JPS63260675A - Multi-electrode submerged arc welding method - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a defective product by detecting the presence or absence of the existence of a molten pool at the rear position at the prescribed distance from a last electrode by ultrasonic waves to regulate the welding speed based on its detected result. CONSTITUTION:A combination transmission and reception type ultrasonic angle beam probe 4 to detect the molten pool 7 at the position separated by 5-25 cm at the rear side from the last electrode 3 among electrodes 1-3 is arranged. The probe 4 set at the position separated by the prescribed distance Y from a melting boundary part 21 of material 6 to be welded emits the ultrasonic waves 22 toward the material 6 to be welded. When the molten pool 7 is not filled on the melting boundary 21, echoes F are generated on a cathode-ray tube of a flaw detector 18 on this part and the danger of the occurrence of an undercut is predicted. Based on this signal, the welding speed is reduced or regulated, by which the occurrence of the undercut can be surely prevented. Accordingly, the occurrence of the defective product is prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to control of submerged arc welding, and particularly relates to control of submerged arc welding.
The present invention relates to a method of detecting conditions for the occurrence of welding defects in multi-electrode submerged arc welding using ultrasonic echoes, and controlling welding conditions based on the detailed information.

[Conventional technology]

Submerged arc welding is still widely used as a highly efficient welding method, and the development of productivity improvement, automation, and labor-saving technologies is progressing. In order to maintain the welding properties, the welding speed is set at the limit speed at which welding defects (undercuts) do not occur. However, as long as welding is performed at such a limit speed, welding defects such as undercuts may occur due to variations in the groove shape, molten slab, and gas generation conditions.

Particularly in unmanned welding, if welding is continued under such conditions, there is a risk of producing a product with continuous defects.

[Problem that the invention seeks to solve]

In order to solve the above problems, it is necessary to monitor welding phenomena and control welding conditions to prevent welding defects from occurring. For visible arc welding method, JP-A-57-7378
As seen in the publication, since welding phenomena can be observed directly, it is relatively easy to monitor them, and automation and labor-saving technology that feeds back the results for control is rapidly progressing with the spread of microcomputers. are doing.

However, in submerged arc welding, there are only a few examples of feedback control based on welding phenomena. This is because the weld zone is shielded by gafflux, making it difficult to directly observe welding phenomena, and it is unclear what welding phenomena should be fed back. The former X-ray fluoroscopy method, which is well known as the welding part 1ilt method, can be used in a laboratory, but requires a large-scale apparatus and is not suitable for application to an actual manufacturing line. In terms of the simplicity of the device, a method for detecting welds using ultrasonic waves is known, and was disclosed in Japanese Patent Application Laid-open No. 59-92.
No. 17/1 proposes a method of controlling weld bead position and penetration by using ultrasonic echoes. However, the above method is aimed at copying the weld line and ensuring weld penetration, and is not effective in preventing undercuts.

Furthermore, in one-sided submerged arc welding, Japanese Patent Laid-Open No. 58-141861 proposes a method in which the arc light penetrating the back surface of the welded material is detected to control the welding conditions and obtain a bead of uniform height. It is difficult to apply this method to double-sided polished submerged arc welding used in the manufacture of high-grade line pipes, and no particular consideration is given to preventing welding defects such as undercuts.

The present invention has been made in view of the current situation, and it is an object of the present invention to provide a high-speed multi-electrode submerged arc welding method that automatically controls the retreating distance of the molten pool and does not cause undercuts.

[Means for solving problems]

The present invention was obtained as a result of various studies on the quantification of the phenomenon of monitoring the occurrence of submerged arc welding defects and its prevention methods. Arrange the electrodes and set the welding speed 1.
In the multi-electrode submerged arc welding method performed at 5 m/ff1 inch or more, the presence or absence of a molten pool at a position 5 to 25 mm behind the final electrode is detected by ultrasonic waves, and a signal indicating that there is no molten pool at that position is obtained. is a multi-electrode submerged arc welding method characterized by reducing the welding speed, and an ultrasonic probe reciprocatingly scans in a direction parallel to the weld line in a range from the final electrode to 25 wa behind it,
The interface between the arc gouging cavity and the molten pool is detected by ultrasonic waves, and the welding speed is increased or decreased so that the distance from the final electrode of the ultrasonic probe at the time of detection matches a reference value. Electrode submerged arc welding method.

[Effect]

The present invention uses ultrasonic waves to monitor the presence or absence of a molten pool near the undercut occurrence limit molten pool retreat distance (hereinafter referred to as reference value) specified by welding conditions, and feeds back the frequency of echo occurrence. , or by monitoring the interface between the arc gouging cavity and the melt pool behind the final electrode by ultrasound and comparing the position with a reference value.

By increasing or decreasing the welding speed as necessary, a bead with high efficiency and no undercut can be provided.

The present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a perspective view showing an embodiment of the present invention in three-electrode submerged mark welding, with flux and molten slag removed from the weld for ease of understanding.

In the figure, 1 to 3 are respectively numbered 1. Second and third (
4 is the final) electrode, and the wire tip of the final electrode 3 is 10 to 2
This is a transmitting and receiving type ultrasonic angle probe arranged so as to be able to detect the molten pool 7 at a position 5 mm behind (distance X).

Here, the probe 4 is always secured at a constant position with respect to the welding electrode by the welding torch holder 8.

In addition, 5 is the arc gouging cavity, 9 is the flux, 1
0 is solidified metal, 11-13 are wire feeding motors, 14-
16 is a welding power source, 17 is a welding operation panel, 18 is an ultrasonic flaw detector, 19 is a calculation/controller, 20 is a welding wheel, and WD is a welding direction.

Now, as shown in FIG. 2, which is a cross-sectional view on a plane perpendicular to the welding direction at the position where the probe 4 is present, a distance Y away from the molten boundary 21 near the surface of the welded material 6 is shown. If the molten boundary 21 is not filled with the molten pool 7, the ultrasonic wave 22 incident on the welded material 6 from the probe 4 set at the position will generate an echo in this area, and the ultrasonic wave 22 will be reflected in the welding line direction. As shown in FIG. 3, which is a combination of a perspective view on a parallel vertical plane and a front view of a cathode ray tube of an ultrasonic flaw detector, in addition to the incident echo T, the cathode ray tube has a molten boundary 21 at the gate part G.
Echo F appears. On the other hand, as shown in FIG. 71 drawn using the same method as FIG. 3, when the molten boundary portion 21 is filled with the molten pool 7, only the incident echo T appears.

That is, while no echo is generated at the gate portion G, the distance X is filled with the molten pool 7, and when an echo is generated, it can be determined that the molten pool 7 is retreating from the distance X.

Upcut occurs when the retreat distance of the molten pool becomes larger due to an increase in welding speed and exceeds a certain limit distance, as described in the known literature (Proceedings of the Welding Society of Japan, vol. 1).
, no, 2. P L36.1983).

Therefore, it is necessary to check in advance the retreat distance of the molten pool at the limit of up-cut occurrence for each welding condition, monitor the presence or absence of the molten pool at that distance, feed back the frequency of echo generation from the boundary 21, and control the welding conditions. For example, it becomes possible to obtain a good bead without welding defects.

Based on this viewpoint, one embodiment of the submerged arc welding automatic control method of the present invention incorporating a molten pool position monitoring system will be described in detail according to the flowchart shown in FIG. 5. First, the groove shape of the workpiece 6 , information such as the target penetration depth is input to the calculation/controller 19 shown in FIG.
Based on that information, the standard welding conditions are extracted from the database created in advance in the storage device of the calculation/controller 19. Step 1: The word step is omitted in parentheses below), welding operation panel 17, the welding conditions are output to the welding power source, etc., and predetermined values are set in each device (2)
. Next, welding is started (3), and ultrasonic waves are made to enter the welding machine 6 from the probe 4 shown in FIG.
The echo of the molten boundary 21 shown in the figure is converted into digital by the A/D converter built in the calculation/controller 19 shown in FIG. is counted and a decision is made to change the welding conditions (6). The reason we decided to change the welding conditions based on the number of times echoes appear is that up-cuts will not occur at levels where echoes appear once every few tens of seconds, and there is no point in changing the welding conditions for such echoes. This is because it targets items that appear multiple times or more per second, which may cause upcuts.

Based on the above knowledge, it is effective to prevent upcut from occurring by lowering the welding speed and keeping the molten pool retreat distance within the standard value.If it is determined that it is necessary to change the welding conditions, the welding speed should be reduced to the current speed. A signal for gradually decreasing the welding speed is outputted to the welding wheel via the welding operation panel 17 shown in FIG. 1 to reduce the welding speed (8) and prevent the occurrence of upcut. However, even if the welding speed decreases, the penetration depth needs to be maintained at a constant value. To extract the required current value for each electrode9), the first
Each electrode welding power source 14 ~ through the welding operation panel 17 shown in the figure
16) to output the current value 10), and at the same time change the welding current to a predetermined value.

Then, it is determined whether the welding is completed (14), and if welding is to be continued, the process from detecting the echo of the welded part (4) is repeated.

On the other hand, if it is not necessary to change the welding conditions, it is necessary to judge whether the current speed is the limit speed of the standard conditions7), and if it is less than the limit speed, the welding speed should be adjusted as described above to approach the limit speed. (11). At this time, it goes without saying that a new welding current value is extracted (12) and outputted (13) in the same manner as described above.

By repeating such control, it is possible to suppress welding defects and obtain a bead with a complete penetration depth.

In the present invention, it is important to monitor the molten pool behavior at the molten pool retreat distance that is the limit for the occurrence of adda cuts.This distance A cavity is formed.

In this section, echoes from the fused defect boundary are always detected, and these echoes cannot be used as a welding defect occurrence monitor. Furthermore, if the molten pool retreat exceeds 25°, adder cuts will occur almost continuously at any welding speed and heat input, so monitoring the molten pool position at a distance greater than this will not be effective.

The welding speed of 1.5 m/min or higher in the present invention is because there is no risk of adder cut occurring in submerged arc welding with two or more electrodes, and in low-speed welding with a welding speed of less than 1.5 m/+*in, especially in the present invention. This is because it is not necessary.

Further, as the couplant between the probe and the material to be welded, it is preferable to use something with a slightly high viscosity such as glycerin, but it is also possible to provide a shoe or the like on the probe and fill it with running water. The point is that the ultrasonic waves should be able to reliably propagate to the material to be welded.

The angle of refraction of the angle probe is most sensitive at around 60°, but
It is preferable that the flaw detection sensitivity is appropriately selected depending on the expected penetration angle θ of the molten boundary 21 (see FIG. 2). It is advantageous to detect the flaw with as high a sensitivity as possible without generating noise. Further, there is no need to pay particular attention to the frequency, and the commonly used 1 to 5 MHz is sufficient for detection.

In FIG. 2, the distance Y between the molten boundary 21 and the incident point of the probe 4 is determined by the refraction angle of the probe selected by predicting the penetration angle θ of the molten boundary 21 in advance. The setting can be calculated based on the plate thickness of the welding material, the number of skips, etc., but due to misalignment during setting or changes in the penetration position, the second
If the position of the molten boundary portion 21 shown in the figure is shifted, the echo will not return and the echo may not be detected even if there is no molten pool. Considering such a case, it is desirable to reciprocate the probe 4 in a direction perpendicular to the weld line to reliably capture the boundary surface 21.

The amplitude of this reciprocating scan does not need to be large, and around 10 m is sufficient. However, the vibration frequency (number of reciprocations/5ee
), if it is too small, there is a problem that the detection failure section becomes long, and in order to perform reliable control, the detection accuracy in the weld line direction needs to be 2.5I or less. Therefore, the frequency is the welding speed v (cw/5ac)
If so, it should be 2Xv (Hz) or more.

In addition, if a surface wave probe is used instead of the angle probe 4 in FIG. 2, there is no need for the above-mentioned back-and-forth scanning and it is considered to be simpler, but the melting at the melting boundary '21 is If the penetration angle θ is large, it becomes impossible to detect echoes in this part, and the detection accuracy varies greatly depending on the shape of the penetration, which limits the usable range.

Note that the detection probe exerts sufficient detection effect even when used alone, but if it is necessary to perform even more precise detection, an additional probe can be installed at a position opposite to probe 4 in Fig. 1 across the welded part. It is also possible to install one probe facing each other and detect the molten pool from both sides.

In the embodiment described above, the probe is placed in the direction of the welding line.
Although the fixed position method was adopted, the probe 4 shown in Fig. 1 was not fixed, but was moved in the welding direction in a range up to 25 mm backward from the final electrode, and the probe position was adjusted using a potentiometer, etc. A detection mechanism is provided, and the probe is moved so as to eliminate the generation of echoes at the molten boundary portion 21 shown in FIG. 2, and the welding speed is varied by detecting the interface between the arc gouging cavity and the molten pool. You may.

That is, at the start of welding, echoes of the probe set immediately after the final electrode are continuously detected from the molten boundary portion 21 by the arc gouging cavity. According to this echo signal, the probe drive device moves the probe in the direction where the echo signal decreases (the direction opposite to the welding direction). Conversely, by driving the probe in the welding direction, the probe is always positioned near the interface between the arc gouging cavity and the molten pool6.Then, the probe position is controlled by a potentiometer, etc. It is detected and compared with the reference value that was input in advance as the limit distance for adda cut occurrence.

Even if a method is adopted in which the welding speed is reduced when the probe position exceeds the reference value, and conversely when it is smaller than the reference value, the welding speed is increased so that it always matches the reference value, Exactly the same effect can be obtained.

〔Example〕

5M50 material in 3-electrode submerged arc welding.

Using a steel plate with a thickness of 12.7 ms, the standard welding conditions were: first electrode welding current 1040A, welding voltage 31V, second electrode welding current 7g0A, welding voltage 33V, third electrode welding current 62V.
The welding voltage was 0 A and the welding voltage was 35 V, the probe position was set at 22 pus behind the third electrode, and the molten pool was monitored in 2 skips. In addition, the longitudinal vibration width tioam and frequency of the probe in the direction perpendicular to the welding line direction are 15 Hz,
The angle probe used was 5 MHz, zircon-lead titanate ceramic resonator, height x width = 10 x IO mm, refraction angle 60
', sensitivity is 70 dB, couplant is glycerin.

The welding speed at which adda cut occurs is 2.6 m/m.
Welding was started at 11 seconds, and after 11 seconds, welding conditions were automatically controlled according to the molten pool monitoring signal. As a result, adder cuts occurred in the welding speeds of 2 and 6 m/min, but good beads without adder cuts were obtained in the parts where automatic control was subsequently applied.

Figure 6 shows the change in echo height of the molten boundary 21 over time. Adder cuts occurred in the part where the welding speed was 2.6 m/1 lin, but no adder cuts occurred in the part where the welding speed was automatically controlled. No good beads were obtained. Figure 6 shows the change in echo height of the molten boundary 21 over time at that time, and shows the welding speed of 2.6m/11in.
In the first half of the part that is not controlled, high-level echoes that cause adder cuts occur frequently, but after 11 seconds when automatic welding sugar control is started, the echoes decrease and the welding speed is 2.4 m/min. As shown in FIG. 7, the change over time in the echo height of the molten boundary portion 21 in the automatically controlled portion where no adder cut occurs shows that no high-level echoes occur at all. In addition, by controlling the welding current value, the welding speed is 2.6 m/m x n + 2.4
Both m/min remained constant at approximately 6I.

〔Effect of the invention〕

With the above technology, welding defects can be minimized and the penetration depth can be kept constant even in welding methods where control of penetration depth is important, such as double-sided submerged arc welding. It becomes possible to automatically control arc welding at the maximum welding speed while maintaining the maximum welding speed. Therefore, even when performing unmanned welding, there is no fear of manufacturing defective products due to welding defects, and it is possible to save labor and equipment by omitting inspections in post-processes, and has extremely high industrial value.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing one embodiment of three-electrode submerged arc welding according to the present invention. Figure 2 is 1 of Figure 1.
FIGS. 3 and 4 are enlarged cross-sectional views taken in a plane perpendicular to the welding direction WD at the position where the probe 4 is present; FIGS.
The figure is an explanatory view that combines a perspective view on a vertical plane parallel to the welding line direction WD and a front view of a cathode ray tube of an ultrasonic flaw detector. FIG. 5 is a flowchart showing one control mode of submerged arc welding according to the present invention. 6 and 7 are waveform diagrams showing the echo heights detected by the probe 4 at the melting boundary portion 21 shown in FIG. 2 over time. 1: First electrode 2: Second electrode 3: Third (final) electrode 4: Ultrasonic angle probe 5: Arc gouging cavity 6: Welded material 7: Molten pool 8: Electrode holder 9: Flags IO= Solidified metal 11-1
3: Wire feeding motor 14-16: Welding power source 1
7: Welding operation panel 18: Ultrasonic flaw detector 19: Calculation/
Controller 20: Welding cart 21: Melting boundary portion 22
: Ultrasonic path 23: Molten slab X:! & Distance between the final electrode and the ultrasonic angle probe in the weld line direction T: Incident echo F: Melt boundary echo G: Gate WD: Welding direction O: Melt penetration angle of the melt boundary

Claims (2)

[Claims] (1) In a multi-electrode submerged arc welding method in which two or more welding electrodes are arranged in a straight line in the direction of the welding line and the welding speed is 1.5 m/min or more,
A multi-electrode submerged arc welding method characterized in that the presence or absence of a molten pool at a position of mm is detected by ultrasonic waves, and when a signal indicating that a molten pool does not exist at the position is obtained, the welding speed is reduced. (2) In a multi-electrode submerged arc welding method in which two or more welding electrodes are arranged in a straight line in the direction of the welding line and performed at a welding speed of 1.5 m/min or more, in a range up to 25 mm behind the final electrode, The ultrasonic probe is scanned back and forth in a direction parallel to the weld line, and the interface between the arc gouging cavity and the molten pool is detected by ultrasonic waves, and the distance from the final electrode of the ultrasonic probe at the time of detection is the reference value. A multi-electrode submerged arc welding method characterized by increasing or decreasing the welding speed to match.