Electron beam welding method for ultrahigh-strength steel shell

Abstract

The invention discloses an electron beam welding method for an ultrahigh-strength steel shell. Comprising the following steps of part machining, demagnetization, laser cleaning, assembly of all parts, preheating welding of shell welding seams, formal welding of the shell welding seams, stress relief welding (modification welding) of the shell welding seams, X-ray detection, welding of external parts, annealing, detection and overall heat treatment (quenching and tempering) X-ray detection, numerical control turning, machining center and inspection are conducted. According to the method, the welding problem of the ultrahigh-strength steel shell is solved, a welding joint meets the GJB1718A-2005 I-level requirement, a welding seam is subjected to one-side welding and double-side forming, the welding seam is thoroughly welded and is free of sunken parts, the excess weld metal of the back face is not larger than 0.4 mm, the excess weld metal of the front face is not larger than 1.0 mm, the defects of undercut, incomplete fusion, cracks and the like are avoided, a welding test plate passes a mechanical property test, and the shell passes a water pressure bursting test. By adopting the method, the welding process is stable, the welding seam quality is good, and the welding qualification rate is high.

Description

Technical Field

[0001] The invention belongs to the technical field of welding, and in particular to a vacuum electron beam welding method for an ultra-high strength steel shell. Background Art

[0002] With the development of solid rocket engine missile technology, missiles are required to have high mass ratio, high maneuverability, high aerodynamic heating and high overload, thus putting forward higher requirements on the performance of missile engines. The shell is an important component of the combustion chamber of a solid rocket engine. It is both a place for propellant storage and a place for propellant chemical reaction. It must withstand high temperature and high pressure loads. At the same time, the shell must also provide support for other parts of the missile (such as cable covers, wings, etc.). When the engine is working, the shell, as a thin-walled part, not only withstands high temperature and high pressure at high burning rates, but also needs to withstand external loads from the entire missile, such as axial pressure, bending moment, shear force, etc. Therefore, the lightweight, thin-walled shell bears the combined effect of internal pressure and external loads. The structural and welding process characteristics of the shell are as follows:

[0003] a) The shell is a thin-walled structure with a large aspect ratio, usually formed by welding the front (rear) joint, front skirt, front (rear) joint and cylinder in sequence, and can withstand high pressure and high temperature environments;

[0004] b) When welding the D406A ultra-high strength steel shell, high precision is required, the welding heat affected zone is small, and strict requirements are placed on the weld defect rate, weld purity, and welding deformation control;

[0005] c) The welding production of D406A ultra-high strength steel shell requires high reliability and high efficiency processing.

[0006] Vacuum electron beam is generally unable to achieve wire filling welding during the welding process, and there is a certain depression problem on the front of the weld; the shell is a thin-walled part, and it is easy to cause deformation and misalignment of the parts during assembly, which cannot meet the requirements of parts assembly and welding; the back of the weld is misaligned, single-sided welding and double-sided forming, which easily leads to defects such as undercut and incomplete penetration, resulting in a low welding qualification rate. Summary of the invention

[0007] The present invention aims to provide an electron beam welding method for an ultra-high strength steel shell, which solves the problems of weld depression, assembly misalignment and low welding qualification rate, and requires the method to be simple, reliable and practical.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] An electron beam welding method for an ultra-high strength steel shell, wherein the ultra-high strength steel shell comprises a front joint, a front skirt, a barrel and a rear joint, wherein the axial first end of the barrel is welded to the front joint, and the axial second end is welded to the rear joint, and the front skirt is mounted on an end of the front joint away from the barrel, and the materials of the front joint, the front skirt, the barrel and the rear joint are all D406A ultra-high strength steel, and the welding method comprises the following steps:

[0010] Step 1: Process the front joint, front skirt, barrel and rear joint respectively, wherein one end of the front joint corresponding to the welding position is provided with a circle of process boss stop along the circumferential direction, and one end of the rear joint corresponding to the welding position is provided with a circle of process boss stop along the circumferential direction, and the surfaces of the two process boss stop are both provided with engraved lines for weld alignment;

[0011] Step 2, demagnetizing the front joint, front skirt, barrel and rear joint;

[0012] Step 3, assemble the front joint, front skirt, barrel and rear joint coaxially, and use a clamp to press the front joint, front skirt, barrel and rear joint along the axial direction;

[0013] Step 4: vacuum electron beam preheating welding of the front joint and the cylinder, and vacuum electron beam preheating welding of the rear joint and the cylinder;

[0014] Step 5: vacuum electron beam welding of the front joint and the cylinder, and vacuum electron beam welding of the rear joint and the cylinder;

[0015] Step six, performing welding stress relief treatment on the weld between the front joint and the cylinder, and performing welding stress relief treatment on the weld between the rear joint and the cylinder.

[0016] Furthermore, the electron beam welding method for ultra-high strength steel shell also includes:

[0017] Step 7: X-ray inspection;

[0018] Step 8: welding of external parts;

[0019] Step nine, annealing the entire ultra-high strength steel shell including the external components;

[0020] Step 10, inspecting the welds of external components;

[0021] Step 11, performing overall heat treatment on the ultra-high strength steel shell by quenching + tempering;

[0022] Step 12, X-ray detection;

[0023] Step 13: CNC lathe to process the inner hole, inner thread and sealing surface of the front joint, and the inner hole, sealing surface and end face of the rear joint;

[0024] Step 14: Processing center, processing a circle of threaded holes on the end faces of the outer parts and rear joints;

[0025] Step 15: inspect and test the machined dimensions of the ultra-high strength steel shell.

[0026] As a solution, in step one, the cylinder is spin-formed to obtain the outer and inner surfaces, and then the two axial end faces are turned to obtain the length of the cylinder. Then, the front joint is butt-jointed with the first axial end of the cylinder, and the rear joint is butt-jointed with the second axial end of the cylinder, and the inner holes of the front joint and the rear joint are respectively turned.

[0027] As a solution, in step 2, ensure that the magnetic flux of the front joint, front skirt, barrel and rear joint after demagnetization is no more than 2 Gauss.

[0028] As a solution, a cleaning process is also included between step 2 and step 3, and the welding surfaces of the front joint and the cylinder and the welding surfaces of the rear joint and the cylinder are degreased and derusted until the base metal color of the D406A ultra-high strength steel is presented.

[0029] As an option, in step 3, the fixture used includes:

[0030] A mandrel, the mandrel passes through the front joint, the front skirt, the barrel and the rear joint, and the surface of the mandrel is provided with external threads;

[0031] An open retaining ring, which is sleeved on the mandrel and pressed against an end of the front joint away from the weld;

[0032] A positioning assembly, wherein the positioning assembly is sleeved on the core shaft and pressed against the end surface of the front skirt;

[0033] A positioning plate, which is sleeved on the mandrel and pressed against an end of the rear joint away from the weld;

[0034] A clamping nut, two of which are connected to the core shaft, one of which is located close to the end surface of the positioning component away from the front skirt, and the other is located on the end of the positioning plate away from the rear joint;

[0035] A compression spring is placed between the positioning assembly and the compression nut, and the axial ends of the compression spring are respectively close to the positioning assembly and the compression nut.

[0036] Further, the fixture is assembled with the front joint, the front skirt, the barrel and the rear joint in the following order:

[0037] Assemble the front joint on the mandrel;

[0038] Assemble the split retaining ring on the front joint;

[0039] Assemble the cylinder at one end of the front joint;

[0040] Assemble the rear joint at the other end of the cylinder;

[0041] Assemble the positioning plate at one end of the rear joint;

[0042] Assemble a compression spring at the other end of the positioning plate;

[0043] Assemble a compression nut on the mandrel to compress the compression spring;

[0044] Assemble the front skirt at the other end of the front joint;

[0045] Assemble the positioning assembly on the mandrel and press the front skirt;

[0046] Assemble another compression nut on the mandrel to hold the positioning assembly down.

[0047] As a solution,

[0048] In the step 4, the vacuum electron beam preheating welding is surface focusing welding, the welding depth is half of the welding thickness, and one circle is welded. After the welding is paused for a period of time, step 5 is immediately performed;

[0049] In the step 5, the vacuum electron beam welding is surface focusing welding, and its focusing current is larger than the surface focusing current in step 4. The acceleration voltage adopts the maximum value of the electron beam welding machine. The welding beam current satisfies the welding process to completely fuse the process boss stop and weld through. After the welding is paused for a period of time, step 6 is immediately performed;

[0050] In the step six, the welding stress removal treatment is vacuum electron beam surface focusing welding, wherein the focusing current is larger than the surface focusing current, the acceleration voltage adopts the maximum value of the electron beam welding machine, the welding beam current is 8mA to 16mA, and after a pause for a period of time after welding, the vacuum chamber is opened to take out the ultra-high strength steel shell.

[0051] It should be noted that electron beam welding is divided into the following three types in the present invention:

[0052] First, surface focusing: the electron beam focus is adjusted to weld on the workpiece surface;

[0053] Second, focusing on the surface: the electron beam focus is adjusted to weld above the workpiece surface;

[0054] Third, subsurface focusing: the electron beam focus is adjusted to weld below the workpiece surface.

[0055] further,

[0056] In the step 4, the welding speed is 800 mm / min to 1200 mm / min, and the step 5 is immediately performed after the welding is paused for 3 minutes;

[0057] In the step 5, the focusing current is 10mA to 20mA greater than the surface focusing current in the step 4, and the step 6 is immediately performed after the welding is paused for 10 minutes;

[0058] In step six, the focusing current is 15 mA to 30 mA greater than the surface focusing current in step five, and the vacuum chamber is opened after a pause of not less than 30 minutes after welding.

[0059] As an option:

[0060] In step 7, the weld must meet the requirements of GJB1718A-2005 Grade I during X-ray inspection;

[0061] In the step nine, the annealing temperature is 650°C to 700°C, the annealing time is 1h to 2h, and then air cooling;

[0062] In the step 10, the weld of the external component in step 8 is inspected by magnetic particle inspection or X-ray inspection;

[0063] In the step eleven, when the ultra-high strength steel shell is quenched and tempered as a whole, the ultra-high strength steel shell is first heated to 920°C to 940°C, kept warm for 35min to 45min, and then quenched in oil, then kept warm at 290°C to 320°C for 3h to 3.5h, and finally air-cooled;

[0064] In the step 12, the circumferential welds of the front joint, the rear joint and the cylinder are inspected by X-ray, and the welds must meet the requirements of GJB1718A-2005 Level I.

[0065] Compared with the prior art, the welding method of the present invention has a stable welding process, good weld quality and high welding pass rate. The present invention solves the problems of weld dents, assembly misalignment and low welding pass rate in the welding process of ultra-high strength steel shells. The welding method of the present invention is simple, reliable and practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 It is a schematic diagram of the assembly of the ultra-high strength steel housing and the fixture in the present invention;

[0067] Figure 2 for Figure 1 An enlarged view of the process boss stop on the middle and rear joint;

[0068] Figure 3 for Figure 1 A partial enlarged view of the weld between the middle and rear joint and the cylinder;

[0069] Figure 4 for Figure 1 A partial enlarged view of the weld between the middle front joint and the cylinder;

[0070] In the figure: 1—front joint; 2—front skirt; 3—cylinder; 4—rear joint; 5—opening retaining ring; 6—positioning plate; 7—compression spring; 8—compression nut; 9—positioning assembly; 10—core shaft. DETAILED DESCRIPTION

[0071] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but it should not be understood that the scope of the subject matter described in the present invention is limited to the following embodiments. Without departing from the above-mentioned technical ideas of the present invention, various modifications, substitutions and changes made according to the common technical knowledge and customary means in the field are included in the scope of the present invention.

[0072] like Figure 1 As shown, a small solid rocket engine combustion chamber shell is made of D406A ultra-high strength steel (forging heat treatment state: normalizing + high temperature tempering), with a diameter of φ100mm~φ300mm, a wall thickness of 0.5mm~3mm, and a length of no more than 2500mm. The shell is welded by a front joint 1, a barrel 3, and a rear joint 4. The front joint 1, the front skirt 2, and the rear joint 4 are machined by forgings, and the barrel 3 is spun by forgings.

[0073] The present invention designs a vacuum electron beam welding method for an ultra-high-strength steel shell, comprising the following steps: parts processing → demagnetization → laser cleaning → assembly of various parts → preheating welding of shell welds → formal welding of shell welds → stress relief welding (decorative welding) of shell welds → X-ray detection → welding of external parts → annealing → detection → overall heat treatment (quenching + tempering) → X-ray detection → CNC lathe → machining center → inspection.

[0074] After vacuum electron beam welding of the ultra-high strength steel shell, the welded joint meets the requirements of GJB1718A-2005 Level I, the weld is single-sided welded and double-sided formed, the weld is fully welded without depression, the back excess height is not more than 0.4mm, the front excess height is not more than 1.0mm, there are no defects such as undercut, lack of fusion, cracks, etc., the welding test plate passes the mechanical properties test, and the shell passes the water pressure bursting test.

[0075] The vacuum electron beam welding method of the present invention comprises the following main points:

[0076] 1. Requirements for welding groove processing of front joint 1 and rear joint 4: a process boss stop is designed (the designed process boss stop has 3 advantages:

[0077] 1) Ensure that the front weld is convex (not concave) during welding;

[0078] 2) When assembling and docking, the cylinder 3 is hooped to ensure that the error is not greater than 0.1mm and the roundness is not greater than 1.0;

[0079] 3) Mark the surface of the process boss to facilitate alignment of the weld. Figure 2 , the size of the process boss stop: thickness is about 0.4mm~0.5mm, width is 1.2mm~1.8mm.

[0080] 2. The cylinder 3 is formed by spin forming, and the two end faces of the cylinder 3 are flattened on a lathe to the designed length; the outer diameters of both ends of the cylinder 3 are measured (for matching the inner hole sizes of the front joint 1 and the rear joint 4); the front joint 1 and the rear joint 4 are connected to the cylinder 3, and the inner holes are matched according to the measured actual sizes to ensure a single-sided gap of 0.015mm to 0.03mm (that is, the inner hole size of the front joint 1, the rear joint 4 and the cylinder 3 is 0.03mm to 0.06mm larger than the outer circle of the cylinder 3), and can be freely assembled (small gap assembly, because the cylinder 3 is a thin-walled part that is easily deformed, and before assembly, the cylinder 3 assembly position needs to be rounded with a tooling, and then assembled with a small gap with the front joint 1 and the rear joint 4).

[0081] 3. Demagnetize each component to ensure that the magnetic flux is no more than 2 Gauss.

[0082] 4. Laser clean the welds and the inner and outer surfaces of each part to remove oil, rust, etc. until the original color of the metal is revealed. The wall thickness reduction is controlled to be no more than 0.02mm, and the wall thickness after cleaning meets the design requirements.

[0083] 5. Press Figure 1 Assemble the parts and the fixture: assemble the front joint 1 → assemble the open retaining ring 5 → assemble the cylinder 3 → assemble the rear joint 4 → assemble the positioning plate 6 → assemble the clamping spring 7 → assemble the clamping nut 8 → assemble the front skirt 2 → assemble the positioning assembly 9 → assemble another clamping nut 8.

[0084] The clamp is mainly composed of an open retaining ring 5, a positioning plate 6, a clamping spring 7, two clamping nuts 8, a positioning assembly 9 and a mandrel 10. The positioning assembly 9 is a disc with a groove on the end surface, and the groove can accommodate the open retaining ring 5. The surface of the positioning plate 6 has a circle of steps to facilitate positioning with the rear joint 4. Four pins are evenly distributed around the circumference of the clamping nut 8 to facilitate the rotation of the clamping nut 8.

[0085] The advantages of this fixture are: the front joint 1 of the shell and the cylinder 3 will shrink when welding, resulting in a gap between the rear joint 4 and the cylinder 3, because the positioning plate 6 and the Figure 1 A compression spring 7 is installed between the left compression nut 8 (the contact section between the mandrel 10 and the positioning plate 6 is processed as Figure 3The middle structure is to process the positioning cylindrical surface of the mandrel 10 into a hexagonal prism or an octagonal prism, which can reduce the contact area and friction, making it easier for the compression spring 7 to push the positioning plate 6. This is because the inner hole of the positioning plate 6 is a round hole, and the assembly contact part of the mandrel 10 and the positioning plate 6 is a cylindrical surface. The contact surface is large, the friction is large during movement, and it is not easy to slide; after the front joint 1 and the cylinder 3 are welded, the weld shrinkage causes a gap to exist at the joint between the rear joint 4 and the cylinder 3, and welding is impossible. The positioning plate 6 will be given a certain pressure, which will automatically eliminate the gap between the rear joint 4 and the cylinder 3. The three welds (the weld between the front joint 1 and the cylinder 3, the weld between the rear joint 4 and the cylinder 3, and the weld between the front skirt 2 and the front joint 1, all of which are electron beam welded, and the front joint 1 and the front skirt 2 are unimportant welds, and can be welded at the end) can be evacuated at one time and welded in sequence, which can save welding time and improve production efficiency. Furthermore, a little vacuum silicone oil may be applied to the contact surface between the mandrel 10 and the positioning plate 6 to further reduce friction and facilitate movement.

[0086] 6. Preheating welding of the weld between the shell front joint 1 and the cylinder 3: Use surface focus welding, the welding depth is generally half of the welding thickness, welding one circle, welding speed 800mm / min ~ 1200mm / min. After the welding pause for about 3 minutes, the formal welding is immediately carried out.

[0087] 7. Formal welding of the weld between the front joint 1 of the shell and the cylinder 3: Use surface focusing welding (the focusing current is 10mA to 20mA larger than the surface focusing current, which satisfies the welding process to completely fuse the process boss stop and weld through). After the welding is paused for about 10 minutes, stress relief welding is immediately performed.

[0088] 8. Stress relief welding (modification welding) of the weld between the front joint 1 of the shell and the cylinder 3: Use surface focusing welding (focusing current is 15mA~30mA larger than the surface focusing current). After welding, pause for no less than 30 minutes, open the vacuum chamber, disassemble the tooling and remove the product.

[0089] 9. Repeat steps 6, 7 and 8 above to complete the weld between the shell rear joint 4 and the cylinder 3.

[0090] 10. X-ray inspection: The welds between the front joint 1 and the cylinder 3, and the rear joint 4 and the cylinder 3 must meet the requirements of GJB1718A-2005 Level Ⅰ.

[0091] 11. External parts welding: Assemble and weld the external parts except the front joint 1, front skirt 2, rear joint 4 and cylinder 3.

[0092] 12. Annealing: The shell including the external parts is subjected to stress relief annealing at a temperature of 650°C to 700°C for 1h to 2h, followed by air cooling.

[0093] 13. Inspection: The welds of external parts are inspected by magnetic particle inspection or X-ray inspection;

[0094] 14. Overall heat treatment of the shell (quenching + tempering): First, heat the shell to 920℃~940℃, keep it warm for 35min~45min, then quench it in oil, then temper it at 290℃~320℃, keep it warm for 3h~3.5h, and then air cool it.

[0095] 15. X-ray inspection: The girth welds of the front joint 1, rear joint 4 and cylinder 3 must meet the requirements of GJB1718A-2005 Level I;

[0096] 16. CNC lathe: process the front joint 1, the rear joint 4, the inner hole and the outer parts, specifically including CNC lathe processing the inner hole thread and the inner hole sealing surface of the front joint 1, and the positioning inner hole and the sealing surface of the rear joint 4;

[0097] 17. Machining center, process a circle of threaded holes on the end faces of the external parts and rear joint 4;

[0098] 18. Inspection: Check the machined dimensions of the shell.

[0099] The above are the main concepts of the invention, and any electron beam welding method designed according to the concept of the invention falls within the protection scope of the invention.

Claims

1. An electron beam welding method for an ultra-high strength steel shell, wherein the ultra-high strength steel shell comprises a front joint (1), a front skirt (2), a cylinder (3) and a rear joint (4), wherein the first axial end of the cylinder (3) is welded to the front joint (1), and the second axial end is welded to the rear joint (4), and the front skirt (2) is mounted on the end of the front joint (1) away from the cylinder (3), and the materials of the front joint (1), the front skirt (2), the cylinder (3) and the rear joint (4) are all D406A ultra-high strength steel, characterized in that: The following steps are involved: Step 1: respectively processing a front joint (1), a front skirt (2), a barrel (3) and a rear joint (4), wherein one end of the front joint (1) corresponding to the welding position is provided with a circle of process boss stoppers along the circumferential direction, and one end of the rear joint (4) corresponding to the welding position is provided with a circle of process boss stoppers along the circumferential direction, and the surfaces of the two process boss stoppers are both provided with engraved lines for weld alignment; Step 2, demagnetizing the front joint (1), the front skirt (2), the barrel (3) and the rear joint (4); Step 3, assembling the front joint (1), the front skirt (2), the barrel (3) and the rear joint (4) coaxially, and using a clamp to axially compress the front joint (1), the front skirt (2), the barrel (3) and the rear joint (4); Step 4: vacuum electron beam preheating welding of the front joint (1) and the cylinder (3), and vacuum electron beam preheating welding of the rear joint (4) and the cylinder (3); Step 5: vacuum electron beam welding of the front joint (1) and the cylinder (3), and vacuum electron beam welding of the rear joint (4) and the cylinder (3); Step six, performing welding stress relief treatment on the weld between the front joint (1) and the cylinder (3), and performing welding stress relief treatment on the weld between the rear joint (4) and the cylinder (3).

2. The electron beam welding method for ultra-high strength steel shell according to claim 1, characterized in that: Also includes: Step 7: X-ray inspection; Step 8: welding of external parts; Step nine, annealing the entire ultra-high strength steel shell including the external components; Step 10, inspecting the welds of external components; Step 11, performing overall heat treatment on the ultra-high strength steel shell by quenching + tempering; Step 12, X-ray detection; Step 13, CNC lathe, processing the inner hole, inner thread and sealing surface of the front joint (1), and positioning the inner hole, sealing surface and end face of the rear joint (4); Step 14: machining a circle of threaded holes on the end faces of the outer component and the rear joint (4) using a machining center; Step 15: inspect and test the machined dimensions of the ultra-high strength steel shell.

3. The electron beam welding method for ultra-high strength steel shell according to claim 1, characterized in that: In the step 1, the outer and inner surfaces of the cylinder (3) are obtained by spin forming, and then the length of the cylinder (3) is obtained by turning the two axial end faces, and then the front joint (1) is butt-jointed with the first axial end of the cylinder (3), and the rear joint (4) is butt-jointed with the second axial end of the cylinder (3), and the inner holes of the front joint (1) and the rear joint (4) are respectively turned.

4. The electron beam welding method for ultra-high strength steel shell according to claim 1, characterized in that: In the step 2, it is ensured that the magnetic flux of the front joint (1), the front skirt (2), the barrel (3) and the rear joint (4) after the demagnetization treatment is not greater than 2 Gauss.

5. The electron beam welding method for ultra-high strength steel shell according to claim 1, characterized in that: The cleaning process is also included between step 2 and step 3, and the surfaces of the welding points between the front joint (1) and the cylinder (3) and the welding points between the rear joint (4) and the cylinder (3) are degreased and derusted until the base metal color of the D406A ultra-high strength steel is present.

6. The electron beam welding method for ultra-high strength steel shell according to claim 1, characterized in that: In step 3, the fixture used includes: A mandrel (10), wherein the mandrel (10) passes through the front joint (1), the front skirt (2), the barrel (3) and the rear joint (4), and the surface of the mandrel (10) is provided with external threads; An open retaining ring (5), the open retaining ring (5) is sleeved on the core shaft (1) and pressed against an end of the front joint (1) away from the weld; A positioning assembly (9), wherein the positioning assembly (9) is sleeved on the core shaft (1) and pressed against the end surface of the front skirt (2); A positioning plate (6), wherein the positioning plate (6) is sleeved on the core shaft (1) and pressed against an end of the rear joint (4) away from the weld; A clamping nut (8), wherein both clamping nuts (8) are connected to the core shaft (1), one of which is located close to the end surface of the positioning component (9) away from the front skirt (2), and the other clamping nut (8) is located on the end of the positioning plate (6) away from the rear joint (1); A compression spring (7) is placed between the positioning assembly (9) and the compression nut (8), and the axial ends of the compression spring (7) are respectively in close contact with the positioning assembly (9) and the compression nut (8).

7. The electron beam welding method for ultra-high strength steel shell according to claim 6, characterized in that: The fixture and the front joint (1), the front skirt (2), the barrel (3) and the rear joint (4) are assembled in the following order: assembling the front joint (1) on the core shaft (10); Assemble the split retaining ring (5) on the front joint (1); Assembling a cylinder (3) at one end of the front joint (1); Assemble a rear joint (4) at the other end of the cylinder (3); A positioning plate (6) is assembled at one end of the rear joint (4); A compression spring (7) is mounted on the other end of the positioning plate (6); A compression nut (8) is mounted on the core shaft (10) to compress the compression spring (7); Assemble the front skirt (2) at the other end of the front joint (1); Assembling a positioning assembly (9) on the core shaft (10) to press the front skirt (2); Assemble another compression nut (8) on the core shaft (10) to press the positioning assembly (9).

8. The electron beam welding method for ultra-high strength steel shell according to claim 1, characterized in that: In the step 4, the vacuum electron beam preheating welding is surface focusing welding, the welding depth is half of the welding thickness, and one circle is welded. After the welding is paused for a period of time, step 5 is immediately performed; In the step 5, the vacuum electron beam welding is surface focusing welding, and its focusing current is larger than the surface focusing current in step 4. The acceleration voltage adopts the maximum value of the electron beam welding machine. The welding beam current satisfies the welding process to completely fuse the process boss stop and weld through. After the welding is paused for a period of time, step 6 is immediately performed; In the step six, the welding stress removal treatment is vacuum electron beam surface focusing welding, wherein the focusing current is larger than the surface focusing current, the acceleration voltage adopts the maximum value of the electron beam welding machine, the welding beam current is 8mA to 16mA, and after a pause for a period of time after welding, the vacuum chamber is opened to take out the ultra-high strength steel shell.

9. The electron beam welding method for ultra-high strength steel shell according to claim 8, characterized in that: In the step 4, the welding speed is 800 mm / min to 1200 mm / min, and the step 5 is immediately performed after the welding is paused for 3 minutes; In the step 5, the focusing current is 10mA to 20mA greater than the surface focusing current in the step 4, and the step 6 is immediately performed after the welding is paused for 10 minutes; In step six, the focusing current is 15 mA to 30 mA greater than the surface focusing current in step five, and the vacuum chamber is opened after a pause of not less than 30 minutes after welding.

10. The electron beam welding method for ultra-high strength steel shell according to claim 2, characterized in that: In step 7, the weld must meet the requirements of GJB1718A-2005 Grade I during X-ray inspection; In the step nine, the annealing temperature is 650°C to 700°C, the annealing time is 1h to 2h, and then air cooling; In the step 10, the weld of the external component in step 8 is inspected by magnetic particle inspection or X-ray inspection; In the step eleven, when the ultra-high strength steel shell is quenched and tempered as a whole, the ultra-high strength steel shell is first heated to 920°C to 940°C, kept warm for 35min to 45min, and then quenched in oil, then kept warm at 290°C to 320°C for 3h to 3.5h, and finally air-cooled; In the step 12, the circumferential welds between the front joint (1), the rear joint (4) and the cylinder (3) are inspected by X-ray, and the welds must meet the requirements of GJB1718A-2005 Level I.

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