JPH0839259A - Gas pulse plasma welding method - Google Patents

Abstract

PURPOSE:To make the most of plasma welding so as to stably execute formation of key hole and deep penetration welding without generating defect of burn through, etc., of molten pool. CONSTITUTION:The gas plasma welding method is that a gas flow rate of plasma gas flow is periodically varied in pulse state. Plasma gas flow is varied so that a period of peak gas flow rate Q1 and a period of base gas flow Q2 are alternately varied in pulse state and the period of base gas flow Q2 is 0.3 to 1 times of the peak flow rate Q1, the base flow rate Q2 is 0.3 to 0.7 times of the peak gas flow rate Q1. Further, between the peak gas flow period and base gas flow period, there is a period of one or >=2 of the flow between the peak gas flow rate and base gas flow rate. Further, a filler metal wire is supplied into the molten pool formed backward in the welding advancing direction by plasma arc column, the method is suitable for welding a horizontal fixed tube in all positions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas pulse plasma welding method for plasma welding, in which the gas flow rate is changed in a pulsed manner to make the plasma gas stronger and weaker and to enable stable welding.

[0002]

2. Description of the Related Art In plasma welding, a plasma gas flow is discharged from the center of a welding torch nozzle, and in the presence of the plasma gas flow between a non-consumable electrode provided at the nozzle center of the welding torch and the material to be welded. An arc voltage is applied to generate a plasma arc column, and a shield gas flow is caused to flow concentrically around the plasma gas flow to protect the plasma arc injection from the outside air. Then, the heat of this plasma arc is used to melt and join the materials to be welded.

The plasma welding methods are roughly classified into the following two types. (1) Plasma keyhole welding method With a plasma arc column, a keyhole is formed through the material to be welded, and the entire thickness of the material to be welded is welded. This is a type of high-efficiency welding method that makes it possible to finish joining. (2) Plasma non-keyhole welding method (soft plasma welding method) This is a welding method of forming multiple layers without forming keyholes. Since the plasma arc has high temperature and high heat, the action of melting the material to be welded is very efficient. By utilizing the characteristics of this plasma arc, a huge molten pool is formed on the surface of the material to be welded, and a filler material (filler wire) is supplied to the molten pool to perform multi-layer welding.

As a conventional plasma welding method, plasma electric pulse welding has been put into practical use in which the welding current is made strong and weak and the welding current is changed in a pulsed manner.

When performing the welding by the plasma welding method, only by the electric pulse welding method in which the welding current is made strong and weak, the weldable range area (welding speed range, weldable metal depth,
Since the plate thickness capable of keyhole welding and the amount of deposited metal are small, it cannot be said that the welding method is more stable than TIG welding and MIG welding.

Particularly, plasma arc welding has a larger penetration depth as compared with TIG welding and MIG welding.
Since the molten pool becomes large, it is difficult to maintain the huge molten pool only by the strength of the electric current (electric pulse welding method).

FIG. 1 is a schematic view showing a state where a plasma arc is generated. The plasma arc 3 generated from the nozzle 1 toward the welded material 2 is composed of a core 4 and a plasma flare 5 around the core 4. That is, when a plasma arc occurs, a high-temperature arc column called the core 4 is formed at the center. The core 4 is a plasma arc which mainly penetrates the material to be welded 2 and has a function of enabling deep penetration welding. On the other hand, around the core 4, an arc is concentrically formed, which is a plasma flare 5 having a relatively low temperature and formed like an umbrella. Like the plasma core 4, the plasma flare 5 has little effect of directly penetrating the material to be welded or obtaining deep penetration. Therefore, a molten pool is formed on the surface of the material to be welded over the entire irradiation range of the plasma flare 5 formed on the umbrella.

As shown in FIG. 2, it has been found from experimental observations that when the plasma gas amount is the same, the plasma flare 5 tends to expand as the welding current increases and the irradiation range tends to widen.

That is, if the welding current is increased, the irradiation range of the plasma flare 5 is likely to be wide and the width of the molten pool 6 is widened, and the amount of the molten pool is increased in proportion to this. As a result, the molten pool 6 may not be held, and the molten pool 6 may melt down.

Therefore, as one of the methods of increasing the welding current value and enabling the deep penetration welding while suppressing the increase of the amount of the molten pool, plasma electric pulse welding in which the welding current is made strong or weak (pulse) is used. The method has been widely used in general.

In this electric pulse welding method, plasma is generated with a current waveform as shown in FIG. That is, as shown in this current waveform, a method of welding with a welding current in which a peak current having a high welding current value and a base current having a low welding current value repeatedly appear in a predetermined time cycle (frequency) is an electric pulse welding method. Say.

In the plasma electric pulse welding method,
At the peak current, keyhole formation and deep penetration welding are mainly performed, and at the base current, the molten pool increased mainly at the peak current is cooled and further solidification is performed. By alternately repeating the keyhole formation and deep penetration process and the cooling and solidification process of the molten pool, the penetration force (keyhole formation) and the deep penetration force (keyhole non-formation) can be maintained while melting. It becomes possible to perform welding while suppressing an increase in the pool amount.

[0013]

However, this electric pulse welding method has a drawback in that the width of the plasma arc becomes unnecessarily large at the peak current, and accordingly, it is difficult to obtain a bead having a deep penetration. As a result, for example, when performing all-position welding, especially in the upward position,
It was also difficult to form the backside bead because the molten pool was liable to sag and it was difficult to obtain deep penetration.

The present invention has been made in view of the above problems, and makes use of the essential advantages of plasma welding to form keyholes and welds with deep penetration without inconvenience such as melt-through of the molten pool. An object of the present invention is to provide a gas pulse plasma welding method capable of performing stable welding.

[0015]

A gas pulse plasma welding method according to the present invention is a gas plasma welding method in which the flow rate of a plasma flow is periodically changed in a pulsed manner, and the plasma flow is for a period of a peak gas flow rate. The period of the base gas flow rate alternates in a continuous pulse shape, the period of the base gas flow rate is 0.3 to 1 times the period of the peak gas flow rate, and the base gas flow rate is 0.3 to 0. It is characterized by being 7 times.

The base gas flow rate is the minimum gas flow rate, and the peak gas flow rate is the other gas flow rates. Therefore, when the gas flow rate is changed a plurality of times instead of once, the peak gas flow rate period refers to all the periods, and the peak gas flow rate refers to all the gas flow rates.

[0017]

FIG. 5 is a schematic diagram showing the size of the molten pool and the penetration depth when the current is constant and the plasma gas flow rates are different. As shown in FIG. 5, even if the plasma gas flow rate increases, the change in the size of the plasma flare is small. Therefore, by increasing the amount of plasma gas, it is possible to deepen only the amount of penetration without increasing the width of the molten pool.

Therefore, in the present invention, the plasma gas flow rate is changed in a pulsed manner. FIG. 6 is a diagram showing the discharge state of the molten pool and the plasma arc when the welding current value is kept constant and the flow rate of the plasma gas flow is changed in a pulsed manner.

As shown in FIG. 6, when the plasma gas flow is strong (at the peak gas flow rate), it is a step of penetrating the plate to be welded in the plate thickness direction, and when the plasma gas flow is weak (base gas flow rate), This is a step of stabilizing the molten pool. By repeating the period during which the plasma gas flow is strong (peak gas flow period) and the period during which the plasma gas flow is weak (base gas flow period) every predetermined period, a stronger key than when the plasma gas flow is constant is provided. It becomes possible to form holes.

FIG. 7 is a schematic diagram showing the discharge state of the molten pool and the plasma arc when the electric pulse welding method and the welding method by the plasma gas flow intensity pulsation of the present invention are used together.

As shown in FIG. 7, a period in which the plasma gas flow rate is high and a period in which the welding current is high are synchronized, and a period in which the plasma gas flow rate is low and the period in which the welding current is low are synchronized, or the plasma gas flow rate is set. By synchronizing the period with high welding current and the period with low welding current, and by synchronizing the period with low plasma gas flow rate and the period with high welding current,
It is possible to stabilize the welding itself and increase the penetrating force more than in the case shown in FIG. 7.

As described above, in the present invention, the contradiction existing in the conventional plasma arc welding method can be eliminated, and the welding can be stabilized by the pulse-like fluctuation of the plasma gas flow rate, resulting in deep penetration. Increased penetration can be obtained.

With this, it is possible to set an appropriate plasma gas flow rate corresponding to the peak current and the base current respectively, to suppress the increase of the melt pool more than necessary, and at the same time, to efficiently discharge the plasma gas. . As a result, it is possible to easily achieve welding in a welding region (thick wall region, increase in deposited metal, all positions) that could not be achieved by conventional electric pulse welding, and other welding methods (TIG / MIG
It becomes possible to perform more efficient welding in the welding field equivalent to ().

[0024]

Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 4 is a diagram showing a welding apparatus that can be used for carrying out the gas pulse welding method of the present embodiment. The plasma gas cylinder 10 is connected via a pipe 11a.
The pipes 14 and 15 are connected to a gas pulse generation pipe system connected in parallel, and the pipes 14 and 15 join the pipe 11b and are connected to the plasma torch 1. The pipe 14 is a base gas flow path, and a base gas flow rate adjusting valve 16 is provided. On the other hand, the pipe 15 is a peak gas flow path, and a peak gas flow rate adjusting valve 18 and a pulse generating solenoid valve 17 are provided in series. The opening / closing of the solenoid valve 17 is turned on / off based on the pulse cycle of the gas pulse set in the controller 13. The flow meter 20 is installed in the pipe 11b.
(For example, a fast response mass type) is provided. The high-speed response mass type flow meter 20 is a device that accurately measures the value of gas flow rate at high speed.

The welding power source 12 supplies the welding voltage to the welding torch 1. The pulse-like change of the welding current generated inside the welding power source 12 is output to the controller 13 as a pulse signal. Based on this pulse signal, the opening / closing timing of the solenoid valve 17 is synchronized.

Next, the procedure for setting the gas pulse will be described. The base gas flow rate is set by closing the electromagnetic valve 17 for pulse generation to prevent gas from flowing through the pipe 15 in FIG. 4, and then adjusting the opening degree of the base gas flow rate adjusting valve 16 to adjust the base gas flow rate. Set the flow rate. When setting the peak gas flow rate, the electromagnetic valve 17 for pulse generation is opened to allow gas to flow through both the pipes 14 and 15, and then the opening of the peak gas flow rate adjusting valve 18 is adjusted to adjust the peak gas flow rate. To set.

After setting the respective flow rates of the peak gas and the base gas in this way, the fully open time (peak gas flow time P ₁ ) and the fully closed time (base gas flow time P ₂ ) of the pulse generating solenoid valve are set. , (A) or (b) shown below. By repeating the valve opening and closing of the solenoid valve 17 at this set time, the peak gas flow rate and the base gas flow rate flow alternately, and it is possible to generate the intensity (gas pulse) in the plasma gas flow.

(A) As shown in FIG. 8, as shown in FIG. 3, the pulse generation solenoid valve 17 has a peak current time T ₁ which can be set inside the welding power source 12 and a base current time T _2.
This is a method of synchronizing the opening / closing timing and the opening / closing time of.

In this method, in the case of positive phase, the peak gas flow rate Q ₁ is assigned to the peak current value T ₁ (high current region).
The base gas flow rate Q ₂ is synchronized with the base current value T ₂ (low current range). In the opposite phase, the base gas flow rate Q ₂ is synchronized with the peak current value T ₁ (high current range), and the peak gas flow rate Q ₁ is synchronized with the base current value T ₂ (low current range). In this way, each gas flow rate is set for each current value.

(B) FIG. 9 shows a method of determining the opening / closing timing and the opening / closing time of the pulse generating solenoid valve 17 according to the timer set time held inside the controller 13.

When this welding is performed, since it is not synchronized with the welding current, the peak gas flow rate time T ₃ and the base gas flow rate time T ₄ can be set independently. Therefore, this method is used when, for example, only the plasma gas flow is pulse-controlled at a constant welding current.

Next, the results of comparing the characteristics of the gas pulse plasma arc welding by the method of this embodiment with those of the comparative example will be described.

Table 1 below shows "Welding current constant and plasma gas constant", "Welding current pulsed and plasma gas constant" and "Welding current constant and plasma gas pulsed".
Plasma welding is performed for the above three methods, and the relationship between the weldable plate thickness and the maximum possible gas flow rate is shown. The welding torch and the welding power source have the same specifications, but the welding current value and the welding speed are considered to be optimal for the plasma gas flow rate, so the conditions are not necessarily the same.

[0034]

[Table 1]

However, ◯ indicates that welding is possible, Δ indicates that welding is not possible, and × indicates that the weld is cut. In the case of pulsing the plasma gas flow, the plasma gas flow rate is the value of the peak gas flow rate, and the base gas flow rate is set to the optimum value each time.

From Table 1, it is the welding method with the combination of "constant welding current and pulsed plasma gas" that has the widest possible welding area, and the narrowest one is "constant welding current and constant plasma gas". It is the welding method by the combination of ".

From the results shown in Table 1, it can be said that the plasma gas pulse welding method is a welding method that allows the maximum flow rate of the plasma gas, and as a result enables thick plate thickness welding.

Table 2 below compares the welding characteristics of the peak gas flow rate period and the base gas flow rate period by changing the ratio of the respective times. From Table 4, assuming that the peak gas flow time is 1, there is a melting effect when the base gas flow time ratio is 1.0 or less, and the base gas flow time ratio is 0.3.
In the above cases, the molten pool has a cooling effect. Therefore, in order to obtain both the penetration effect and the cooling effect of the molten pool, the base gas flow time ratio is set to 0.3 to 1.0.

[0039]

[Table 2]

Table 3 below shows a comparison of welding characteristics by changing the ratio between the peak gas flow rate value and the base gas flow rate value. From Table 3, assuming that the peak gas flow rate is 1,
When the base gas flow rate ratio is 0.3 to 0.7, there is a melt-in effect, and when the base gas flow rate ratio is 0.7 or less, there is a melt pool cooling effect. Therefore, the base gas flow rate ratio is set to 0.3 to 0.7.

[0041]

[Table 3]

Table 4 below shows that a horizontal fixed pipe (material to be welded) having a plate thickness of 12 mm is provided with an I-shaped groove-shaped welding line along the circumference, and a plasma torch is provided along the circumferential welding line. The result of having evaluated the welding characteristic when plasma keyhole welding (penetration depth 12mm) was implemented, turning [circle] clockwise. The welding characteristics are obtained by paying attention to the backside bead shape and evaluating the evaluation for each posture (every time).

[0043]

[Table 4]

Regarding the posture, however, the upper end of the fixed tube is assumed to be at 12 o'clock and the lower end is assumed to be at 6 o'clock, and the welding position is indicated by a clock.

The combinations of welding construction methods are, in order from the left column of Table 4, "constant welding current and constant plasma gas flow rate",
Four conditions of "Welding current pulsed and plasma gas flow rate constant", "Welding current constant and plasma gas flow rate pulsed" and "Welding current pulsed and plasma gas pulsed" were carried out. The evaluation criteria are as follows. “Good” → As shown in FIG. 10, it is a case where a back wave formed on the back surface of the welded portion has a bead shape in which the back wave is convex or flush with the base metal. Also, no harmful undercut is generated on the surface. “Backside depression” → This is a case where a bead shape in which the backside wave formed on the backside of the welded portion is more concave than the base metal as shown in FIG. Generally, it is evaluated as inappropriate as a weld bead. "Melting through" → As shown in Fig. 12, the molten pool that is supposed to be formed during plasma welding is affected by gravity and flows down from the base metal. In this evaluation test, the phenomenon of burn-through was often observed when the user was in the upward posture.

As is clear from Table 4, in the case of "constant welding current and constant plasma gas flow rate", good welding was obtained only in the range from 12:00 to 1:00 among the welding positions. . It can be said that the welding method in which both the welding current and the gas flow rate are constant, only the downward welding posture is established, and there is almost no flexibility to follow the posture change.

In the case of "Welding current pulsed and plasma flow rate constant", good welding was obtained in the range from 10:00 to 5:00. This is because, except for the upward posture (5:30 to 6 o'clock) and the upward upward posture (range from 6 o'clock to 9 o'clock), a good weld bead can be obtained, but the upward posture and the upward upward posture (6 o'clock to 6 o'clock). In the posture range (9 o'clock range), it is shown that due to the effect of gravity, the molten pool undergoes rapid melt-down, and the weld bead does not hold.

In the case of "Welding current constant and plasma gas flow rate pulsed" and "Welding current pulsed and plasma gas pulsed", good welding beads were obtained over almost the entire circumference except for a part, and slightly. In the case of the upward posture and the upward upward posture (range from 6 o'clock to 9 o'clock), the inner surface dent of the welding bead appears.

From the above results, as the plasma keyhole welding which has the flexibility to follow the ever-changing posture like the fixed pipe all-position welding, the method of giving strength to the plasma gas flow is the best. You can see that Even if only the welding current is pulsed (electric pulse welding method), it is possible to follow a certain degree of posture change, but depending on the posture, there are places where welding does not work at all. Further, by synchronizing with the method of making the plasma gas flow strong and weak (gas pulsing), it is possible to further expand the proper welding range as compared with "constant welding current and pulsing plasma gas flow rate".

As described above, from Table 4, the method of giving strong and weak pulsation to the plasma gas flow (gas pulse plasma arc welding method) is sufficiently superior to the conventional plasma welding with a constant gas amount. Is recognized. However, even if a method of giving strong and weak pulsations to the plasma gas flow is used,
The drawback that it is difficult to move upward (up to 6 o'clock to 9 o'clock) has not been solved.

Therefore, this part is improved as follows. FIG. 13 shows an upward upward posture (from 6 o'clock to 9 o'clock).
In the welding of (time range), the plasma arc column, the molten pool, and the direction in which the gravity related to the molten pool influences (the arrow in the figure) is shown.

FIG. 14 shows a plasma arc column, a molten pool, and a direction of gravity (indicated by an arrow in the figure) on the molten pool in welding in an upward and downward posture (range from 3:00 to 6:00). It is a thing.

In FIGS. 13 and 14, the welding proceeding directions are opposite to each other, and the welding postures are the same. However, when welding is not possible in the welding attitude of FIG. 13, welding is possible in the welding attitude of FIG. 14, the following can be inferred.

Plasma welding is another welding method (TIG,
Compared with MIG), the positional relationship between the welding torch generating the arc and the molten pool formed is greatly different. In the case of plasma welding, the molten pool is always formed in the direction opposite to the traveling direction when viewed from the plasma arc column. In other welding methods (TIG, MIG), the molten pool is located directly under the arc column.

When the difference in posture is taken into consideration in the positional relationship between the plasma arc column and the molten pool, the process proceeds upward (see FIG. 1).
3) and the downward progression (Fig. 14), the position of the molten pool with respect to the plasma arc column and the influence of gravity are completely opposite, and in the case of downward progression where welding is possible, the plasma arc is directed ahead of the direction affected by gravity. There is a column and the arc column supports it to maintain the molten pool. on the other hand,
In the upward progression, there is nothing that supports the molten pool ahead of the direction in which gravity affects, so the molten pool melts down under the influence of gravity.

Further, although one of the forces for holding the molten pool is surface tension, it is difficult to hold the molten pool larger than other welding methods (TIG, MIG) only by the surface tension.

From the above, in order to hold the molten pool over the entire circumference, as shown in FIG. 15, the filler wire is directly melted from the direction opposite to the welding advancing direction toward the welding advancing direction. Supply in the pool. As a result, the effects of adjusting the viscosity of the molten pool, controlling the solidification phenomenon of the molten pool, and expanding the allowable range for gaps and misalignments are obtained, and it becomes easier to put into practical use.

Table 5 below shows the welding characteristics when the filler wire was supplied to the molten pool. Table 5 was welded under the same conditions as Table 4 except that the filler wire was supplied. Plasma keyhole welding (penetration depth 12 mm)
In particular, the shape of the bead on the back surface is particularly noticed and the evaluation is expressed for each posture (for each time). The evaluation criteria are the same as in Table 4.

As is clear from Table 5, as shown in FIG. 15, only by supplying the filler material wire, the burn-through phenomenon was not observed under any of the conditions of the four kinds of welding methods. In the case of "Welding current constant and plasma gas flow rate pulsed" and "Welding current pulsed and plasma gas pulsed", stable backside bead could be obtained in all positions.

From the results shown in Table 5, during plasma keyhole welding, the horizontal fixed tube was completely removed by using both the strong and weak pulsation of the plasma gas flow (gas pulse plasma welding method) and the backward supply of filler material (filler welding method). Posture welding becomes possible.

Further, by adding the function of automatically controlling the arc length so as to keep it constant, it is possible to obtain a more stable back bead in all postures.

[0062]

[Table 5]

FIG. 16 is a schematic diagram showing the second embodiment of the present invention. 16, the same components as those in FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted. 16 is different from FIG. 4 in that a third pipe 21 is provided in parallel with the pipes 14 and 15,
In this pipe 21, a second peak gas flow rate adjusting valve 22 and
The difference is that the second pulse generating solenoid valve 23 is provided in series. The opening / closing timing of the solenoid valve 23 is set by the controller 13, and the opening degree of the flow rate adjusting valve 22 is also set by the controller 13.

When a plasma gas is supplied to the torch 1 by the apparatus thus constructed, the pulse-like change in the gas flow rate becomes as shown in FIG. That is, gas flow rate Q
2 is a base gas flow rate, and is a gas flow rate that is determined according to the opening degree of the adjusting valve 16 provided in the pipe 14 when the solenoid valves 17 and 23 are both closed. The gas flow rate Q ₁ is the first peak gas flow rate, which is determined based on the opening degree of the flow rate adjusting valve 18 and the opening degree of the flow rate adjusting valve 16 when the solenoid valve 23 is closed and the solenoid valve 17 is open. Is. Gas flow rate Q ₃
Is the flow control valves 16, 1 when the solenoid valves 17, 23 are open.
It is a gas flow rate determined based on the opening degrees of 7 and 22. The pulse period T ₁ is a period in which only the solenoid valve 17 is open, and the pulse period T ₅
Is the period when the solenoid valve 23 is open. Also, the pulse period T ₂
Is the period when both the solenoid valves 17 and 23 are closed, and the period D ₁
Is a delay time after the solenoid valve 17 is opened until the solenoid valve 23 is opened.

As described above, the apparatus shown in FIG. 16 can change the gas flow rate in a pulsed manner of three stages shown in FIG. As a result, as shown in FIGS. 18 to 20, in addition to the base gas flow rate, various pulse-like changes in the gas amount having two peak gas flow rates can be given.

In FIG. 18, the period D ₁ is 0, and the pulse period T ₁ > T
_In the case of _2, the period D ₁ is 0 <D ₁ ≦ T ₁ −T ₂ and the pulse period T ₁ > T ₂ in FIG. Further, FIG. 20 shows a period D
₁ is the case where D ₁ = T ₁ −T ₂ and the pulse period T ₁ > T ₂ .

When the apparatus having the two gas supply pipes shown in FIG. 4 is used to provide the gas flow rate with the two-step pulse-shaped waveform fluctuations shown in FIGS. 8 and 9, in practice, as shown in FIG. The change in the plasma gas flow rate is not an accurate pulse waveform, and rises and falls tend to be dull. This is because the plasma gas is a compressible fluid, so it cannot follow the opening / closing operation of the electromagnetic valve for pulse generation with good responsiveness, and uses a resin hose such as Teflon hose whose cross-sectional area changes in the piping path depending on the flow rate and pressure. If the gas flow rate suddenly increases, the cross-sectional area swells first and an accurate gas flow rate cannot be instantaneously supplied.If the torch tip and the gas supply source are in a distant positional relationship, the plasma hose in the cable It is considered that the pressure loss increases due to the increase in the pressure loss and the delay in the supply of the plasma gas.

On the other hand, since the current pulse can sufficiently provide a high-speed response, it is possible to instantaneously switch between the peak current and the base current. Therefore, the gas flow rate is delayed with respect to the change of the welding current. This delay has an adverse effect when welding a material to be welded having a large plate thickness.

In the case of plasma welding, during the peak current period or the period in which the peak current period and the peak gas flow rate period are synchronized, the plasma arc column penetrates the entire region of the material to be welded in the plate thickness direction to form a keyhole. While welding. In this case, as shown in FIG. 22, if there is a delay in the pulse waveform of the plasma gas flow rate, the keyhole to be formed in the material to be welded instantly when the welding current and the plasma gas enter the peak period. It is not formed, and the molten pool does not grow instantaneously, which is delayed in time. For this reason,
At the beginning of the peak period of the welding current and plasma gas, the plasma arc may be disturbed or the molten pool may be disturbed. It is also conceivable that the welding conditions that can be adopted are narrowed or that the molten pool is destroyed in an extreme case due to the disturbance of the plasma arc.

On the other hand, when the pulse waveform is set to change in three steps as shown in FIGS. 17 to 20 by the device shown in FIG. 16, the pulse waveform is changed in two steps as shown in FIG. Also becomes closer to the set value on the program. That is, as shown in FIG. 23, when the gas flow rate is pulse-changed in two steps up to now, the delay of the rise of the gas pulse is about 0.3 seconds, whereas as shown in FIG. When changing in three steps, the delay of the rise of the gas pulse was 0.1 second.

FIG. 25 shows the case where the gas flow rate is changed in two steps, and FIGS. 26 and 27 show the case where the gas flow rate is changed in three steps. In FIG. 26, the gas flow rate is changed in two steps even when the pulse falls. 27 is a graph showing the actual change of the plasma gas flow rate and the key wheel depth when the peak gas flow rate period is not provided during the fall. As shown in these figures, by changing the gas flow rate in three steps, the actual change in the plasma gas flow rate becomes closer to the set value.

From this, the maximum flow velocity of the plasma gas flow can be delayed together with the time required for the keyhole depth to reach the deepest portion and the time until the molten pool grows to the maximum extent. Disturbance of the molten pool can be suppressed.

As described above, as a specific application of the gas pulse plasma arc welding method in which the plasma gas flow rate is changed in three steps, keyhole welding of a material to be welded having a thick plate thickness (for example, a plate thickness of 12 mm or more) is performed. There is deep penetration welding that does not intentionally form a keyhole (non-keyhole welding). When the gas pulse welding is performed in the mode of the three-step pulse change at the time of the strong plasma gas flow and the condition of poor gas flow discharge, the disturbance of the plasma gas flow can be suppressed. When the plate thickness is thin, such a turbulence of the plasma gas flow is unlikely to be a problem.

Particularly, when the gas flow rate is changed in a pulse manner in the mode shown in FIG. 20, the rising process of the peak gas rises in two steps, and the fall decreases from the maximum flow rate Q ₃ to the base gas flow rate Q ₂ all at once. The ratio between the peak gas flow rate and the base gas flow rate can be extremely increased as compared with the case of the pulse. This makes it easy to perform non-continuous keyhole welding, which was difficult with current pulses and two-stage gas pulses, that is, keyholes are formed only at peak times and disappear at base times. can do.

With this discontinuous keyhole welding, since the difference between the peak time and the base time is large, the pulse effect becomes more prominent than that of the embodiment shown in FIG. It is possible to perform welding under a welding condition close to a limit condition such as a keyhole welding of a material (16 mm or more) and a deep penetration welding without forming a keyhole (non-keyhole welding).

Next, the results of actual welding experiments in the gas pulse mode shown in FIGS. 18 to 20 will be described. Table 6 below shows the relationship between the plate thickness and the welding result when keyhole welding is performed in the three types of gas pulse modes shown in FIGS. 18 to 20.

[0077]

[Table 6]

When the plate thickness is 16 mm or less, the welding quality is good in the gas pulse mode shown in FIG. 18, and when the plate thickness is 6 mm or more, the gas pulse mode shown in FIGS. there were. When the plate thickness is 6 to 16 mm, it is good in any of the gas pulse modes, but from Table 6, in the case of a medium wall thickness or less that does not require much energy for keyhole formation, as shown in FIG. In addition, it can be said that the case where the maximum peak gas flow rate is increased at once and decreased in two steps does not affect the shape of the molten pool and the keyhole formation. On the other hand, in the case of a thick wall that requires a large amount of energy and a long time to form the keyhole, the gas pulse mode shown in FIGS. The turbulence of the plasma gas generated in 1 was reduced, and the amount of spatter and drose discharged on the back surface was extremely small, and stable welding was possible throughout.

23 and 24 show two-stage gas pulse welding,
The result of comparing the plasma gas flow rates actually obtained in the three-stage gas pulse welding is shown. In case of 2-stage gas pulse, set peak gas flow rate (4.0 liter / min)
Since 0.3 seconds have passed since the solenoid valve was opened, the peak gas flow rate period should be 0.3 seconds or more if the welding condition requires this peak gas flow rate setting value. It must be set, and the pulse period cannot be shortened. Further, if the peak gas flow rate is increased to 5.5 liters / minute and the rising of the peak is accelerated, the gas flow rate becomes excessive in the latter half of the peak gas flow rate period, and extra force is applied to the plasma arc, the molten pool, etc. , Welding itself becomes quite unstable.

On the other hand, in the case of three-stage gas pulse welding, the second peak gas flow rate was set to 5.5 liter / min, and
By setting the peak gas flow rate to 4.0 liters / minute, which is a target for welding quality, a rise time of 0.1 seconds is sufficient. This is about 1/3 of the two-step gas pulse method
The time is shortened and a gas pulse with extremely excellent responsiveness can be obtained.

Next, the results of welding in the gas pulse mode shown in FIGS. 19 and 20 will be described in comparison with the case of the two-stage gas pulse. FIG. 25 shows pulsing of plasma gas in the two-stage gas pulse welding method, and FIG. 26 shows pulsing of plasma gas in the three-system gas pulse welding method shown in FIG.

This welding condition is that the plate thickness of the material to be welded is 19 m.
Since it is thick as m, the set value of peak gas flow rate is 7.0 liters /
It's a lot. In the case of welding by the two-stage gas pulse welding method of FIG. 19, the peak gas flow set value (= 7.
It takes 0.4 seconds to reach 0 liters / minute). However, if you look at the diagram of the relationship between keyhole depth and time in the lower row,
It takes 0.5 seconds from the opening of the solenoid valve to the formation of the keyhole, which is later than the time required to reach the peak gas flow rate set value.
Due to this delay, even if a long peak gas flow rate period of 0.6 seconds is set, the period during which the keyhole is actually formed is only 0.1 seconds, and only 1/6 of the set value can be expected. . Also, looking at the actual gas flow rate diagram in the middle stage, it took about 0.4 seconds to reach the base gas flow rate setting value of 3.0 liters / minute after the solenoid valve was closed. There is almost no base holding time. As a result, from the diagram of the lower keyhole depth and time,
At the base time, the keyhole depth is expected to return to 7 mm, but the keyhole depth is actually returned to 9 mm. If this is repeated, the keyhole depth and the molten pool will grow excessively, and eventually the weld will be destroyed.

On the other hand, in the case where the three-stage gas pulse welding method shown in FIG. 26 was used, the peak gas flow rate (5. 5%) for relaxing the delay time of keyhole formation was reached in the middle of reaching the peak gas flow rate = 8.5 liters / minute. Since 0 liter / min) is provided, the peak gas flow rate can be selected according to the keyhole formation state.

Regarding the time during which the keyhole is formed,
In the three-step gas pulse welding method, keyhole formation time = 0.
Since it was actually formed in about 0.2 seconds for the setting of 3 seconds,
About 2/3 of the set value can be expected. Further, even when the peak gas flow rate is lowered to the base gas flow rate, since it is lowered in two steps, it is possible to hold time, and it is possible to return to the original keyhole depth during the base period. The growth of the molten pool could be suppressed. Therefore, it can be said that the gas pulse control shown in FIG. 22 is a control method effective for a thick plate thickness.

As a special example of the case of FIG. 19, the control method of FIG. 20 is effective when it is desired to make the difference in the welding mode between the peak gas flow rate period and the base gas flow rate period larger than that of the control method of FIG. In the gas pulse mode of FIG. 20, as shown in FIG. 27, the time to reach the maximum peak gas flow rate can be set longer than that of the control method of FIG. Due to this effect, the keyhole diameter and the amount of the molten pool can be made larger than in the control method of FIG. 19, and the keyhole formation time can be further lengthened.

In this state, since the first and second electromagnetic valves for pulse control are closed at the same time, the molten pool flows into the keyhole portion all at once and is completely blocked. Then, the cycle of repeating the process of forming a keyhole again on the surface of the completely welded material to be welded and growing the molten pool is repeated. This makes it possible to perform continuous keyhole welding instead of continuous keyhole welding. Therefore, although the welding speed is not high, stable keyhole welding is possible, and it can also be utilized for deep penetration welding such as multi-layer welding in which keyholes are welded.

Next, an example of a gas pulse plasma arc welding method for supplying a filler wire will be described. In this embodiment, the filler metal wire is supplied to the molten pool formed by the plasma arc from two or more places. The adjustment of cooling and solidification of the molten pool, the increase of the amount of weld metal and the welding speed, and the respective welding positions (Down, standing and up)
This is a welding method that is effective in improving the adverse effects of the above and adjusting the performance of the weld metal.

In order to achieve both high quality and high efficiency by the non-consumable electrode welding method such as plasma welding, it is necessary to increase the heat input amount. Therefore, it is necessary to enlarge the molten pool and widen the welding area. There is. However, when the molten pool is increased, the non-consumable electrode welding method has the following new problems. (1) As shown in FIG. 28, in the plasma welding method,
There are gravity (FG) applied to the melt pool and surface tension (FR) applied to the melt pool as main forces that affect the melt pool, and the relationship between these two forces makes the melt pool as follows. When (FG) ≤ (FR), the molten pool can be maintained. When (FG)> (FR), the molten pool cannot be maintained.

When the gravity (FG) applied to the melt pool increases in proportion to the increase of the melt pool and becomes larger than the surface tension (FR) applied to the melt pool, it becomes impossible to maintain the melt pool. (2) As shown in FIG. 29, in the case of plasma welding, the depth of the molten pool is extremely deep only in the region directly below the irradiation of the plasma arc, but when leaving the region immediately below the irradiation of the plasma arc, the molten pool itself becomes shallow. Become. Even if the filler material wire is supplied to this shallow molten pool, it cannot be efficiently melted, and if the supply speed of the filler material wire is increased,
It will hit the base material without melting and there is a restriction on the feed rate of the filler wire. (3) As shown in FIG. 30, when the welding speed is low, the molten pool is contained in the area surrounded by the shield gas flow around the plasma gas flow, but when the welding speed is increased, the melting pool is melted. There is a problem in that the pool greatly extends rearward in the welding direction, its entire length becomes long, and the pool comes out of the protection region by the shield gas, and the weld surface is oxidized at this portion.

Therefore, two or more filler material wires are simultaneously or alternately supplied to one melting pool. As a result, it becomes possible to supply the filler material wire in an amount corresponding to the large amount of the molten pool formed at the time of high current. Therefore, welding can be performed in a high welding speed range, and a welding speed equal to or higher than that of the consumable electrode welding method such as MIG welding and submerged welding can be achieved.

FIG. 31 is a schematic diagram showing the structure of an apparatus for simultaneously supplying two filler metal wires. Welding is performed by causing a plasma arc to be generated from the welding torch 30 on the material to be welded 28 to form the welding bead 29. Then, with respect to one non-consumable electrode welding torch 30, two or more (two in the illustrated example) filler material wires 31 are accurately supplied to a predetermined position from the same direction by the guide tip 32. It has become. Two filler material wires 31 are delivered from a wire controller 35 including a remote control box 36, and the filler material wires 31 are supplied to the guide tip 32 by a wire feeder 34 provided for each filler material wire 31. Is
The filler wire 31 is guided by the guide tip 32 and supplied to the molten pool.

Further, the oscillation device 33 oscillates the guide tip 32 in the direction orthogonal to the welding direction (indicated by the arrow in the drawing). The wire controller 35 controls the feeding of the filler material wire 31 by the signal from the welding power source 37 and also controls the oscillation of the guide tip 32 by the oscillation device 33. The welding power source 37 applies a welding voltage between the non-consumable electrode of the welding torch 30 and the material to be welded 28.

As a basic operation, as shown in FIG. 33, a plasma arc is generated on the surfaces of the welding torch and the material to be welded (base material) in the presence of a shielding gas, and the heat quantity of the arc is utilized to make the material to be welded. The (base metal) surface is welded while forming a molten pool, and two filler metal wires 31 are melted in a predetermined supply amount from the rear through the guide tip 32 to the formed molten pool. Weld metal is formed while being supplied to the pool. The supply amount and supply timing of the filler wire 31 are sequentially changed according to the welding conditions.

Next, the specific operation will be described. With non-consumable electrode welding method (TIG welding, plasma welding),
In order to simply obtain high-efficiency welding, it is naturally necessary to melt the filler material (wire) more in a short time, which inevitably results in a high welding current value and a high welding speed.
Under these conditions, supplying two or more filler material wires is effective in the following points.

FIG. 33 is a diagram showing the effects of cooling the molten pool when the number of supply wires is one and when it is two. As shown in FIG. 33, the keyhole 40 is formed between the materials to be welded 28 by the plasma 41 protected from the outside air by the shield gas 42 supplied from the welding torch 1, and the molten pool is formed behind the welding torch 1 in the traveling direction. 43 is formed. 33A shows the case where only one filler wire 31 is supplied, and FIG. 33B shows the case where two filler wire 31 are supplied. In the figure, the range in which the molten pool 43 is affected by the supply of the filler material wire 31, that is, the cooling region 44 is shown by hatching. However, when the filler metal wire 31 is one, the cooling region 44 is small. , The area not affected by it is wide. However, when the number of the filler material wires 31 is two, the range affected by the cooling is large, and the entire melt pool on the surface of the material to be welded 28 extends. Thus, by supplying the two filler material wires 31, it is possible to efficiently suppress the increase in the molten pool 43 due to the increase in the current.

FIG. 34 (a) shows the filler material wire 31 supplied at a high speed to increase the cooling effect of the melt pool 43, and FIG. 34 (b) shows the filler material wire 31 having a large diameter. The cooling effect is increased by (c), and the cooling effect is increased by supplying two filler material wires 31.

In FIG. 34, when the supply amount of the filler material wire 31 is two or more, the supply speed of the filler material wire 31 is increased and the wire diameter of one filler material wire 31 is increased. It has been shown that by increasing the thickness, it is possible to effectively supply a large amount of filler material. In particular, in non-keyhole overlay welding as shown in FIG. 34, the molten pool has a large surface area, but the penetration depth is extremely shallow compared to the surface area. For this reason, if only one filler wire is supplied, the depth of the pool is shallow and the filler reaches the bottom of the molten pool before completely melting and hits the base metal. Therefore, the amount of the filler material supplied cannot be increased. Further, even if the wire diameter is made thicker, it takes an additional melting time to hit the base metal in the same manner, so that the effect of increasing the amount of the filler material supplied can hardly be expected.

On the other hand, when two or more filler materials (wires) are supplied, the supply amount can be secured by the number of wires without increasing the supply rate per wire, and in addition, the melt pool formed widely and shallowly can be used. It becomes possible to effectively apply the amount of heat to the melting of the filler material.

Even in the same molten pool 43, the shape and the penetration depth are slightly different between the front and the rear of the fusion pool, but when a plurality of filler wires are supplied, the filler material to be melted at each position is melted. It becomes possible to change the supply amount of the filler metal, and it becomes possible to increase the supply amount of the filler metal without difficulty in the molten pool.

FIG. 35 is a diagram showing a welding mode in which two filler metal wires 31a and 31b are supplied aiming at two positions separated from each other in the traveling direction of the welding torch 1, showing the effect when the welding speed is high. Show. That is, the total length of the molten pool 43 formed behind the welding torch 1 in the advancing direction becomes longer on the surface side of the material to be welded as the welding speed increases. This causes the tail portion of the molten pool to come off the shield gas protection region, as described with reference to FIG. As shown in FIG. 35, the main wire 31a of the filler material is supplied to the front of the welding pool and the cooling wire 31b is supplied to the rear of the molten pool. In this way, by supplying the two filler metal wires 31a and 31b to positions separated in the welding direction, it is possible to prevent the total length of the molten pool 42 from increasing even if the welding speed is high, Enables stable welding.

Mainly, the filler wire 3 ahead of the welding direction.
Reference numeral 1a is a main wire for obtaining a predetermined amount of filler material to be supplied, and a cooling wire 31b for cooling a tail portion (last portion) of a molten pool with a wire located behind at a predetermined interval.
Becomes With such a positional relationship, solidification is promoted by rapidly cooling the tail portion (last portion) of the molten pool, which tends to be long due to the high speed, so that the entire length of the molten pool can be inevitably shortened.

As described above, the selection of the cooling rate at each position of the molten pool, which was not possible with the normal supply of one wire, allows the second wire to play a clear role, thereby making a positive and fine adjustment. The melt pool can be easily controlled.
Further, even when used in combination with weaving, when supplying two or more wires, it is more effective than supplying one wire.

Further, in the case of non-keyhole welding / soft plasma welding, by heating the filler metal wire in advance to form a so-called hot wire, the wire supply amount during welding can be greatly increased. The efficiency can be improved.

[0104]

As described above, in the present invention, the plasma gas flow rate is changed in a pulsed manner, and the time and the gas flow rate are set to an appropriate ratio between the peak gas flow period and the base gas flow period. Therefore, the molten pool can be stabilized and a deep penetration can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a core and a flare that form a plasma arc.

FIG. 2 is a diagram comparing flare and spread of a molten pool in a case where welding is performed at a low current (a) and a case where welding is performed at a high current (b).

FIG. 3 is a diagram showing a current waveform.

FIG. 4 is a diagram showing an apparatus used in an embodiment of the present invention.

FIG. 5: When the gas flow rate is low (a) and high (b)
FIG. 8 is a diagram comparing the flare and the size of the molten pool in FIG.

FIG. 6 is a diagram showing a state of keyhole formation in the case of peak gas flow rate (a) and the case of base gas flow rate (b).

FIG. 7 is a diagram showing the state of keyhole formation in the case of peak gas flow rate and peak current (a) and in the case of base gas flow rate and base current (b).

FIG. 8 is a diagram showing current and gas flow rate waveforms.

FIG. 9 is a diagram showing current and gas flow rate waveforms.

FIG. 10 is a view showing a shape of a welding bead.

FIG. 11 is a view showing a shape of a welding bead.

FIG. 12 is a diagram showing a shape of a molten pool.

FIG. 13 is a schematic diagram showing the falling of the molten pool in the case of upward upward welding.

FIG. 14 is a schematic diagram showing a state of a molten pool in the case of upward downward welding.

FIG. 15 is a schematic view showing an example of supplying a filler wire.

FIG. 16 is a view showing an apparatus used in a method according to another embodiment of the present invention.

FIG. 17 is a diagram showing a gas flow rate waveform of this example.

FIG. 18 is a diagram showing various aspects of the gas flow rate waveform.

FIG. 19 is a diagram showing various aspects of the gas flow rate waveform.

FIG. 20 is a diagram showing various aspects of the gas flow rate waveform.

FIG. 21 is a diagram showing a comparison between a current waveform and a gas flow rate waveform when the gas flow rate is changed in two steps.

FIG. 22 is a view showing changes in the keyhole depth and the amount of molten pool in the same manner.

FIG. 23 is a diagram showing changes in the set value and the detected value of the gas flow rate showing the two-step gas pulse welding method.

FIG. 24 is a diagram showing changes in set value and detected value of gas flow rate in the three-step gas pulse welding method.

FIG. 25 is a diagram showing a plasma gas flow rate and a keyhole depth in the case of a two-step gas pulse welding method.

FIG. 26 is a diagram showing a plasma gas flow rate and a keyhole depth in the case of a three-step gas pulse welding method.

FIG. 27 is a diagram showing a plasma gas flow rate and a keyhole depth in the case of a three-step gas pulse welding method.

FIG. 28 is a diagram showing a molten pool depth.

FIG. 29 is a cross-sectional view showing the shape of a molten pool.

FIG. 30 is a plan view showing the shape of a molten pool.

FIG. 31 is a perspective view showing another embodiment of the present invention.

FIG. 32 is a cross-sectional view showing a molten pool in the case of supplying the filler material wire in this example.

FIG. 33 is a diagram showing a comparison of the molten pool cooling states when the number of the filler wire is one and when the number of the filler wire is two.

FIG. 34 is a diagram showing a comparison of the cooling states of the molten pools for various filler metal wires and their supply modes.

FIG. 35 is a view showing a cooling state when two filler metal wires are supplied to positions separated in the welding direction.

[Explanation of symbols]

 1: Welding tip 2: Material to be welded 3: Plasma arc 4: Core 5: Flare 16, 18, 22: Gas flow rate adjusting valve 17, 23: Solenoid valve for pulse generation 31, 31a, 31b: Filler material wire 41: Plasma arc 42: Shield gas 43: Molten pool 44: Cooling area

Claims (4)

[Claims] 1. A gas plasma welding method for periodically varying the gas flow rate of a plasma gas flow in a pulsed form, wherein the plasma gas flow is a pulse in which a period of peak gas flow and a period of base gas flow are alternately continuous. The base gas flow rate period is 0.3 to 1 times the peak gas flow rate period, and the base gas flow rate is 0.3 times the peak gas flow rate.
To 0.7 times the gas pulse plasma welding method. 2. The plasma gas flow rate is one of a flow rate between the peak gas flow rate and the base gas flow rate between the peak gas flow rate period and the base gas flow rate period.
Alternatively, the gas pulse plasma welding method according to claim 1, wherein the method fluctuates with two or more periods. 3. The gas pulse plasma welding method according to claim 1, wherein the horizontal fixed tube is welded in all positions by combining and synchronizing the welding current value and the plasma gas flow rate. 4. A horizontal fixed pipe is welded in all positions by supplying a filler metal wire to a molten pool formed at the rear of the welding progress direction by a plasma arc column. The gas pulse plasma welding method according to claim 1.