JP2011177741A - Plasma welding method, plasma torch assembled body, and plasma welding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma welding method and device which are highly efficient and excellent in operability, by which occurrence of arc turbulence caused by magnetic blow is prevented even in a method in which an electric current is supplied to a wire, and which have high stability. <P>SOLUTION: In the plasma welding, plasma arcs from a plurality of plasma torches (1a, 1b) are applied to the same position of a weld line symmetrically about the vertical line which is vertical to the weld line of the object (5) to be welded and by being inclined with respect to the vertical line, the plasma arcs are concentrated to the same position by magnetic pinching force which acts on the all plasm arcs commonly and shielding gas is spouted toward the object (5) to be welded from the surrounding of the outer periphery of each insert chip (1ac, 1bc) of the plurality of the plasma torches. A welding wire or build-up powder is fed by vertical descent. The multiple plasma torches (1a, 1b) are mounted on one shielding cover (4) to form one plasma torch assembled body, and the one plasma torch assembled body is used for the plasma welding. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a welding method and apparatus for performing welding by overlapping a plurality of arcs in plasma welding.

  There are various forms of plasma welding depending on the type of high heat processing such as welding, overlaying and cutting. In Patent Document 1, a wire is fed from the side just below the tip of the electrode rod, and a base material (material to be processed) below the tip of the electrode rod is plasma welded, hot wire plasma welded, plasma MIG welded or A method for plasma wire overlaying is described. Patent Document 2 discloses plasma MIG welding in which a wire is sent vertically from a central wire feed hole of an insert tip to a lower base material, and plasma is injected into a plasma hole in which the wire feed hole is opened to melt the wire tip. A torch is described. Patent Document 3 describes a hot-wire-type plasma welding method and a plasma wire build-up method in which a wire is fed from the side below a plasma nozzle of an insert chip in which an electrode rod is disposed at the center position. Patent Document 4 describes plasma MIG welding in which a wire as a consumable electrode is fed from the side of the plasma torch toward the pool formed by the plasma of the plasma torch in which an electrode rod is arranged at the center position of the insert tip. Has been. Patent Document 5 discloses that a bottomed cylindrical plasma electrode disposed above and in the center of a plasma injection nozzle of an insert tip is perpendicular to a lower base material through a bottom hole as a central hole and a nozzle plasma injection nozzle below the bottom hole. Describes a plasma MIG welding method in which a wire is fed and melted with plasma generated by a plasma electrode.

Japanese Examined Patent Publication No. 39-15267 JP 52-138038 A JP-A-53-31544 JP-T-2006-519103 JP 2008-229641 A.

  As shown to (a) of FIG. 9, when generating a plasma arc between the electrode rod of one plasma welding torch 1 and the base material 5 which is a welding object material, the plasma arc is stable, A circular molten pool 8 is formed immediately below the electrode rod. However, in the case of the welding method and the plasma torch disclosed in Patent Documents 1 to 4 using the welding wire 9, as shown in FIG. 9C, the electrode is formed in the plasma flow formed between the electrode rod and the base material 5. Since the wire 9 is fed and energized from the side between the rod / base material, a magnetic imbalance occurs due to the interaction between the magnetic flux generated by the wire current and the magnetic flux generated by the plasma current. That is, the plasma arc state differs between the upper side of the wire (insert chip side) and the lower side of the wire (base metal side), and the plasma above the wire is away from the wire as shown in FIG. The plasma on the lower side of the wire receives the arc in the direction approaching the wire. The solution material (wire droplets) on the base material 5 flows downstream in the welding direction y as shown in FIG. The plasma arc is unstable because the plasma action position on the base material fluctuates as the wire tip melts.

  In Patent Document 5, since the arc concentrates on the circumferential edge of the bottom hole of the bottomed cylindrical plasma electrode and the concentration point moves in the circumferential direction, the plasma is also shaken, and the circumference of the bottom hole in the plasma electrode Severe wear of the nozzle edge at the edge and insert tip and adhesion of the molten wire to the plasma electrode and plasma nozzle occur. Therefore, stable welding work for a long time cannot be maintained.

  In addition, as shown by arrows on FIGS. 9 (a) and 9 (b), the plasma arc has a force that blows from the tip hole to the base material. In the plasma welding method in which a wire is supplied and welding is performed, the droplets are blown outward, making it difficult to increase the height of the bead center. This is disadvantageous when it is desired to secure the throat thickness, particularly during lap fillet welding.

  The first object of the present invention is to provide a plasma welding method and apparatus with high arc stability, high efficiency and good workability, and even in a method of energizing a wire, arc turbulence due to magnetic blowing does not occur. A second object is to provide a plasma welding method and apparatus having high stability.

  (1) A plasma arc from a plurality of plasma torches (1a, 1b) is symmetrical with respect to a vertical line perpendicular to the welding line of the material to be welded (5) and is inclined with respect to the vertical line at the same position of the welding line. The plasma arc is concentrated at the same position by a magnetic pinch force that acts on all plasma arcs in common with each other, and a shielding gas is applied from around the outer periphery of each insert tip (1ac, 1bc) of the plurality of plasma torches to the object to be welded. A plasma welding method that ejects toward the material (5).

  For ease of understanding, reference numerals of corresponding elements in the examples shown in the drawings and described later are added in parentheses for reference. The same applies to the following.

  A plasma arc from a plurality of plasma torches (1a, 1b) is applied to the same position of the welding line symmetrically with respect to the vertical line perpendicular to the welding line of the material to be welded (5) and inclined with respect to the vertical line. As a result of the combined magnetic field formed between the plasma torch (1a, 1b) and the material to be welded (5) by each plasma arc, all the plasma arcs as shown by the dotted line in FIG. Circulating magnetic flux flows. Between the combined magnetic field and each arc current, a Lorentz force, that is, a force for converging the arc at the orbital center of the orbiting magnetic flux is generated, and the plasma arc (7a and 7b) of the plasma torch (1a and 1b) is shown in FIG. As shown in (b), it is strong near the surface of the material 5 to be welded, and is narrowed in a direction to bring the plasma arcs (7a, 7b) relatively close to each other. Therefore, if the welding direction is the y direction, the molten pool 8 converges in the x direction orthogonal to the welding direction y, that is, the width direction x of the weld bead, as shown in FIG. The width becomes narrower. If the welding direction is the x direction, which is the direction in which the plasma torches are arranged, conversely, the molten pool 8 spreads in the y direction orthogonal to the welding direction x, that is, the width direction y of the weld bead, and the bead width increases. However, at the time of welding in the x direction, which is the direction in which the plasma torches are arranged, the nozzle holes are angled so that the points where the plasma arcs 7a and 7b are in contact with the material to be welded 5 do not overlap as shown in FIG. If the insert tip is used, the heat source becomes long and thin with respect to the weld line, and an ideal heat source for high-speed welding can be obtained.

  A mode of hot wire welding in which a welding wire (9) is fed to an intermediate point between plasma arcs (7a, 7b) of a plasma torch, and a current is passed between the material to be welded (5) and the welding wire (9). Then, the lines of magnetic force formed by the plasma arcs (7a, 7b) and the welding wire (9) are as shown in FIG. At this time, in the vicinity of the wire, the directions of the magnetic lines of force alternate and cancel each other. Therefore, unlike the conventional method in which the wire is supplied from the side, no magnetic imbalance occurs. In addition, since the plasma torches are arranged at an equiangular pitch with the wire supply portion as the central axis, that is, the torches are arranged symmetrically, the directivity stability of the plasma arc is high. This means that even when the wire is not supplied or when the powder is supplied, the magnetic field lines between the arcs cancel each other out at the upper center, resulting in a similar magnetic field, and the directional stability of the plasma arc is high.

  Since each arc converges in the vicinity of the material to be welded, the current is added in the same direction, and a combined magnetic flux between the arcs is generated. Since this magnetic flux can obtain a stronger magnetic pinch effect than in the case of a single arc, the heat convergence effect that is characteristic of plasma welding is further enhanced.

  Further, in the conventional method of supplying the wire from the side, a force acts in the direction in which the wire droplet is pushed out of the bead by the arc blowing ((a) and (b) of FIG. 9) (FIG. 9). (C), (d)), in the case of the present invention, the spraying direction is toward the center of the bead (corresponding to 8) as shown in FIG. 3C. Then, the droplet flow tends to remain in the center of the bead. Therefore, compared with the conventional method, the height of the center of the bead can be increased by normal downward welding, and the throat thickness can be increased by fillet welding, which has an effect of obtaining a higher strength bead.

  According to the present invention, it is possible to obtain an improved arc stability by eliminating magnetic imbalance, high heat convergence by a strong magnetic pincher, and a good bead shape obtained by improving the wire insertion direction. Furthermore, it is possible to perform high-speed welding by expanding the mutual arc irradiation points to form an elongated heat source.

It is a top view which shows the outline | summary of the plasma welding apparatus of 1st Example of this invention. FIG. 2 is an enlarged cross-sectional view of a shield cover 4 shown in FIG. (A) shows the electromagnetic force acting on the plasma arcs 7a, 7b coming from the insert tips 1ac, 1bc of the plasma torches 1a, 1b shown in FIG. 1, and (b) shows the plasma arcs 7a, 7b converged by the electromagnetic forces. (C) shows the molten pool 8 formed by the plasma arcs 7a and 7b, respectively. It is a top view which shows the outline | summary of the plasma welding apparatus of 2nd Example of this invention. FIG. 5 is an enlarged cross-sectional view of the shield cover 4 shown in FIG. 4. It is a top view which shows the outline | summary of the plasma welding apparatus of 3rd Example of this invention. (A) is a front view showing the magnetic flux induced by the plasma arcs 7a, 7b coming out of the insert tips 1ac, 1bc of the plasma torches 1a, 1b shown in FIG. 6 and the magnetic flux induced by the current flowing through the welding wire 9, (b). Is a front view showing the resultant magnetic flux of the magnetic flux induced by the plasma arcs 7a and 7b, and (c) is a plan view of the molten pool 8 formed by the plasma arcs 7a and 7b. It is a top view which shows the outline | summary of the plasma overlay welding apparatus of 4th Example of this invention. (A) is a front view which shows the plasma arc shape of the plasma welding using one plasma torch, (b) is a top view which shows the direction of the force added by a molten pool shape and plasma spraying to it with an arrow. (C) is a front view showing the magnetic flux when supplying the welding wire 8 to the plasma arc 7a, (d) is a front view showing the fluctuation of the plasma arc by the magnetic flux, and (e) is a plan view showing the shape of the molten pool. It is. (A) is a longitudinal cross-sectional view which shows the outline | summary of the plasma welding of 5th Example of this invention, (b) is an enlarged plan view which shows the irradiation point of arc 7a, 7b shown to (a) with respect to the welding target material 5 , (C) is a transverse cross-sectional view of a welding beat obtained by welding with only one arc, for example, arc 7a only, and (d) is formed by the preceding arc 7a in the case of two arc welding shown in (a) and (b). It is a cross-sectional view which shows typically the bead formed of the bead and the trailing arc 7b.

  (2) The plasma welding method according to (1), wherein the welding wire (9) is further fed to an intermediate point between the plasma arcs of the plurality of plasma torches.

  (3) The plasma welding method according to the above (1), wherein the overlaying powder is further fed to an intermediate point between the plasma arcs of the plurality of plasma torches.

  (4) The plasma according to any one of (1) to (3), wherein a current that is positive on the welding target material side and negative on the electrode side is passed between the welding target material and an electrode of each plasma torch. Welding method.

  (5) A current that is positive on the welding target material side and a negative electrode side is passed between the welding target material and the electrode of each plasma torch, and the welding target material side is between the welding target material and the welding wire. The plasma welding method according to (2), wherein the positive and welding wire side conducts a negative current.

(6) A plurality of plasma torches (1a, 1b) which are inclined with respect to a vertical line perpendicular to the weld line of the material to be welded (5) and are arranged symmetrically with respect to the weld line and symmetrically with respect to the vertical line;
An opening into which each tip of the plurality of plasma torches is inserted, and a shield cover (4) having a gas flow path for guiding shield gas around the outer periphery of each inserted insert tip (1ac, 1bc);
A plasma comprising a support member (2, 3) for holding the plurality of plasma torches or the shield cover in order to position the plurality of plasma torches (1a, 1b) as a unit with respect to the material to be welded. Torch assembly.

  (7) The plasma torch assembly according to (6), further comprising a wire guide (10) for guiding the welding wire (9) to an intermediate point between plasma arcs of the plurality of plasma torches.

  (8) The plasma torch assembly according to the above (6), further comprising a powder guide (14) for guiding the overlaying powder to an intermediate point between the plasma arcs of the insert tips of the plurality of plasma torches.

  (9) The plasma torch assembly according to any one of (6) to (8) above; and between the welding target material and the electrode of each plasma torch, the welding target material side is positive and the electrode side is negative. A plasma welding power source (6a, 6b) for supplying a current of

  (10) The plasma torch assembly according to the above (7); a plasma welding power source (6a, 6a, 6b) between which the welding target material and the electrode of each plasma torch are energized with a positive current on the welding target material side and a negative current on the electrode side 6b); and a hot wire power source (12) for supplying a current that is positive on the welding target material side and negative on the welding wire side between the welding target material and the welding wire.

  Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

-1st Example-
FIG. 1 shows a plasma welding apparatus according to the first embodiment, and FIG. 2 shows a cross section of a shield cover 4 part in FIG. In this embodiment, two plasma torches 1a and 1b are supported by the assembly arm 2 at their torch holders 1ah and 1bh. The upper end surface of one shield cover 4 common to both torches 1a and 1b has a pair of openings into which the tip portions of both torches 1a and 1b are inserted. It intersects on the end face side, and forms an approximately 8-shaped opening on the lower end face. The pair of holes are symmetric with respect to the vertical line z of the welding target material 5 (also perpendicular to the welding line), and the center lines of the holes are inclined so as to intersect at the same position on the vertical line z. is doing. That is, the plasma torches 1 a and 1 b are inclined with respect to the vertical line z perpendicular to the welding line of the welding target material 5, aiming at the welding line, and symmetrically arranged with respect to the vertical line z. It is supported as a thing. Further, the shield cover 4 is fixed to the vertical arm 3 fixed to the assembly arm 2, and the plasma torches 1a and 1b are also supported as a set by this. The distance from the tip of the torch to the base material is suitably 3 to 10 mm. As shown in FIG. 2, the shield gas flow path ends of the torches 1a and 1b inserted into the holes are continuous with the holes in the shield cover 4, thereby being fed into the torches 1a and 1b from the outside. The shield gas is ejected from each hole toward the material to be welded 5 along the outer periphery of the insert tips 1ac and 1bc of the torches 1a and 1b. The distance from the tip of the torch (lower end) to the weld line of the material to be welded 5 is suitably 3 to 10 mm.

  In this embodiment, the pair of plasma torches 1a and 1b, the assembly arm 2 that supports them, and the shield cover 4 and the vertical arm 3 common to both torches form a plasma torch assembly.

  As shown in FIG. 1, an arc is generated between the electrodes of the plasma torches 1 a and 1 b and the welding target material 5 by plasma power sources 6 a and 6 b that flow a plasma arc current that is negative on the electrode side and positive on the base material side. Then, a plasma arc current flows between each electrode and the welding object material 5, and 1 pool 2 arc welding is implement | achieved. As shown in FIG. 3 (a), each arc current flowing between the electrodes in the insert tips 1ac and 1bc of the plasma torches 1a and 1b and the material to be welded 5 is combined with the magnetic flux induced by each arc current. A pinch force expressed by Fleming's left-hand rule acts between the magnetic fluxes, and as shown in FIGS. 3B and 3C, the plasma arcs 7a and 7b are narrowed in the torch alignment direction x. In addition, the heat convergence effect (energy density) on the material to be welded 5 is high, and the stability of the plasma with no fluctuation of the action position is high.

  When the welding direction is the y direction shown in FIG. 3, the bead width is narrow because the plasma arc drawing direction by the pinch force is the x direction perpendicular to the welding direction y. However, if the welding direction is the x direction shown in FIG. 3, the bead width is widened because the plasma arc drawing direction by the pinch force is the y direction perpendicular to the welding direction x.

-Second Example-
FIG. 4 shows a plasma welding apparatus according to the second embodiment, and FIG. 5 shows a cross section of the shield cover 4 part in FIG. In this embodiment, the shield cover 4 has a vertical central hole in the middle of a pair of holes into which the plasma torches 1a and 1b are inserted, and a wire guide 10 for guiding the welding wire 9 is provided in the central hole. Has been inserted. The wire supply unit 11 includes a conduit liner and a wire cover insertion unit. Other configurations are the same as those of the first embodiment.

  When an arc is generated at the electrodes by the plasma power sources 6a and 6b that flow a plasma arc current that is negative on the electrode side and positive on the base material side between the electrodes in the plasma torches 1a and 1b and the material to be welded 5, the plasma arc current is generated. 1 pool 2 arc welding is realized by flowing between each electrode and the material 5 to be welded. The welding wire 9 is fed to the plasma arcs 7a and 7b, and the electrodes and the nozzles of the insert tips 1ac and 1bc are positioned symmetrically with respect to the welding wire 9, so that the plasma is stabilized with respect to the welding wire 9. That is, a pinch force expressed by Fleming's left-hand rule acts on each arc current flowing between each electrode and the material to be welded 5 between the combined magnetic fluxes induced by each of the arc currents. Is balanced and plasma stability is high. That is, no arc wobbling due to magnetic blowing occurs. The pinch force is strong, the heat convergence effect (energy density) on the material to be welded 5 is high, and the working position does not fluctuate. In addition, the welding wire 9 enters from the upper ends of the plasma arcs 7a and 7b and receives heat from the arc until it reaches the molten pool 8, which acts as an effective preheating effect and increases the welding efficiency of the wire. High speed welding and high efficiency welding are possible. In the case of the conventional wire feeding from the side (FIG. 9 (c)), the wire 9 enters almost at right angles to the plasma arc, so that it melts into the molten pool at a short distance from the plasma arc. There is almost no preheating effect of the wire 9. For this reason, the welding efficiency is low and the welding speed is also slow.

  In addition, according to the second embodiment, since the wire 9 is inserted vertically from the center, there is no insertion direction of the wire, and control for rotating the torch is not necessary even in curve welding. Conventionally, since the wire is inserted from the direction of travel of the torch, a device for controlling the rotation of the torch or the wire relative to the curve is necessary during curve welding.

-Third Example-
FIG. 6 shows a plasma welding apparatus according to the third embodiment. In this embodiment, the shield cover 4 has a vertical central hole between a pair of holes into which the plasma torches 1a and 1b are inserted, and a wire guide 10 for guiding the welding wire 9 is provided in the central hole. Has been inserted. The wire supply unit 11 includes a conduit liner, a wire energization unit, and a wire cover insertion unit. The configuration up to this point is the same as that of the second embodiment, but in the third embodiment, a hot wire power supply that further flows a negative current on the wire side and a positive current on the base material side between the welding wire 9 and the material to be welded 5. 12 is provided. The power source 12 energizes the wire 9 to generate residual heat and facilitate melting of the wire. Other configurations are the same as those of the first embodiment.

  The hot wire power supply 12 energizes the welding wire 9 through the wire supply unit 11, heats the wire 9 with Joule heat, joins with the plasma arcs of the plasma torches 1 a and 1 b with the plasma arcs 7 a and 7 b, and the welding target material 5 Flow into. At this time, since the Joule heat of the hot wire current is maximized (concentrated) in the plasma region, the welding heat input is large, the welding amount is high, the efficiency is high, and high-speed welding is possible. In addition, since the hot wire current and the plasma arc current are symmetrical and coaxial, the magnetic balance is achieved, and no arc wobbling due to magnetic blowing occurs. Other functions and operational effects are the same as in the second embodiment.

-Fourth embodiment-
FIG. 8 shows a plasma welding apparatus according to the fourth embodiment. In this embodiment, the shield cover 4 has a vertical central hole in the middle of a pair of holes into which the plasma torches 1a and 1b are inserted. Is inserted. Powder is fed from the powder supply port 15 at the lower end of the powder guide 14 between the plasma arcs of the plasma torches 1a and 1b. Other structures are the same as those of the first embodiment. The powder in the powder tank 13 is fed into the powder guide 14 at a constant speed.

  The plasma power supplies 6a and 6b cause a plasma arc current to flow between the electrodes in the plasma torches 1a and 1b and the material to be welded 5 that is negative on the electrode side and positive on the base material side. Since the powder flow is fed vertically to the material 5 to be welded, the yield of the powder is better than the conventional example in which the powder is fed from the side to the plasma arc, and the powder is inserted into the insert tips 1ac, 1bc. In addition, since the powder passage of the powder guide can be thickened and the powder guide 14 is vertical and straight, it is possible to use cutting powder having poor feedability. Since symmetrical plasma arcs join and collide with each other directly above the welding target material 5, the downward plasma flow to the welding target material 5 becomes weak, so that low-dilution powder overlaying is possible. Other functions and operational effects are the same as in the first embodiment.

-Fifth embodiment-
FIG. 10A shows a plasma welding apparatus according to the fifth embodiment. In this embodiment, the insert tips 1ac and 1bc have a central hole centered on the extension line of the electrode. The position of the torch is such that when the arc is generated at the angle of the center hole of the insert tip described above, the distance between the irradiation points of the arc is wider than that of the first embodiment and becomes one pool. Other configurations are the same as those of the first embodiment.

  When a current is passed in the same manner as in the first embodiment, an arc is generated in which the arc irradiation points do not overlap as shown in FIG. At this time, when the welding direction is set to the X-axis direction, a molten pool that is longer in the weld line direction than a normal molten pool is obtained. In the conventional high-speed welding, the cooling is finished when the molten pool is raised behind the arc by the spraying of the arc and the surface tension, and the undercut is likely to occur. However, in this embodiment, it is heated by the rear arc 7b. Therefore, the molten pool also becomes longer, the pool can be flattened by gravity, and the cooling is completed thereafter, so that there is an effect of preventing the occurrence of undercut. Further, when compared with the conventional one-arc welding, since the current per one is small, the bead width can be narrowed, so the distortion of the welding object is small.

1a, 1b: Plasma torch 1ac, 1bc: Insert tip 2: Assembly arm 3: Vertical arm 4: Shield cover 5: Materials to be welded 6a, 6b: Plasma power sources 7a, 7b: Plasma arc 8: Molten pool 9: Welding wire 10: Wire guide 11: Wire supply unit 12: Hot wire power supply 13: Powder tank 14: Powder guide 15: Powder supply port

Claims (10)

  A plasma arc from a plurality of plasma torches is applied symmetrically to the vertical line perpendicular to the weld line of the material to be welded and tilted with respect to the vertical line and applied to the same position of the weld line to act on all plasma arcs in common. A plasma welding method in which a plasma arc is concentrated at the same position by a magnetic pinch force, and a shielding gas is ejected from the periphery of each insert tip of the plurality of plasma torches toward the welding target material.   The plasma welding method according to claim 1, further comprising feeding a welding wire to an intermediate point between plasma arcs of the plurality of plasma torches.   The plasma welding method according to claim 1, further comprising feeding a build-up powder to an intermediate point between plasma arcs of the plurality of plasma torches.   The plasma welding method according to any one of claims 1 to 3, wherein a current that is positive on the welding target material side and negative on the electrode side is passed between the welding target material and an electrode of each plasma torch.   Between the welding target material and the electrode of each plasma torch, a current that is positive on the welding target material side and negative on the electrode side is energized, and the welding target material side is positive and welded between the welding target material and the welding wire. The plasma welding method according to claim 2, wherein the wire side conducts a negative current. A plurality of plasma torches that are inclined with respect to a vertical line perpendicular to the welding line of the material to be welded and are arranged symmetrically with respect to the welding line and symmetrically with respect to the vertical line;
A shield cover having an opening into which each tip portion of the plurality of plasma torches is inserted, and a gas flow path for guiding a shield gas around the outer periphery of each inserted insert chip; and
A plasma torch assembly comprising: a support member that holds the plurality of plasma torches or the shield cover in order to position the plurality of plasma torches as one unit with respect to the material to be welded.   The plasma torch assembly according to claim 6, further comprising a wire guide for guiding a welding wire to an intermediate point between plasma arcs of the plurality of plasma torches.   The plasma torch assembly according to claim 6, further comprising: a powder guide for guiding the overlaying powder to an intermediate point between plasma arcs of the insert tips of the plurality of plasma torches.   The plasma torch assembly according to any one of claims 6 to 8, and plasma in which a current that is positive on the welding target material side and negative on the electrode side is passed between the welding target material and an electrode of each plasma torch. A plasma welding apparatus comprising: a welding power source.   The plasma torch assembly according to claim 7; a plasma welding power source in which a current to be welded is positive and a current to the electrode side is negative between the welding target material and an electrode of each plasma torch; and the welding target material And a welding wire power source for supplying a current that is positive on the welding target material side and negative on the welding wire side.

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