JP2515273B2 - Short-circuit transfer arc welding method and apparatus - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of short-circuit transfer arc welding, and in particular, droplet transfer is reliably performed in a short time by controlling an output current to a predetermined waveform during a short-circuit section. The present invention relates to a method and an apparatus for generating a more stable arc and continuously performing an efficient short-circuit transfer arc.

2. Description of the Related Art The short-circuit transfer arc welding method is one in which a consumable electrode is fed at a constant speed, and a short circuit to the base material of the consumable electrode and separation are alternately performed to generate an arc for welding.

The problem in doing this is that it is strongly desired to suppress the generation of spatter (especially difficult when a short circuit occurs and when an arc occurs) and to constantly generate an arc during welding in a stable manner.

Therefore, conventionally, in order to meet such a request, the delay characteristic of the DC reactor is used to control the short-circuit current.However, in such a method, a reactor having a time constant required every time the welding conditions change is used. In addition to being difficult to select, there is a drawback that the time constant required when the current changes is also very large. Therefore, the required inductance reaches several hundred μH, making it difficult to design and manufacture. As a result, the manufacturing cost becomes high. In addition, the current at the time of short-circuit becomes a large value of several hundred amperes, so a large inductance is required, and a very large reactor is required. For this reason, conventionally, a large inductance is obtained by using the iron core, but in such a case, the problem of the saturation of the iron core cannot be ignored and there are various problems.

Therefore, in recent years, in order to solve the above-mentioned problems that the DC reactor has, a phase delay element is inserted in the output feedback circuit, and a phase delay is substantially given to the output change with respect to the change of the load. Various proposals have been made to generate the effect of a DC reactor.

For example, the one proposed in Japanese Patent Application Laid-Open No. 58-112659 is an improved representative example.

That is, this one uses a switching control method by a switching element for the output control of the DC power supply, and is provided with a circuit for giving a phase delay to the output control circuit with respect to the change of the load, and this phase delay amount when the output increases. It is characterized in that it has a circuit configuration that can be adjusted independently for each of the power increase and decrease times, without using a large DC reactor as in the past. The advantage is that the welding stability can be dramatically improved, and the bead shape can be controlled.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention is a further improvement of the arc welding method using a phase delay element, which is more efficient than the conventional method and has good arc stability and reliability. It is a problem to be solved to provide a high short-circuit transfer arc welding method, and in particular, by controlling the output current at the time of short circuit, which has not been recognized in the conventional method, to a specific waveform, It solves the problems that you have made.

Means for Solving the Problems In order to solve the above problems, the inventors of the present invention have made various investigations when carrying out the short-circuit transfer arc welding method, and as a result, claim the waveform of the output current at the time of short-circuit. By setting as described in the range, the droplet transfer can be performed reliably in an extremely short time, and at the same time, the current value at the time of arc generation is suppressed to promote heat generation for droplet transfer and stabilize the arc. The present invention has been made based on the knowledge that efficient arc welding can be performed by continuously continuously generating electric arcs.

That is, the method provided by the method of the present invention, while feeding the consumable electrode at a constant speed, in a short-circuit transfer arc welding method for alternately generating a short circuit and an arc, constant voltage control by a closed loop at the time of arc generation, In addition, when the current is short-circuited, the current control is switched to the closed loop, and the waveform of the output current I ₂ supplied to the load during the short-circuiting period is I ₂ = Ia + Is + It in the normal state, where Ia is the arc current immediately before the short circuit and Is is The set rising amount, It is a change amount that increases substantially linearly with the passage of time), and during the short-circuit section, until the arc is generated, the above It is a preset reference value. until it reaches a value Io, while controlling the output current I _2, when said it is not occurring arc even when it reaches the reference value Io, the current I ₂ out at that time It is large, and for switching control to output current Ib of a level sufficient to generate an arc.

Further, the apparatus provided for carrying out the method of the present invention is a combination of a constant voltage control circuit and a current control circuit for controlling the output voltage and current supplied to the load by driving the switching control circuit. In addition, an arc welding device in which these circuits are alternately switched and operated according to arc generation and short circuit, and in particular, the constant voltage control circuit is a voltage detector for detecting a load voltage at the time of arc generation. Is driven by receiving an arc detection signal from the voltage detector, receives a signal output from the voltage detector, and outputs a control signal according to a preset control value to the switching control circuit. The current control circuit increases the welding output current I ₂ by I ₂ = Ia + Is + It (Ia is the arc current immediately before the short circuit, Is is the preset rising amount, and It is a linear increase over time. Waveform current control circuit for controlling the waveform current specified by
A current setter for controlling the output current Ib larger than the above I ₂ and at a level sufficient to generate an arc, and
It has a comparison circuit that compares It with a preset reference value Io, and the output current is increased until It increases to the reference value Io.
While the signal generated by the waveform current control circuit to output I ₂ is output to the switching control circuit as a drive signal, when the It reaches the reference value Io, when no arc occurs, the output In order to switch the current to Ib, the present invention is characterized by comprising a current switching circuit for outputting the signal generated by the current setting device to the switching control circuit as a drive signal. The current control circuit is configured to include a short-circuit current upper limit setting unit that limits the upper limit value of the output current I ₂ supplied to the load at the time of short circuit to a preset value Imax.

According to the method and effect of the present invention, constant voltage control is performed when an arc occurs, and current control is automatically switched when a short circuit occurs, so that arc welding is continuously performed by shifting to a short circuit.
Then, when the output current I ₂ supplied to the load is normal during the short circuit section, I ₂ = Ia + Is + It [where Ia is the arc current immediately before the short circuit, Is is the preset rise amount, It is
Is a change that increases linearly with the passage of time.]
When a short circuit is detected by the voltage detector, the current is the sum of the arc current Ia immediately before the short circuit and the preset preset rise I _s. Will be supplied to the load,
Further, as the short-circuit progresses, this current is supplemented with a variation 1t that increases linearly with time. As a result, the load is rapidly heated by a large short-circuit current at the time when the contact resistance is large to quickly become droplets, and further, when the heating temperature of the droplets increases and the contact resistance of the load increases,
Since this short-circuit current is supplemented by It, that is, a change that increases with the passage of time, the consumable electrode becomes a small droplet in an extremely short time and is reliably divided, and at the same time the arc Since the current value at the time of generation is suppressed and heat generation for droplet transfer is promoted, extremely fine beads can be obtained, and efficient and continuous welding work becomes possible.

Further, even when the output current supplied to the load in the short-circuit section is energized to the load for a predetermined time, for example, under normal conditions for several hundreds of microseconds to several milliseconds, the following When no arc is generated, a sufficient level of current Ib, which is larger than the current I ₂ level determined by the current setter at that time, is supplied to the load. Then, the welding work can be continuously performed.

As a result, the output current I ₂
However, I ₂ = Ia + Is + It [where Ia is the arc current immediately before the short circuit, Is is the preset rise amount, and It is the change amount that increases substantially linearly with the passage of time] The output current to the load is larger than the level I ₂ at that time in the abnormal condition that the arc that should be generated next does not occur even if the output current is supplied to the load for a predetermined time during the above control. By switching to the level Ib and forcibly generating the arc, it is possible to continuously perform reliable short-circuit transfer arc welding continuously.

Furthermore, when the short-circuit current upper limit setting circuit is provided in the current control circuit, the output current supplied to the load is constantly monitored, so it is possible to prevent an infinite increase during a short-circuit and to prevent spatter from occurring. There is also an advantage that the arc welding can be continuously performed.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the method of the present invention will be described in detail with reference to the accompanying drawings together with the configuration of the apparatus.

FIG. 1 is a block diagram showing the configuration of the device of the present invention.

As shown in the drawing, the device of the present invention is configured by combining a constant voltage control circuit for driving the switching control circuit 10 and performing closed loop control of the output voltage and current supplied to the load, and a current control circuit. The constant voltage control is performed when an arc occurs, and the current control is performed when a short circuit occurs.

In the figure, 1 is a consumable electrode (welding wire) which is fed at a predetermined speed by a control system (not shown), 2 is a base material which is a member to be welded, 3 is a welding arc generated when an arc occurs, and 4 is current detection. , 5 is a voltage detector, 6 is a voltage control circuit driven in the constant voltage control mode, 7 is a current control circuit driven in the current control mode, 8 is a smoothing circuit, 9 is a rectifier circuit, 10 is a load. Switching control circuit provided to supply necessary voltage and current, 11 is the voltage detector 5
It is a switching means that alternately switches the constant voltage control and the current control according to the arc detection signal and the short circuit detection signal.

Here, the voltage control circuit 6 is driven when the voltage detector 5 detects the generation of an arc, and the switching control circuit 10 is closed-loop controlled in order to stably maintain the generated arc 3 and heat and melt the consumable electrode 1. Then, during the arc generation section (T2 to T1), a constant output voltage V as shown in FIG. 3 (a) is stably supplied to the load.

The current control circuit 7 is driven when the voltage detector 5 detects a short circuit, and supplies the output current I ₂ as shown in FIG. 3 (b) to the load under normal conditions. Is continuously supplied to the load for a predetermined time t ₀ (in the embodiment, the time until the output It of the integrating circuit, which increases with the passage of time, reaches a predetermined reference value Io is set to), in the case where the arc should have no generation of an electric current supplied to the load as indicated by I _b in FIG. 3 (c), forcibly generate arc is switched to the large level Ib than the level I ₂ at that time Is configured to.

That is, the current supplied to the load during the short-circuit section (T1 to T2) is normally expressed as I ₂ , that is, Ia + Is + It as shown in FIG. sometimes I _'2, exhibits a waveform as that is shown in FIG. 3 (c).

FIG. 2 is a more detailed block diagram of the block diagram of FIG. 1, in which the switching control circuit 10 has a configuration in which an output adjusting element 101 embodied by a power transistor or the like is driven by a driver 102. In the driver 102, the pulse width of the drive pulse can be adjusted by the pulse width control circuit 103.

Further, as the switching means 11, a switching circuit 11 provided at a subsequent stage of the pulse width control circuit 103 is adopted, and this switching circuit 11 determines a control mode when it receives an arc detection signal from the voltage detector 5 described above. When the voltage control is selected and the short circuit detection signal is further received, the control mode is switched from the constant voltage control to the current control.

In the subsequent stage of the switching circuit 11, the voltage control circuit 6
And the current control circuit 7 are connected to each other, and the voltage control circuit 6 is configured to include an error amplifier 61 and a voltage controller 62 in the embodiment. The error amplifier 61 outputs the output from the voltage detector 5. The signal is compared with the output signal from the voltage setting device 62, and the error output of both is sent to the pulse width control circuit 103 via the switching circuit 11.

Here, the voltage setter 62 regulates the control value in the constant voltage control mode, and when the constant voltage control mode is executed, a signal corresponding to the control value is sent to the output adjusting element 101 to apply a constant voltage to the load. Supply feedback control is performed.

On the other hand, the current control circuit 7 is composed of an integrating circuit 77 that detects a short circuit and starts integration, a sample hold circuit 78, a rising amount setting device 79, and an adding circuit 74, and outputs a signal for controlling the output current to I2. Generate the waveform control circuit and output current
72 with a current setter to generate a signal to be Ib
It is configured by combining with the current switching circuit configured by the switching circuit 70.
70 and error amplifier 71, current setting device 72 and comparator 73, addition circuit 74, I / V converter 75, time setting device 76, integrating circuit 77, sample hold circuit 78, rising amount setting device 79 are combined. The switching circuit 70 enables selective switching between the adder circuit 74 and the current setter 72 by the inverted output signal of the comparator 73, and when the inverted output signal is output from the comparator 73, the adding circuit 74 Is connected to the current setting device 72.

Here, the error amplifier 71 compares the output from the I / V converter 75 with the output from the adder circuit 74 output via the switching circuit 70 as a reference, and amplifies both output errors. The error output is sent to the pulse width control circuit 103 via the switching circuit 11, and FIG.
Current control is performed during the short-circuit section (T1 to T2) shown in.
That is, in the normal state during the short circuit section, the output current I ₂ having the peculiar waveform defined by the addition output from the addition circuit 74 and shown in FIG. 3B is supplied to the load.

On the other hand, the comparator 73 compares the output of the integrator circuit 77 and the output of the time setter 76, and the short circuit time continues for a certain period of time.
When it exceeds the limit, an inverted output signal is output and the switching circuit
70 is operated, the output from the adder circuit 74 is cut off, and the output from the current setting device 72 is output to the error amplifier 71. In other words, in this comparator 73, the output of the integration circuit 77
By comparing the output of 76 as a reference, the conduction time t ₀ of the output current supplied to the load at the time of a short circuit is determined, and when the output of the integrating circuit 77 exceeds the output of the time setter 76, a predetermined value is determined. It is determined that the energization time t ₀ has elapsed, and the inverted output signal is sent to the switching circuit 70 to supply the large level current I _b defined by the current setting device 72 to the load.

Figure 3 (c) is 'shows a _second waveform, initially I' the current I supplied to the load in this case the rise in _s, t ₀ hour current of this level continues to load It can be seen that the current level increases rapidly as shown by _Ib .

On the other hand, the sample hold circuit 78 is the I / V converter 75.
The voltage signal corresponding to the output current Ia sent via the terminal is sampled, and each time the short circuit detection signal is received from the voltage detector 5 described above, the sampled signal is held and output. The volume setting device 79
Outputs a voltage signal of a level determined according to the welding conditions in order to arbitrarily define the rise Is of the output current, and
Defines the slope value tan δ of the variation It that is supplemented after the output current rises by Is.

Therefore, in this embodiment, when the current control mode is normal, the error amplifier 71 outputs the output signal of the I / V converter 75 and the output of the adder circuit 74, that is, the sample and hold circuit 7.
8, rising amount setter 79, the added signal of the integration circuit 77 and I
The output signals from the / V converter 75 are input, these error signals are supplied to the switching circuit 11, and the output current during the short-circuit section is controlled to the waveform as shown in FIG. 3 (b).

However, in such a current control mode,
The comparator 73 is an output signal of the integrating circuit 77 and a time setter.
The output signal of 76 is being compared and the control abnormality is detected.

That is, even if the output current I ₂ is supplied to the load for a predetermined time to, the voltage detector 5 does not output the arc detection signal,
When no arc is generated, an inverted output signal is sent from the comparator 73 to the switching circuit 70 to shut off the output of the adding circuit 74, and the error amplifier 71 outputs the output of the current setting device 72 via the switching circuit 11 to the pulse width control circuit. Since it is sent to 103, the output current to the load is switched to a level Ib sufficient to generate an arc larger than the level I _{2 at} that time, and the output current as shown in FIG. Will be supplied, which will result in a forced arc.

Although not shown, a circuit that defines the upper limit current Imax so that the short circuit current does not rise indefinitely during normal operation in the current control mode, as a short circuit current upper limit setter,
It is desirable to incorporate it on the output side of the adder circuit 74.By doing so, it is possible to prevent the output current I ₂ at the time of short circuit from increasing indefinitely, and the occurrence of spatter at the time of short circuit control becomes effective. Will be suppressed.

Next, the operation of the circuit and the method of the present invention will be described with reference to the block diagram shown in FIG. 2 and the waveform diagram shown in FIG.

At the start of arc welding, proper pre-control is performed to facilitate the generation of the arc, the consumable electrode 1 is fed at a constant speed, and the arc 3 is forcibly generated.

When the arc 3 is generated, an arc detection signal is sent from the voltage detector 5 to the switching circuit 11 and the voltage control circuit 7 is connected to the pulse width control circuit 103. Therefore, the normal constant voltage control mode is selected for control, and the output voltage preset by the voltage setter 62 is supplied to the load. The waveform of the output voltage V at this time is shown in FIG.

However, the supply of the consumable electrode 1 is further continued,
The gap distance between the consumable electrode 1 and the base material 2 gradually decreases, leading to a short circuit from the arc.

Then, the voltage detector 5 immediately detects the state,
Outputs a short circuit detection signal.

That is, in this state, the output voltage suddenly changes from several tens of volts to around zero volts.
The voltage detector 5 may be configured to be able to be compared with the reference voltage by a comparator, for example.

In the embodiment shown in FIG. 2, the switching circuit 11 is driven by the detection signal at this time to immediately cut off the voltage control circuit 6 and connect the current control circuit 7 to the pulse width setting circuit 103. At the same time, a drive signal is also sent to the integration circuit 77 and the sample hold circuit 78 to enable current control by a closed loop.

Then, when the voltage detector 5 outputs the short circuit detection signal, the switching circuit 11 is switched to the current control mode, the integrating circuit 77 is driven, and the sample and hold circuit is driven.
The 78 holds the sampled signal. As a result,
When the current control mode is normal, the addition signal output from each of the integrating circuit 77, the sample hold circuit 78, and the rising amount setting device 79 is input to the error amplifier 71 as a control value reference signal, and The output current I ₂ is compared with the output current Ia sent from the current detector 4 via the V converter 75 and has the peculiar waveform as described above defined by the addition signal (see FIG. 3 (b)). ) Will be output. Then, an abnormality occurs in such a current control mode, and the output current supplied to the load is kept for a predetermined time t _0.
In the case where the arc that should be generated next is not generated even when the power is supplied, the output current is set to a sufficient value preset for generating the arc, as shown by I _b in FIG. 3 (c). It will switch to a higher level and force an arc.

As a result of these controls, when an arc occurs, the device is in the constant voltage control mode, and when a short circuit occurs, it is in the current control mode, and when it is normal, the output current I ₂ of the peculiar waveform shown in FIG. 3B is generated. In the case of an abnormality in which the load is supplied and the arc is incompletely generated, the output current I ₂ ′ having the waveform as shown in FIG. 3 (c) is supplied to the load, which causes a small amount of melting in a short time. Drops are surely divided,
That is, efficient arc welding is performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of the device of the present invention,
FIG. 2 is a block diagram showing the apparatus shown in FIG. 1 in more detail, and FIG. 3 is a waveform diagram of output voltage and output current controlled by the method of the present invention. (Explanation of Codes) In the figure, 1 is a consumable electrode, 2 is a base metal, 3 is an arc generated during welding, 4 is a current detector, 5 is a voltage detector, and 10 is a switching control circuit.

Claims (3)

(57) [Claims] 1. A short-circuit transfer arc welding method in which a consumable electrode is fed at a constant speed and a short circuit and an arc are alternately generated. A constant voltage control is performed by a closed loop when an arc occurs, and a closed loop is performed when a short circuit occurs. Switch to current control,
Output current I supplied to the load during the short-circuit section
₂ is I ₂ = Ia + Is + It (Ia is the arc current just before the short circuit, Is
Is a preset rise amount, and It is a change amount that increases almost linearly with the passage of time). Is the reference value Io preset by It above
While the output current is controlled to I ₂ during the time until reaching, the arc current is larger than the output current I _{2 at} that time when the arc current is not generated even when it reaches the reference value Io. Output current Ib of sufficient level to generate
A short-circuit transfer arc welding method characterized by performing switching control. 2. A constant voltage control circuit and a current control circuit, which drive a switching control circuit to control an output voltage and a current supplied to a load in a closed loop, are combined to generate an arc and a short circuit. An arc welding apparatus adapted to be alternately operated according to the above, wherein the constant voltage control circuit is driven by receiving an arc detection signal from a voltage detector that detects a load voltage at the time of arc generation, The switching control circuit is provided with a voltage control circuit that outputs a control signal according to a preset control value in response to an output signal from the voltage detector, and the current control circuit includes an output current I ₂ during welding. I ₂ = Ia + Is + It (Ia is the arc current just before the short circuit, Is
Rising amount that is set in advance, It is a waveform current control circuit for controlling the waveform current defined by him with a variation which increases substantially linearly) over time, than the output current I ₂ It has a large current setting device for controlling the output current Ib at a level sufficient to generate an arc, and a comparison circuit that compares the It and a preset reference value Io, and the It is the reference value. Until reaching Io, the signal generated by the waveform current control circuit is output as a drive signal to the switching control circuit in order to set the output current to I ₂ , while it reaches the reference value Io. In order to switch the output current to Ib when no arc is generated, a configuration is provided including a current switching circuit that causes the switching control circuit to output the signal generated by the current setting device as a drive signal. Arc welding equipment. 3. The current control circuit comprises a short-circuit current upper limit setting device for limiting the upper limit value of the output current I ₂ supplied to the load during a short circuit to a preset value Imax. The arc welding device according to item 2.