Stress redundancy control method for high-strength metal-based material welding structure

Abstract

The invention provides a stress redundancy control method for a high-strength metal-based material welding structure, namely a method for reducing the internal stress of a welding joint and improving the bearing capacity of the welding joint through welding process control according to the fact that the bearing capacity of the welding joint is equal to the sum of the internal stress and the external stress of the joint. The method comprises the steps that welding angle deformation tendency analysis is conducted on all to-be-welded parts of a welding structural part, and direction control tools are installed on the to-be-welded parts with the space displacement tendency due to welding angle deformation; and during overall welding, one end of each to-be-welded part is welded firstly, the other end of each to-be-welded part is an unconstrained end, the other end of each to-be-welded part is welded after one end is welded and fully cooled, welding stress is effectively released, and finally welding of the complete welding structural part is completed. The method achieves the purpose of fully releasing the internal stress of the joint structure caused by the crystallization shrinkage of the welding seam, so that the bearing capacity of the welding structure is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of stress control technology, and specifically relates to a method for controlling stress redundancy in welded structures made of high-strength metal-based materials. Background Technology

[0002] Welded structures made of various metal-based high-strength materials (tensile strength ≥ 900 MPa) are widely used in key load-bearing components in aerospace, aviation, marine, land transportation, and rail transit due to their excellent load-bearing performance. They can withstand complex alternating loads and structural load-bearing requirements under complex operating conditions, thus meeting the effective application requirements of load-bearing structures such as rockets, aircraft, ships, high-speed trains, and heavy trucks, ensuring the safe operation of products with high kinetic energy loads. Therefore, stress control of welded structures made of metal-based high-strength materials is a core element in ensuring that these products have a large load redundancy.

[0003] Various high-strength alloy structures based on metals, due to their high structural rigidity and poor weldability, are prone to developing internal stresses in the weld crystallization process under welding stress. This reduces the structural load-bearing capacity, and during static pressure or fatigue tests, the required test data may not be met, affecting the qualified delivery and use of the product. Even if the test data requirements are met, the internal stresses in the weld, existing in the intergranular structure, reduce the external stress bearing capacity. If the structure encounters special and complex stress impact conditions, it is highly susceptible to failure due to the superposition of internal and external stresses in the weld and the exponential increase in load. Therefore, controlling the internal stresses in the weld crystallization process is crucial to ensuring the reliable application of key high-strength metal-based products in various welded structures. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, the inventors conducted in-depth research and provided a method for controlling stress redundancy in welded structures made of high-strength metal-based materials. By rationally designing and using the starting position, welding direction, welding sequence, welding specifications, and welding tooling involved in the stress trend during the weld crystallization process, the method aims to fully release the internal stress during weld crystallization, thereby significantly improving the load-bearing capacity of the welded structure.

[0005] The technical solution provided by this invention is as follows:

[0006] A method for controlling stress redundancy in welded structures made of high-strength metal matrix materials includes:

[0007] Clean the welding areas of each part to be welded in the welded structure to ensure that the welding areas are free of rust and oil. Pickle and dry the welding filler material for later use.

[0008] An analysis of the tendency of spatial displacement caused by stress changes during the weld crystallization process of each part of the welded structure to be welded is performed. A control fixture is installed on the part to be welded that has a tendency of spatial displacement due to weld angle deformation. The control fixture is fixed on the part to be welded and applies a force in the opposite direction of the spatial displacement caused by the angular deformation of the part to be welded, thereby controlling the spatial displacement of the part to be welded due to the change of weld angle, without restricting the controlled welding shrinkage of the part to be welded.

[0009] Grind and assemble the parts to be welded according to the welding sequence, and control the assembly gap within the required range. After clamping and fixing, the local joints are welded between the parts to be welded according to the controlled welding sequence. When welding the whole, weld one end of the part to be welded first. The other end of the part to be welded is the unconstrained end. After one end is welded and cooled sufficiently, weld the other end of the part to be welded to effectively release the welding stress and finally complete the welding of the complete welded structure.

[0010] The stress redundancy control method for high-strength metal-based welded structures provided by the present invention has the following beneficial effects:

[0011] The stress redundancy control method for high-strength metal-based welded structures provided by this invention changes the traditional methods of overall assembly, positioning, welding start position, welding direction, and welding sequence. By utilizing directional tooling and targeted welding methods, the internal stress of weld crystallization is controlled within a minimum limit. Compared with other control methods, the internal stress of weld crystallization is reduced by more than 35%, the static load-bearing capacity of the welded structure is increased by more than 35%, and the fatigue strength is increased by more than 10 times. The engineering redundancy of the welded structure is significantly improved, and it also provides a reliable basis for further weight reduction of such structures, which is of great significance. It can be widely applied to the welding of high-strength metal-based spatial structures such as frames, racks, trusses, and tie rods. It can greatly improve the load-bearing capacity of high-strength metal-based welded load-bearing structures such as rockets, aircraft, ships, high-speed trains, and heavy trucks, and provide important support for reducing the structural weight of various products. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the engine frame and control tooling structure for an embodiment;

[0013] Figure 2 This is a schematic diagram of the upper frame structure of the engine mount;

[0014] Figure 3 This is a sectional view of the upper frame of the engine block along the DD direction.

[0015] Figure 4 A schematic diagram of partial welding of the traditional lower support of the engine frame;

[0016] Figure 5This is a schematic diagram of partial welding of the lower support after the improvement of the engine frame;

[0017] Figure 6 This is a schematic diagram of the butt welding of the cylinder section. The left side shows the welding direction of the outer part of the cylinder section, and the right side shows the welding direction of the inner part of the cylinder section.

[0018] Figure 7 A schematic diagram of a segmented reverse welding method for long weld seams;

[0019] Figure 8 This is a schematic diagram of the high-strength titanium alloy bicycle frame and tooling structure in Example 2;

[0020] Figure 9 This is a schematic diagram of partial welding of the fork-shaped support in Example 2;

[0021] Figure 10 This is a schematic diagram of partial welding of the fork-shaped tie rod in Example 2. Detailed Implementation

[0022] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0023] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0024] When welding high-strength, easily quenchable, or brittle metal-based materials such as carbon steel, nickel-based alloy steel, or titanium alloys, martensite, Widmanstätten structures and various strengthening phases are easily formed. This leads to the superposition of welding stresses, reducing the structural load-bearing capacity of the product and thus failing to meet the actual application requirements. Based on the formation conditions of welding stress under different causal environments, how to avoid stress concentration in the welded structure, thereby creating superimposed loads that reduce the structural load-bearing capacity, engineering redundancy, or even structural failure, has become crucial for achieving high-quality and efficient engineering applications when welding various high-strength metal-based materials, i.e., high-strength, easily quenchable, or brittle metal-based materials.

[0025] Therefore, the present invention provides a method for controlling stress redundancy in welded structures made of high-strength metal-based materials, comprising:

[0026] (1) Pickling or sandblasting is performed on the welding areas of each part to be welded in the welded structure to ensure that there is no rust or oil stains in the welding areas. The welding filler material is pickled and dried for later use.

[0027] (2) Analyze the tendency of spatial displacement caused by the weld angle deformation due to the weld crystallization process and stress change trend of each part to be welded in the welded structure. Install a control fixture on the part to be welded where there is a tendency of spatial displacement due to weld angle deformation. The control fixture is fixed on the part to be welded and applies a force in the opposite direction of the spatial displacement caused by the angle deformation of the part to be welded to control the spatial displacement of the part to be welded due to the change of welding angle, and does not restrict the controlled welding shrinkage of the part to be welded.

[0028] (3) Grind and assemble the parts to be welded in the welding sequence. The assembly gap is controlled within 1.0mm. After the control direction is fixed, the local joints are welded between the parts to be welded in the control direction welding sequence. When welding the whole, weld one end of the part to be welded first. The other end of the part to be welded is the unconstrained end. After one end is welded and cooled sufficiently, weld the other end of the part to be welded to effectively release the welding stress and finally complete the welding of the complete welded structure.

[0029] For directional control fixtures, the design needs to be based on the specific structure of the welded structural components, such as... Figure 1 The engine frame shown includes an upper frame ( Figure 2 The machine consists of a lower side rod, a lower support, and a connecting rod. The lower side rods are welded together via the lower support to form a lower frame. The two ends of the connecting rod connect to the upper frame and the lower support, respectively, providing support and reinforcement. To prevent angular deformation when the connecting rod is welded to the lower support or the upper frame, the designed directional control fixture has a square frame structure. The inner surface of the square frame structure matches the shape at a certain height in the upper middle part of the frame. The square frame fits over the connecting rod of the frame, controlling the welding angle of the connecting rod without restricting the welding shrinkage of the connecting rod. For example, when welding between cylinder sections, to ensure coaxial welding, annular directional control fixtures are fitted at the other end of the first cylinder section and at a position on the second cylinder section away from the weld seam. The annular directional control fixtures are fixed to the base surface of the product tooling platform (or other stationary parts). The annular directional control fixtures apply force in the opposite direction of the angular bending of the first and second cylinder sections, controlling the welding angle of the parts to be welded without restricting the axial welding shrinkage of the first cylinder section.

[0030] Through research, the inventors discovered that when welding structural components such as beams, trusses, or any other welded structure with fixed constraints, if the welding of multiple parts connecting the two ends of the welded structure is completed sequentially, i.e., when the parts to be welded later in the welding sequence are welded, the two ends of the parts to be welded earlier in the welding sequence have already been fixed. The stress generated by welding the two ends of the parts to be welded later in the welding sequence is difficult to release through the expansion and contraction deformation of the parts, and the stress is concentrated in the formed structural component, resulting in a decrease in the load-bearing capacity of the welded structural component.

[0031] Therefore, when welding structural components such as beams, trusses, or any other welded structure with fixed constraints, the overall welding sequence of the structural components is determined as follows: Based on the connection relationship of the beams, trusses, or other welded structures, welding begins from one end of the beam, truss, or any other welded structure. One end of the component to be welded, connecting both ends of the beam, truss, or any other welded structure, is fixed, while the other end is unconstrained. After one end of the beam or truss is welded, the other end is welded. At this point, the other ends of the components to be welded, connecting both ends of the beam or truss, are sequentially welded and fixed. For example... Figure 1 As shown in the diagram, the connecting rods are first welded to the lower support. At this point, one end of all the connecting rods in the height direction is welded and fixed, while the other end is unrestrained. After one end of the frame is welded, the other end is welded. At this point, the other ends of all the connecting rods in the height direction are sequentially welded and fixed to the upper frame.

[0032] In traditional welding technology, when welding structural components such as beams or trusses, the welding sequence for local weld joints is as follows: starting from the initial weld point on the inner side of the structural component, weld in segments along the weld path, allowing each segment to cool fully before proceeding to the next segment. That is, weld the inner side of the structural component first, then the outer side. Figure 4 As indicated by the arrow. However, this method involves welding the inner side of the structural components first. After welding, the welded structural components with both ends fixed together generate inward welding stress. Stress concentration occurs in the overlapping section of the inner side weld joint. When welding the outer side, the two parts that were welded first are already fixed together, and the welding stress of the outer side weld cannot be released through the expansion and contraction deformation of the parts. This results in stress concentration in the overall welded structural components after welding, which reduces the structural load-bearing capacity and may even cause structural failure before the structure reaches its rated load.

[0033] Therefore, when the welded structural component is determined to be a beam, truss, or any other welded structure, the welding sequence of the local welded joints, under the action of the directional control fixture, is as follows: welding is performed segmentally along the weld trajectory from the starting point of the weld on the outer side of the structural component. Each segment is fully cooled before the next segment is welded. There is overlap at the junction of adjacent welded segments; that is, the outer side of the structural component is welded first, followed by the inner side, or segmented symmetrical layered directional unconstrained welding is used. Figure 3 As shown, the welding sequence of the rectangular structure is outer weld ①→②, inner weld ③→④; corresponding to Figure 5 As shown, the welding sequence is ③→①→⑤, ④→②→⑥.

[0034] When welding two parts to be welded is a double-sided welding process, such as Figure 6 As shown, butt welding between cylinder sections requires not only welding from the outside of the cylinder section, but also welding from the inside of the cylinder section again; or as... Figure 5As shown, the connecting rod and the lower support are assembled to form an insert plate structure. Welding is required on both the upper and lower sides of the lower support along the weld seams of the insert plate structure. The arrows indicate the weld seam trajectory on the upper side of the lower support along the insert plate structure. For double-sided welding, the welding trajectory directions and welding sequence on the weld seams of the two parts to be welded are opposite. Figure 6 When welding between cylinder sections is double-sided welding, the external welding starts from point A and proceeds counterclockwise around the circumference until the starting point and the ending point coincide; the internal welding starts from point A at point B, which is symmetrical to point A, and proceeds clockwise around the circumference until the starting point and the ending point coincide. Figure 5 The arrows indicate the weld trajectory along the insert plate structure on the upper side of the lower support. During welding on the lower side of the lower support, the two starting points correspond to the endpoints of trajectories ⑥ and ⑤, respectively, and the endpoints correspond to the starting points of trajectories ④ and ③. That is, the welding trajectory is ⑤→①→③, ⑥→②→④. This reverse welding method can effectively control welding deformation and counteract welding stress concentration in the same direction.

[0035] In practice, the inventors discovered that when the weld length of two parts to be welded is greater than 50mm, a segmented reverse welding method is adopted. Specifically, first, welding is performed along the weld in the same direction in a first direction, and the welding trajectory in the same direction is discontinuous to form segmented welding; after welding is completed, welding is performed along the weld in the same direction in a second direction, which is opposite to the first direction, and the segmented welding parts in the second direction correspond to the middle section of the welding in the first direction. Figure 7 As shown, the welding sequence for the long straight weld is ①→②→③→④.

[0036] Welding between parts can be single-layer or multi-layer. For multi-layer welding, to better release welding crystallization stress and structural stress, a multi-layer, multi-pass reverse welding method is adopted, that is, the welding directions of adjacent weld passes are opposite. For example... Figure 5 As shown, if the weld between the connecting rod and the lower support requires multi-layer welding, the welding direction and sequence for the first pass are: upper side of the lower support ③→①→⑤→ lower side of the lower support ⑤→①→③; the welding direction and sequence for the second pass are: upper side of the lower support ④→②→⑥→ lower side of the lower support ⑥→②→④; repeat the welding direction and sequence for the first and second passes until the weld is completed. Figure 6 As shown, when welding between cylinder sections is a double-sided, multi-pass welding process, the first pass, on the outside, involves counter-clockwise circumferential welding from starting point A until the starting and ending points coincide. The first pass, on the inside, involves clockwise circumferential welding from starting point B, the symmetrical position of point A, until the starting and ending points coincide. The second pass, on the outside, involves counter-clockwise circumferential welding from starting point B until the starting and ending points coincide. The second pass, on the inside, involves clockwise circumferential welding from starting point A until the starting and ending points coincide. This welding direction and sequence are repeated for the first and second passes until the weld is completed. Figure 7As shown, the welding sequence for the first pass of the long straight weld is: ①→②→③→④, and the welding sequence for the second pass is: ③→④→①→②. ​​Repeat the welding direction and sequence for the first and second passes until the weld is completed.

[0037] Example 1

[0038] like Figures 1 to 5 As shown, the low-alloy high-strength steel engine frame includes an upper frame, lower side bars, a lower support, and connecting rods. The lower side bars are welded together via the lower support to form the lower frame. The upper frame is assembled and welded from the upper support, I-beams, and diagonal tie rods. The upper support is a solid structure of 70×110×20mm, the I-beam is 3mm thick, and the diagonal tie rod is 2mm thick. The two ends of the connecting rods connect to the upper and lower supports respectively, providing support and reinforcement. Four connecting rods are used on one side of the frame, for a total of twelve connecting rods on all four sides. The parts to be welded on the frame are assembled, positioned, and connected using welding fixtures.

[0039] Leave a welding assembly gap of less than 1.0mm between the upper frame, lower side rod, lower support and connecting rod. Then, under the action of welding clamping positioning fixture and control fixture, use shielded metal arc welding to connect the entire frame into a low-stress truss structure that can bear the engine.

[0040] I. Assembly

[0041] (a) Fix the upper frame in the welding space position tooling waiting area and press it tightly.

[0042] (b) Fix the lower support in the welding platform tooling waiting area and tighten it.

[0043] (c) Adjust the welding current parameters to control the current at 80–120A, the thrust current at 10–25A, and the arc-starting current at 30–60A. Use welding electrode grade J507. Clamp the connecting rod with the welding control fixture and perform positioning welding on the entire frame. Perform symmetrical positioning welding at two points on the left and right sides of each joint. The length of each positioning point should not exceed 12mm, and the width should not exceed 10mm. Ensure that the dimensional and positional tolerances meet the drawing requirements.

[0044] Before welding the frame, the areas of the parts to be welded are sandblasted and polished to ensure that the areas to be welded are clean and free of contamination.

[0045] II. Welding

[0046] The engine frame assembly includes an upper frame, lower side members, a lower support, and connecting rods. The lower side members are welded together via the lower support to form the lower frame. The upper frame is assembled and welded from the upper support, I-beams, and diagonal tie rods. The structure is as follows: Figure 1 , Figure 2 As shown.

[0047] The frame welds are welded under the action of welding clamping fixtures and orientation control fixtures:

[0048] 1) First weld the connecting rod to the lower support, then weld the connecting rod to the upper frame;

[0049] 2) First, complete the welding of the connecting rod and the lower support in a circumferential symmetrical manner. At this time, one end of all connecting rods is fixed and the other end is free. After the weld between one end of the frame connecting rod and the lower support is completed, weld the other end of the connecting rod and the upper frame in a circumferential symmetrical manner.

[0050] 3) Finally, weld the lower rod to the lower support, making the welds symmetrical in space.

[0051] Specific welding sequence in steps:

[0052] (a) Weld the vertical welds between the upper frame and the connecting rod, with spatial symmetrical welding;

[0053] (b) Weld the vertical welds of the lower support and connecting rod, with spatial symmetrical welding;

[0054] (c) Weld the transverse welds between the upper frame and the connecting rod, with spatial symmetrical welding;

[0055] (d) Weld the transverse welds of the lower support and connecting rod, with spatial symmetrical welding;

[0056] (e) Weld the connecting rod to the lower support with spatially symmetrical welding.

[0057] The vertical and horizontal welds of the upper frame, lower support, and connecting rod are welded on the outside first, then on the inside. After welding one end, the other end is welded, until all welds on the engine frame are completed.

[0058] III. Effects

[0059] Welding of low-alloy high-strength steel often results in joint hardening, which can easily lead to brittle structures, stress concentration, and large deformation. This technology addresses these issues by: 1) achieving low-stress welding control of low-alloy high-strength steel; and 2) increasing the static pressure bearing capacity of welded low-alloy high-strength steel structures by over 35%, with a test pressure reaching 2000 kN.

[0060] 3) It increases the engineering redundancy of low-alloy high-strength steel welded structures.

[0061] Example 2

[0062] like Figures 8 to 10 As shown, the high-strength titanium alloy bicycle frame is a space truss welded structure. The titanium alloy bicycle frame is welded together from a front beam, crossbeam, support beam, connecting rods, and fork supports. The connecting rod wall thickness is 0.5–2 mm, and the support and connecting seat thickness is 5–20 mm.

[0063] A welding assembly gap of less than 0.5mm is left between the connecting seat, support seat and each beam and tie rod. Then, the entire frame is connected into a low-stress truss structure that can bear alternating loads by using high-frequency pulse TIG welding.

[0064] I. Assembly

[0065] Assembly is performed under the action of welding clamping fixtures and orientation control fixtures:

[0066] (a) Fix the connecting sleeve seat in the welding space position tooling waiting area and press it tightly.

[0067] (b) Fix the support seat in the welding platform tooling waiting area and tighten it.

[0068] (c) Adjust the welding current parameters to maintain a base value of 10–25A, a peak value of 60–80A, a duty cycle of 30–50%, and a frequency of 20–50Hz. Use TC4 welding wire. Clamp the connecting rods and beams with the welding control fixture and perform positioning welding on the entire frame. Perform symmetrical positioning welding at two points on each joint, with each positioning point not exceeding 3mm in length and 4mm in width. Ensure that the dimensional and positional tolerances meet the drawing requirements.

[0069] Before welding the bicycle frame, each part was pickled to ensure that the area to be welded was clean and free of contamination.

[0070] II. Welding

[0071] Under the constraint of the directional tooling, the bicycle frame is welded symmetrically from the inside to the outside in the order of local joints. The overall welding sequence adopts the control principle of welding the lower weld first and then the upper weld.

[0072] III. Effects

[0073] Titanium alloys have high specific strength, but welding deformation control is difficult, resulting in high residual stress after welding. Titanium alloy bicycles are generally used in high-end mountain bikes and road bikes, placing high demands on the strength and fatigue life of the frame structure. This invention achieves: 1) a controlled shrinkage tooling and a welding order control method based on the spatial displacement prediction caused by the weld angular deformation of the parts to be welded, combining multiple benefits; 2) the frame vibration data has increased from 7,000 cycles of failure to 200,000 cycles without failure; and 3) significantly improved the frame strength and service life.

[0074] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0075] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for controlling stress redundancy in welded structures made of high-strength metal-based materials, characterized in that, include: Clean the welding areas of each part to be welded in the welded structure to ensure that the welding areas are free of rust and oil. Pickle and dry the welding filler material for later use. The welding angle deformation tendency of each part to be welded in the welded structure is analyzed. A control fixture is installed on the part to be welded that has a tendency to spatial displacement due to welding angle deformation. The control fixture is fitted on the part to be welded and applies a force in the opposite direction of the spatial displacement caused by the angle deformation of the part to be welded, thereby controlling the spatial displacement of the part to be welded due to the change of welding angle, without restricting the controlled welding shrinkage of the part to be welded. Grind and assemble the parts to be welded according to the welding sequence, control the assembly gap within the required range, and after clamping and fixing, weld the parts to be welded together in the controlled welding sequence for local joints. When welding the whole, weld one end of the part to be welded first, and the other end of the part to be welded is the unconstrained end. After one end is welded and cooled sufficiently, weld the other end of the part to be welded to effectively release the welding stress and finally complete the welding of the complete welded structure.

2. The method for controlling stress redundancy in high-strength metal-based welded structures according to claim 1, characterized in that, When the welded structural component is a beam or truss, the overall welding sequence of the welded structural component is determined as follows: according to the structural connection relationship of the beam or truss, welding starts from one end of the beam or truss. One end of the part to be welded connecting the two ends of the beam or truss is spot welded and fixed under the clamping of the directional tooling, while the other end is an unconstrained end and is not spot welded and fixed. After one end of the beam or truss is welded, the other end is welded.

3. The method for controlling stress redundancy in high-strength metal-based welded structures according to claim 1, characterized in that, When the welded structural component is a beam or truss, the welding sequence of the local welded joint is as follows: first, start welding from the outer end of the weld on the outer side of the structural component and weld along the weld track in sections. After each section has cooled sufficiently, the next section is welded. There is an overlapping section at the junction of two adjacent welded sections, that is, the outer side of the structural component is welded first, and then the inner side is welded.

4. The method for controlling stress redundancy in high-strength metal-based welded structures according to claim 1, characterized in that, When the parts to be welded are welded on both sides, the welding trajectory direction and welding sequence on the weld seams on both sides of the parts to be welded are opposite.

5. The method for controlling stress redundancy in high-strength metal-based welded structures according to claim 1, characterized in that, When the weld length of the part to be welded is greater than 50mm, a segmented reverse welding method is adopted. Specifically, firstly, welding is carried out in the same direction along the weld in the first direction, and the welding trajectory in the same direction is discontinuous to form segmented welding; after the welding is completed, welding is carried out in the same direction along the weld in the second direction, which is opposite to the first direction and the segmented welding part in the second direction corresponds to the middle section of the welding in the first direction.

6. The method for controlling stress redundancy in high-strength metal-based welded structures according to claim 1, characterized in that, When the weld of the part to be welded is a multi-layer weld, a multi-layer, multi-pass reverse welding method is adopted, and the welding directions of adjacent two passes are opposite.

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