JPS61276769A - Ignition method for main plasma arc in non-key hole type plasma arc welding - Google Patents

Abstract

PURPOSE:To enable the use for a long period of a nonconsumable electrode without its readjustment by changing over a center gas from the previously flowed bigger flow to the ordinary one in case of igniting a main plasma arc. CONSTITUTION:A pilot arc is ignited by the DC power source 11 for pilot arc in a nonconsumable electrode 1 and constraining a 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 the 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 main plasma arc ignition, the center gas fed from the flow path 13 is changed from the bigger flow passed in advance to the ordinary one. The ignition of the main plasma arc is thus made easy by projecting the pilot arc from the tip of the constraining nozzle electrode 2. to the external part.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention provides 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. Regarding.

(b) In the conventional technology-transfer type plasma arc welding method, an inert gas such as argon gas is used as the center gas, and several liters of the gas is ejected per minute through a restrained nozzle electrode, thereby controlling the welding process. 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.St/min), and is used in a small current range. There is also a non-keyhole type plasma arc welding method, typified by microplasma arc welding, in which welding proceeds without making a keyhole in the workpiece.

When using non-keyhole plasma arc welding methods such as micro plasma arc welding, due to the limitations of the welding method, the flow rate of the center gas cannot be as large as in keyhole plasma arc welding methods. To,
The pilot arc is weak, and the stability of the pilot arc is often impaired due to the shape of the electrode, the condition of the electrode surface, the flow rate of the center gas, etc.

For example, if used continuously for several hours, the tip of a pure tungsten electrode will wear out due to impurities such as oxygen and nitrogen contained in the center gas, as well as the influence of metal vapor, and a recrystallized ring will appear on the tip of a tungsten electrode containing tungsten. The tip of the non-consumable electrode is deformed, such as the formation of K.
The pilot arc cannot protrude sufficiently from the tip of the restrained nozzle electrode to the outside, and even when the plasma torch approaches the workpiece, the non-consumable electrode and the workpiece are electrically bridged by the busy pilot arc. becomes impossible,
Even if the main plasma arc power is applied, the main plasma arc cannot be generated.

FIG. 5 shows a state in which a tungsten electrode containing tungsten is used as the non-consumable electrode 21 and used continuously for several hours. Eventually this electrode 2
1 and the inner wall of the restrained nozzle electrode 23 becomes the outer periphery of this grown ring, making it difficult to project the pilot arc 24 to the outside of the restrained nozzle electrode 23.

Note that FIG. 4 shows the non-consumable electrode 21 in its initial state of use, with reference numeral 25 representing a shielding gas nozzle, 26 representing a center gas supply passage, and 27 representing a shielding gas supply passage.

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 the non-consumable electrode out of the torch and reshape it with a grinder or sandpaper.The other method is to momentarily increase the pilot arc current when a plasma arc occurs, and remove the ionized electrode from the pilot arc. This is a method of increasing the amount of hot gas.

(c) Problems to be solved by the invention However, among the conventional methods described above, reshaping the electrode is a relatively easy task when the torch is used manually, but If it is installed in the machine,
Setup time for electrode replacement and positioning becomes a problem.
There was a drawback that the work efficiency as an automatic machine decreased.

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.

The present invention improves the starting characteristics of the main plasma arc caused by the instability of the pilot arc, which is a drawback of the above-mentioned non-life-Hall type plasma arc welding torch, and reshapes the non-consumable electrode once set in the torch. 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 that can be used for a long time without any problems.

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 type plasma arc welding, in which the main plasma arc is ignited between objects and a keyhole is formed in the workpiece, the center gas is The flow rate is changed from a pre-prepared one with a higher flow rate to a normal one.

(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 a gap between the non-consumable electrode and the workpiece. However, in the present invention, when igniting the main plasma arc, that is, when applying the main plasma arc power, In order to switch the center gas from a previously flowed one with a larger flow rate to a normal one, the main plasma arc is ignited with the center gas flow rate larger than normal. Therefore, even with a non-consumable electrode whose tip has been deformed due to continuous use, the pilot arc can be projected 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 70 chart when the main plasma arc ignition method of the present invention is implemented in micro plasma arc welding.
, which shows the relationship between shielding gas, pilot arc current, and main plasma arc current.

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, with the center gas ■ being supplied and the pilot arc current flowing to ignite the pilot arc, shielding gas is supplied and welding is started at point A, and the preflow of this shielding gas (time 1+ ) and then center gas at point P...
At the same time, the welding power is turned on, the main plasma arc current flows, and the main plasma arc is ignited. Then, the welding power source is stopped at point B. 1. indicates the aftershield time.

Center gas ■ Uses the same type of inert gas such as Ar as center gas I, and the relationship between the two is that while center gas I has a flow rate in normal micro plasma arc welding, center gas ■ It is assumed that the flow rate is large. However, if the flow rate of the center gas H is too large, the pilot arc will be extinguished, and if the flow rate is as small as the flow rate of the center gas I, the effect of the present invention cannot be achieved, so it must be determined appropriately.

Moreover, the timing of switching between the center gas and I is performed near point P. The one shown in Figure 1 closes the pulp for center gas ■ in the gas supply path at point P and opens the pulp for center gas I, and the welding power is turned on and the gas is switched at the same time. , since there is some distance from the gas pulp position in the gas supply route to the torch tip,
The main plasma arc is ignited under the influence of the center gas (2), which has a larger flow rate. If the gas switching timing is too early relative to the turning on of the welding power source, the effect of the present invention will not be achieved at all, and if it is too late, there is a risk that a keyhole will be formed in the workpiece. In short, in the present invention, when the welding power source is turned on, the main plasma arc must be ignited under the influence of the center gas (b) whose flow rate is larger than usual.

FIG. 2 is a configuration and electrical connection diagram of a welding torch embodying the present invention. In the figure, l is a non-consumable electrode, 2# is a restraining nozzle electrode, 3 is a shielding gas nozzle, 4 is a molding material with electrical insulation, and 5 is a conductive metal for fixing the non-consumable electrode 1 to the torch body. collet chuck,
6 #'i A cap for tightening the collector chuck 5; 7 an electrically insulating electrode holder for setting the non-consumable electrode on the center axis of the restraining nozzle electrode; 8 a gas lens for shielding gas; 9 a cap for tightening the collector chuck 5; The O-ring and IO are connected to the non-consumable electrode 1 and 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 2. 13 is a center gas supply channel, and 14 is a shield gas supply channel. The welding torch shown in Fig. 2 is not different from conventional ones. Fig. 3 shows a center gas supply device used in combination with the torch shown in Fig. 2, and is filled with an inert gas such as argon. From the gas supply source set at an appropriate pressure and flow rate, gas is received from the gas inlet end 20 of the center gas supply channel 13', and from the start of welding to point P after tl.
The center gas ■, which is provided in a bypass shape in the center gas I supply flow path 13', is supplied to the torch through the center gas supply flow path 15, and the center gas ■, which has a larger flow rate than the center gas ■, is supplied to the torch near the point P. The gas pulp 171 of the passage 15 is closed to stop the supply of the center gas ■, and the gas pulp 17 of the center gas ■ supply passage 13' is closed.
is opened to supply center gas I to the torch. These gas pulps 17, 17' are controlled by electrical signals output from a control device built into the welding power source. 16 and 16' indicate flow rate regulators.

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 2 below.

Table 1 Setting conditions (1) Electrode・・・・・・・・・・・・・・・-Y
WT h -2φ2.4m (2) Steady pilot current・
・・7A (4) Center gas 1 ・Ar O-5t/
-(5) Center gust”...Ar 1.01/
m(6) Shield gas・・・・・・・・・A r +
7chi Ha 4t/m (7) Base material...
・・・・・・・・・Water-cooled copper plate (8) Distance between nozzle and base metal...3■ (9) Arc on/off time...Main arc load time 10 seconds Arc pause time 10 seconds ell) Judgment conditions・・・・・・・・・・・・・・・Make sure that the ignition of the main plasma arc never fails by repeating the arc on and off continuously. Note) The total time according to the setting conditions is the sum of the main arc load time. This is the sum of the total downtime.

Note) The above times are the average values of 5 times each, rounded to the nearest whole number.

Thus, 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 starting characteristics of the main plasma arc without reshaping, compared to the conventional method. This was confirmed.

(G) Effects of the Invention As described above, the present invention overcomes the drawbacks of non-keyhole type plasma arc welding torches (i.e., improves the starting characteristics of the main plasma arc caused by the instability of the keyhole type plasma arc welding torch), It is now possible to use the non-consumable electrode set in the welder for a long time without having to reshape it.This also improves the efficiency of welding work, especially when it is installed in a robot or automatic machine. It has a great effect.

[Brief explanation of the drawing]

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. FIGS. 4 and 5 are explanatory diagrams of the tip of the welding torch. l, 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 - Center gas supply channel 131 - Center gas supply channel 15 -
Center gas ■ Supply channel 17, 17' ~ Gas valve 24 ~ Pilot arc

Claims (1)

[Claims] The main plasma arc is ignited between the non-consumable electrode and the object to be welded through the plasma gas flow generated by the pilot arc generated between the non-consumable electrode and the restrained nozzle electrode, forming a keyhole in the object to be welded. A non-keyhole type plasma characterized in that when igniting the main plasma arc in plasma arc welding performed without a keyhole, the center gas is switched from a previously flowed one with a larger flow rate to a normal one. Main plasma arc ignition method in arc welding.