Method for preparing welded expansion joint from ultrathin plate

Abstract

The invention relates to the technical field of ultra-thin plate welding, in particular to a method for preparing a welded expansion joint from an ultra-thin plate. And the used welding fixture is simple and effective in structure, easy to implement and low in cost. In the test piece welding step, target welding parameters capable of enabling the welding quality to be high are obtained before the to-be-welded membrane is actually welded. When a membrane is welded, the automatic welding guide device is used for limiting the movement track of a machine head of the welding machine, the position can be automatically adjusted according to the shape of a to-be-welded part, the welding speed of the welding machine is greatly increased, the welding quality can be guaranteed, gaps of the membrane are filled with copper wires, and heat generated by welding is dispersed through good heat conductivity of copper. And the problems of deformation and cracks caused by local heat concentration of the diaphragm are avoided. Expansion joints with different diaphragm thicknesses can be welded and formed under the condition that the die is not replaced.

Description

Technical Field

[0001] The invention relates to the technical field of ultra-thin plate welding, and in particular to a method for preparing a welded expansion joint from an ultra-thin plate. Background Art

[0002] A metal expansion joint is a thin-walled cylinder with an axially corrugated shape. It is an elastic component. It can change shape and size under small external loads and recover after unloading. Therefore, it provides functions such as displacement compensation, vibration and noise reduction, stress relief caused by thermal deformation of the structure, and sealing. The bellows section of the expansion joint can be either integral or welded.

[0003] Integral expansion joints have high production costs, relatively high rigidity, and long fatigue life, but their displacement compensation capabilities are insufficient. They can only meet the requirements of some high-strength and small deformation working conditions, and are not suitable for scenarios where the thermal adaptation expansion joints of aircraft require relatively large expansion and contraction amounts.

[0004] Welded expansion joints are made by plastically deforming a thin plate into an annular corrugated diaphragm, which is then welded alternately to adjacent diaphragms along its inner and outer edges. This method is relatively simple and easy to implement, allowing for very small wave spacing, high wall thickness uniformity, and the flexibility to manufacture expansion joints with various irregular cross-sectional shapes. Diaphragms used for welding come in a variety of shapes, and based on the overall waveform, they can be essentially categorized into two types: symmetrical and stacked. In a symmetrical waveform, two adjacent diaphragms are symmetrical about the plane formed by the circumferential weld; in a stacked waveform, two adjacent diaphragms can be superimposed together in a compressed state, resulting in a large axial displacement. However, when stacking ultra-thin sheet metal, due to the extreme thinness of the sheet, it is difficult to precisely align the welding head with the welded position, making it difficult to achieve good weld quality. Furthermore, due to the heat input at the weld, deformation easily occurs near the weld point, causing the thin sheet metal to twist and deform after welding. Summary of the Invention

[0005] The present invention aims to solve the problems of difficulty in aligning the welding head with the weld seam and large welding deformation when welding ultra-thin plates in the existing method, and proposes a method for preparing welded expansion joints from ultra-thin plates.

[0006] According to one aspect of the present application, a method for preparing a welded expansion joint from an ultra-thin sheet is provided, characterized in that:

[0007] A special device for automatic guide welding deformation control of ultra-thin plates is used;

[0008] The device consists of an inner ring welding fixture 2, an outer ring welding fixture 7, a flange welding fixture 11 and an automatic welding guide device 5;

[0009] The inner ring welding fixture 2 consists of an upper fixture 2-1 and a lower fixture 2-2;

[0010] The outer ring welding fixture 7 includes two upper and lower ones;

[0011] The flange welding fixture 11 includes two upper and lower parts;

[0012] The automatic guided welding device 5 is composed of a guide wheel 5-1, a guide wheel frame 5-2, a connecting mechanism 5-3 and a telescopic mechanism 5-4;

[0013] The following steps are involved:

[0014] 1. Pretreatment: Surface treatment of the welding parts of the diaphragm to be welded, such as grinding, cleaning, deburring, degreasing, and descaling the welding surface to meet the surface requirements of subsequent welding;

[0015] 2. Welding test piece: Obtain a test piece with the same brand and thickness as the diaphragm to be welded, and conduct a welding test on the test piece to obtain target welding parameters that meet the welding quality requirements. Specifically, the test piece can be welded with the preset welding parameters to obtain a welding test piece assembly, and the welding quality of the welded test piece is inspected. If the inspection is qualified, the preset welding parameters can be used as the target welding parameters in the subsequent steps;

[0016] 3. Welding: Install the diaphragm group 8. According to the target welding parameters obtained above, first weld the inner ring of the diaphragm group 8, then weld the outer ring of the diaphragm group 8, and finally weld the diaphragm group 8 to the flanges 1-1 at both ends to obtain a welded expansion joint.

[0017] The upper fixture 2-1 is annular;

[0018] The lower fixture 2 - 2 is disc-shaped as a whole, with a protrusion with a rectangular cross-section along the edge of the upper surface and a through hole in the center.

[0019] The upper and lower outer ring welding fixtures 7 are both disc-shaped with a through hole in the center. The lower surface of the upper outer ring welding fixture 7 and the upper surface of the lower outer ring welding fixture 7 both have protrusions with rectangular cross-sections along the edges, and the cross-sections of the protrusions are the same.

[0020] The upper and lower flange welding fixtures 11 are both disc-shaped with a through hole in the center;

[0021] The outer edge of each guide wheel 5-1 is provided with a slope foot 5-5 pointing inward at 45°, and the two guide wheels form a guide wheel group. The connecting mechanism 5-3 is rectangular, and there is a through hole in the center with the same cross-sectional shape as the welding gun 6. A group of rectangular telescopic mechanisms 5-4 are provided at each end. One end of the telescopic mechanism 5-4 is located inside the connecting mechanism 5-3, and the other end is welded to the guide wheel frame 5-2 as a whole. The interior is a cavity, and a spring connected to the connecting mechanism 5-3 is provided in the cavity, and the spring is in a stretched state.

[0022] The pretreatment step specifically involves removing oil stains and adhering debris from the surface of the diaphragm assembly 8 using an acetone solution before welding.

[0023] The welding test piece specifically includes the following steps:

[0024] Preset welding parameters: design multiple sets of preset welding parameter combinations according to the specific target welding parameter range;

[0025] Test piece welding, welding the part test piece according to preset welding parameters to obtain a welded test piece assembly;

[0026] Welding quality inspection, inspecting the welding quality of the welding test piece assembly;

[0027] Target welding parameters are obtained, and welding test pieces welded according to different preset welding parameters are compared, wherein the preset welding parameters corresponding to the welded piece with the best welding quality are the target welding parameters.

[0028] The welding specifically comprises the following steps:

[0029] (1) Installing the diaphragm group 8: Place a pair of diaphragms to be welded, i.e., the diaphragm group 8, into the inner ring welding fixture 2, ensuring that the diaphragm group 8 coincides with the axis of the fixture, the diaphragms in the fixture are well connected, and there is no misalignment of the diaphragms. Use a gasket 3 to separate the gap in the middle of the fixture, clamp the fixture with an external fixture, and fix the diaphragm to be welded 4;

[0030] (2) Welding the inner ring of the diaphragm group 8: Connect the automatic guide welding device 5 and the welding gun 6 to form a welding device, connect the external fixture to the rotary welding machine, move the telescopic mechanism 5-4 along the normal line of the contact surface between the telescopic mechanism 5-4 and the connecting mechanism 5-3 and away from the contact surface, expand the gap between the two relative guide wheels, move the welding device so that the part to be welded 4 is located in the gap between the two relative guide wheels, loosen the telescopic mechanism 5-4, and each guide wheel is tightly fitted with the surface of the adjacent diaphragm to complete the preparation before welding;

[0031] Using the target welding parameters obtained above, weld the inner ring of the diaphragm assembly 8 along the inner ring welding fixture 2. Then, move the telescopic mechanism 5-4 in the same direction as in the welding preparation to separate the welding device and the diaphragm assembly 8. Loosen the external fixture and the inner ring welding fixture 2, and remove the diaphragm assembly 8.

[0032] (3) Repeat steps (1) and (2) to connect the inner circles of each diaphragm group 8;

[0033] (4) Diaphragm group outer ring welding: After all the inner rings of the diaphragm groups 8 are welded, all the diaphragm groups 8 are clamped together using the outer ring welding fixture 7 to ensure that the diaphragm groups 8 are clamped accurately, without misaligned diaphragms, and the axis coincides with the axis of the fixture. The gaps within the same diaphragm group 8 are separated by copper wire 10. The fixture is clamped with an external fixture to fix the diaphragm portion to be welded 9;

[0034] Connect the automatic guide welding device 5 and the welding gun 6 to form a welding device. Connect the external fixture to the rotary welding machine. Adjust the telescopic mechanism 5-4 according to the method in step 2 so that the welding part 9 is sequentially located between the two opposing guide wheels, and each guide wheel is in close contact with the surface of the adjacent diaphragm. Using the target welding parameters obtained above, weld the outer ring of the diaphragm group 8 along the outer ring welding fixture 7. Then, loosen the external fixture and the outer ring welding fixture 7, and remove the diaphragm group 8.

[0035] (5) End flange welding: Place the diaphragm group 8 and the flanges 1-1 at both ends into the flange welding fixture 11, ensuring that the axes of the three coincide and the flanges and the corrugated section are properly butted together. Use a gasket 13 to separate the gap in the middle of the diaphragm group 8, and use an external fixture to clamp the fixture to fix the diaphragm group 8 and the flanges 1-1 at both ends.

[0036] Connect the external fixture to the rotary welding machine, use the target welding parameters obtained above, weld the flange to be welded 12 along the flange welding fixture 11, then loosen the external fixture and the flange welding fixture 11, and take out the welded expansion joint.

[0037] In step (2), a spring which is always in a stretched state is provided inside the telescopic mechanism 5-4, which can always keep the guide wheels acting on the inner ring welding portion 4 of the diaphragm and the outer ring welding portion 9 of the diaphragm.

[0038] In step (2), the washer 3 is used to support the upper and lower fixtures.

[0039] In step (4), copper wires 10 are filled to separate the gaps between the same diaphragm group 8 to ensure that all diaphragms are inside the copper wires 10 .

[0040] In step (5), the gasket 13 is used to support the upper and lower diaphragms of each diaphragm group 8.

[0041] In order to ensure close contact between the guide wheel 5-1 and the welded portion 9 of the outer ring of the diaphragm, the outer edge of each guide wheel 5-1 is provided with a 45° inward slope foot 5-5, so as to increase the contact area between the guide wheel 5-1 and the welded portion 9 of the outer ring of the diaphragm.

[0042] The beneficial effects of the present invention are:

[0043] 1. The welding fixture used in the present invention has a simple and effective structure, is easy to implement, and has low cost.

[0044] Second, the present invention obtains target welding parameters that can achieve higher welding quality before actually welding the diaphragm to be welded through the welding test piece step.

[0045] 3. When welding the diaphragm, the present invention adopts the welding automatic guide device to limit the movement trajectory of the welding machine head, which can automatically adjust the position according to the shape of the workpiece to be welded, greatly improving the welding speed of the welding machine and ensuring the welding quality.

[0046] Fourth, when welding the diaphragm, the present invention uses copper wire to fill the gap between the diaphragms and uses the good thermal conductivity of copper to disperse the heat generated by welding, thereby avoiding deformation and cracking of the diaphragm due to local heat concentration.

[0047] 5. The present invention can weld expansion joints with different diaphragm thicknesses without changing the mold. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Flowchart of the method for preparing welded expansion joints for ultra-thin plates;

[0049] Figure 2 This is the axonometric view of the target expansion joint;

[0050] Figure 3 This is the main view of the target expansion joint after being cut along the axis;

[0051] Figure 4 This is a three-dimensional assembly drawing of the diaphragm, inner ring welding fixture, and gasket;

[0052] Figure 5 This is the main view of the diaphragm, inner ring welding fixture, and gasket assembly cut along the axis;

[0053] Figure 6 This is a top view of the diaphragm and welding device during the inner ring welding stage;

[0054] Figure 7 This is the axonometric view of the diaphragm and welding device cut along the axis during the inner ring welding stage;

[0055] Figure 8 This is the main view of the welding automatic guide device;

[0056] Figure 9 It is a side view of the welding device;

[0057] Figure 10 This is a three-dimensional assembly drawing of the diaphragm group and outer ring welding fixture;

[0058] Figure 11 This is the main view of the diaphragm group and outer ring welding fixture assembly after being cut along the axis;

[0059] Figure 12This is a top view of the diaphragm assembly and welding device during the outer ring welding stage;

[0060] Figure 13 This is the axonometric view of the diaphragm group and welding device cut along the axis during the outer ring welding stage;

[0061] Figure 14 This is a three-dimensional assembly drawing of the expansion joint bellows section, flange and flange welding fixture;

[0062] Figure 15 This is the main view of the expansion joint bellows section, flange and flange welding fixture assembly after being cut along the axis;

[0063] Among them, 1-1 is the flange at both ends, 1-2 is the upper diaphragm, 1-3 is the lower diaphragm, 2-1 is the upper fixture for inner ring welding, 2-2 is the lower fixture for inner ring welding, 3 is the inner ring welding gasket, 4 is the inner ring welding part of the diaphragm group, 5 is the automatic guide welding device, 6 is the welding gun, 7 is the outer ring welding fixture, 8 is the diaphragm group, 9 is the outer ring welding part of the diaphragm group, 10 is the copper wire, 11 is the flange welding fixture, 12 is the flange to be welded, and 13 is the flange welding gasket. DETAILED DESCRIPTION

[0064] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0065] Device example 1

[0066] A special device for controlling deformation of ultra-thin plate automatic guide welding;

[0067] The device consists of an inner ring welding fixture 2, an outer ring welding fixture 7, a flange welding fixture 11 and an automatic welding guide device 5;

[0068] The inner ring welding fixture 2 consists of an upper fixture 2-1 and a lower fixture 2-2;

[0069] The outer ring welding fixture 7 includes two upper and lower ones;

[0070] The flange welding fixture 11 includes two upper and lower parts;

[0071] The automatic guided welding device 5 is composed of a guide wheel 5-1, a guide wheel frame 5-2, a connecting mechanism 5-3 and a telescopic mechanism 5-4;

[0072] The upper fixture 2-1 is annular;

[0073] The lower fixture 2 - 2 is disc-shaped as a whole, with a protrusion with a rectangular cross-section along the edge of the upper surface and a through hole in the center.

[0074] The upper and lower outer ring welding fixtures 7 are both disc-shaped with a through hole in the center. The lower surface of the upper outer ring welding fixture 7 and the upper surface of the lower outer ring welding fixture 7 both have protrusions with rectangular cross-sections along the edges, and the cross-sections of the protrusions are the same.

[0075] The upper and lower flange welding fixtures 11 are both disc-shaped with a through hole in the center;

[0076] The outer edge of each guide wheel 5-1 is provided with a slope foot 5-5 pointing inward at 45°, and the two guide wheels form a guide wheel group. The connecting mechanism 5-3 is rectangular, and there is a through hole in the center with the same cross-sectional shape as the welding gun 6. A group of rectangular telescopic mechanisms 5-4 are provided at each end. One end of the telescopic mechanism 5-4 is located inside the connecting mechanism 5-3, and the other end is welded to the guide wheel frame 5-2 as a whole. The interior is a cavity, and a spring connected to the connecting mechanism 5-3 is provided in the cavity, and the spring is in a stretched state.

[0077] Example 1

[0078] The apparatus described in Apparatus Example 1 was used.

[0079] The target expansion joint has a circular cross-section and is made of GH4169 high-temperature alloy. The specific dimensions are as follows: the distance between the flanges at both ends of the expansion joint is L = 38 mm, the inner and outer diameters of the expansion joint are 276 mm and 304 mm respectively, the wall thickness is 0.3 mm, the corrugated structure is an asymmetric corrugated structure, the wave spacing λ = 4 mm, and the number of corrugations n = 5.

[0080] Step 1: Pretreatment: Use acetone solution to remove oil stains and adhering debris on the surface of parts before welding;

[0081] Step 2: Welding test piece:

[0082] Welding tests were conducted on high-temperature alloy GH4169 thin plates (strips). Experiments were conducted using different welding parameters, and the optimal welding parameters were determined by analyzing the welding results. Tests were conducted on plates of different thicknesses to determine the optimal welding parameters.

[0083] Key laser welding process parameters include laser power, welding speed, defocus, and spot width. Based on literature and previous welding experience, we investigated the optimal welding parameters for 0.3mm thick GH4169 superalloy sheets using a fixed laser power of 150W and a fixed spot width of 1mm, varying only the welding speed and defocus. The preliminary selected process parameters are shown in Table 1.

[0084] Table 1 GH4169 high temperature alloy sheet welding process parameters

[0085]

[0086] After the welding tests, uniaxial tensile test specimens were obtained using wire cutting. Uniaxial tensile tests were then conducted to test the mechanical properties of welds under different welding conditions. Microscopic hardness tests were performed on four sets of vertical weld specimens from the weld center to the base metal. Metallographic and through-thickness microstructure tests were also performed on the welds obtained using the four sets of process parameters. Based on the results of hardness testing, weld macromorphology, and microstructure testing, the optimal welding process parameters for 0.3mm thick GH4169 superalloy sheet were determined to be a welding speed of 33mm / s and a defocus of 3mm.

[0087] Step 3: Place a pair of diaphragms to be welded into the inner ring welding fixture 2, so that the lower surface of the upper fixture 2-1 is tightly fitted with the upper surface of the upper diaphragm 1-2 and the upper surface of the edge protrusion of the lower fixture 2-2 is tightly fitted with the lower surface of the lower diaphragm 1-3, and the axes coincide. Ensure that the surfaces of the upper and lower diaphragms at the welding position 4 are tightly fitted, the edges are aligned, and there is no misalignment. Use a washer 3 to separate the gap in the middle of the fixture, and use an external fixture to clamp the fixture to fix the welding position 4 of the diaphragm;

[0088] Step 4: Welding the inner ring of the diaphragm group: Pass the welding gun 6 through the through hole at the center of the connecting mechanism 5-3, and form a welding device with the automatic guide welding device 5. Connect the external fixture to the rotary welding machine, move the telescopic mechanism 5-4 along the normal line of the contact surface between the telescopic mechanism 5-4 and the connecting mechanism 5-3 and away from the contact surface, expand the gap between the two relative guide wheels, move the welding device so that the part to be welded 4 is located in the gap between the two relative guide wheels, loosen the telescopic mechanism 5-4, and each guide wheel is tightly fitted with the surface of the adjacent diaphragm, completing the preparation before welding;

[0089] Using the target welding parameters obtained in step 2, laser power 150W, fixed spot width 1mm, welding speed 33mm / s, defocus 3mm, weld the inner ring of the diaphragm assembly along the inner ring welding fixture 2, then move the telescopic mechanism 5-4 in the same direction as in the welding preparation to separate the welding device and the diaphragm assembly, loosen the external fixture and the inner ring welding fixture 2, and remove the diaphragm assembly;

[0090] Step 5: Repeat steps 3 and 4 to connect the inner rings of each pair of diaphragm groups;

[0091] Step 6. After the inner rings of all 5 pairs of diaphragm groups are welded, use the outer ring welding fixture 7 to assemble and clamp all the diaphragms together, so that the lower surface of the upper fixture edge protrusion and the upper surface of the upper diaphragm of the top diaphragm group are tightly fitted with the upper surface of the lower fixture edge protrusion and the lower surface of the lower diaphragm of the bottom diaphragm group, and the axes coincide, ensuring that the surfaces of the butt joints of adjacent diaphragm groups in the part to be welded 9 are tightly fitted, the edges are aligned, and there is no misalignment. Copper wire 10 is used to fill the gaps in the middle of the diaphragms of the same group, and the external fixture is used to clamp the fixture to fix the part to be welded 9 of the diaphragm;

[0092] Step 7: Welding the outer ring of the diaphragm assembly: Insert the welding gun 6 through the through hole in the center of the connecting mechanism 5-3, and assemble it into a welding device with the automatic guide welding device 5. Connect the external fixture to the rotary welding machine. Adjust the telescopic mechanism 5-4 according to the method in step 4 so that the part to be welded 9 is sequentially located between the two opposing guide wheels, and each guide wheel is in close contact with the surface of the adjacent diaphragm.

[0093] Using the target welding parameters obtained in step 2, laser power 150W, fixed spot width 1mm, welding speed 33mm / s, defocus 3mm, weld the outer ring of the diaphragm assembly along the outer ring welding fixture 7, then loosen the external fixture and outer ring welding fixture 7, and remove the diaphragm assembly 8;

[0094] Step 8. Place the diaphragm group 8 and the flanges 1-1 at both ends into the flange welding fixture 11, so that the lower surface of the upper fixture and the upper surface of the upper flange are tightly fitted with the upper surface of the lower fixture and the lower surface of the lower flange, and the axes coincide. Ensure that the surfaces of the diaphragm group 8 and the flanges 1-1 at both ends of the welded part 12 are tightly fitted, the edges are aligned, and there is no misalignment. Use a gasket 13 to separate the gap in the middle of the diaphragm group, clamp the fixture with an external fixture, and fix the welded part 12;

[0095] Step 9. End flange welding: Connect the external fixture to the rotary welding machine, use the target welding parameters obtained in step 2, laser power 150W, fixed spot width 1mm, welding speed 33mm / s, defocus amount 3mm, weld the diaphragm group 8 and the flanges 1-1 at both ends along the flange welding fixture 11, then loosen the external fixture and flange welding fixture 11, and take out the welded expansion joint.

[0096] Example 2

[0097] The characteristics of this embodiment are: the thickness of the diaphragm is 0.3 mm, the wave spacing λ=2 mm, and the number of corrugations n=19.

[0098] Example 3

[0099] The characteristics of this embodiment are: the thickness of the diaphragm is 0.15 mm, the wave spacing λ=2 mm, and the number of corrugations n=19.

[0100] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art may make various modifications or substitutions within the technical scope disclosed in the present invention, and all such modifications or substitutions shall be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A method for preparing a welded expansion joint from an ultra-thin plate, characterized in that: A special device for automatic guide welding deformation control of ultra-thin plates is used; The device is composed of an inner ring welding fixture (2), an outer ring welding fixture (7), a flange welding fixture (11) and an automatic welding guide device (5); The inner ring welding fixture (2) consists of an upper fixture (2-1) and a lower fixture (2-2); The outer ring welding fixture (7) comprises two upper and lower parts; The flange welding fixture (11) comprises two upper and lower parts; The automatic guide welding device (5) is composed of a guide wheel (5-1), a guide wheel frame (5-2), a connecting mechanism (5-3) and a telescopic mechanism (5-4); The following steps are involved:

1. Pretreatment; 2. Welding test piece: Obtain a test piece with the same brand and thickness as the diaphragm to be welded, and conduct welding tests on the test piece to obtain the target welding parameters that meet the welding quality requirements; 3. Welding: Install the diaphragm group (8). According to the target welding parameters obtained above, first weld the inner ring of the diaphragm group (8), then weld the outer ring of the diaphragm group (8), and finally weld the diaphragm group (8) and the flanges (1-1) at both ends to obtain a welded expansion joint.

2. The method according to claim 1, characterized in that The upper fixture (2-1) is in the shape of a circular ring; The lower fixture (2-2) is disc-shaped as a whole, with a protrusion with a rectangular cross-section along the edge of the upper surface and a through hole in the center; The upper and lower outer ring welding fixtures (7) are both disc-shaped as a whole, with a through hole in the center, and the lower surface of the upper outer ring welding fixture (7) and the upper surface of the lower outer ring welding fixture (7) both have a protrusion with a rectangular cross-section along the edge, and the cross-section shape of the protrusion is the same; The upper and lower flange welding fixtures (11) are both disc-shaped and have a through hole in the center; The outer edge of each guide wheel (5-1) is provided with a slope foot (5-5) with an inward angle of 45 degrees. Two guide wheels relative to each other form a guide wheel group. The connecting mechanism (5-3) is rectangular, and a through hole with a cross-sectional shape identical to that of the welding gun (6) is provided at the center. A set of rectangular telescopic mechanisms (5-4) are provided at each end. One end of the telescopic mechanism (5-4) is located inside the connecting mechanism (5-3), and the other end is welded to the guide wheel frame (5-2) as a whole. The interior is a cavity. A spring connected to the connecting mechanism (5-3) is provided in the cavity, and the spring is in a stretched state.

3. The method according to claim 1, characterized in that The pretreatment step specifically involves removing oil stains and adhered debris from the surface of the diaphragm group (8) using an acetone solution before welding.

4. The method according to claim 1, wherein The welding test piece is specifically The following steps are involved: Preset welding parameters: design multiple sets of preset welding parameter combinations according to the specific target welding parameter range; Test piece welding, welding the part test piece according to preset welding parameters to obtain a welded test piece assembly; Welding quality inspection, inspecting the welding quality of the welding test piece assembly; Target welding parameters are obtained, and welding test pieces welded according to different preset welding parameters are compared, wherein the preset welding parameters corresponding to the welded piece with the best welding quality are the target welding parameters.

5. The method according to claim 2, characterized in that The welding specifically comprises the following steps: (1) Installing the diaphragm group (8): Place a pair of diaphragms to be welded, i.e., the diaphragm group (8), into the inner ring welding fixture (2), ensuring that the diaphragm group (8) and the axis of the fixture coincide with each other, the diaphragms in the fixture are well connected, and there is no misalignment of the diaphragms. Use a gasket (3) to separate the gap in the middle of the fixture, clamp the fixture with an external fixture, and fix the diaphragm to be welded (4); (2) Welding the inner ring of the diaphragm group (8): connect the automatic guide welding device (5) and the welding gun (6) to form a welding device, connect the external fixture to the rotary welding machine, move the telescopic mechanism (5-4) along the normal line of the contact surface between the telescopic mechanism (5-4) and the connecting mechanism (5-3) and away from the contact surface, expand the gap between the two relative guide wheels, move the welding device so that the part to be welded (4) is located in the gap between the two relative guide wheels, loosen the telescopic mechanism (5-4), and each guide wheel is tightly fitted with the surface of the adjacent diaphragm, completing the preparation before welding; Using the target welding parameters obtained above, weld the inner ring of the diaphragm assembly (8) along the inner ring welding fixture (2), then move the telescopic mechanism (5-4) in the same direction as in the welding preparation work to separate the welding device and the diaphragm assembly (8), loosen the external fixture and the inner ring welding fixture (2), and remove the diaphragm assembly (8); (3) Repeat steps (1) and (2) to connect the inner rings of each diaphragm group (8); (4) Welding the outer ring of the diaphragm group: After the inner rings of all diaphragm groups (8) are welded, all diaphragm groups (8) are clamped together using the outer ring welding fixture (7), ensuring that the diaphragm groups (8) are clamped accurately, without misaligned diaphragms, and that the axes coincide with the axes of the fixture. The gaps within the same diaphragm group (8) are separated by copper wire (10), and the fixture is clamped using an external fixture to fix the diaphragm portion to be welded (9); Connect the automatic guide welding device (5) and the welding gun (6) to form a welding device, connect the external fixture and the rotary welding machine, adjust the telescopic mechanism (5-4) according to the method in step (2), so that the part to be welded (9) is located between the two relative guide wheels in sequence, and each guide wheel is tightly fitted with the surface of the adjacent diaphragm, and the target welding parameters obtained above are used to weld the outer ring of the diaphragm group (8) along the outer ring welding fixture (7), then loosen the external fixture and the outer ring welding fixture (7), and remove the diaphragm group (8); (5) End flange welding: Place the diaphragm group (8) and the flanges at both ends (1-1) into the flange welding fixture (11), ensure that the axes of the three coincide, and that the flanges and the corrugated section are properly butted together. Use a gasket (13) to separate the gap in the middle of the diaphragm group (8), and use an external fixture to clamp the fixture to fix the diaphragm group (8) and the flanges at both ends (1-1); The external fixture is connected to the rotary welding machine, and the target welding parameters obtained above are used to weld the flange to be welded (12) along the flange welding fixture (11), and then the external fixture and the flange welding fixture (11) are loosened to remove the welded expansion joint.

6. The method according to claim 5, characterized in that In step (2), a spring which is always in a stretched state is provided inside the telescopic mechanism (5-4), which can always keep the guide wheels acting on the inner ring welding portion (4) and the outer ring welding portion (9) of the diaphragm.

7. The method according to claim 5, characterized in that In step (2), the washers (3) are used to support the upper and lower fixtures.

8. The method according to claim 5, characterized in that In step (4), the copper wire (10) is filled to separate the gaps between the same diaphragm group (8) to ensure that all diaphragms are inside the copper wire (10).

9. The method according to claim 5, characterized in that In step (5), the gasket (13) is used to support the upper and lower diaphragms of each diaphragm group (8).

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