Automatic welding method for header large pipe joint without displacement and capable of multi-station operation

Abstract

The present application relates to the technical field of boiler welding, and discloses an automatic welding method for header large pipe joint without position change and capable of multi-station operation, which adopts a special welding sequence combining whole-circle welding and small-section welding, and better avoids the problem of poor weld forming under non-flat welding position, so that the workpiece does not need to be changed and linked during the welding process, thereby saving the equipment cost and providing a prerequisite for multi-station parallel efficient operation. The large pipe joint adopts an equal-angle groove design, has low requirement on the processing equipment, is good in economy, and is particularly suitable for the header large pipe joint with small cylinder diameter ratio specifications and the like which cannot be processed into an equal-section groove.

Description

Technical Field

[0001] This invention relates to the field of boiler welding technology, specifically to an automatic welding method for header pipe joints that allows for multi-station operation without the need for repositioning. Background Technology

[0002] The header is one of the important pressure-bearing components of a boiler, typically ranging from several meters to over ten meters in length. Its cylindrical body is equipped with numerous pipe fittings (also known as pipe seats) that are welded to the heating surfaces and connecting pipes. These pipe fittings are connected to the header cylindrical body using bevel welding. They are made of carbon steel, low-alloy steel, and high-alloy heat-resistant steel, with outer diameters ranging from Φ28mm to Φ355.6mm and wall thicknesses from 4mm to 80mm. A key characteristic is the variety of pipe fitting materials and specifications, the wide range of outer diameters, and the large wall thickness. The pipe fittings are arranged in rows along the axial and circumferential directions on the header cylindrical body. For pipe fittings with outer diameters ranging from Φ100mm to Φ355.6mm (commonly referred to as large pipe fittings, see the instruction manual attached),... Figure 1 As shown in the figure, due to its wall thickness typically exceeding 20mm, numerous weld passes, large weld seam saddle drop, drastic changes in weld cross-section from shoulder to belly, and extremely uneven weld filler, coupled with the fact that the belly usually requires transverse welding, the weld formation control requirements are high, making welding and ensuring weld quality very difficult. Currently, manual or semi-automatic welding operations are still widely used, resulting in low automation, high labor intensity, poor welding environment, and the weld quality entirely dependent on the welder's skill.

[0003] Currently, the welding equipment and methods for header pipe joints with a high degree of automation in the industry mainly include two categories: semi-automatic mechanical welding and robotic automatic welding. The welding processes used include submerged arc welding, tungsten inert gas welding, and gas metal arc welding. For example, invention patent CN111014905A discloses an invention patent for a mechanical welding method for closely spaced header pipe joints. This method uses simple tooling to fix the workpiece, then manually adjusts the welding torch position before using CNC equipment for mechanized welding. However, its automation level is low; each pipe joint requires both mechanical and manual positioning, making the operation cumbersome and preventing continuous multi-station operation.

[0004] For example, invention patent CN103111730A discloses an automated welding method for a saddle-shaped trajectory of a header large pipe joint. This method first uses mathematical methods to plan the weld bead layout before welding, then uses arc tracking to perform the first layer of welding and records the actual saddle-shaped trajectory. Based on this, and combined with the pre-welding planning results, offsets are applied layer by layer to complete subsequent multi-layer, multi-pass welding. However, all weld beads planned by this method are 360-degree full-circle welds. To avoid the welding difficulties caused by significant differences in bevel filling volume between the belly and shoulder of the large pipe joint, the preceding process must use costly CNC equipment to process the bevel between the pipe joint and the header into a uniform cross-section, which is economically inefficient. Moreover, for large pipe joints with a small cylinder diameter ratio (header outer diameter / large pipe joint outer diameter < 1.5), such a uniform cross-section bevel is simply not feasible in terms of technology. Furthermore, this method requires rotating the entire header during welding to keep the molten pool horizontal, thus it cannot support parallel operation of multiple machines and multiple workstations.

[0005] For example, invention patent CN111872524A discloses an automatic welding method for variable cross-section bevel header pipe seats. This method first discretizes the variable cross-section bevel to be welded into multiple two-dimensional cross-sections. Then, software algorithms are used to plan the weld bead layout for each cross-section. Based on the weld bead layout, the matching welding current, welding speed, and welding torch angle are automatically inferred. Finally, the planning results for all cross-sections are output as an automatic robotic welding program. This method requires welding a full 360-degree circle for each layer and pass. It solves the variable cross-section welding problem by continuously changing parameters, speed, and posture during the rotation process. However, for pipe joints with a small cylinder diameter to a large pipe joint, the ratio of filler volume between the belly and shoulder is often as high as 180%-220%, exceeding the adjustment range allowed by the welding process, making it difficult to guarantee welding quality. Summary of the Invention

[0006] To address the problems of existing methods for welding large pipe joints in headers, such as cumbersome operation, high equipment requirements, poor economic efficiency, narrow applicability, and poor feasibility of welding large pipe joints, this invention provides an automatic welding method for large pipe joints in headers that can be performed at multiple workstations without the need for repositioning.

[0007] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows: An automated welding method for header pipe joints that requires no repositioning and allows for multi-station operation, the main welding method includes the following steps: Step a. Design and process the large pipe joint into a V-shaped equal-angle bevel; Step b. Use a support frame to support and fix the header so that the pipe holes to be welded on the header body face upwards; Step c. Manually assemble the large pipe joint with the pipe hole to be welded on the header cylinder, fix it with welding rod spot welding, and then complete the first layer of root welding by manual welding. Step d. Use visual sensing equipment to identify and locate the assembled large pipe joint and header, and establish a coordinate system at the intersection of the axis of the large pipe joint and the axis of the header; Step e. Using automated welding equipment, based on the coordinate reference of step d, create a multi-layer, multi-pass welding program in a specific welding sequence through teach programming, offline programming, or autonomous programming. Step f. Execute the welding operation procedure in step e) to perform multi-layer, multi-pass automatic welding on the assembled large pipe joints; Step g. After the large pipe joint welding is completed, move the automatic welding equipment to the next station, repeat step d to rescan and position, and step f to directly execute the welding program previously written in step e to perform automatic welding of the next large pipe joint.

[0008] In this invention, the specific welding sequence is as follows: welding layer by layer from the root of the bevel to the outside of the bevel. For each layer of weld, the first pass is welded at the lowest point of the saddle line, and then welding is carried out layer by layer from bottom to top.

[0009] Furthermore, during welding, when the difference in bevel opening width between the abdomen and the shoulder is more than 10mm, a small section of welding is performed starting from the lowest point of the abdomen with the larger opening, without welding to the shoulder; when the difference in the remaining bevel opening width between the abdomen and the shoulder is within 10mm, the remaining passes of this layer of weld are performed with 360-degree full-circle welding.

[0010] In this invention, the automatic welding equipment is an industrial robot or an automatic welding machine, and the equipment typically has at least 6 degrees of freedom.

[0011] In this invention, the support frame for supporting the fixed container is typically a roller frame.

[0012] In this invention, the thickness of the first layer of root pass is typically 3-4 mm.

[0013] In this invention, when the automatic welding equipment performs multi-layer and multi-pass welding, the welding process can be gas metal arc welding or tungsten inert gas welding.

[0014] The beneficial effects of this invention are: 1. This invention adopts a special welding sequence that combines full-circle welding and short-segment welding, which effectively avoids the problem of poor weld formation in non-flat welding positions. The workpiece does not need to be repositioned during the welding process, which not only saves equipment costs, but also provides the prerequisite for multi-station parallel and efficient operation.

[0015] 2. This invention uses visual scanning positioning to establish coordinate reference. Welding programs of the same specifications only need to be programmed once and can be applied to multiple workstations, resulting in a high degree of automation.

[0016] 3. This invention adopts an equal-angle bevel design, which has low requirements for processing equipment, good economy, and wide applicability. It is especially suitable for large pipe joints of headers that cannot be processed into equal-section bevels, such as those with small cylinder diameter ratios. Attached Figure Description

[0017] The foregoing and hereinafter detailed description of the invention becomes clearer when read in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the header large pipe joint structure of the present invention; Figure 2 This is a schematic diagram of the equal-angle bevel of the large pipe joint of the present invention; Figure 3 This is a schematic diagram of the header support and fixing of the present invention; Figure 4 This is a schematic diagram of the assembly and initial welding of the header large pipe joint of the present invention; Figure 5 This is a schematic diagram of the automatic welding operation reference used in this invention; Figure 6 This is a schematic diagram of the single-layer welding sequence used in this invention; Figure 7 This is a schematic diagram of the pre-welding contour at a typical cross-sectional location of the present invention; Figure 8 This is a schematic diagram of the equally divided cross-sectional positions during pre-welding planning for multi-layer, multi-pass welding in Embodiment 2 of the present invention; Figure 9 This is a schematic diagram of the weld surface line calculation when planning the cross-section weld bead in this invention; Figure 10 This is a schematic diagram of the equidistant division of the weld layer in the shoulder section of the present invention; Figure 11 This is a schematic diagram of the weld layer equidistantly divided in other two-dimensional sections of the present invention; Figure 12 This is a schematic diagram of the weld bead segmentation at a typical cross-sectional location of the present invention; Figure 13 This is a schematic diagram of the overall planning results of multiple layers and multiple channels at a typical cross-sectional location of the present invention; Figure 14 This is a schematic diagram of the process parameter planning for a single weld pass according to the present invention. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solutions of this invention, several specific embodiments will be used to further illustrate the technical solutions for achieving the objectives of this invention. It should be noted that the technical solutions claimed by this invention include, but are not limited to, the following embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort should fall within the scope of protection of this invention.

[0019] The header is one of the important pressure-bearing components of a boiler, typically ranging from several meters to over ten meters in length. Its cylindrical body is equipped with numerous pipe fittings (also known as pipe seats) that are welded to the heating surfaces and connecting pipes. These pipe fittings are connected to the header cylindrical body using bevel welding. They are made of carbon steel, low-alloy steel, and high-alloy heat-resistant steel, with outer diameters ranging from Φ28mm to Φ355.6mm and wall thicknesses from 4mm to 80mm. A key characteristic is the variety of pipe fitting materials and specifications, the wide range of outer diameters, and the large wall thickness. The pipe fittings are arranged in rows along the axial and circumferential directions on the header cylindrical body. For pipe fittings with outer diameters ranging from Φ100mm to Φ355.6mm (commonly referred to as large pipe fittings, see the instruction manual attached),... Figure 1 As shown in the figure, due to its wall thickness typically exceeding 20mm, numerous weld passes, large weld seam saddle drop, drastic changes in weld cross-section from shoulder to belly, and extremely uneven weld filler, coupled with the fact that the belly usually requires transverse welding, the weld formation control requirements are high, making welding and ensuring weld quality very difficult. Currently, manual or semi-automatic welding operations are still widely used, resulting in low automation, high labor intensity, poor welding environment, and the weld quality entirely dependent on the welder's skill.

[0020] Current welding equipment and methods for header pipe joints generally suffer from problems such as narrow applicability, low degree of automation, stringent requirements for workpieces, and high overall cost. In particular, there is no automated welding method that offers both good welding quality and cost-effectiveness for large pipe joints.

[0021] Based on this, the present invention proposes an automatic welding method for header large pipe joints that allows for multi-station operation without the need for repositioning. This invention employs a special welding sequence combining full-circle welding and short-segment welding, effectively avoiding the problem of poor weld formation in non-flat welding positions. During the welding process, the workpiece does not require repositioning or linkage, which not only saves equipment costs but also provides the prerequisite for efficient parallel operation at multiple stations. The following specific embodiments will further illustrate and explain the solution involved in the present invention.

[0022] Example 1 The present invention discloses an automatic welding method for header large pipe joints that can be operated at multiple stations without displacement. The method mainly includes the following steps: Step a. Design and machine the large pipe fitting into a V-shaped bevel with equal angles, meaning that the angle between the bevel's hypotenuse and the outer wall of the pipe is 50 degrees at any point along the pipe's circumference. In this invention, a conventional lathe is used to complete the beveling process, and the typical bevel angle is usually 40 degrees.

[0023] Step b. Use a roller support frame to support and fix the header so that the pipe holes to be welded on the header cylinder face upwards.

[0024] Step c. Manually assemble the large pipe joint with the pipe hole to be welded on the header cylinder, fix it with welding rod spot welding, and then complete the first layer of root pass welding by manual welding. The manual welding can be any welding method such as manual argon arc welding, manual electric arc welding, or manual gas welding, with manual argon arc welding being preferred. After welding, the thickness of the first layer of root pass welding should be 3-4mm, and the weld surface should be flat, circumferentially uniform, and with a smooth transition.

[0025] Step d. Use a line laser scanner to scan the assembled header and pipe joint to obtain the three-dimensional point cloud data of the workpiece. Then, use a random sampling consensus algorithm to calculate the axis of the header and the axis of the pipe joint respectively. Establish a rectangular coordinate system with the intersection of the two as the origin, the axis of the header as the Y-axis, and the axis of the pipe joint as the Z-axis.

[0026] Step e. Using automated welding equipment based on the coordinate reference of step d, create a multi-layer, multi-pass welding program with a specific welding sequence through teach programming, offline programming, or autonomous programming. Specifically, the specific welding sequence refers to welding layer by layer from the root of the bevel to the outside of the bevel. For each layer of weld, the first pass is welded at the lowest point of the saddle line, and welding is performed layer by layer from bottom to top.

[0027] In this invention, it should be noted that during welding, when the difference in bevel opening width between the abdomen and shoulder is too large, a small section of welding is performed starting from the lowest point of the abdomen with the larger opening, without welding to the shoulder; when the remaining bevel opening widths of the abdomen and shoulder are similar, the remaining passes of that weld layer are then welded in a 360-degree circle. Generally, a difference of more than 10mm in the bevel opening width is considered excessive; a difference of less than 10mm in the remaining bevel opening width is considered similar.

[0028] Step f. Execute the welding operation procedure in step e) to perform multi-layer, multi-pass automatic welding.

[0029] After each large pipe joint is welded, the automatic welding equipment is moved to the next station, and step d is repeated to rescan and reposition the workpiece. Then, the previously programmed welding program in step e is executed to automatically weld the next large pipe joint. In this invention, since the workpiece does not need to be repositioned during programming and welding, multiple automatic welding equipment can be used to simultaneously perform steps d, e, and f at their respective stations, achieving the effect of multi-station parallel operation.

[0030] In this invention, the automated welding equipment used during welding is typically an industrial robot or an automated welding machine, and the equipment usually has at least six degrees of freedom. When the equipment performs a multi-layer, multi-pass welding process, the welding method can be gas metal arc welding (GMAW) or tungsten inert gas (TIG) welding.

[0031] Example 2 This embodiment discloses an automatic welding method for header large pipe joints that can operate at multiple stations without repositioning. Based on Embodiment 1, this embodiment achieves trajectory planning for the automatic welding equipment through autonomous programming. Ultimately, the automatic welding equipment performs multi-layer, multi-pass automatic welding of the header large pipe joint according to the specific welding sequence in Embodiment 1. The specific trajectory planning method is as follows: Step S1. As Figure 8 As shown, taking the axis of the large pipe joint as the axis of rotation, the entire bevel of the large pipe joint is divided into several equal sections along the circumference. Then, based on the workpiece specifications and the design dimensions of the bevel, the pre-welding contour line of each section is calculated. This pre-welding contour line refers to a multi-segment line formed by connecting the straight line of the outer wall of the pipe seat, the straight line of the bevel's hypotenuse, and the curve of the upper surface of the header. It can be obtained using solid geometry calculation methods, as shown in the attached instruction manual. Figure 9 As shown.

[0032] In this invention, the design dimensions of the bevel include data such as the bevel angle, the wall thickness of the pipe seat, and the inner and outer diameters of the pipe seat.

[0033] Step S2. Figure 9 As shown, according to the weld leg size requirements, a straight line is drawn as the weld surface line in each two-dimensional section in step S1. The starting point of the weld surface line is the inflection point between the bevel edge and the outer wall of the pipe seat, and the ending point is located on the upper surface of the header. The horizontal distance between the weld surface line and the outer wall of the pipe seat is equal to the weld leg size. The area between the weld surface line and the pre-weld outline is the area on the section that needs to be filled by multiple layers and multiple passes of welding. Furthermore, based on the geometric characteristics of the saddle-shaped weld, it can be seen that the total area of ​​this filling area increases monotonically from the shoulder to the belly of the section, with the smallest filling area at the shoulder section and the largest filling area at the belly section.

[0034] Step S3. Based on the previous experiments, select a set of relatively stable welding process parameters (including wire feed speed f and welding speed v), and measure the single-pass filling amount s (i.e., the cross-sectional area of ​​each weld in the two-dimensional section) and the single-layer thickness δ under the welding process parameters by macroscopic metallographic analysis.

[0035] Step S4. Based on the weld leg size requirements and the single-layer thickness δ in step c, calculate the number of weld layers for each cross section and divide the cross section.

[0036] like Figure 10 As shown, on the shoulder section in step b, multiple equidistant parallel lines are drawn along the weld surface line to divide the area to be filled into m weld layers, where m = [d / δ] (rounded up when the calculation result is a decimal), and d is the perpendicular distance from the weld surface line to the root of the groove. Obviously, the distance between these parallel lines is approximately equal to the single layer thickness δ in step c. like Figure 11As shown, in step b, on the remaining k-1 sections (k is the number of sections initially divided equally), multiple equidistant parallel lines are drawn along the weld surface line to divide the filling area of ​​the remaining sections into m weld layers, thus ensuring that the number of weld layers in each section is consistent.

[0037] In this invention, since the preliminary test in step c is usually done by splicing two flat plates into a right angle (similar to the shape of a shoulder), the shoulder weld layer has the highest accuracy. Therefore, other sections are used as a reference for the shoulder.

[0038] Step S5. Figure 12 As shown, based on the single-pass filler amount s in step c, a horizontal line is drawn to divide each weld layer in each equally divided two-dimensional section into n weld passes. Since the cross-sectional filler area from the shoulder to the belly monotonically increases, for any weld layer, the number of weld passes must also monotonically increase with the cross-sectional position from the shoulder to the belly (e.g., ...). Figure 13 (As shown).

[0039] In this invention, the number of weld passes equally divided in each weld layer of the cross-sectional filling region is equal to the area of ​​a single weld layer divided by the single-pass filling amount s, rounded up. (Refer to the appendix of the specification.) Figure 11 As shown, the area of ​​a single weld layer can be calculated using the area formula of the polygon enclosing each weld layer.

[0040] In this invention, for the bevel of the large pipe joint, the number of welding layers in all sections divided along the 360-degree circumference is equal. However, for a single weld layer, the number of passes in all sections along the 360-degree circumference is not equal, and the number of passes in each section from the shoulder to the belly increases monotonically.

[0041] Step S6. Based on the weld bead segmentation results of each section in Step S5 and the wire feeding speed f in Step S3, calculate the main process parameters required by the automatic welding equipment when welding each layer and each pass to this point, including the welding torch point coordinates, welding speed, welding torch angle, etc.; wherein, the welding torch point coordinates are approximately taken as the centroid position of the equally divided weld bead in Step S5, and the welding torch angle is taken as the angle bisector of the dihedral angle between the header cylinder body and the outer wall of the pipe joint at the welded location. Finally, select a matching welding speed (e.g., based on the weld bead area and wire feeding speed) Figure 14 (As shown).

[0042] Step S7. For any layer of weld, based on the number of passes in each section estimated in Step S5, stitch together the welds in three-dimensional space to obtain the starting and ending section positions for each pass. The specific stitching method is as follows: First, the sections with the most weld passes are joined to form the first pass, located at the lowest point of the weld layer. Then, the sections with the most remaining weld passes (excluding the first pass) are joined to form the second pass, located above the first pass. Next, the sections with the most remaining weld passes (excluding the first two passes) are joined to form the third pass, located above the second pass. This process continues. Because the filler volume is greatest in the belly of the large pipe joint and smallest in the shoulder, the first pass is always closest to the belly and has the shortest weld length. The second pass overlaps the first pass and is slightly longer than it. The third pass overlaps the second pass and is slightly longer than it. When the number of remaining passes in all sections is equal to that in the shoulder, these remaining passes are naturally joined to form a 360-degree circumference weld (e.g., ...). Figure 6 (As shown).

[0043] Step S8. Repeat step S7 to plan other weld layers one by one, to obtain a multi-layer, multi-pass overall weld arrangement.

[0044] Step S9. Based on the three-dimensional overall weld bead layout obtained in Step S8, the main process parameters on each cross-section in Step S6 are connected and combined to form a multi-layer, multi-pass welding process and trajectory planning result, ultimately achieving automatic welding of the header large pipe joint. During welding, each weld uses the same and stable wire feed speed, and the welding current remains basically constant throughout the welding process.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. An automatic welding method for header pipe joints that can be operated at multiple stations without displacement, characterized in that, Includes the following steps: Step a. Design and process the large pipe joint into a V-shaped equal-angle bevel; Step b. Use a support frame to support and fix the header so that the pipe holes to be welded on the header body face upwards; Step c. Manually assemble the large pipe joint with the pipe hole to be welded on the header cylinder, fix it with welding rod spot welding, and then complete the first layer of root welding by manual welding. Step d. Use visual sensing equipment to identify and locate the assembled large pipe joint and header, and establish a coordinate system at the intersection of the axis of the large pipe joint and the axis of the header; Step e. Using automated welding equipment, based on the coordinate reference of step d, create a multi-layer, multi-pass welding program with a specific welding sequence; Step f. Execute the welding operation procedure in step e) to perform multi-layer, multi-pass automatic welding on the assembled large pipe joints; During welding, when the difference in bevel opening width between the abdomen and the shoulder is too large, start welding a small section from the lowest point of the abdomen with the larger opening without welding to the shoulder; when the remaining bevel opening widths of the abdomen and the shoulder are similar, then perform 360-degree full-circle welding on the remaining passes of the current weld layer. Excessive difference in bevel opening width between the abdomen and shoulder means a difference of more than 10mm; similar remaining bevel opening widths between the abdomen and shoulder mean a difference of less than 10mm.

2. The automatic welding method for header large pipe joints that can be operated at multiple stations without displacement, as described in claim 1, is characterized in that... The specific welding sequence is as follows: weld layer by layer from the root of the bevel to the outside of the bevel. For each layer of weld, weld the first pass at the lowest point of the saddle line, and then weld layer by layer from bottom to top.

3. The automatic welding method for header large pipe joints that requires no repositioning and allows for multi-station operation according to claim 1, characterized in that, The thickness of the first layer of root pass is 3-4mm.

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