JP2019198877A - Monitoring method, monitoring system, and monitoring program for electric resistance welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate how far the input power during welding is away from the input power at the time of shifting from a second type welding state to a two-stage convergent type second type welding state. A monitoring method disclosed in the present application is a monitoring method for monitoring a welding state of a metal plate in ERW. The monitoring method is a distance (LV0-LV1) between a geometrical V convergence point V0 point and a V convergence point V1 point, based on images obtained by photographing the abutting portions at both ends of the metal plate and the peripheral portion thereof from the radial direction. And the SPLcr that is a value indicating the reference input power determined as the input power in the transition region from the second-kind welding state to the two-stage convergence type second-kind welding state, at a certain monitoring target time point. A step of calculating a power evaluation value ξ, which is a value indicating how far the input powers are apart, by using the distance (LV0-LV1) at the time point to be monitored, the thickness t of the metal plate, and the diameter D of the metal tube. Have. [Selection diagram] Fig. 17

Description

  The present invention relates to a technique for managing the quality of a welded portion in electric resistance welding (ie, electric resistance welding, hereinafter referred to as ERW).

  Steel pipes manufactured using ERW technology are called ERW steel pipes. ERW steel pipes are used, for example, for oil or natural gas line pipes, oil well pipes, nuclear power generation facilities, geothermal power generation facilities, chemical plants, piping of various machines, and general piping. When manufacturing an electric resistance steel pipe, a strip-shaped steel plate, for example, a hot-rolled steel strip is formed into a tubular shape. At that time, both ends of the steel plate in the circumferential direction, that is, end surfaces facing each other, are butted so as to be V-shaped when viewed from the radial direction. By passing a high-frequency current through a portion where these both ends abutted against each other abut (contact), the abutting portion is heated and melted to form a weld seam.

  In ERW, in order to suppress welding defects, it is required to control the heat input amount (that is, input power), the welding speed, and the like within an appropriate range. For example, when the heat input is insufficient or the welding speed is high, an unwelded part may occur. On the other hand, if the heat input is excessive or the welding speed is slow, a large amount of oxide may remain in the weld.

  Generally, the welding state in electric resistance welding is roughly divided into a first type welding state, a second type welding state, and a third type welding state. In the first type welding state, the position fluctuation of the welding point where the end face of the steel plate first contacts is very small. The position fluctuation of the welding point increases in the order of the second type welding state and the third type welding state. In the second type welding state, a melting slit is generated at the abutting portion. Moreover, when the welding speed and the heat input amount satisfy certain conditions, a two-stage convergence type second type welding state with two-stage convergence appears. In addition, a welding state may be called a welding phenomenon. Therefore, the first type welding state is the first welding phenomenon, the second type welding state is the second type welding phenomenon, the third type welding state is the third type welding phenomenon, and the two-stage convergence type second type welding state is Sometimes referred to as a two-stage convergence type second welding phenomenon.

  In the second-stage convergent type second welding state, both ends (edges) of the steel sheet are at points where the extension lines of both ends of the steel sheet converging in a V shape when viewed from the radial direction intersect (geometric V convergence point: V0 point). Do not touch. The V convergence point (V1 point) at which the end face of the steel plate first contacts is downstream of the V0 point in the pipe making direction. That is, both ends (edges) of the steel plate have a two-step taper shape when viewed from the radial direction. The V convergence point (V1 point) is a point at which the circumferential end of the metal plate converging in a V shape physically abuts (contacts). The welding point (W point) is the end point of the melting slit, that is, the downstream end of the melting slit in the pipe forming direction.

  FIG. 1 is a diagram conceptually showing the relationship between various welding states, welding speed, and input power. In FIG. 1, a region 2001 is a region corresponding to the first type welding state, a region 2002 is a region corresponding to the second type welding state, a region 2003 is a region corresponding to the third type welding state, and a region Reference numeral 2004 denotes a region corresponding to the two-stage convergence type second type welding state. Vm is the critical welding speed at which the two-stage convergent type second welding state appears, and Tm is the melting point of the steel sheet. T is the temperature of both ends (edges) of the steel plate at the point V0. In the region above the line of T = Tm, both ends of the steel sheet are melted over the entire thickness at the point V0.

  When the welding speed is less than the critical welding speed Vm and the input power is low, the welding state is the first type welding state (region 2001). Even if the welding speed is less than the critical welding speed Vm, if the input power is increased, the welding state becomes the second type welding state (region 2002), and if the input power is further increased, the third type welding state (region 2003). ). On the other hand, when the welding speed is equal to or higher than the critical welding speed Vm, the welding state shifts from the first type welding state (region 2001) to the second type welding state (region 2002) as the input power increases, and the input power further increases. Is increased, a two-stage convergence type second welding state (region 2004) is obtained.

  Japanese Patent No. 5510615 (Patent Document 1) describes an ERW welding operation management device that manages ERW operation when manufacturing an ERW steel pipe. This electric-welding welding operation management apparatus inputs an image of an area (image of a V-shaped convergence area) including the surface of the V-shaped convergence area, the melt slit end, and the welding point imaged by the imaging device. The electric seam welding operation management device uses the processing result for the image of the V-shaped convergence area to calculate the amount of power output from the high-frequency power supply so that the welding state becomes the second-stage convergence type second welding state. Control.

Japanese Patent No. 5510615

  The inventors conducted a laboratory test and an actual machine test, clarified the relationship between the input power (heat input) and the welding state (welding phenomenon), and the relationship between the welding state and the weld defect area ratio, and examined optimum welding conditions. As a result, it was found that a transition region appears when shifting from the second type welding state to the two-stage convergence type second type welding state. The welding condition in which the weld defect area ratio satisfies the target value may be a two-stage convergent second welding state at an input power increased by about 10% from the reference input power SPLcr determined as the input power in the transition region. I found out.

  For example, as described above, when the input power increased by about 10% from the reference input power SPLcr is set as the optimum input power (target input power) and welding operation is performed, the current input power is deviated by what percentage from the reference input power. It is useful to monitor whether

  Therefore, the present invention has an object to make it possible to estimate how far the input power during welding is away from the input power in the transition region from the second type welding state to the two-stage convergence type second type welding state. And

In the monitoring method according to the embodiment of the present invention, a metal plate is conveyed in the conveyance direction and formed into a cylindrical shape, and both ends in the circumferential direction of the metal plate are opposed to each other so as to be V-shaped when viewed from the outside in the radial direction. In the manufacturing process of the metal tube for forming and welding the molten metal by flowing an alternating current through the abutting portion where both ends are in contact, the monitoring method monitors the molten state of the abutting portion.
The monitoring method is based on an image obtained by photographing the abutting portions at both ends of the metal plate and its peripheral portion from the radial direction, and the extension lines at the both ends before contact at the upstream of the abutting portions at both ends of the metal plate. Detecting a distance (LV0-LV1) between a geometric V convergence point V0 which is a geometric intersection of the metal plate and a V convergence point V1 which is an abutting point where both ends of the metal plate start to come into contact with each other; The input power (or heat input) at a certain monitoring target time is a value indicating the reference input power determined as the input power in the transition region from the second type welding state to the two-stage convergent second type welding state. On the other hand, the power evaluation value ξ, which is a value indicating how far away, is obtained by using the distance (LV0-LV1) at the monitoring target time point, the thickness t of the metal plate, and the diameter D of the metal tube to be formed. And calculating.

  According to the present invention, how far the input power during welding is away from the reference input power determined as the input power in the transition region from the second type welding state to the two-stage convergence type second type welding state, Can be easily estimated.

FIG. 1 is a diagram conceptually showing the relationship between various welding states, welding speed, and input power. FIG. 2 is a diagram illustrating an example of a configuration of an electric resistance welded pipe manufacturing system according to an embodiment of the present invention. FIG. 3A is a diagram conceptually illustrating an example of a V-shaped convergence region in a two-stage convergence type second type welding state. FIG. 3B is a diagram conceptually illustrating an example of a V-shaped convergence region in the two-stage convergence type second type welding state. FIG. 4 is a diagram illustrating input power, a welded part image example, and a welded part shape measurement value. FIG. 5 is a graph showing the relationship between input power and LV0, LV1, and LW. FIG. 6 is a graph showing the relationship between input power and LV0-LV1. FIG. 7 is a diagram showing a welding state determination result and a welded part image for each input power at a plate thickness of 6.4 mm. FIG. 8 is a diagram showing a welding state determination result and a welded part image for each input power at a plate thickness of 12.7 mm. FIG. 9 is a diagram illustrating a welding state determination result and a welded part image for each input power at a plate thickness of 19 mm. FIG. 10 is a graph showing the relationship between the input power at the plate thickness of 6.4 mm, LV0-LV1, and the welding state. FIG. 11 is a graph showing the relationship between the input power at the plate thickness of 12.7 mm, LV0-LV1, and the welding state. FIG. 12 is a graph showing the relationship between the input power at a plate thickness of 19 mm, LV0-LV1, and the welding state. FIG. 13 is a graph showing the relationship between the power evaluation value ξ and LV0-LV1 for each plate thickness. FIG. 14 is a graph showing the relationship between LV0-LV1 and power evaluation value ξ accompanying t / D change. FIGS. 15A, 15B, and 15C are graphs showing the relationship between t / D and LV0-LV1 when the power evaluation value ξ is 5%, 10%, and 15%, respectively. FIG. 16 is a graph showing the relationship between the actually measured value and the calculated value of the power evaluation value ξ. FIG. 17 is a diagram illustrating a configuration example of a management system including a monitoring system. FIG. 18 is a flowchart illustrating an example of a welding state monitoring process performed by the management system 100. FIG. 19 is a diagram illustrating an example of an image of the V-shaped convergence area. FIG. 20 is a diagram illustrating an example of a binarized image. FIG. 21 is a diagram illustrating an example of a binarized image on which a labeling process has been performed. FIG. 22 is a diagram illustrating an example of a state where the blob 91 in the V-shaped convergence area is extracted. FIG. 23 is a diagram illustrating an example of how the V convergence point V1 is detected. FIG. 24 is a diagram illustrating an example of how the V convergence point V1 is detected.

  As a result of careful observation of the shape of the end portion of the metal pipe during welding, the inventors have found that a transition region exists at the time of transition from the second type welding state to the two-stage convergent second welding state. Furthermore, the inventors have found that the distance (LV0−LV1) changes with an increase in input power (that is, heat input) in the transition region and the two-stage convergent second welding state. Furthermore, the inventors have found that the distance (LV0-LV1) changes as the thickness t and diameter D of the metal tube change. Based on these findings, the inventors determined the relative value of the current input power to the reference input power determined as the input power in the transition region, the distance (LV0−LV1), the thickness t of the metal plate, and It was conceived that calculation can be performed using the diameter D of the metal tube to be formed. That is, it is found that by using the distance (LV0−LV1), the thickness t of the metal plate, and the diameter D of the metal tube, it is possible to estimate how far the input power at a certain point is away from the reference input power. It was. Based on this knowledge, the following embodiments were conceived.

In the monitoring method according to the embodiment of the present invention, a metal plate is conveyed in the conveyance direction and formed into a cylindrical shape, and both ends in the circumferential direction of the metal plate are opposed to each other so as to be V-shaped when viewed from the outside in the radial direction. In the manufacturing process of the metal tube for forming and welding the molten metal by flowing an alternating current through the abutting portion where both ends are in contact, the monitoring method monitors the molten state of the abutting portion.
The monitoring method is based on an image obtained by photographing the abutting portions at both ends of the metal plate and its peripheral portion from the radial direction, before contacting the upstream of the abutting portions at both ends of the metal plate (in the pipe making direction). The distance (LV0-LV1) between the geometric V convergence point V0, which is the geometric intersection of the extension lines of the two ends, and the V convergence point V1, which is an abutting point where both ends of the metal plate start to contact And the reference input power determined as the input power in the transition region from the second type welding state to the two-stage convergent second type welding state, where the input power (or heat input) at a certain monitoring target time is A power evaluation value ξ that is a value indicating how far away from the SPLcr that is a value that is indicated is a distance (LV0−LV1) at the monitoring target time point, a thickness t of the metal plate, and a metal tube to be formed Calculated using diameter D of And a that process.

  An apparatus for realizing the above monitoring method, a program for causing a computer to execute the above monitoring method, and a recording medium storing the program are also included in the embodiments of the present invention.

  The monitoring system as an embodiment of the apparatus for realizing the monitoring method includes an abutting portion at both ends of the metal plate based on an image obtained by photographing the abutting portions at both ends of the metal plate and the peripheral portion thereof from the radial direction. The distance between the geometric V convergence point V0, which is the geometric intersection of the extension lines of the both ends before contact, upstream of the metal plate, and the V convergence point V1, which is an abutting point where both ends of the metal plate start to contact each other Image information detection unit that detects (LV0-LV1), and a reference in which input power at a certain monitoring target time point is determined as input power in a transition region from the second type welding state to the two-stage convergence type second type welding state A power evaluation value ξ, which is a value indicating how far away from the SPLcr, which is a value indicating the input power, a distance (LV0-LV1) at the monitoring target time point, a thickness t of the metal plate, and Metal pipe With diameter D, and a evaluation calculation unit for calculating.

  A monitoring program as an embodiment of a program for causing a computer to execute the monitoring method described above is based on an image obtained by photographing the abutting portions at both ends of the metal plate and the periphery thereof from the radial direction. A geometric V convergence point V0, which is a geometric intersection of the extension lines of the both ends before contact, upstream of an abutting portion at both ends, and a V convergence point, which is an abutting point where both ends of the metal plate start to contact each other The process of detecting the distance (LV0-LV1) from the point V1 and the input power at a certain monitoring target time point are determined as the input power in the transition region from the second type welding state to the two-stage convergence type second welding state. The power evaluation value ξ, which is a value indicating how far away from the SPLcr which is a value indicating the reference input power, is a distance (LV0-LV1) at the monitoring target time, a thickness t of the metal plate, With a diameter D of the metal tube is finely formed, and a process of calculating, causes the computer to execute.

  According to the monitoring method, the monitoring system, or the monitoring program described above, it is possible to estimate how far the input power during welding is away from the input power that generates the transition region state. Here, the input power is power for supplying an alternating current that flows to the abutting portion of the metal plate. By adjusting the input power, the amount of heat input in the welding of the metal plate can be adjusted. That is, the amount of heat input in the welding of the metal plate depends on the input power. Therefore, the value of input power may be expressed as a value of heat input.

  In the above configuration, the input power when the welding state is in the transition region from the second type welding state to the two-stage convergence type second type welding state can be determined as the reference input power. The reference input power is not limited to the input power when the welding state is strictly within the transition region. For example, the input power when the welding state is close to the transition region to the extent that it can be regarded as the transition region even outside the transition region. There may be. Whether or not the welding state is the transition region can be determined based on, for example, a processing result of an image obtained by photographing the abutting portion and its peripheral portion from the radial direction.

In the above monitoring method, monitoring system, or monitoring program, the power evaluation value ξ can be calculated by, for example, the following equation (1).
ξ = f (t / D) × (LV0-LV1) + g (t / D) (1)
t: Metal tube thickness
D: Diameter of the metal tube
f (t / D): Function with t / D as a variable
g (t / D): Function with t / D as a variable

  In the above equation (1), f (t / D) and g (t / D) are constants when t and D are determined. The above equation (1) is a linear function in which the value determined by t and D is a coefficient and a constant term, and the distance (LV0−LV1) is a variable. By using Expression (1), it is possible to accurately estimate how far the input power during welding is away from the reference input power SPLcr.

  Note that the formula for calculating the power evaluation value ξ is not limited to the above formula. For example, a quadratic function, an exponential function, or another function may be used instead of the linear function having the distance (LV0−LV1) as a variable. For example, at least one of the coefficient and the constant term may be a value depending on other values in addition to t and D. In the above example, the power evaluation value ξ is, for example, a value expressed as a percentage (that is, a value having a unit of%). As described above, the power evaluation value ξ can be represented by the ratio of the input power to the reference input power SPLcr. The power evaluation value ξ may be represented by a difference or a relative value with respect to another reference value in addition to the ratio with respect to the reference value.

In the above monitoring method, monitoring system, or monitoring program, the power evaluation value ξ can be calculated by, for example, the following formula (2).
ξ = {1945 × (t / D) ² −152 × (t / D) +3.7} × (LV0-LV1)
+ {− 49834 × (t / D) ² + 4198 × (t / D) −82.5} (2)

  The inventors have found that the power evaluation value ξ can be calculated with high accuracy by using f (t / D) and g (t / D) in Equation (1) as quadratic functions. The equation (2) is obtained by fitting based on experimental data using f (t / D) and g (g / D) in the equation (1) as a quadratic function. Therefore, the power evaluation value ξ can be calculated with high accuracy by using the above equation (2).

  Embodiments of the present invention also include a metal tube manufacturing method including the monitoring method, a metal tube manufacturing system including a monitoring system, or a metal tube manufacturing program including a monitoring program. This manufacturing method, manufacturing system, or manufacturing program outputs the calculated power evaluation value to a monitor (display device) or controls the input power based on the calculated power evaluation value, function A part or a process may be further included. Moreover, the process of determining a welding state, a function part, or a process may be included depending on whether or not the power evaluation value satisfies a predetermined condition. Thereby, control of input power using a power evaluation value can be facilitated.

  The manufacturing method may include, for example, a step of displaying the power evaluation value and a predetermined target input power range on a monitor in a state where the power evaluation value can be visually recognized simultaneously. In addition, the manufacturing method may include a step of controlling input power so that the power evaluation value falls within a predetermined target input power range. The range of the target input power can be, for example, within a range of input power that is 5% to 20% larger than SPLcr. As an example, the range of the target input power can be within a predetermined range from the input power increased by 10% from SPLcr.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Embodiment 1]
<ERW pipe manufacturing system>
FIG. 2 is a diagram illustrating an example of a configuration of an electric resistance welded pipe manufacturing system according to an embodiment of the present invention. In the present embodiment, the position of each component of the ERW steel pipe manufacturing system and the position of the captured image are represented by the same three-dimensional orthogonal coordinates (x, y, z coordinates), respectively. To do. That is, the x, y, and z coordinates shown in each figure indicate only the direction, and the position of the origin is the same in each figure.

  In FIG. 2, the ERW steel pipe manufacturing system includes squeeze rolls 2 a and 2 b, contact chips 3 a and 3 b, an impeder 4, an imaging device 5, a high-frequency power source 6, and a management system 100.

  First, the outline of the production equipment for ERW steel pipe will be described. As shown in FIG. 2, the strip-shaped steel sheet 1 is continuously formed into a cylindrical shape by a roll group (not shown) while being conveyed in the positive direction of the x-axis. An impeder 4 for concentrating the magnetic flux on the abutting portion of the steel plate 1 is disposed inside the steel plate 1 formed into a cylindrical shape. When high-frequency power is supplied from the high-frequency power source 6, a high-frequency current flows from the pair of contact chips 3 a and 3 b (or a dielectric coil (not shown)) to the surface of the region that converges in a V shape of the steel plate 1. At this time, pressing force is applied to the steel plate 1 from both sides by the squeeze rolls 2a and 2b. Thereby, the both ends 11a and 11b in the circumferential direction of the steel plate 1 are brought into contact with each other while converging in a V shape, and the abutting portions where the both ends 11a and 11b are in contact are heated and melted to melt-bond the steel plate 1. . Such melt bonding is referred to as electric resistance welding (ERW). In the following description, the “region that converges in a V-shape of the steel plate 1” is referred to as a “V-convergence region” as necessary. Moreover, the both ends 11a and 11b of the circumferential direction of the steel plate 1 are faced | matched, and the part observed in one linear form is called a "welding line" as needed.

  The imaging device 5 images a self-luminous pattern (radiation pattern) in a region including the surface of the V-shaped convergence region. As the imaging device 5, for example, a 3CCD color camera having 1920 × 512 pixels is used. The imaging device 5 is, for example, under the conditions of a shooting field of view of 50 [mm] × 190 [mm], a resolution of 100 [μm / pixel], a shooting frame rate of 500 [fps], and an exposure time of 1/10000 [sec]. The region including the surface of the V-shaped convergence region is imaged. Imaging by the imaging device 5 is continuously performed at regular time intervals. One image in a plurality of images taken continuously is called a frame. In the following description, an “image” captured by the imaging device 5 is referred to as an “image of a V-shaped convergence area” as necessary.

  The management system 100 inputs an image of the V-shaped convergence area captured by the imaging device 5. And the management system 100 performs the process etc. with respect to the image of a V-shaped convergence area | region, and monitors a welding state. That is, data indicating a welding state is generated as a result of the image processing. The management system 100 determines welding conditions based on data indicating a welding state obtained by image processing. For example, the management system 100 can control the amount of power (VA) output from the high-frequency power source 6 so that the welding state becomes a two-stage convergence type second-type welding state.

  The management system 100 controls the operations of the squeeze rolls 2a and 2b, the contact tips 3a and 3b, the high frequency power supply 6 or other members so as to satisfy the determined welding conditions. As described above, the management system 100 can include a monitoring device (monitoring system) that monitors the state of welding and a control device (control unit) that controls welding based on the monitoring result. In addition to the image captured by the imaging device 5 described above, the monitoring device may acquire information regarding the welding conditions as necessary. For example, information indicating the operation of the apparatus used for welding, such as the output values of the contact chips 3a and 3b and the high-frequency power source 6, the pressure of the squeeze rolls 2a and 2b, and the distance between the rolls, can be acquired.

<Description of 2-stage convergence type second welding state>
3A and 3B are diagrams conceptually illustrating an example of a V-shaped convergence region in a two-stage convergence type second type welding state. Specifically, FIG. 3A is a view of the V-shaped convergence region as viewed from above (z direction), and FIG. 3B is a V convergence point from the upstream side in the conveyance direction (x-axis direction) of the steel plate 1, that is, the pipe forming direction. It is the figure which looked at the direction of V1 point.

  In the two-stage convergent type second welding state, both ends 11a and 11b are brought into contact with each other while the melted portion in the thickness direction (z-axis direction) of both ends 11a and 11b in the circumferential direction of the steel plate 1 is discharged. At that time, the central portions in the thickness direction of both ends 11a and 11b are melted, and the melted portions are discharged outward from the center (see the arrow line shown in FIG. 3B).

  The self-luminous pattern in the region including the V-shaped convergence region from above the steel plate 1 is imaged with high definition and no image flow (imaging resolution: 100 [μm / pixel], exposure time: 1/10000 [sec]). When the V convergence point was measured with high accuracy, a two-stage convergence type second-type welding state was observed. When the welding state is a two-stage convergence type second-type welding state, as shown in FIG. A geometric V convergence point V0, which is a V convergence point, and a V convergence point V1, which is a collision point, exist in a relatively downstream region. The geometrical V convergence point V0 is a point where the extension lines (shown by broken lines) downstream of the circumferential ends 11a and 11b of the steel sheet 1 converging in a V shape intersect geometrically. On the other hand, the V convergence point V1, which is an abutting point, is a point at which both ends 11a and 11b in the circumferential direction of the steel sheet 1 converging in a V shape first physically abut (contact). Both ends 11a, 11b forming the V-shape are two-stage tapered in a two-stage convergent type second welding state, bent at a certain position k1, k2 upstream from the V-shaped tip in the tube forming direction. It becomes a shape. On the other hand, both ends 11a and 11b in the transition region show an unstable form in which linear and two-step tapered states appear alternately.

  When input power equal to or higher than the input power at which the welding state is the second type welding state is given, the welding point W that is the terminal point of the fusion slit is further in the direction of pipe formation than the V convergence point V1 that is the abutting point. It exists in the downstream area. Between the V convergence point V1 and the welding point W, a melting slit S that penetrates the steel plate 1 in the thickness direction of the steel plate 1 is formed. Further, the melting slit S disappears after extending from the V convergence point V1 toward the downstream side in the conveying direction (x-axis direction) of the steel plate 1, that is, the pipe forming direction. Such a change in the size of the melt slit S in the x-axis direction (growth and disappearance of the melt slit S) is periodically performed with a period of several [msec]. Both the V convergence point V1 and the welding point W are on the weld line.

  The inventors have found that the optimum welding condition may be the input power in the two-stage convergence type second welding state that is about 10% larger than the input power in the transition region state, that is, the reference input power SPLcr. However, in the two-stage convergence type second type welding state, it is difficult to specify how far the input power is from the reference input power SPLcr, and it is difficult to monitor the input power.

  On the other hand, it has been known that when the input power changes, the welded portion shape (V0 point, V1 point, W point) observed from directly above (radial direction) the welded portion changes. Therefore, the inventors carefully observed the shape of the weld when the weld was observed from directly above. As a result, it has been found that there is a relationship between the welded part shape and the input power. Using this relationship. A method for monitoring welding conditions was invented. Details of the experiments and examinations by the inventors will be described below.

<Experiment using a lab simulator>
Welding experiments were performed using a lab test apparatus (hereinafter referred to as a lab simulator). The test material was carbon steel. The shape of the test piece was 8 mm thick, 32 mm wide, and 4000 mm long. The welding speed was 20 m / min, and the input power was 425.9 to 474.7 VA. The amount of squeeze was 4 mm. Welding state judgment was performed mainly by video using a video camera.

  The weld shape was measured from an image taken with a video camera. As shown in FIG. 3A, the point where the extension line of the steel plate edge contacts is defined as a geometric V convergence point (V0 point), and a line (squeeze roll center: SQC) connecting the squeeze roll shaft cores, The distance of V0 point was set to LV0 (mm). When the steel plate edge contacts the downstream side in the pipe making direction from the V0 point, the contact point is defined as the V1 point. The distance between the SQC and the point V1 is V1 (mm), and the distance between the points V0 and V1 is LV0-LV1 (mm). The welding point was the W point, and the distance between the SQC and the W point was LW (mm). The distances LV0, LV1, LW, and LV0-LV1 were measured as an average value of 100 images (frames) taken continuously.

  4 to 6 show experimental results by the lab simulator. FIG. 4 shows input power, a welded part image example, and a welded part shape measurement value. FIG. 5 shows the relationship between the input power and the distances LV0, LV1, and LW, and FIG. 6 shows the relationship between the input power and the distance (LV0-LV1).

  LV0 (mm) increased with increasing input power. LV1 (mm) and LW (mm) decreased with increasing input power. Moreover, LV0-LV1 (mm) was 0 mm in the second type welding state, and began to increase in the transition region, and further increased as the input power increased. That is, it was found that there is a correlation between the input power and the distance (LV0-LV1) in the input power above the transition region.

  By examining the results of this laboratory simulator experiment, measuring LV0-LV1 (mm) at the appropriate input power in advance, and comparing it with LV0-LV1 (mm) during welding, the change in input power from the appropriate value The inventors have come up with the possibility of monitoring.

<Verification on actual machine>
The inventors verified the relationship between the distance (LV0-LV1) and the input power by using various plate thicknesses with an actual machine in response to the experimental results obtained from the lab simulator. Details will be described below.

(1) Experimental conditions A steel pipe having a thickness of 6.4 mm, 12.7 mm, 19.0 mm, and an outer diameter of 404.4 mm was formed. The input power was increased stepwise from the second type welding state to the two-stage convergent second type welding state.

(2) Measuring method of distance (LV0-LV1) The distance (LV0-LV1) was measured using an image taken from above the weld. The measured value was an average value of 100 images (frames) taken continuously.

  7, 8, and 9 show welding state determination results and welded portion images for each input power at plate thicknesses of 6.4 mm, 12.7 mm, and 19.0 mm, respectively. 10, FIG. 11, and FIG. 12 show the relationship between input power, distance (LV0-LV1), and welding state. In any plate thickness, the distance (LV0-LV1) in the second type welding state is 0 mm, but when the input power is increased and changed to the transition region state, the points V0 and V1 are separated. When the input power is further increased, the distance (LV0−LV1) is changed to the two-stage convergence type second welding state, and the distance (LV0− LV1) increased.

  FIG. 13 shows the relationship between the power evaluation value ξ, the distance (LV0−LV1), and the plate thickness. ξ represents the ratio (%) of the increment of the input power with respect to the reference input power SPLcr. From FIG. 13, it was confirmed that the distance (LV0-LV1) increases as ξ increases, and the distance (LV0-LV1) decreases as the plate thickness increases.

  From these results, it was confirmed that the distance (LV0-LV1) increased with increasing input power in the range of the second-stage convergent type second welding state in the actual machine as well as in the laboratory simulator. From the above, it was found that there is a possibility of monitoring optimum welding conditions by measuring LV0-LV1 (mm) at preset input power and comparing with LV0-LV1 (mm) during welding. .

<Sophistication proposal of appropriate welding condition monitoring technology by constructing LV0-LV1 prediction formula>
Based on the above experimental results, the prediction formula is examined on the assumption that the power evaluation value ξ is obtained by the distance (LV0−LV1) and t / D in which the thickness t is made dimensionless by the diameter D of the metal tube. did.

First, FIG. 14 shows the relationship between ξ and distance (LV0−LV1) associated with t / D change. Since ξ has a substantially linear relationship with the distance (LV0−LV1), the ξ prediction equation is assumed to be the following equation (1).
ξ (%) = f (t / D) × (LV0-LV1) + g (t / D) (1)

FIGS. 15A, 15B and 15C show the relationship between t / D and distance (LV0-LV1) when ξ is 5%, 10% and 15%, respectively. Since both can be approximated by a quadratic function, fitting is performed assuming that f (t / D) and g (t / D) in the above formula (1) are quadratic functions, and the following prediction formula ( 2) was calculated.
ξ (%) = {1945 × (t / D) ² −152 × (t / D) +3.7} × (LV0-LV1)
+ {− 49834 × (t / D) ² + 4198 × (t / D) −82.5} (2)

  In the above formula (2), f (t / D) and g (t / D) are quadratic functions, but f (t / D) and g (t / D) are limited to quadratic functions. Absent. F (t / D) and g (t / D) can be determined by fitting a linear function or another function to an actual measurement value. In the example shown in FIGS. 15A, 15B and 15C, f (t / D) and g (t / D) decrease as t / D increases in the problematic t / D range. The function can be f (t / D), g (t / D).

  FIG. 16 is a graph showing the relationship between the actually measured value of ξ and the calculated value. From the results shown in FIG. 16, it was found that the calculated value using the above formula (2) matches the actual measured value.

  From the above results, it was found that the distance (LV0-LV1) can be predicted when the present experimental data is used. Based on this finding, the inventors have invented a method and system for monitoring welding conditions by capturing a distance (LV0-LV1) from an image during welding. Specific examples will be described below.

<Specific example of monitoring welding conditions>
FIG. 17 is a functional block diagram illustrating a configuration example of a management system 100 (an example of a manufacturing system) including a monitoring system. The management system 100 includes a monitoring system 101, a control unit 104, and a monitor 105. The monitoring system 101 includes an image information detection unit 102 and an evaluation calculation unit 103. The image information detection unit 102 acquires an image obtained by photographing the abutting portion at both ends of the metal plate and its peripheral portion from the radial direction by the imaging device 5. The image information detection unit 102 detects the distance (LV0−LV1) between the geometric V convergence point V0 and the V convergence point V1 from the acquired image. The evaluation calculation unit 103 is a power evaluation that is a value indicating how far the input power at a certain monitoring target time point is away from the SPLcr that is a value indicating the reference input power determined as the input power in the transition region. The value ξ is calculated. For the calculation of the power evaluation value ξ, the distance (LV0−LV1) at the monitoring target time, the thickness t of the metal plate, and the diameter D of the metal tube to be formed are used.

  The monitoring system 101 can output the power evaluation value calculated by the evaluation calculation unit 103 to the monitor 105. The monitoring system 101 may calculate power evaluation values at each of a plurality of consecutive time points during operation and output them to the monitor 105. Thereby, the power evaluation value can be displayed on the monitor 105 in real time.

  The monitoring system 101 further includes a control unit 104 that controls input power based on the power evaluation value calculated by the evaluation calculation unit 103. For example, the control unit 104 can control the input power so that the power evaluation value satisfies a predetermined condition. For example, an upper limit and a lower limit of the power evaluation value may be set in advance. In this case, the control unit 104 can perform control to reduce the input power when the power evaluation value exceeds the upper limit and increase the input power when the power evaluation value falls below the lower limit.

  The monitoring system 101 is configured by a computer including a processor and a memory. Each unit of the image information detection unit 102 and the evaluation calculation unit 103 can be realized by one or a plurality of computers executing a program. Such a program and a non-transitory recording medium on which the program is recorded are also examples of the embodiment of the present invention. The processor executes processing according to a program recorded in the memory. The program can include instructions for a processor for providing the image information detection unit 102 and the evaluation calculation unit 103 described above. The control unit 104 can also be realized by one or a plurality of computers executing a program.

  FIG. 18 is a flowchart illustrating an example of a welding state monitoring process performed by the management system 100.

  In S1, the management system 100 acquires the input power EpIp input to the welded part. For example, the management system 100 can obtain the value EpIp (t) of the input power EpIp at each time t = t1, t2, t3,. EpIp (t) can be calculated, for example, from the output voltage and output current of the high-frequency power supply 6. Note that the management system 100 may acquire a value indicating another heat input amount instead of the input power EpIp.

  In S <b> 2, the management system 100 acquires an image of the welded part imaged by the imaging device 5. Here, as an example, the management system 100 receives images (frames) captured at each of consecutive times t = t1, t2, t3,. The management system 100 calculates the distance (LV0-LV1) between the points V0 and V1 for each acquired image (S3). Thereby, the distance (LV0-LV1) at each time t is obtained.

  The image acquired in S2 is an image obtained by capturing the abutting portions of the both ends 11a and 11b of the steel pipe and the periphery thereof from the radial direction (upward). The imaging range of this image is that the two ends upstream of the pipe forming direction at the point V1 where both ends 11a and 11b start to contact each other are tapered or V-shaped and facing each other, and the welding point W downstream from the point V1. It is preferable to include at least the point. An example of processing for detecting the distance (LV0-LV1) based on the image will be described later.

  In S4, the management system 100 detects a value SPLcr indicating the reference input power based on the input power EpIp acquired in S1 and the time transition of the distance (LV0-LV1) obtained in S3. For example, the management system 100 determines a time point tv at which the distance (LV0-LV1) becomes LV0-LV1> 0 and the state of LV0-LV1> 0 continues thereafter for a certain time. When LV0-LV1 at time tv exceeds a predetermined threshold value Th1, input power EpIp (tv) at that time tv can be determined as SPLcr. The threshold value Th1 is determined according to, for example, the size and material of the metal tube. The SPLcr detection process is not limited to the above example.

  When the time transition of the distance (LV0-LV1) satisfying the above condition is not detected, the management system 100 can determine that SPLcr is not detected, that is, the input power has not reached the reference input power (No in S5). . For example, when the input power is low and the first type welding state or the second type welding state is set, it is determined that the input power has not reached the reference input power SPLcr.

  If it is determined that SPLcr is not detected in S5 (No in S5), the input power is increased to increase the amount of heat input, and the processes of S1 to S4 are repeated. When SPLcr is detected (Yes in S5), the management system 100 calculates a power evaluation value ξ (S7). The power evaluation value ξ can be calculated by substituting the distance (LV0−LV1) calculated in S3 into the above equation (1), for example. As f (t / D) and g (t / D) in the above formula (1), values calculated in advance based on the thickness t and the diameter D of the metal tube can be used.

  In S8, the management system 100 determines the welding state using the power evaluation value ξ calculated in S7. Here, when the power evaluation value ξ is within a preset range, it can be determined that the welding state is good. The threshold value for determining the range can be set to a value indicating around 10%, for example, 5 to 15%, preferably 8 to 12%. Further, when the power evaluation value ξ is larger than the above range, it can be determined that the amount of heat input is too large. When the power evaluation value ξ is smaller than the above range, it can be determined that the amount of heat input is too small.

  In S9, the management system 100 displays the result determined in S8. For example, the determination result can be output via an output device such as a monitor 105 (display), a speaker, or a printer provided or connected to the management system. The determination result may be information indicating the quality of the welding state, or may be information indicating whether the heat input (input power) is appropriate, excessive or insufficient, or excessive or insufficient.

  In S10, the management system 100 controls the input power by controlling the AC power supply 6 based on the result determined in S8. For example, the output value of the AC power supply 6 can be changed based on the amount of excess or deficiency of the input power determined in S8. In S10, the input power is adjusted and welding is continued. While welding is continued, the processes of S1 to S10 are repeatedly executed. For example, the management system 100 can control the input power so that the power evaluation value ξ calculated in S7 is within the preset range.

  According to the process shown in FIG. 18, the quality of the welding state is determined by monitoring the power evaluation value ξ and the distance (LV0−LV1) that change as the input power increases. Thereby, it is possible to determine the optimum input power in the two-stage convergence type second type welding state. For example, after the input power is gradually increased from the first type welding state and after entering the transition region through the second type welding state, that is, after SPLcr is detected, in the two-stage convergent type second welding state, for example, The input power when the power evaluation value ξ is 10% can be determined as the optimum welding condition.

  The above formula (1) makes it possible to predict the distance (LV0−LV1) when the proper welding condition is satisfied (for example, when the power evaluation value ξ is 10%) using t / D as a parameter. As described above, when the proper welding condition is satisfied, this distance (LV0-LV1) is highly predicted, and the appropriate welding condition is monitored and controlled without measuring the distance (LV0-LV1) of the appropriate welding condition before welding. Is possible.

  In the above example, the power evaluation value ξ is calculated using LV0−LV1 and t / D. However, the power evaluation value ξ can be determined using elements other than these elements. For example, a term determined by other parameters such as welding speed or outer diameter data may be added to the above equation (1), and the value calculated using the above equation (1) may be added using other parameters. It may be corrected.

  In the example shown in FIG. 18, when SPLcr is calculated in S4, the welding state determination using the power evaluation value ξ is executed. On the other hand, calculation of SPLcr of S4, its determination (S5), and power control based on the determination result (S10) can be omitted.

(Example of calculating distance (LV0L-V1))
The image information detection unit 102 performs processing for obtaining the geometric V convergence point V0, processing for obtaining the V convergence point V1, and processing for obtaining the distance (LV0-LV1) based on the image including the V-shaped convergence unit. Execute.

  The process for obtaining the geometrical V convergence point V0 is, for example, a process for binarizing an image to generate a binarized image, a process for determining both ends in the circumferential direction of the metal plate from the binarized image, And a process of determining an intersection of these two approximate lines as a geometric V convergence point V0. Alternatively, the process for obtaining the geometrical V convergence point V0 includes an edge extraction process in the image, a process for determining both ends and intersections in the circumferential direction of the metal plate by template matching with the extracted edges, May be included as a geometric V convergence point V0. The process for obtaining the geometric V convergence point V0 is not limited to these examples.

  The process for obtaining the V convergence point V1 can include, for example, a process for binarizing an image to generate a binarized image and a process for determining the V convergence point V1 from the binarized image. Alternatively, the process for obtaining the V convergence point V1 may include an edge extraction process in the image and a process for determining the V convergence point V1 by performing template matching on the extracted edge. Note that the process for obtaining the V convergence point V1 is not limited to these examples.

  For example, the image information detection unit 102 can calculate the distance (LV0−LV1) from the geometric V convergence point V0, the V convergence point V1, and the coordinates.

  Next, an example of processing of the image information detection unit 102 will be specifically described. FIG. 19 is a diagram illustrating an example of an image of the V-shaped convergence area captured by the imaging device 5.

  As shown in FIG. 19, in the image of the V-shaped convergence region imaged by the imaging device 5, high-heat regions 81 a and 81 b with high luminance levels appear along the circumferential ends 11 a and 11 b of the steel plate 1. In addition, in a region 82 on the downstream side in the conveyance direction (x-axis direction) of the steel plate 1, a wavy pattern formed by discharging the melted portions of the circumferential ends 11 a and 11 b appears on the steel plate 1. Further, a melting slit S appears along the conveying direction (x-axis direction) of the steel plate 1 from the vicinity of the region converging in a V shape.

  The image data processing is realized, for example, by the CPU acquiring image data from the imaging device 5 via the communication interface and temporarily storing the acquired image data in a RAM or the like.

(Red component extraction process)
The image information detection unit 102 extracts a red component (wavelength 590 [nm] to 680 [nm]) from the image data in order to clarify the contrast of the input image data in the V-shaped convergence area.

  The red component extraction processing is realized, for example, by the CPU reading out image data from a RAM or the like, extracting a red component, and temporarily storing the extracted red component image data in the RAM or the like.

(Binarization processing)
The image information detection unit 102 binarizes (inverts) the red component image data obtained by the red component extraction processing. Here, the image information detection unit 102 gives a pixel value “0” to a pixel having a luminance level equal to or higher than a threshold, and a pixel value “1” to a pixel lower than the threshold. In the processing of the geometric V convergence point V0 and the V convergence point V1, the threshold of the luminance level may be different. FIG. 20 is a diagram illustrating an example of a binarized image.

  In the binarization process of the image information detection unit 102, for example, the CPU reads the red component image data from the RAM or the like, performs the binarization process, and temporarily stores the binarized image data in the RAM or the like. It is realized by.

(Labeling process)
The image information detection unit 102 performs a labeling process for attaching a label for each blob to the binarized image obtained by the binarization process. A blob here is a pixel to which a pixel value “1” is given in any of 8 adjacent pixels including 4 pixels adjacent in the vertical and horizontal directions and 4 pixels adjacent in an oblique direction with respect to a certain pixel. When they are adjacent to each other, it means an individual connected region obtained by connecting the pixels for each pixel. The labeling process is to extract a specific blob by assigning a label number to each blob, and the position of the extracted blob in the image (maximum point and minimum point of x coordinate, maximum point and minimum point of y coordinate) , Width, length, area, and the like.

  FIG. 21 is a diagram illustrating an example of a binarized image on which a labeling process has been performed.

  In the example shown in FIG. 21, the case where the label numbers “1”, “2”, and “3” are respectively attached to the three blobs is shown.

  The labeling process is realized, for example, by the CPU reading the binarized image data from the RAM or the like, performing the labeling process, and temporarily storing the result in the RAM or the like.

  Note that, in the calculation of the geometric V convergence point V0 and the calculation of the V convergence point V1, when the threshold of the luminance level used in the binarization process is the same, the binarization process and the labeling process are shared. can do.

(V convergence point derivation process)
The V convergence point deriving process includes a process of determining whether or not a blob that matches a predetermined condition is extracted from the blobs assigned the label number by the labeling process. In the V convergence point deriving process, when the image information detection unit 102 determines that there is a blob that matches a predetermined condition, the blob (the blob assigned the label number “2” in the example illustrated in FIG. 21) Extracted as a blob 91 in the V-shaped convergence area. Then, the image information detection unit 102 acquires shape information such as coordinates and area of the extracted blob 91 in the extracted V-shaped convergence region. FIG. 22 is a diagram illustrating an example of a state where the blob 91 in the V-shaped convergence area is extracted. FIG. 23 is a diagram showing an example of how the V convergence point V1 is detected.

Here, for example, in the binarized image shown in FIG. 20, the image information detection unit 102 extracts a blob that touches the left end and has a predetermined area condition as a blob 91 in the V-shaped convergence region. To do. As the predetermined area condition, for example, the actual dimension of the blob area is 15 [mm ² ] to 150 [mm ² ], and the actual dimension of the rectangular block circumscribing the blob is 25 [mm ² ] to 320. What is necessary is just to set conditions, such as satisfy | filling at least any one of the conditions of [mm < ² >].

  As shown in FIG. 24, the image information detection unit 102 uses the tip of the blob 91 in the V-shaped convergence area in the positive direction of the x-axis (the downstream direction in the conveyance direction of the steel plate 1) as a collision point. Detect as point V1 (position).

  In this embodiment, as an example, when measuring the distance (LV0−LV1) between the V convergence point V1 and the geometric V convergence point V0 for one monitoring target time point, the image information detection unit 102 is used. Detects the position of the V convergence point V1 for each of the plurality of V-shaped convergence region images continuously captured by the imaging device 5 over 3 [sec]. Since the imaging device 5 captures an image at an imaging frame rate of 500 [fps], the image information detection unit 102 detects the positions of 1500 V convergence points V1. However, for example, when the variation in the position of the V convergence point V1 is slight, the image information detection unit 102 may detect the position of the V convergence point V1 derived from one image (that is, a plurality of points are not necessarily included). It is not necessary to derive the V convergence point V1 from each of the images.

  Note that when the ERW operation management apparatus 100 controls the heat input to the steel plate 1, the image information detection unit 102 is not extracted unless a blob that matches a predetermined condition is extracted continuously for a predetermined number of frames or more. Can output an error message to the operator.

  In the V convergence point deriving process, for example, the CPU reads the binarized image data subjected to the labeling process from the RAM or the like, derives the coordinates of the V convergence point V1, and temporarily stores the result in the RAM or the like. This is realized by memorizing.

(Geometric V convergence point derivation process)
The geometrical V convergence point deriving process includes a process of determining whether or not a blob that matches a predetermined condition is extracted from the blobs assigned label numbers by the labeling process. When the image information detection unit 102 determines that there is a blob that matches a predetermined condition, the image information detection unit 102 extracts the blob as a blob 91 in the V-shaped convergence area. And the image information detection part 102 acquires shape information, such as the coordinate of the blob 91 of the extracted V-shaped convergence area | region, an area, etc. (refer FIG. 21, FIG. 22). Note that the image information detection unit 102 can also use the information of the blob 91 in the V-shaped convergence area extracted in the V convergence point derivation process.

  Next, the image information detection unit 102 searches the extracted blob 91 of the V-shaped convergence region for a region corresponding to the end portions 11 a and 11 b in the circumferential direction of the steel plate 1.

  FIG. 23 is a diagram illustrating an example of a state in which the image information detection unit 102 searches for a region corresponding to the circumferential ends 11 a and 11 b of the steel plate 1.

  As shown in FIG. 23, the image information detection unit 102 has the most downstream point in the conveyance direction (x-axis direction) of the blob 91 in the V-shaped convergence region (V convergence point V1 detected by the V convergence point derivation process). And the pixel value changes from “1” to “0” from a straight line parallel to the x-axis direction (a chain line shown in FIG. 23) in a positive direction of the y-axis and a negative direction of the y-axis. Each of the points is searched, and a search process is performed in which the points are used as the end portions 11 a and 11 b in the circumferential direction of the steel plate 1.

  The image information detection unit 102 performs this search process from a predetermined range in the direction of convergence in the V shape (x-axis direction), for example, from the left end of the binarized image (upstream side in the conveyance direction of the steel plate 1). Of the range up to the tip of the blob 91 in the convergence area, the process is executed within a range of 2/3 from the left end (see “Linear approximation area” shown in FIG. 23). Then, the image information detection unit 102 linearly approximates the regions corresponding to the end portions 11a and 11b in the circumferential direction of the searched steel plate 1, and detects the intersection of the approximate straight lines as the geometric V convergence point V0. .

  In the present embodiment, the image information detection unit 102 detects the geometric V convergence point V0 for each of the images in the same V-shaped convergence region used when the position of the V convergence point V1 is detected. .

  In the above embodiment, the case where the metal pipe to be manufactured is a steel pipe has been described, but the present invention may be applied to the manufacture of a metal pipe other than a steel pipe.

  While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

2a, 2b Squeeze rolls 3a, 3b Contact chip 4 Impeder 5 Imaging device 6 High frequency power supply 100 Management system

Claims (6)

While the metal plate is conveyed in the conveying direction and formed into a cylindrical shape, both ends in the circumferential direction of the metal plate are opposed to each other so as to be V-shaped when viewed from the outside in the radial direction, and the abutting portions are in contact with both ends In a manufacturing process of a metal tube for forming and welding a molten metal by flowing an alternating current to the monitoring method, the monitoring method for monitoring the molten state of the abutting portion,
Based on the images obtained by photographing the abutting portions at both ends of the metal plate and the peripheral portion thereof from the radial direction, the geometrical lines of the extension lines at both ends before the contact upstream of the abutting portions at both ends of the metal plate are obtained. Detecting a distance (LV0-LV1) between a geometric V convergence point V0 that is an intersection and a V convergence point V1 that is an abutment point at which both ends of the metal plate start to contact;
How much is the input power at a certain monitoring target time with respect to SPLcr which is a value indicating the reference input power determined as the input power in the transition region from the second type welding state to the two-stage convergence type second type welding state? A step of calculating a power evaluation value ξ that is a value indicating whether they are separated by using a distance (LV0-LV1) at the monitoring target time point, a thickness t of the metal plate, and a diameter D of a metal tube to be formed; A monitoring method. The monitoring method according to claim 1,
The power evaluation value ξ is a monitoring method calculated by the following formula (1).
ξ = f (t / D) × (LV0-LV1) + g (t / D) (1)
t: Metal tube thickness
D: Diameter of the metal tube
f (t / D): Function with t / D as a variable
g (t / D): Function with t / D as a variable The monitoring method according to claim 2,
The power evaluation value ξ is a monitoring method calculated by the following formula (2).
ξ = {1945 × (t / D) ² −152 × (t / D) +3.7} × (LV0-LV1)
+ {− 49834 × (t / D) ² + 4198 × (t / D) −82.5} (2) A method for manufacturing a metal tube, including the monitoring method according to claim 1, for manufacturing a metal tube,
A method of manufacturing a metal tube, further comprising a step of outputting the calculated power evaluation value to a monitor or controlling the input power based on the calculated power evaluation value. While the metal plate is conveyed in the conveying direction and formed into a cylindrical shape, both ends in the circumferential direction of the metal plate are opposed to each other so as to be V-shaped when viewed from the outside in the radial direction, and the abutting portions where both ends contact In a manufacturing process of a metal tube for forming and welding a molten metal by passing an alternating current through the monitoring system, the monitoring system monitors the molten state of the abutting portion,
Based on the images obtained by photographing the abutting portions at both ends of the metal plate and the peripheral portion thereof from the radial direction, the geometrical lines of the extension lines at both ends before the contact upstream of the abutting portions at both ends of the metal plate are obtained. An image information detection unit for detecting a distance (LV0-LV1) between a geometric V convergence point V0 that is an intersection and a V convergence point V1 that is an abutting point at which both ends of the metal plate start to contact;
How much is the input power at a certain monitoring target time with respect to SPLcr which is a value indicating the reference input power determined as the input power in the transition region from the second type welding state to the two-stage convergence type second type welding state? Evaluation calculation for calculating a power evaluation value ξ, which is a value indicating whether or not the object is separated, using the distance (LV0-LV1) at the monitoring target time point, the thickness t of the metal plate, and the diameter D of the metal tube to be formed. And a monitoring system. While the metal plate is conveyed in the conveying direction and formed into a cylindrical shape, both ends in the circumferential direction of the metal plate are opposed to each other so as to be V-shaped when viewed from the outside in the radial direction, and the abutting portions are in contact with both ends In a manufacturing process of a metal tube for forming and welding a molten metal by flowing an alternating current to a monitoring program, the monitoring program monitors the molten state of the abutting portion,
Based on the images obtained by photographing the abutting portions at both ends of the metal plate and the peripheral portion thereof from the radial direction, the geometrical lines of the extension lines at both ends before the contact upstream of the abutting portions at both ends of the metal plate are obtained. A process of detecting a distance (LV0-LV1) between a geometric V convergence point V0 that is an intersection point and a V convergence point V1 point that is an abutment point where both ends of the metal plate start to contact;
How much is the input power at a certain monitoring target time with respect to SPLcr which is a value indicating the reference input power determined as the input power in the transition region from the second type welding state to the two-stage convergence type second type welding state? A process of calculating a power evaluation value ξ that is a value indicating whether or not the object is separated by using a distance (LV0-LV1) at the monitoring target time point, a thickness t of the metal plate, and a diameter D of a metal tube to be formed; A monitoring program that causes a computer to execute.

Images