Welding method, electric resistance welded steel pipe manufacturing method, control device, and steel pipe manufacturing apparatus

Abstract

The present invention provides a welding method, an electric resistance welded steel pipe manufacturing method, a control device, and a steel pipe manufacturing apparatus that can suppress variations in welded pipe quality, increases in equipment area, and increases in manufacturing costs. [Solution] The welding method includes a welding step, a size calculation step, and a control step. The control step variably controls the welding parameters by changing control values ​​so that the size is within a preset control range while monitoring the size. The control values ​​include the transport speed and the welding power. The control step includes a power control step for changing the welding power and a speed control step for changing the transport speed. The control step performs at least one of the power control step and the speed control step.

Description

Technical Field

[0001] The present invention relates to a welding method, an electric welded steel pipe manufacturing method, a control device, and a steel pipe manufacturing device.

Background Art

[0002] One type of welded pipe, an electric resistance welded pipe, is manufactured by butt welding as follows. First, a hot-rolled steel strip used as a raw material is formed into a tubular shape using a multi-stage roll stand. Next, a high-frequency large current is passed through both ends of the formed tubular steel strip to generate joule heat. The end portions of the steel strip are melted by this joule heat. And almost simultaneously with the melting, the tubular steel strip is passed through squeeze rolls (= diameter-reducing rolls). At this time, the tubular steel strip is pressure-welded by the squeeze rolls. Then, the melted end portions are welded together. By such butt welding, an electric resistance welded pipe is manufactured.

[0003] In the welded portion of this electric resistance welded pipe (= the end portion of the steel strip, which is the portion where joule heat is generated and welded by pressure welding), a so-called weld bead is formed. The weld bead is the portion where the molten part of the steel strip is extruded onto the inner and outer surfaces of the pipe and becomes a bulge of molten steel during the above-described pressure welding.

[0004] The weld bead has an adverse effect on the welding operation between electric resistance welded pipes when connecting and using a plurality of electric resistance welded pipes (for example, when used as a pipe for gas transportation). Therefore, the weld bead is cut during the manufacturing process of the electric resistance welded pipe.

[0005] On the other hand, it has long been known that the shape of the weld bead before cutting (specifically, bead height, bead width, etc.) is related to the mechanical properties of the final product, i.e., the quality of the final product. For this reason, the quality of a weld is sometimes judged from the shape of the outer surface of the weld bead (hereinafter simply referred to as "outer surface bead shape"). In this case, for example, during welding, the worker checks the outer surface bead shape before cutting and adjusts the welding conditions sequentially to ensure a good weld. Such adjustments are made to ensure that the quality of the final product is good.

[0006] The external bead shape is confirmed by the worker directly visually inspecting the weld bead, or by visually inspecting an image of the weld bead projected onto a monitor or similar device using optical methods. The welding conditions described above also include, for example, control values ​​input to the welding machine. The welding machine operates (=welds) in a manner based on the input control values.

[0007] Therefore, in the cases described above, the worker will adjust the control values ​​either by directly visually inspecting the weld bead or by visually inspecting the image of the weld bead projected onto a monitor using an optical method.

[0008] Traditionally, the shape of the outer bead was confirmed visually. In other words, the quality of the weld was judged based on qualitative information (i.e., information dependent on the worker's experience, senses, etc.) such as the shape of the outer bead obtained through visual inspection by the worker. Therefore, if the worker performing the welding work changes, the evaluation of the outer bead shape, and consequently the criteria for judging the quality of the weld, will also change. Consequently, variations occur in the adjustment of control values ​​among workers. When there are variations in the adjustment of control values ​​among workers, it becomes impossible to universally control the adjustment of control values.

[0009] To overcome these problems, methods and apparatus for quantitatively measuring the outer bead shape using optical or mechanical methods have been proposed (Patent Document 1, Patent Document 2).

[0010] Patent Document 1 discloses a method for quantitatively measuring the outer bead shape using an optical method. This method first detects the profile of the weld bead shape of an electric resistance welded pipe using the light section method. Then, multiple approximation curves are derived from the detected profile. Finally, the bead region is identified using these approximation curves.

[0011] Furthermore, Patent Document 2 discloses a method for quantitatively measuring the outer bead shape using a mechanical method. This method is used when manufacturing UO steel pipes. In this method, a touch roller and a pair of laser displacement sensors, one in front of the touch roller and one behind, are first placed on the outer circumference of the UO steel pipe. The touch roller is then brought into contact with the outer surface of the UO steel pipe, and the UO steel pipe is rotated in the circumferential direction. When the touch roller rides up over a raised area (=weld bead), the output of the laser displacement sensors changes. The bead shape is calculated by detecting this change in the output of the laser displacement sensors. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2004-117053 [Patent Document 2] Japanese Patent Publication No. 2012-6059 [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] However, the methods described in Patent Documents 1 and 2 merely quantitatively measure the shape of the outer bead. Therefore, even if the shape of the outer bead is measured using these methods, the evaluation of the measurement results will be a qualitative evaluation based on the evaluator's (=worker's) senses, experience, etc. Consequently, during welding, the worker will make a qualitative evaluation based on the measurement results and then adjust the control value. Therefore, even if the methods described in Patent Documents 1 and 2 are used, there will be variations in the adjustment of control values ​​among workers.

[0014] Furthermore, the method described in Patent Document 2 requires the steel pipe (UO steel pipe in Patent Document 2), which is the object to be measured, to be rotated in the circumferential direction. Unlike the manufacturing line for UO steel pipes, a typical electric resistance welded pipe manufacturing line performs the aforementioned electric resistance welding (butt welding) in a manner continuous with the forming of hot-rolled steel strips. In such a manufacturing line, there is no equipment or mechanism for rotating the electric resistance welded pipe in the circumferential direction. Therefore, when measuring the outer bead shape using the method described in Patent Document 2, it is necessary to install new special equipment that rotates the electric resistance welded pipe in the circumferential direction in a manner continuous with the forming of hot-rolled steel strips. Such equipment would be relatively large, leading to an increase in equipment area and increased manufacturing costs.

[0015] Furthermore, even if large-scale equipment is introduced and the method described in Patent Document 2 is adopted, as mentioned above, variations in the adjustment of control values ​​among workers will remain.

[0016] As mentioned above, if there is variation in the adjustment of control values ​​among workers, it becomes impossible to universally control the adjustment of control values. Therefore, if we attempt to introduce feedback control that variably controls the control value by feeding back the measurement results of the outer bead shape, there is a risk that variations in adjustment among workers will result in variations in the quality of welded pipes.

[0017] This invention has been made in view of the above problems. Specifically, it aims to provide a welding method, an electric resistance welded steel pipe manufacturing method, a control device, and a steel pipe manufacturing apparatus that can suppress variations in the quality of welded pipes and suppress increases in equipment area and manufacturing costs. [Means for solving the problem]

[0018] To achieve the above objective, the welding method according to the present invention includes a welding step of forming a welded pipe by welding the end of a tubular metal strip with a welding machine that performs electric resistance welding according to welding parameters determined based on input control values; a measurement step of measuring the outer surface shape of the weld bead formed on the outer surface of the welded pipe after the welding step; a size calculation step of calculating the size of the weld bead based on the outer surface shape obtained in the measurement step; and a control step of variably controlling the welding parameters by changing the control values ​​so that the size is within a preset control range while monitoring the size calculated in the size calculation step, wherein the control values ​​include the transport speed of the metal strip in the welding step and the welding power of electric resistance welding, and the welding parameters are determined based on the transport speed, welding power, and the thickness of the metal strip, and the control step includes a power control step of changing the welding power so that the size is within a control range while monitoring the size calculated in the size calculation step, and a speed control step of changing the transport speed so that the size is within a control range while monitoring the size calculated in the size calculation step, and the control step performs at least one of the power control step and the speed control step (first configuration).

[0019] Furthermore, the welding method relating to the first configuration includes a control range which includes a first control range determined based on welding power and size, and a second control range determined based on transport speed and size, and the power control process includes a first determination step which determines whether the size calculated by the size calculation step is outside the first control range, a target power calculation step which calculates a target power value for welding power such that the size falls within the first control range if the size is determined to be outside the first control range in the first determination step, a power change step which changes the welding power as a control value input to the welding machine to the target power value, a first monitoring step which monitors the determination result of the first determination step for a first period with the welding power changed by the power change step, and a first flag setting step which sets a first flag in the first monitoring step if the size calculated by the size calculation step during the first period does not fall within the value of the first control range, and the speed control process is large The control process includes a second determination step which determines whether the size calculated by the size calculation step is outside the second control range; a target speed calculation step which calculates a target transport speed such that the size falls within the second control range if the second determination step determines that the size is outside the second control range; a second modification step which changes the transport speed, which is input as a control value to the welding machine, to the target speed value obtained by the target speed calculation step; a second monitoring step which monitors the determination result of the second determination step for the second period with the transport speed changed to the target speed value by the second modification step; and a second flag setting step which sets a second flag if the size calculated by the size calculation step during the second period does not fall within the second control range (second configuration). The control process executes the power control step when the first flag is not set, and executes the speed control step when the first flag is set and the second flag is not set.

[0020] In the welding method according to the first or second configuration, the measurement step involves a distance meter configured to measure the distance to the outer surface of the welded pipe by emitting laser light onto the outer surface of the welded pipe and receiving the reflected light, and the outer surface shape is acquired by distance meters arranged in at least one pair on either side of the weld bead (third configuration).

[0021] The welding method according to the third configuration includes a pair of distance meters arranged on both sides of the weld bead, and the measurement process includes a left image generation step in which one distance meter emits laser light towards the weld bead, receives the light reflected by the weld bead, and generates a left image according to the light reception state; a right image generation step in which the other distance meter emits laser light towards the weld bead, receives the light reflected by the weld bead, and generates a right image according to the light reception state; and a synthesis step in which the generated right and left images are combined to generate a composite image, and the outer surface shape is obtained based on the composite image (fourth configuration).

[0022] In a welding method relating to any of the first to fourth configurations, the size is the cross-sectional area of ​​the weld bead, and the size calculation step includes the step of deriving a quadratic curve that approximates the outer surface shape, and the step of calculating the area of ​​the weld bead region within the region enclosed by the quadratic curve as the cross-sectional area (fifth configuration).

[0023] The welding method for the fourth configuration involves a size calculation step in which, based on a composite image, the first and second inflection points located at the starting point of the rise of the weld bead from the weld pipe are determined, the length of the straight line connecting the first and second inflection points is defined as the bead width, the straight-line distance parallel to the perpendicular bisector from the intersection of the perpendicular bisector of the straight line and the outer surface of the weld bead to the first or second inflection point is defined as the bead height, and any on the side of the first inflection point with respect to the perpendicular bisector on the weld bead is determined. The first straight line is determined connecting the first point and the first inflection point, the first angle between the first straight line and the outer surface of the welded pipe is determined, the second straight line is determined connecting an arbitrary second point on the second inflection point side, separated by the perpendicular bisector on the weld bead, and the second inflection point, the second angle between the second straight line and the outer surface of the welded pipe is determined, and a quadratic curve is derived based on the bead width, bead height, first angle, and second angle, and the area of ​​the weld bead region is calculated using integration on the quadratic curve (sixth configuration).

[0024] The welding method according to any one of the first to sixth configurations has a first management range which is a predetermined area set on a first map with the welding power on the horizontal axis and the size on the vertical axis, and a second management range which is a predetermined area set on a second map with the conveyance speed on the horizontal axis and the size on the vertical axis (seventh configuration).

[0025] Also, the electric welded steel pipe manufacturing method described in the specification manufactures an electric welded steel pipe by electric resistance welding a steel plate which is a metal strip using the welding method according to the second configuration (eighth configuration).

[0026] Also, the control device described in the specification includes a bead shape calculator that calculates the size of a weld bead based on the outer shape measured by an outer bead shape measuring device that measures the outer shape of the weld bead formed by welding a metal strip, and a welder output control unit that controls the welding parameters of a welder that welds the metal strip based on the size calculated by the bead shape calculator. When the calculated value of the size is outside the predetermined management range, the bead shape calculator calculates a set target value of the welding parameters such that the size is within the management range, and the welder output control unit acquires the set target value from the bead shape calculator, inputs a control value corresponding to the set target value to the welder, and controls the welding parameters (ninth configuration).

[0027] Also, the steel pipe manufacturing apparatus described in the specification includes a molding machine that molds a metal strip into a tubular shape, a welder that performs electric resistance welding according to welding parameters determined based on an input control value on the ends of the metal strip molded into a tubular shape to form a welded pipe, a bead shape measuring device that measures the outer shape of the welded pipe including the weld bead formed on the outer surface of the welded pipe, and a control device according to the ninth configuration (tenth configuration).

Advantages of the Invention

[0028] According to the present invention, it is possible to provide a welding method, an electric welded steel pipe manufacturing method, a control device, and a steel pipe manufacturing apparatus that can suppress variations in the quality of welded pipes and can suppress an increase in the area of equipment and an increase in manufacturing costs.

Brief Description of the Drawings

[0029] [Figure 1] Figure 1 is a schematic diagram illustrating the configuration of a steel pipe manufacturing apparatus 100 according to an embodiment of the present invention. [Figure 2] Figure 2 shows the configuration of the bead shape measuring device 5. [Figure 3] Figure 3 shows an example of the first image, im1. [Figure 4] Figure 4 shows an example of the second image, im2. [Figure 5] Figure 5 shows an example of the composite image im3. [Figure 6] Figure 6 shows the first management scope matrix map MP1. [Figure 7] Figure 7 shows the second management scope matrix map MP2. [Figure 8] Figure 8 shows the approximate curve of the outer surface profile pf derived by the bead shape calculator 52 based on the outer surface profile pf. [Figure 9] Figure 9 is a flowchart showing the configuration of the welding method of the present invention. [Figure 10] Figure 10 is a flowchart showing a more detailed configuration of the welding process. [Figure 11] Figure 11 is a flowchart showing a more detailed configuration of the measurement process. [Figure 12] Figure 12 is a flowchart showing a more detailed configuration of the area calculation process. [Figure 13] Figure 13 is a flowchart showing the detailed configuration of the control process. [Figure 14] Figure 14 is a flowchart showing the detailed configuration of the power control process. [Figure 15] Figure 15 is a flowchart showing the detailed configuration of the speed control process. [Modes for carrying out the invention]

[0030] The welding method according to the present invention is a method of welding steel plates using a steel pipe manufacturing apparatus 100 (more specifically, at least a welding machine and a shape measuring device) described later. For this reason, the steel pipe manufacturing apparatus 100 will be described first, and then the welding method according to the present invention will be described.

[0031] <Regarding the steel pipe manufacturing apparatus 100 according to an embodiment of the invention> The steel pipe manufacturing apparatus 100 according to an embodiment of the present invention forms a steel pipe pa by shaping a metal strip ba into a tubular shape and butt welding both ends of the metal strip ba together. The specific configuration of the steel pipe manufacturing apparatus 100 is as follows.

[0032] Figure 1 is a schematic diagram illustrating the configuration of a steel pipe manufacturing apparatus 100 according to an embodiment of the present invention. As shown in Figure 1, the steel pipe manufacturing apparatus 100 comprises a forming machine 1, a squeeze roll 2, a welding machine 3, a diameter measuring machine 4, a bead shape measuring device 5, a control device 50, and a bead cutting device 6.

[0033] The forming machine 1 can be a tandem rolling mill with multiple roll stands. The forming machine 1 forms the metal strip ba into a tubular shape while conveying the metal strip ba along its longitudinal direction. The metal strip ba can be a steel strip (e.g., hot-rolled steel sheet), a metal sheet, etc. In the following, the direction in which the metal strip ba is conveyed will be simply referred to as the "conveying direction." The direction perpendicular to the conveying direction will be simply referred to as the "width direction." That is, the width direction can be understood as the direction parallel to the width of the metal strip ba.

[0034] The squeeze roll 2 is positioned downstream of the welding machine 3 in the conveying direction. The squeeze roll 2 consists of a pair of rolls, a top roll 7 and a bottom roll 8. The squeeze roll 2 presses the top roll 7 and bottom roll 8 against the tubular metal strip ba, thereby reducing the diameter of the tubular metal strip ba and pressing both ends of the metal strip ba in the width direction against it.

[0035] The top roll 7 is housed within the top roll housing 9. In Figure 1, the top roll housing 9 is simply shown with a dashed line. The top roll housing 9 supports the top roll 7 so that it can rotate. The top roll housing 9 can be raised and lowered together with the top roll 7. The top roll 7 moves up and down together with the raising and lowering of the top roll housing 9, and is positioned at a height suitable for pressure welding to the metal strip ba.

[0036] The bottom roll 8 is housed within a bottom roll housing (not shown). The bottom roll housing supports the bottom roll 8 so that it can rotate. The bottom roll 8 moves up and down in conjunction with the raising and lowering of the bottom roll housing, and is positioned at a height suitable for pressing against the metal strip ba.

[0037] The welding machine 3 is positioned between the molding machine 1 and the squeeze roll 2 with respect to the conveying direction. The welding machine 3 welds both ends of the metal strip ba, which has been formed into a tubular shape by the molding machine 1, in the width direction. The welding machine 3 welds the metal strip ba by electric resistance welding (more specifically, high-frequency resistance welding). Specifically, it is as follows:

[0038] The welding machine 3 applies a high-frequency current to both ends of the tubular metal strip ba, generating Joule heat. This Joule heat melts the ends of the metal strip ba. The molten metal strip ba passes through the squeeze roll 2 almost simultaneously with the melting. At this time, the metal strip ba is pressed by the squeeze roll 2, reducing its diameter, and the molten ends are pressed together. As a result, the ends of the metal strip ba are welded together, forming a steel pipe pa.

[0039] For the sake of explanation, the welded metal strip ba will be referred to as the steel pipe pa. When the metal strip ba is welded, a weld bead wb is formed on the outer surface of the steel pipe pa at the weld points (i.e., at both ends of the metal strip ba in the width direction before welding).

[0040] The welding machine 3 receives a control signal s1 from the control device 50 and operates based on the control signal s1. The control signal s1 includes at least one control value. The control value is a value for controlling the operation of the welding machine 3 (specifically, the mode of electric resistance welding). The control value is, for example, the power set value of welding power Wa, the current set value of welding current, the set resistance value of welding resistance (variable resistor), the voltage set value of welding voltage, etc. The welding machine 3 receives the control signal s1 and acquires each control value. The welding machine 3 then changes the welding parameter pr based on the acquired control values.

[0041] The welding parameter pr is a parameter that determines the manner of electric resistance welding performed by the welding machine 3. For example, the amount of heat input (Joule heat) to the metal strip ba during welding is determined according to the welding parameter pr.

[0042] The welding parameter pr can be, for example, the heat coefficient C. The heat coefficient C is a coefficient that can be treated as an indicator of the amount of heat input to the metal strip ba during welding. In other words, a higher heat coefficient C results in a higher amount of heat input to the metal strip ba during welding. Conversely, a lower heat coefficient C results in a lower amount of heat input to the metal strip ba during welding.

[0043] The heat coefficient C is defined by the following equation (1), where pipe thickness Ta, welding power Wa, and mill speed Va. Pipe thickness Ta is the thickness of the metal strip ba (steel pipe pa).

number

[0044] The welding power Wa is the power supply used for electric resistance welding. The welding power Wa can also be considered a parameter that determines the amount of Joule heat generated by the welding machine 3 (= amount of heating relative to the metal strip ba). As shown in equation (1) above, the heat coefficient C is proportional to the integrated result of the welding current and welding voltage supplied to the welding machine 3 (= welding power Wa). Therefore, by controlling the welding power Wa by changing the welding current or welding voltage, the Joule heat generated by the welding machine 3 can be adjusted.

[0045] When the Joule heat generated by the welding machine 3 increases, the amount of metal strip ba that melts increases. Conversely, when the Joule heat generated by the welding machine 3 decreases, the amount of metal strip ba that melts decreases. When the amount of metal strip ba that melts increases, a larger weld bead wb is formed by the diameter reduction and pressure welding by the squeeze roll 2.

[0046] In other words, the size of the weld bead wb formed at this time (for example, the bead cross-sectional area Sa, the rising angles θ1 and θ2 of the weld bead wb, which will be discussed later) becomes relatively large. Therefore, the size of the weld bead wb can be adjusted by controlling the welding power Wa by changing the amount of welding current or welding voltage supplied (= the control value mentioned above).

[0047] The mill speed Va corresponds to the conveying speed of the metal strip ba. When the mill speed Va of the metal strip ba is high, the heating time of the metal strip ba by the welding machine 3 is shortened. When the heating time of the metal strip ba is shortened, the amount of metal strip ba melted is reduced. Conversely, when the heating time of the metal strip ba is lengthened, the amount of metal strip ba melted is increased. Therefore, the size of the weld bead wb can be adjusted by controlling the heating time of the metal strip ba by changing the mill speed Va. Thus, the mill speed Va may be used as the welding parameter pr. Alternatively, both welding power Wa and mill speed Va may be used in combination as the welding parameter pr.

[0048] The diameter shaping machine 4 can be a tandem rolling mill with multiple roll stands. The diameter shaping machine 4 is positioned downstream of the squeeze roll 2 with respect to the conveying direction. The diameter shaping machine 4 presses the steel pipe pa, which has been welded by the welding machine 3 and the squeeze roll 2, to shape the outer diameter of the steel pipe pa to a target value.

[0049] The bead shape measuring device 5 is positioned between the squeeze roll 2 and the bead cutting device 6 in the direction of transport. The bead shape measuring device 5 measures the shape of the weld bead wb formed on the outer surface of the steel pipe pa. The specific configuration of the bead shape measuring device 5 is as follows.

[0050] Figure 2 shows the configuration of the bead shape measuring device 5. As shown in Figure 2, the bead shape measuring device 5 includes laser distance meters 10a and 10b and a distance meter stand 11.

[0051] The laser distance meters 10a and 10b are configured to emit laser light toward an object (in this case, the outer surface of a steel pipe pa including the weld bead wb), receive the reflected light from the object, and create an image of the object's outline according to the state of reception of this reflected light. Laser distance meters 10a and 10b have the same configuration.

[0052] A laser distance meter 10a is positioned on one side (left side in Figure 2) with respect to the width direction (x direction in Figure 2), with a weld seam (=the part where the weld bead wb is formed) in between, and a laser distance meter 10b is positioned on the other side (right side in Figure 2).

[0053] Figure 3 shows an example of the first image im1. The laser distance meter 10a emits laser light and receives the light reflected from the outer surface of one side of the steel pipe pa (the left side shown in Figure 2) to generate (acquire) the first image im1 as shown in Figure 3. In other words, the first image im1 is an image of the outer shape of one side (the left side shown in Figure 2) of the weld bead wb in the horizontal direction.

[0054] Figure 4 shows an example of the second image im2. The laser distance meter 10b emits laser light and receives the light reflected from the outer surface of the other side (right side in Figure 2) of the steel pipe pa to generate (acquire) the second image im2 shown in Figure 4. In other words, the second image im2 is an image of the outer shape of the other side (right side in Figure 2) of the weld bead wb in the horizontal direction.

[0055] Returning to Figure 2, the laser distance meter 10a generates a measurement result signal s2a including the first image im1 and inputs it to the control device 50 (more specifically, the bead shape calculator 52). The laser distance meter 10b generates a measurement result signal s2b including the second image im2 and inputs it to the control device 50 (more specifically, the bead shape calculator 52).

[0056] The distance meter mount 11 is supported on the top roll housing 9 so as to be able to move up and down. The distance meter mount 11 moves up and down in conjunction with the raising and lowering of the top roll (the raising and lowering of the top roll housing 9).

[0057] Each of the laser distance meters 10a and 10b is rotatably supported on the distance meter mount 11 so as to be able to change the direction of laser beam emission. The laser distance meters 10a and 10b move up and down in conjunction with the raising and lowering of the distance meter mount 11 (and consequently the raising and lowering of the top roll housing 9).

[0058] In other words, the installation height of the laser distance meters 10a and 10b will depend on the raising and lowering position of the distance meter stand 11 (and consequently, the raising and lowering position of the top roll housing 9). Also, the installation angles of the laser distance meters 10a and 10b (the emission angle of the laser light and the incidence angle of the reflected light) will depend on the respective support angles of the laser distance meters 10a and 10b by the distance meter stand 11.

[0059] Furthermore, the distance meter mount 11 is supported so as to be able to move up and down relative to the top roll housing 9. That is, the approximate height positions of the laser distance meters 10a and 10b are determined by moving the top roll housing 9 up and down. After that, the distance meter mount 11 moves up and down relative to the top roll housing 9. This allows for fine adjustment of the height positions of the laser distance meters 10a and 10b.

[0060] As shown in Figures 1 and 2, the control device 50 receives measurement result signals s2a and s2b from the bead shape measuring device 5 (more specifically, from the laser distance meters 10a and 10b, respectively) and generates a control signal s1. The control device 50 inputs the control signal s1 to the welding machine 3. In other words, the welding machine 3 (more specifically, the welding parameter pr) is feedback controlled in real time based on the measurement results from the laser distance meters 10a and 10b. The specific configuration of the control device 50 is as follows.

[0061] The control device 50 includes a bead shape calculator 52 and a welding machine output control unit 53.

[0062] Figure 5 shows an example of the composite image im3. The bead shape calculator 52 acquires the first image im1 and the second image im2 based on the input measurement result signals s2a and s2b (see Figure 2). The bead shape calculator 52 then combines the acquired first image im1 and second image im2 to generate (acquire) the composite image im3 shown in Figure 5. The composite image im3 corresponds to the outer surface shape profile pf. The outer surface shape profile pf is a profile that shows the outer surface shape of the steel pipe pa including the weld bead wb.

[0063] Furthermore, the bead shape calculator 52 calculates the size of the weld bead wb based on the outer surface shape profile pf (composite image im3). The size of the weld bead wb can be determined by the bead cross-sectional area Sa, the rising angle θ1, θ2, etc. Here, we will primarily explain the case where the bead cross-sectional area Sa is used as the size of the weld bead wb.

[0064] The bead cross-sectional area Sa is the cross-sectional area of ​​the weld bead wb when it is cut by a plane parallel to the width direction and perpendicular to the conveying direction. The rising angles θ1 and θ2 are the angles corresponding to the angles made between the weld bead wb and the steel pipe pa in the same cross-section. Details on the calculation of the bead cross-sectional area Sa and the rising angles θ1 and θ2 of the weld bead wb will be described later. The bead shape calculator 52 sequentially calculates the size of the weld bead wb (specifically, the bead cross-sectional area Sa, rising angles θ1 and θ2, etc.) during the welding operation of the metal strip ba.

[0065] The bead shape calculator 52 determines whether the calculated size of the weld bead wb (specifically, the value of the bead cross-sectional area Sa, or the values ​​of the rise angles θ1 and θ2) falls within the predetermined control ranges Ms1 and Ms2.

[0066] The control ranges Ms1 and Ms2 are predetermined numerical ranges set in advance. The control ranges Ms1 and Ms2 are quantitatively derived numerical ranges, which may be values ​​derived from experimental results, for example, or values ​​quantitatively derived based on the experience of one or more workers. The above experiment may be an experiment to confirm that proper welding is being performed. Examples of such experiments include mechanical tests (specifically, weld flattening tests, tensile tests, Charpy impact tests, etc.) or non-destructive testing (specifically, ultrasonic testing).

[0067] If the size of the weld bead wb falls within the control ranges Ms1 and Ms2, the size of the weld bead wb can be considered favorable. In other words, in this case, the welding condition can be said to be good. To determine whether or not the size of the weld bead wb falls within the control ranges Ms1 and Ms2, refer to the first control range matrix map MP1 (Figure 6 shown later) and the second control range matrix map MP2 (Figure 7 shown later). Details of the determination using the first control range matrix map MP1 and the second control range matrix map MP2 will be described later.

[0068] The bead shape calculator 52 sequentially determines whether the bead cross-sectional area Sa, which is calculated sequentially during the welding operation on the metal strip ba, is within the control ranges Ms1 and Ms2.

[0069] The bead shape calculator 52 calculates the welding parameter target value t based on the above determination result (see Figure 2). The welding parameter target value t is the target value for setting the welding parameter pr.

[0070] Specifically, the following occurs: Suppose that the determination result is that the size of the weld bead wb is outside the control range Ms1 and Ms2. In this case, it can be said that the welding condition is not good. Therefore, the bead shape calculator 52 changes the appropriate welding parameter pr to an appropriate value so that the size of the weld bead wb is within the control range Ms1 and Ms2. Specifically, in this case, the bead shape calculator 52 calculates the welding parameter target value t as the value after changing the welding parameter pr. Examples of welding parameter target values ​​t include target power tw1 and tw2, and target speed tv1 and tv2 (details will be described later).

[0071] The bead shape calculator 52 transmits the calculated welding parameter target value t to the welding machine output control unit 53 using a predetermined control signal or the like (see Figure 2).

[0072] The welding machine output control unit 53 transmits the welding parameter target value t, received from the bead shape calculator 52, to the welding machine 3 in an appropriate format, thereby controlling the welding machine 3 (more specifically, the welding parameter pr). Specifically, it does so as follows:

[0073] As shown in Figure 2, the welding machine output control unit 53 generates a control signal s1 based on the welding parameter target value t transmitted from the bead shape calculator 52. The control signal s1 includes the control value described above. The welding machine output control unit 53 inputs the control signal s1 to the welding machine 3.

[0074] As described above, the welding machine 3 receives the control signal s1 and acquires a control value. The welding machine 3 then changes the welding parameter pr based on this control value. As a result, the welding parameter pr changes to a value corresponding to the welding parameter target value t.

[0075] For example, when the heat coefficient C described above is used as the welding parameter pr, the following occurs. In this case, the welding machine output control unit 53 inputs a control signal s1 to the welding machine 3 to change the value of the welding power Wa. The control signal s1 at this time includes, as control values, the set value of the welding current, the set value of the welding resistance, the set value of the welding voltage, etc.

[0076] The welding machine 3 receives the input of the control signal s1 and acquires control values ​​(set value of welding current, set value of welding resistance, set value of welding voltage, etc.). Based on the acquired control values, the welding machine 3 changes the welding power Wa. When the welding power Wa is changed, the heat coefficient C changes in conjunction. As a result, the heat coefficient C changes to a value corresponding to the welding parameter target value t.

[0077] If the bead shape calculator 52 determines that the size of the weld bead wb is within the control ranges Ms1 and Ms2, the following occurs. In this case, the bead shape calculator 52 omits the calculation of the welding parameter target value t and transmits a command to the welding machine output control unit 53 to maintain the current welding parameter pr (for example, a command that makes the welding parameter target value t match the current welding parameter pr). Upon receiving this command, the welding machine output control unit 53 generates a control signal s1 to the welding machine 3 to continue welding with the current welding parameter pr. In this way, the welding machine 3 welds the metal strip ba while being feedback-controlled in real time using the welding parameter pr by the control device 50. Details of the feedback control using the welding parameter pr will be described later.

[0078] The bead cutting device 6 is positioned upstream of the diameter control machine 4 with respect to the conveying direction. The bead cutting device 6 cuts and removes the weld bead wb formed on the outer surface of the steel pipe pa. Specifically, it works as follows: The bead cutting device 6 is a cutting tool with a cutting blade (not shown) formed at its tip. The tip (=cutting blade) of the bead cutting device 6 is in contact with the outer surface of the steel pipe pa. When the steel pipe pa is conveyed, the weld bead wb comes into contact with the cutting blade, and the weld bead wb is scraped off from the steel pipe pa by the cutting blade. The amount of weld bead wb removed can be adjusted by adjusting the vertical position of the bead cutting device 6.

[0079] <Details on the feedback control of welding machine 3> The feedback control of welding machine 3 using the welding parameter pr will be explained in more detail, with specific examples. This feedback control will also be referred to as the control process (corresponding to step St4 in the flowchart of Figure 9 shown later). The control process performs at least one of the following: a power control process and a speed control process. First, the power control process will be explained.

[0080] In the power control process, the welding power Wa is varied using the first control range matrix map MP1, and feedback control of the welding machine 3 is performed. Specifically, this is done as follows:

[0081] Figure 6 shows the first control range matrix map MP1. The first control range matrix map MP1 is a map used to determine the position of the calculated bead cross-sectional area Sa relative to the control range Ms1. In the example shown in Figure 6, the bead cross-sectional area Sa is used to indicate the size of the weld bead wb.

[0082] The first control range matrix map MP1 in Figure 6 shows the welding power Wa on the horizontal axis and the bead cross-sectional area Sa (= size of the weld bead wb) on the vertical axis. The first control range matrix map MP1 is divided into the area within the control range Ms1, areas α1 and β1, and the other areas.

[0083] As described above, as the welding power Wa increases, the amount of heat (Joule heating) to the metal strip ba also increases, the amount of melting in the metal strip ba increases, and the bead cross-sectional area Sa increases. Due to this relationship, in the case of the first control matrix map MP1 in which welding power Wa is adopted as the control target, the shape of the boundary of the control range Ms1 becomes a parallelogram tilted to the right (positive direction), as shown in Figure 6.

[0084] The bead shape calculator 52 calculates the bead cross-sectional area Sa and compares the calculation result with the control range Ms1. If the comparison shows that the bead cross-sectional area Sa is within the control range Ms1 (not shown), the bead shape calculator 52 maintains the welding power Wa and allows the welding machine 3 to continue welding.

[0085] On the other hand, if the bead cross-sectional area Sa is located outside the control range Ms1, the bead shape calculator 52 determines whether the bead cross-sectional area Sa is located in region α1 or region β1.

[0086] Region α1 is the region where the bead cross-sectional area Sa is smaller than the control range Ms1. More specifically, region α1 is the region where the welding power Wa is lower than the median value of the control range Ms1, and the calculated value of the bead cross-sectional area Sa is lower than the lower limit of the control range Ms1.

[0087] In other words, region α1 is the region where the bead cross-sectional area Sa is insufficient. When the bead cross-sectional area Sa is located in region α1, it is highly likely that the amount of heat applied to the metal strip ba is insufficient. In other words, it is highly likely that the welding power Wa is insufficient.

[0088] On the other hand, region β1 is a region where the bead cross-sectional area Sa is larger than the control range Ms1. More specifically, region β1 is a region where the welding power Wa is higher than the median value of the control range Ms1, and the calculated value of the bead cross-sectional area Sa is higher than the upper limit of the control range Ms1.

[0089] In other words, region β1 is the region where the bead cross-sectional area Sa is excessive. When the bead cross-sectional area Sa is located in region β1, there is a high probability that the amount of heat applied to the metal strip ba is excessive. In other words, there is a high probability that the welding power Wa is excessive.

[0090] For example, suppose it is determined that the bead cross-sectional area Sa is located in region α1. For the sake of explanation, let's call this bead cross-sectional area Sa1 (see Figure 6). Also, for the sake of explanation, let's call this welding power Wa1 (see Figure 6).

[0091] In this case, as mentioned above, there is a high probability that the welding power Wa is insufficient. Therefore, the bead shape calculator 52 increases the welding power Wa1 based on the above determination result (the determination result that the bead cross-sectional area Sa1 is in region α1).

[0092] Specifically, the bead shape calculator 52 first calculates an arbitrary value as the welding parameter target value t (see Figure 2), which is higher than the welding power Wa1 and falls within the control range Ms1. The target value of the welding power Wa calculated at this time is defined as the target power tw1.

[0093] The bead shape calculator 52 inputs the calculated target power tw1 to the welding machine 3 using the control signal s1 as described above. As a result, the welding machine 3 changes the welding power Wa1 to a value corresponding to the target power tw1. This increases the amount of heat applied to the metal strip ba. Consequently, the weld bead wb gradually becomes larger.

[0094] As described above, the bead shape calculator 52 sequentially calculates the bead cross-sectional area Sa and sequentially determines whether the sequentially calculated bead cross-sectional area Sa falls within the control range Ms1. Therefore, as the amount of heating to the metal strip ba increases, the calculated result of the bead cross-sectional area Sa1 increases sequentially.

[0095] Then, at a predetermined timing in the sequential determination process, it is determined that the bead cross-sectional area Sa1 is within the control range Ms1. In this case, the bead shape calculator 52 maintains the welding power Wa1 as it is (at a value equivalent to the target power tw1). This stops the expansion of the weld bead wb.

[0096] For example, suppose it is determined that the bead cross-sectional area Sa is located in region β1. For the sake of explanation, let's call this bead cross-sectional area Sa2. Let's also call the welding power Wa at this time welding power Wa2.

[0097] In this case, as mentioned above, there is a high probability that the welding power Wa is excessive. Therefore, the bead shape calculator 52, upon receiving the above determination result (the determination result that the bead cross-sectional area Sa2 is in region β1), reduces the welding power Wa2.

[0098] Specifically, the bead shape calculator 52 first calculates an arbitrary value as the welding parameter target value t, which is lower than the welding power Wa2 and falls within the control range Ms1. The target value of the welding power Wa calculated at this time is set as the target power tw2.

[0099] The bead shape calculator 52 inputs the calculated target power tw2 to the welding machine 3 using the control signal s1 as described above. As a result, the welding machine 3 changes the welding power Wa2 to a value corresponding to the target power tw2. This reduces the amount of heat applied to the metal strip ba. Consequently, the welding bead wb gradually becomes smaller.

[0100] As described above, the bead shape calculator 52 sequentially calculates the bead cross-sectional area Sa and sequentially determines whether the sequentially calculated bead cross-sectional area Sa falls within the control range Ms1. Therefore, as the amount of heating to the metal strip ba decreases, the calculated result of the bead cross-sectional area Sa2 becomes progressively smaller.

[0101] Then, at a predetermined timing in the sequential determination process, it is determined that the bead cross-sectional area Sa2 is within the control range Ms1. In this case, the bead shape calculator 52 maintains the welding power Wa2 as it is (at a value equivalent to the target power tw2). This stops the shrinkage of the weld bead wb.

[0102] If the sequential determination described above determines that the bead cross-sectional area Sa is outside the control range Ms1 and is not located in either region α1 or β1, then the setting of the control range Ms1 may be inappropriate. In this case, the bead shape calculator 52 notifies the worker to reset the control range Ms1. This notification can be provided by displaying it on a monitor or by outputting a notification sound from a speaker. Upon receiving this notification, the worker reviews and resets the control range based on the calculated bead cross-sectional area Sa value, experimental results, etc. The control range can be reset while the steel pipe manufacturing machine 100 is stopped or while it is running.

[0103] Next, the speed control process will be described. In the speed control process, the mill speed Va is varied using the second control range matrix map MP2, and feedback control of the welding machine 3 is performed. Specifically, it is as follows.

[0104] Figure 7 shows the second control range matrix map MP2. Similar to the first control range matrix map MP1, the second control range matrix map MP2 is a map used to determine the position of the calculated bead cross-sectional area Sa relative to the control range Ms2.

[0105] The second control range matrix map MP2 in Figure 7 shows the mill speed Va on the horizontal axis and the bead cross-sectional area Sa (= size of the weld bead wb) on the vertical axis. The second control range matrix map MP2 is divided into the region within the control range Ms2, regions α2 and β2, and the other regions.

[0106] As mentioned above, as the milling speed Va increases, the heating time of the metal strip ba decreases, and the amount of metal strip ba melted decreases. Therefore, as the milling speed Va increases, the bead cross-sectional area Sa tends to decrease. Conversely, as the milling speed Va decreases, the heating time of the metal strip ba increases, and the amount of metal strip ba melted increases. Therefore, as the milling speed Va decreases, the bead cross-sectional area Sa increases.

[0107] Generally, when the milling speed Va is relatively fast, the quality of the weld improves. For this reason, in the second control range matrix map MP2, the control range Ms2 increases as the milling speed Va increases, resulting in a larger range of allowable bead cross-sectional area Sa (i.e., the vertical axis size of the control range Ms2).

[0108] The bead shape calculator 52 compares the calculated bead cross-sectional area Sa with the control range Ms2 and determines that the bead cross-sectional area Sa is within the control range Ms2. In this case, the bead shape calculator 52 maintains the mill speed Va and instructs the welding machine 3 to continue welding.

[0109] On the other hand, if the bead cross-sectional area Sa is located outside the control range Ms2, the bead shape calculator 52 determines whether the bead cross-sectional area Sa is located in region α2 or region β2.

[0110] Region α2, like region α1 described above, is a region where the bead cross-sectional area Sa is smaller than the control range Ms2. In other words, region α2 is a region where the bead cross-sectional area Sa is insufficient. When the bead cross-sectional area Sa is located in region α2, it is highly likely that the amount of heating to the metal strip ba is insufficient. In other words, it is highly likely that the milling speed Va is faster than the ideal state.

[0111] On the other hand, region β2, like region β1 described above, is a region where the bead cross-sectional area Sa is larger than the control range Ms2. In other words, region β2 is a region where the bead cross-sectional area Sa is excessively large. When the bead cross-sectional area Sa is located in region β2, it is highly likely that the amount of heating to the metal strip ba is excessive. In other words, it is highly likely that the milling speed Va is slower than the ideal state.

[0112] For example, suppose that in the speed control process, it is determined that the bead cross-sectional area Sa is located in region α2. For the sake of explanation, let's call this bead cross-sectional area Sa3 (see Figure 7). Also, for the sake of explanation, let's call this mill speed Va1.

[0113] In this case, the bead shape calculator 52 reduces the mill speed Va1. Specifically, the bead shape calculator 52 first calculates an arbitrary value for the mill speed Va (welding parameter target value t) that is slower than the mill speed Va1 and falls within the control range Ms2. This value is designated as the target speed tv1.

[0114] The bead shape calculator 52 inputs the calculated target speed tv1 to the welding machine 3 using the control signal s1 as described above. This changes the mill speed Va to a value corresponding to the target speed tv1. As a result, the amount of heat applied to the metal strip ba increases. Consequently, the welding bead wb gradually becomes larger. Therefore, the calculated bead cross-sectional area Sa3 by the bead shape calculator 52 increases progressively.

[0115] Then, at a predetermined timing in the sequential determination process, it is determined that the bead cross-sectional area Sa3 is within the control range Ms2. In this case, the bead shape calculator 52 maintains the mill speed Va at the target speed tv1. This stops the expansion of the weld bead wb.

[0116] For example, suppose that in the speed control process, it is determined that the bead cross-sectional area Sa is located in region β2. For the sake of explanation, let's call this bead cross-sectional area Sa4 (see Figure 7). Also, for the sake of explanation, let's call this mill speed Va2.

[0117] In this case, the bead shape calculator 52 increases the mill speed Va2. That is, the bead shape calculator 52 first calculates an arbitrary value for the mill speed Va (welding parameter target value t) that is faster than the mill speed Va2 and falls within the control range Ms2. This value is set as the target speed tv2.

[0118] The bead shape calculator 52 inputs the calculated target speed tv2 to the welding machine 3 using the control signal s1 as described above. This changes the mill speed Va to a value corresponding to the target speed tv2. As a result, the amount of heat applied to the metal strip ba decreases. Consequently, the welding bead wb gradually becomes smaller. Therefore, the calculated bead cross-sectional area Sa4 by the bead shape calculator 52 becomes progressively smaller.

[0119] Then, at a predetermined timing in the sequential determination process, it is determined that the bead cross-sectional area Sa4 is within the control range Ms2. In this case, the bead shape calculator 52 maintains the mill speed Va at the target speed tv2. This stops the shrinkage of the weld bead wb.

[0120] As mentioned above, if the bead shape calculator 52 compares the calculated bead cross-sectional area Sa with the control range Ms2 and finds that the bead cross-sectional area Sa is outside the control range Ms2, then, basically, feedback control is first performed using the first control range matrix map MP1. If, after a predetermined period of time, the bead cross-sectional area Sa is still not within the control range, then feedback control is performed using the second control range matrix map MP2. The flow of feedback control using the first control range matrix map MP1 and the second control range matrix map MP2 will be described later.

[0121] <Regarding the calculation method of the bead cross-sectional area Sa> Next, the method for calculating the bead cross-sectional area Sa will be explained. In calculating the bead cross-sectional area Sa, the bead shape calculator 52 first obtains the outer surface shape profile pf using the method described above (see Figure 5). Next, the bead shape calculator 52 derives an approximate curve from the obtained outer surface shape profile pf that approximates the outer surface shape of the steel pipe pa including the weld bead wb. Next, the bead shape calculator 52 calculates the bead cross-sectional area Sa by integral calculus, using the area of ​​the portion of this approximate curve corresponding to the weld bead wb. First, the method for deriving the approximate curve of the outer surface shape profile pf will be explained in detail.

[0122] <Regarding the derivation of the approximation curve for the external shape profile pf> Figure 8 shows the approximate curve of the outer surface profile pf derived by the bead shape calculator 52 based on the outer surface profile pf. The bead shape calculator 52 calculates an approximate curve of the outer surface profile pf as shown in Figure 8, based on the outer surface profile pf. Specifically, it is as follows:

[0123] The bead shape calculator 52 approximates the parts on either side of the vertex p0 of the weld bead wb (the first part A and the second part B shown in Figure 5) using two quadratic curves Z1 and Z2, based on the outer surface shape profile pf. The bead shape calculator 52 then combines these two approximate curves Z1 and Z2 to generate a single curve representing the outer surface of the weld bead wb. Furthermore, the bead shape calculator 52 combines this curve representing the outer surface of the weld bead wb with the curve representing the outer surface of the steel pipe pa to generate a single curve. A more detailed explanation follows.

[0124] As shown in Figure 5, the bead shape calculator 52 first defines the horizontal direction of the outer surface shape profile pf as the X-axis, the vertical direction as the Z-axis, and the direction perpendicular to the X-axis and Z-axis (= the longitudinal direction of the steel pipe pa, which is the transport direction) as the Y-axis. The bead shape calculator 52 also sets the vertex p0 of the weld bead wb based on the outer surface shape profile pf. The vertex p0 can also be said to be the point where the height (Z coordinate) of the weld bead wb in the Z-axis direction is maximum. The bead shape calculator 52 then sets the X coordinate of the vertex p0 to 0. In other words, the X-axis in the outer surface shape profile pf is based on the vertex p0 (= 0).

[0125] The bead shape calculator 52 sets the first inflection point p1 and the second inflection point p2 in the outer shape profile pf. The first inflection point p1 and the second inflection point p2 are the starting points for the rise of the weld bead wb. The first inflection point p1 is located on the laser distance meter 10a side of the weld bead wb in the width direction (the region where X≦0 in Figure 5). The second inflection point p2 is located on the laser distance meter 10b side of the weld bead wb in the width direction (the region where X≧0 in Figure 5).

[0126] The bead shape calculator 52 also derives a straight line L1 connecting the first inflection point p1 and the second inflection point p2. The bead shape calculator 52 defines the length of the straight line L1 as the width of the weld bead wb (hereinafter simply referred to as "bead width"). The bead width may also be calculated from the difference in the X coordinates of the first inflection point p1 and the second inflection point p2.

[0127] Furthermore, the bead shape calculator 52 sets the Z coordinate of either the first inflection point p1 or the second inflection point p2 to 0. In other words, the Z axis in the composite image im3 is based on (=0) the first inflection point p1 or the second inflection point p2.

[0128] The bead shape calculator 52 then derives the X and Z coordinates of the vertex p0 of the weld bead wb. Specifically, it does as follows: First, the bead shape calculator 52 derives the perpendicular bisector L2 of the line L1. Then, the bead shape calculator 52 derives the intersection point of the perpendicular bisector L2 and the weld bead wb as the vertex p0. The bead shape calculator 52 defines the distance from the intersection point of the line L1 and the perpendicular bisector L2 to the vertex p0 as the height of the weld bead wb (hereinafter simply referred to as "bead height"). The bead height may also be calculated from the difference between the Z coordinate of either the first inflection point p1 or the second inflection point p2 and the Z coordinate of the vertex p0.

[0129] Next, the bead shape calculator 52 sets an arbitrary point p3 in the weld bead wb that is on the laser distance meter 10a side of the perpendicular bisector L2 (the region X≦0 in Figure 5). The bead shape calculator 52 also derives an arbitrary point p4 in the weld bead wb that is on the laser distance meter 10b side of the perpendicular bisector L2 (the region X≧0 in Figure 5). Point p3 is preferably set around the midpoint between the first inflection point p1 and the vertex p0. Similarly, point p4 is preferably set around the midpoint between the second inflection point p2 and the vertex p0.

[0130] <Definition of the approximation curves for Part 1 A and Part 2 B> The curve used to approximate the outer surface shape of the weld bead wb is a curve obtained by combining the approximation curve Z1 and the approximation curve Z2 (see Figure 8).

[0131] The approximate curve Z1 is a curve that approximates the first part A of the weld bead wb. The first part A is the portion of the weld bead wb located at p1 ≤ X ≤ p0. The approximate curve Z1 is defined by equation (2) below. In this case, the constants a, b, and c are obtained from the X coordinates of three points on the first part A of the outer surface profile pf. Specifically, a is the X coordinate of vertex p0, b is the X coordinate of the first inflection point p1, and c is the X coordinate of point p3.

number

[0132] The approximate curve Z2 is a curve that approximates the second part B of the weld bead wb. The second part B is the portion of the weld bead wb located at p0 ≤ X ≤ p2. The approximate curve Z2 is defined by equation (3) below. In this case, the constants d, e, and f are obtained from the X coordinates of three points on the second part B of the outer surface profile pf. Specifically, d is the X coordinate of vertex p0, e is the X coordinate of the second inflection point p2, and f is the X coordinate of point p4. That is, d = a.

number

[0133] The bead shape calculator 52 then combines the approximation curve Z1 and the approximation curve Z2 at the position X=0. This obtains an approximation curve that approximates the outer surface shape of the weld bead wb.

[0134] Furthermore, the approximation curve Z1 of the first part A and the approximation curve Z2 of the second part B are combined so that they are always tangent at vertex p0. If the shape of the weld bead wb is perfectly symmetrical on both sides of vertex p0, then the approximation curve approximating the outer surface of the weld bead wb can be approximated by an approximation curve defined by a single function.

[0135] Next, an approximate curve approximating the outer surface shape of the steel pipe pa is superimposed on this approximate curve. Here, the region of the outer surface shape profile pf where X ≤ 0 and part A' located on the negative side of the X coordinate more than the first part A corresponds to the outer surface of the steel pipe pa. Similarly, the region of the outer surface shape profile pf where X ≥ 0 and part B' located on the positive side of the X coordinate more than the second part B corresponds to the outer surface of the steel pipe pa. Therefore, the curves of parts A' and B' can be approximated as circular arcs with curvature equal to the curvature of the steel pipe pa.

[0136] The bead shape calculator 52 then combines the approximate curves Z1 for the first part A, Z2 for the second part B, the approximate curve for part A', and the approximate curve for part B'. This combined approximate curve becomes the approximate curve for the outer surface shape profile pf (see Figure 8).

[0137] <Regarding the calculation of the bead cross-sectional area Sa> The bead shape calculator 52 calculates the bead cross-sectional area Sa from the approximate curve of the outer surface shape profile pf obtained by the method described above. Specifically, it is as follows:

[0138] First, the bead shape calculator 52 derives an approximate curve of the outer surface profile pf as shown in Figure 8 using the method described above. Then, the bead shape calculator 52 calculates the area of ​​the region enclosed by the approximate curve Z1, approximate curve Z2, and line L1 using the integral method.

[0139] In this case, the bead shape calculator 52 may calculate the area of ​​the region enclosed by the approximation curve Z1, the straight line L1, and the perpendicular bisector L2, and the area of ​​the region enclosed by the approximation curve Z2, the straight line L1, and the perpendicular bisector L2 separately, and then combine the areas of each region to calculate the bead cross-sectional area Sa.

[0140] <Regarding the calculation of rising angles θ1 and θ2> The bead shape calculator 52 calculates the rise angles θ1 and θ2 of the weld bead wb based on the outer surface shape profile pf (or the approximate curve of the outer surface shape profile pf). This will be explained in detail below.

[0141] The rising angle θ1 is the angle of the rise of the first part A of the weld bead wb. The rising angle θ1 corresponds to the exterior angle when the angle between the first line L3 and line L1 is taken as the interior angle. The bead shape calculator 52 calculates the rising angle θ1 as follows.

[0142] First, the bead shape calculator 52 derives a first straight line L3 that passes through the first inflection point p1 and point p3. Then, the bead shape calculator 52 calculates the rising angle θ1 from the slope of the first straight line L3 using trigonometric ratios. Specifically, the bead shape calculator 52 calculates the rising angle θ1 from the triangle defined by the perpendicular line L1 extending from point p3 to line L1, line L1, and the first straight line L3 using trigonometric ratios.

[0143] The bead shape calculator 52 similarly calculates the rising angle θ2 of the second part B of the weld bead wb. That is, first the bead shape calculator 52 derives a second straight line L4 that passes through the second inflection point p2 and point p4. Then the bead shape calculator 52 calculates the rising angle θ2 from the slope of the second straight line L4 using trigonometric ratios. Specifically, the bead shape calculator 52 calculates the rising angle θ2 from the triangle defined by the perpendicular line L1 extending from point p4 to line L1, line L1, and the second straight line L4 using trigonometric ratios.

[0144] <Regarding the welding method according to embodiments of the present invention> Next, a welding method according to an embodiment of the present invention will be described. The welding method according to the present invention can use the steel pipe manufacturing apparatus 100 described above. In the following description, an embodiment using the steel pipe manufacturing apparatus 100 as the welding method will be described, but the method is not limited to the steel pipe manufacturing apparatus 100; a steel pipe manufacturing apparatus equivalent to the steel pipe manufacturing apparatus 100 may be used.

[0145] Figure 9 is a flowchart showing the configuration of the welding method of the present invention. As shown in Figure 9, the welding method of the present invention includes a welding step (step St1), a measurement step (step St2), an area calculation step (step St3), and a control step (step St4). The welding method of the present invention also includes a waiting phase (step St0), which is the state before the welding step (step St1).

[0146] First, in the standby phase (step St0), the steel pipe manufacturing apparatus 100 determines whether or not to start welding to the metal strip ba. At this time, the steel pipe manufacturing apparatus 100 waits until a command is input from the worker to the steel pipe manufacturing apparatus 100 (more specifically, the control device 50) to perform welding to the metal strip ba.

[0147] When the above command is input (Yes in step St0), the steel pipe manufacturing apparatus 100 proceeds to the welding process (step St1). At this time, the steel pipe manufacturing apparatus 100 starts the welding operation to the metal strip ba (= the operation of welding the metal strip ba to form the steel pipe pa). The welding of the metal strip ba and the formation of the steel pipe pa are performed by the forming machine 1, the squeeze roll 2, and the welding machine 3 as described above. The welding process continues from the measurement process (step St2) until the determination of the end of welding is made in step St5 (Yes in step St5).

[0148] The steel pipe manufacturing apparatus 100 performs a measurement process (step St2) while the welding process is in progress. At this time, the steel pipe manufacturing apparatus 100 acquires an external surface profile pf. The method for acquiring the external surface profile pf is in accordance with the method described above.

[0149] The steel pipe manufacturing apparatus 100 performs an area calculation process (step St3) during the welding process. At this time, the steel pipe manufacturing apparatus 100 calculates the bead cross-sectional area Sa. The method for calculating the bead cross-sectional area Sa is in accordance with the method described above.

[0150] During the execution of the welding process, the steel pipe manufacturing apparatus 100 provides feedback control to the welding machine 3 in the control process (step St4) so ​​that the bead cross-sectional area Sa falls within the control range Ms1 (control range Ms2). This feedback control is in accordance with the above-described method.

[0151] Then, in step St5, the steel pipe manufacturing apparatus 100 determines whether or not to terminate the welding process. At this time, the steel pipe manufacturing apparatus 100 determines whether or not a command to terminate welding to the metal strip ba has been input from the worker to the steel pipe manufacturing apparatus 100 (more specifically, the control device 50). If the above command has been input (Yes in step St5), the steel pipe manufacturing apparatus 100 terminates all of the welding process, measurement process and control process, and ends the series of welding operations to the metal strip ba.

[0152] If the above command is not entered (No in step St5), the steel pipe manufacturing apparatus 100 returns to the measurement process (step St2), recalculates the bead cross-sectional area Sa, and repeats steps St2 to St5 until it is determined to be Yes in step St5. During this time, the welding operation (welding process) to the metal strip ba naturally continues.

[0153] The following provides a more detailed explanation of each process, from the welding process (Step St1) to the control process (Step St4).

[0154] <Step St1: Welding Process> Figure 10 is a flowchart showing a more detailed configuration of the welding process (step St1). As shown in Figure 10, in the welding process, first the metal strip ba is formed into a tubular shape by the forming machine 1 (step St11). Next, Joule heat is applied to both ends of the tubular metal strip ba by the welding machine 3 (step St12). The amount of Joule heat applied at this time is based on the welding parameter pr set in the welding machine 3 at this point.

[0155] Then, the ends of the heated metal strip ba are pressed together by the squeeze roll 2 (step St13). Step St13 is performed almost simultaneously with step St12 (strictly speaking, slightly after step St12). Step St13 forms the weld bead wb. Then, the process moves to step St2, where the operation to acquire the outer surface profile pf is performed. As mentioned above, welding of the metal strip ba continues even after moving to step St2.

[0156] <Step St2: Measurement Process> Figure 11 is a flowchart showing a more detailed configuration of the measurement process (step St2). As shown in Figure 11, in the measurement process, first, the laser distance meters 10a and 10b generate the first image im1 and the second image im2 (step St21). Next, the first image im1 and the second image im2 are combined to generate a combined image im3 (step St22). As described above, the combined image im3 generated at this time corresponds to the outer surface shape profile pf. If the outer surface shape profile pf has already been acquired through iterative control, the acquired outer surface shape profile pf is updated with the newly acquired one in step St22. Then, the process proceeds to step St3.

[0157] <Step St3: Area Calculation Process> Figure 12 is a flowchart showing a more detailed configuration of the area calculation process (step St3). As shown in Figure 12, in the area calculation process, first, vertex p0 is set based on the outer shape profile pf (step St31). Next, the first inflection point p1 and the second inflection point p2 are set (step St32). Next, the straight line L1 is derived (step St33). Next, the perpendicular bisector L2 is derived (step St34). Next, the approximate curves Z1 and Z2 are derived (step St35). Next, the area of ​​the first region enclosed by the approximate curve Z1, the straight line L1, and the perpendicular bisector L2 is calculated using the integral method (step St36). Next, the area of ​​the second region enclosed by the approximate curve Z2, the straight line L1, and the perpendicular bisector L2 is calculated using the integral method (step St37). Finally, the area of ​​the first region and the area of ​​the second region are added together to calculate the bead cross-sectional area Sa (step St38). Then, proceed to step St4.

[0158] <Step St4: Control Process> Figure 13 is a flowchart showing the detailed configuration of the control process (step St4). As shown in Figure 13, in the control process, it is first determined whether the first flag N1 is set or not, that is, whether N1=0 or not (step St41). If the first flag N1 is not set (N1=0) (No in step St41), the power control process is executed (step St42).

[0159] If the first flag N1 is set in step St41, i.e., N1=1 (Yes in step St41), then it is determined whether the second flag N2 is set, i.e., whether N2=1 (step St43). If the second flag N2 is not set in step St43 (N2=0) (No in step St43), then the speed control process is executed (step St44).

[0160] If the second flag N2 is set in step St43, i.e., N2=1 (Yes in step St43), the worker is notified via a notification means such as a monitor or speaker (step St45). Then, the first flag N1 and the second flag N2 are reset, i.e., N1=0 and N2=0 (step St46), and the process returns to step St41.

[0161] Figure 14 is a flowchart showing the detailed configuration of the power control process. As shown in Figure 14, the power control process first determines whether the bead cross-sectional area Sa is located within the control range Ms1 by referring to the first control range matrix map MP1 (step St42a). If the bead cross-sectional area Sa is located within the control range Ms1 (Yes in step St42a), the process proceeds to step St5.

[0162] If the bead cross-sectional area Sa is located outside the control range Ms1 (No in step St42a), it is determined whether the bead cross-sectional area Sa is located outside region α1 or region β1 (step St42b). If the bead cross-sectional area Sa is located outside region α1 or region β1 (Yes in step St42b), the control range Ms1 is reviewed (step St42c). Specifically, the worker conducts the experiment again to consider the relationship between the optimal bead cross-sectional area Sa and the welding parameter pr (illustration omitted). Based on the results of the consideration, the size, position, inclination, shape, etc. of the control range Ms1 on the first control range matrix map MP1 are changed. Then, the process returns to step St42a.

[0163] If steps St42a to St42c are repeated a predetermined number of times, the first flag N1 is set (N1=1), and the process returns to step St41 (not shown in the diagram).

[0164] In step St42b, if the bead cross-sectional area Sa is located within region α1 or region β1, the target powers tw1 and tw2 are calculated (step St42d). At this time, if the bead cross-sectional area Sa is located in region α1, the target power tw1 is calculated, and if it is located in region β1, the target power tw2 is calculated. Then, the welding power Wa is changed to the target powers tw1 and tw2 (step St42e).

[0165] Next, the system monitors whether the bead cross-sectional area Sa is located within the control range Ms1 for a predetermined first period (step St42f). The length of the first period is set arbitrarily. Then, at the end of the first period, it is determined whether the bead cross-sectional area Sa is located outside the control range Ms1 (step St42g).

[0166] If the bead cross-sectional area Sa is outside the control range Ms1 (Yes in step St42g), set the first flag N1, i.e., set N1=1 (step St42h), and return to step St42. If the bead cross-sectional area Sa is within the control range Ms1 (No in step St42g), proceed to step St5.

[0167] Figure 15 is a flowchart showing the detailed configuration of the speed control process. As shown in Figure 15, the speed control process first determines whether the bead cross-sectional area Sa is located within the control range Ms2 by referring to the second control range matrix map MP2 (step St44a). If the bead cross-sectional area Sa is located within the control range Ms2 (Yes in step St44a), the process proceeds to step St5.

[0168] If the bead cross-sectional area Sa is outside the control range Ms2 (No in step St44a), it is determined whether the bead cross-sectional area Sa is outside region α2 or region β2 (step St44b). If the bead cross-sectional area Sa is outside region α2 or region β2 (Yes in step St44b), the control range Ms2 is reviewed (step St44c). Specifically, the worker conducts the experiment again to consider the relationship between the optimal bead cross-sectional area Sa and the welding parameter pr (illustration omitted). Based on the results of the consideration, the size, position, inclination, shape, etc. of the control range Ms2 on the second control range matrix map MP2 are changed. Then, the process returns to step St44a.

[0169] If steps St44a to St44c are repeated a predetermined number of times, the second flag N2 is set (N2=1), and the process returns to step St43 (not shown in the diagram).

[0170] In step St44b, if the bead cross-sectional area Sa is located within region α2 or region β2, the target velocities tv1 and tv2 are calculated (step St44d). At this time, if the bead cross-sectional area Sa is located in region α2, the target velocity tv1 is calculated, and if it is located in region β2, the target velocity tv2 is calculated. Then, the mill velocity Va is changed to the target velocities tv1 and tv2 (step St44e).

[0171] Next, the system monitors whether the bead cross-sectional area Sa is located within the control range Ms2 for a predetermined second period (step St44f). The length of the second period is set arbitrarily. Then, at the end of the second period, it is determined whether the bead cross-sectional area Sa is located outside the control range Ms2 (step St44g).

[0172] If the bead cross-sectional area Sa is outside the control range Ms2 (Yes in step St44g), set the second flag N2, i.e., set N2=1 (step St44h), and return to step St44. If the bead cross-sectional area Sa is within the control range Ms2 (No in step St44g), proceed to step St5.

[0173] By using the steel pipe manufacturing apparatus 100 or welding method of the present invention, metal strip ba can be welded (electric resistance welding) with an appropriate amount of heat input. Specifically, the size of the weld bead wb (e.g., bead cross-sectional area Sa, rise angle θ1, θ2, etc.) can be quantitatively calculated and quantitatively evaluated. Based on the quantitative evaluation results, the welding parameter pr (more specifically, the amount of heat input to the metal strip ba) can be feedback controlled to optimize the size of the weld bead wb and, consequently, the welding of the metal strip ba.

[0174] For example, if the bead cross-sectional area Sa falls outside the control range Ms1, a power control process is executed to bring the bead cross-sectional area Sa to an appropriate size (i.e., within the control range Ms1). If the bead cross-sectional area Sa does not converge within the control range Ms1 even after the power control process, speed control is further executed. This makes it possible to perform electric resistance welding of metal strip ba while maintaining an appropriate heat input at all times.

[0175] Furthermore, in the power control process and speed control process described above, the control values ​​to be controlled are welding power Wa, welding current, welding voltage, welding resistance, and mill speed Va. These control values ​​are indicators that can be easily varied according to the characteristics of the electric resistance welded steel pipe manufacturing mill. Therefore, according to the present invention, it is possible to suppress the complexity of the control system, which would lead to an increase in the manufacturing cost of the steel pipe manufacturing apparatus 100, a complicated welding method for the steel pipe pa, and an increase in the cost of the steel pipe pa.

[0176] As mentioned above, the distance meter mount 11 is supported by the top roll housing 9. Therefore, the installation height of the laser distance meters 10a and 10b is linked to the raising and lowering position of the top roll housing 9, i.e., the raising and lowering position of the top roll 7. Consequently, the installation height of the laser distance meters 10a and 10b is adjusted simultaneously with the height adjustment of the squeeze roll 2.

[0177] Furthermore, it is preferable to use laser distance meters 10a and 10b with a relatively wide measurable distance range. This allows the height of the bead shape measuring device to be adjusted simply by raising and lowering the top roll housing 9 to which the distance meter stand 11 is attached. This eliminates the need to adjust the mounting height of the laser distance meters 10a and 10b relative to the distance meter stand 11, and the mounting height of the distance meter stand 11 relative to the top roll housing 9, each time the size of the steel pipe pa being measured changes.

[0178] <Variation> Furthermore, the present invention is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the invention. For example, in the above embodiment, the welding machine output control unit 53 inputs a control signal s1 to the welding machine 3 to change the value of the welding power Wa and variably control the welding parameter pr (heat coefficient C), but it is not limited to this. For example, the control signal s1 may be input to the welding machine 3 to change the mill speed Va and variably control the welding parameter pr. In this case, it is preferable that the control value of the control signal s1 includes the set value of the mill speed Va.

[0179] Furthermore, point p3, as described above, is a point on the weld bead wb and can be set at any position as long as it lies between the first inflection point p1 and the vertex p0 in the X-axis direction, as long as it does not coincide with the first inflection point p1 and the vertex p0. However, when the rising angle of the weld bead wb (= the angle between the steel pipe pa and the first part A) is used as the control range Ms1 and Ms2, the position of point p3 is preferably as close to the first inflection point p1 as possible.

[0180] On the other hand, as the distance in the Z direction between the first inflection point p1 and point p3 approaches 0, the calculation of the rise angles θ1 and θ2 of the weld bead wb becomes inaccurate. For this reason, when using the rise angles θ1 and θ2 of the weld bead wb as control ranges Ms1 and Ms2, it is preferable that the setting position of point p3 be as close as possible to the first inflection point p1, and that a predetermined distance be maintained between it and the first inflection point p1. This predetermined distance is the minimum distance within which the rise angles θ1 and θ2 of the weld bead wb can be accurately calculated.

[0181] The same applies to point p4. That is, point p4 is a point on the weld bead wb and can be set at any position as long as it is located between the second inflection point p2 and the vertex p0 in the X-axis direction, as long as it does not coincide with the second inflection point p2 and the vertex p0. However, when the rising angles θ1 and θ2 of the weld bead wb are used as control ranges Ms1 and Ms2, the position of point p4 is preferably as close to the second inflection point p2 as possible.

[0182] On the other hand, as the distance in the Z direction between the second inflection point p2 and point p4 approaches 0, the calculation of the angles θ1 and θ2 of the weld bead wb becomes inaccurate. For this reason, when using the rising angles θ1 and θ2 of the weld bead wb as control ranges Ms1 and Ms2, it is preferable that the setting position of point p4 be as close as possible to the second inflection point p2, and that a predetermined distance equivalent to that described above be maintained between point p4 and the second inflection point p2.

[0183] Furthermore, while step St3 in the welding method of the present invention is defined as an area calculation step for calculating the cross-sectional area of ​​the weld bead wb as the size of the weld bead wb, it is not limited to this. That is, step St3 can be understood as a size calculation step for calculating the size of the weld bead wb. For example, step St3 may be an angle calculation step for calculating the rising angles θ1 and θ2 as the size of the weld bead wb.

[0184] In this case, the "size of the bead cross-sectional area Sa" in the welding method described above corresponds to the "size of the rising angles θ1 and θ2". In other words, in this case, the control process (step St4) described above determines whether the rising angles θ1 and θ2 calculated in step St3 are within the control ranges Ms1 and Ms2. Then, the term "bead cross-sectional area Sa" in the explanation of step St4 described above is replaced with "rising angles θ1 and θ2" and interpreted accordingly.

[0185] Furthermore, in the welding method of the present invention, steps St42c and St44c are described as reviewing the ranges of control ranges Ms1 and Ms2, but this may be replaced with the following: For example, it is determined whether the equipment settings, manufacturing conditions, etc., related to predetermined factors other than the welding parameter pr are appropriate. If they are determined to be inappropriate, these are inspected and reviewed. Note that this determination, inspection, and review may be performed by an operator.

[0186] In the power control process, one method for determining the adjustment amount (control amount) of the welding power Wa was to calculate a target power tw such that the weld bead cross-sectional area Sa falls within the control range Ms1. However, instead, the following method may be used. For example, instead of calculating the target power tw, the welding power Wa is changed by a certain amount (a predetermined amount). After the size of the welding bead wb changes, it is determined whether the bead cross-sectional area Sa calculated by the bead shape calculator 52 is within the control range Ms1. The welding power Wa is changed by the same amount as described above until the bead cross-sectional area Sa falls within the control range Ms1. The same applies to the adjustment amount of the mill speed Va in the speed control process. [Explanation of Symbols]

[0187] 1 Molding machine 2 squeeze rolls 3. Welding machine 4 Diameter machine 5. Bead shape measuring device 6. Bead cutting device 7 Top Roll 8 Bottom Roll 9 Top Roll Housing 10a, 10b Laser Rangefinder 11 Rangefinder stand 50 Control device 52 Bead Shape Calculator 53 Welding machine output control unit 100 Steel pipe manufacturing equipment A Part 1 B Second part C Heat coefficient L1 straight line L2 perpendicular bisector L3 1st straight line L4 Second Straight Line MP1 First Management Range Matrix Map (First Map) MP2 Second Management Scope Matrix Map (Second Map) Ms1, Ms2 Management Scope Sa, Sa1~Sa4: Bead cross-sectional area (size of the weld bead) Ta tube thickness Va, Va1, Va2 Mill speed Wa, Wa1, Wa2 welding power Z1, Z2 approximate curve ba metal strip im1 First image im2 Second image im3 composite image p0 vertex p1 1st inflection point p2 2nd inflection point p3 points p4 points pa steel pipe pf external shape profile pr welding parameters s1 control signal s2a, s2b Measurement result signals t Welding parameter target value tv, tv1, tv2 target speed tw, tw1, tw2 target power wb welding bead α1, α2, β1, β2 region θ1, θ2: Rise angle (size of weld bead)

Claims

1. A welding process in which a welding machine performs electric resistance welding according to welding parameters determined based on input control values, and welds the ends of a tubular metal strip to form a welded pipe, A measurement step for measuring the outer shape of the weld bead formed on the outer surface of the welded pipe after the welding process, A size calculation step is performed to calculate the size of the weld bead based on the outer surface shape obtained in the measurement step, A control step that monitors the size calculated in the size calculation step and modifies the control value so that the size is within a preset control range, thereby variably controlling the welding parameters. Includes, The control values ​​include the transport speed of the metal strip in the welding process and the welding power of the electric resistance welding. The welding parameters are determined based on the transport speed, the welding power, and the thickness of the metal strip. The control process described above is: A power control step which, while monitoring the size calculated by the size calculation step, changes the welding power so that the size falls within the control range; A speed control step which, while monitoring the size calculated by the size calculation step, changes the transport speed so that the size falls within the control range; Includes, The control step is a welding method that performs at least one of the power control step and the speed control step.

2. The aforementioned scope of control is: A first control range determined based on the welding power and the size, A second control range determined based on the aforementioned transport speed and size, Includes, The power control process described above is: A first determination step to determine whether the size calculated by the size calculation step is outside the first control range, If the size is determined to be outside the first control range in the first determination step, a target power calculation step is performed to calculate a target power value for the welding power such that the size falls within the first control range. A power changing step of changing the welding power, which is input to the welding machine as a control value, to the value of the target power, With the welding power changed by the power change process, a first monitoring process monitors the determination result of the first determination process during the first period, In the first monitoring step, if the size calculated by the size calculation step during the first period does not fall within the first control range, a first flag setting step sets a first flag. Includes, The speed control step described above is: A second determination step is to determine whether the size calculated by the size calculation step is outside the second control range, If the second determination step determines that the size is outside the second control range, a target speed calculation step is performed to calculate a target speed for the transport speed such that the size falls within the second control range. A second modification step involves changing the transport speed, which is input to the welding machine as a control value, to the target speed value obtained in the target speed calculation step. With the transport speed changed to the value of the target speed by the second modification step, a second monitoring step monitors the determination result of the second determination step during the second period. In the second monitoring step, if the size calculated by the size calculation step during the second period does not fall within the second control range, a second flag setting step is performed to set a second flag. Includes, The welding method according to claim 1, wherein the control step is performed when the first flag is not set, and the speed control step is performed when the first flag is set and the second flag is not set.

3. The welding method according to claim 1 or 2, wherein the measurement step involves a distance meter configured to measure the distance to the outer surface of the welded pipe by emitting laser light onto the outer surface of the welded pipe and receiving the reflected light, and the outer surface shape is obtained by using at least one pair of distance meter configurations arranged on either side of the weld bead.

4. The distance meters are arranged in pairs, two on each side of the weld bead. The measurement process described above is: One of the steps involves using the distance meter to emit laser light towards the weld bead, receiving the light reflected by the weld bead, and generating a left-side image according to the light reception state. The other distance meter emits laser light towards the weld bead, receives the light reflected by the weld bead, and generates a right-side image according to the light reception state; A synthesis step of generating a composite image by combining the generated right image and the left image, and obtaining the outer shape based on the composite image, The welding method according to claim 3, including the following:

5. The aforementioned size is the cross-sectional area of ​​the weld bead, The aforementioned size calculation step is: A step of deriving a quadratic curve that approximates the aforementioned external shape, The steps include calculating the area of ​​the weld bead region within the region enclosed by the quadratic curve as the cross-sectional area, A welding method according to claim 1 or 2, comprising:

6. The aforementioned size is the cross-sectional area of ​​the weld bead, The aforementioned size calculation step is: A step of deriving a quadratic curve that approximates the aforementioned external shape, The steps include calculating the area of ​​the weld bead region within the region enclosed by the quadratic curve as the cross-sectional area, The welding method according to claim 3, including the following:

7. The aforementioned size calculation step is: Based on the composite image, the first and second inflection points located at the starting point of the rise of the weld bead from the welded pipe are determined. The length of the straight line connecting the first inflection point and the second inflection point is defined as the bead width. The bead height is defined as the straight-line distance parallel to the perpendicular bisector, from the intersection point of the perpendicular bisector of the straight line and the outer surface of the weld bead to the first or second inflection point. Determine a first straight line connecting an arbitrary first point on the side of the first inflection point, separated by the perpendicular bisector on the weld bead, to the first inflection point, and determine a first angle between the first straight line and the outer surface of the welded pipe. Determine a second straight line connecting an arbitrary second point on the side of the second inflection point, separated by the perpendicular bisector on the weld bead, to the second inflection point, and determine a second angle between the second straight line and the outer surface of the welded pipe. Based on the bead width, the bead height, the first angle, and the second angle, the quadratic curve is derived. The welding method according to claim 4, wherein the area of ​​the weld bead region is calculated using an integral method on the quadratic curve.

8. The first control range is a predetermined area set on a first map where the horizontal axis is the welding power and the vertical axis is the size. The welding method according to claim 2, wherein the second control range is a predetermined area set on a second map where the horizontal axis is the transport speed and the vertical axis is the size.

9. A method for manufacturing an electric resistance welded steel pipe, comprising using the welding method described in claim 1 or 2 to electric resistance weld a steel plate, which is a metal strip, to produce an electric resistance welded steel pipe.

10. A bead shape calculator calculates the size of a weld bead based on the outer surface shape measured by a bead shape measuring device that measures the outer surface shape of a weld bead formed by welding a metal strip, A welding machine output control unit controls the welding parameters of a welding machine that performs welding on the metal strip based on the size calculated by the bead shape calculator, Equipped with, If the calculated size of the bead shape is outside the predetermined control range, the bead shape calculator calculates a target value for setting the welding parameter such that the size falls within the control range. The welding machine output control unit is a control device that obtains the set target value from the bead shape calculator, inputs a control value corresponding to the set target value to the welding machine, and controls the welding parameters.

11. A molding machine for forming the aforementioned metal strip into a tubular shape, A welding machine that forms a welded pipe by performing electric resistance welding on the end of the tubularly formed metal strip according to the welding parameters determined based on the input control value, A bead shape measuring device for measuring the outer surface shape of the welded pipe, including the weld bead formed on the outer surface of the welded pipe, The control device according to claim 10, A steel pipe manufacturing apparatus equipped with the following features.

Images