JP7119561B2 - MONITORING METHOD, MONITORING SYSTEM AND MONITORING PROGRAM FOR ERW WELDING - Google Patents

Description

TECHNICAL FIELD The present invention relates to a technique for managing welded portion quality in electric resistance welding (hereinafter referred to as ERW).

Steel pipes manufactured using ERW technology are called electric resistance welded steel pipes. Electric resistance welded 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 for various machines, and general piping. When manufacturing an electric resistance welded 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, ie, the end surfaces facing each other, are butted against each other so as to form a V shape when viewed from the radial direction. A high frequency current is passed through the abutment (contact) of these abutting ends to heat and melt the abutment to form a weld seam.

In ERW, in order to suppress welding defects, it is required to control heat input (that is, input power), welding speed, etc. within appropriate ranges. For example, when the heat input is insufficient or the welding speed is high, unwelded portions 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.

In general, the state of welding in electric resistance welding is roughly classified into a first-class welding state, a second-class welding state, and a third-class welding state. In the first-class welding state, the positional variation of the welding point where the end faces of the steel plates first come into contact is very small. This positional variation of the welding point increases in the order of the second-class welding state and the third-class welding state. In the second-class welding state, molten slits are generated at the abutting portion. In addition, when certain conditions of welding speed and heat input are satisfied, a two-step convergence type second-class welding state with two-step convergence appears. Note that the welding state is sometimes referred to as a welding phenomenon. Therefore, the first-class welding state is the first welding phenomenon, the second-class welding state is the second-class welding phenomenon, the third-class welding state is the third-class welding phenomenon, and the two-stage convergence type second-class welding state is This phenomenon is sometimes referred to as a two-stage convergence Type 2 welding phenomenon.

In the two-stage convergence type type 2 welding state, at the point where extension lines of both ends of the steel plate converging in a V shape when viewed from the radial direction intersect (geometric V convergence point: V0 point), both ends (edges) of the steel plate no contact. The V convergence point (V1 point) where the end faces of the steel plate first come into contact is downstream of the V0 point in the tube-making direction. That is, both ends (edges) of the steel plate are tapered in two stages when viewed from the radial direction. The V convergence point (V1 point) is the point where the ends of the metal plates converging in the V shape in the circumferential direction physically collide (contact). The welding point (W point) is the terminal point of the fusion slit, that is, the downstream end of the fusion slit in the tube-making 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 corresponds to the first-class welding state, a region 2002 corresponds to the second-class welding state, and a region 2003 corresponds to the third-class welding state. A region 2004 corresponds to a two-stage convergence type second welding state. In addition, Vm is the critical welding speed at which a two-stage convergence type 2 welding state appears, and Tm is the melting point of the steel plate. T is the temperature of both ends (edges) of the steel plate at the V0 point. In the region above the T=Tm line, both ends of the steel sheet melt over the entire thickness at 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-class welding state (area 2001). Even if the welding speed is less than the critical welding speed Vm, if the input power is increased, the welding state will be in the second-class welding state (region 2002), and if the input power is further increased, it will be in the third-class 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-class welding state (region 2001) to the second-class welding state (region 2002) as the input power increases. is increased, a two-stage convergence type second-class welding state (area 2004) is obtained.

Japanese Patent No. 5510615 (Patent Literature 1) describes an electric resistance welding operation control device that controls the operation of ERW when manufacturing an electric resistance welded steel pipe. This electric resistance welding operation management device receives an image of an area including the surface of the V-shaped convergence area, the edge of the fusion slit, and the welding point (image of the V-shaped convergence area) captured by the imaging device. The electric resistance welding operation management device uses the result of processing the image of the V-shaped convergence area to adjust the amount of electric power output from the high-frequency power source so that the welding state becomes a two-stage convergence type second type welding state. Control.

Japanese Patent No. 5510615

The inventors conducted laboratory tests and actual equipment tests, 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 the optimum welding conditions. As a result, it was found that a transition region appeared when transitioning from the second type welding state to the two-stage convergence type second type welding state. Welding conditions that satisfy the target value of the weld defect area ratio may be a two-step convergence type 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. It turns out there is.

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 the welding operation is performed, what percentage difference is the current input power from the reference input power? It is useful to monitor whether

Therefore, an object of the present invention is to make it possible to estimate how far the input power during welding is 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, while a metal plate is transported in the transport direction and formed into a cylindrical shape, both ends of the metal plate in the circumferential direction face each other so as to form a V shape when viewed from the outside in the radial direction. A monitoring method for monitoring the molten state of the abutting portion in a manufacturing process of a metal pipe in which molten metal is formed and welded by applying an alternating current to the abutting portion where both ends are in contact with each other.
The monitoring method is based on an image of the abutting portions at both ends of the metal plate and its peripheral portion photographed from the radial direction, and an extension line of the both ends of the metal plate before contact upstream of the abutting portions at both ends of the metal plate. a step of detecting a distance (LV0-LV1) between a geometrical V convergence point V0, which is a geometrical intersection point of the metal plate, and a V convergence point V1, which is an abutment point where both ends of the metal plate start to come into contact; The input power (or heat input) at a certain monitoring target time is set 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. On the other hand, the power evaluation value ξ, which is a value indicating how far apart, is obtained by using the distance (LV0-LV1) at the time of the monitoring target, 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 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 showing an example of the configuration of an electric resistance welded steel pipe manufacturing system according to an embodiment of the present invention. FIG. 3A is a diagram conceptually showing an example of a V-shaped convergence region in a two-stage convergence type 2 welding state. FIG. 3B is a diagram conceptually showing an example of a V-shaped convergence region in a two-stage convergence type 2 welding state. FIG. 4 is a diagram showing an input power, an example image of a welded portion, and a measured value of the shape of the welded portion. 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 welding state determination results and welded portion images for each input power at a plate thickness of 6.4 mm. FIG. 8 is a diagram showing welding state determination results and welded portion images for each input power at a plate thickness of 12.7 mm. FIG. 9 is a diagram showing welding state determination results and welded portion images for each input power at a plate thickness of 19 mm. FIG. 10 is a graph showing the relationship between input power, LV0-LV1, and welding state at a plate thickness of 6.4 mm. FIG. 11 is a graph showing the relationship between input power, LV0-LV1, and welding state at a plate thickness of 12.7 mm. FIG. 12 is a graph showing the relationship between input power, LV0-LV1, and welding state at a plate thickness of 19 mm. 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 with changes in t/D. FIGS. 15A, 15B, and 15C are graphs respectively showing the relationship between t/D and LV0-LV1 when the power evaluation value ξ is 5%, 10%, and 15%. FIG. 16 is a graph showing the relationship between the measured power evaluation value ξ and the calculated value. FIG. 17 is a diagram showing a configuration example of a management system including a monitoring system. FIG. 18 is a flow chart showing an example of a welding state monitoring process by the management system 100. As shown in FIG. FIG. 19 is a drawing of an example of an image of a V-shaped convergence area. FIG. 20 is a drawing showing an example of a binarized image. FIG. 21 is a drawing showing an example of a binarized image subjected to labeling processing. FIG. 22 is a drawing showing an example of how the blob 91 of the V-shaped convergence area is extracted. FIG. 23 is a drawing showing an example of how the V convergence point V1 is detected. FIG. 24 is a drawing showing an example of how the V convergence point V1 is detected.

As a result of careful observation of the shape of the end of the metal pipe during welding, the inventors found that there is a transition region at the time of transition from the second type welding state to the two-step convergence type second welding state. Furthermore, the inventors found that the distance (LV0-LV1) changes with increasing input power (ie, heat input) in the transition region and in the two-step convergence second welding state. Furthermore, the inventors found that when the thickness t and diameter D of the metal tube change, the distance (LV0-LV1) also changes. Based on these findings, the inventors calculated the relative value of the current input power to the reference input power determined as the input power in the transition region by the distance (LV0-LV1), the thickness of the metal plate t and It occurred to me that it could be calculated using the diameter D of the metal tube to be formed. That is, 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 from the reference input power. rice field. Based on this finding, the following embodiments were conceived.

In the monitoring method according to the embodiment of the present invention, while a metal plate is transported in the transport direction and formed into a cylindrical shape, both ends of the metal plate in the circumferential direction face each other so as to form a V shape when viewed from the outside in the radial direction. A monitoring method for monitoring the molten state of the abutting portion in a manufacturing process of a metal pipe in which molten metal is formed and welded by applying an alternating current to the abutting portion where both ends are in contact with each other.
The monitoring method is based on an image of the butted portions at both ends of the metal plate and the peripheral portion taken from the radial direction. The distance (LV0-LV1) between the geometric V convergence point V0 point, which is the geometric intersection of the extension lines of both ends of the metal plate, and the V convergence point V1 point, which is the contact point where both ends of the metal plate start and a reference input power in which the input power (or heat input) at a certain monitoring target time is 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 The power evaluation value ξ, which is a value indicating how far away from the indicated value SPLcr, is calculated by the distance (LV0-LV1) at the time of the monitoring target, the thickness t of the metal plate, and the formed metal tube and a step of calculating using the diameter D of

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

A monitoring system as an embodiment of a device that implements the above-described monitoring method detects the butted portions at both ends of the metal plate based on images of the butted portions at both ends of the metal plate and their peripheral portions photographed from the radial direction. The distance between the geometric V convergence point V0 point, which is the geometric intersection of the extension lines of the both ends before contact, and the V convergence point V1 point, which is the contact point where the both ends of the metal plate start to contact An image information detection unit that detects (LV0-LV1) and a reference for determining the input power at a certain monitoring target time as the input power in the transition region from the second type welding state to the two-stage convergence type second type welding state The power evaluation value ξ, which is a value indicating how far away from SPLcr, which is a value indicating the input power, is the distance (LV0-LV1) at the monitoring target time, the thickness t of the metal plate, and the formed and an evaluation calculation unit that calculates using the diameter D of the metal pipe.

A monitoring program, which is an embodiment of a program for causing a computer to execute the above-described monitoring method, monitors the metal plate based on an image of the abutting portions at both ends of the metal plate and the peripheral portion thereof photographed from the radial direction. A geometrical V convergence point V0, which is a geometric intersection of the extension lines of the both ends before contact, upstream of the abutting portions of both ends, and a V convergence point, which is the abutment point where both ends of the metal plate start to contact. The process of detecting the distance (LV0-LV1) to the V1 point and the input power at a certain monitoring target time are 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. The power evaluation value ξ, which is a value indicating how far away from SPLcr, which is a value indicating the reference input power, is the distance (LV0-LV1) at the monitoring target time, the thickness t of the metal plate, and Using the diameter D of the metal pipe to be formed, a computer is caused to perform the calculation process.

The monitoring method, system, or program described above makes it possible to estimate how far the input power during welding is from the input power that causes the transition region condition. Here, the input power is the power for supplying the alternating current to the contacting portion of the metal plates. By adjusting the input power, the amount of heat input in welding the metal plates can be adjusted. That is, the amount of heat input in welding metal plates depends on the input power. Therefore, the input power value may be expressed as a heat input value.

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. There may be. Whether or not the welded state is in the transition region can be determined, for example, based on the result of processing an image of the butted portion and its peripheral portion taken from the radial direction.

In the monitoring method, monitoring system, or monitoring program described above, the power evaluation value ξ can be calculated by, for example, the following formula (1).
ξ = f(t/D)×(LV0-LV1)+g(t/D) (1)
t: Thickness of metal tube
D: Diameter of 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 once t and D are determined. The above formula (1) is a linear function with the values determined by t and D as coefficients and constant terms, and the distance (LV0-LV1) as a variable. By using equation (1), it is possible to accurately estimate how far the input power during welding is 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, instead of a linear function with the distance (LV0-LV1) as a variable, a quadratic function, an exponential function, or other functions may be used. Also, for example, at least one of the coefficient and the constant term may be a value that depends on other values in addition to t and D. Also, in the above example, the power evaluation value ξ is, for example, a value expressed as a percentage (that is, a value whose unit is %). Thus, the power evaluation value ξ can be represented by the ratio of the input power to the reference input power SPLcr. Note that the power evaluation value ξ may be represented by a difference or other value relative to the reference value, in addition to the ratio to the reference value.

In the monitoring method, monitoring system, or monitoring program described above, the power evaluation value ξ can be calculated, for example, 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)

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

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 are also included in embodiments of the present invention. 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. A part or process may further be included. Moreover, a process, a functional part, or a process of judging the welding state depending on whether or not the power evaluation value satisfies a predetermined condition may be included. This makes it possible to easily control the input power using the power evaluation value.

The manufacturing method may include, for example, a step of simultaneously displaying the power evaluation value and a predetermined target input power range in a visible state on a monitor. Further, the manufacturing method may include a step of controlling input power such that the power evaluation value is within a predetermined target input power range. The target input power range can be, for example, within a range of input powers that are 5% to 20% greater than SPLcr. As an example, the range of target input power can be within a predetermined range of input power increased by 10% from SPLcr.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same reference numerals are given to the same or corresponding parts in the drawings, and the description thereof will not be repeated.

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

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

First, an overview of the equipment for manufacturing electric resistance welded steel pipes will be given. As shown in FIG. 2, a strip-shaped steel plate 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 is arranged inside the steel plate 1 formed into a cylindrical shape for concentrating the magnetic flux on the abutting portion of the steel plate 1 . When high-frequency power is supplied from the high-frequency power source 6, high-frequency current flows from the pair of contact tips 3a, 3b (or dielectric coil (not shown)) to the surface of the steel plate 1 in the V-shaped converging region. At this time, pressing force is applied to the steel plate 1 from both sides thereof by the squeeze rolls 2a and 2b. As a result, both ends 11a and 11b in the circumferential direction of the steel plate 1 are brought into contact with each other while being converged in a V shape, and the abutting portions where the ends 11a and 11b contact are heated and melted to melt and join the steel plates 1. . Such fusion bonding is referred to as electric resistance welding (ERW). In the following description, "the region of the steel plate 1 converging in a V-shape" will be referred to as a "V-shaped convergence region" as necessary. Moreover, the part which the both ends 11a and 11b of the steel plate 1 of the circumferential direction are butted|matched, and is observed as one line is called a "welding line" as needed.

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

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

The management system 100 controls the operation of the squeeze rolls 2a, 2b, the contact tips 3a, 3b, the high-frequency power source 6, or other members so as to achieve the determined welding conditions. Thus, the management system 100 can include a monitoring device (monitoring system) that monitors the state of welding and a control device (control section) that controls welding based on the monitoring results. In addition to the image captured by the image capturing device 5, the monitoring device may acquire information on welding conditions as necessary. For example, it is possible to obtain information indicating the operation of the device used for welding, such as the output values of the contact tips 3a and 3b and the high frequency power source 6, the pressure of the squeeze rolls 2a and 2b, the distance between the rolls, and the like.

<Explanation of two-stage convergence type second-class welding state>
3A and 3B are diagrams conceptually showing 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 area viewed from above (z direction), and FIG. It is the figure which looked at the direction of V1 point.

In the two-step convergence type second-class welding state, both circumferential ends 11a and 11b of the steel plate 1 are butted against each other while the melted portions in the thickness direction (z-axis direction) of the steel plates 1 are 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 arrow lines shown in FIG. 3B).

The self-luminous pattern of the area including the V-shaped convergence area is imaged from above the steel plate 1 with high definition without image flow (imaging resolution: 100 [μm / pixel], exposure time: 1/10000 [sec] conditions). When the V convergence point was measured with high accuracy, a two-step convergence type second class welding state was observed. When the welding state becomes a two-stage convergence type second-class welding state, as shown in FIG. A geometrical 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 area. The geometrical V convergence point V0 is a point where downstream extension lines (indicated by dashed lines) of both ends 11a and 11b in the circumferential direction of the steel plate 1 converging in a V shape geometrically intersect. On the other hand, the V convergence point V1 point, which is a contact point, is a point where both ends 11a and 11b in the circumferential direction of the steel plate 1 converging in a V shape first physically meet (contact). Both ends 11a and 11b forming the V shape are bent at some positions k1 and k2 on the upstream side in the pipe-making direction from the tip of the V shape in a two-step converging type second-class welding state to form a two-step tapered shape. shape. On the other hand, both ends 11a and 11b in the transition region exhibit an unstable form in which a straight line and a two-step tapered state alternately appear.

When an input power equal to or higher than the input power that brings the welding state to the second type welding state is applied, the welding point W point, which is the end point of the fusion slit, is further in the tube-making direction than the V convergence point V1 point, which is the abutting point. exists in the region downstream of Between the V convergence point V1 and the welding point W, a molten slit S is formed that penetrates the steel sheet 1 in the thickness direction of the steel sheet 1 . Further, the fusion slit S disappears after extending downstream from the V convergence point V1 in the conveying direction (x-axis direction) of the steel plate 1, that is, in the pipe-making direction. Such fluctuations in the size of the molten slit S in the x-axis direction (growth and disappearance of the molten slit S) occur periodically at intervals 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 an input power in the two-stage convergence Type 2 welding condition that is as much as 10% greater than the input power in the transition region condition, ie, the reference input power SPLcr. However, in the two-stage convergence type 2 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 the shape of the weld (V0 point, V1 point, W point) observed from directly above (radial direction) changes when the input power changes. Therefore, the inventors carefully observed the shape of the weld when observing the weld from directly above. As a result, it was found that there is a certain relationship between the weld shape and the input power. using this relationship. A method for monitoring welding conditions has been invented. The details of the experiments and studies by the inventors are described below.

<Experiments using a lab simulator>
Welding experiments were conducted using a lab test apparatus (hereinafter referred to as a lab simulator). Carbon steel was used as the test material. 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 425.9-474.7 VA. The squeeze amount was 4 mm. Judgment of the welding state was mainly carried out by moving images using a video camera.

The weld shape was measured from images captured by a video camera. As shown in FIG. 3A, the point where the extension lines of the steel plate edges contact is defined as the geometric V convergence point (V0 point), and the line connecting the axial centers of the squeeze rolls (squeeze roll center: SQC); The distance of the V0 point was set to LV0 (mm). When the steel plate edges come into contact on the downstream side in the tube-making direction of point V0, the point of contact was defined as point V1. The distance between SQC and V1 point was V1 (mm), and the distance between V0 point and V1 point was 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 by averaging 100 consecutively shot images (frames).

4 to 6 show the results of experiments using the lab simulator. Fig. 4 shows the input power, an example image of the welded part, and the measured value of the welded part shape. 5 shows the relationship between input power and distances LV0, LV1, and LW, and FIG. 6 shows the relationship between input power and distance (LV0-LV1).

LV0 (mm) increased with increasing input power. LV1 (mm) and LW (mm) decreased with increasing input power. In addition, LV0-LV1 (mm) was 0 mm in the second type welding state, started 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) at 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, we can determine changes in input power from the appropriate value. The inventors conceived of the possibility of monitoring.

<Verification on actual equipment>
Based on the experimental results obtained by the laboratory simulator, the inventors verified the relationship between the distance (LV0-LV1) and the input power using various plate thicknesses in an actual machine. The details are described below.

(1) Experimental conditions Steel pipes having plate thicknesses of 6.4 mm, 12.7 mm and 19.0 mm and an outer diameter of 404.4 mm were produced. The input power was increased stepwise from the second type welding state to the two-stage convergence type second type welding state.

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

Figs. 7, 8, and 9 show the welding state determination results and welded portion images for each input power for plate thicknesses of 6.4 mm, 12.7 mm, and 19.0 mm, respectively. 10, 11, and 12 show the relationship between the input power, the distance (LV0-LV1), and the welding state. At any plate thickness, the distance (LV0-LV1) in the second type welding state is 0 mm, but when the input power is increased to change to the transition region state, the V0 point and the V1 point are separated. When the input power is further increased, the welding state changes to two-step convergence type 2nd class welding, and the distance (LV0-LV1) increases. 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 input power increase with respect to the reference input power SPLcr. From FIG. 13, it was confirmed that the larger the ξ, the larger the value of the distance (LV0-LV1), and the larger the plate thickness, the smaller the distance (LV0-LV1).

From these results, it was confirmed that the distance (LV0-LV1) increases as the input power increases in the range of the two-stage convergence type 2nd class 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 the optimum welding conditions by measuring LV0-LV1 (mm) at a preset input power and comparing it with LV0-LV1 (mm) during welding. .

<Proposal for advancement of appropriate welding condition monitoring technology by constructing LV0-LV1 prediction formula>
Based on the above experimental results, consider a prediction formula assuming that the power evaluation value ξ is obtained by the distance (LV0-LV1) and t/D, which is the plate thickness t made dimensionless by the diameter D of the metal pipe. did.

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

15(a), 15(b) and 15(c) show the relationship between t/D and the distance (LV0-LV1) when ξ is 5%, 10% and 15%, respectively. From these, both can be approximated by quadratic functions, so f (t / D) and g (t / D) in the above formula (1) are assumed to be quadratic functions, fitting is performed, 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. do not have. By fitting linear functions or other functions to the measured values, f(t/D) and g(t/D) can be determined. In the examples shown in FIGS. 15A, 15B, and 15C, in the range of t/D in question, f(t/D) and g(t/D) decrease as t/D increases. The functions can be f(t/D), g(t/D).

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

From the above results, it was found that it is possible to predict the distance (LV0-LV1) when using the experimental data of this time. Based on this knowledge, the inventors invented a method and system for monitoring welding conditions by capturing the distance (LV0-LV1) from images during welding. A specific example thereof will be described below.

<Specific example of welding condition monitoring>
FIG. 17 is a functional block diagram showing a configuration example of a management system 100 (an example of a manufacturing system) including a monitoring system. Management system 100 includes monitoring system 101 , control unit 104 , and monitor 105 . The monitoring system 101 includes an image information detector 102 and an evaluation calculator 103 . The image information detection unit 102 acquires an image of the abutting portions at both ends of the metal plate and their peripheral portions captured by the imaging device 5 from the radial direction. 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 calculates the power evaluation, which is a value indicating how far the input power at a certain monitoring target time is from SPLcr, which is a value indicating the reference input power determined as the input power in the transition region. Calculate the value ξ. The distance (LV0-LV1), the thickness t of the metal plate, and the diameter D of the formed metal pipe are used to calculate the power evaluation value ξ.

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

Monitoring system 101 further includes control unit 104 that controls input power based on the power evaluation value calculated by evaluation calculation unit 103 . The control unit 104 can control the input power, for example, 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 decrease the input power when the power evaluation value exceeds the upper limit and to increase the input power when the power evaluation value is below the lower limit.

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

FIG. 18 is a flow chart showing an example of a welding state monitoring process by the management system 100. As shown in FIG.

At S1, the management system 100 acquires the input power EpIp input to the weld. For example, the management system 100 can acquire the value EpIp(t) of the input power EpIp at each time t=t1, t2, t3, . . . , tn. EpIp(t) can be calculated from the output voltage and output current of the high frequency power supply 6, for example. 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 portion captured by the imaging device 5 . Here, as an example, the management system 100 receives images (frames) captured by the imaging device 5 at consecutive times t=t1, t2, t3, . The management system 100 calculates the distance (LV0-LV1) between the V0 point and the V1 point for each acquired image (S3). As a result, the distance (LV0-LV1) at each time t is obtained.

The image acquired in S2 is an image of the butted portion of the both end portions 11a and 11b of the steel pipe and its surroundings taken from the radial direction (above). The imaging range of this image is the portion where both ends in the pipe-making direction upstream of point V1 where both ends 11a and 11b begin to contact are tapered or V-shaped and face each other, and the welding point W downstream from point V1. It is preferable to include at least up to 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 the value SPLcr indicating the reference input power based on the input power EpIp obtained in S1 and the time transition of the distance (LV0-LV1) obtained in S3. For example, the management system 100 determines the time point tv at which the distance (LV0-LV1) becomes LV0-LV1>0, and thereafter the state of LV0-LV1>0 continues for a certain period of time. When LV0-LV1 at time tv exceeds a predetermined threshold Th1, the input power EpIp(tv) at time tv can be determined as SPLcr. The threshold Th1 is determined, for example, according to the size and material of the metal pipe. Note that the SPLcr detection process is not limited to the above example.

If the time transition of the distance (LV0-LV1) that satisfies the above conditions is not detected, the management system 100 can determine that the SPLcr has not been 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 welding state is the first type or the second type, it is determined that the input power has not reached the reference input power SPLcr.

If it is determined in S5 that SPLcr is not detected (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 the 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. Pre-calculated values can be used for f(t/D) and g(t/D) in the above formula (1) based on the thickness t and the diameter D of the metal tube.

At S8, the management system 100 determines the welding state using the power evaluation value ξ calculated at 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 for determining the above range can be set to a value near 10%, such as 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 heat input is too large. When the power evaluation value ξ is smaller than the above range, it can be determined that the 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 whether the welding state is good or bad, or may be information indicating whether the amount of 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 excess or deficiency of the input power determined in S8. At S10, the input power is adjusted and welding continues. While welding continues, 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 processing 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 with an increase in the input power. This makes it possible to determine the optimum input power in the two-stage convergence type 2 welding state. For example, after the input power is gradually increased from the first-class welding state and the transition region is reached through the second-class welding state, that is, after SPLcr is detected, in the two-stage convergence type second-class welding state, for example, , the input power when the power evaluation value ξ becomes 10% can be determined as the optimum welding condition.

Using the above equation (1), it is possible to predict the distance (LV0-LV1) when the appropriate welding conditions are satisfied (for example, when the power evaluation value ξ becomes 10%) using t/D as a parameter. In this way, by highly predicting the distance (LV0-LV1) when the proper welding conditions are satisfied, the proper welding conditions are monitored and controlled without measuring the distance (LV0-LV1) of the proper welding conditions before welding. becomes possible.

In the above example, the power evaluation value ξ is calculated using LV0-LV1 and t/D, but it is also possible to determine the power evaluation value ξ 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 formula (1), and the value calculated using the above formula (1) may be changed using other parameters. can be corrected.

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

(Calculation example of distance (LV0L-V1))
The image information detection unit 102 performs processing for obtaining a geometrical V convergence point V0, processing for obtaining a V convergence point V1, and processing for obtaining a distance (LV0-LV1) based on an image including a V-shaped convergence portion. Run.

The process of obtaining the geometric V convergence point V0 includes, for example, a process of binarizing an image to generate a binarized image, a process of determining both ends of the metal plate in the circumferential direction from the binarized image, and determining the intersection of these two approximate lines as the geometric V convergence point V0. Alternatively, the processing for obtaining the geometrical V convergence point V0 includes edge extraction processing in the image, processing for determining both end portions and intersection points in the circumferential direction of the metal plate by performing template matching on the extracted edges, as the geometric V convergence point V0 point. Note that the processing for obtaining the geometric V convergence point V0 is not limited to these examples.

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

The image information detection unit 102 can, for example, calculate the distance (LV0-LV1) from the coordinates of the geometric V convergence points V0 and V1.

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

As shown in FIG. 19 , in the image of the V-shaped convergence area captured by the imaging device 5 , high heat areas 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 conveying direction (x-axis direction) of the steel plate 1, a wavy pattern formed by the molten portions of the circumferential ends 11a and 11b of the steel plate 1 being discharged appears. Further, a molten 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.

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

(Red component extraction processing)
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 of the V-shaped convergence area.

The red component extraction process is realized, for example, by the CPU reading image data from RAM or the like, extracting the 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 process. Here, the image information detection unit 102 gives a pixel value of "0" to pixels whose luminance level is equal to or higher than the threshold, and gives a pixel value of "1" to pixels whose luminance level is less than the threshold. The brightness level threshold may be different between the processing of the geometric V convergence point V0 and the V convergence point V1. FIG. 20 is a drawing showing an example of a binarized image.

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

(labeling process)
The image information detection unit 102 performs a labeling process of labeling each blob of the binarized image obtained by the binarization process. A blob here means a pixel given a pixel value of "1" in any one of eight pixels adjacent to a certain pixel, including four pixels adjacent in the vertical and horizontal directions and four pixels adjacent in the diagonal direction. When contiguous, it means an individual connected region obtained by connecting those pixels for each pixel. In addition, the labeling process involves assigning a label number to each blob, extracting a specific blob, and determining the position of the extracted blob in the image (maximum and minimum points of x coordinates, maximum and minimum points of y coordinates). , width, length, and area.

FIG. 21 is a drawing showing an example of a binarized image subjected to labeling processing.

In the example shown in FIG. 21, three blobs are labeled with the label numbers "1", "2" and "3", respectively.

The labeling process is realized, for example, by having the CPU read the binarized image data from the RAM or the like, perform the labeling process, and temporarily store the result in the RAM or the like.

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

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

Here, for example, in the binarized image shown in FIG. 20, if there is a blob that touches the left end and has a predetermined area condition, the image information detection unit 102 extracts it as the blob 91 of the V-shaped convergence area. do. As the predetermined area conditions, for example, the condition that the actual size of the area of the blob is 15 [mm ² ] to 150 [mm ² ], and the condition that the actual size of the rectangular block circumscribing the blob is 25 [mm ² ] to 320 [mm 2 ]. A condition such as satisfying at least one of the condition of [mm ² ] may be set.

As shown in FIG. 24, the image information detection unit 102 detects the tip of the blob 91 in the V-shaped convergence area in the positive x-axis direction (downstream direction in the conveying direction of the steel plate 1) as the V convergence point, which is the collision point. It is detected as (the position of) the V1 point.

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, the image information detection unit 102 detects the position of the V convergence point V1 for each of a plurality of V-shaped convergence area images continuously captured by the imaging device 5 over 3 [sec]. Since the imaging device 5 captures images at a shooting frame rate of 500 [fps], the image information detection unit 102 detects the positions of 1500 V convergence points V1. However, for example, if the positional variation of the V convergence point V1 is slight, the image information detection unit 102 may detect the positions of the V convergence points V1 derived from one image (that is, a plurality of , it is not necessary to derive the V convergence point V1 from each of the images of ).

Note that when the electric resistance welding operation management device 100 is controlling the amount of heat input to the steel plate 1, if no blobs that meet a predetermined condition are extracted continuously for a predetermined number of frames or more, the image information detection unit 102 can print an error message to the operator.

In the V convergence point deriving process, for example, the CPU reads the binarized image data that has undergone 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. It is realized by memorizing.

(Geometric V convergence point derivation process)
The geometric V convergence point deriving process includes a process of determining whether or not a blob that meets 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 satisfies the predetermined condition, the image information detection unit 102 extracts the blob as the blob 91 of the V-shaped convergence area. Then, the image information detection unit 102 acquires shape information such as the coordinates and area of the blob 91 of the extracted V-shaped convergence area (see FIGS. 21 and 22). The image information detection unit 102 can also use the information of the blob 91 of the V-shaped convergence area extracted by the V-convergence point derivation process.

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

FIG. 23 is a drawing showing an example of how the image information detection unit 102 searches for regions corresponding to the circumferential ends 11a and 11b of the steel plate 1. As shown in FIG.

As shown in FIG. 23, the image information detection unit 102 detects the most downstream point (V convergence point V1 detected by the V convergence point derivation process) in the conveying direction (x-axis direction) of the blob 91 of the V-shaped convergence area. and the pixel value changes from "1" to "0" in the positive direction of the y-axis and the negative direction of the y-axis from a straight line (one-dot chain line shown in FIG. 23) parallel to the x-axis direction. Each point is searched for, and a search process is performed to set the points to the ends 11a and 11b of the steel plate 1 in the circumferential direction.

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

In this embodiment, the image information detection unit 102 detects the geometrical V convergence point V0 for each image of the same V-shaped convergence area used when detecting the position of the V convergence point V1. .

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 metal pipes other than steel pipes.

Although 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 of the present invention.

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

Claims (6)

While conveying the metal plate in the conveying direction and forming it into a cylindrical shape, both ends in the circumferential direction of the metal plate are opposed to each other so as to form a V shape when viewed from the radial outside, and the abutment portion where the both ends come into contact. A monitoring method for monitoring the molten state of the abutting portion in a metal pipe manufacturing process in which molten metal is formed and welded by applying an alternating current to the pipe,
Based on the image of the abutting portion at both ends of the metal plate and its peripheral portion photographed from the radial direction, a geometric extension of the extension lines of the both ends of the metal plate before contact upstream of the abutting portion at both ends of the metal plate is obtained. a step of detecting a distance (LV0-LV1) between a geometrical V convergence point V0, which is an intersection point, and a V convergence point V1, which is an abutment point where both ends of the metal plate start to come into contact;
A reference input in which the input power at the monitoring target time when the welding state is the two-step convergence type second type welding state is the input power in the transition region from the second type welding state to the two-step convergence type second type welding state. The power evaluation value ξ, which is a value indicating how far away from SPLcr, which is a value indicating power, is calculated from the distance (LV0-LV1) at the monitoring target time, the thickness t of the metal plate, and the formed and calculating using the diameter D of the metal pipe.
A monitoring method according to claim 1, comprising:
The monitoring method, wherein the power evaluation value ξ is calculated by the following formula (1).

ξ = f(t/D)×(LV0-LV1)+g(t/D) (1)
t: Thickness of metal tube
D: Diameter of metal tube
f(t/D): function with t/D as a variable
g(t/D): function with t/D as a variable
A monitoring method according to claim 2, wherein
The monitoring method, wherein the power evaluation value ξ is 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 pipe, comprising the monitoring method according to any one of claims 1 to 3,
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 conveying the metal plate in the conveying direction and forming it into a cylindrical shape, both ends in the circumferential direction of the metal plate are opposed to each other so as to form a V shape when viewed from the radial outside, and the abutment portion where the both ends come into contact. A monitoring system for monitoring the molten state of the abutting portion in a metal pipe manufacturing process in which molten metal is formed and welded by applying an alternating current to the
Based on the image of the abutting portion at both ends of the metal plate and its peripheral portion photographed from the radial direction, a geometric extension of the extension lines of the both ends of the metal plate before contact upstream of the abutting portion at both ends of the metal plate is obtained. an image information detection unit for detecting a distance (LV0-LV1) between a geometrical V convergence point V0 which is an intersection and a V convergence point V1 which is a collision point where both ends of the metal plate start to come into contact;
A reference input in which the input power at the monitoring target time when the welding state is the two-step convergence type second type welding state is the input power in the transition region from the second type welding state to the two-step convergence type second type welding state. The power evaluation value ξ, which is a value indicating how far away from SPLcr, which is a value indicating power, is calculated from the distance (LV0-LV1) at the monitoring target time, the thickness t of the metal plate, and the formed A monitoring system, comprising: an evaluation calculator that calculates using the diameter D of the metal pipe.
While conveying the metal plate in the conveying direction and forming it into a cylindrical shape, both ends in the circumferential direction of the metal plate are opposed to each other so as to form a V shape when viewed from the radial outside, and the abutment portion where the both ends come into contact. A monitoring program for monitoring the molten state of the abutting portion in a metal pipe manufacturing process in which molten metal is formed and welded by applying an alternating current to the
Based on the image of the abutting portion at both ends of the metal plate and its peripheral portion photographed from the radial direction, a geometric extension of the extension lines of the both ends of the metal plate before contact upstream of the abutting portion at both ends of the metal plate is obtained. A process of detecting the distance (LV0-LV1) between the geometrical V convergence point V0 point that is the intersection and the V convergence point V1 point that is the contact point where both ends of the metal plate start to come into contact;
A reference input in which the input power at the monitoring target time when the welding state is the two-step convergence type second type welding state is the input power in the transition region from the second type welding state to the two-step convergence type second type welding state. The power evaluation value ξ, which is a value indicating how far away from SPLcr, which is a value indicating power, is calculated from the distance (LV0-LV1) at the monitoring target time, the thickness t of the metal plate, and the formed A monitoring program that causes a computer to execute a process of calculating using the diameter D of the metal pipe.

Images