from the current detector 9, the voltage detector 10, and the wire feed speed setting device 17, and controls the welding voltage and welding current from the voltage reduction control circuit 15 and the current reduction control circuit 16. The output of the DC power supply 1 is controlled to follow the output of the DC power supply 1.

Note that the drop time, target value, and waveform of the welding voltage and welding current may be fixed in advance based on experimental results, or, for example,
It may be set in the voltage reduction control circuit 15 and the current reduction control circuit 16 as a function of the wire feeding speed or switching frequency or as a function of the time after arc reoccurrence for automatic 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 allows setting of the welding current with reverse polarity. is set lower than the normal welding current value, so that when switching to positive polarity, the output of the DC power supply 1 is controlled by the output control circuit 18, and the welding current at the time of switching to positive polarity is lowered.

For example, as shown in Figures 2 (a) and (b), a predetermined time before switching from reverse polarity to positive polarity, the current is lowered than the previous current value as a preparation for positive polarity welding. At the beginning [see part B of Fig. 2 (b)], the current value at which the welding current □ does not promote the increase of droplets immediately after the polarity reversal, that is, the current value immediately after the polarity reversal, is the current value that flows during the original positive polarity welding. The DC power supply 1 controls the output so that the current value is approximately equal to or less than the power current value rs (see section C in FIG. 2(b)).

Note that instead of reducing the current setting value immediately before polarity reversal, the voltage setting value may be reduced by a voltage reduction control circuit (not shown), or the current setting value and the voltage setting value may be reduced simultaneously. [See FIGS. 2(a) and (b)].

Furthermore, more preferably, the voltage reduction control circuit 15
Either set the welding voltage lower than the original setting value [see section D in Figure 2 (a)], or set the current or both settings lower instead of the voltage [Figure 2 (a)]. ),
(b)]. Furthermore, the output reduction control as described above may be performed immediately before and after the polarity switching [Fig. 2 (a)
), (b)].

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

■If current reduction control is performed before switching, base material thickness 1
, 2 m+++, horizontal lap joint with gap 0.4 mn+, welding wire diameter 1, 2 mm, shielding gas CO, wire feeding speed 4 m/min, welding speed 0.8 m/min
minutes, polarity ratio (positive polarity ratio) 60%, switching frequency 50H
When welding was performed at z, without waveform control, the droplets grew large, the arc became unstable, and spatter occurred frequently, resulting in poor workability. The number of short circuits at this time was as small as 15 to 25 times/second. However, if the waveform control of the current reduction is performed before switching [see section D in Figure 2 (b)], droplet growth is suppressed and the number of short circuits is reduced to 60//.
After about a second, the arc stabilized.

■When voltage drop control is performed after switching, the base metal plate thickness is 1
, 2mm, in a horizontal lap joint with a gap of 0.4n+m, welding wire diameter 1, 2mm, shielding gas CO
,, wire feeding speed 6 m/min, welding speed 1.2 m/min,
When welding was performed at a polarity ratio of 50% and a switching frequency of 100 Hz, we found that without waveform control, the droplets grew large, the arc became unstable, and spatter occurred frequently, resulting in poor workability. A thin constriction appeared on the skin. The number of short circuits at this time was about 20 times for 1 second. However, when the waveform control of the voltage drop was performed after one switching [see section D in FIG. 2(a)], droplet growth was suppressed, the number of short circuits was reduced to 50 times for 1 second, and the arc was stabilized. Furthermore, continuous beads with good appearance were 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 thicknesses of 1 and 6 mm and a gap of 0.5 mm, welding wire diameters of 1 and 2 mm, shielding gas CO□, wire feed Feeding speed 9.5 m/min, welding speed 1.5 m/min, polarity ratio 70%, switching frequency 300
When welding was carried out at Hz, 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,
If waveform control is performed to reduce the current before switching and to reduce the voltage after switching [see section B in Figure 2 (b) and section D in Figure 2 (a)], droplet growth is suppressed and the number of short circuits is also reduced to 40. ~45 times/
The arc stabilized and large spatter decreased. And, it was possible to obtain a continuous and stable bead.

Note that the above welding example uses CO2 welding using solid wire.
Although the case of AC arc welding is explained, Ar-
Go□It can also be applied to mixed gas shield AC welding and non-gas shield AC welding using composite wire.

[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 burnout of the consumable electrode and abnormal growth of droplets can be prevented when switching the polarity. As a result, the number of short circuits is reduced and irregularity is prevented, and AC arc stabilization and high-speed welding are realized. This eliminates poor workability caused by polarity switching, and provides the effect of maximizing the benefits of AC welding.

[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; FIGS. 2(a) and (b) are graphs showing the voltage and current waveforms when waveform control is performed by the device of the above embodiment, respectively, and FIGS. 3(a) and (b) are graphs showing the conventional waveform control, respectively. 5 is a graph showing voltage waveforms and current waveforms when waveform control is performed. 1--DC power supply, 2--inverter circuit, 3--welding wire (consumable electrode), 4--arc, 5--base material, 6-
- wire feeding 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 engineering~T
r, - power transistor; Patent applicant: Kobe Steel, Ltd.

Claims (1)

[Claims] In the control method of 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 polarity of the DC voltage applied between the consumable electrode and the base metal is Control of 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 the welding voltage is lowered for a predetermined period at least one of immediately before and after the switching. Method.