JPH048149B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a plasma welding method for piping, and is particularly suitable for welding circumferential joints of piping that require a uniform uranami bead shape by keyhole welding. This article relates to a plasma welding method for piping, which is a competitive advantage.

[Background of the invention]

Normally, when joining pipes together by welding,
TIG (Tungsten−Inert−Gas arc welding) or MIG (Metal−Inert−Gas arc welding)
Welding is commonly used.

Even if you try to join pipes together using TIG or MIG welding, when the pipes are butted together,
Misalignment or gaps often occur, and the alignment of the piping grooves greatly influences the welding condition.

In the above-mentioned TIG and MIG welding, misalignment and gap limits are strictly controlled so that the pipe groove alignment is normal, and in some cases the groove alignment must be redone or manually performed by skilled workers. Performing welding work. On the other hand, when automatic welding is used, the method shown in FIG. 7a or b is used. Fig. 7a shows an example in which pipes 1 and 2 with plate thickness t _2a are to be welded with a groove angle β _2a .
ta, length l, and this results in pipe 1,
2, the uneven dimensions are eliminated to make the groove alignment work as easy as possible, and the groove alignment state is managed. Moreover, what is shown in FIG. 7b is an example in which pipes 1 and 2 with plate thickness t _2b are to be welded with a groove angle β _2b , and an insert ring 3 is attached to the butt part of pipes 1 and 2. This is used to maintain a good groove alignment condition as in FIG. 7a.

On the other hand, there is plasma welding, which has a higher energy density and a longer arc length than TIG welding, etc., so that it can perform arc welding efficiently with high heat input. This plasma welding uses a high-temperature plasma jet to penetrate the base metal.
This is a method of arc welding while forming a keyhole.

However, plasma welding, which involves arc welding while making a keyhole, has a narrower stable range of welding conditions than regular TIG and MIG welding.

Therefore, even if it is desired to use plasma welding, there is a problem of lack of reliability due to a narrow stable range of welding conditions, and an attempt to solve this problem results in an increase in the number of welding steps.

Regarding the plasma welding method, please refer to Japanese Unexamined Patent Application Publication No. 1987-
Disclosures are made in JP-A No. 191568, JP-A-60-27473, and the like.

[Purpose of the invention]

The present invention has been made in view of the above points, and its purpose is to enable plasma welding according to the groove alignment state, and to improve reliability by widening the stable range of welding conditions. To provide a plasma welding method for piping which can reduce the number of welding steps and which does not increase the number of welding steps.

[Summary of the invention]

In the present invention, when the pipes are butted against each other and the two pipes are joined by plasma welding, the welding current value, welding speed, and plasma gas amount in the ideal state of groove alignment of the pipes are set in advance, Based on this, the misalignment between the pipes, the gap between the pipes, and the respective numerical values and the posture position of the welding torch in a state in which both occur simultaneously are input into the control device, and the welding torch is welded by the orbiting device. The welding torch moves around the pipe while changing its posture, and the control device outputs a command value according to the position and orientation of the welding torch, and the command value controls a welding current controller, welding speed controller, and plasma gas amount control. By operating the welding current value, welding speed, and adjusting the plasma gas amount,
It was designed to achieve the intended purpose.
In other words, as mentioned above, plasma welding has a narrower stable range of welding conditions than general TIG and MIG welding, but this is due to the welding method with high heat input and high energy concentration, and Although it may be due to the welding method used, we focused on the fact that the condition of the welded joint, that is, the condition of the groove alignment, has a large effect, and we incorporated this condition into the welding conditions to achieve the above purpose. This is what was done.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail based on embodiments shown in the drawings.

As shown in Fig. 3a, this is a workpiece to which pipes 1 and 2 are welded, and in Fig. 3b, when viewed from the axial direction of these pipes 1 and 2, there is a round frame on the outer periphery, like the dial of a clock. The attached number is the welding posture position.

Fig. 4 shows the state in which pipes 1 and 2 are actually plasma keyhole welded. In this figure, the welding torch 4 is composed of an electrode 4a, a tip 4b, and a cover 4c.The welding torch 4 has a pole for welding current at the electrode 4a, a pilot current for the pole at the tip 4b, and a main pole for the welding current. A pole is connected to the pipe 1 or 2 as a current, and power is supplied from a welding current device (not shown). A plasma gas passage is provided inside the welding torch 4,
Plasma gas 6 flows. Also, shield gas 7
flows from the inside of the cover 4c and surrounds the welding location. These gases are supplied from gas cylinders (not shown). Then, the welding torch 4 moves while forming a plasma keyhole welding bead 5 at the abutting portion of the pipes 1 and 2 (in the direction perpendicular to the plane of the paper in FIG. 4).
Then, pipes 1 and 2 are joined.

Figure 1 shows the control status during plasma welding. As shown in the figure, the welding torch 4 is rotated around the pipes 1 and 2 by the orbiting device 8 while changing the welding posture. Here, the control device 9 controls the welding torch 4
A command value is issued according to the position and orientation of. Based on the command value, the welding current controller 1 of the controller 10
0a, the pulse time controller 10b, the welding speed controller 10c, and the plasma gas flow rate controller 10d operate to supply the electrical energy and gas amount supplied from the power source 11 and the gas cylinder 12 to the welding torch 4. Plasma welding is performed as explained using FIG.

FIG. 2a shows a control sequence based on the posture and position of the welding torch 4. This figure shows the pilot arc (PA) and welding current ( MC),
This is the control state of welding speed (V) and plasma gas (PG). First, after the posture position of the welding torch 4 is set at 4 or 5 o'clock, when the welding start command "S" is given, the plasma gas "PG" flows, and after the time "T ₁ " the pilot arc "PA" lights up. do.
Plasma keyhole welding supplies energy to melt pipes 1 and 2 using welding current "MC", narrows down the energy using plasma gas "PG", and punches the thickness of pipes 1 and 2 into a keyhole shape. To establish.

Therefore, it is mainly controlled by the welding current "MC" and the plasma gas "PG", and the pulse time and speed are secondarily controlled. In addition, plasma gas "PG" is
After the preflow time "T ₁ + T ₂ ", the amount of gas is controlled to the amount required for the keyhole. Plasma gas "PG"
After the time “T ₃ ” when the welding current transitions to a stable state, the welding current “MC” is ramped up to the keyhole start current “MCS” at the up slope time “T ₄ ”,
It is held for the keyhole time "T ₅ ", and after the keyhole is confirmed, it is controlled to the current value at each posture position. As shown in Figure 2b, the welding current "MC" is equal to the peak current "MCP" at the interval of time "TP" and "TB".
The quality of keyhole welding is improved by controlling the base current "MCB" in a pulsed manner.

On the other hand, the welding torch has a keyhole time of "T ₅ "
After that, welding current “MC”, plasma gas flow rate “PG”, and appropriate speed “V” for each posture position.
Operate pipes 1 and 2 in circles. After the welding torch that performed keyhole welding returns to the initial position after the rotation, that is, at 4 or 5 o'clock, the welding torch returns to the position where it was first set up after the orbit, and after the wrap time "T ₆ ", the welding torch continues during the crater treatment time "T ₇ ". stop orbiting and perform crater treatment,
The welding current is cut off by the downslope time "T ₃ ". Plasma gas flow rate “PG” is welding current “MC”
stop at the same time. Downslope time “T ₃ ”
After a few seconds, turn off the pilot arc “PA” and
The welding is complete and becomes "F". Incidentally, the horizontal axis in FIG. 2a shows "TC" when time control is in progress, and "PC" when attitude control is in progress.

By the way, as mentioned above, when performing plasma welding, the groove alignment condition of the pipes greatly affects the welding.
Although the groove alignment shown in the figure is the best groove alignment condition, it is actually very difficult to align the grooves in this way. In general, as shown in Figure 5a, the pipings 1 and 2 are misaligned as shown in "e", and as shown in Figure 5b, the abutting ends of the pipings 1 and 2 are slanted and the gap is "e". Normally, a state in which there is a "g" or a state in which the grooves are aligned as shown in FIG. 5c, where both the misalignment in FIG. 5a and the gap in FIG. 5b are combined, occur. Moreover, the direction of the misalignment e and the gap g is not limited to the 0 o'clock direction in FIG. 3b, and it is necessary to consider all postures. In particular, in plasma keyhole welding, the welding quality is easily affected by misalignment "e" and gap "g", so it is necessary to take these conditions into consideration in the welding conditions. Therefore, by correcting the welding sequence with respect to the groove alignment state, that is, the misalignment "e" and the gap "g", and the posture position, it is possible to obtain a good welded joint. That is, Figure 2a
If welding condition setting values in a poor groove alignment state (the state shown in Fig. 3a) are shown as a sequence by a solid line, for example, the misalignment "e" is 6 in Fig. 3b.
If the position is in the direction of 12 o'clock and
If there is an increase in the apparent plate thickness, the welding current "MC" and plasma gas flow rate "PG" are increased from the values shown by the solid line, which is the ideal groove alignment state, in order to increase the keyhole force. ). On the other hand, if the gap "g" is at the 12 o'clock position in Figure 3b,
Correct the plasma gas flow rate "PG" as shown in the two-dot chain line in Figure 2a (for example, if there is a gap "g", keyholes are likely to be formed, so adjust the plasma gas flow rate "PG" to the ideal groove ). Furthermore, when considering the welding speed "V", it was found that if there was a misalignment "e", the welding speed "V" could be adjusted without correction, but if there was a gap "g" , as shown by the two-dot chain line in Figure 2a,
The welding speed "V" is increased only at the posture position where the gap "g" is present (in the illustrated case, the gap "g" is at the 0 o'clock position).

Even if the misalignment "e" and the gap "g" overlap, a good welded joint can be obtained by making a corresponding correction in the same manner as described above.

By using the plasma welding method of this embodiment as described above, it becomes possible to perform plasma keyhole welding in which the groove alignment condition of the weld joint is taken into consideration in the welding conditions. It can be roughened and has the effect of reducing welding man-hours. Furthermore, even when comparing the entire welding process, it is extremely effective in streamlining the parts where keyhole welding is possible, as beveling can be omitted and the amount of melting can be reduced.

In the above embodiment, the welding groove command is given after the welding torch position is set to 4 or 5 o'clock; Of course, hole welding is possible, and in this case, Fig. 2a
It can be interpreted by shifting the horizontal axis, that is, the time axis. The reason why the welding start points were selected at 4 and 5 o'clock in the above embodiment will be explained with reference to FIG. When performing keyhole welding, the direction of the force that causes the bead to unravel, that is, the direction of gravity F _b
The point near the range where the vector sum of the keyhole force F _K at base current I _B and the surface tension F _n of the molten metal cancels out is at 4 and 5 o'clock, and the welding start point is set at 4 and 5 o'clock.
Good plasma welding can be achieved by selecting the appropriate temperature.

〔Effect of the invention〕

According to the above-described plasma welding method for pipes of the present invention, when the pipes are butted against each other and both pipes are joined by plasma welding, the welding current value and welding speed in the ideal state of groove alignment of the pipes, and the welding speed. , and the amount of plasma gas are set in advance, and based on these values, the misalignment of the pipes, the gap between the pipes, and the values in the state where both of these occur simultaneously and the values in the state where welding occurs simultaneously are calculated. The attitude and position of the welding torch is input to the control device, and the welding torch goes around the pipe while changing the welding attitude by the orbiting device, and the control device generates a command value according to the position and attitude of the welding torch. The welding current controller, welding speed controller, and plasma gas amount controller operate based on the command value to adjust the welding current value, welding speed, and plasma gas amount. It is possible to perform plasma welding according to the pre-alignment condition, and since the welding conditions are incorporated into welding, the stability range is widened and reliability is improved.
Moreover, the number of welding steps is not increased, and it is very effective when used in plasma welding for this type of piping.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the control state during plasma welding in an embodiment of the present invention, FIG. 2a is a diagram showing a sequence operation for welding pipes by the plasma welding method of the present invention, and FIG. 2b is a diagram showing a state in which the welding current in FIG. 2a is controlled in a pulsed manner, FIG. Figure a is viewed from the axial direction, Figure 4 is a diagram showing the relationship between the piping and welding torch during plasma welding, Figure 5 shows the state of alignment for plasma welding, and a is a diagram showing the alignment of the piping and welding torch during plasma welding. Fig. 6 shows the relationship between the forces acting on the molten bead at the 4 and 5 o'clock positions. , 7th
The figure shows the state of groove alignment of a conventional welded joint performed by TIG and MIG welding, where a shows an example of groove alignment performed to match the inner dimensions, and b shows an example of using an insert ring. . 1, 2... Piping, 4... Welding torch, 4a...
Electrode, 4b...chip, 4c...cover, 5...
Molten bead, 6... Plasma gas, 7... Shield gas, 8... Orbiting device, 9... Control device, 10
...Controller, 10a...Welding current controller,
10b...Pulse time controller, 10c...Welding speed controller, 10d...Plasma gas flow rate controller,
11...Power supply, 12...Gas cylinder.

Claims (1)

[Claims] 1. When the pipes are butted against each other and both pipes are joined by plasma welding, the welding current value, welding speed, in the ideal state of groove alignment of the pipes,
and plasma gas amount are set in advance, and based on these values, the misalignment of the pipes, the gap between the pipes, and the respective values and the posture position of the welding torch in a state where both of these occur simultaneously are input into the control device. , and the welding torch orbits around the piping while changing the welding posture by an orbiting device, a command value according to the position and orientation of the welding torch is outputted by the control device, and a welding current controller is controlled based on the command value. , a welding speed controller, and a plasma gas amount controller operate to adjust the welding current value, welding speed, and plasma gas amount.