JPH0331499Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a DC arc welding machine for DC arc welding a welding load consisting of a consumable electrode and a base material.

[Prior Art] Conventionally, this type of DC arc welding machine that automatically feeds a consumable electrode to perform DC arc welding is constructed as shown in Figure 2, in which 1 is a primary winding 1a and a The welding transformer has a secondary winding 1b, and the primary winding 1a is connected to an AC power source such as a commercial AC power source, a generator, or a high frequency power source.

Reference numeral 2 denotes a rectifier having first and second controlled rectifying elements 2a and 2b made of thyristors, etc., and the anode of the rectifying element 2a is connected to one end of the secondary winding 1b, and the other end of the secondary winding 1b is connected to the anode of the rectifying element 2a. Rectifying element 2
The anode of b is connected.

3 is a DC reactor whose one end is connected to the cathodes of the rectifying elements 2a and 2b; 4 is a DC reactor 3;
A wire-shaped consumable electrode 5 connected to the other end is a base metal connected to the tap terminal ta of the secondary winding 1b, and the electrode 4 and the base metal 5 form a welding load 6.

7 is a wire feeding device that feeds the consumable electrode 4 in the direction of the base material 5; 8 is a wire feeding motor that drives the feeding device 7; 9 is a motor control device for controlling the drive of the motor 8; The speed of the motor 8 is controlled to the feeding speed set by the feeding speed setting device 10.

11 is a gate drive device that outputs a gate signal for ignition control to the gates of both rectifying elements 2a and 2b, and performs ignition control of both rectifying elements 2a and 2b based on the setting value of gate signal setting device 12. .

Then, the power AC of the AC power supply is transformed by the transformer 1, and an output AC of a desired voltage is generated in the secondary winding 1b of the transformer 1, and the output AC is converted into a full wave by both rectifying elements 2a and 2b of the rectifier 2. rectified,
The rectified output of the rectifier 2 is input to the reactor 3.

The reactor 3 is provided to smooth the rectified output and control the current when the welding load 6 is short-circuited, and the rectified output is smoothed by the reactor 3.
DC welding output is supplied from the reactor 3 to the welding load 6 .

By the way, both rectifier elements 2a and 2b of the rectifier 2 are ignited by a gate signal from the drive device 11, and thereby the voltage of the rectified output is controlled to a predetermined constant voltage.

On the other hand, the consumable electrode 4 is fed toward the base material 5 at a constant speed under feeding control of the feeding device 7 based on the rotation of the motor 8.

Then, an arc is generated between the consumable electrode 4 and the base metal 5, and the arc is started. After the arc is started, the current flowing from the consumable electrode 4 to the base metal 5 increases to a certain amount, resulting in a steady arc. Then arc welding is performed.

By repeating the above operations, arc starting is repeated and arc welding is sequentially performed.

[Problem that the invention attempts to solve]

By the way, since the consumable electrode 4 is fed in the direction of the base material 5 at a constant speed, the contact resistance between the tip of the electrode 4 and the base material 5 increases when the arc starts, as shown by the solid line A in FIG. After startup, it decreases according to the feeding speed.

Then, the tip of the consumable electrode 4 is fused and arc welded due to the current flowing through the welding load 6 and the Joule heat based on the contact resistance.

On the other hand, if the inductance of the reactor 3 is small, the current flowing through the welding load 6 is indicated by the solid line B in FIG.
As shown in the figure, the rise at the time of starting the arc becomes steep. Conversely, if the inductance of the reactor 3 is large, the rise becomes gentle as shown by the solid line C in the figure.

Then, arc welding is performed using Joule heat at the intersection α of the solid lines A and B or Joule heat at the intersection β between the solid lines A and C. At this time, the Joule heat at the intersection α becomes larger than the Joule heat at the intersection β, and the solid line Welding can be performed with the current having the characteristic B, with better arc starting characteristics than with the current having the characteristic C, as shown by the solid line.

However, in the case of the characteristic shown by solid line B, that is, when the inductance of the reactor 3 is small, the arc shifts to a steady state, and the short circuit current when the consumable electrode 4 shorts to the base material 5 and shifts to the short circuit region becomes too large. The spatter becomes large, and the ripple component also becomes large in the globile region, making the welding bead rough and making it impossible to obtain a good welding result.

That is, if the inductance of the reactor 3 is reduced in order to improve the arc starting characteristics,
Steady arc characteristics deteriorate after arc starting, and conversely,
Reactor 3 to improve steady arc characteristics
When the inductance of the arc is increased, the arc starting characteristics deteriorate.

In the case of Figure 2, the inductance of the reactor 3 is set so that neither the arc starting characteristics nor the steady arc characteristics are good, but they do not break the lock.In this case, both characteristics are good. There is a problem that it is not possible to perform optimal arc welding using a DC arc welding machine.In particular, when a DC arc welding machine is formed by a welding robot because the arc starting characteristics are not good, the length of the bead becomes uneven and There is also the problem of spatter adhering to the robot.

[Means for solving problems]

This invention consists of first and second rectifiers each having a controlled rectifying element configuration that rectifies the AC output of the welding transformer, and the rectified outputs of the two rectifiers are input to both ends of the welding transformer. a DC reactor that supplies a welding direct current to the welding load, a current detector that detects the current flowing through the welding load, a first gate drive device that constantly drives the first rectifier, and a detection output of the current detector. and a second gate drive device that drives the second rectifier to ignite only when the arc reaches a predetermined value.

[Effect]

When the arc starts, the rectified outputs of the first and second rectifiers are supplied to the DC reactor, and at this time, the direction of the current flowing through the DC reactor is determined based on the rectified output of the first rectifier and the rectified output of the second rectifier. The direction of the flowing current is different, the inductance of the DC reactor decreases, and the rise of the current flowing through the welding load becomes steep.

Further, when the arc starts to shift to a steady arc, the rectified output of the second rectifier is cut off, and at this time, the inductance of the DC reactor increases and the steady arc characteristics improve.

〔Example〕

Next, this invention will be described in the first part showing its practical example.
This will be explained in detail with reference to figures. In the same figure, 13
is a welding transformer having a primary winding 13a and a secondary winding 13b, and the primary winding 13a is connected to an AC power source such as a commercial AC power source, a generator, or a high frequency power source.

14 is a first rectifier having third and fourth controlled rectifying elements 14a and 14b made of thyristors, etc.; the anode of the rectifying element 14a is connected to one end of the secondary winding 13b; The anode of the rectifying element 14b is connected to the other end.

Reference numeral 15 denotes a second rectifier having fifth and sixth controlled rectifying elements 15a and 15b made of thyristors, etc., and the rectifying element 15a is connected to the anode of the rectifying element 14a.
The anode of the rectifying element 14 is connected, and the rectifying element 14
The anode of the rectifying element 15b is connected to the anode of the rectifying element 15b.

A DC reactor 16 has one end connected to the cathodes of the rectifiers 14a and 14b, and has a tap terminal tb, and the other end is connected to the cathodes of the rectifiers 15a and 15b via a current-limiting resistor 18. .

19 is a wire-shaped consumable electrode connected to the tap terminal tb of the DC reactor 16; 20 is a base material connected to the tap terminal tc of the secondary winding 13b via the current detector 21; A welding load 22 is formed by the base material 20 .

23 is a wire feeding device that feeds the consumable electrode 19 in the direction of the base material 20; 24 is a wire feeding motor that drives the feeding device 23; 25 is a motor control device for controlling the drive of the motor 24; The speed of the motor 24 is controlled to the feeding speed set by the feeding speed setting device 26.

27 is the rectifying element 14a, 14 of the first rectifier 14
This is a first gate driving device that outputs a gate signal for ignition control to the gate of gate b, and controls both rectifying elements 14a and 1 based on the setting value of the gate signal setting device 28.
4b ignition control is performed.

29 is the rectifying element 15a, 15 of the second rectifier 15
This is a second gate driving device that outputs a gate signal for ignition control to the gate of gate b, and performs ignition control of both rectifying elements 15a and 15b only at the time of arc starting based on the detection signal of the current detector 21.

Then, the output AC of the secondary winding 13b of the transformer 13 is supplied in parallel to rectifiers 14 and 15, and the rectifier 1
Since the rectifying elements 14a and 14b of No. 4 are always ignited by the gate signal of the drive device 27, main welding is performed from the rectifier 14 to one end of the reactor 16 and to the electrode 19 via the tap terminal tb based on the rectified output of the rectifier 14. DC Ia is always supplied.

On the other hand, the detector 21 detects the current flowing through the welding load 22, that is, the current flowing from the electrode 19 to the base material 20, and supplies a detection signal proportional to the current to the drive device 29.

Then, the drive device 29 sends a gate signal to the rectifier elements 15a and 15b of the rectifier 15 only when the current flowing from the electrode 19 to the base metal 20 increases and the arc starts to shift to a steady arc and the detection signal reaches a predetermined value. is output, and both rectifying elements 15a and 15b are ignited.

At this time, the rectified output of the rectifier 15 that is ignited is supplied to the other end of the reactor 16 via the resistor 18, the rectified output of the rectifier 15 is smoothed by the reactor 16, and the rectified output from the rectifier 15 is passed through the resistor 18 and the reactor 16. A sub-welding direct current Is based on the rectified output of the rectifier 15 is supplied to the electrode 19.

Therefore, when starting the arc, main and sub welding DC Ia,
Is flows from the electrode 19 through the base material 20 and the detector 21 to the tap terminal tc of the secondary winding 13b.

By the way, the reactor 16 is formed by winding a coil around one iron core, and since the directions of the main and sub-welding DC currents Ia and Is flowing through the reactor 16 are different, the main and sub-welding DC currents Ia and Is cancel each other out. Magnetic flux is generated.

Therefore, when starting the arc, reactor 1
The inductance from one end of 6 to the tap terminal tb and the inductance from the other end to the tap terminal tb are reduced compared to when only one of the welding DC currents Ia, Is flows, and both the welding DC currents Ia,
Since Is is supplied to the electrode 19, the welding direct current supplied to the welding load 22 has a sufficient magnitude and steep rise for arc starting, and good arc starting characteristics are obtained.

Next, when the current flowing through the welding load 22 increases to a certain amount due to arc activation and shifts to a steady arc, the ignition drive of the rectifier 15 by the drive device 29 is stopped.

Therefore, after the arc starts, the rectified output from the rectifier 15 to the reactor 16 is cut off, and the auxiliary welding DC current Is
will no longer be supplied.

Since only the main welding direct current Ia flows, the inductance of the reactor 16 with respect to the main welding direct current Ia increases compared to when the arc is started, thereby obtaining good steady arc characteristics, and short circuiting when the electrode 19 shorts to the base metal 20. An excessive current is prevented and an increase in the ripple component is also prevented, thereby stabilizing the arc.

Therefore, according to the above embodiment, at the time of arc starting, the rectified outputs of the rectifiers 14 and 15 are both supplied to the reactor 16, and the inductance of the reactor 16 is reduced to perform arc starting with good arc starting characteristics. After startup, the supply of the rectified output of the rectifier 15 to the reactor 16 is cut off, the inductance of the reactor 16 is increased, and welding can be performed with good steady arc characteristics.
By using multiple reactors 16, it is possible to improve both the arc starting characteristics and the steady arc characteristics, form a good welding beat, and perform optimal arc welding. For example, in the case of a welding robot, the length of the bead is uniform. At the same time, adhesion of spatter to the robot is prevented.

[Effect of idea]

Therefore, according to the DC arc welding machine of this invention, the rectified output cutoff means supplies the rectified output of the second rectifier 15 to the DC reactor 16 only at the time of starting the arc, and after starting the arc, the rectified output of the second rectifier 15 is supplied to the DC reactor 16.
Since the supply of the rectified output of No. 5 to the reactor 16 is cut off, the inductance of the reactor 16 decreases at the time of arc starting, and good arc starting characteristics can be obtained, and at the same time, the inductance of the reactor 16 increases after the arc starts. It is possible to obtain good steady arc characteristics, ensure good arc starting, prevent excessive spatter, stabilize the arc, and obtain good welding results. In particular, this method can be applied to welding robots with good results.

[Brief explanation of drawings]

Figure 1 is a wiring diagram of one embodiment of the DC arc welding machine of this invention, Figure 2 is a wiring diagram of a conventional DC arc welding machine, and Figure 3 shows the relationship between time, contact resistance, and current flowing through the welding load. It is a relationship explanatory diagram. 13...Welding transformer, 14...First rectifier, 1
5...Second rectifier, 16...DC reactor, 2
1... Current detector, 22... Welding load, 27...
First gate driving device, 29... second gate driving device.

Claims (1)

[Claims for Utility Model Registration] First and second rectifiers each having a controlled rectifying element configuration for rectifying the alternating current output of a welding transformer, and a consumable electrode and a motherboard to which the rectified outputs of the two rectifiers are inputted to both ends, respectively, from tap terminals. a DC reactor that supplies a welding direct current to a welding load of materials; a current detector that detects the current flowing through the welding load; a first gate drive device that constantly drives the first rectifier to spark; the current detector a second gate drive device that drives the second rectifier to ignite only when the arc is started until the detected output reaches a predetermined value.