JPH0337831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an arc ignition method in a reverse polarity non-consumable electrode type arc welding process.

[Conventional technology]

A feature of the reverse polarity non-consumable electrode arc welding method is that cathode spots are formed on the surface of the base metal, and the oxide film around the weld bead is destroyed and removed as the base metal surface is bombarded with cations, resulting in a beautiful surface. The cleaning action can be mentioned as follows. Furthermore, since an inert gas is used as a shielding gas to shield the arc and weld metal from the atmosphere, the arc is extremely stable, a smooth bead is obtained, and impurities do not enter the weld metal. As a result of the above, it is widely used for welding materials whose surface oxide has a melting point higher than that of the base metal, specifically, for high-quality welding of Al alloys, Mg alloys, etc.

Now, as an arc ignition method in the conventional reverse polarity non-consumable electrode type arc welding method, a method generally called a high frequency ignition method has been used. Figure 2 shows its configuration. In this, the cathode side of the welding power source 1 having DC drooping characteristics is connected to the base material 3 to be welded.
The anode side is connected to the tungsten electrode 2 in the welding torch 7 via the high frequency power source 4. Note that 5 is a high frequency bypass capacitor.

With inert gas being supplied as a shielding gas through the shielding cap 6 (description of the shielding gas will be omitted in the following explanation),
A high frequency voltage of several thousand V or more is applied between the tungsten electrode 2 and the base metal 3 by the high frequency power source 4 to cause spark discharge and dielectric breakdown, and then a current is supplied by the welding power source 1. It ignites an arc.

[Problem that the invention seeks to solve]

However, such high-frequency ignition methods generate electromagnetic noise due to high frequencies, which can cause malfunctions or damage to various peripheral electronic devices such as microcomputers built into automatic welding equipment. It was necessary to take special measures against noise, such as using a noise filter.

Furthermore, the high-frequency ignition method has the disadvantage that it cannot be easily connected to the welding electric circuit 8 because the measuring device is damaged when a high-frequency voltage is applied.

Due to these factors, it has been difficult to automate the reverse polarity non-consumable electrode type arc welding method using precision equipment such as welding robots and to control welding phenomena using precision measuring equipment.

The touch ignition method was developed as an improvement method. Figure 3 shows its configuration. A base material 3 to be welded is placed on the cathode side of a welding power source 1 having DC drooping characteristics.
and connect the tungsten electrode 2 in the welding torch 7 to the anode side.

This method involves applying the no-load voltage of the welding power source 1 between the tungsten electrode 2 and the base metal 3.
The tungsten electrode 2 is brought into contact with the base material 3 to create a short circuit, a short circuit transient current is caused to flow, and then the tungsten electrode 2 is separated from the base material 3 to ignite an arc.

However, in this method, the tungsten electrode 2 is subject to wear and tear such as melting and deformation due to the excessive current generated during a short circuit, which significantly shortens the electrode life and sometimes makes it difficult to perform welding.

In order to improve this, the contact between the tungsten electrode 2 and the base material 3 is electrically detected in Japanese Patent Application Laid-open No. 59-50970 and Japanese Patent Application Laid-Open No. 59-76675, and based on this, A method has been proposed for controlling the timing of separating the tungsten electrode 2 from the base material 3 and further suppressing the current flowing during a short circuit to suppress the wear and tear on the tungsten electrode 2 during a contact short circuit.

However, this does not completely eliminate electrode wear, and some electrode wear occurs, shortening the electrode life.

Non-consumable electrode arc welding, which is characterized by high-quality welding with a stable arc, has a fatal disadvantage of electrode wear that leads to arc instability.

The present invention provides an arc ignition method in a reverse polarity non-consumable electrode type arc welding method that prevents malfunction or damage to peripheral measuring instruments, control equipment, etc. by eliminating electrode wear and eliminating the influence of high frequency noise. The purpose is to

[Means for solving problems]

The gist of the present invention is a reverse polarity non-consumable electrode type arc welding method characterized by injecting plasma toward the base material into an electric field generated between the non-consumable electrode and the base metal, and igniting the arc. In the arc ignition method.

The present invention will be described in detail below with reference to the drawings.

First, FIG. 1 shows a schematic diagram of a welding apparatus for carrying out one embodiment of the method of the present invention. In Fig. 1, reference numeral 1 denotes a welding power source having DC drooping characteristics, to which a tungsten electrode 2 (hereinafter referred to as the main electrode) in a welding torch 7 is connected to its anode side, and to the cathode side to which the workpiece to be welded is connected. The materials 3 are connected to form a welding electric circuit 8 consisting of a welding power source 1, a tungsten electrode 2, and a base material 3. Further, a plasma nozzle 13 and a tungsten electrode 12 (hereinafter referred to as a sub-electrode) are arranged near the base material 3, and the sub-electrode is placed on the cathode side of the plasma device 10, and the plasma nozzle 13 is placed on the anode side.
are connected to form a plasma jet circuit 18 consisting of a plasma device 10, a sub-electrode 12, and a plasma nozzle 13.

[Action of the invention]

By turning on the welding power source 1, an electric field is generated between the main electrode 2 and the base material 3 from the main electrode 2 toward the base material 3. In this state, plasma gas is supplied into the plasma nozzle 13 (description of the plasma gas will be omitted in the following explanation), the plasma device 10 is turned on, plasma is generated using the plasma jet circuit 18, and the base material is Inject plasma towards point 3. At this time, the positive ions in the plasma injected into the electric field are accelerated by the electric field and collide with the base material 3, raising the temperature of the collision part. As a result, the arc is easily ignited by the voltage of the welding power source 1.

According to the present invention, since an arc can be ignited without using a high frequency power source in the welding electric circuit 8, a device for measuring electric signals such as arc voltage can be directly connected. Furthermore, there is no risk of malfunction or damage to the control device due to high frequency noise. Therefore, according to the present invention, automation using precision equipment and control of welding phenomena using precision measuring equipment, which has been extremely difficult in the past, becomes possible.

Further, according to the present invention, the plasma jet circuit 1
8, it is sufficient to generate a low current plasma jet of about 5 to 30 A and inject it into the electric field for a short time of about 0.01 to 1 second to ignite the arc. Furthermore, the plasma nozzle 13 can be miniaturized because only the plasma gas is required to generate the plasma jet and no shielding gas is required.

Furthermore, the discharge gap between the sub-electrode 12 and the plasma nozzle 13, as well as the shape and material of each, can be arbitrarily set to facilitate discharge.

In addition, since the plasma jet for arc ignition requires low current and only short-term use, the sub-electrode 1
2 and the plasma nozzle 13 are extremely slight.

The outline of the present invention has been described above. Then the first
A method of igniting the plasma device 10 and plasma jet circuit 18 used in the figure will be explained with reference to FIGS. 4 and 5.

FIG. 4 is a schematic diagram showing a plasma jet circuit for arc ignition using the touch ignition method. 11
is a plasma power supply having DC drooping characteristics, with a sub-electrode 12 on the cathode side and a plasma nozzle 1 on the anode side.
3 are connected to form a plasma jet circuit consisting of a plasma power supply 11, a sub-electrode 12, and a plasma nozzle 13. Plasma power supply 11
is turned on, and with the no-load voltage applied, the sub-electrode 12 is contacted and short-circuited to the plasma nozzle 13 using manual, electric, bimetal, spring-loaded, or other means, and a short-circuit transient current is applied to the sub-electrode 12. 12 from the plasma nozzle 13 to ignite the plasma jet.

In the conventional touch ignition method, there was a problem of wear and tear on the tip of the main electrode due to excessive current during a short circuit, but in plasma jet for arc ignition, since the current is originally low (about 5 to 30 A), the sub electrode There is very little wear and tear on the tip. Further, even if it is slightly worn out, it is enough to ignite the plasma jet, and it is not related to the welding electric circuit 8, so it does not cause any problem in welding.

FIG. 5 is a schematic diagram showing a plasma jet circuit for arc ignition using the high frequency ignition method. 11
is a plasma power supply having DC drooping characteristics, a sub-electrode 12 is connected to its cathode side via a high-frequency power supply 14, and a plasma nozzle 13 is connected to its anode side. Note that 15 is a high frequency bypass capacitor.
A plasma jet circuit 18 is formed by a plasma power source 11, an auxiliary electrode 12, a plasma nozzle 13, a high frequency power source 14, and a high frequency bypass capacitor 15. In this circuit, a high frequency voltage is applied between a sub-electrode 12 and a plasma nozzle 13 by a high frequency power source 14 to cause spark discharge and dielectric breakdown, and then a current is supplied by a plasma power source 11 to point an arc. It is an arc. However, the discharge gap between the plasma nozzle 13 and the sub-electrode 12 is 0.1.
Since minute settings on the order of mm are possible, it is sufficient for the output voltage of the high frequency electrode 14 to be approximately 1,000 V at maximum, and the level of high frequency noise generated due to this is also low. Therefore, by covering the plasma jet circuit 18 with the shield 16 and connecting it to an external power source through the noise filter 17, high frequency noise can be easily and completely suppressed.

Note that the high-frequency power source 14 does not need to be connected to the cathode side of the plasma power source 11, and if a circuit is formed by the sub-electrode 12, the plasma nozzle 13, the high-frequency power source 14, and the high-frequency bypass capacitor 15,
You can place it anywhere.

In FIG. 5, the high frequency voltage generated by the high frequency power source 14 is used to ignite the plasma jet circuit 18, but any power source capable of supplying the same voltage can be incorporated into the plasma jet circuit 18. In fact, it is possible to ignite the plasma jet in the same way by using the capacitor discharge voltage from the capacitor power source or the surge voltage generated when the current is cut off.

〔Example〕

An example using the apparatus shown in FIG. 6a is shown below. Note that details of the plasma jet circuit 18 shown in FIG. 6a are shown in FIG. 6b.

Plasma jet circuit side: No-load voltage of plasma power supply 11 100V, plasma jet current 10A, plasma gas flow rate 3/
min・Ar, D=1.0mm, lt=1.0mm, lp=1.2mm, ds
=1.0mm.

Welding electric circuit side: Welding power supply 1 no-load voltage 47V, set welding current
50A, shielding gas flow rate 20/min・Ar, la=4
mm, lb=5mm, lc=5mm, dm=3.2mm, θ=
45deg.

Continuously inject plasma for 0.1 seconds under the above conditions
Arc ignition was attempted 100 times, and arc ignition was achieved extremely stably in each case. Moreover, no wear was observed on the main electrode 2, the sub-electrode 12, and the plasma nozzle 13. In addition, almost no voltage fluctuations in the external power supply were observed when high-frequency waves were generated, and although the measuring equipment or control device used at this time had a built-in microcomputer, no malfunctions due to high-frequency noise occurred.

〔Effect of the invention〕

As detailed above, according to the present invention, there is no need to use means that cause noise, such as a high frequency power supply, in the welding electric circuit, so noise countermeasures are taken into the control device using electronic equipment such as a microcomputer. There is no need to apply it. Furthermore, since there is no fear of damage to measuring equipment, etc., even more precise measurements are possible. Furthermore, since it is a non-contact type of arc ignition, there is no problem with wear and tear on the main electrode, and it has great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of an apparatus for carrying out one embodiment of the present invention, and FIGS.
The figure is a block diagram showing a conventional example, FIGS. 4 and 5 are schematic diagrams showing a configuration example of a plasma jet circuit for arc ignition, and FIG. A sectional view showing an example of the arrangement,
6b is a block diagram showing details of the plasma jet circuit 18 shown in FIG. 6a. 1: Welding power source, 2: Tungsten electrode (main electrode), 3: Base material, 4: High frequency power source (for arc ignition), 5: High frequency bypass capacitor (for arc ignition), 6: Shield cap, 7: welding torch,
8: Electric circuit for welding, 10: Plasma device, 1
1: Plasma power supply, 12: Tungsten electrode (auxiliary electrode), 13: Plasma nozzle, 14: High frequency power supply (for plasma), 15: High frequency bypass capacitor (for plasma), 16: Shield, 17: Noise filter, 18: Plasma jet circuit.

Claims (1)

[Claims] 1. Connect a non-consumable electrode to the positive side of a DC welding power source and the base material to the negative side, and generate an electric field from the non-consumable electrode toward the base material, then ignite plasma from near the non-consumable electrode toward the base material. An arc ignition method in a reverse polarity non-consumable electrode type arc welding method, which is characterized by igniting an arc by injecting .