Method for electron beam repair welding of through cracks in large-thickness curved plate

Abstract

The application discloses a kind of curved surface state large-thickness plate through crack electron beam repair welding methods, comprising: twice repair welding is carried out on the front of plate, and two welds are formed, wherein the first weld is passed the one end of crack and parallel with the welding direction of original weld, the second weld is offset along the width direction of crack in the state of keeping parallel with the first weld, so that the first weld and the second weld cover crack;Flip plate, and the same repair welding process is carried out on the back of plate.The application further discloses a kind of methods for realizing curved plate crack repair welding using backing plate.The application ensures the uniformity of performance after crack repair welding, significantly improves repair welding efficiency and quality.

Description

Technical Field

[0001] This invention belongs to the field of welding technology and relates to an electron beam welding method for repairing through cracks in thick plates with curved surfaces. Background Technology

[0002] The Φ5m tank bottom is a crucial component of my country's launch vehicle propellant tanks. With my country's significant breakthroughs in space station construction and manned spaceflight, higher demands have been placed on the reliability of launch vehicles. Therefore, the design of the tank bottom has focused on optimizing its structure to reduce weight and further enhance weld joint strength. Taking a specific tank bottom design as an example, the original circular bottom structure, formed by welding together segments and flanges, has been replaced with a spherical bottom structure formed by integral spinning. This is achieved using electron beam plate welding, pre-forming by pressure drum, and spinning. This improved process significantly reduces the number of welds, avoiding the strength reduction caused by over-aging softening in the weld area. However, due to the immaturity of the current pressure drum process, cracks easily appear at weak points in the electron beam welds, sometimes even forming penetrating cracks with a certain width in the transverse weld area. In this case, the plate is in a curved state, posing challenges for subsequent repair welding. Penetrating cracks, such as... Figure 1 As shown.

[0003] Currently, weld defect repair is still mainly carried out using traditional fusion welding technology. For thick plates, there are problems such as poor penetration, large heat input, and grain coarsening. Compared with the original electron beam weld, this will lead to the deterioration of joint performance. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned defects and provide an electron beam welding method for repairing through-cracks in thick plates with curved surfaces. This method solves the technical problem that traditional welding methods are difficult to achieve high-quality welding and further solves the technical problem that traditional welding methods are difficult to achieve curved surface welding. This invention ensures the uniformity of performance after crack repair welding and significantly improves welding efficiency and quality.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] An electron beam welding method for repairing through-cracks in thick plates includes:

[0007] Two welds are made on the front side of the plate to form two welds. The first weld passes through one end of the crack and is parallel to the original weld direction. The second weld is offset along the crack width direction while remaining parallel to the first weld, so that the first and second welds cover the crack.

[0008] The plate is turned over, and two times of repair welding are performed on the back of the plate to form two welds, wherein the first weld is parallel to the original weld in the direction of welding and passes through one end of the crack, and the second weld is offset in the direction of crack width while keeping parallel to the first weld, so that the first weld and the second weld cover the crack.

[0009] Further, for a crack with a width of W, where the width refers to the offset width of the crack on the upper and lower surfaces of the weld perpendicular to the welding direction, as shown in the figure, the second weld is offset in the direction of crack width by a distance of W1 while keeping parallel to the first weld, and W1 satisfies the following relationship: Figure 4

[0010]

[0011] Further, for a crack with a depth of B, the depth B1 of the first weld and the second weld satisfies the following relationship:

[0012]

[0013] Further, when performing the first repair welding on the front or back of the plate, the following method is used:

[0014] An auxiliary line parallel to the original weld in the direction of welding is made through one end of the crack, and a plurality of impact points are arranged along the auxiliary line;

[0015] The arc termination point and the arc starting point of the repair welding are determined;

[0016] At least one of the plurality of impact points, the arc termination point, and the arc starting point are selected as teaching points;

[0017] Using the teaching points under the camera, the repair welding is performed in a trajectory teaching manner to obtain the first weld.

[0018] Further, the impact points are formed by tapping the surface of the plate with a tap, the distance L between adjacent two impact points is 5-8 mm, and the plurality of impact points are uniformly distributed along the auxiliary line.

[0019] Further, the arc termination point falls on the arc termination plate, and the arc starting point is located in front of one end of the crack, and the distance L' between the arc starting point and one end of the crack is 48-53 mm.

[0020] Further, when performing the repair welding, when the plate is in a curved state, a backing plate is used to pad one side of the plate so that the tangent plane at the position of the crack is perpendicular to the direction of the electron gun.

[0021] The backing plate and the crack are located on the two sides of the center point of the curved surface.

[0022] Further, when performing the repair welding on the concave surface of the plate, the height H1 of the backing plate satisfies the following formula:

[0023] ​H1≥R-Rcosθ1

[0024] Wherein, R is the curvature radius of the center point of the curved surface, θ1 is the included angle between the line connecting the crack and the center of the sphere and the line connecting the center point of the curved surface and the center of the sphere;

[0025] The arc length between the contact position of the backing plate and the curved surface and the center point of the curved surface is 200-300mm;

[0026] The length L1 of the backing plate is 500-1000mm.

[0027] Further, when the backing plate is welded on the convex surface of the plate, the height H3 of the backing plate satisfies the following formula:

[0028]

[0029] Wherein, H * is the height of the center point of the curved surface when the plate is placed horizontally, H" is the height of the crack from the horizontal workbench when the tangent line of the curved surface at the crack is perpendicular to the direction of the electron gun, R is the curvature radius of the center point of the curved surface, and θ2 is the included angle between the line connecting the crack and the center of the sphere and the line connecting the center point of the curved surface and the center of the sphere;

[0030] The length L2 of the backing plate is 1000-1500mm.

[0031] Further, when the backing plate is welded on the concave surface of the plate, the working distance H2 of the electron gun is greater than the distance H' between the crack and the edge of the curved surface in the direction of the electron gun;

[0032] When the backing plate is welded on the convex surface of the plate, the working distance H4 of the electron gun is greater than or equal to H max -H", wherein H max is the limit working distance of the electron gun, and H" is the height of the crack from the horizontal workbench when the tangent line of the curved surface at the crack is perpendicular to the direction of the electron gun.

[0033] Compared with the prior art, the present application has at least one of the following beneficial effects:

[0034] (1) The present application creatively proposes a large-thickness plate through crack electron beam repair welding method, which realizes one-time complete repair welding of a through crack with a certain width, and avoids the performance degradation problem caused by multiple repair weldings;

[0035] (2) The present application adopts a double-sided repair welding multi-pass weld method, which realizes full coverage in the depth direction, width direction and length direction of the crack;

[0036] (3) The present application proposes a determination method for repair welding teaching track and starting and ending points, which is beneficial to improve the repair welding quality and efficiency;

[0037] (4) The application develops a curved surface state large thickness plate through crack simulation plane electron beam repair welding method, through the bottom adding backing plate and the optimization of process parameters, the complexity of numerical control track programming is reduced, and the uniformity of the performance in the length direction after crack repair welding is ensured, the repair welding efficiency and quality are significantly improved;

[0038] (5) The application comprehensively considers various factors of concave and convex repair welding, gives the relationship and regular expression of the backing plate and the crack position, can accurately control the backing plate size, improves the stability of the welding process, avoids a large number of trial and error costs;

[0039] (6) The application adopts electron beam repair welding, the energy density is high, the heat input is concentrated, the penetration is deeper than other welding methods, the repair welding times can be effectively reduced, the serious welding deformation and welding stress caused by multi-layer and multi-pass welding are avoided, and the welding efficiency can be improved to a certain extent. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 It is a typical through crack physical diagram, wherein (a) and (b) are physical diagrams of cracks with different shapes respectively;

[0041] Figure 2 It is a crack impact point position schematic diagram of the application;

[0042] Figure 3 It is a crack trajectory teaching schematic diagram of the application;

[0043] Figure 4 It is a welded crack schematic diagram of the application;

[0044] Figure 5 It is a repair welding seam schematic diagram of the application;

[0045] Figure 6 It is a crack repair welding effect diagram of the application; wherein (a) is a size schematic diagram, and (b) is a physical diagram after repair welding;

[0046] Figure 7 It is a concave surface schematic diagram of a curved surface plate;

[0047] Figure 8 It is a backing plate height determination method schematic diagram of the application for the concave surface of the curved surface plate;

[0048] Figure 9 It is an electron gun working distance schematic diagram of the application for the concave surface of the curved surface plate;

[0049] Figure 10 It is a convex side schematic diagram of a curved surface plate;

[0050] Figure 11 It is a backing plate height determination method schematic diagram of the application for the convex side of the curved surface plate;

[0051] Figure 12 The schematic diagram of the working distance of the electron gun for the convex side of the curved plate of the present application. DETAILED DESCRIPTION

[0052] The features and advantages of the present application will become more apparent from the detailed description, when taken in conjunction with the accompanying drawings, in which:

[0053] The term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations. Unless specifically stated otherwise, the present disclosure is not to be construed as using terms or phrases for the purpose of excluding the use of such terms or phrases after the words "such as" or "including."

[0054] The current crack repair welding method is mainly based on TIG welding process. Due to the characteristics of the heat source, the welding process has large heat input, the joint structure is obviously coarsened, and the joint strength is severely reduced after repair welding. In addition, although TIG welding usually uses inert gas for protection, it is still not ruled out that harmful substances enter the molten pool, and defects such as pores and inclusions are difficult to completely avoid. Moreover, the heat dissipation condition of large-thickness plate is good, which will inevitably lead to greater heat input during welding, otherwise it is difficult to open the molten pool, and the tungsten tip is easy to locally melt and invade the molten pool, resulting in serious tungsten inclusion defects. In addition, for the repair welding of large-thickness plate, TIG welding usually uses the process method of opening groove + multi-layer multi-pass welding, which not only takes time and effort, but also the multiple heating of the weld will also deteriorate the joint performance. In summary, combined with the new generation of manned spacecraft, the existing TIG repair welding method has the problems of poor joint strength, internal defects, poor efficiency, etc., and is not suitable for the repair welding of through cracks in large-thickness plate.

[0055] As a high-energy beam welding method, electron beam welding process has the advantages of strong penetration ability, large weld depth-to-width ratio, small heat-affected zone, good grain structure, and can reduce the joint performance deterioration caused by repair welding to the minimum. The high depth-to-width ratio feature is also completely suitable for through crack repair welding. However, the through crack not only penetrates the entire thickness, but also exhibits a certain width in the transverse direction of the weld. The high depth-to-width ratio characteristic of electron beam welding itself has an adverse effect because the weld is too narrow and single-pass welding cannot completely realize the transverse repair welding of the through crack.

[0056] Electron beam welding in flat plate state does not need to consider the interference problem of electron gun and the change problem of welding gun working distance, but for curved large-thickness plate, the electron beam repair welding needs to consider the climbing welding in the curved direction, and there is an interference problem between the electron gun and the edge of the curved plate, which brings great difficulty to the repair welding work.

[0057] The present application can not only realize the electron beam repair welding of the large-thickness plate in the flat state, solve the technical problems of large labor intensity, low efficiency and poor repair welding effect caused by TIG manual welding, but also is suitable for the electron beam repair welding of the crack of the curved plate.

[0058] In combination with the drawings Figures 2-12 The present application is a method for the electron beam repair welding of the through crack of the large-thickness plate in the curved state, which comprises the following steps:

[0059] (1) Repair welding process of the through crack

[0060] According to the characteristics of the crack, a repair welding process of the through crack of the plate in the curved state is developed.

[0061] 1) Auxiliary line is made at the crack position, and a punch point is struck

[0062] As Figure 2 , first, an auxiliary line is made at one end of the crack, which is parallel to the welding direction of the original weld, and by means of the auxiliary line, a punch point is struck on the surface of the plate every distance L by a tap, L is usually 5-8 mm, and the punch points are uniformly distributed along the auxiliary line, so that the crack is clear and bright under the camera, and the subsequent trajectory teaching is facilitated.

[0063] Then, an arc extinguishing plate is clamped at the arc collecting end of the repair welding seam to ensure that the arc collecting end of the repair welding falls on the arc extinguishing plate, so as to prevent a pit from appearing on the surface of the plate.

[0064] 2) Trajectory teaching of the camera

[0065] As Figure 3 , after the vacuum is completed, the trajectory teaching is performed under the camera, wherein the starting point should be located in front of the crack tip at a distance L', L' is about 50 mm, the arc collecting point should be located on the arc extinguishing plate, and a total of 5 points are taught to ensure the accuracy of the trajectory.

[0066] 3) Repair welding of the through crack

[0067] The repair welding of the crack is based on the following method:

[0068] The repair welding adopts the repair welding method of 2 welds on the front surface and 2 welds on the back surface, and for the through crack with a depth of B, the weld depth B1 should meet the following requirements:

[0069]

[0070] The distance W1 between the center positions of the two welds, when the repair welding is performed, the first welding is performed in the original welding direction (length direction) as the reference, then the welding of the other weld is performed by offsetting a distance W1 to one side, and the offset direction is perpendicular to the original welding direction (along the crack width direction), the purpose is to cover the crack area by the two weld areas, and this method is adopted on the front surface and the back surface.

[0071] For the through crack with a width of W, the offset distance W1 should satisfy the following requirements:

[0072]

[0073] After the front surface repair welding is completed, the plate is turned over, and the back surface weld is repaired. Thus, the adverse effects of multiple heatings on the structure near the crack are avoided, and through the repair welding process method of offsetting from the crack initiation position downward and to one side, full coverage in the depth direction, width direction and length direction of the crack is achieved. Among them, the weld depth and offset distance can be adjusted according to the characteristics of the crack. The crack schematic diagram and repair welding scheme are shown in Figure 4 、 Figure 5 The repair welding test effect of a certain curved plate with a thickness of 53mm is shown in Figure 6 .

[0074] 4) Post-weld treatment

[0075] The weld surface excess height and arc plate are milled after welding to be flush with the base material itself, and the overall plate repair welding work is completed.

[0076] The above repair welding process has the following advantages:

[0077] 1) Compared with the traditional TIG repair welding method, the overall repair welding process is carried out in the vacuum chamber, which avoids the invasion of harmful gas into the molten pool, and the weld composition is pure. In addition, due to the difference in welding method, there is no tungsten loss, thereby avoiding the internal porosity and tungsten inclusion defects of the weld.

[0078] 2) The energy density is high during electron beam repair welding, the heat input is concentrated, the penetration is deeper than other welding methods, the repair welding times can be effectively reduced, the serious welding deformation and welding stress caused by multi-layer and multi-pass welding can be avoided, and the welding efficiency can be improved to a certain extent.

[0079] 3) Through the double-sided + multi-pass repair welding method, the repair welding width is significantly improved, and complete repair welding of the through crack with a certain width can be achieved, and there is no internal repair welding after welding.

[0080] 4) By clamping the arc extinguishing plate at the end of the repair welding weld, the end of the arc is led to the arc extinguishing plate, which effectively avoids the weld collapse and arc extinguishing crack caused by the arc of the repair welding.

[0081] (2) Curved plate crack repair welding method

[0082] The electron beam repair welding of the curved plate involves multi-axis synchronous motion, and the numerical control teaching program is complex to write, and it is easy to cause inconsistency of the welding parameters in the length direction, and finally feedback to the unevenness of the plate repair welding performance, therefore, the invention proposes a simulated plane repair welding method.

[0083] AsFigure 7 As shown in the process of curved surface concave side repair welding, a backing plate is added at the bottom of the curved surface, and the length L1 and height H1 of the backing plate can be adjusted according to the crack position and the curvature radius of the curved surface, so that the crack position is kept as flat as possible to avoid the multi-axis movement of the electron gun as much as possible.

[0084] Wherein, for the height of the backing plate, the following method is used:

[0085] Wherein, for the curved surface with a large curvature radius, the electron beam repair welding engineering can be approximated as a spherical surface, that is, the curvature radius R is equal at each position of the curved surface.

[0086] The curvature radius of the center point of the curved surface is R, and the arc length A1 of the crack position from the center point is measured, and the angle θ1 between the crack position and the center of the sphere and the center of the curved surface is obtained, as shown in the figure. Figure 7

[0087] Wherein:

[0088]

[0089] Obviously, after the curved surface is rotated by an angle θ1, the crack can reach a flat state, that is, the tangent line of the crack position is perpendicular to the direction of the electron gun, as shown in the figure. Figure 8

[0090] After the curved surface is rotated by θ1 to reach a flat state, the arc length A2 of the contact surface of the backing plate from the center point is measured, and A2 cannot be too long, otherwise the height H1 of the selected backing plate will be too high, and A2 is generally selected to be 200-300mm.

[0091] After measuring the arc length A2, a vertical line is drawn from the side of the arc length away from the center point to the horizontal plane, and the distance H1 is measured, which is the height of the selected backing plate.

[0092] In order to maintain the stability of the curved surface panel, the backing plate should be located on the left side of the center point of the curved surface, and the following formula is obtained: H1≥R-Rcosθ1(4-4)

[0093] As described above, the height H1 of the backing plate should meet the formula (4-4) and the condition of A2=200-300mm.

[0094] The length L1 of the backing plate should ensure the stability of the curved surface after the backing plate is raised, and L1 is generally selected to be 500-1000mm, as shown in the figure. Figure 8

[0095] The vertical height H' of the crack position and the edge of the curved surface should be measured before welding, as shown in the figure. Figure 9 The working distance of the electron gun, that is, the vertical distance H2 between the emission end of the gun body and the crack position, should be determined according to the process parameters and H', and has:​​​

[0096] H2≥H'(4-5)

[0097] In a specific embodiment, for the repair welding of a certain concave curved panel with a thickness of 53 mm, the height H1 of the backing plate is set to 240 mm, the length L1 is set to 700 mm, the height H2 of the electron gun is set to 500 mm, and the process parameters are shown in Table 1:

[0098] Table 1 Welding process parameters (500 mm)

[0099]

[0100] When performing repair welding on the convex side of the curved surface, a backing plate also needs to be added on the edge side of the curved surface. The length L2 and the height H3 of the backing plate can be adjusted according to the crack position and the curvature of the curved surface to keep the crack position as flat as possible.

[0101] Among them, for the height of the backing plate, the following method is used:

[0102] For a curved surface with a large curvature radius, the electron beam repair welding engineering application can be approximated as a spherical surface, that is, the curvature radius R is equal at each position on the curved surface.

[0103] The curvature radius of the center point of the curved surface is R, and the height of the center point of the curved surface (that is, the distance from the center point of the curved surface to the workbench when the panel is placed on the workbench) H * . Taking the center point as the starting point, the arc length A3 of the crack position from the center point is measured, and the angle θ2 between the crack position and the center of the sphere and the center of the curved surface and the center of the sphere is obtained, as shown in Figure 10 .

[0104] Among them, the angle θ2 has the formula:

[0105]

[0106] Obviously, after the curved surface with a repair welding angle θ2, the crack can reach a flat state, as shown in Figure 11 . At this time, the height H" of the crack position from the horizontal plane is measured.

[0107] In order to maintain the stability of the curved panel and control the height of the backing plate, the contact position of the backing plate and the curved panel should be within the arc length A3, so for the height H3 of the backing plate, there is the formula:

[0108]

[0109] The length L2 of the backing plate should ensure the stability of the curved backing, and L2 is generally selected to be 1000-1500 mm.

[0110] The working distance H4 of the electron gun should be determined according to the limit working distance H max of the electron gun, as shown in Figure 12As shown.

[0111] That is:

[0112] H4≥H max -H"(4-8)

[0113] In a preferred embodiment, for the repair welding of a certain concave curved panel with a thickness of 53 mm, the height H3 of the backing plate is set to 400 mm, the length L2 is 1000 mm, the height H4 of the electron gun is set to 300 mm, and the process parameters are as shown in Table 2:

[0114] Table 2 Welding process parameters (300 mm)

[0115]

[0116] In summary, the simulation plane electron beam repair welding of the large-thickness panel in the curved state is realized.

[0117] The repair welding process has the following advantages:

[0118] 1) By installing a backing plate, the repair welding in the curved state is converted to the flat state, effectively avoiding the programming of complex welding procedures, and at the same time, the repair welding is converted from curved ramp welding to flat welding, which minimizes the influence of gravity on the molten pool state, and the weld after welding is well formed and has uniform mechanical properties.

[0119] 2) Only a certain thickness of the backing plate can realize the leveling of the curved panel, without using any complex tooling, and the operation is simple, the cost is low, and the welding efficiency is high.

[0120] 3) The relationship between the backing plate and the crack position and the regular expression are summarized, the size of the backing plate can be accurately controlled, the stability of the welding process is improved, and a large number of trial and error costs are avoided.

[0121] The present application is suitable for the repair welding of large-thickness panels with a thickness of 30-60 mm.

[0122] The present application has been described in detail in combination with specific embodiments and exemplary examples, but these descriptions cannot be understood as limiting the present application. Those skilled in the art understand that the technical solutions and embodiments of the present application can be variously replaced, modified or improved without deviating from the spirit and scope of the present application, and these all fall within the scope of the present application. The protection scope of the present application is subject to the appended claims.

[0123] The contents not described in detail in the specification of the present application are the known technology of those skilled in the art.

Claims

1. A method of electron beam repair welding of a through crack in a large thickness plate, characterized in that, The method comprises the following steps: Two times of repair welding are performed on the front surface of the plate to form two welds, wherein the first weld passes through one end of the crack and is parallel to the welding direction of the original weld, and the second weld is offset along the crack width direction while keeping parallel to the first weld, so that the first weld and the second weld cover the crack; The plate is turned over, and two times of repair welding are performed on the back surface of the plate to form two welds, wherein the first weld passes through one end of the crack and is parallel to the welding direction of the original weld, and the second weld is offset along the crack width direction while keeping parallel to the first weld, so that the first weld and the second weld cover the crack; When the first time of repair welding is performed on the front surface or the back surface of the plate, the following method is adopted: An auxiliary line parallel to the welding direction of the original weld is made at one end of the crack, and a plurality of impact points are arranged along the auxiliary line; The arc ending point and the arc starting point of the repair welding are determined; At least one of the plurality of impact points, the arc ending point and the arc starting point are selected as teaching points; The repair welding is performed in the manner of trajectory teaching by using the teaching points under the camera, and the first weld is obtained.

2. A method of electron beam repair welding of a through crack in a large thickness plate according to claim 1, characterized in that, For the crack with a width of W, the second weld is offset along the crack width direction by a distance of W1 while keeping parallel to the first weld, and W1 satisfies the following relationship:

3. The method of claim 1, wherein the method is a method of electron beam repair welding of a through-thickness crack in a thick plate, characterized by, For the crack with a depth of B, the depth B1 of the first weld and the second weld satisfies the following relationship:

4. The method of claim 1, wherein the method is a method of electron beam repair welding of a through-thickness crack in a thick plate, characterized by, The impact points are formed by knocking the plate surface with a tap, the distance L between two adjacent impact points is 5-8 mm, and the plurality of impact points are uniformly distributed along the auxiliary line.

5. A method of electron beam repair welding of a through crack in a large thickness plate according to claim 4, characterized in that, The arc ending point falls on the arc ending plate, and the arc starting point is located in front of one end of the crack, and the distance L' between the arc starting point and one end of the crack is 48-53 mm.

6. The method of claim 1, wherein the method is a method of electron beam repair welding of a through-thickness crack in a thick plate, characterized by, When the plate is in a curved surface state during the repair welding, a backing plate is used to pad one side of the plate, so that the tangent plane at the position of the crack is perpendicular to the direction of the electron gun; The backing plate and the crack are located on the two sides of the center point of the curved surface.

7. A method of electron beam repair welding of a through crack in a large thickness plate according to claim 6, characterized in that, When the repair welding is performed on the concave surface of the plate, the height H1 of the backing plate satisfies the following formula: H1≥R-Rcosθ1 Wherein, R is the radius of curvature of the center point of the curved surface, and θ1 is the included angle between the line connecting the crack and the center point of the curved surface and the line connecting the center point of the curved surface and the center of the sphere; The arc length between the contact position of the backing plate and the center point of the curved surface is 200-300 mm; The length L1 of the backing plate is 500-1000 mm.

8. The method of claim 6, wherein the method is a method of electron beam repair welding of a through-thickness crack in a thick plate, characterized by, When the repair welding is performed on the convex surface of the plate, the height H3 of the backing plate satisfies the following formula: wherein H * is the height of the center point of the curved surface when the plate is placed horizontally, H" is the height of the crack from the horizontal workbench when the tangent line of the curved surface at the crack is perpendicular to the direction of the electron gun, R is the radius of curvature of the center point of the curved surface, and θ2 is the included angle between the line connecting the crack and the center of the sphere and the line connecting the center point of the curved surface and the center of the sphere; The length L2 of the backing plate is 1000-1500 mm.

9. The method of claim 6, wherein the method is a method of electron beam repair welding of a through-thickness crack in a thick plate, characterized by, When the repair welding is performed on the concave surface of the plate, the working distance H2 of the electron gun is greater than the distance H' between the crack and the edge of the curved surface along the direction of the electron gun. When the repair welding is carried out on the convex surface of the plate, the working distance H4 of the electron gun is greater than or equal to H max -H", wherein H max is the limit working distance of the electron gun, and H" is the height of the crack from the horizontal workbench when the tangent of the curved surface at the crack is perpendicular to the direction of the electron gun.

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