JPS61276768A - Ignition method for main plasma arc in non-key hole type plasma arc welding - Google Patents

Abstract

PURPOSE:To enable the use of nonconsumable electrode for a long period without its readjustment by adding inpulsive center shock gas to center gas and enlarging the flow rate of center gas in an instant in case of igniting the main plasma arc. CONSTITUTION:A pilot arc is ignited by the DC power source 11 for the pilot arc between a nonconsumable electrode 1 and constraining nozzle electrode 2. The plasma welding is then performed without forming a key hole on the body 12 to be welded by igniting the main plasma arc via a plasma flow between the nonconsumable electrode 1 and the body 12 to be welded by the DC power source 10 for welding. In case of this plasma arc ignition, the center gas is fed from a flow paths 13, and the impulsive center shock gas is added from a flow path 15 to the center gas to enlarge the flow rate of the center gas in an instant. The ignition of the main plasma arc is thus made easy by projecting the pilot arc to the external part from the tip of the constraining nozzle electrode 2.

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention relates to a method for igniting the main plasma arc in transitional plasma arc welding (non-keyhole type) in which welding is performed without forming a keyhole in the workpiece. I'm busy.

(b) The conventional technology transition type plasma arc welding method uses an inert gas such as argon gas as the center gas, and jets out several liters of the gas per minute through a restrained nozzle electrode to attach the key to the workpiece. The keyhole type plasma arc welding method involves opening a hole to proceed with welding, and the flow rate of the center gas is reduced to a smaller amount than the above method (for example, about 0.2 to 0.8 t/min), and is used in a small current range. There is also a Harry-hole type plasma arc welding method, which is typified by micro plasma arc welding, in which welding proceeds without making a keyhole in the workpiece.

In non-keyhole type plasma arc welding methods such as micro plasma arc welding, due to constraints imposed by the welding method, the flow rate of the center gas cannot be as large as in keyhole type plasma arc welding methods.
The pilot arc is weak, and the stability of the pilot arc is often impaired due to factors such as the electrode shape, electrode surface condition, and center gas flow rate.

For example, if used continuously for several hours, the tip of a pure tungsten electrode will wear out due to the influence of impurities such as oxygen and nitrogen contained in the center gas, as well as metal vapor, and the tip of a tungsten electrode containing a tungsten electrode will wear out the recrystallized ring at the tip. The tip of the non-consumable electrode may be deformed due to the formation of a gas, and the pilot arc cannot protrude far enough from the tip of the restrained nozzle electrode to the outside, causing the non-consumable electrode to deform even when the plasma torch is brought close to the object to be welded. It becomes impossible to create an electrical bridge between the pilot arc and the workpiece, and the main plasma arc cannot be generated even if the main plasma arc power source is applied.

Fig. 7 shows a state in which a tungsten electrode containing tungsten is used as the non-consumable electrode 21 and is used continuously for several hours. Eventually, the shortest part between the electrode 21 and the inner wall of the restrained nozzle electrode 23 becomes the outer periphery of the grown ring, and the pilot arc 24 is connected to the restrained nozzle electrode 2.
3. It becomes difficult to protrude to the outside.

In addition, FIG. 6 shows the state of the non-consumable electrode 21 at the initial stage of use, 25 is a shield gas nozzle, 26 is a center gas supply channel, and 27/fi is a shield gas supply channel.

For this reason, two methods have been conventionally employed in order to properly project the pilot arc to the outside of the restrained nozzle electrode. One method is to take out the non-consumable electrode from inside the torch and reshape it with a grinder or sandpaper.The other method is to instantaneously increase the pilot arc current when a plasma arc occurs, and the ionized electrode is removed by the pilot arc. This is a method of increasing the amount of hot gas.

e→ Problems to be Solved by the Invention However, among the above conventional methods, when reshaping the electrode, the FC is a relatively easy task when using the torch manually; In the case of built-in devices, setup time for electrode replacement, positioning, etc. is a problem, and the work efficiency as an automatic machine is reduced.

In addition, in the method of instantaneously increasing the pilot current,
It is effective to some extent during a period when the deformation of the electrode is relatively slight, but if the deformation progresses further, it becomes ineffective, and eventually
It could not be used continuously for a long time.

It is an object of the present invention to provide a method for igniting a main plasma arc in non-keyhole type plasma arc welding, in which a non-consumable electrode once set in a torch can be used for a long time without having to be reshaped.

B) Means for Solving the Problems The present invention solves the above problems by connecting the non-consumable electrode to the welded object through a plasma gas flow generated by a pilot arc generated between the non-consumable electrode and the restrained nozzle electrode. In non-keyhole plasma arc welding, in which the main plasma arc is ignited between objects without forming a keyhole in the workpiece, an impulse-like center shock is generated in the center gas when the main plasma arc is ignited. Add gas,
This is to instantaneously increase the flow rate of the center gas.

(E) Effect Conventionally, when the tip of the non-consumable electrode deforms after several hours of continuous use, the pilot arc cannot fully protrude from the tip of the restrained nozzle electrode, and the pilot arc forms between the non-consumable electrode and the workpiece. However, in the present invention, the main plasma arc could not be generated because it was impossible to create an electrical bridge, but in the present invention, the center shock gas is added to instantly increase the flow rate of the center gas. Even if the non-consumable electrode has a deformed tip due to use, the pilot arc can be made to protrude to the outside from the tip of the restrained nozzle electrode, and therefore the main plasma arc can be easily ignited.

(f) Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sequence flowchart when the main plasma arc ignition method of the present invention is implemented in microplasma arc welding, and shows the relationship among center gas, shield gas, pilot arc current, main plasma arc current, and center shock gas. This shows that.

In Figure 1, point A is when welding is started, point B is when welding is stopped, and point P is when the main plasma arc power source (welding power source) is applied between the non-consumable electrode and the workpiece, and the main plasma is generated. This is the point at which the arc ignites. As shown in the figure, while the center gas is supplied, the pilot arc current is flowing, and the pilot arc is ignited, shielding gas is supplied and welding is started at point A, and after the preflow of this shielding gas, welding is started at point FcP. The welding power is turned on, the main plasma arc current flows, and the main plasma arc reaches 1
ignite. Then, the welding power source is stopped at point B. tl indicates aftershield time.

These sequences have conventionally been carried out normally, but in the present invention, when igniting the main plasma arc, in other words, the main plasma power source (welding power source) is connected between the non-consumable electrode and the workpiece. The characteristic is that it is made larger when it is applied.

As shown in FIG. 1, when the main plasma arc is ignited (near point P), an innocuous center shock gas is added to the center gas. To be more specific,
After an appropriate time tl from the welding start (point A), the gas pulp in the gas supply path is opened to begin supplying center shock gas to the torch, and then the welding power is turned on and the main plasma arc is turned on. If the above-mentioned gas pulp is closed to end the supply of center shock gas at the point when the gas is ignited (point P), there is a slight distance from the position of the gas pulp in the gas supply path to the tip of the torch, The falling portion overlaps with point P, and when the main plasma arc is ignited (point P), the center shock gas joins the tip of the torch, and the center gas flows out at a flow rate larger than usual.

However, the timing (t+tb) of starting and ending the supply of center shock gas can be changed as appropriate.
It is not limited to the one shown in FIG. In short, it is sufficient to set the state so that when the main plasma arc is ignited (point P), the center shock gas is mixed with the center shock gas at the tip of the torch, and the center gas flows out at a larger flow rate.

However, if the center shock gas is continued to be supplied for a relatively long time after the main plasma arc is ignited, the flow rate of the center gas will become larger than necessary at the start of welding, causing a keyhole to be drilled in the workpiece. This will cause some inconvenience. Therefore, in the embodiment shown in Fig. 1, the gas pulp of the center shock gas is closed as soon as the welding power is turned on, but the point is that the flow rate of the center gas is limited at least at the time of ignition of the main plasma arc. Since it is sufficient to temporarily increase the center shock gas, the supply time of the center shock gas may be extremely short, for example, 20 to 30 m5ec.

In addition, this center gas temporarily adjusts the flow rate of the center gas in addition to the impulse flow of the center gas, and since it becomes part of the center gas and flows out from the tip of the torch, it is of the same type as the center gas. An inert gas such as Ar may be used. The amount to be added is selected appropriately because if it is too large, the pilot arc will disappear, and if it is too small, the effect of the present invention cannot be achieved.

FIG. 2 is a configuration and electrical connection diagram of a welding torch used in Himi Akiban. In the figure, the l#i non-expendable non-consumable electrode is a restraining nozzle electrode, 3 is a shielding gas nozzle, 4 is a molding material with electrical insulation, and 5 is a conductive material for fixing the non-consumable electrode 1 to the torch body. metal collet chuck,
6 is a cap for tightening the collet chuck 5, 7
numeral 8 is an electrically insulating electrode holder for setting the emergency consumable electrode on the central axis of the restrained nozzle electrode, 8 is a seal with a gas lens for degas, 9 is an 0 ring, io, h is the non-consumable electrode l and the non-consumable electrode holder. A welding DC power source 11 is connected to the workpiece 12 to ignite the main plasma arc between them, and 11 is connected to the non-consumable electrode 1 and the restraint nozzle electrode 2I/c to ignite the pilot arc between them. 13 is a pilot arc DC power source, 13 is a center gas supply channel, 14 is a shield gas supply channel, and 15 is a center shock gas supply channel. The welding torch shown in FIG. 2 differs from the conventional one only in that a center shock gas supply passage 15 is provided.

Figure 3 shows a center gas and center shock gas supply device used in combination with the torch shown in alE2, which supplies gas at an appropriate pressure and flow rate from a gas supply source filled with an inert gas such as argon. A receiver is inserted from the gas inflow end 20 of the center gas supply channel 13, and a constant amount of center gas is always supplied to the torch through the flow rate regulator 16. In addition, a center shock gas supply flow path 15 is connected to the upstream side of the center gas supply flow path 13 from the position where the flow rate regulator 16 is provided, and the center shock gas flowing through the center shock gas flow path 15 is connected to the center shock gas supply flow path 15. A gas pulp 17 is provided to control the start and stop of supplying the gas to the torch.

This gas pulp 17 is controlled to open and close according to control signals from a control device built into the welding power source.

FIG. 4 is a configuration and electrical connection diagram of another welding torch embodying the present invention, and the torch shown in FIG. ,
The welding torch in FIG. 4 represents the conventional type. The center gas and center shock gas supply device shown in FIG. 5 is used in the torch shown in FIG. 4. This means that if the gas supply device shown in FIG. 5 is used, a conventional torch can be used as is without any particular modification.

Since the gas supply device shown in FIG. 5 does not have the center shock gas supply flow path 15 in the torch, the center gas and the center shock gas do not meet inside the torch as in the case described above, but in front of the torch. Please join me at
are doing. For this reason, a center shock gas supply bypass passage 15"j- is provided in the center gas supply flow passage 13 connected to the inside of the torch. 17'#i Bypass passage 151C is provided to control the timing of supply of center shock gas. It is a gas pulp that is controlled.

The present inventors conducted an experiment to compare the method of the present invention with the conventional method, and obtained the results shown in Table 1 below.

Table 1 Setting conditions (1) Electrode・・・・・・・・・・・・・・・・・・
...YWT h -2φ2.4■ (2) Steady pilot current ...7A (3) Welding current @@+ *
** +6$ 6@・・・・・・・・・100A (main plasma arc) (4) Center character change −≠Gas “・・”・Ar 0.
5t/ah (5) Center shock
= A T 1 , 017/h (6) Shield gas *
411mm..., 4r+7%[,42/aim(7
) Base material・・・・・・・・・・・・・・・・・・
Water-cooled copper plate (8) no μ/distance between base metals...---
3 ■ (9) Arc on fist off time...1 Self...Main arc load time 10 seconds Arc pause time 10 seconds Scream Judgment conditions...Self...Axis...River...Arc on/off The total time under the Kotoda setting conditions in which ignition of the main plasma arc does not fail even once in the continuous repetition of is the sum of the total main arc load time and the total arc rest time.

The above times are the average values of five times, rounded to the nearest whole number.

In this way, according to the method of the present invention, once a non-consumable electrode is set in the torch, it can be used for a long time with excellent main plasma A/D characteristics without having to reshape it, compared to conventional methods. It was confirmed that it can be used.

(g) Effects of the Invention As described above, the present invention improves the starting characteristics of the main plasma arc that arises from the instability of the pilot arc, which is a drawback of non-life-Hall type plasma arc welding torches, and It is now possible to use the set non-consumable electrodes for a long time without having to reshape them. And this will help improve the efficiency of welding work,
This is particularly effective when incorporated into robots or automatic machines.

[Brief explanation of drawings]

Fig. 1 is a welding sequence flowchart according to an embodiment of the present invention, Fig. 2 is a configuration and electrical connection diagram of a welding torch implementing the present invention, and Fig. 3 is a center gas supply in combination with the welding torch of Fig. 2. FIG. 4 is a configuration 1 of another welding torch for carrying out the present invention, and an electrical connection diagram;
FIG. 5 is a center gas supply device combined with the welding torch of FIG. 4, and FIGS. 6 and 7 are explanatory diagrams of the tip of the welding torch. 1.21 ~ Non-consumable electrode 2.23 ~ Restricted nozzle electrode lO ~ DC power source for welding 11 ~ DC power source for pilot arc 12 ~
Object to be welded 13.26 ~ Center gas supply flow path 15 ~ Center shock gas supply flow path 15' ~ Center shock gas supply bypass path 17.17' ~ Gas pulp 24 ~ Pilot arc patent applicant Toa Seine Co., Ltd. No. Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] igniting a main plasma arc between the non-consumable electrode and the workpiece through a plasma gas flow generated by a pilot arc generated between the non-consumable electrode and the restrained nozzle electrode;
In plasma arc welding, which is performed without forming a keyhole in the workpiece, when the main plasma arc is ignited, an impulse-like center shock gas is added to the center gas to instantly increase the flow rate of the center gas. A method for igniting the main plasma arc in non-keyhole plasma arc welding.