JP7539003B2 - Welding Equipment - Google Patents

Description

The present disclosure relates to a welding device that generates an arc by applying an alternating voltage between an electrode and a workpiece.

The welding device disclosed in Patent Document 1 includes an inverter circuit that switches the polarity of an AC voltage between a positive polarity that makes the workpiece have a higher potential than the electrode and a reverse polarity that makes the workpiece have a lower potential than the electrode, a capacitor, a charging circuit that charges the capacitor, a discharge circuit that performs a discharge operation to increase the current flowing from the electrode to the workpiece due to arc discharge by discharging the capacitor, and a control unit that causes the discharge circuit to perform the discharge operation when the polarity of the AC voltage is switched from the positive polarity to the reverse polarity. In this welding device, when the polarity of the AC voltage is switched from the positive polarity to the reverse polarity, the current flowing from the electrode to the workpiece due to arc discharge is increased by discharging the capacitor, so that arc interruption is unlikely to occur. The frequency of the AC voltage is set to 500 Hz, and the discharge period during which the control unit causes the discharge circuit to perform the discharge operation is set to 300 μs after the polarity of the AC voltage is switched from positive polarity to reverse polarity.

JP 2019-89093 A

However, in Patent Document 1, the period during which the discharge circuit performs the discharge operation occupies 15% of the AC voltage cycle, so the amount of change in the welding current due to the discharge operation significantly affects the effective value of the welding current, which may lead to problems during welding. This problem is particularly noticeable when welding is performed with a relatively small current. Specifically, the effective value of the welding current increases in the low current range, and if the workpiece is a thin plate or the like, there is a possibility that the workpiece may melt through.

This disclosure has been made in consideration of these points, and its purpose is to suppress defects during welding caused by the discharge operation.

In one aspect of the present disclosure, a welding device generates an arc by applying an AC voltage between an electrode and a workpiece, and is characterized in that it includes an inverter circuit that switches the polarity of the AC voltage between a positive polarity that places the workpiece at a higher potential than the electrode and a reverse polarity that places the workpiece at a lower potential than the electrode, a capacitor, a charging circuit that charges the capacitor, a discharge circuit that performs a discharge operation to increase the current flowing from the electrode to the workpiece due to arc discharge by discharging the capacitor, and a control unit that, when the polarity of the AC voltage is switched from the positive polarity to the reverse polarity, causes the discharge circuit to perform the discharge operation continuously for a discharge period of 5% or less of the cycle of the AC voltage.

According to this embodiment, the effect that the change in welding current due to the discharge operation has on the effective value of the welding current can be reduced compared to when the discharge period is made longer than 5% of the AC voltage cycle, thereby suppressing problems during welding caused by the discharge operation.

According to the present disclosure, defects during welding caused by discharge operations can be suppressed.

FIG. 1 is a diagram showing a schematic configuration of a welding device according to an embodiment of the present disclosure. FIG. 2 is a circuit diagram of the welding power supply. FIG. 3 is a circuit diagram of the second inverter circuit. FIG. 4 is a circuit diagram of the charging circuit. FIG. 5 is a circuit diagram of the discharge circuit. FIG. 6 is a timing chart showing the polarity switching signal, the welding current, the capacitor voltage, the charge signal, and the discharge signal. FIG. 7 is a diagram equivalent to FIG. 6, but showing a case where the discharging operation is performed throughout the reverse polarity period.

Below, an embodiment of the present disclosure is described with reference to the drawings.

Figure 1 shows a welding device 1 according to an embodiment of the present disclosure. This welding device 1 includes a welding torch 10 and a welding power source 20. This welding device 1 is an AC TIG welding device in which the welding torch 10 is a non-consumable electrode torch.

The welding torch 10 has a nozzle 11 that sprays shielding gas SG supplied from a gas supply device (not shown). A roughly cylindrical collet 12 is disposed inside the nozzle 11 so as to be aligned with the direction of spraying of the nozzle 11. A rod-shaped tungsten electrode TE is fixed inside the collet 12.

The welding power source 20 generates an arc A by applying an AC voltage between the tungsten electrode TE of the welding torch 10 and the workpiece (work) W.

Using this welding device 1, an operator can generate an arc A between the tungsten electrode TE and the workpiece W, forming a molten pool P on the workpiece W, and then insert a filler rod R into this molten pool P to form a weld bead.

In detail, as shown in FIG. 2, the welding power source 20 includes a first rectifying and smoothing circuit 21, a first inverter circuit 22, a first transformer 23, a second rectifying and smoothing circuit 24, first and second reactors 25, 26, a second inverter circuit 27, a re-ignition circuit 30, and a control device 40.

The first rectifying and smoothing circuit 21 converts the input AC power input from the commercial power source 2 into DC power and outputs it.

The first inverter circuit 22 is, for example, a single-phase full-bridge type PWM control inverter, and is equipped with four switching elements (not shown). The first inverter circuit 22 converts the DC power output by the first rectifying and smoothing circuit 21 into AC power and outputs it by switching these four switching elements in response to a switching signal S1 output by the control device 40. Here, the output voltage of the first inverter circuit 22 is the first AC voltage. Note that the first inverter circuit 22 may be an inverter circuit of another configuration, such as a half-bridge type inverter.

The first transformer 23 converts the first AC voltage output by the first inverter circuit 22 into a second AC voltage and outputs it. The first transformer 23 has a first primary coil 23a and a first secondary coil 23b. The first AC voltage output by the first inverter circuit 22 is applied to the first primary coil 23a. The voltage of the first secondary coil 23b becomes the second AC voltage.

The second rectifying and smoothing circuit 24 converts the second AC voltage output by the first transformer 23 into a first DC voltage and outputs it from the positive output terminal 24a and the negative output terminal 24b. The second rectifying and smoothing circuit 24 is a diode bridge circuit consisting of four diodes 24c.

3, the second inverter circuit 27 is a single-phase half-bridge type inverter circuit. The second inverter circuit 27 includes first and second input terminals 271, 272, and an upper arm switching element 273 and a lower arm switching element 274 connected in series between the first and second input terminals 271, 272. The upper arm switching element 273 receives a polarity switching signal S2 output by the control device 40, while the lower arm switching element 274 receives an inverted signal of the polarity switching signal S2. The first input terminal 271 of the second inverter circuit 27 is connected to the positive output terminal 24a of the second rectifying and smoothing circuit 24 via the first reactor 25. The second input terminal 272 of the second inverter circuit 27 is connected to the negative output terminal 24b of the second rectifying and smoothing circuit 24 via the second reactor 26. The output terminal 275 of the second inverter circuit 27 is connected to the workpiece W.

Therefore, with the upper arm switching element 273 turned on and the lower arm switching element 274 turned off, the second inverter circuit 27 sets the workpiece W at a higher potential than the tungsten electrode TE, while with the upper arm switching element 273 turned off and the lower arm switching element 274 turned on, the second inverter circuit 27 sets the workpiece W at a lower potential than the tungsten electrode TE. When a pulse signal that switches between a high level and a low level at a predetermined period is input to the second inverter circuit 27 as a polarity switching signal S2, the second inverter circuit 27 periodically switches the polarity of the AC voltage applied between the workpiece W and the tungsten electrode TE between a positive polarity that sets the workpiece W at a higher potential than the tungsten electrode TE and a reverse polarity that sets the workpiece W at a lower potential than the tungsten electrode TE.

The restrike circuit 30 includes a capacitor 31, a first diode 32, a voltage sensor 33, a charging circuit 34, and a discharging circuit 35.

One electrode of the capacitor 31 is connected to the middle of the first secondary coil 23b of the first transformer 23 via a first diode 32.

The cathode of the first diode 32 is connected to one electrode of the capacitor 31, and the anode of the first diode 32 is connected to a mid-portion of the first secondary coil 23b of the first transformer 23.

The voltage sensor 33 measures the voltage of the capacitor 31 and outputs the measurement value MV.

As shown in FIG. 4, the charging circuit 34 has a third rectifying and smoothing circuit 341, a second transformer 342, a charging switching element 343, a drive circuit 344, second and third diodes 345, 346, and a third reactor 347.

The third rectifying and smoothing circuit 341 converts the input AC voltage input from the commercial power source 2 into a DC voltage and outputs it.

The second transformer 342 transforms the voltage obtained by subtracting the source-drain voltage of the charging switching element 343 from the DC voltage output by the third rectifying and smoothing circuit 341 into a charging DC voltage and outputs the voltage. The second transformer 342 has a second primary coil 342a and a second secondary coil 342b. A voltage obtained by subtracting the source-drain voltage of the charging switching element 343 from the DC voltage output by the third rectifying and smoothing circuit 341 is applied to the second primary coil 342a. The voltage of the second secondary coil 342b becomes the charging DC voltage.

The charging switching element 343 turns on and off the connection between the third rectifying and smoothing circuit 341 and the second primary coil 342a of the second transformer 342. The charging switching element 343 is composed of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

The drive circuit 344 turns on the charging switching element 343 when the conditions that the measured value MV of the voltage sensor 33 is less than a predetermined charging voltage CV and the charging signal S3 output by the control device 40 is at a high level are satisfied, and turns off the charging switching element 343 when these conditions are not satisfied.

The cathode of the second diode 345 and the cathode of the third diode 346 are connected to each other.

One end of the second secondary coil 342b is connected to the anode of the second diode 345, and the other end of the second secondary coil 342b is connected to the anode of the third diode 346. The connection point between the second secondary coil 342b and the third diode 346 is connected to the second inverter circuit 27 side (workpiece W side) of the capacitor 31.

One end of the third reactor 347 is connected to the connection point of the second diode 345 and the third diode 346. The other end of the third reactor 347 is connected to the capacitor 31 and the cathode of the first diode 32.

Therefore, the charging circuit 34 configured as described above charges the capacitor 31 using AC power from the commercial power source 2 when the conditions are met that the measured value MV of the voltage sensor 33 is less than a predetermined charging voltage CV and the charging signal S3 is at a high level.

As shown in FIG. 5, the discharge circuit 35 has a resistor 351 and a discharge switching element 352.

One end of resistor 351 is connected to tungsten electrode TE. The other end of resistor 351 is connected to one end of discharge switching element 352. The other end of discharge switching element 352 is connected to the electrode of capacitor 31 on the first diode 32 side.

The discharge switching element 352 is turned on when the discharge signal S4 output by the control device 40 is at a high level and is turned off when the discharge signal S4 is at a low level.

Therefore, the discharge circuit 35 configured as described above electrically connects the tungsten electrode TE and the capacitor 31 when the discharge signal S4 is at a high level, thereby performing a discharge operation in which the current flowing from the tungsten electrode TE to the workpiece W by arc discharge is increased by discharging the capacitor 31.

The control device 40 includes a current control unit 41, a polarity switching control unit 42, a charging control unit 43, and a discharging control unit 44.

Based on the measured value of the welding current I input from a current sensor (not shown), the current control unit 41 outputs a switching signal S1 to the first inverter circuit 22 by PWM control so that the effective value of the welding current I becomes the set value SV. In this embodiment, the set value SV of the welding current I is 10 A. The set value SV of the welding current I can be changed by the user's input to an input means (not shown).

The polarity switching control unit 42 outputs a polarity switching signal S2 that switches the polarity of the AC voltage applied between the electrode TE and the workpiece W. The polarity switching signal S2 is a 1 kHz pulse signal. Therefore, the frequency of the AC voltage applied between the tungsten electrode TE and the workpiece W is 1 kHz.

The charging control unit 43 outputs a charging signal S3. The charging signal S3 is at a high level when the polarity switching signal S2 is at a high level, and is at a low level when the polarity switching signal S2 is at a low level.

The discharge control unit 44 outputs a discharge signal S4. The discharge signal S4 is a signal that remains at a high level for a discharge period L from when the polarity switching signal S2 switches from a high level to a low level until 25 μs has elapsed, and remains at a low level for the rest of the period. 25 μs is a period that is 2.5% of the period of the AC voltage applied between the tungsten electrode TE and the workpiece W. In other words, when the polarity of the AC voltage applied between the tungsten electrode TE and the workpiece W switches from positive polarity to reverse polarity, the discharge control unit 44 causes the discharge circuit 35 to perform the discharge operation continuously for a discharge period L that is 2.5% of the period of the AC voltage.

In the welding device 1 configured as described above, as shown in FIG. 6, at timing t1, the voltage of the capacitor 31 is the charging voltage CV. When the polarity switching signal S2 switches from high level to low level at timing t1, the charging signal S3 changes from high level to low level. In addition, the polarity of the AC voltage applied between the tungsten electrode TE and the workpiece W switches from positive polarity to reverse polarity, and the discharge signal S4 changes from low level to high level. The discharge signal S4 maintains a high level during the discharge period L of 25 μs from timing t1. Therefore, during the discharge period L, the discharge switching element 352 is turned on, the tungsten electrode TE and the capacitor 31 are electrically connected, and a current flows from the capacitor 31 to the tungsten electrode TE. As a result, the current flowing from the tungsten electrode TE to the workpiece W increases when the current polarity is switched, and the fall rate (decrease rate) of the welding current I increases accordingly, so that arc interruption is less likely to occur than when the fall rate of the welding current I is not increased. Furthermore, due to the discharge of capacitor 31, welding current I drops to a value smaller than −10 A, which is −1 times the set value SV, by the amount of discharge of capacitor 31. At this time, the voltage of capacitor 31 drops due to the discharge of capacitor 31. In this manner, during discharge period L, discharge circuit 35 performs a discharge operation to increase the current flowing from tungsten electrode TE to workpiece W by arc discharge, by discharging capacitor 31.

At time t2, 25 μs after time t1, the discharge signal S4 switches from high to low. This causes the discharge circuit 35 to stop discharging, and the welding current I becomes -10 A, which is -1 times the set value SV.

After that, when the polarity switching signal S2 switches from low level to high level at timing t3, the charging signal S3 changes from low level to high level, the charging switching element 343 of the charging circuit 34 turns on, and the capacitor 31 is charged to the charging voltage CV using the AC power of the commercial power source 2. When the voltage of the capacitor 31, i.e., the measured value MV of the voltage sensor 33, reaches the charging voltage CV, the charging switching element 343 turns off and charging ends. After that, when the polarity switching signal S2 switches from high level to low level, the same operation as that from timing t1 described above is repeated again.

7, if the discharge signal S4 is kept at a high level throughout the period when the polarity switching signal S2 is at a low level, i.e., during the period when the polarity of the AC voltage applied between the tungsten electrode TE and the workpiece W is reversed, the discharge operation continues even after timing t2. Therefore, the period during which the welding current I becomes smaller than -10 A due to the discharge operation exceeds 25 μs, and the amount of reduction in the welding current I due to the discharge operation significantly affects the effective value of the welding current I, which may lead to defects during welding such as burn-through of the workpiece W.

In contrast, in this embodiment, the discharge operation is performed for a discharge period L of 25 μs after the polarity of the AC voltage applied between the tungsten electrode TE and the workpiece W is switched from positive to reverse polarity, so the period during which the welding current I becomes smaller than -10 A due to the discharge operation is shorter than when the discharge period L is longer than 25 μs. This reduces the effect that the amount of change in welding current I due to the discharge operation has on the effective value of welding current I, and suppresses problems during welding caused by the discharge operation to prevent arc interruption.

In this way, in this embodiment, the period of the AC voltage applied between the tungsten electrode TE and the workpiece W is set to 600 Hz or more, so the concentration of the arc A can be improved compared to when the period is less than 600 Hz. This makes it easier to perform low-current welding in which the arc A is prone to fluctuating.

In this embodiment, the period of the polarity switching signal S2, i.e., the period of the AC voltage applied between the tungsten electrode TE and the workpiece W, is 1 kHz, but it may also be another period of 600 Hz or more.

In addition, in this embodiment, the discharge period L is set to 2.5% of the period of the AC voltage applied between the tungsten electrode TE and the workpiece W, but other periods of 5% or less may be used. By setting the discharge period L to 5% or less of the period of the AC voltage, the effect of the change in the welding current I due to the discharge operation on the effective value of the welding current I is reduced compared to when the discharge period L is longer than 5%, and defects during welding caused by the discharge operation can be suppressed. In addition, by setting the discharge period L to 3% or less of the period of the AC voltage applied between the tungsten electrode TE and the workpiece W, defects during welding caused by the discharge operation can be suppressed more effectively compared to when the discharge period L is longer than 3%.

In addition, in this embodiment, the set value SV of the welding current I is 10 A, but it may also be other values such as 20 A, 30 A, etc.

The welding device disclosed herein can suppress defects during welding caused by discharge operations, and is useful as a welding device that performs arc welding by applying an AC voltage between an electrode and a workpiece to generate an arc between the electrode and the workpiece.

1 Welding device 27 Second inverter circuit 31 Capacitor 34 Charging circuit 35 Discharging circuit 40 Control device (control unit)
A Arc L Discharge period TE Tungsten electrode W Workpiece

Claims (3)

A welding device that generates an arc by applying an AC voltage between an electrode and a workpiece,
an inverter circuit that switches the polarity of the AC voltage between a positive polarity that makes the workpiece have a higher potential than the electrode and a reverse polarity that makes the workpiece have a lower potential than the electrode;
A capacitor;
a charging circuit for charging the capacitor;
a discharge circuit that performs a discharge operation to increase a current flowing from the electrode to the workpiece by arc discharge by discharging the capacitor;
and a control unit that, when switching the polarity of the AC voltage from the positive polarity to the reverse polarity, causes the discharge circuit to perform the discharge operation continuously for a discharge period that is 5% or less of a cycle of the AC voltage. 2. The welding apparatus according to claim 1,
13. A welding device according to claim 12, wherein the discharge period is equal to or less than 3% of the period of the AC voltage. The welding device according to claim 1 or 2,
A welding device characterized in that the frequency of the AC voltage is 600 Hz or more.

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