JP2711965B2 - Plasma arc welding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma arc welding machine suitable for welding a material having an oxide film having a high melting point, such as aluminum and its alloys.

2. Description of the Related Art Generally, a plasma arc welding machine for welding a steel sheet or the like applies a negative voltage to an electrode rod and applies a positive voltage to a workpiece to be welded, thereby forming a plasma between them. An arc is generated and the heat is used to weld the workpiece. However, since an oxide film having a high melting point is formed on the surface of aluminum, an aluminum alloy, a magnesium alloy, and the like, removing or cleaning the oxide film is an important factor for these weldings. FIG. 5 shows a conventional plasma arc welding machine of this type, which will be described with reference to FIG. The plasma arc torch 1 includes an electrode rod 2, a nozzle 3 surrounding the electrode rod, and a gas passage 4 formed by the electrode rod 2 and the nozzle 3. The main power supply 9 supplies AC power between the electrode rod 2 and the workpiece 8 having a high melting point oxide film formed on the surface of aluminum, aluminum alloy, magnesium alloy, etc., and supplies power of a desired frequency. An inverter power supply or the like that can be generated is used. The auxiliary power supply 10 applies a DC voltage between the electrode rod 2 and the nozzle 3 to make the electrode rod 2 negative and the nozzle 3 positive, and superimposes high-frequency power to generate a pilot arc 2 between the electrode rod 2 and the nozzle 3. To make it happen. First, an argon gas is supplied as a start gas from a gas supply source (not shown) to the gas passage 4, and then the auxiliary power source 10 is operated so that the electrode rod 2 is negative and the nozzle 3 is positive between the electrode rod 2 and the nozzle 3. Is applied, a pilot arc is generated between the electrode rod 2 and the nozzle 3. Next, when the main power supply 9 applies an AC voltage between the electrode rod 2 and the work 8, an arc column A is generated between the plasma arc torch 1 and the work 8, as shown in FIG. Currents I ₁ and I ₂ alternately flow. . The arc column A, in cooperation with argon gas, the electrode rod 2 is welded object 8 is negative duration positive, i.e. removing the oxide film of the weld bead around the object to be welded 8 during a period current I ₂ flows, That is, cleaning is performed and desired welding is performed. Further, a reverse-polarity plasma jet generator as disclosed in Japanese Patent Publication No. 49-24781 has already been disclosed. This will be described with reference to FIG. 6. The feature of this device is that the first nozzle 3 is provided between the first nozzle 3 and the workpiece 8.
Is connected to the main power supply 9 via the switch S1 with the polarity that the workpiece 8 is negative and the workpiece 8 is negative.
The auxiliary power source 10 is connected via the switch S2 with the polarity that the electrode rod 2 is negative and the space between the first nozzles 3 is positive. Reference numeral 5 denotes a second nozzle which is provided outside the first nozzle 3 so as to surround the first nozzle 3 and forms a second gas passage 6 between the first nozzle 3 and the first nozzle 3. This is a sild member through which an inert gas for flowing is applied. this is,
First, the switch S2 is closed with the inert gas flowing in the first gas passage 4, and a pilot arc is generated between the electrode rod 2 and the first nozzle 3 by the auxiliary power supply 10. Next, the switch S1 is closed with the inert gas flowing in the second gas passage 6, and an arc column A is generated between the first nozzle 3 and the workpiece 8 by the main power supply 9. The arc column A is a plasma jet of the opposite polarity with the tip of the first nozzle 3 as the anode point.

However, such a first conventional welding method, that is, temporarily supplying power to make a positive voltage on an electrode rod to an object to be welded in order to clean an oxide film. In the method having a period, there is a problem that the electrode rod is more worn out than the method of supplying electric power to the workpiece to make the electrode rod a negative voltage. In addition, in the second conventional welding method, although the electrode rods are less worn, a plasma jet of the opposite polarity is generated at both the machining and the cleaning with the tip of the first nozzle 3 as the anode point. , The welding penetration is shallow, and it is essentially the same as other conventional plasma welding methods of opposite polarity, and it is difficult to obtain appropriate conditions that satisfy both cleaning performance and welding penetration. There are various restrictions on the above, and there is a problem that it is difficult to implement. In the present invention, the conditions for cleaning the oxide film and the welding conditions can be set separately so that both cleaning and welding can be performed under favorable conditions, and there is no wear of the electrode rods during cleaning, and aluminum, steel plate, etc. An object of the present invention is to provide a plasma arc welding machine capable of performing both-polarity welding.

SUMMARY OF THE INVENTION An electrode rod of a plasma arc torch having one or more nozzles surrounding an electrode rod is supplied with a voltage that makes the electrode rod negative and the work to be welded intermittently, and a current is intermittently applied between them. In a plasma arc welding machine having a main power supply means capable of supplying a current, a voltage is applied between the nozzle and the work to apply a voltage between the nozzle and the work while the main power supply is off while the nozzle is positive and the work is negative. And a cleaning power supply unit for supplying an electric power for cleaning the oxide film of the workpiece with an arc generated between the nozzle and the workpiece.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. In these figures, FIG.
The same symbols as those shown in FIG. 6 and FIG. 6 indicate corresponding members. In FIG. 1, a power supply device 11 cooperates with switching switches 12 and 13 to operate a switch 13.
When the switch 12 is open and the switch 12 is closed, it functions as a main power supply means for supplying a current between the electrode rod 2 and the work 6, and when the switch 12 is open and the switch 13 is closed, the nozzle 3 and the work 6 are connected. It functions as a cleaning power supply unit for supplying a current to the power supply. The power supply device 11 is a power supply device having a normal circuit configuration, and includes a commercial AC power supply 11A, a rectifier 11B, a smoothing circuit 11C, a MOSFET capable of switching at a frequency higher than the commercial frequency, or an IGBT.
Switching semiconductor circuit 1 composed of semiconductor elements such as
1D, a transformer 11E having a primary winding connected to the switching semiconductor circuit 11D and a secondary winding of a center tap,
Inductor 11G for sustaining rectifier circuit 11F a diode D ₁ to D _4, and the plasma arc column A
Etc. Here, the switching semiconductor circuit 11D
And the transformer 11E constitute a high-frequency inverter circuit, and the switches 12 and 13 are composed of semiconductor elements such as transistors which can be operated by electric signals, and perform the switching operation at a frequency considerably lower than the switching frequency of the normal switching semiconductor circuit 11D. Then, switching between the generation of the plasma arc column A and the generation of the cleaning arc is performed. Although not particularly shown here, the nozzle 3 is a liquid-cooled nozzle that is water-cooled as in the prior art or even more.
This high cooling capacity enables the present invention. Accordingly, although not particularly described in the following embodiments, it is assumed that the nozzle is a liquid-cooled nozzle. Next, the operation of this apparatus will be described. First, the gas passage 4 of the plasma arc torch 1
A plasma gas is caused to flow, and the pilot arc power supply means 10 is operated to generate a pilot arc between the tip of the electrode rod 2 and the nozzle 3 as in the conventional apparatus.
Next, argon gas is caused to flow through the shield member 7 surrounding the torch 3 to cover the welding surface of the workpiece 8, the power supply device 11 is operated, and only the switch 13 is closed. Accordingly, a closed circuit of the switch 13 → nozzle 3 → welded object 8 → inductor 11G → secondary winding → rectifier circuit 11F of the transformer 11E diode D ₁ or D ₃ → switch 13 is formed, the from the nozzle 3 A current I ₂ flows through the weld 8. In other words, a cleaning arc column (indicated by a dotted line) having a negative polarity is formed between the nozzle 3 and the workpiece 8 using the workpiece 8 as a cathode and the nozzle 3 as an anode. In this period, nozzle 3
Oxide film on the welding surface is removed by the cleaning arc column of negative polarity generated between the welding surface and the welding object 8 in combination with the air shielding action of the argon gas from the welding surface. The cleaning arc column during this period is the same as the conventional one.
Also contributes to welding. Therefore, since the electrode rod 2 is not involved in the cleaning action, the electrode rod 2 is not worn by the cleaning action during this period. As described above, since the nozzle 3 is water-cooled as in the conventional case or more, the wear of the nozzle 3 is extremely small even by the heat of the cleaning arc column. Next, the power supply device 1
The switch 13 is opened while the switch 1 is operated, and the switch 1 is opened.
Close 2. Accordingly, the cleaning arc column generated between the nozzle 3 and the workpiece 8 is extinguished, and the switch 1 is turned off.
2 → Diode D ₂ or D _{4 of} rectifier circuit 11F → Secondary winding of transformer 11E → Inductor 11G → Workpiece 8 →
A closed circuit from the electrode rod 2 to the switch 12 is formed, and a current I ₁ flows from the workpiece 8 to the electrode rod 2. That is, electrode rod 2
Is formed between the electrode rod 2 and the workpiece 8 with the positive pole as the cathode and the workpiece 8 as the anode. During this period, only the normal welding by the heat of the arc column A of the positive polarity is performed, and the electrode rod 2 is not worn away by the cleaning action. As described above, in this embodiment, by alternately switching the switches 12 and 13, the electrode rod 2
A positive and negative plasma arc as shown in FIG. 2 can be generated alternately between the plasma arc torch 1 and the workpiece 8 without having the positive polarity. In this embodiment, the switching semiconductor circuit 11D is of a pulse width control type suitable for controlling the value of the arc current,
Negative plasma arc current I during cleaning
During the _second occurrence, the switching semiconductor circuit 11D is controlled so that the current value is larger than the positive polarity during the generation of the plasma arc current I ₁ during welding. Also, the switch 13
Is set to have an ON period shorter than the ON period of the switch 12. Such control negative plasma arc current I ₂ at the time of cleaning as compared to the plasma arc current I ₁ of the positive polarity, short energizing period, the greater the current waveform of the peak value. As can be understood from the above description, a positive plasma arc is generated between the electrode rod 2 and the workpiece 8 as one common electrode, and a negative plasma arc is separately formed between the nozzle and the nozzle. Therefore, the magnitude of the plasma arc current of the positive polarity and the magnitude of the plasma arc current of the negative polarity can be respectively set to any desired values, and therefore, welding can be performed under optimum conditions from a thin plate to a thick plate. Table 1 below shows specific examples of I-type butt welding of aluminum plates. Next, FIG. 3 shows an electric power applied between the second nozzle 5 of the plasma arc torch 1 and the work 8 to make the second nozzle 5 positive and the work 8 negative. An example is shown in which electric power is supplied alternately between the electrodes 8 such that the electrode rod 2 is negative and the workpiece 8 is positive. 11A and 11B are power supply devices of the polarity shown in the figure which share the power supply device 11 shown in the previous embodiment by switching the switches 12 and 13, but may be separate control type power supplies. In this embodiment, the switch 1
2 and 13 open and close alternately, and when the switch 12 is closed, a current flows from the workpiece 8 to the electrode rod 2 with the workpiece 8 as an anode by the power supply device 11A, and the electrode rod 2 and the workpiece 8 A positive plasma arc column A is formed therebetween.
Next, when the switch 12 is opened and the switch 13 is closed, a current flows from the second nozzle 5 to the work 8 by using the second nozzle 5 as an anode by the power supply device 11B, and the second nozzle 5 and the work A negative-polarity plasma arc for cleaning is formed between 8. Here, the auxiliary power source 10 is the electrode rod 2
And the second nozzle 5 are connected with the polarity shown. Therefore, also in this embodiment, by alternately switching the switches 12 and 13, the positive polarity between the plasma arc torch 1 and the workpiece 8 can be achieved without making the electrode rod 2 positive.
A negative-polarity plasma arc can be generated alternately. Next, FIG. 4 shows that the first nozzle 3 is inserted between the first nozzle 3 and the workpiece 8 of the plasma arc torch 1 and the workpiece 8 is connected.
An example is shown in which an electric power is supplied between the electrode rod 2 and the workpiece 8 alternately, and a power is supplied between the electrode rod 2 and the workpiece 8 such that the electrode rod 2 is negative and the workpiece 8 is positive. Also in this embodiment, the switches 12 and 13 are alternately opened and closed. When the switch 12 is closed, a current flows from the workpiece 8 to the electrode rod 2 with the workpiece 8 as an anode by the power supply device 11A, A plasma arc column A having a positive polarity is formed between the workpiece 8 and the workpiece 8. Then switch 1
2 and the switch 13 is closed, the power supply 11
B causes a current to flow from the first nozzle 3 to the workpiece 8 using the first nozzle 3 as an anode, thereby forming a negative-polarity plasma arc for cleaning between the first nozzle 3 and the workpiece 8. Therefore, also in this embodiment, the switches 12 and 1
By alternately switching the electrode poles 3, the optimum positive and negative plasma arcs are alternately generated between the plasma arc torch 1 and the workpiece 8 without making the electrode rod 2 positive. Can be. Further, an advantage of the present invention is that when welding a steel plate or the like, it is only necessary to turn off the power supply means for supplying a current between the nozzle and the work to be welded. Since it is only necessary to maintain the state, a single plasma arc welding machine can weld both polarities such as aluminum and steel plates. In the above embodiments, ordinary nozzles are often made of copper or its alloy. However, when the nozzle is made of copper or its alloy, a narrow melting hole is made of tungsten material or tungsten composite material with a high melting point. If a ring or cylinder is provided and a plasma arc for cleaning is formed between the ring and the workpiece 8, wear of the nozzle can be further reduced.

As described above, according to the present invention, (1) a workpiece to be welded is used as one of the common electrodes to generate a positive plasma ark between the electrode and the electrode rod; Since the negative-polarity plasma arc can be generated under different conditions, the magnitudes of the positive-polarity plasma arc current and the negative-polarity plasm-mark current can be set to any desired values. Welding can be performed up to the plate under the optimum conditions suitable for the workpiece. (2) Positive and negative plasma arcs can be generated alternately between the plasma arc torch and the workpiece without making the electrode rod positive, so there is no electrode rod wear due to cleaning and aluminum Can be welded well. (3) A steel plate or the like can be welded only by turning off a power supply means for supplying a current between the nozzle and the workpiece, and bipolar welding of aluminum, a steel plate, and the like can be performed with a single plasma arc welding machine.

[Brief description of the drawings]

FIG. 1 is a view for explaining an embodiment of a plasma arc welding machine according to the present invention.

FIG. 2 is a diagram showing current waveforms for explaining an embodiment of the present invention.

FIG. 3 is a diagram for explaining another embodiment of the present invention.

FIG. 4 is a diagram for explaining still another embodiment of the present invention.

FIG. 5 is a view for explaining an example of a conventional plasma arc welding machine.

FIG. 6 is a view for explaining an example of another conventional plasma arc welding machine.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Plasma arc torch 2 ... Electrode rod 3,5 ... First and second nozzles 4,6 ... First and second gas flow paths 7 ... Shield member 8 ...・ Workpiece to be welded 10 ・ ・ ・ Auxiliary power supply 11 ・ ・ ・ Power supply device 12,13 ・ ・ ・ Switch

Claims (4)

(57) [Claims] 1. A plasma arc torch comprising an electrode rod and a nozzle surrounding the electrode rod and forming a gas flow path for flowing an inert gas between the electrode rod and a plasma arc torch. In the plasma arc welding machine for generating and welding the object to be welded, a current is supplied between the electrode rod and the object to be welded by applying a voltage that makes the electrode rod negative and the object to be welded positive. 1 current supply means, 2nd current supply means for supplying a current between the electrode rod and the nozzle by applying a voltage with the electrode rod being negative and the nozzle being positive, and the nozzle and the welding target And a third current supply means for supplying a current by applying a voltage between the objects to make the nozzle positive and the object to be welded negative. 2. A first nozzle surrounding an electrode rod, a first nozzle surrounding the electrode rod and forming a gas flow path for flowing an inert gas between the electrode rod, and a first nozzle surrounding the first nozzle. A plasma arc torch comprising a second nozzle forming a gas flow path through which an inert gas flows, and generating a plasma arc between the workpieces and welding the workpieces A first current supply means for supplying a current between the electrode rod and the workpiece by applying a voltage with the electrode rod being negative and the workpiece being positive; Negative electrode between the nozzles of
A second current supply means for supplying a current by applying a voltage to make the second nozzle positive, between the second nozzle and the workpiece, the second nozzle is positive, and the workpiece is And a third current supply means for supplying a current by applying a negative voltage. 3. A first nozzle which surrounds the electrode rod, forms a gas flow path surrounding the electrode rod and flows an inert gas between the electrode rod, and a first nozzle which surrounds the first nozzle A plasma arc torch comprising a second nozzle forming a gas flow path through which an inert gas flows, and generating a plasma arc between the workpieces and welding the workpieces A first current supply means for supplying a current between the electrode rod and the workpiece by applying a voltage with the electrode rod being negative and the workpiece being positive; Negative electrode between the nozzles of
A second current supply means for supplying a current by applying a voltage to make the second nozzle positive, between the first nozzle and the workpiece, the first nozzle is positive, and the workpiece is And a third current supply means for supplying a current by applying a negative voltage. 4. The plasma arc welding machine according to claim 1, wherein the first current supply means and the third current supply means perform a current supply operation alternately with each other. .