JP6444804B2 - Plasma welding power supply - Google Patents

Description

  The present invention relates to a technique for improving the start of a plasma welding power supply device.

In plasma welding, the output power generated by the plasma welding power supply is supplied to the torch and the plasma gas is also supplied to the torch, and these cooperate to generate a plasma arc between the torch and the base material for welding. It is. As such a torch used for plasma welding, a torch having an electrode in the center, a nozzle having a double structure for plasma gas injection around the electrode, and a nozzle for shielding gas injection around the nozzle is known. It has been.

FIG. 3 is a connection diagram of a conventional plasma welding power source apparatus.
In the figure, a main power generation unit that generates a main current is formed by a primary side rectifier circuit DR1, an inverter circuit INV, a main transformer T1, a secondary side rectifier circuit DR2, a DC reactor DCL, and an output current detection circuit ID1. Yes.

The primary side rectifier circuit DR1 shown in FIG. 3 rectifies the commercial AC voltage into a DC voltage and inputs it to the inverter circuit INV. The inverter circuit INV forms a full bridge circuit using a semiconductor switching element such as an IGBT, and converts a DC voltage into a high-frequency AC voltage by a switching operation. The inverter circuit INV is subjected to switching control (PWM control) by the main control circuit SC. The main transformer T1 converts the high-frequency AC voltage into a voltage suitable for plasma arc welding and outputs it. And it converts into a DC voltage by secondary side rectifier circuit DR2 and DC reactor DCL.

  In FIG. 3, a pilot generator for generating a pilot arc current is formed by an auxiliary transformer T2, a secondary side rectifier circuit DR3, a smoothing capacitor C1, a secondary switching element TR1, a diode D1, a reactor L, and a pilot current detection circuit ID2. Has been.

  The main control circuit SC shown in FIG. 3 controls the secondary switching element TR1 of the pilot generation unit based on the value of the pilot current detection signal Id2 detected by the pilot current detection circuit ID2, and the pilot arc having a preset value. Output current.

  In the torch TH having a double nozzle structure for plasma gas injection shown in FIG. 3, the first nozzle b and the second nozzle c are sequentially formed from the electrode a side. The high frequency high voltage applied is applied between the electrode a and the first nozzle b to generate a high frequency high voltage. In this state, when the pilot generator is activated to output a pilot arc current, the pilot arc is generated by the high frequency high voltage and a pilot arc is generated between the electrode a and the second nozzle b. When the main power generation unit is activated and outputs a main current, the pilot arc is transferred to the main arc between the electrode a and the workpiece M. ,

Thus, when performing welding, the pilot arc is ignited as a standby state, and when shifting to actual welding, the main current generated in the main power generation unit is between the electrode a and the base material M. It is supplied and moves to the main arc.
However, since the no-load voltage of the pilot generator is low in the past, the pilot arc may not fire. As a countermeasure, there is a method of improving the arc start performance by applying a DC high voltage instead of a high frequency high voltage as in Patent Document 1, but it requires a high voltage component, leading to an increase in cost. .

JP-A-11-254144

In the conventional plasma welding apparatus, the pilot arc is ignited by generating a high frequency in response to the activation signal Ts being turned on. However, since the no-load voltage of the pilot generator is low, the pilot arc often extinguishes just before the ignition.
The present invention is for solving the above-described problems, and an object of the present invention is to provide a plasma welding power supply device that can improve the startability of a pilot arc.

In order to solve the above-mentioned problem, the invention according to claim 1 is a main power generation unit that generates a main current, an output current detection circuit that detects and outputs the main current, and a pilot that generates a pilot arc current. A generator, a pilot current detection circuit that detects and outputs the pilot arc current, a main control circuit that controls the output of the main power generator based on a value of a first output current , a torch and a workpiece; A high-frequency generation circuit that generates a high-frequency high voltage to generate an arc between
A plasma welding power supply for supplying the pilot arc current to the torch before supplying the main current to the torch;
The pilot generator has a secondary switching element, a reactor and a switch,
The main control circuit conducts the secondary switching element of the pilot generation unit in response to an input of an activation signal, closes the contact of the switch, supplies the pilot arc current to the reactor, and charges the power When the charge of the reactor reaches a predetermined value, the contact of the switch is opened from the closed state, the electric power charged in the reactor is discharged to the torch, and the pilot arc current is supplied to the torch. It is a plasma welding power supply device.

  According to a second aspect of the present invention, the main control circuit opens the contact of the switch from closed to open when a pilot current value detected by the pilot current detection circuit reaches a predetermined current reference value. The plasma welding power source device according to claim 1, wherein the power source is a plasma welding power source.

The invention according to claim 3 is characterized in that the main control circuit opens the switch from closed to open after a predetermined time from when the value of the pilot current becomes the current reference value. 2. The plasma welding power supply device according to 2.

The invention according to claim 4 is characterized in that the main control circuit generates the high-frequency high voltage when the value of the pilot current becomes larger than the current reference value. It is a plasma welding power supply device of description.

The invention according to claim 5 is characterized in that the main control circuit supplies the main current to the torch after a predetermined time after the switch is opened from the closed state. 5. The plasma welding power source device according to claim 4.

In the present invention, when the pilot arc is generated, when the electric power charged in the reactor is discharged, the no-load voltage increases momentarily at the time of the arc generation due to the released energy, thereby improving the arc startability.

It is a block diagram of the plasma welding power supply device of the embodiment of the present invention. It is a wave form diagram explaining operation | movement of embodiment. It is a block diagram of the plasma welding power supply device of a prior art.

The operation of the embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a block diagram of a plasma welding apparatus according to an embodiment of the present invention. In the figure, components having the same reference numerals as those in the block diagram of the prior art plasma welding apparatus shown in FIG. 3 perform the same operations, and thus description thereof will be omitted. Only components having different reference numerals will be described.

The main power generation unit shown in FIG. 1 is a circuit that generates power of a main arc used for welding. In such a main power generation unit, the minus side is connected to the minus side output terminal T1, and the plus side output terminal is connected to the plus side output terminal T2. That is, the main arc power generated by the main power generation unit is output from the output terminals T1 and T2.

  The pilot generation unit is a circuit that generates a pilot arc current that ignites a pilot arc as a standby state when welding is performed. The pilot generation unit is formed of an auxiliary transformer T2, a secondary rectifier circuit DR3, a smoothing capacitor C1, a secondary switching element TR1, a diode D1, a reactor L, a pilot current detection circuit ID2, and a switch CH. Then, the pilot generator performs constant current control in order to output a predetermined current suitable for starting the pilot arc. Further, the negative output terminal of the pilot generation unit is connected to the negative output terminal T1 common to the main power generation unit. On the other hand, the plus output terminal of the pilot generator is connected to the output terminal T3 of the power supply device.

  The main control circuit SC shown in FIG. 1 outputs the secondary switching drive signal Tr1 in response to the input of the start signal Ts, and the first main control signal Sc1 and the second main control signal Sc1 in response to the input of the inverter operation signal P-Wcr. The main control signal Sc2 is output. Then, when the value of the pilot current detection signal Id2 reaches a predetermined current reference value detected by the pilot current detection circuit ID2, the high frequency drive signal Hf is output.

  The pilot control unit is formed by the delay circuit SL, the switch driving circuit CR, and the inverter starting circuit P-WCR shown in FIG. Then, the delay circuit SL outputs a delay signal S1 having a predetermined time Ta according to the inputs of the delay start signal So and the switching element drive signal Tr1. The switch drive circuit CR outputs a switch drive signal Cr and stops outputting the switch drive signal Cr in response to the input of the delay signal Sl. The switch CH closes the switch contact Ch1 while the switch drive signal Cr is being input.

  The torch TH shown in FIG. 1 is provided with an electrode a at the center, a first nozzle b on the outer side, a second nozzle c on the outer side, and a shield cap d on the outermost side. Plasma gas is injected from between the electrode a and the first nozzle b and between the first nozzle b and the second nozzle c, and shield gas is injected from between the second nozzle c and the shield cap d. Is done. A gas supply path and a supply source are not shown. In such a torch TH, the electrode a is connected to the output terminal T1 of the plasma welding power source, the first nozzle b is connected to the output terminal T4, and the second nozzle c is connected to the output terminal T3. The workpiece M to be welded is connected to the output terminal T2 of the power supply device.

  The main control circuit SC shown in FIG. 1 controls operations of the inverter circuit INV, the secondary switching element TR1, and the high frequency generation circuit HF. In addition, the injection timing and injection amount of the plasma gas and the shield gas are controlled, and the overall control of the operation related to plasma arc welding is performed.

FIG. 2 is a waveform diagram for explaining the operation of the embodiment. The waveform in FIG. 2A shows the switch drive signal Cr, the waveform in FIG. 2B shows the activation signal Ts, and FIG. ) Shows the first main control signal Sc1, the waveform in (D) shows the second main control signal Sc2, the waveform in (E) shows the secondary switching drive signal Tr1, The waveform in FIG. (F) shows the pilot current detection signal, the waveform in (G) shows the high frequency drive signal Hf, the waveform in (H) shows the delay signal Sl, and the waveform in (I) of FIG. Indicates the pilot voltage waveform Vci, the waveform in FIG. 10J indicates the inverter start signal P-Wcr, and the waveform in FIG. 10I indicates the main current detection signal Id1.

  Next, the operation of the plasma welding power source apparatus, particularly the operation at the start of the pilot arc will be mainly described with reference to FIGS. Note that the gas injection mode is appropriately performed from time to time, and is omitted in the following description.

When the activation signal Ts shown in FIG. 2B is input to the main control circuit SC at time t = t1, the main control circuit SC outputs the secondary switching drive signal Tr1 shown in FIG. The switch drive circuit CR is driven to output a switch drive signal Cr shown in FIG. When the secondary switching drive signal Tr1 is input to the secondary switching element TR1 shown in FIG. 1, it is turned on, and when the switch drive signal Cr is input to the switch CH, the switching contact Ch1 is closed.

  At time t = t1, when the switching contact Ch1 is closed and the secondary switching element TR1 is turned on, the pilot current is supplied to the reactor L via the switching contact Ch1 and the electric power is charged.

  A current is detected by pilot current detection circuit ID2 shown in FIG. 1, and is output as pilot current detection signal Id2 shown in FIG. The main control circuit SC compares the value of the pilot current detection signal Id2 with a predetermined current reference value Irf and determines that the power of the reactor L is charged when t = t2 when the current reference value Irf is reached. Then, the high frequency drive signal Hf shown in FIG. 2G is output, and high frequency discharge is started between the electrode a of the torch TH and the first nozzle b.

At time t = t2, when the value of the pilot current detection signal Id2 reaches the current reference value Irf, the main control circuit SC outputs a delay start signal So (not shown) to operate the delay circuit SL. Then, a delay signal Sl having a predetermined delay time (Ta) shown in FIG.
Further, when the value of pilot current detection signal Id2 increases and reaches a preset pilot current set value (for example, 10 A) at time t = t3, secondary switching element TR1 is set to maintain this current value. Constant current control is performed by PWM control.
Further, the delay time (Ta) is set to t = t3, which is delayed by one cycle when the secondary switching drive signal Tr1 shown in FIG. 2 (E) first becomes a high level from time t = t2. Further, the secondary switching drive signal Tr1 may be t = t4, for example, during the High level period.

  At time t = t4 when the pilot current is charged to the reactor L via the switching contact Ch1 and the secondary switching drive signal Tr1 is at the high level, the delay signal Sl shown in FIG. 2 (H) is set to the low level. To do. At this time, the switch drive circuit CR sets the switch drive signal Cr shown in FIG. 2A to the Low level in response to the delay signal S1 at the Low level, and opens the switch contact Ch1 of the switch CH from the closed state to the open state.

  At time t = t4 when high frequency discharge is maintained between the electrode a of the torch TH and the first nozzle b, when the switching contact Ch1 is opened from the closed state, the electric power charged in the reactor L is output from the output terminal T3. It is supplied to the second nozzle c of the torch TH. At this time, when the electric power charged in the reactor L is discharged in a state where a high-frequency discharge is generated between the electrode a and the first nozzle b, the gap between the electrode a and the second nozzle c is as shown in FIG. I) The high pilot voltage Vci shown is applied and the pilot arc is easily ignited.

  After the switch drive signal Cr becomes low level at time t = t4, the inverter control circuit P-WCR determines that the value of the pilot current detection signal Id2 and the pilot current set value (for example, 10A) And the inverter start signal P-Wcr is output at time t = t5 shown in FIG. 2 (J) where the pilot current value becomes equal to the pilot current set value and is stably controlled. The main control circuit SC outputs the first main control signal Sc1 and the second main control signal Sc2 when the inverter operation signal P-Wcr becomes High level, and power is supplied to the output terminal T2 and the base material M of the power supply device. The main arc is ignited between the electrode a and the base material M based on the pilot arc.

When the inverter operating signal P-Wcr shown in FIG. 2 (J) becomes High level during high frequency discharge, the high frequency driving signal Hf shown in FIG. 2 (G) is set to Low level at time t = t5, and the electrode of the torch TH The high frequency discharge between a and the first nozzle b is stopped. Further, at time t = t6 when the value of the first current detection signal Id1 shown in FIG. 2 (K) becomes larger than the predetermined welding current reference value Wcr, the high-frequency drive signal Hf shown in FIG. Thus, the high frequency discharge between the electrode a of the torch TH and the first nozzle b may be stopped.

The characteristic effects of this embodiment will be described.
(1) The pilot arc current is supplied to the second nozzle c, and at the same time, the electric power charged in the reactor L is supplied from the output terminal T3 to the second nozzle c of the torch TH. The high voltage generated when this electric power is supplied is superimposed on the pilot arc voltage, and the increased pilot voltage Vci shown in FIG. 2 (I) is applied between the electrode a and the second nozzle c, and the pilot arc is applied. Can be easily ignited, leading to improved starting.
Therefore, repeated restarts can be suppressed, leading to quality improvements and work efficiency.
(2) Since the main power generation unit that generates the main arc power and the pilot generation unit that generates the pilot arc power are configured as separate power generation units, the circuit configuration and the control can be performed individually. .

In addition, you may change the said embodiment as follows.
As the on / off operation, a switch is used as the switch means that can be switched, but the configuration of the switch means is not limited thereto. For example, a semiconductor switch element may be used.

C1 Smoothing capacitor CR Switch drive circuit Cr Switch drive signal CH Switch Ch1 Switch contact DR1 Primary rectifier circuit DR2 Secondary rectifier circuit DR3 Secondary rectifier circuit D1 Diode DCL DC reactor HF High frequency generator circuit Hf High frequency drive signal ID1 Output current detection Circuit Id1 Output current detection signal ID2 Pilot current detection circuit Id2 Pilot current detection signal INV Inverter circuit L Reactor M Workpiece SC Main control circuit Sc1 First main control signal Sc2 Second main control signal SL Delay circuit Sl Delay signal T1 Main transformer T2 Auxiliary transformer TR1 Secondary switching element Tr1 Secondary switching drive signal Ts Start signal TH Torch P-WCR Inverter start circuit P-Wcr Inverter operation signal

Claims (5)

A main power generation unit that generates a main current, an output current detection circuit that detects and outputs the main current, a pilot generation unit that generates a pilot arc current, and a pilot current detection that detects and outputs the pilot arc current A circuit, a main control circuit for controlling the output of the main power generation unit based on the value of the first output current , and a high frequency generation for generating a high frequency high voltage to generate an arc between the torch and the workpiece A circuit,
A plasma welding power supply for supplying the pilot arc current to the torch before supplying the main current to the torch;
The pilot generator has a secondary switching element, a reactor and a switch,
The main control circuit conducts the secondary switching element of the pilot generation unit in response to an input of an activation signal, closes the contact of the switch, supplies the pilot arc current to the reactor, and charges the power When the charge of the reactor reaches a predetermined value, the contact of the switch is opened from the closed state, the electric power charged in the reactor is discharged to the torch, and the pilot arc current is supplied to the torch. Plasma welding power supply. 2. The main control circuit according to claim 1, wherein when the value of the pilot current detected by the pilot current detection circuit reaches a predetermined current reference value, the contact of the switch is opened from closed. Plasma welding power supply.   3. The plasma welding power source apparatus according to claim 2, wherein the main control circuit opens the switch from a closed state after a predetermined time after the pilot current value becomes the current reference value. . 4. The plasma welding power source device according to claim 2, wherein the main control circuit generates the high-frequency high voltage when a value of the pilot current becomes larger than the current reference value. 5.   5. The main control circuit according to claim 1, wherein the main current is supplied to the torch after a predetermined time from when the switch is opened from the closed state. Plasma welding power supply.

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