Inward shrinkage type laser welding method suitable for intensive tube plate

Abstract

The invention discloses an internal shrinkage type laser welding method suitable for an intensive tube plate. The internal shrinkage type laser welding method is used for welding a plate with high welding hole density and a tube body to form the intensive tube plate. The method specifically comprises the steps that firstly, the edge of the upper end of a plate hole in a plate is chamfered to form a horn-shaped opening, the lower end of the plate hole is expanded to form a stepped hole, the to-be-welded end of a pipe body is cut to form a cylindrical step section, and the length of the cylindrical step section is equal to the depth of the stepped hole; the cylindrical step section is inserted into the step hole, so that the pipe body and the plate are in transition fit, and a lap joint of the pipe body and the plate is formed; and the positions of the pipe body and the plate are kept unchanged, and laser is emitted into the pipe body and the plate from the horn-shaped port to weld the lap joint of the pipe body and the plate. The stepped hole design and turning of the to-be-welded end of the tube body are combined to form tube plate inward shrinkage type welding, galvanometer pulse laser accurately regulates and controls welding heat input, and the problems that in the prior art, when intensive tube plates are welded, a welding gun is poor in accessibility, and welding quality is difficult to control are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of materials processing technology, and in particular to an inward-shrinking laser welding process method suitable for dense tube sheets. Background Technology

[0002] Tubesheet heat exchangers, condensers, and steam generators are core products for achieving efficient heat exchange. The core structure of these vessels connects hundreds or even thousands of heat exchange tubes to a thick tubesheet, forming numerous dense tubesheet joints with welds. These welds bear the multiple demanding responsibilities of sealing the medium, withstanding pressure, and resisting thermal stress and fluid erosion. Poor weld quality can easily lead to catastrophic accidents such as leaks, fires, and even explosions, causing not only enormous loss of life and property but also severe environmental pollution.

[0003] Current tube sheet welding methods primarily employ TIG welding. A typical process involves first machining a bevel on the tube sheet, spot welding the tube ends to the tube sheet, and then filling the bevel with multiple layers of filler wire. However, this method has inherent drawbacks: First, welding efficiency is low, as multi-layer filler wire welding results in slow speeds, making it difficult to meet the demands of large-scale production. Second, the high heat input during welding easily induces tube sheet deformation, with the cumulative deformation effect being particularly pronounced in dense tube sheet structures, affecting assembly accuracy and equipment performance. Most critically, there is an unavoidable risk of incomplete fusion at the weld root, becoming a potential source of failure during long-term service. Although high-pressure applications tend to use flush or extended joints and emphasize strength welding (penetration depth > 2mm), the TIG welding process itself has reached bottlenecks in ensuring root fusion quality, controlling thermal deformation, and improving efficiency, necessitating more advanced technologies.

[0004] Based on the relative position of the tube end and the tube sheet surface, tube sheet welding is mainly divided into three types: extended (tube end protrudes from the plate surface), flush (tube end is flush with the plate surface), and recessed (tube end retracts into the plate hole). In the recessed structure, the tube end is recessed into the hole, so the weld is located inside the tube sheet hole rather than on the surface. The main advantages of this structure are: firstly, the weld is mechanically protected and supported by the hole wall, theoretically providing better impact resistance, vibration resistance, and fatigue resistance; secondly, the tube sheet surface remains flat, facilitating cleaning and avoiding the increased flow resistance or fouling problems that may occur with extended joints; and thirdly, for certain specific operating conditions, it helps improve the flow pattern of the medium or reduce the risk of the weld being directly exposed to a highly corrosive / erosive environment. However, traditional welding methods have poor accessibility for recessed joints, making it difficult to guarantee uniform penetration and root quality of the circumferential weld in deep holes. Especially for recessed welding of densely packed tube sheets, the welding torch accessibility is poor, and weld quality is difficult to control. Summary of the Invention

[0005] To address the problems of poor weld torch accessibility and difficulty in controlling weld quality during the welding of dense tube sheets, this invention provides an inward-shrinking laser welding method suitable for dense tube sheets.

[0006] This invention utilizes a specially designed inward-recessed lap joint combined with precise control of the welding laser heat input using a pulsed galvanometer laser to weld the tube body to the plate, forming an inward-recessed laser welding method suitable for dense tube sheets. This method is applicable to welding plates with high weld hole density to a large number of tube bodies to form dense tube sheets. The main steps of this method are as follows: First, holes are drilled in the plate material. The upper edge of the holes is chamfered to form a flared opening, ensuring laser reachability. The lower end of the holes is enlarged to form a stepped hole. The end of the tube to be welded is cut (e.g., turned) to form a cylindrical platform stage, the length of which is equal to the depth of the stepped hole. The outer diameter of the cylindrical platform stage is equal to the diameter of the stepped hole. The cylindrical platform stage of the tube is inserted into the stepped hole, creating a transition fit between the tube and the plate material. The tube is tightly fitted against the inner wall of the stepped hole, forming an lap joint between the tube and the plate material. Keeping the tube and plate material in place, the laser is injected through the flared opening to weld the lap joint between the tube and the plate material.

[0007] The laser source is a pulsed laser. The laser beam incident angle is adjusted by a galvanometer to ensure the reachability of the scanning path. During the welding process, the welding power is adjusted in real time through programming. The laser performs full penetration welding along the lap joint of the pipe and plate.

[0008] Specifically, to ensure full penetration and welding quality at both the start and end points of the circumferential weld, the laser's incident angle is adjusted via a galvanometer, welding counterclockwise 405° from the starting point to the ending point. During the initial welding phase, the laser power remains constant. When the laser returns to the starting point, the laser power begins to decrease until it completely decreases to zero at the ending point. This achieves matching and control between the laser position and heat input, ensuring weld formation. The laser power gradually decreases to zero during repeated welding sections to prevent excessive laser power in these sections from causing weld metal evaporation.

[0009] After laser welding is completed, the weld is subjected to penetrant testing and radiographic testing to detect the welding effect.

[0010] Compared with the prior art, the advantages of the present invention are: This invention combines a stepped hole design with machining of the tube body's weldable end to form a tube-to-sheet inward-shrink joint, which is then used in conjunction with galvanometer pulsed laser welding. The welding torch has good reachability, and the galvanometer pulsed laser precisely controls the welding heat input, enabling precise matching and control of the laser position and heat input. This achieves precise control of welding quality during the welding of dense tube-to-sheet groups. It effectively solves the problems of incomplete welding of circumferential weld joints and metal evaporation or cracking defects caused by excessive heat input, and provides a new method for inward-shrink laser welding of dense tube-to-sheets.

[0011] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0012] Figure 1 This is a flowchart of the laser welding method for dense tube sheets applicable to the present invention.

[0013] Figure 2 This is a structural diagram of the lap joint between the pipe body and the plate.

[0014] Figure 3 This is a schematic diagram of laser welding.

[0015] Figure 4 This is a schematic diagram illustrating the matching and control of laser position and thermal input.

[0016] Figure 5 This is a schematic diagram of the dense tube sheet layout in this embodiment. Detailed Implementation

[0017] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0018] like Figure 1 As shown, the present invention provides a method for inward-shrinking laser welding of dense tube sheets, the steps of which are as follows: S1. Preparation: Grind and polish the welding end of the pipe body to be welded, and clean the surface of the pipe hole.

[0019] S2. Joint assembly: The holes of the pipe body and the plate are processed and the pipe body is radially installed into the plate hole through transition fit, so that the pipe wall is tightly fixed to the inner wall of the hole, forming an lap joint between the pipe body and the plate.

[0020] Specific methods are as follows Figure 2As shown, firstly, holes are made in the plate material. The upper edge of the hole is chamfered to form a flared opening, through which the laser enters. The flared opening not only ensures the reachability of the laser beam but also provides scanning space for laser welding. The lower end of the hole is enlarged to form a stepped hole. In this embodiment, a stepped hole with a depth of 5mm is machined at the lower end of the hole. The end of the pipe to be welded is machined to form a cylindrical platform stage. In this embodiment, the diameter of the cylindrical platform stage after machining is within the range of the outer diameter of the pipe body d-0.1mm to d-0.3mm. Simultaneously, the diameter of the cylindrical platform stage is equal to the diameter of the stepped hole, with a deviation not exceeding 0.5mm. The length of the machined section is 5mm, that is, the length of the cylindrical platform stage is 5mm, equal to the depth of the stepped hole; moreover, the inner diameter of the pipe to be welded is equal to the diameter of the plate hole. The cylindrical platform of the pipe to be welded is inserted into the stepped hole to form a transition fit between the pipe and the plate, ensuring that the pipe is tightly attached to the inner wall of the stepped hole, thus forming an lap joint between the pipe and the plate.

[0021] S3. Welding: After forming the lap joint of the tube and plate, keep the tube and plate in place and let the pulsed laser enter from the horn-shaped port to weld the lap joint of the tube and plate.

[0022] The laser uses a galvanometer to adjust the beam incident angle to ensure the reachability of the scanning path, and the welding power is adjusted in real time during the welding process through programming. Specifically, such as... Figure 3 and Figure 4 As shown, the laser travels counterclockwise 360° from the starting position back to the starting position, then continues welding 45° to reach the ending position, for a total welding distance of 405°. In the early stages of welding, the laser power remains constant. When the laser returns to the starting position, the laser power begins to decrease until it completely decreases to zero at the ending position. This achieves laser position matching and heat input control, ensuring weld formation. The laser power gradually decreases to zero during repeated welding sections to prevent excessive laser power in these sections from causing weld metal evaporation.

[0023] S4. Inspection: Perform penetrant testing and radiographic testing on the weld.

[0024] In this embodiment, the dense tube sheet arrangement to be welded is as follows: Figure 5 As shown, the tube arrangement density and arrangement method are as follows: five tubes with a diameter of 7.5mm are welded on a plate with an area of ​​25mm*25mm. The plate holes are located at the geometric center of the square area and the geometric center of the small square area formed by connecting the midpoints of the sides. The tube plate utilization rate is about 70%, and the distance between the center of the tube holes is about 10mm.

[0025] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A recessed laser welding method suitable for dense tube sheets, characterized in that, This is used to weld a tube body to a plate to form a compact tube; the plate has holes, the upper edge of the holes is chamfered to form a flared opening, the lower end of the holes is enlarged to form a stepped hole, the end of the tube body to be welded is cut to form a cylindrical platform stage, the length of the cylindrical platform stage is equal to the depth of the stepped hole, and the outer diameter of the cylindrical platform stage is equal to the diameter of the stepped hole; the cylindrical platform stage is inserted into the stepped hole to form a transition fit between the tube body and the plate, the tube body is tightly attached to the inner wall of the stepped hole to form an lap joint between the tube body and the plate; keeping the tube body and the plate body in place, a laser is injected from the flared opening to weld the lap joint between the tube body and the plate body.

2. The inward-curving laser welding method for dense tube sheets as described in claim 1, characterized in that, The laser is used to perform full penetration welding along the lap joint of the tube and the plate.

3. The inward-shrinking laser welding method for dense tube sheets as described in claim 2, characterized in that, The laser source is a pulsed laser, and the welding power is adjusted in real time through programming during the welding process.

4. The inward-curving laser welding method for dense tube sheets as described in claim 3, characterized in that, The laser is adjusted by a galvanometer to change the incident angle, and it welds 405º counterclockwise from the starting position to the ending position. In the early stage of welding, the laser power is kept constant. When the laser travels back to the starting position, the laser power begins to decay until it completely decays to 0 at the ending position, thus achieving matching and control of the laser position and heat input.

5. The inward-curving laser welding method for dense tube sheets as described in claim 1, characterized in that, The diameter of the plate hole is equal to the inner diameter of the tube.

6. The recessed laser welding method for dense tube sheets as described in claim 1, characterized in that, The ends of the tube to be welded need to be ground and polished beforehand.

7. The inward-curving laser welding method for dense tube sheets as described in claim 1, characterized in that, After laser welding is completed, the weld is subjected to penetrant testing and radiographic testing to detect the welding effect.

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