External spinning machining method for cylindrical part with inner step

Abstract

The invention discloses an external spinning machining method for a cylindrical part with an inner step, and belongs to the field of spinning machining forming. The method comprises the following steps: designing a special spinning core mold with an inward concave step, designing a spinning blank which is matched with the spinning core mold and is provided with an inward convex step, and designing a tail top for fixing the spinning blank. Outer spinning machining of the cylindrical part with the inner step is achieved through a series of technological methods of blank selection and heat treatment of a spinning blank, machining of the spinning blank, spinning of a core mold and a tail top, clamping of the spinning blank on spinning equipment, spinning machining of a straight barrel section of a barrel, heat treatment annealing after spinning, turning of the outer diameter of the inner step section of the barrel and removal of a material head. The problems that in an existing outer spinning machining method for the cylindrical part with the inner step, an inner step section and a straight barrel section need to serve as independent parts to be machined and then welded, so that weld joints are increased, the machining efficiency is low, and the quality is difficult to guarantee are solved.

Description

Technical Field

[0001] The invention belongs to the field of spinning forming, and in particular relates to an external spinning method for a cylindrical part with an inner step. Background Art

[0002] The combustion chamber casing of a solid rocket engine is usually composed of a front connecting piece 1, a barrel 3, and a rear connecting piece 4. Figure 1 The barrel 3 is a thin-walled spinning part, which is generally made of ultra-high strength steel and is formed by strong spinning; the front and rear connecting parts are generally machined and then connected by welding.

[0003] For the spinning process of the barrel 3, external spinning equipment is generally used. If the barrel has an inner step, when using external spinning equipment for processing, since the inner step is difficult to support, the inner platform stage 32 and the straight barrel section 31 of the barrel 3 are usually divided into two parts for separate processing, and then the two are connected by welding or other methods. This method will increase the number of welds of the barrel 3, so that there is a weld 2 on each side of the inner platform stage 32 of the barrel. Especially for the combustion chamber shell with multiple inner steps on the barrel part, each additional inner platform stage 32 will increase two welds, resulting in increased difficulty in welding the combustion chamber shell, increased processing cycle and cost, and at the same time, it will make the shell coaxiality difficult to control and increase the difficulty of later heat treatment.

[0004] In order to avoid the increase of welds, the barrel can be spun by using a dedicated internal spinning equipment, but due to the strong specialization of internal spinning equipment, the equipment is expensive and rare, the cost of use is high, and it is difficult to promote its use. Therefore, it is worth studying how to use a highly versatile external spinning equipment to achieve external spinning of cylindrical parts with inner steps. Summary of the invention

[0005] Technical issues to be solved:

[0006] In order to avoid the shortcomings of the prior art, the present invention provides a method for external spinning of cylindrical parts with inner steps. By designing a special spinning core mold with an inner concave step, a spinning blank with an inner convex step matching the spinning core mold is designed, and corresponding process methods are used to achieve external spinning of cylindrical parts with inner steps, thereby solving the problem of increased welds caused by the need to process the inner platform stage and the straight cylinder section as separate parts and then weld them in the existing external spinning method of cylindrical parts with inner steps.

[0007] The technical solution of the present invention is: a method for external spinning of a cylindrical part with an inner step, comprising the following steps:

[0008] Step 1. According to the size of the finished cylindrical part with inner platform, design a spinning core mold with an inner concave step, design a spinning blank with an inner convex step matching the spinning core mold, and design a special tail top according to the spinning core mold and the spinning blank;

[0009] The spinning core mold is a stepped shaft, which is provided with a core mold installation section, a core mold straight section and a core mold inner stage in sequence;

[0010] The spinning blank is a cylindrical part, which is provided with a straight barrel section, a barrel inner platform section and a barrel tail top section in sequence;

[0011] Step 2. Softening and heat treating the spun blank;

[0012] Step 3. Process the blank after heat treatment in step 2 to obtain the spinning blank designed in step 1; process the spinning core mold and tail top designed in step 1;

[0013] Step 4. Assemble the spinning core mold, the spinning blank and the tail top on the external spinning equipment; put the straight section of the cylinder on the straight section of the core mold, the inner platform stage of the cylinder cooperates with the inner platform stage of the core mold, and the inner end surface of the tail top section of the cylinder abuts against the outer end surface of the inner platform stage of the core mold; fix the spinning blank by tightening the outer end of the inner platform stage of the core mold and the outer end surface of the tail top section of the cylinder;

[0014] Step 5. Use the forward spinning method to spin the straight section of the cylinder to the finished size of the section, without spinning the inner platform stage of the cylinder and the tail top section of the cylinder, to obtain the spinning semi-finished product;

[0015] Step 6. heat treatment and annealing of the spinning semi-finished product;

[0016] Step 7. For the spun semi-finished product annealed in step 6, the outer diameter of the inner step of the cylinder is turned to make it flush with the outer diameter of the straight cylinder section after spinning in step 5, and the tail top section of the cylinder and the process head away from the end of the tail top section are turned away to obtain a finished cylindrical part with an inner step.

[0017] A further technical solution of the present invention is: the core mold installation section is designed in conjunction with the external spinning equipment and is used to install the spinning core mold; the diameter of the core mold straight section is 0.1 to 0.2 mm smaller than the inner diameter of the straight section of the finished cylindrical part, and the axial length of the core mold straight section is 200 to 300 mm longer than the length of the straight section of the finished cylindrical part; the diameter of the core mold inner step is smaller than the inner diameter of the inner step of the finished cylindrical part, and the axial length of the core mold inner step is 20 to 30 mm longer than the length of the inner step of the finished cylindrical part.

[0018] A further technical solution of the present invention is that an inner concave hole is provided at the center position of the outer end surface of the inner platform stage of the core mold along the axial direction of the spinning core mold for coaxial docking with the tail top.

[0019] A further technical solution of the present invention is: the inner diameter of the straight section of the cylinder is 0.1 to 0.2 mm larger than the diameter of the straight section of the core mold, the outer diameter of the straight section of the cylinder is calculated based on the thickness of the straight section of the finished cylindrical part and the spinning thinning rate, and the axial length of the straight section of the cylinder is calculated based on its thickness before spinning, the spinning thinning rate and the length of the straight section of the finished cylindrical part; the step profile and size of the inner platform stage of the cylinder are consistent with the inner step of the finished cylindrical part, and a 10 mm straight section is added on both sides of the step of the inner platform stage of the cylinder for transition to both sides; the outer diameter of the inner platform stage of the cylinder is 2 to 3 mm larger than the outer diameter of the finished cylindrical part, and transitions with a 20° slope to the outer diameter of the straight section of the cylinder; the outer diameter of the tail top section of the cylinder is the same as the outer diameter of the inner platform stage of the cylinder, its inner diameter is 20 to 30 mm smaller than the diameter of the inner platform stage of the core mold, and its axial length is 10 mm.

[0020] A further technical solution of the present invention is: in the step 3, the spun blank is an integrated structure or a split welded combined structure; the integrated structure is: the blank processed in step 2 is turned into a straight barrel section, a barrel inner platform stage and a barrel tail top section; the split welded combined structure is: the blank processed in step 2 is turned into a straight barrel section and a barrel inner platform stage, and the barrel tail top section uses a separate annular sheet material and is welded and fixed to the barrel inner platform stage.

[0021] A further technical solution of the present invention is: one end of the tail top is a working end, used to tighten the spinning core mold and the spinning blank, and the other end is a clamping end, used to be installed and connected with the external spinning equipment; the working end of the tail top is a stepped shaft, the center of which is provided with an outwardly protruding boss, and the boss and the peripheral edge form a step surface; the boss is embedded in the inner concave hole at the outer end of the inner stage of the core mold, and the end face of the boss is in surface contact with the bottom surface of the inner concave hole; the step surface is against the outer end face of the tail top section of the cylinder.

[0022] A further technical solution of the present invention is: the blank of the spinning blank in step 2 is a tube material or a forged cylindrical blank.

[0023] A further technical solution of the present invention is: the softening heat treatment in step 2 is spheroidizing annealing, and the spheroidizing annealing temperature is determined according to the material of the spun blank.

[0024] Beneficial Effects

[0025] The beneficial effects of the present invention are as follows: the present invention provides an external spinning processing method for a cylindrical part with an inner step. According to the structural dimensions of the product, a spinning core mold and a spinning blank with an inner step are designed, and a special tail top is designed. The spinning core mold is clamped on a universal external spinning device, and the spinning blank is coaxially mounted on the spinning core mold, and the inner steps of the two are assembled correspondingly. The spinning blank is fixed by a special tail top, and the straight barrel section of the barrel of the spinning blank can be spun. Since the inner step consistent with the product has been pre-processed in the spinning blank, it is only necessary to turn the outer diameter of the inner platform stage of the barrel to the outer diameter of the straight barrel section of the barrel after spinning to complete the inner platform stage of the barrel. For the tail top section of the barrel used as a clamp, it plays a role in fixing the spinning blank during the spinning process. It can be turned off when processing the outer diameter of the inner platform stage of the barrel, and the process head at the other end can be turned at the same time to ensure the axial length of the product.

[0026] This method processes the cylindrical parts with inner steps that need to be spun as an integral structure. Compared with the prior art process of processing the straight barrel section and the inner platform section as independent parts and then welding and assembling them, it reduces the number of welds. It is used for spinning of straight barrels with inner steps such as solid rocket engine casings, which can effectively reduce the number of casing welds, improve the processing efficiency of the casing, and greatly improve the overall coaxiality quality. It is also suitable for spinning of cylindrical parts with inner steps such as alloy structural steel and ultra-high strength steel in the fields of aviation, aerospace, and petroleum. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the structure of the combustion chamber shell of a solid rocket motor;

[0028] Figure 2 The process flow chart of the present invention is as follows;

[0029] Figure 3 Schematic diagram of the spinning process of the process method of the present invention;

[0030] Figure 4 It is a schematic diagram of the spinning core mold structure;

[0031] Figure 5 It is a schematic diagram of the spinning blank structure;

[0032] Figure 6 It is a schematic diagram of the finished structure of a cylindrical part with an inner step after the spinning blank is processed;

[0033] Figure 7 Schematic diagram of the combustion chamber casing structure of a solid rocket engine processed by the process method of the present invention in an embodiment.

[0034] Explanation of the accompanying drawings: 1. front connecting part, 2. weld, 3. cylinder, 31. straight section, 32. inner platform stage, 4. rear connecting part, 5. spinning core mold, 51. core mold installation section, 52. core mold straight section, 53. core mold inner platform stage, 531. inner concave hole, 6. spinning blank, 61. cylinder straight section, 62. cylinder inner platform stage, 63. cylinder tail top section, 7. tail top, 71. boss, 72. step surface, 8. rotating wheel, 9. finished cylindrical part with inner step, 91. finished cylindrical part straight section, 92. finished cylindrical part inner step, V. indicates the spinning direction. DETAILED DESCRIPTION

[0035] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0037] This embodiment uses processing Figure 7 Taking the cylinder part of the combustion chamber shell of a solid rocket engine as an example, the external spinning processing method of the cylindrical part with inner step according to the present invention is described in detail. Figure 7 As shown in the middle cylinder part, due to the presence of three inner steps in the cylinder, the cylinder needs to be divided into four straight sections and three inner steps for independent processing and welding. There will be welds on both sides of the inner steps, and there will be six welds in the cylinder part alone (excluding the welds of the front and rear connectors at both ends of the welding). By adopting the processing method of the present invention, the cylinder can be divided into four sections, of which three sections are cylindrical parts with inner steps and one section is a straight section. After the cylinder is welded, there are only three welds, which reduces the number of welds, improves the processing efficiency of the shell, and ensures the overall coaxiality requirements of the shell.

[0038] The following processing Figure 7 The external spinning method of the present invention is introduced by taking a cylindrical part with an inner step as an example. The process flow chart is as follows Figure 2The product information of the finished cylindrical part 9 with inner step is as follows: the material is D406A ultra-high strength steel, the thin wall size of the straight part, i.e. the finished straight section 91 of the cylindrical part, is φ500×t3mm (outer diameter×wall thickness), and the length of the finished straight section 91 of the cylindrical part is 500mm.

[0039] Step 1. Design the spinning core mold 5, the spinning blank 6 and the tail top 7 according to the size of the finished cylindrical part 9 with an inner platform.

[0040] Specifically, Figure 4 As shown, the spinning core mold 5 is a concentric stepped shaft, which is provided with a core mold installation section 51, a core mold straight section 52 and a core mold inner stage 53 from left to right. The size of the core mold installation section 51 is designed to match the external spinning equipment and is used to install the spinning core mold 5.

[0041] The diameter of the core mold straight section 52 is 0.1 to 0.2 mm smaller than the inner diameter of the finished straight section 91 of the cylindrical part. In this embodiment, the diameter of the core mold straight section 52 is φ493.8 mm. The axial length of the core mold straight section 52 is 200 to 300 mm longer than the length of the finished straight section 91 of the cylindrical part to ensure the spinning stroke. In this embodiment, the dimension is 300 mm.

[0042] The diameter of the core mold inner platform stage 53 is smaller than the inner diameter of the inner step 92 of the finished cylindrical part, and the axial length of the core mold inner platform stage 53 is 20 to 30 mm longer than the length of the inner step 92 of the finished cylindrical part, ensuring that there is no interference between the two during assembly. In this embodiment, the axial length of the core mold inner platform stage 53 is 20 mm longer than the length of the inner step of the finished cylindrical part. An inner concave hole 531 is provided at the center position of the outer end surface of the core mold inner platform stage 53 along the axial direction of the spinning core mold, which is used to coaxially dock with the top end of the tail top 7.

[0043] like Figure 5 As shown, the spun blank 6 is a cylindrical part, which is provided with a straight barrel section 61, a barrel inner platform section 62 and a barrel tail top section 63 from left to right.

[0044] The inner diameter of the cylinder straight section 61 is 0.1-0.2 mm larger than the diameter of the core mold straight section 52. In this embodiment, the inner diameter of the cylinder straight section 61 is φ494 mm. The outer diameter of the cylinder straight section 61 is calculated based on the thickness of the finished straight section 91 of the cylindrical part and the spinning thinning rate. The calculation formula for the outer diameter of the cylinder straight section 61 is:

[0045]

[0046] Wherein: D is the outer diameter of the straight section 61 of the cylinder, d is the inner diameter of the straight section 61 of the cylinder, which is φ494mm; t is the thickness of the straight section 91 of the finished cylindrical part, which is 3mm; and f is the thinning rate.

[0047] In this embodiment, the thinning rate f is determined to be 75% based on the material, process route and spinning equipment, and the outer diameter of the straight barrel section 61 is calculated to be φ518 mm according to formula (1).

[0048] The axial length of the straight section 61 of the cylinder is calculated based on its thickness before spinning, the spinning thinning rate and the length of the straight section 91 of the finished cylindrical part. The specific calculation method is:

[0049]

[0050] Wherein: L is the length of the straight section 61 of the cylinder; t is the thickness of the finished straight section 91 of the cylinder, which is 3 mm; l is the length of the finished straight section 91 of the cylinder, which is 500 mm; D is the outer diameter of the straight section 61 of the cylinder, which is φ518 mm; d is the inner diameter of the straight section 61 of the cylinder, which is φ494 mm; e is the process margin, which is 200 mm in this embodiment, and the excess process margin will be removed as material head in the final processing step. According to formula (2), the length of the straight section 61 of the cylinder is calculated to be 175 mm.

[0051] The step profile and size of the inner step of the cylinder inner platform stage 62 are consistent with the inner step of the finished cylindrical part. A 10 mm straight section is added on both sides of the step of the inner step of the cylinder inner platform stage 62 for transition to both sides.

[0052] The outer diameter of the inner platform stage 62 of the cylinder is 2 to 3 mm larger than the outer diameter of the finished cylindrical part 9. In this embodiment, the outer diameter of the inner platform stage 62 of the cylinder is φ502 mm. The outer diameter of the inner platform stage 62 of the cylinder forms a 20° slope transition with the outer diameter of the straight barrel section 61 of the cylinder, which is convenient for subsequent processing.

[0053] The outer diameter of the cylinder tail top section 63 is the same as the outer diameter of the cylinder inner platform stage 62, and its inner diameter is 20 to 30 mm smaller than the diameter of the core mold inner platform stage 53. Its axial length is 10 mm. In this embodiment, the inner diameter of the cylinder tail top section 63 is 30 mm smaller than the diameter of the core mold inner platform stage 53, and is used to be stuck on the outer end surface of the core mold inner platform stage 53.

[0054] The tail top 7 is used to fix the spinning blank 6, and its top size is designed to match the spinning core mold 5 and the spinning blank 6. One end of the tail top 7 is the working end, which is used as the top to tighten the spinning core mold 5 and the spinning blank 6; the other end is the clamping end, which is used to be installed and connected with the external spinning equipment. The top of the tail top 7 is a stepped shaft, and a cylindrical boss 71 is provided in the center thereof, which protrudes outward along its axis. The boss 71 and the peripheral edge of the end of the tail top 7 form a stepped surface 72.

[0055] The design of the spinning core mold 5, the spinning blank 6 and the tail top 7 satisfies the following matching relationship during subsequent spinning: the spinning blank 6 is coaxially mounted on the spinning core mold 5, the inner platform stage 62 of the cylinder body of the spinning blank 6 cooperates with the inner platform stage 53 of the core mold of the spinning core mold 5, the tail top section 63 of the cylinder body of the spinning blank 6 is stuck on the outer end surface of the inner platform stage 53 of the core mold, and the inner wall of the tail top section 63 of the cylinder body contacts the outer end surface of the inner platform stage 53 of the core mold. The boss 71 at the top of the tail top 7 is embedded in the inner concave hole 531 at the outer end of the inner platform stage 53 of the core mold, and the end surface of the boss 71 contacts the bottom surface of the inner concave hole 531. At the same time, the step surface 72 abuts against the outer end surface of the tail top section 63 of the cylinder body, and the tail top section 63 of the cylinder body is sandwiched between the spinning core mold 5 and the tail top 7 to fix the position of the spinning blank 6.

[0056] Step 2. Selection of the blank of the spun blank 6 and pretreatment before machining. The blank can be directly cut from a pipe or a cylindrical material formed by forging. In this embodiment, D406A seamless steel pipe is used as the blank for processing the spun blank 6.

[0057] The selected billet is subjected to spheroidizing annealing: the billet is placed in a heating furnace, heated to 860°C±10°C for 4 hours, then reduced to 720°C±10°C for 6 hours, then cooled to below 600°C and air-cooled.

[0058] Step 3. Process the blank after heat treatment in step 2 to obtain the spinning blank 6 designed in step 1. And process the spinning core mold 5 and tail top 7 designed in step 1.

[0059] The blank is processed by CNC turning to integrally process the straight barrel section 61, the inner platform section 62 and the tail top section 63 of the spun blank 6, so that the wall thickness of the straight barrel section 61 is 12 mm, and the wall thickness difference is ensured to be no greater than 0.08 mm.

[0060] In another embodiment of the present invention, the barrel tail top section 63 of the spun blank 6 is realized by welding and splicing, that is, the blank after heat treatment in step 2 is turned to only process the barrel straight barrel section 61 and the barrel inner platform stage 62 of the spun blank 6, and the barrel tail top section 63 adopts an annular bottom plate of corresponding size, which is coaxially welded and fixed to the barrel inner platform stage 62 by welding.

[0061] Step 4. Assemble the spinning core mold 5, the spinning blank 6 and the tail top 7 on the external spinning equipment.

[0062] like Figure 3As shown, the spinning core mold 5 is placed horizontally, and its core mold installation section 51 is installed on the external spinning equipment. The spinning blank 6 is coaxially mounted on the spinning core mold 5, so that the straight barrel section 61 of the cylinder is mounted on the straight barrel section 52 of the core mold, the inner platform stage 62 of the cylinder cooperates with the inner platform stage 53 of the core mold, and the inner end surface of the tail top section 63 of the cylinder contacts the outer end surface of the inner platform stage 53 of the core mold, and the outer end surface of the tail top section 63 of the cylinder is pressed against the outer end of the inner platform stage 53 of the core mold and the outer end surface of the tail top section 63 of the cylinder to fix the spinning blank 6.

[0063] Step 5: Spin the straight barrel section 61 of the spun blank 6.

[0064] Use three-wheel CNC high-power spinning machine, the wheel has 8 edges Figure 3 The wall thickness of the straight barrel section 61 of the barrel is 12 mm and spun to 3 mm ± 0.10 mm. In this process, only the straight barrel section 61 of the barrel is spun, and the inner platform section 62 of the barrel and the tail top section 63 of the barrel are not spun. Therefore, the inner platform section 62 of the barrel is avoided during spinning. After step 5 is completed, a spinning semi-finished product is obtained.

[0065] Step 6. Heat treatment annealing of the semi-finished spinning product. Annealing temperature and time requirements: 400℃±10℃ for 240min.

[0066] Step 7. Turn the outer diameter of the inner platform section 62 of the spinning semi-finished product after annealing in step 6 to make it flush with the outer diameter of the straight barrel section after spinning, and turn and remove the barrel tail top section 63 and the process head away from the end of the barrel tail top section 63 to obtain Figure 6 The cylindrical part finished product 9 with inner step is shown. When turning the process material head, the axial length of the straight tube section 91 of the cylindrical part finished product should be ensured.

[0067] Processing Figure 7 When manufacturing the combustion chamber casing of the solid rocket engine shown in the figure, the three finished cylindrical parts 9 and a section of straight cylinder processed by the above steps are coaxially welded in sequence to form a total of three welds 2, and the front connecting parts 1 and the rear connecting parts 4 are welded correspondingly at both ends, so that the entire combustion chamber casing has only five welds 2, which reduces the number of welds, improves the casing processing efficiency, effectively guarantees the coaxiality requirements of the overall welding of the casing, and is also conducive to reducing the difficulty of the later heat treatment of the casing.

[0068] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for external spinning of a cylindrical part with an inner step, characterized in that: The following steps are involved: Step 1. According to the size of the finished cylindrical part with inner platform, design a spinning core mold with an inner concave step, design a spinning blank with an inner convex step matching the spinning core mold, and design a special tail top according to the spinning core mold and the spinning blank; The spinning core mold is a stepped shaft, which is provided with a core mold installation section, a core mold straight section and a core mold inner stage in sequence; The spinning blank is a cylindrical part, which is provided with a straight barrel section, a barrel inner platform section and a barrel tail top section in sequence; Step 2. Softening and heat treating the spun blank; Step 3. Process the blank after heat treatment in step 2 to obtain the spinning blank designed in step 1; process the spinning core mold and tail top designed in step 1; Step 4. Assemble the spinning core mold, spinning blank and tail top on the external spinning equipment; The straight section of the cylinder is put on the straight section of the core mold, the inner platform stage of the cylinder cooperates with the inner platform stage of the core mold, and the inner end surface of the tail top section of the cylinder abuts against the outer end surface of the inner platform stage of the core mold; the tail top is pressed against the outer end of the inner platform stage of the core mold and the outer end surface of the tail top section of the cylinder to fix the spinning blank; Step 5. Use the forward spinning method to spin the straight section of the cylinder to the finished size of the section, without spinning the inner platform stage of the cylinder and the tail top section of the cylinder, to obtain the spinning semi-finished product; Step 6. heat treatment and annealing of the spinning semi-finished product; Step 7. For the spun semi-finished product annealed in step 6, the outer diameter of the inner step of the cylinder is turned to make it flush with the outer diameter of the straight cylinder section after spinning in step 5, and the tail top section of the cylinder and the process head away from the end of the tail top section are turned away to obtain a finished cylindrical part with an inner step.

2. The method according to claim 1, characterized in that The core mold installation section is designed in conjunction with the external spinning equipment and is used to install the spinning core mold; the diameter of the core mold straight section is 0.1 to 0.2 mm smaller than the inner diameter of the straight section of the finished cylindrical part, and the axial length of the core mold straight section is 200 to 300 mm longer than the length of the straight section of the finished cylindrical part; the diameter of the core mold inner step is smaller than the inner diameter of the inner step of the finished cylindrical part, and the axial length of the core mold inner step is 20 to 30 mm longer than the length of the inner step of the finished cylindrical part.

3. The method according to claim 2, characterized in that An inner concave hole is arranged at the center position of the outer end surface of the inner platform stage of the core mold along the axial direction of the spinning core mold for coaxial docking with the tail top.

4. The method according to claim 3, characterized in that The inner diameter of the straight section of the cylinder is 0.1 to 0.2 mm larger than the diameter of the straight section of the core mold, the outer diameter of the straight section of the cylinder is calculated based on the thickness of the straight section of the finished cylindrical part and the spinning thinning rate, and the axial length of the straight section of the cylinder is calculated based on its thickness before spinning, the spinning thinning rate and the length of the straight section of the finished cylindrical part; the step profile and size of the inner platform stage of the cylinder are consistent with the inner step of the finished cylindrical part, and a 10 mm straight section is added on both sides of the step of the inner platform stage of the cylinder for transition to both sides; the outer diameter of the inner platform stage of the cylinder is 2 to 3 mm larger than the outer diameter of the finished cylindrical part, and transitions with a 20° slope to the outer diameter of the straight section of the cylinder; the outer diameter of the tail top section of the cylinder is the same as the outer diameter of the inner platform stage of the cylinder, its inner diameter is 20 to 30 mm smaller than the diameter of the inner platform stage of the core mold, and its axial length is 10 mm.

5. The method according to claim 4, characterized in that In the step 3, the spun blank is an integrated structure or a split welded combined structure; the integrated structure is: the blank processed in step 2 is turned into a straight barrel section, a barrel inner platform stage and a barrel tail top section; the split welded combined structure is: the blank processed in step 2 is turned into a straight barrel section and a barrel inner platform stage, and the barrel tail top section uses a separate annular sheet material and is welded and fixed to the barrel inner platform stage.

6. The method according to claim 5, characterized in that One end of the tail top is the working end, which is used to tighten the spinning core mold and the spinning blank, and the other end is the clamping end, which is used to be installed and connected with the external spinning equipment; the working end of the tail top is a stepped shaft, and an outwardly protruding boss is provided at the center, and the boss and the peripheral edge form a step surface; the boss is embedded in the inner concave hole at the outer end of the inner stage of the core mold, and the end face of the boss is in surface contact with the bottom face of the inner concave hole; the step surface is against the outer end face of the tail top section of the cylinder.

7. The method according to claim 1, characterized in that The blank of the spinning blank in step 2 is selected from a tube material or a forged cylindrical blank.

8. The method according to claim 1, characterized in that The softening heat treatment in step 2 is spheroidizing annealing, and the spheroidizing annealing temperature is determined according to the material of the spun blank.

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