Welding device

Abstract

In a welding device that generates an arc by applying an alternating voltage between a tungsten electrode (TE) and a workpiece (W), a capacitor (31), a charging circuit (34) that charges the capacitor (31), a discharging circuit (35) that performs a discharging operation that increases a current flowing from the tungsten electrode (TE) to the workpiece (W) by arc discharge by discharging the capacitor (31), and a control device (40) that causes the discharging circuit (35) to continuously perform the discharging operation during a discharging period of 5% or less of a cycle of the alternating voltage when switching a polarity of the alternating voltage from a positive polarity to a negative polarity are provided.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a welding device that generates an arc by applying an alternating-current voltage between an electrode and a workpiece. BACKGROUND

[0002] The welding device disclosed in Patent Literature 1 has an inverter circuit that switches a polarity of an alternating-current voltage to a positive polarity in which a workpiece is set to a higher potential than an electrode, and a reverse polarity in which the workpiece is set to a lower potential than the electrode; a capacitor; a charging circuit that charges the capacitor; a discharging circuit that performs a discharging operation in which a current flowing from the electrode to the workpiece by arc discharge is increased by discharging of the capacitor; and a control section that causes the discharging circuit to perform the discharging operation when the polarity of the alternating-current voltage is switched from the positive polarity to the reverse polarity. In this welding device, when the polarity of the alternating-current voltage is switched from the positive polarity to the reverse polarity, the current flowing from the electrode to the workpiece by arc discharge is increased by discharging of the capacitor, and thus arc interruption is less likely to occur. In addition, the frequency of the alternating-current voltage is set to 500 Hz, and the discharging period in which the control section causes the discharging circuit to perform the discharging operation is set to 300 μsec from when the polarity of the alternating-current voltage is switched from the positive polarity to the reverse polarity.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2019-89093 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] However, in Patent Literature 1, the period in which the discharging circuit performs the discharging operation accounts for 15% of the period of the alternating-current voltage, and thus the amount of change in the welding current based on the discharging operation is large, which affects the effective value of the welding current, and can cause a poor situation at the time of welding. This problem is particularly significant in the case of welding with a small current. Specifically, in a low current region, the effective value of the welding current rises, and in the case of a workpiece such as a thin plate, a phenomenon in which the workpiece is burned through, or the like, can occur.

[0008] The present disclosure is made in view of this point, and aims to suppress a poor situation at the time of welding caused by a discharging operation.

[0009] MEANS FOR SOLVING THE PROBLEMS

[0010] In one embodiment of the present disclosure, a welding device generates an arc by applying an alternating-current voltage between an electrode and a workpiece, the welding device characterized by comprising: an inverter circuit that switches a polarity of the alternating-current voltage to a positive polarity in which the workpiece is set to a higher potential than the electrode, and a reverse polarity in which the workpiece is set to a lower potential than the electrode; a capacitor; a charging circuit that charges the capacitor; a discharge circuit that performs a discharge operation in which a current flowing from the electrode to the workpiece by arc discharge is increased by discharging the capacitor; and a control unit that causes the discharge circuit to continuously perform the discharge operation during a discharge period of 5% or less of a cycle of the alternating-current voltage when the polarity of the alternating-current voltage is switched from the positive polarity to the reverse polarity.

[0011] By this, compared to a case in which the discharge period is set to longer than 5% of a cycle of the alternating-current voltage, the influence of a variation amount of a welding current based on the discharge operation on an effective value of the welding current can be reduced, and thus a poor condition during welding due to the discharge operation can be suppressed.

[0012] -Effects of Invention-

[0013] By the present disclosure, a poor condition during welding due to the discharge operation can be suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a diagram showing a schematic configuration of a welding device according to an embodiment of the present disclosure.

[0015] Figure 2 is a circuit diagram of a welding power source.

[0016] Figure 3 is a circuit diagram of a second inverter circuit.

[0017] Figure 4 is a circuit diagram of a charging circuit.

[0018] Figure 5 is a circuit diagram of a discharge circuit.

[0019] Figure 6 is a timing chart showing a polarity switching signal, a welding current, a voltage of a capacitor, a charging signal, and a discharge signal.

[0020] Figure 7 is a diagram equivalent to Figure 6 in a case in which the discharge operation is continuously performed during the reverse polarity period. DETAILED DESCRIPTION

[0021] Hereinafter, an embodiment of the present disclosure will be described based on the drawings.

[0022] Figure 1A welding device 1 according to an embodiment of the present disclosure will be described. The welding device 1 is an alternating current TIG welding device in which a welding torch 10 is a non-consumable electrode type welding torch.

[0023] The welding torch 10 has a nozzle 11 that ejects shielding gas SG supplied from an unillustrated gas supply device. On the inner side of the nozzle 11, a substantially cylindrical collet 12 is disposed along the ejection direction of the nozzle 11. On the inner side of the collet 12, a rod-shaped tungsten electrode TE is fixed.

[0024] The welding power source 20 generates an arc A by applying an alternating current voltage between the tungsten electrode TE of the welding torch 10 and a workpiece W.

[0025] An operator generates the arc A between the tungsten electrode TE and the workpiece W using the welding device 1, thereby forming a molten pool P in the workpiece W, and can form a weld by inserting an electrode rod R into the molten pool P.

[0026] In detail, as shown in Figure 2 The welding power source 20 includes a first rectifier-smoothing circuit 21, a first inverter circuit 22, a first transformer 23, a second rectifier-smoothing circuit 24, first and second reactors 25 and 26, a second inverter circuit 27, an arc-restruck circuit 30, and a control device 40.

[0027] The first rectifier-smoothing circuit 21 converts input alternating current power input from a commercial power source 2 into direct current power and outputs the direct current power.

[0028] The first inverter circuit 22 is, for example, a single-phase full-bridge type PWM control inverter that includes four switching elements (not shown). The first inverter circuit 22 converts the direct current power output from the first rectifier-smoothing circuit 21 into alternating current power and outputs the alternating current power by causing the four switching elements to switch in accordance with a switching signal S1 output from the control device 40. Here, the output voltage of the first inverter circuit 22 is set to a first alternating current voltage. Alternatively, other types of inverter circuits, such as a half-bridge type inverter, can be used as the first inverter circuit 22.

[0029] The first transformer 23 changes the first alternating current voltage output from the first inverter circuit 22 into a second alternating current voltage and outputs the second alternating current voltage. The first transformer 23 includes a first primary coil 23a and a first secondary coil 23b. The first primary coil 23a is supplied with the first alternating current voltage output from the first inverter circuit 22. The voltage of the first secondary coil 23b is the second alternating current voltage.

[0030] The second rectifying and smoothing circuit 24 converts the second AC voltage outputted from the first transformer 23 into a first DC voltage and outputs the first DC voltage from the positive output terminal 24a and the negative output terminal 24b. The second rectifying and smoothing circuit 24 is a diode bridge circuit including four diodes 24c.

[0031] like Figure 3 As shown, the second inverter circuit 27 is a single-phase half-bridge inverter circuit. The second inverter circuit 27 includes first and second input terminals 271 and 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 and 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 a signal that inverts 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 rectifier-smoothing circuit 24 via the first inductor 25. The second input terminal 272 of the second inverter circuit 27 is connected to the negative output terminal 24b of the second rectifier-smoothing circuit 24 via the second inductor 26. The output terminal 275 of the second inverter circuit 27 is connected to the workpiece W.

[0032] Therefore, when the upper arm switching element 273 is turned on and the lower arm switching element 274 is turned off, the second inverter circuit 27 sets the workpiece W to a higher potential than the tungsten electrode TE. On the other hand, when the upper arm switching element 273 is turned off and the lower arm switching element 274 is turned on, the second inverter circuit 27 sets the workpiece W to a lower potential than the tungsten electrode TE. When a pulse signal that switches between high and low levels 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 to a higher potential than the tungsten electrode TE and a reverse polarity that sets the workpiece W to a lower potential than the tungsten electrode TE.

[0033] The restriking circuit 30 includes a capacitor 31 , a first diode 32 , a voltage sensor 33 , a charging circuit 34 , and a discharging circuit 35 .

[0034] One electrode of the capacitor 31 is connected to a midway portion of the first secondary coil 23 b of the first transformer 23 via the first diode 32 .

[0035] 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 midway portion of the first secondary coil 23 b of the first transformer 23 .

[0036] The voltage sensor 33 measures the voltage of the capacitor 31 and outputs a measured value MV.

[0037] As shown in FIG. 3, the charging circuit 34 has a 3rd rectifier smoothing circuit 341, a 2nd transformer 342, a charging switch element 343, a drive circuit 344, 2nd and 3rd diodes 345, 346, and a 3rd reactor 347. Figure 4

[0038] The 3rd rectifier smoothing circuit 341 converts an input AC voltage input from the commercial power source 2 into a DC voltage and outputs it.

[0039] The 2nd transformer 342 transforms a voltage obtained by subtracting a voltage between a source and a drain of the charging switch element 343 from a DC voltage output by the 3rd rectifier smoothing circuit 341 into a charging DC voltage and outputs it. The 2nd transformer 342 has a 2nd primary coil 342a and a 2nd secondary coil 342b. The 2nd primary coil 342a is applied with a voltage obtained by subtracting a voltage between a source and a drain of the charging switch element 343 from a DC voltage output by the 3rd rectifier smoothing circuit 341. A voltage of the 2nd secondary coil 342b is a charging DC voltage.

[0040] The charging switch element 343 turns on and off connection of the 3rd rectifier smoothing circuit 341 and the 2nd primary coil 342a of the 2nd transformer 342. The charging switch element 343 includes a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

[0041] The drive circuit 344 turns on the charging switch element 343 when a condition that a measured value MV of the voltage sensor 33 is less than a prescribed charging voltage CV and a charging signal S3 output from the control device 40 is a high level is satisfied, and on the other hand, turns off the charging switch element 343 when the condition is not satisfied.

[0042] A cathode of the 2nd diode 345 and a cathode of the 3rd diode 346 are connected to each other.

[0043] At one end of the 2nd secondary coil 342b, an anode of the 2nd diode 345 is connected, and at the other end of the 2nd secondary coil 342b, an anode of the 3rd diode 346 is connected. A connection point of the 2nd secondary coil 342b and the 3rd diode 346 is connected to the 2nd inverter circuit 27 side (the workpiece W side) of the capacitor 31.

[0044] One end of the 3rd reactor 347 is connected to a connection point of the 2nd diode 345 and the 3rd diode 346. The other end of the 3rd reactor 347 is connected to cathodes of the capacitor 31 and the 1st diode 32.

[0045] ​Therefore, the charging circuit 34 configured as described above charges the capacitor 31 using the alternating-current power of the commercial power supply 2 when the condition that the measured value MV of the voltage sensor 33 is less than the prescribed charging voltage CV and the charging signal S3 is at the high level is satisfied.

[0046] As shown in FIG. 1, the discharge circuit 35 has a resistor 351 and a discharge switching element 352. Figure 5

[0047] One end of the resistor 351 is connected to the tungsten electrode TE. The other end of the resistor 351 is connected to one end of the discharge switching element 352. The other end of the discharge switching element 352 is connected to the electrode of the capacitor 31 on the side of the first diode 32.

[0048] The discharge switching element 352 is turned on when the discharge signal S4 output from the control device 40 is at the high level, and is turned off when the discharge signal S4 is at the low level.

[0049] Therefore, the discharge circuit 35 configured as described above performs the discharge operation of increasing the current flowing from the tungsten electrode TE to the workpiece W by the arc discharge through the capacitor 31 by electrically connecting the tungsten electrode TE to the capacitor 31 when the discharge signal S4 is at the high level.

[0050] The control device 40 includes a current control section 41, a polarity switching control section 42, a charging control section 43, and a discharge control section 44.

[0051] The current control section 41 outputs a switching signal S1 to the first inverter circuit 22 so that the effective value of the welding current I is a set value SV by PWM control based on the measured value of the welding current I input from a not-shown current sensor. In the present embodiment, the set value SV of the welding current I is set to 10 A. The set value SV of the welding current I can be changed by the input of a user to a not-shown input unit.

[0052] The polarity switching control section 42 outputs a polarity switching signal S2 that switches the polarity of the alternating-current voltage applied between the electrode TE and the workpiece W. The polarity switching signal S2 is a pulse signal of 1 kHz. Therefore, the frequency of the alternating-current voltage applied between the tungsten electrode TE and the workpiece W is 1 kHz.

[0053] The charging control section 43 outputs a charging signal S3. The charging signal S3 is at the high level when the polarity switching signal S2 is at the high level, and is at the low level when the polarity switching signal S2 is at the low level.

[0054] ​The discharge control unit 44 outputs a discharge signal S4. The discharge signal S4 is a signal that remains high for a discharge period L, which lasts 25 μs from the time the polarity switching signal S2 switches from high to low, and remains low for the remaining period. 25 μs is 2.5% of the cycle 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 to negative polarity, the discharge control unit 44 causes the discharge circuit 35 to continue the discharge operation for a discharge period L, which is 2.5% of the cycle of the AC voltage.

[0055] In the welding device 1 constructed as described above, Figure 6 As shown, at time t1, the voltage across capacitor 31 is at charging voltage CV. If polarity switching signal S2 switches from high to low at time t1, charging signal S3 changes from high to low. Furthermore, the polarity of the AC voltage applied between the tungsten electrode TE and the workpiece W switches from positive to negative polarity, causing discharge signal S4 to change from low to high. Discharge signal S4 remains high during the 25μs discharge period L from time t1. Therefore, during discharge period L, discharge switching element 352 is turned on, electrically connecting the tungsten electrode TE and capacitor 31, and current flows from capacitor 31 to tungsten electrode TE. Consequently, the current flowing from tungsten electrode TE to the workpiece W increases when the current polarity switches, correspondingly increasing the rate of decrease (decrease) of welding current I. This makes arc interruption less likely to occur compared to a case where the rate of decrease of welding current I is not increased. Furthermore, due to the discharge of the capacitor 31, the welding current I decreases to a value less than -10 A, which is -1 times the set value SV, in accordance with the discharge amount of the capacitor 31. At this time, the voltage of the capacitor 31 decreases due to the discharge of the capacitor 31. Thus, during the discharge period L, the discharge circuit 35 performs a discharge operation in which the current flowing from the tungsten electrode TE to the workpiece W due to arc discharge is increased by the discharge of the capacitor 31.

[0056] At timing t2, 25 μs after timing t1, discharge signal S4 switches from high level to low level. As a result, discharge circuit 35 ends its discharge operation, and welding current I becomes -10 A, which is -1 times the set value SV.

[0057] Then, at timing t3, when polarity switching signal S2 switches from low to high, charging signal S3 changes from low to high, turning charging switch element 343 of charging circuit 34 on. Using the AC power from commercial power supply 2, capacitor 31 is charged to charging voltage CV. When the voltage of capacitor 31, i.e., the value MV measured by voltage sensor 33, reaches charging voltage CV, charging switch element 343 turns off, completing charging. Subsequently, when polarity switching signal S2 switches from high to low, the same operations as those from timing t1 are repeated.

[0058] like Figure 7 As shown, while the polarity switching signal S2 is set to a low level, that is, while the polarity of the AC voltage applied between the tungsten electrode TE and the workpiece W is reversed, if the discharge signal S4 is kept at a high level, the discharge operation continues even after timing t2. Therefore, there is a concern that the period during which the welding current I falls below -10A due to the discharge operation exceeds 25 μs, and the reduction in welding current I due to the discharge operation will significantly affect the effective value of the welding current I, leading to welding defects such as burn-through of the workpiece W.

[0059] In contrast, in this embodiment, the discharge operation is performed during the 25 μs discharge period L after the polarity of the AC voltage applied between the tungsten electrode TE and the workpiece W is switched from positive to reverse polarity. Therefore, compared to a case where the discharge period L is longer than 25 μs, the period during which the welding current I falls below -10 A due to the discharge operation is shortened. Therefore, the effect of the change in welding current I due to the discharge operation on the effective value of the welding current I can be reduced, and welding defects caused by the discharge operation to prevent arc interruption can be suppressed.

[0060] Thus, in this embodiment, since the cycle of the AC voltage applied between the tungsten electrode TE and the workpiece W is set to 600 Hz or more, the arc A can be more concentrated than when the cycle is less than 600 Hz. Therefore, low-current welding in which the arc A tends to fluctuate can be facilitated.

[0061] In the present embodiment, the period of the polarity switching signal S2 , that is, the period of the AC voltage applied between the tungsten electrode TE and the workpiece W is set to 1 kHz, but may be set to another period of 600 Hz or higher.

[0062] Further, in the present embodiment, the discharge period L is set to 2.5% of the period of the alternating voltage applied between the tungsten electrode TE and the workpiece W, but can be set to other periods of 5% or less. By setting the discharge period L to 5% or less of the period of the alternating voltage, compared to a case where it is longer than 5%, the influence of the amount of change in the welding current I based on the discharge operation on the effective value of the welding current I can be reduced, and the adverse situation during welding caused by the discharge operation can be suppressed. Further, by setting the discharge period L to 3% or less of the period of the alternating voltage applied between the tungsten electrode TE and the workpiece W, compared to a case where it is longer than 3%, the adverse situation during welding caused by the discharge operation can be further effectively suppressed.

[0063] Further, in the present embodiment, the set value SV of the welding current I is set to 10 A, but can be set to 20 A, 30 A, or other values.

[0064] Industrial Applicability

[0065] The welding device of the present disclosure can suppress an adverse situation during welding caused by a discharge operation, and is useful as a welding device that generates an arc between an electrode and a workpiece by applying an alternating voltage between the electrode and the workpiece and performs arc welding.

[0066] -Explanation of Symbols-

[0067] 1 Welding device

[0068] 27 Second inverter circuit

[0069] 31 Capacitor

[0070] 34 Charging circuit

[0071] 35 Discharge circuit

[0072] 40 Control device (control section)

[0073] A Arc

[0074] L Discharge period

[0075] TE Tungsten electrode

[0076] W Workpiece

Claims

1. A welding device that generates an arc by applying an alternating voltage between an electrode and a workpiece, the welding device comprising: an inverter circuit that switches a polarity of the alternating voltage to a positive polarity in which the workpiece is set to a higher potential than the electrode, and a reverse polarity in which the workpiece is set to a lower potential than the electrode; a capacitor; a charging circuit that charges the capacitor; a discharging circuit that performs a discharging operation in which a current flowing from the electrode to the workpiece through an arc discharge is increased by discharging of the capacitor; and a control unit that causes the discharging circuit to continuously perform the discharging operation during a discharging period of 5% or less of a cycle of the alternating voltage when the polarity of the alternating voltage is switched from the positive polarity to the reverse polarity.

2. The welding device according to claim 1, wherein the discharging period is 3% or less of the cycle of the alternating voltage.

3. The welding device according to claim 1 or 2, wherein a frequency of the alternating voltage is 600 Hz or more. ​ ​ ​ ​ ​ ​ ​ ​

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