JP2013123740A - Welding method by two-electrode plasma torch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further suppress generation of undercut at a tail edge to be welded, and to further improve defective weld at both ends to be welded, in the welding by a two-electrode plasma torch.SOLUTION: In a welding method by a two-electrode plasma torch, by using the two-electrode plasma torch 30 provided with an insert chip 1 having electrode arrangement spaces 2a, 2b and two nozzles 3a, 3b which are respectively communicated therewith, a weld line is welded by generating plasma arc by respective electrodes 12a, 12b, while the alignment direction of the two nozzles is parallel to the weld line to travel-drive at least any one of the torch and objects 31a, 31b to be welded in the direction along the weld line. Rear end tabs 39a, 39b are provided, and the plasma arc of the preceding electrode is continued until the succeeding electrode finishes the welding at the rear end of the object to be welded and stops the plasma arc. Preheating is performed by the preceding electrode and the keyhole welding is performed by the succeeding electrode, or the keyhole welding is performed by the preceding electrode and the thermal conduction welding is performed by the succeeding electrode.

Description

  The present invention uses a two-electrode plasma torch having an insert tip having two electrode arrangement spaces and two nozzles communicating with each of the electrode arrangement spaces, and the arrangement direction of the two nozzles is determined as a weld line. A welding method using a two-electrode plasma torch in which at least one of the torch and the welding target material is driven to run in a direction along the welding line while generating a plasma arc at each electrode in each electrode arrangement space About.

The cross section of the plasma arc of the plasma arc welding by the conventional one-electrode torch is substantially circular. If the plate thickness is less than 3 mm, keyhole welding by plasma arc is impossible, so tanning welding (heat conduction type welding) is adopted. However, in keyhole welding and tanning welding, if speed is increased,
B) Undercut occurs,
B) Hot-cracking due to wide beads tends to occur during tanning welding. In high-speed welding, the current is a high current and a wide arc, so a wide, shallow bead shape is formed, and high temperature cracking is likely to occur during solidification.

  In conventional plasma arc welding with a one-electrode torch, if the speed of keyhole welding is increased with a plate thickness of 3 to 10 mm, the bead shape can be raised with a convex shape with a raised central portion, and an undercut with a lowered edge portion. Difficult to make. Although there is a one-pool speedup with two torches, torches must be tilted greatly to make a one-pool, and the arc is easily disturbed and unstable due to the attracting arc force and magnetic blown by tilting.

  Therefore, the present inventors have provided an insert tip capable of realizing high-speed welding without a hot crack and undercut with a stable arc, and a plasma torch using the insert tip (Patent Document 1). The welding method while forming the back wave includes keyhole welding and butt welding, but in the following description, for the sake of convenience, the back wave formation is represented by keyhole welding.

  The plasma torch of Patent Document 1 includes two electrode arrangement spaces, two nozzles that are distributed on the same diameter line, communicate with each electrode arrangement space, and open to face a welding line parallel to the diameter line. , And a plasma torch equipped with the chip and having each electrode inserted into each electrode arrangement space. According to this plasma torch, one pool 2 arc welding can be performed in which one arc is formed by two arcs. Since the cross section of the plasma arc is a heat source that is long and thin in the welding progress direction (y), the bead width (x direction) with respect to the amount of heat is kept narrow, and hot cracking does not occur even if the speed is increased. Moreover, by using one pool 2 arc, the front bead can be flattened by remelting by the subsequent plasma arc. Although a somewhat similar effect can be obtained by parallel welding using two plasma torches separated by a certain distance, the arc distance in the welding direction is widened, so a workpiece with a short welding length (base material: material to be welded) ) Cannot be welded in the same pass, requires two-pass welding, and high speed is difficult. Further, since the arc interval is wide, the succeeding arc must remelt the bead once solidified, and high heat input is required for the subsequent welding. According to the one-pool two-arc welding that uses an insert tip having two nozzles per tip presented in Patent Document 1, the nozzle interval is short, so these problems are solved.

  By the way, in two arc plasma arc welding with one insert tip, the heat load applied to the insert tip becomes large. In order to increase the speed, it is necessary to improve the cooling capacity of the insert tip.

  Therefore, the present inventors have provided an insert tip having a high cooling capacity that can perform welding without a high-temperature crack or undercut with a stable arc at a higher speed (Patent Document 2). This insert tip intersects two electrode arrangement spaces, two nozzles respectively communicating with each electrode arrangement space, and a plane in which the two nozzles are distributed at an intermediate point between the two nozzles. A V-shaped cooling water flow path is provided which is flat and the cooling water is turned back. Thereby, the cooling water smoothly turns back near the tip end surface (base material facing surface), the water or bubbles do not stay locally, and the chip cooling ability is high. A V-shaped cooling water flow path can be formed at low cost by making a hole obliquely with respect to the end surface of the chip and intersecting at the tip. Therefore, welding can be performed at a higher speed by increasing the welding current. Patent Document 2 further presented an insert chip in which a pair of nozzle members are detachably coupled to a chip base. According to this, when the nozzle part at the lower end of the nozzle member is deformed or damaged by high heat, the nozzle member can be replaced with a new one, and the chip base can be used as it is, so that the maintenance cost can be reduced.

  Further, in order to reduce the wear replacement cost of the insert tip, the present inventors have a cap portion with a nozzle open at the center, a trunk portion continuing to the cap portion, and a male screw portion continuing to the trunk portion, An insert chip is provided in which two nozzle members are detachably attached to the insert chip base body with a sealing material between male screw portions and an electrode arrangement space communicating with the nozzle inside (Patent Document 3). . When the nozzle portion at the lower end of the nozzle member is deformed or damaged by high heat, the nozzle member can be replaced with a new one, and the chip base can be used as it is, thereby reducing the maintenance cost.

  However, in the two-electrode plasma welding in which the arrangement direction of the two nozzles of the two-electrode plasma torch is parallel to the welding line and at least one of the torch and the welding target material is driven to run along the welding line, for example, FIG. As shown in FIG. 2A, a plasma arc 19b in which a leading electrode (electrode rod 12b inside the nozzle member 20b: FIG. 2) that acts on the welding line in advance in the welding direction y (direction in which the welding line extends) is generated. The plasma arc in which the upper surface of the abutting end face (weld line) between the welded pieces 31a and 31b, which are materials to be welded, is preheated to generate the trailing electrode (electrode rod 12a inside the nozzle member 20a: FIG. 2). In the mode in which the weld line is keyhole welded at 19a, the start end of the weld line is caused by the preheating time lag corresponding to the distance between the leading nozzle member 20b and the trailing nozzle member 20a and the nozzle angle in the welding direction y. Likely to cause the back-wave-forming shortage (left) due to insufficient heat input in. This shortage of heat input (insufficient formation of the back wave: remaining) increases as the welding speed increases, as shown in FIG.

  Further, for example, as shown in FIG. 18 (a), the welding line is keyhole welded by a plasma arc in which a leading electrode that acts on the welding line precedes in the welding direction y (the direction in which the welding line extends) is generated. In the aspect in which the welding line is heated (tanned) by the plasma arc in which the row electrode is generated, the molten metal in the molten pool generated by the preceding keyhole welding is sucked into the pool of the subsequent tanned plasma arc, and the keyhole is obtained. There is a flow of molten metal from the leading electrode side to the trailing electrode side between the welded portion and the butt welded portion A, and the welding ends in a reduced thickness state at the rear end portion of the weld line.

  That is, in welding with a two-electrode plasma torch, poor welding tends to occur at the front end (starting end of the weld line) and the rear end (end end of the weld line) of the weld piece. In continuous pipe making by welding, the welding start and end are cut off, so poor welding at the start and end is not a special problem, but in the case of short materials, cutting off the start and end makes the material yield worse. In addition to the excision work, the cost increases.

Therefore, the present inventors have two electrode arrangement spaces (2a, 2b) and two nozzles that communicate with each electrode arrangement space in order to improve poor welding at the end of the material to be welded. Using a two-electrode plasma torch with an insert tip, the arrangement direction of the two nozzles is parallel to the weld line, and at least one of the torch and the material to be welded is driven to run along the weld line, In a welding method using a two-electrode plasma torch in which a plasma arc is generated at each electrode in the electrode arrangement space to weld a welding line,
(1) One electrode of each electrode is set to generate a plasma arc that preheats the material to be welded as the preceding electrode, that is, the leading electrode in the direction in which the welding line extends, and the other wave is formed as the following electrode, that is, the trailing electrode. When the trailing electrode set to welding plasma arc and set to back wave forming welding is before the tip of the material to be welded, the plasma arc of back wave forming welding by the following electrode is started, and the leading electrode The plasma arc is started simultaneously with or before the generation of the plasma arc in the back wave forming welding, and the driving is started simultaneously with or after the start of the preceding or simultaneous plasma arc. The plasma arc is stopped when each pole is after the rear end of the material to be welded, and a welding method using a two-electrode plasma torch, and
(2) One electrode of each electrode is set to a plasma arc of back wave forming welding as the preceding electrode or leading electrode in the direction in which the welding line extends, and the other is tanned with the welding line as the following electrode or trailing electrode. The plasma arc of the back electrode forming welding with the leading electrode is started, and the plasma arc of the trailing electrode is activated at the same time as the plasma arc of the back electrode forming welding or at the tip of the material to be welded. Start, and start driving simultaneously with or after the start of the preceding or simultaneous plasma arc, and the plasma arc of the leading electrode and the trailing electrode is when each pole is after the rear end of the material to be welded A stopping method by a two-electrode plasma torch was proposed (Patent Document 4).

  According to the above (1), a preheating time lag corresponding to the distance between the leading electrode and the trailing electrode is generated ((b) in FIG. 19). In this cold steel plate section without preheating, the traveling drive speed is reduced. Therefore, it is possible to reduce the back wave formation failure at the tip of the material to be welded. After the preheating time lag interval, the steel plate at the trailing electrode is easily melted by the preheating effect of the leading electrode, so that the traveling drive speed can be increased and the productivity of welding can be increased. The rear end of the material to be welded has a low-speed, low-current crater treatment that shortens the molten pool that extends at the high-speed, high-current back behind the back wave forming arc (for example, keyhole arc) and flows backward. By pulling the molten metal back to the trailing back-arc arc side, the dent on the rear end surface can be corrected to be flat, and rear end defects can be reduced. By these, the yield of the raw material of the front-end | tip of a welding object material and a rear end can be improved.

  By starting a plasma arc (preheating) on the leading electrode (for preheating) when the leading electrode (for preheating) is at the tip of the material to be welded, a preheating time lag corresponding to the distance between the leading electrode and the trailing electrode (see FIG. 19). It is possible to avoid the back wave formation failure ((b) of FIG. 19) at the tip of the welding target material due to (a)). When the keyhole is formed by the trailing electrode, the steel plate at the trailing electrode is easily melted by the preheating effect of the leading station, and the traveling drive speed is increased, so that the productivity of welding can be increased. The rear end of the material to be welded has a low-speed, low-current crater treatment to shorten the molten pool that extends long behind the back-forming arc at a high speed, high current, and the molten metal that flows backward By pulling back to the wave arc side, the recess on the rear end surface can be corrected to be flat, and rear end defects can be reduced. By these, the yield of the raw material of the front-end | tip of a welding object material and a rear end can be improved.

  According to the above (2), a soft plasma arc with a low pilot gas flow rate and a low current at the trailing electrode from the front end to the rear end of the material to be welded. Only by arc melting, the welding surface is tanned, and surface beads with less undercut can be obtained even in high-speed welding. When the trailing electrode reaches the tip of the material to be welded, the plasma arc current of the leading electrode is switched to a higher value and the traveling drive speed is increased at the same time, thereby reducing the remainder of the back end welding (FIG. 19 (b)). Productivity can be increased.

JP2011-50982A Japanese Patent Application No. 2010-264955 Japanese Patent Application No. 2011-17342 Japanese Patent Application No. 2011-243218.

  However, although the yield of the material at the front and rear ends of the material to be welded can be significantly improved and the productivity of welding can be considerably increased, the suppression of the undercut at the rear end can be further effectively suppressed although there is improvement. It is hoped that. Therefore, the following knowledge was obtained by studying the occurrence of undercut at the rear end.

  During plasma welding by the two-electrode plasma torch 30 shown in FIG. 21A (steady state), a magnetic flux that circulates around the plasma arc is generated, but the molten pool indicated by the dotted line in the figure and its vicinity have a magnetic transformation temperature. Since the magnetic flux is difficult to pass at a high temperature of (about 730 ° C.) or higher, as shown in FIG. 21B, the circulating magnetic flux is far from the plasma frame behind the trailing pole (T). However, since the plasma arc current flows through both electrodes, the plasma flame (arc current) of the two electrodes attracts each other, and the plasma flame of the trailing electrode (T) is drawn in the welding progress direction y. As shown in FIG. 21C, the weld bead has no undercut.

  However, when the torch 30 becomes the rear end position of the material to be welded and the leading electrode (L) is in front of the rear end of the material to be welded as shown in FIG. The magnetic flux that circulates in the plasma frame of the trailing electrode is only generated by the plasma frame of the trailing electrode as shown in FIG. The plasma frame of the trailing electrode is not pulled by the plasma frame of the leading electrode, and swings behind the trailing electrode (T) by interaction with the circulating magnetic flux generated by the plasma frame of its own. The center of the molten pool is pushed up by the backward deflection of the plasma flame. As a result, the surface bead is elongated backward, so that the hot water (molten metal) on both sides of the bead is attracted to the center of the bead, and the bead cross-section has a deep undercut shape as shown in FIG. Become. This undercut can be problematic because it reduces the strength of the weld.

  A first object of the present invention is to further suppress the occurrence of an undercut at the tail end of a material to be welded in welding using a two-electrode plasma torch. In welding by a two-electrode plasma torch, a second object is to further improve the welding failure at both ends of the material to be welded.

(1) A two-electrode plasma torch (30) having an insert tip (1) having two electrode arrangement spaces (2a, 2b) and two nozzles (3a, 3b) communicating with each electrode arrangement space, respectively ), The arrangement direction of the two nozzles is made parallel to the weld line, and at least one of the torch and the welding target material (31a, 31b) is driven and driven in the direction along the weld line. In a welding method using a two-electrode plasma torch that generates a plasma arc at each electrode (12a, 12b) in space and welds a weld line,
A rear end tab (39a, 39b) is provided at the rear end of the welding target material (31a, 31b) in the welding direction, and the electrode that follows in the direction in which the weld line extends, i.e., the trailing electrode finishes welding at the rear end. The two-electrode plasma torch welding method (FIGS. 7, 9, 11, and 14) is characterized in that the preceding electrode, that is, the leading electrode plasma arc is continued in the direction in which the weld line extends until the plasma arc is stopped. , FIG. 16).

  In addition, in order to facilitate understanding, in parentheses, the correspondence of the examples shown in the drawings and described later, or the symbols or corresponding matters of corresponding elements are added for reference. The same applies to the following.

  Since the plasma electrode of the leading electrode is continued until the trailing electrode finishes welding at the rear end of the material to be welded and stops the plasma arc, the plasma frame and the leading electrode of the trailing electrode are continued until the welding of the material to be welded is completed. Since the plasma frame attracts the back and the rear end of the plasma frame of the trailing pole at the rear end does not cause rearward deflection (FIG. 20), the surface bead is not elongated rearward at the rear end, and the rear end is undercut. Disappears.

(A) is a block diagram which shows an example of the system configuration | structure of the welding apparatus which implements the welding method by the two-electrode plasma torch of this invention, and the aspect which drive | works the two-electrode plasma torch 30 with respect to the welding pieces 31a and 31b Indicates. (B) is a block diagram of a mode in which the welding pieces 31 a and 31 b are driven to travel with respect to the two-electrode plasma torch 30. FIG. 2 is an enlarged view of a longitudinal section yz of the two-electrode plasma torch 30 shown in FIG. FIG. 2 is an enlarged view of a longitudinal section xz of the two-electrode plasma torch 30 shown in FIG. 2A is a bottom view in which the tip of the two-electrode plasma torch 30 shown in FIG. 2 is looked up in the IVa-IVa line direction, FIG. 3B is a bottom view in which the tip is looked up in the IVb-IVb line direction shown in FIG. FIG. 4 is a cross-sectional view looking down in the direction of the IVc-IVc line shown in FIG. 2. FIG. 2A is a longitudinal sectional view showing the insert tip and inner cap 6 at the tip of the plasma torch shown in FIG. 2 removed from the torch body, and FIG. 2B shows only the chip base 1 and the inner cap 6 shown in FIG. (C) is a front view (outside view) showing nuts 25a and 25b shown in (a) removed from the nozzle members 20a and 20b, the nozzle member being extracted from the chip base 1, and the nuts 25a and 25b. (A1) is a longitudinal sectional view of the nozzle member 20a shown in FIG. 5 (c), and (a2) is a bottom view of the nozzle member 20a. (B1) is a longitudinal sectional view of a nozzle member 20c of the first modified embodiment that can be mounted on the chip substrate 1 by replacing one or both of the nozzle members 20a, 20b shown in FIG. 2, and (b2) is a bottom surface of the nozzle member 20c. FIG. (C1) is a longitudinal sectional view of a nozzle member 20d of the second modified embodiment that can be mounted on the chip substrate 1 by replacing one or both of the nozzle members 20a, 20b shown in FIG. 2, and (c2) is a bottom surface of the nozzle member 20d. FIG. 1 shows the relative position of the two-electrode plasma torch 30 with respect to the weld pieces 31a and 31b when the welding method of the first embodiment of the present invention using the welding apparatus shown in FIG. (2) shows the position where the succeeding electrode reaches the position where the preceding electrode which performs preheating at the start of welding is opposed to the position where the succeeding electrode reaches and is opposed. , (3) is the position of the steady welding state, (4) is the position immediately before the leading electrode reaches the rear end of the welding pieces 31a, 31b, and (5) is the trailing electrode is the rear end of the welding pieces 31a, 31b. (6) shows the position where the traveling drive is stopped after the welding is finished. Outline (basic pattern) of the welding current and plasma gas supply amount switching timing and stop timing and the stop timing of welding travel (speed) in the welding method of the first embodiment of the present invention ), And the timings T1 to T4 respectively correspond to the positions of the leading poles shown in (3) to (6) of FIG. 1 shows the relative position of the two-electrode plasma torch 30 with respect to the welding pieces 31a and 31b when the welding method of the second embodiment of the present invention using the welding apparatus shown in FIG. (2) is the position where the trailing electrode that performs keyhole welding has reached the tip of the welded pieces 31a, 31b, (3) The position in the steady welding state, (4) indicates the position where the trailing electrode reaches the rear end of the welded pieces 31a and 31b, and (5) indicates the position where the traveling drive is stopped after the welding is finished. In the welding method of the second embodiment of the present invention, it is a time chart showing an overview (basic pattern) of the stop timing of the welding current and plasma gas and the stop timing of welding travel (speed) for the leading electrode and the trailing electrode, Timings T1 to T3 correspond to the positions of the leading poles shown in (3) to (5) of FIG. 1 shows the relative position of the two-electrode plasma torch 30 with respect to the weld pieces 31a and 31b when the welding method of the third embodiment of the present invention using the welding apparatus shown in FIG. (2) is the position where the leading electrode for hole welding starts welding at the tips of the weld pieces 31a, 31b, (2) is the position where the trailing electrode for preheating reaches the tips of the weld pieces 31a, 31b, (3) (4) is the position immediately before the leading electrode reaches the rear end of the welding pieces 31a and 31b, and (5) is the position where the trailing electrode reaches just before the rear end of the welding pieces 31a and 31b. And (6) shows the position where the traveling drive is stopped after the welding is finished. Time showing an outline (basic pattern) of switching timing and stopping timing of welding current and plasma gas supply amount for leading and trailing electrodes and switching timing of welding traveling speed in the welding method of the third embodiment of the present invention In the chart, timings T1 to T4 correspond to the positions (3) to (6) shown in FIG. 1 shows the relative position of the two-electrode plasma torch 30 with respect to the welding pieces 31a and 31b when the welding method of the present invention using the welding apparatus and the front and rear end tabs shown in FIG. (B) shows the plane of the weld line (the surface of the weld piece) at the timing of starting welding. (C) shows the cross section of the weld line at the welding end timing. 1 shows the relative position of the two-electrode plasma torch 30 with respect to the welding pieces 31a and 31b when the welding method of the fourth embodiment of the present invention using the welding apparatus shown in FIG. (2) is the position where the leading electrode for hole welding starts welding at the tips of the weld pieces 31a, 31b, (2) is the position where the trailing electrode for preheating reaches the tips of the weld pieces 31a, 31b, (3) The position in the steady welding state, (4) indicates the position where the trailing electrode reaches the rear end of the welded pieces 31a and 31b, and (5) indicates the position where the traveling drive is stopped after the welding is finished. The outline (basic pattern) of the welding current and plasma gas supply / stop timing and supply amount switching timing and welding speed switching timing for the leading electrode and the trailing electrode in the welding method of the fourth embodiment of the present invention is shown. It is a time chart, and timings (1) to (4) correspond to timings (1) to (4) shown in FIG. 1 shows the relative position of the two-electrode plasma torch 30 with respect to the welding pieces 31a and 31b when the welding method of the fifth embodiment of the present invention using the welding apparatus shown in FIG. (2) is the position of the steady welding state, (3) is the succeeding electrode for performing keyhole welding, the welding electrode 31a, The position at which the rear end of 31b is reached, and (4) shows the position at which the traveling drive is stopped after the welding is finished. It is a time chart which shows the outline | summary (basic pattern) of the stop timing of the welding current and plasma gas with respect to a leading electrode and a trailing electrode, and the stop timing of welding travel in the welding method of 5th Example of this invention, Timing T1- T4 corresponds to the positions (1) to (4) shown in FIG. (A) is sectional drawing of the weld line site | part which shows the state in which the molten metal of the pool of a keyhole welding of a leading electrode is sucked in the pool of the tanning welding of a trailing electrode. (B) is a cross-sectional view of a weld line portion showing a state in which the welding pieces 31a and 31b and the two-electrode plasma torch 30 are inclined in the downward direction to the extent that suction is prevented. (A) is a case where welding is started simultaneously with the leading electrode at the tip of the welding pieces 31a and 31b because the trailing electrode that performs keyhole welding is separated from the leading electrode that performs preheating. It is sectional drawing which shows the preheating time lag (preheating insufficient area | region) of one front-end | tip part. (B) is a side view which shows the keyhole defect area | region (remaining) by a preheating time lag with a dotted line. (A) According to the present invention, a rear end tab is provided at the rear ends of the weld pieces 31a and 31b, and the plasma frame of the leading electrode is detached from the weld pieces while the plasma frame of the trailing electrode is in the weld piece region. A longitudinal sectional view showing the relative position of the two-electrode plasma torch 30 with respect to the welding pieces 31a and 31b, in which the plasma arc of the leading electrode is continued even in the region of the rear end tabs 39a and 39b, FIG. It is a cross-sectional view which shows the weld bead of a BB line cross section. (A) is a longitudinal sectional view showing the interaction of the plasma frame of the leading electrode and the trailing electrode while the two-electrode plasma torch 30 is in a steady welding region between the front and rear ends of the welding pieces 31a and 31b. (b) is a plan view showing the distribution of magnetic flux induced in the weld piece by the plasma frame of the leading electrode and the trailing electrode, and (c) is a transverse sectional view showing the weld bead of the CC line section in (a). is there. (A) is a case where the two-electrode plasma torch 30 reaches the rear end of the weld piece without the rear end tab, and the leading electrode is disengaged from the rear end, so that the plasma arc of the leading electrode is stopped. The longitudinal cross-sectional views of the welding pieces 31a and 31b and the two-electrode plasma torch 30 when the plasma electrode of the trailing electrode is deflected backward, (b) shows the magnetic flux induced in the welding piece by the plasma frame of the trailing electrode. The top view which shows distribution, (c) is a cross-sectional view which shows the weld bead where the undercut of the CC line cross section on (a) appeared.

  (2) The two electrodes according to (1), wherein when the rear end welding by the trailing electrode is finished, the plasma arc of the leading electrode and the trailing electrode is stopped, and then the traveling drive is stopped. A welding method using a plasma torch (FIGS. 7, 9, 11, 14, and 16).

  (3) The welding target material and the rear end tab are inclined to a posture in which the rear end is lower than the front end of the welding target material, and the traveling drive is set in a direction parallel to the welding line. A welding method using a two-electrode plasma torch (FIG. 18B). When the material to be welded is horizontal, the molten metal in the pool caused by the back surface forming plasma is sucked into the pool for tanning welding at the rear end of the material to be welded, and the bead at the rear end tends to be thinned. This becomes more prominent with thicker plates and lower viscosity metals. When the material to be welded is tilted as in this embodiment, gravity is applied to the molten metal in the pool in the welding direction to suppress the suction, reducing the thinning of the rear end bead and reducing the rear bead surface. Becomes flat.

  (4) The welding method by the two-electrode plasma torch according to the above (3), wherein the two-electrode plasma torch (30) is in a vertical posture with respect to the surface of the material to be welded. According to this, since the two-electrode plasma torch 30 is in a vertical posture with respect to the surfaces of the welding pieces 31a and 31b, it is easy to set or adjust the back electrode forming welding conditions for the leading electrode and the tanning welding conditions for the trailing electrode. It is.

(5) The leading electrode is set to generate a plasma arc for preheating the welding target material, and the trailing electrode is set to a plasma arc for back wave forming welding,
When the trailing electrode set for back wave forming welding is before the tip of the material to be welded (including the tip), the plasma arc of back wave forming welding by the following electrode is started,
The plasma electrode of the leading electrode is started at the same time or before the plasma arc generation of the back wave forming welding, and starts the traveling drive at the same time or after the start of the preceding or simultaneous plasma arc.
A welding method using the two-electrode plasma torch according to any one of the above (1) to (4) (FIGS. 7, 9, and 16).

  According to this, a preheating time lag corresponding to the distance between the leading electrode and the trailing electrode (remaining (a) and (b) in FIG. 19) is generated, but the cooled steel plate section without preheating has a speed of traveling driving. By making it low, it is possible to reduce the back wave formation failure at the tip of the material to be welded. After the preheating time lag interval, the steel plate at the trailing electrode is easily melted by the preheating effect of the leading electrode, so that the traveling drive speed can be increased and the productivity of welding can be increased.

  By starting a plasma arc (preheating) on the leading electrode (for preheating) when the leading electrode (for preheating) is at the tip of the material to be welded, a preheating time lag corresponding to the distance between the leading electrode and the trailing electrode (see FIG. 19). It is possible to avoid the back wave formation failure at the tip of the material to be welded due to (a)) (remaining in FIG. 19B). When the keyhole is formed by the trailing electrode, the steel plate at the trailing electrode is easily melted by the preheating effect of the leading electrode, and the productivity of welding can be increased by increasing the traveling drive speed.

  By applying a low-speed, low-current crater treatment to the rear end of the material to be welded (Fig. 7, Fig. 8, Table 1), a high-speed, high-current rear wave forming arc (for example, keyhole arc) is placed behind By shortening the molten pool that has been extended for a long time and pulling back the molten metal that has flowed backward to the trailing back-arc arc side, the recess on the rear end surface can be corrected to be flat, and rear end defects can be reduced. By these, the yield of the raw material of the front-end | tip of a welding object material and a rear end can be improved.

(6) The leading electrode is set to a plasma arc for back wave forming welding, and the trailing electrode is set to a plasma arc for tanning a welding line,
When the leading electrode set for back wave forming welding is before the tip of the material to be welded (including the tip), a plasma arc of back wave forming welding by the leading electrode is started,
The plasma electrode of the trailing electrode is activated at the same time as the activation of the plasma arc of the back wave forming welding or at the tip of the material to be welded, and at the same time as or after the activation of the preceding or simultaneous plasma arc. Start driving,
A welding method using the two-electrode plasma torch according to any one of the above (1) to (4) (FIGS. 11 and 14).

  According to this, a soft plasma arc with a low pilot gas flow rate at the trailing electrode and a low current from the front end to the rear end of the material to be welded, and only the surface melts in the vicinity immediately behind the preceding back-wave forming arc. By doing so, the weld surface is tanned, and a surface bead with less undercut is obtained even in high-speed welding. When the trailing electrode reaches the tip of the material to be welded, the plasma arc current of the leading electrode is switched to a higher value and the traveling drive speed is increased at the same time, thereby reducing the remainder of the back end welding (FIG. 19 (b)). Productivity can be increased.

  By applying low-speed, low-current crater processing to the rear end of the material to be welded (FIGS. 11, 12, and Table 3), the high-speed, high-current rear wave forming arc (for example, keyhole arc) is placed behind By shortening the melt pool that has been extended for a long time and pulling back the melt that has flowed backward to the trailing back wave arc side, the recess on the rear end surface can be corrected to be flat, and the rear end defects can be reduced. By these, the yield of the raw material of the front-end | tip of a welding object material and a rear end can be improved.

(7) When the trailing electrode is at the tip of the material to be welded, simultaneously start the plasma arc of the leading electrode and the trailing electrode, and simultaneously start the traveling drive at a low speed,
When the trailing electrode reaches the position where the leading electrode has started the plasma arc, the traveling drive is switched at a high speed and both or one of the plasma arc current and the plasma gas flow rate of the trailing electrode are switched high.
Immediately before the leading electrode reaches the rear end of the material to be welded, both or one of the plasma arc current and the plasma gas flow rate of the leading electrode is decreased, and when the trailing electrode reaches the trailing end, the traveling drive speed is decreased, and The two-electrode plasma according to (5), wherein both or one of the plasma arc current and plasma gas flow rate of the trailing electrode is lowered, and the plasma arc of the leading electrode and the trailing electrode is stopped after the crater treatment period by the trailing electrode. Welding method with torch (Fig. 7, Table 1).

  According to this, since the leading electrode (for preheating) that enters the welding target material region from the tip of the welding target material and the trailing electrode (for back wave forming welding) at the leading end of the welding target material simultaneously activate the plasma arc. Although a preheating time lag corresponding to the distance between the leading electrode and the trailing electrode is generated (remaining in (b) of FIG. 16), the traveling drive speed is low, so that the back-wave formation failure at the tip of the material to be welded is small. Since the traveling drive speed is increased after the preheating time lag section, the welding productivity is high. The rear end of the material to be welded is cratered at a low speed and with a low current or low plasma gas flow rate, so that the recess on the rear end surface is corrected to be flat, and there are few rear end defects. By these, the yield of the raw material of the front-end | tip of a welding object material and a rear end improves.

(8) When the leading electrode is at the tip of the material to be welded, the plasma drive (preheating) of the leading electrode is started and simultaneously the traveling drive is started at a low speed, and the trailing electrode reaches the tip of the material to be welded. Then, the plasma arc of the trailing electrode is activated,
The two electrodes according to (5), wherein when the keyhole is formed by the trailing electrode, the traveling drive is switched at a high speed and either or both of the plasma arc current and the plasma gas flow rate of the trailing electrode are switched to high. Welding method using plasma torch (FIGS. 9, 10, Table 2).

  According to this, since the leading electrode (for preheating) activates the plasma arc (preheating) when the leading electrode (for preheating) is at the tip of the material to be welded, a preheating time lag corresponding to the distance between the leading electrode and the trailing electrode. The back wave formation defect at the tip of the material to be welded due to ((b) of FIG. 16) does not occur. When a back wave (for example, a keyhole) is formed by the trailing electrode, the traveling drive speed is increased, so that the welding productivity is high.

(9) When the leading electrode is at the tip of the material to be welded, the plasma drive (back wave forming welding) of the leading electrode is started and simultaneously the traveling drive is started at a low speed. When it reaches the tip, it activates the plasma arc (tanning) of the trailing electrode,
When the trailing electrode reaches the tip of the material to be welded, the traveling drive is switched at high speed, and the plasma arc current and the plasma gas flow rate of the leading electrode are switched to high or both,
Immediately before the leading electrode reaches the rear end of the material to be welded, both or one of the plasma arc current and the plasma gas flow rate of the leading electrode is lowered to switch the traveling drive to a low speed and the plasma arc of the leading and trailing electrodes at the rear end. The welding method using the two-electrode plasma torch described in the above (6) (FIGS. 11, 12, and Table 3).

  According to this, the welding surface is tanned by the plasma of the trailing electrode from the front end to the rear end of the material to be welded, and a surface bead with less undercut is obtained even in high-speed welding. High welding productivity. When the trailing electrode reaches the tip of the material to be welded, the plasma arc current of the leading electrode is switched high and the traveling drive speed is increased at the same time, so that the welding productivity is high. The rear end of the material to be welded is cratered at a low speed and with a low current or low plasma gas flow rate, so that the recess on the rear end surface is corrected to be flat, and there are few rear end defects. By these, the yield of the raw material of the front-end | tip of a welding object material and a rear end improves.

  (10) A tip tab (38a, 38b) is provided at the tip of the welding target material (31a, 31b) in the welding direction, and the leading electrode and the trailing electrode are located before the tip of the welding target material (31a, 31b) ( The welding method using the two-electrode plasma torch according to any one of the above (1) to (4), wherein a plasma arc is simultaneously started in both electrodes when the electrode is in a position (including the tip) (FIGS. 13, 14, and 16) .

  According to this, since the plasma arc is started and stopped outside the front end and rear end of the material to be welded, poor welding does not occur at the front end and rear end. The yield of the material at the front and rear ends of the material to be welded is improved. Depending on the plate thickness and material, the current, plasma gas flow rate, and welding speed on the trailing back wave forming welding side are lowered at the leading and trailing edges, and the welding residue at the leading edge and the crater treatment at the trailing edge are performed.

  (11) The welding method using the two-electrode plasma torch according to the above (4), wherein the traveling drive is started when the plasma arc is simultaneously activated in both electrodes (FIGS. 14 and 16).

(12) The leading electrode is set to a plasma arc for back wave forming welding, and the trailing electrode is set to a plasma arc for tanning a welding line,
When the leading electrode set for back wave forming welding is before the tip of the material to be welded (including the tip), a plasma arc of back wave forming welding by the leading electrode is started,
The plasma electrode of the trailing electrode is activated at the same time as the activation of the plasma arc of the back wave forming welding or at the tip of the material to be welded, and at the same time as or after the activation of the preceding or simultaneous plasma arc. Start driving,
A welding method using the two-electrode plasma torch described in (10) above (FIGS. 14 and 15 and Table 4).

(13) The leading electrode is set to generate a plasma arc for preheating the welding target material, and the trailing electrode is set to a plasma arc for back wave forming welding,
When the trailing electrode set for back wave forming welding is before the tip of the material to be welded (including the tip), the plasma arc of back wave forming welding by the following electrode is started,
The plasma electrode of the leading electrode is started at the same time or before the plasma arc generation of the back wave forming welding, and starts the traveling drive at the same time or after the start of the preceding or simultaneous plasma arc.
A welding method using the two-electrode plasma torch described in (10) above (FIGS. 16 and 17).

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

  FIG. 1 (a) shows an example of the system configuration of a welding apparatus for carrying out the welding method using the two-electrode plasma torch of the present invention. In this example, welded pieces 31a and 31b that form a weld line by abutting opposite end surfaces in a horizontal direction x perpendicular to the paper surface are fixed, and a two-electrode plasma torch 30 is supported by a travel mechanism (not shown). The traveling motor 36 faces the welding line in a direction y parallel to the welding line from the left end of the welding line (the tip of the weld piece) to the right side of the right end (the rear end of the weld piece). , Is driven to travel. In the embodiment for carrying out the present invention, instead of driving the two-electrode plasma torch 30 to travel, the two-electrode plasma torch 30 is fixedly installed as shown in FIG. , 31b is supported by a traveling platform, and the traveling platform is a workpiece traveling motor via a traveling mechanism, from a position where the starting end of the welded piece is on the right side of the torch 30 to a position where the starting end of the welded piece is on the left side of the torch 30. There is also an aspect of traveling driving in a direction y parallel to the weld line. However, in order to simplify the description, the former, that is, a mode in which the two-electrode plasma torch 30 is driven to travel is shown below.

  Referring again to FIG. 1 (a), the parallel operation control panel 35 that performs welding control is a computer control circuit that includes a sequencer (microcomputer) incorporating a CPU and memory, a display, and an operation board (such as a touch panel) as main elements. Yes, a two-electrode plasma arc welding control sequence programmed by the operator is executed. The two-electrode plasma torch 30 incorporates two sets of plasma arc generating mechanisms, and the welding current / gas supply devices 32a and 32b execute starting and stopping of the plasma arc of one set and the other set, respectively.

  Each of these welding current / gas supply devices 32a, 32b has a parallel operation control panel 35 instructing each plasma arc current, each plasma gas flow rate, starting and stopping, and the welding current / gas supply devices 32a, 32b Each plasma arc is started, plasma arc current is switched, gas flow rate is switched and stopped according to the command, and each group of state information is given to the parallel operation control panel 35. The parallel operation control panel 35 also commands the motor driver (motor controller: not shown) for driving, stopping and speed control of the torch travel motor 36 to start (run), stop and speed, and the motor driver Then, the motor 36 is started, stopped, and the speed is changed, and the travel drive position of the torch 30 (the position in the welding direction y with respect to the weld piece) is measured and the position data is given to the parallel operation control panel 35. The parallel operation control panel 35 refers to this position data and switches the contents of the sequence control (FIG. 8, Table 1).

  FIG. 2 shows an enlarged longitudinal section of a part of the two-electrode plasma torch 30 shown in FIG. The chip base 1 of the insert chip is fixed to the chip base 5 by screwing the insert cap 6 to the chip base 5. The chip base 5 is fixed to the insulating body 7, and the electrode bases 10 a and 10 b and the insulating spacer 11 are fixed to the insulating body 7.

  The shield cap 8 is fixed to the insulating body 7. The first electrode base 10a and the second electrode base 10b separated in the diameter direction of the outer cylinder 14 by two are separated by an insulating spacer 11.

  The illustrated insert chip is obtained by mounting two nozzle members 20a and 20b on a chip base 1. Referring to FIG. 5 showing the details, each nozzle member 20a and 20b has a nozzle 3a and 3b in the center. There are open cap portions 21a, 21b, trunk portions 22a, 22b continuing to the cap portions, and male screw portions 24a, 24b continuing to the trunk portion, and O-rings 23a, 23b which are sealing materials between the trunk portions and the male screw portions. There are electrode arrangement spaces 2a and 2b communicating with the nozzles 3a and 3b.

  In the chip base 1, the nozzle member insertion holes 18a and 18b through which the male threaded portion to the trunk portion of the nozzle members are inserted, and the cap portions of the nozzle members inserted through the nozzle member insertion holes contact the tip planes 1d and 1e. Cooling water circulation holes 1f, 1g, water receiving holes 1h (FIG. 4), water outlet holes 1i, which form part of the nozzle member insertion holes and form a cooling water flow space with the trunk, which are closed by contact. There are a lateral water hole 1j that connects the matching cooling water circulation holes, a horizontal water hole 1k that connects the cooling water circulation hole 1f to the water receiving hole 1h, and a horizontal water hole 1l that connects the cooling water circulation hole 1g to the water outlet hole 1i.

  As shown in FIG. 5A, the nut members 25a and 25b are screwed to the male screw portions 24a and 24b of the nozzle members 20a and 20b and fastened to the chip base 1 so that the nozzle members 20a and 20b are attached to the chip base 1. Are connected.

  Referring to FIG. 2 again, the electrode arrangement spaces 2a and 2b of the nozzle members 20a and 20b are distributed on the same diameter line (y) orthogonal to the central axis (z) of the chip base 1, and are equidistant from the central axis. Thus, it extends parallel to the central axis (z). In this embodiment, the nozzles 3a and 3b continuing to the electrode arrangement spaces 2a and 2b are concentric with the central axis of the electrode arrangement spaces 2a and 2b and face a base material (not shown). In the present embodiment, these nozzles 3a and 3b are also distributed on the same diameter line (y) perpendicular to the central axis (z) of the chip base (outer cylinder 14), parallel to the central axis and equidistant from the central axis. is there.

  A first electrode 12a and a second electrode 12b, each having a tip inserted into each electrode arrangement space 2a and 2b, pass through the insulating body 7, and are fixed to each electrode base 10a and 10b with screws 13a and 13b. Centering stones 9a and 9b are positioned at the axial center positions of 2a and 2b. Nozzles 3a and 3b connected to the electrode arrangement spaces 2a and 2b are opened on the tip surface (lower end surface) of the chip base 1 facing the base material (not shown). The direction in which the straight line (y) connecting the nozzles 3a and 3b extends is the welding direction. The tip base 1 is wide in the direction (welding direction) in which the straight line (y) extends, as shown in FIG. 2, but the direction (x) perpendicular to the straight line (y), that is, the width of the groove to be welded. The direction is wedge-shaped, and the side surfaces are inclined surfaces 1a and 1b (FIG. 4A).

Referring also to FIG. 4 (a) showing the tip surface of the torch (the lower end surface where the nozzle is open in FIG. 2),
There is a tip projection 1c at the center axis position of the tip of the tip base 1, and a tip plane 1d that faces the back surfaces of the caps 21a, 21b of the nozzle members 20a, 20b on both sides of the tip projection 1c in the y direction as the welding direction. There is 1e. There are nozzle member insertion holes 18a and 18b (FIG. 5B) at the center positions of the respective tip planes 1d and 1e. The notch surfaces 26a and 26b obtained by removing a part of the arc in a straight line from the cap portions 21a and 21b of the nozzle members 20a and 20b inserted into the nozzle member insertion holes 18a and 18b are the side surfaces of the tip protrusion 1c. Contact the surface exactly. That is, it engages. Thereby, the rotation of the nozzle members 20a and 20b with respect to the chip base 1 around the central axis is prevented. This engagement is achieved when the nozzle members 20a and 20b are inserted into the chip base 1 and screwed with the nuts 25a and 25b and fixed, and the nozzle members 20a and 20b are prevented from rotating. It functions as a detent for the nozzle members 20a, 20b when the nuts 25a, 25b are loosened to be removed from the nozzle 1. This engagement further has a function of fixing (setting) the inclination direction of the nozzle shaft of the nozzle members 20c and 20d (FIG. 6) whose nozzle shaft is inclined with respect to the chip base central axis (z) in the welding direction (y). There is also.

  The portions of the nozzle member insertion holes 18a, 18b on the tip planes 1d, 1e side are large-diameter cooling water circulation holes 1f, 1g, and the outer circumferences of the cooling water circulation holes 1f, 1g and the trunk portions 22a, 22b penetrating therethrough. A cooling water flow space (refrigerant flow space) is formed between the surfaces.

  FIG. 4C shows a cross section of the chip substrate 1 (IVc-IVc line cross section in FIG. 2). The chip base 1 includes a water receiving hole 1h, a water outlet hole 1i, a lateral water hole 1j that connects the cooling water circulation holes 1f and 1g, a horizontal water hole 1k that connects the cooling water circulation hole 1f to the water receiving hole 1j, and cooling. There is a lateral water hole 1l that connects the water circulation hole 1g to the water outlet hole 1i.

  FIG. 3 shows a cross section orthogonal to the cross section of FIG. The water receiving hole 1h of the chip base 1 communicates with the water flow pipe 16a, and the water outlet hole 1i communicates with the water flow pipe 16b. Referring also to FIG. 4 (c), the cooling water injected into the water flow pipe 16a enters the water receiving hole 1h of the chip base 1 through the electrode base 10a, the insulating body 7 and the water flow path of the chip base 5, and has a hole. It reaches the bottom, and then enters the cooling water flow space between the water circulation hole 1f and the outer peripheral surface of the trunk portion 22a through the horizontal water flow hole 1k, and then passes through the horizontal water flow hole 1j and passes through the water circulation hole 1g. Enters the cooling water flow space between the main portion 22b and the outer peripheral surface of the trunk portion 22b, then enters the water outlet hole 1i through the lateral water passage hole 11 and flows to the water flow pipe 16b and flows out of the torch.

  While the cooling water flows through the cooling water flow space between the water circulation hole 1f and the outer peripheral surface of the trunk portion 22a and the cooling water flow space between the water circulation hole 1g and the outer peripheral surface of the trunk portion 22b, the nozzle The trunk portions 22a and 22b of the members 20a and 20b are effectively cooled, and the cooling water is supplied to the water receiving hole 1h, the lateral water passage hole 1k, the water circulation hole 1f, the lateral water passage hole 1j, the water circulation hole 1g, and the lateral water passage hole. Since the chip base 1 is effectively cooled while it flows through 11 and the water outlet hole 1i, the cooling capacity of the insert chip is high. The nozzle members 20a and 20b are most heated during welding, but the outer peripheral surfaces of the nozzle members 20a and 20b are cooled by direct contact with cooling water, so that the service life of the nozzle members 20a and 20b is long.

  Referring to FIG. 2 again, the pilot gas enters the electrode arrangement spaces 2a and 2b through the pilot gas pipes 15a and 15b and the electrode insertion space, becomes a plasma arc at the electrode tip, and passes through the nozzles 3a and 3b. Erupts from the tip of The shield gas enters the cylindrical space between the inner cap 7 and the shield cap 8 through the shield gas pipe 17, and is ejected from the tip of the torch toward the welding pieces 31a and 31b which are the welding target materials. .

  As shown in FIG. 2, the pilot power sources 34 a and 34 b that generate a pilot arc between the electrodes 12 a and 12 b and the tip 20, and the electrodes 12 a and 12 b and the welding pieces 31 a and 31 b are welded with a negative electrode side. There are plasma arc power supplies 33a and 33b that flow a positive plasma arc current on one side. Pilot power sources 34a and 34b and plasma arc power sources 33a and 33b are in welding current / gas supply devices 32a and 32b. Plasma arc power sources 33a and 33b are all preheated, keyhole welding (main welding), and tanning welding. The condition can be set, which one of the two electrodes 12a and 12b is set as the leading electrode leading in the welding direction, and which of the leading electrode and the trailing electrode is set to keyhole welding, and the other electrode is leading If it becomes a pole, it can be preheated and if it becomes a trailing electrode, it can be set to tanning and each plasma arc current can be set. FIG. 2 shows a welding mode in which the leading electrode 12b is set to preheating and the trailing electrode 12a is set to keyhole welding. The plasma arcs 19a and 19b act to attract each other due to magnetic interference, and the arcs are slightly bent as shown in the figure.

  A pilot arc is generated between each electrode 12a, 12b and the tip 1 by each pilot power source 34a, 34b, and the electrode side is negative and the base metal side is positive between the electrodes 12a, 12b and the weld pieces 31a, 31b. When a welding arc (plasma arc) is generated by a plasma arc power source 33b that feeds a plasma arc current and feeds the preceding electrode 12b in the welding direction and a plasma arc power source 33a that feeds the subsequent electrode 12a in the welding direction, The arc current flows between the electrodes 12a and 12b and the weld pieces 31a and 31b, thereby realizing 1 pool 2 arc welding. FIG. 2 shows an embodiment in which preheating is performed at the leading electrode 12b and keyhole welding (main welding) is performed at the trailing electrode 12a. Keyhole welding is performed at the leading electrode 12b and tanning welding (smoothing welding) is performed at the trailing electrode 12a. ) Can also be implemented. That is, the plasma pool of the subsequent electrode 12a hits the molten pool generated by the keyhole welding of the preceding electrode 12b, and the deep undercut of the surface bead generated by, for example, the high-speed keyhole welding is followed. The tanning welding is leveled. As a result, a weld bead with less undercut can be obtained even at high speed.

  6 (b1) shows a longitudinal section of the nozzle member 20c of the first modified embodiment used in place of the nozzle member 20a and / or 20b shown in FIG. 2, and FIG. 6 (b2) shows the bottom surface of the nozzle member 20c. (Tip surface) is shown. The central axes of the nozzles 3a and 3b of the nozzle members 20a and 20b shown in FIG. 2 are concentric with the central axis of the nozzle member. However, since the nozzle 3c of the nozzle member 20c is inclined with respect to the central axis of the nozzle member 20c, when the nozzle member 20c is mounted on the chip base 1, the notch surface 26c is formed on the tip protrusion 1c of the chip base 1. In the engaged state, the central axis of the nozzle 3c is inclined in a direction away from the central axis of the chip base (the intermediate point of the nozzle member insertion hole). That is, it is inclined to the front side (in the case of a leading nozzle) or the rear side (in the case of a trailing nozzle) in the welding direction (y) with respect to the central axis of the chip base 1, and between the poles (between the front and rear welding points). Welding with a wider distance is possible.

  6 (c1) shows a longitudinal section of the nozzle member 20d of the second modified embodiment used in place of the nozzle member 20a and / or 20b shown in FIG. 2, and FIG. 6 (c2) shows the bottom surface of the nozzle member 20d. (Tip surface) is shown. Since the nozzle 3d of the nozzle member 20d is inclined in the direction opposite to the nozzle 3c with respect to the central axis of the nozzle member 20d, when the nozzle member 20d is attached to the chip base 1, the notch surface 26d becomes the chip base 1 The center axis of the nozzle 3d is inclined in a direction approaching the center axis of the chip base 1 (the middle point of the nozzle member insertion hole) in a state of being engaged with the tip protrusion 1c. That is, it is inclined so as to approach the central axis of the chip base 1 in the welding direction (y), and the plasma arc of the trailing electrode becomes an advancing angle with respect to the traveling direction of the welding, and the welding becomes stable due to the welding. .

In addition, as an insert chip in which the nozzle member is mounted on the chip base 1,
(1) The embodiment shown in FIGS.
(2) A mode in which the nozzle member 20a shown in FIG. 2 is replaced with a nozzle member 20c, and the nozzle member 20c is a leading nozzle in the welding direction (y),
(3) A mode in which the nozzle member 20b shown in FIG. 2 is replaced with a nozzle member 20c, and the nozzle member 20c is used as a subsequent nozzle,
(4) A mode in which the nozzle members 20a and 20b shown in FIG.
(5) A mode in which the nozzle member 20a shown in FIG. 2 is replaced with a nozzle member 20d, and the nozzle member 20d is a preceding nozzle,
(6) A mode in which the nozzle member 20b shown in FIG. 2 is replaced with a nozzle member 20d, and the nozzle member 20d is a subsequent nozzle,
(7) A mode in which the nozzle members 20a and 20b shown in FIG.
(8) A mode in which the nozzle members 20a and 20b shown in FIG. 2 are replaced with the nozzle members 20c and 20d, and the nozzle member 20c is a preceding nozzle, and
(9) A mode in which the nozzle members 20a and 20b shown in FIG. 2 are replaced with the nozzle members 20c and 20d, and the nozzle member 20d is a preceding nozzle,
There is. Any of the above aspects (1) to (9) can be selected in accordance with the thickness of the plate to be welded and the desired welding current, welding speed and welding quality (for example, the desired bead shape). 20 to 22, the nozzle member 20a shown in FIG. 2 is replaced with the nozzle member 20d shown in FIGS. 6C1 and 6C2, and the nozzle member 20b shown in FIG. The aspect which substituted to the nozzle member 20c shown to (b2) is shown. In any of the following embodiments, the nozzle member 20a shown in FIG. 2 is replaced with the nozzle member 20d shown in (c1) and (c2) of FIG. The nozzle member 20b shown in No. 2 is replaced with the nozzle member 20c shown in FIGS. 6B1 and 6B2, and a forward angle nozzle is used. Next, an example of the welding method of the present invention using a two-electrode plasma torch will be described.

-1st Example-
1. Subsequent keyhole mode (simultaneous ignition of leading electrode and trailing electrode)-FIG. 7, FIG. 8, Table 1
The first embodiment uses a two-electrode plasma torch 30 provided with an insert tip 1 having two electrode arrangement spaces 2a, 2b and two nozzles 3a, 3b communicating with the electrode arrangement spaces, respectively. Rear end tabs 39a and 39b are provided at the rear ends of the pieces 31a and 31b, the alignment direction of the two nozzles is made parallel to the weld line, and the torch 30 is aligned with the weld pieces 31a and 31b along the weld line. While driving in the direction, a plasma arc is generated at each electrode 12a, 12b in each electrode arrangement space to weld a weld line.

  In this embodiment and all the embodiments described later, the rear end tabs 39a and 39b are water-cooled copper tabs having slits at positions immediately below the plasma frame, and the later-described front end tabs 38a and 38b are similar water-cooled copper tabs. However, there is also an aspect in which a concave groove is formed in place of the slit.

  In the first embodiment, the leading electrode is set to a preheated plasma arc, the trailing electrode is set to a keyhole plasma arc, and the trailing electrode (nozzle member 20a) is welded 31a as shown in FIG. , 31b, the plasma electrode of the leading electrode (nozzle member 20b) and the trailing electrode is started at the same time, and simultaneously the driving of the two-electrode plasma torch 30 is started at a low speed.

  As shown in (2) of FIG. 7, when the trailing pole reaches the position where the leading pole has started the plasma arc, the driving drive of the torch 30 is performed at high speed, and the plasma arc current and trailing pole of the trailing pole are increased. Change the plasma gas flow rate higher. After that, as shown in (3) of FIG. 7, the same condition is continued. Then, as shown in FIG. 7 (4), immediately before the leading electrode reaches the rear ends of the welding pieces 31a and 31b, the plasma arc current of the leading electrode is lowered, and the leading electrode reaches the rear ends of the welding pieces 31a and 31b. The plasma arc is stopped, and when the trailing electrode reaches the trailing end as shown in FIG. 7 (5), the speed of the traveling drive is lowered, and the plasma arc current of the trailing electrode is lowered, and the crater by the trailing electrode After the treatment period, the plasma arc of the trailing electrode is stopped. Thereafter, the driving of the torch is stopped ((6) in FIG. 7).

  FIG. 8 shows a basic pattern of switching of the welding current, the plasma gas flow rate, and the welding speed at timings T1 to T4 when the leading electrode reaches each position shown in (3) to (6) of FIG. Shows the welding condition values employed in the first embodiment. The welding pieces 31a and 31b are made of mild steel having a plate thickness of 3.6 mm (thick plate) and a length of 200 mm, and welding is performed for each of the 12 steps from the start of welding (STEP 1) to the end of welding (STEP 12). A condition value is set. Between the steps, the welding condition value of the preceding step is continuously maintained. Incidentally, the nozzle inclination angle 20 ° advance angle means that the nozzle is inclined 20 ° in the forward direction of the welding direction y, and the nozzle member 20b into which the leading electrode 12b shown in FIG. By replacing the nozzle member 20c shown in (b2) with the nozzle member 20a into which the trailing electrode 12a shown in FIG. 2 enters the nozzle member 20d shown in (c1) and (c2) of FIG. A 20 ° advance angle was achieved.

  According to the first embodiment, the preheating leading electrode that has entered the welding piece region from the tip of the welding pieces 31a and 31b, which are materials to be welded, and the trailing electrode for the keyhole at the tip of the welding piece are simultaneously plasma arc. Therefore, although a preheating time lag corresponding to the distance between the leading electrode and the trailing electrode is generated ((b) in FIG. 16), the traveling drive speed is low, so that the back-wave formation failure at the tip of the welded piece is small. Since the traveling drive speed is increased after the preheating time lag section, the welding productivity is high. The rear ends of the welded pieces 31a and 31b are corrected to be flat by a low speed, low current crater process, and the trailing electrode finishes welding at the rear end of the material to be welded and stops the plasma arc. Since the plasma arc of the leading electrode is continued until the welding of the material to be welded is finished, the plasma frame of the trailing electrode attracts the plasma frame of the leading electrode, and the rear of the plasma frame of the trailing electrode at the rear end. Since no deflection occurs, the surface bead is not elongated rearward at the rear end, and the undercut at the rear end is eliminated. By these, the yield of the raw material of the front-end | tip of a welding piece 31a, 31b and a rear end becomes good.

-Second Example-
2. Subsequent keyhole mode (preceding lead preceding ignition)-FIG. 9, FIG. 10, Table 2-
The second embodiment also uses a two-electrode plasma torch 30 provided with an insert tip 1 having two electrode arrangement spaces 2a and 2b and two nozzles 3a and 3b communicating with the respective electrode arrangement spaces. Rear end tabs 39a and 39b are provided at the rear ends of the pieces 31a and 31b, the alignment direction of the two nozzles is made parallel to the weld line, and the torch 30 is aligned with the weld pieces 31a and 31b along the weld line. While driving in the direction, a plasma arc is generated at each electrode 12a, 12b in each electrode arrangement space to weld a weld line.

  The leading electrode is set to a preheating plasma arc, the trailing electrode is set to a keyhole plasma arc, and the traveling drive of the torch 30 is started at a low speed. As shown in FIG. 9 (1), the leading electrode (nozzle member 20b ) Is at the tip of the welded pieces 31a, 31b, the leading electrode plasma arc is activated. As shown in (2) of FIG. 9, when the trailing electrode reaches the start end of the welded pieces 31a and 31b, the plasma arc of the trailing electrode is activated, and when the keyhole is formed by the trailing electrode, traveling driving is performed. The plasma arc current of the trailing electrode and the plasma gas flow rate of the trailing electrode are switched at a high speed. Thereafter, as shown in (3) of FIG. 9, the same condition is continued. Then, as shown in (4) of FIG. 9, when the trailing electrode reaches the rear ends of the weld pieces 31a and 31b, the plasma arc of the leading electrode and the trailing electrode is stopped. Thereafter, the driving of the torch is stopped ((5) in FIG. 9).

  FIG. 10 shows a basic pattern of switching of the welding current, the plasma gas flow rate, and the welding speed at the timings T1 to T3 when the leading electrode reaches each position shown in (3) to (5) of FIG. Shows the welding condition values employed in the second embodiment. This is because welding pieces 31a and 31b are made of mild steel having a plate thickness of 2.3 mm (thin plate) and a length of 220 mm, and welding conditions are set for each of the 13 steps from welding start (STEP 1) to welding end (STEP 13). A value is set. Between the steps, the welding condition value of the preceding step is continuously maintained.

  According to the second embodiment, since the leading electrode (for preheating) activates the plasma arc (preheating) when the leading electrode (for preheating) is at the tip of the welded pieces 31a and 31b, between the leading electrode and the trailing electrode. A back wave formation defect does not occur at the tips of the welded pieces 31a and 31b due to the preheating time lag corresponding to the distance ((b) of FIG. 16). When the keyhole is formed by the trailing electrode, the traveling drive speed is increased, so that the welding productivity is high. Since the plasma electrode of the leading electrode is continued until the trailing electrode finishes welding at the rear end of the material to be welded and stops the plasma arc, the plasma frame and the leading electrode of the trailing electrode are continued until the welding of the material to be welded is completed. Since the plasma flame is attracted to the rear flame and the rear flame is not deflected backward at the rear end, the surface bead is not elongated rearward at the rear end, and the undercut at the rear end is eliminated. By these, the yield of the raw material of the front-end | tip of a welding piece 31a, 31b and a rear end becomes good.

-Third Example-
3. Leading keyhole mode (leading lead preceding ignition)-Fig. 11 and Fig. 12-
The third embodiment also uses a two-electrode plasma torch 30 provided with an insert tip 1 having two electrode arrangement spaces 2a and 2b and two nozzles 3a and 3b communicating with each electrode arrangement space, respectively. Rear end tabs 39a and 39b are provided at the rear ends of the pieces 31a and 31b, the alignment direction of the two nozzles is made parallel to the weld line, and the torch 30 is aligned with the weld pieces 31a and 31b along the weld line. While driving in the direction, a plasma arc is generated at each electrode 12a, 12b in each electrode arrangement space to weld a weld line.

  The leading electrode is set to a keyhole plasma arc, the trailing electrode is set to a tanning plasma arc, and the driving drive of the torch is started at a low speed. As shown in FIG. 11 (1), the leading electrode (nozzle member 20b) Is at the beginning of the welded pieces 31a, 31b, the leading electrode plasma arc (keyhole welding) is started, and the trailing electrode reaches the beginning of the welded pieces 31a, 31b as shown in FIG. Then, the plasma arc (tanning) of the trailing electrode is started, the traveling drive is switched at a high speed, and the plasma arc current of the leading electrode and the plasma gas flow rate of the leading electrode are switched high, and thereafter, as shown in (3) of FIG. Continue the same conditions. Then, as shown in (4) of FIG. 11, immediately before the leading electrode reaches the rear ends of the welded pieces 31a and 31b, the plasma arc current and plasma gas flow rate of the leading electrode are lowered and the traveling drive is switched to low speed. As shown in (5), when the trailing electrode reaches the trailing end, the plasma arc current of the trailing electrode is lowered, and after the crater treatment period by the trailing electrode, the plasma arc of the leading electrode and the trailing electrode is stopped. Thereafter, the driving of the torch is stopped ((6) in FIG. 11).

  FIG. 12 shows a basic pattern of switching of the welding current, the plasma gas flow rate, and the welding speed at timings T1 to T4 when the leading electrode reaches each position shown in (3) to (6) of FIG. Shows the welding condition values employed in the third example. The welding pieces 31a and 31b are made of mild steel having a plate thickness of 5.0 mm (thick plate) and a length of 300 mm, and welding is performed for each of the 15 steps from the start of welding (STEP 1) to the end of welding (STEP 15). A condition value is set. Between the steps, the welding condition value of the preceding step is continuously maintained.

  According to the third embodiment, the weld surface is tanned by the plasma of the trailing electrode from the front end to the rear end of the weld pieces 31a and 31b, and a surface bead with less undercut is obtained even in high-speed welding. High welding productivity. When the trailing electrode reaches the tips of the welded pieces 31a and 31b, the plasma arc current of the leading electrode is switched high, and the traveling drive speed is increased at the same time, so that the welding productivity is high. Since the plasma electrode of the leading electrode is continued until the trailing electrode finishes welding at the rear end of the material to be welded and stops the plasma arc, the plasma frame and the leading electrode of the trailing electrode are continued until the welding of the material to be welded is completed. Since the plasma flame is attracted to the rear flame and the rear flame is not deflected backward at the rear end, the surface bead is not elongated rearward at the rear end, and the undercut at the rear end is eliminated. By these, the yield of the raw material of the front-end | tip of a welding piece 31a, 31b and a rear end becomes good.

-Fourth embodiment-
4). Leading keyhole mode (using tab material; simultaneous ignition of leading and trailing electrodes)
The fourth embodiment uses a two-electrode plasma torch 30 including an insert tip 1 having two electrode arrangement spaces 2a and 2b and two nozzles 3a and 3b communicating with the electrode arrangement spaces, respectively. As shown in FIG. 13, tip tabs 38a and 38b and rear end tabs 39a and 39b are provided at the tip and rear ends of the weld pieces 31a and 31b, and the alignment direction of the two nozzles is made parallel to the weld line. While driving the torch 30 in a direction along the weld line with respect to the weld pieces 31a and 31b, a plasma arc is generated at each electrode 12a and 12b in each electrode arrangement space to weld the weld line.

  The leading electrode is set to a keyhole plasma arc, the trailing electrode is set to a tanned plasma arc, and the leading electrode (nozzle member 20b) is at the start of the welding pieces 31a and 31b as shown in FIG. Sometimes, the leading electrode plasma arc (keyhole welding) and the trailing electrode plasma arc (tanning welding) are started, and the torch travel drive is started at a low speed, as shown in FIG. When the row electrode reaches the start end of the welded pieces 31a and 31b, the traveling drive is switched at a high speed and the plasma arc current of the leading electrode and the plasma gas flow rate of the leading electrode are switched high. Thereafter, as shown in FIG. Continue the same conditions. Then, as shown in FIG. 14 (4), when the trailing electrode reaches the rear ends of the weld pieces 31a and 31b, the plasma arc of the leading electrode and the trailing electrode is stopped. Thereafter, the driving of the torch is stopped ((5) in FIG. 14).

  FIG. 15 shows a basic pattern of switching of the welding current, plasma gas flow rate, and welding speed at the timings T1 to T3 when the leading electrode reaches each position shown in (3) to (5) of FIG. Shows the welding condition values employed in the fourth embodiment. This is because the welding pieces 31a and 31b are made of mild steel having a plate thickness of 1.4 mm (thin plate) and a length of 300 mm, and welding conditions are set for each step of 11 steps from welding start (STEP 1) to welding end (STEP 11). A value is set. Between the steps, the welding condition value of the preceding step is continuously maintained.

  According to the fourth embodiment, the weld surface is tanned by the plasma of the trailing electrode from the front end to the rear end of the weld pieces 31a and 31b, and a surface bead with less undercut is obtained even in high-speed welding. High welding productivity. When the trailing electrode reaches the tips of the welded pieces 31a and 31b, the plasma arc current of the leading electrode is switched high, and the traveling drive speed is increased at the same time, so that the welding productivity is high. Front end tabs 38a and 38b and rear end tabs 39a and 39b are provided at the front and rear ends of the material to be welded, and the trailing electrode is at the rear end of the material to be welded from when the leading electrode is at the front end of the material to be welded. Until then, the plasma arc of the leading electrode and the trailing electrode is continued. Therefore, until the welding of the material to be welded starts and ends, the plasma frame of the trailing electrode attracts the plasma frame of the leading electrode, and the tip of the material to be welded・ Because there is no forward deflection or backward deflection of the plasma frame of the trailing electrode at the rear end, the surface bead is not elongated rearward immediately after the front end and at the rear end, and there is no undercut at the front end and rear end. . By these, the yield of the raw material of the front-end | tip of a welding piece 31a, 31b and a rear end becomes good.

-Fifth embodiment-
5. Subsequent keyhole mode (using tab material; simultaneous ignition of leading and trailing electrodes)
The fifth embodiment also uses a two-electrode plasma torch 30 provided with an insert tip 1 having two electrode arrangement spaces 2a and 2b and two nozzles 3a and 3b communicating with the electrode arrangement spaces, respectively. As shown in FIG. 13, tip tabs 38a and 38b and rear end tabs 39a and 39b are provided at the tip and rear ends of the weld pieces 31a and 31b, and the alignment direction of the two nozzles is made parallel to the weld line. While driving the torch 30 in a direction along the weld line with respect to the weld pieces 31a and 31b, a plasma arc is generated at each electrode 12a and 12b in each electrode arrangement space to weld the weld line.

  The leading electrode is set to a preheated plasma arc, and the trailing electrode is set to a keyhole plasma arc. As shown in FIG. 16 (1), the leading and trailing electrode plasma arcs are activated at positions where the leading electrode faces the tips of the weld pieces 31a and 31b and the trailing electrode faces the slits of the tip tabs 38a and 38b. Then, the traveling drive of the two-electrode plasma torch 30 is started, and the trailing electrode reaches the rear ends of the welded pieces 31a and 31b as shown in FIG. Stop the plasma arc. FIG. 17 shows a basic pattern of switching of the welding current, plasma gas flow rate, and welding speed at timings T1 to T4 when the leading electrode reaches each position shown in (1) to (4) of FIG.

  According to the fifth embodiment, the welding target material is preheated by the plasma of the leading electrode from the front end to the rear end of the welding pieces 31a and 31b, and a surface bead with less undercut is obtained even in high-speed welding. High welding productivity. When the trailing electrode reaches the tips of the welded pieces 31a and 31b, the plasma arc current of the leading electrode is switched high, and the traveling drive speed is increased at the same time, so that the welding productivity is high. When the leading electrode is at the starting end of the welded pieces 31a and 31b and the trailing electrode is opposed to the slit of the tip tabs 38a and 38b, the plasma arc of the leading and trailing electrodes is activated, and the trailing electrode is the welding pieces 31a and 31b. Since the plasma arc of the leading electrode and the trailing electrode is stopped when the leading electrode is at the trailing edge and faces the slits of the trailing tabs 38a and 38b, the welding is continued until the welding of the welding target material is started and finished. Since the plasma frame of the row electrode and the plasma frame of the leading electrode attract each other, the front and rear ends of the plasma frame of the trailing electrode do not occur at the front and rear ends of the material to be welded. Will not be elongated backward, and there will be no undercut at the front and rear ends. By these, the yield of the raw material of the front-end | tip of a welding piece 31a, 31b and a rear end becomes good.

  Regarding the fourth and fifth embodiments, not only the leading electrode and the trailing electrode are simultaneously ignited and simultaneously stopped, but each electrode may be ignited separately when both are in the region of the tip tab material, Moreover, you may stop separately when each pole exists in the area | region of a rear-end tab material. Further, crater processing of the trailing electrode can be performed at the rear end.

-Modification of the first to fifth embodiments-
In the welding using the two-electrode plasma torch 30, the distance between the leading electrode and the trailing electrode is short. Depending on the welding conditions, as shown in FIG. 18 (a), the melting of the molten pool generated by the preceding keyhole welding is performed. The metal is sucked directly under the subsequent tanning plasma arc, and there is a flow of molten metal from the leading electrode side to the trailing electrode side between the keyhole weld and the butt weld, and after the weld line At the end, welding may end in a reduced thickness state. This becomes more prominent with thicker plates and with lower viscosity metals. In order to avoid this, the welding pieces 31a and 31b are inclined to a posture in which the rear end is lower than the tip, and the two-electrode plasma torch 30 is set in a vertical posture with respect to the surfaces of the welding pieces 31a and 31b, and the traveling drive is welded. The direction is parallel to the line. In this way, when the weld piece is tilted, gravity is applied to the molten metal of the pool in the welding direction to suppress the suction, reducing the thinning of the rear end bead and flattening the rear end bead surface. Become. Since the two-electrode plasma torch 30 is perpendicular to the surfaces of the welding pieces 31a and 31b, it is easy to set or adjust the leading electrode keyhole welding conditions and the trailing electrode tanning welding conditions.

  In any of the above-described Examples 1 to 5 and the modified examples, depending on the material and the plate thickness, when the thickness of the front bead is large even after the rear end crater treatment, the wire is fed to the rear end portion. It can also be served. In the above, welding between flat plates has been shown. However, the present invention is not limited to this. Circumferences such as butt welding at both ends of a single plate bent into a cylindrical shape, butt welding between pipes, lap fillet welding, etc. It can also be applied to welding.

1: Chip base 1a, 1b: Inclined surface 1c: Tip protrusion 1d, 1e: Tip flat surface 1f, 1g: Water circulation hole 1h: Water receiving hole 1i: Water outlet hole 1j, 1k, 11: Transverse water holes 2a to 2d: Electrode arrangement spaces 3a to 3d: Nozzle 5: Tip base 6: Inner cap 7: Insulating body 8: Shield cap 9a, 9b: Centering stone 10a, 10b: Electrode base 11: Insulating spacers 12a, 12b: Electrodes 13a, 13b: Pressers Screw 14: Outer cylinder 15a, 15b: Pilot gas pipes 16a, 16b: Water flow pipe 17: Shield gas pipes 18a, 18b: Nozzle member insertion holes 19a, 19b: Plasma arcs 20a-20d: Nozzle members 21a-21d: Caps 22a -22d: trunk portions 23a-23d: O-rings 24a-24d: male screw portions 25a, 25b: nuts 26a-26d: notch surface 3 : Torch 31a, 31b: Weld piece 31p: Pool 32a, 32b: Welding current / gas supply device 33a, 33b: Welding power supply 34a, 34b: Pilot power supply 35: Parallel operation control panel 36: Torch travel motor 37: Work travel motor 38a , 38b: front end tabs 39a, 39b: rear end tabs

Claims (13)

Using a two-electrode plasma torch having an insert tip having two electrode arrangement spaces and two nozzles communicating with each electrode arrangement space, the arrangement direction of the two nozzles is made parallel to the weld line. Welding by a two-electrode plasma torch that welds the welding line by generating a plasma arc at each electrode in each electrode arrangement space while driving at least one of the torch and the material to be welded in a direction along the welding line In the method
A rear end tab is provided at the rear end in the welding direction of the material to be welded, and until the electrode that follows in the direction in which the weld line extends, that is, the rear electrode finishes welding at the rear end and stops the plasma arc, A welding method using a two-electrode plasma torch, characterized in that the preceding electrode, that is, the plasma arc of the leading electrode is continued in the extending direction.   The welding by the two-electrode plasma torch according to claim 1, wherein when the welding of the trailing end by the trailing electrode is finished, the plasma arc of the leading electrode and the trailing electrode is stopped, and then the traveling drive is stopped. Method.   2. The two-electrode plasma torch according to claim 1, wherein the welding target material and the rear end tab are tilted in a posture in which the rear end is lower than the leading end of the welding target material, and the traveling drive is set in a direction parallel to the welding line. Welding method by.   The welding method by a two-electrode plasma torch according to claim 3, wherein the two-electrode plasma torch is in a vertical posture with respect to a surface of a material to be welded. The leading electrode is set to generate a plasma arc for preheating the material to be welded, and the trailing electrode is set to a plasma arc for back wave forming welding,
When the trailing electrode set for back wave forming welding is before the tip of the material to be welded, the plasma arc of back wave forming welding by the following electrode is started,
The plasma electrode of the leading electrode is started at the same time or before the plasma arc generation of the back wave forming welding, and starts the traveling drive at the same time or after the start of the preceding or simultaneous plasma arc.
The welding method by the two-electrode plasma torch as described in any one of Claims 1 thru | or 4. The leading electrode is set to a plasma arc for back wave forming welding, and the trailing electrode is set to a plasma arc for tanning a welding line,
When the leading electrode set for back wave forming welding is before the tip of the material to be welded, a plasma arc of back wave forming welding with the leading electrode is started,
The plasma electrode of the trailing electrode is activated at the same time as the activation of the plasma arc of the back wave forming welding or at the tip of the material to be welded, and at the same time as or after the activation of the preceding or simultaneous plasma arc. Start driving,
The welding method by the two-electrode plasma torch as described in any one of Claims 1 thru | or 4. When the trailing electrode is at the tip of the material to be welded, simultaneously start the plasma arc of the leading electrode and the trailing electrode, and simultaneously start the traveling drive at a low speed,
When the trailing electrode reaches the position where the leading electrode has started the plasma arc, the traveling drive is switched at a high speed and both or one of the plasma arc current and the plasma gas flow rate of the trailing electrode are switched high.
Immediately before the leading electrode reaches the rear end of the material to be welded, both or one of the plasma arc current and the plasma gas flow rate of the leading electrode is decreased, and when the trailing electrode reaches the trailing end, the traveling drive speed is decreased, and 6. The two-electrode plasma torch according to claim 5, wherein both or one of the plasma arc current and plasma gas flow rate of the trailing electrode is lowered and the plasma arc of the leading electrode and the trailing electrode is stopped after the crater treatment period by the trailing electrode. Welding method by. When the leading electrode is at the tip of the material to be welded, the plasma arc of the leading electrode is started and at the same time the traveling drive is started at a low speed, and when the trailing electrode reaches the tip of the material to be welded, the plasma of the trailing electrode Start the arc and
6. The two-electrode plasma according to claim 5, wherein when the keyhole is formed by the trailing electrode, the traveling drive is switched at a high speed and both or one of the plasma arc current and the plasma gas flow rate of the trailing electrode is switched high. Welding method with torch. When the leading electrode is at the tip of the material to be welded, the plasma arc of the leading electrode is started and at the same time the traveling drive is started at a low speed, and when the trailing electrode reaches the tip of the material to be welded, the plasma of the trailing electrode Start the arc and
When the trailing electrode reaches the tip of the material to be welded, the traveling drive is switched at high speed, and the plasma arc current and the plasma gas flow rate of the leading electrode are switched to high or both,
Immediately before the leading electrode reaches the rear end of the material to be welded, both or one of the plasma arc current and the plasma gas flow rate of the leading electrode is lowered to switch the traveling drive to a low speed and the plasma arc of the leading and trailing electrodes at the rear end. The welding method by the two-electrode plasma torch according to claim 6, wherein   The tip of the welding direction of the welding target material is provided with a tip tab, and when the leading electrode and the trailing electrode are located before the leading end of the welding target material, a plasma arc is simultaneously started on both electrodes. Welding method using the two-electrode plasma torch according to any one of   The welding method using a two-electrode plasma torch according to claim 4, wherein the traveling drive is started when a plasma arc is simultaneously activated in both electrodes. The leading electrode is set to a plasma arc for back wave forming welding, and the trailing electrode is set to a plasma arc for tanning a welding line,
When the leading electrode set for back wave forming welding is before the tip of the material to be welded, a plasma arc of back wave forming welding with the leading electrode is started,
The plasma electrode of the trailing electrode is activated at the same time as the activation of the plasma arc of the back wave forming welding or at the tip of the material to be welded, and at the same time as or after the activation of the preceding or simultaneous plasma arc. Start driving,
A welding method using the two-electrode plasma torch according to claim 10. The leading electrode is set to generate a plasma arc for preheating the material to be welded, and the trailing electrode is set to a plasma arc for back wave forming welding,
When the trailing electrode set for back wave forming welding is before the tip of the material to be welded, the plasma arc of back wave forming welding by the following electrode is started,
The plasma electrode of the leading electrode is started at the same time or before the plasma arc generation of the back wave forming welding, and starts the traveling drive at the same time or after the start of the preceding or simultaneous plasma arc.
A welding method using the two-electrode plasma torch according to claim 10.

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