Spinning forming method for outer wall of expansion section of liquid rocket engine

Abstract

The invention relates to the technical field of rocket engine expansion section outer walls, in particular to a liquid rocket engine expansion section outer wall spinning forming method. A spinning forming method for the outer wall of an expansion section of a liquid rocket engine comprises the following steps that S1, a stainless steel plate is cut, and a round blank is obtained; s2, carrying out primary heat treatment on the blank; s3, primary spinning is conducted on the blank subjected to primary heat treatment; s4, carrying out secondary heat treatment on the blank subjected to primary spinning; s5, secondary spinning is conducted on the blank subjected to secondary heat treatment, and a formed blank is obtained; s6, spinning finishing is conducted on the formed blank; and S7, the finished formed blank is subjected to solution treatment, and the outer wall of the expansion section of the liquid rocket engine is obtained. The outer wall of the expansion section of the liquid rocket engine is prepared through spinning forming, the material utilization rate is higher, and through cooperation of heat treatment and the spinning technology, work hardening in the spinning forming process can be reduced, anisotropy is eliminated, the high-temperature strength is improved, and the fatigue life is prolonged.

Description

Technical Field

[0001] This invention relates to the field of rocket engine expansion section outer wall preparation technology, specifically to a method for spin forming of the outer wall of a liquid rocket engine expansion section. Background Technology

[0002] The outer wall of the expansion section in a liquid rocket engine is a critical component of the engine nozzle. Its structure is typically a thin-walled cone, and it must operate under high temperature, high pressure, and severe vibration environments. Therefore, the material must possess excellent strength, heat resistance, and fatigue resistance. Currently, stainless steel (such as 304 and 316) is a commonly used material for the outer wall of the expansion section due to its excellent overall performance.

[0003] However, the outer wall of traditional stainless steel expansion sections is mainly formed by forging. Forging requires a large machining allowance (usually 50% to 70%), which leads to a large amount of material being wasted by cutting, resulting in high costs and low material utilization. Furthermore, forging requires multiple heating and forging processes, followed by extensive machining, resulting in a long production cycle and difficulty in meeting the needs of mass production. Secondly, the complex metal flow during forging can easily lead to problems such as coarse grains and anisotropy, affecting the mechanical properties and fatigue life of the components. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for spinning the outer wall of the expansion section of a liquid rocket engine.

[0005] The technical solution of this invention is: a method for spin forming the outer wall of the expansion section of a liquid rocket engine, comprising the following steps:

[0006] S1. Cut the stainless steel sheet to obtain a circular blank;

[0007] S2. Perform a heat treatment on the billet. The heat treatment method is as follows: hold the billet at 1020-1040℃ for 1-2 hours, and then cool it rapidly.

[0008] S3. Perform a first spinning on the billet after heat treatment to obtain a first-spun billet. The first spinning is performed in the forward direction, the heating temperature is 650~750℃, the rotation speed is 20~40rpm, the feed ratio is 10~20mm / min, the thinning rate is 30~40%, and the spinning thrust is 300-600kN.

[0009] S4. Perform a second heat treatment on the blank after one spinning. The second heat treatment method is to keep the blank after one spinning at 1020~1040℃ for 1~2h, and then cool it rapidly.

[0010] S5. Perform secondary spinning on the blank after secondary heat treatment to obtain the shaped blank. The secondary spinning is performed in reverse spinning. The heating temperature is 650-750℃, the rotation speed is 20-40rpm, the feed ratio is 20-40mm / min, the thinning rate is 40-60%, and the spinning thrust is 400-800kN.

[0011] S6. Spin finishing is performed on the formed blank to obtain the finished formed blank. The heating temperature during spin finishing is 650~750℃, the rotation speed is 20~40rpm, the feed ratio is 100~150mm / min, the thinning rate is ≤5%, and the spin thrust is 300-500kN.

[0012] S7. The finished blank is subjected to solution treatment to obtain the outer wall of the expansion section of the liquid rocket engine.

[0013] Note: This application describes the preparation of the outer wall of the expansion section of a liquid rocket engine by spin forming, which has a higher material utilization rate than the forging method. Furthermore, the combination of heat treatment and spin forming can effectively improve the microstructure and properties of the outer wall of the expansion section of the liquid rocket engine, reduce work hardening during spin forming, eliminate anisotropy, and enhance high-temperature strength and fatigue life.

[0014] Furthermore, during the first spinning, second spinning, and spinning finishing processes, the radius of the rotary wheel fillet is R38 to R42 mm.

[0015] Note: Limiting the radius of the rotary wheel's fillet ensures the contact area and prevents stress concentration from causing localized cracking.

[0016] Furthermore, the solution treatment method is as follows: the finished molded blank is kept at 1050-1150℃ for 1-2 hours, and then cooled to room temperature with water.

[0017] Note: Solution treatment can homogenize the microstructure, prevent segregation within the stainless steel, and ensure its corrosion resistance.

[0018] Furthermore, the first spinning, second spinning, and spinning finishing processes each involve 1 to 2 passes.

[0019] Note: Limiting the number of spinning cuts ensures production efficiency while maintaining the surface quality of the outer wall of the expansion section of the liquid rocket engine.

[0020] Furthermore, the cooling rate during the first heat treatment is 60-80℃ / s, and the cooling rate during the second heat treatment is 100-120℃ / s.

[0021] Note: Limiting the cooling rate during primary and secondary heat treatments can improve the plastic deformation properties of the billet and prevent work hardening.

[0022] Furthermore, during the primary spinning, secondary spinning, and spinning finishing processes, an emulsion is sprayed onto the surface of the billet, and the spraying rate Q of the emulsion conforms to the following relationship:

[0023]

[0024] Where Q is the spraying rate of the emulsion, retained to two decimal places, in L / s; k is a coefficient, with a value of 4 to 6; V is the cooling rate during the previous heat treatment, in ℃ / s; T2 is the temperature during the previous heat treatment, in ℃; T1 is the heating temperature during this spinning, in ℃; and ρ is the mass concentration of the emulsion, in g / L.

[0025] Note: Emulsion can reduce resistance during spinning. The spraying rate of emulsion can be adjusted by heat treatment parameters to avoid the billet temperature dropping too quickly during spinning, which would lead to poor plastic deformation performance. This ensures the surface quality and microstructure of the billet, and gives the outer wall of the expansion section of the prepared liquid rocket engine good strength and fatigue resistance.

[0026] Furthermore, during the spinning finishing process, an emulsion is sprayed onto the surface of the formed blank to ensure that the surface temperature of the formed blank is ≤250℃.

[0027] Note: Spraying emulsion during spinning finishing can reduce the surface temperature of the formed blank, preventing grain growth and increased dimensional deviations due to excessively high temperatures.

[0028] Furthermore, the emulsion is prepared by mixing 10-20g of base liquid with 1L of water. The base liquid, by weight, includes the following components: 30-40 parts of paraffin oil, 10-15 parts of sulfurized castor oil, 10-20 parts of sodium dodecylbenzenesulfonate, 5-10 parts of borate ester, 3-6 parts of polysiloxane, 1-5 parts of triethanolamine, and 6-12 parts of sorbitan monooleate.

[0029] Note: The above emulsion has good lubrication properties, which can effectively reduce the deformation resistance during the spinning process, and at the same time reduce the surface temperature of the blank, thus preventing the surface temperature of the blank from rising rapidly during the spinning process.

[0030] The beneficial effects of this invention are:

[0031] (1) The present invention prepares the outer wall of the expansion section of the liquid rocket engine by spinning, which has a higher material utilization rate than the forging method. Furthermore, by combining heat treatment with spinning process, the microstructure and properties of the outer wall of the expansion section of the liquid rocket engine can be effectively improved, the work hardening during spinning process can be reduced, anisotropy can be eliminated, and high-temperature strength and fatigue life can be enhanced.

[0032] (2) The present invention can reduce the resistance during spinning by using emulsion. The spraying rate of emulsion can be adjusted by heat treatment parameters to avoid the billet temperature dropping too quickly during spinning, which would lead to poor plastic deformation performance. This ensures the surface quality and microstructure of the billet, so that the outer wall of the expansion section of the prepared liquid rocket engine has good strength and fatigue resistance. Attached Figure Description

[0033] Figure 1 This is a cross-sectional view of the outer wall of the expansion section of the liquid rocket engine of the present invention. Detailed Implementation

[0034] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0035] Example 1: A method for spinning the outer wall of the expansion section of a liquid rocket engine, comprising the following steps:

[0036] S1. Cut the stainless steel sheet to obtain a circular blank; the diameter of the circular blank is 800mm and the thickness is 40mm.

[0037] S2. Perform a heat treatment on the billet. The heat treatment method is as follows: hold the billet at 1030℃ for 1.5h, and then cool it rapidly.

[0038] S3. Perform a first spinning on the billet after heat treatment to obtain a first-spun billet. The first spinning is performed in the forward direction, the heating temperature is 700℃, the rotation speed is 30rpm, the feed ratio is 15mm / min, the thinning rate is 35%, and the spinning thrust is 450kN.

[0039] S4. Perform a second heat treatment on the blank after one spinning. The second heat treatment method is to keep the blank after one spinning at 1030℃ for 1.5h and then cool it rapidly.

[0040] S5. The blank after secondary heat treatment is spun twice to obtain the shaped blank. The secondary spinning is reverse spinning, the heating temperature is 700℃, the rotation speed is 30rpm, the feed ratio is 30mm / min, the thinning rate is 50%, and the spinning thrust is 600kN.

[0041] S6. Spin finishing is performed on the formed blank to obtain the finished formed blank. The heating temperature during spin finishing is 700℃, the rotation speed is 30rpm, the feed ratio is 125mm / min, the thinning rate is 3%, and the spin thrust is 400kN.

[0042] S7. The finished blank is subjected to solution treatment to obtain the outer wall of the expansion section of the liquid rocket engine, as shown in Figure 1. Figure 1As shown; the solution treatment method is as follows: the finished molded blank is kept at 1100℃ for 1.5h, and then water-cooled to room temperature;

[0043] During the first spinning, second spinning, and spinning finishing processes, the radius of the spinning wheel fillet is R40mm. Each of the first spinning, second spinning, and spinning finishing processes involves two passes. In this embodiment, water cooling is used for both the first and second heat treatments at a rate of 500℃ / s. Commercially available emulsion is sprayed onto the blank during the first spinning, second spinning, and spinning finishing processes to keep the surface temperature of the formed blank consistently below 200℃.

[0044] Example 2: This example is basically the same as Example 1, except that nitrogen is used for cooling in both the first and second heat treatments, and the cooling rate is 70℃ / s in the first heat treatment and 110℃ / s in the second heat treatment.

[0045] During the primary spinning, secondary spinning, and spinning finishing processes, an emulsion is sprayed onto the surface of the billet. The spraying rate Q of the emulsion conforms to the following relationship:

[0046]

[0047] Where Q is the spraying rate of the emulsion, rounded to two decimal places, in L / s; k is a coefficient, with a value of 5; V is the cooling rate during the previous heat treatment, in °C / s; T2 is the temperature during the previous heat treatment, in °C; T1 is the heating temperature during this spinning process, in °C; and ρ is the mass concentration of the emulsion, in g / L.

[0048] The emulsion is prepared by mixing 15g of base liquid with 1L of water. The base liquid consists of the following components by weight: 35 parts paraffin oil, 12 parts sulfurized castor oil, 15 parts sodium dodecylbenzene sulfonate, 8 parts borate ester, 4 parts polysiloxane, 3 parts triethanolamine, and 9 parts sorbitan monooleate.

[0049] Example 3: This example is basically the same as Example 2, except that the cooling rate during the first heat treatment is 60℃ / s.

[0050] Example 4: This example is basically the same as Example 2, except that the cooling rate during the first heat treatment is 80℃ / s.

[0051] Example 5: This example is basically the same as Example 2, except that the heating temperature during the first spinning is 650℃, the rotation speed is 20rpm, the feed ratio is 10mm / min, the thinning rate is 30%, and the spinning thrust is 300kN.

[0052] Example 6: This example is basically the same as Example 2, except that the heating temperature during the first spinning is 750℃, the rotation speed is 40rpm, the feed ratio is 20mm / min, the thinning rate is 40%, and the spinning thrust is 600kN.

[0053] Example 7: This example is basically the same as Example 2, except that the cooling rate during the secondary heat treatment is 100℃ / s.

[0054] Example 8: This example is basically the same as Example 2, except that the cooling rate during the secondary heat treatment is 120℃ / s.

[0055] Example 9: This example is basically the same as Example 2, except that the heating temperature during the second spinning is 650℃, the rotation speed is 20rpm, the feed ratio is 20mm / min, the thinning rate is 40%, and the spinning thrust is 400kN.

[0056] Example 10: This example is basically the same as Example 2, except that the heating temperature during the second spinning is 750℃, the rotation speed is 40rpm, the feed ratio is 40mm / min, the thinning rate is 60%, and the spinning thrust is 800kN.

[0057] Example 11: This example is basically the same as Example 2, except that the heating temperature during spinning finishing is 650℃, the rotation speed is 20rpm, the feed ratio is 100mm / min, the thinning rate is 5%, and the spinning thrust is 300kN.

[0058] Example 12: This example is basically the same as Example 2, except that the heating temperature during spinning finishing is 750℃, the rotation speed is 40rpm, the feed ratio is 150mm / min, the thinning rate is 1%, and the spinning thrust is 500kN.

[0059] Example 13: This example is basically the same as Example 2, except that the value of k is 4.

[0060] Example 14: This example is basically the same as Example 2, except that the value of k is 6.

[0061] Example 15: This example is basically the same as Example 2, except that the emulsion is prepared by mixing 10g of base liquid with 1L of water.

[0062] Example 16: This example is basically the same as Example 2, except that the emulsion is prepared by mixing 20g of base liquid with 1L of water.

[0063] Example 17: This example is basically the same as Example 2, except that the components of the base liquid, by weight, include the following: 30 parts paraffin oil, 10 parts sulfurized castor oil, 10 parts sodium dodecylbenzene sulfonate, 5 parts borate ester, 3 parts polysiloxane, 1 part triethanolamine, and 6 parts sorbitan monooleate.

[0064] Example 18: This example is basically the same as Example 2, except that the components of the base liquid, by weight, include the following: 40 parts paraffin oil, 15 parts sulfurized castor oil, 20 parts sodium dodecylbenzene sulfonate, 10 parts borate ester, 6 parts polysiloxane, 5 parts triethanolamine, and 12 parts sorbitan monooleate.

[0065] Comparative Example 1: Referring to Example 2, the spraying rate of the emulsion during the first and second spinning processes was kept constant at 0.07 L / s.

[0066] Comparative Example 2: Referring to Example 2, the emulsion was replaced with a commercially available emulsion.

[0067] Experimental Example: To investigate the performance of the outer wall of the expansion section of the liquid rocket engine based on the preparation parameters of each embodiment, the specific investigation is as follows:

[0068] Experiment Example 1: Investigating the effect of emulsifier spraying method on the outer wall performance of the expansion section of a liquid rocket engine.

[0069] Using Examples 1 and 2 as experimental comparisons, the performance of the outer wall of the expansion section of the liquid rocket engine under different emulsifier spraying methods is shown in Table 1 below:

[0070] Table 1. Performance of the outer wall of the expansion section of a liquid rocket engine under different emulsifier spraying methods.

[0071] Group Tensile strength / MPa elongation Example 1 652 38.5％ Example 2 687 44.8％

[0072] As shown in Table 1, compared with Example 1, Example 2 has higher tensile strength and elongation, indicating that the outer wall of the expansion section of the liquid rocket engine in Example 2 has better performance. This may be because the outer wall of the expansion section of the liquid rocket engine in Example 2 has smaller grains and more uniform structure, thus the emulsion spraying method in Example 2 is better.

[0073] Experiment Example 2: Investigating the effect of the cooling rate of a single heat treatment on the performance of the outer wall of the expansion section of a liquid rocket engine.

[0074] Using Examples 2, 3, and 4 as experimental comparisons, the performance of the outer wall of the expansion section of the liquid rocket engine under different cooling rates during a single heat treatment is shown in Table 2 below:

[0075] Table 2. Performance of the outer wall of the expansion section of a liquid rocket engine under different cooling rates after a single heat treatment.

[0076] Group Tensile strength / MPa elongation Example 2 687 44.8％ Example 3 672 42.5％ Example 4 677 43.1％

[0077] As shown in Table 2, compared with Examples 2, 3, and 4, Example 2 has higher tensile strength and elongation, indicating that the outer wall of the expansion section of the liquid rocket engine in Example 2 has better performance. This may be because the internal structure of the billet is the most uniform under the cooling rate of the first heat treatment in Example 2. Therefore, the cooling rate selected for the first heat treatment in Example 2 is optimal.

[0078] Experiment Example 3: Investigating the Influence of Primary Spinning Parameters on the Performance of the Expansion Section Outer Wall of a Liquid Rocket Engine

[0079] Using Examples 2, 5, and 6 as experimental comparisons, the performance of the outer wall of the expansion section of the liquid rocket engine under different primary spin compression parameters is shown in Table 3 below:

[0080] Table 3 Performance of the outer wall of the expansion section of a liquid rocket engine under different primary spinning parameters

[0081]

[0082]

[0083] As shown in Table 3, compared with Examples 2, 5, and 6, Example 2 has higher tensile strength and elongation, indicating that the outer wall of the expansion section of the liquid rocket engine in Example 2 has better performance. This may be because the blank has the fewest internal defects under the first spinning parameters of Example 2. Therefore, the first spinning parameters selected in Example 2 are optimal.

[0084] Experiment Example 4: Investigating the effect of the cooling rate of secondary heat treatment on the performance of the outer wall of the expansion section of a liquid rocket engine.

[0085] Using Examples 2, 7, and 8 as experimental comparisons, the performance of the outer wall of the expansion section of the liquid rocket engine under different cooling rates during secondary heat treatment is shown in Table 4 below:

[0086] Table 4. Performance of the outer wall of the expansion section of a liquid rocket engine under different cooling rates during secondary heat treatment.

[0087] Group Tensile strength / MPa elongation Example 2 687 44.8％ Example 7 675 42.9％ Example 8 681 43.2％

[0088] As shown in Table 4, compared with Examples 2, 7, and 8, Example 2 has higher tensile strength and elongation, indicating that the outer wall of the expansion section of the liquid rocket engine in Example 2 has better performance. This may be because the internal structure of the billet is the most uniform under the secondary heat treatment cooling rate in Example 2. Therefore, the cooling rate selected for the secondary heat treatment in Example 2 is optimal.

[0089] Experiment Example 5: Investigating the Influence of Secondary Spinning Parameters on the Performance of the Expansion Section Outer Wall of a Liquid Rocket Engine

[0090] Using Examples 2, 9, and 10 as experimental comparisons, the performance of the outer wall of the expansion section of the liquid rocket engine under different secondary spin compression parameters is shown in Table 5 below:

[0091] Table 5 Performance of the outer wall of the expansion section of a liquid rocket engine under different secondary spinning parameters

[0092] Group Tensile strength / MPa elongation Example 2 687 44.8％ Example 9 678 43.6％ Example 10 684 44.1％

[0093] As shown in Table 5, compared with Examples 2, 9, and 10, Example 2 has higher tensile strength and elongation, indicating that the outer wall of the expansion section of the liquid rocket engine in Example 2 has better performance. This may be because the internal defects of the billet are the fewest under the secondary spinning parameters of Example 2. Therefore, the secondary spinning parameters selected in Example 2 are the optimal.

[0094] Experiment Example 6: Investigating the Influence of Spinning Finishing Parameters on the Performance of the Expansion Section Outer Wall of a Liquid Rocket Engine

[0095] Using Examples 2, 11, and 12 as experimental comparisons, the performance of the outer wall of the expansion section of the liquid rocket engine under different spin finishing parameters is shown in Table 6 below:

[0096] Table 6 Performance of the outer wall of the expansion section of a liquid rocket engine under different spinning finishing parameters

[0097] Group Tensile strength / MPa elongation Example 2 687 44.8％ Example 11 680 43.7％ Example 12 682 43.9％

[0098] As shown in Table 6, compared with Examples 2, 11, and 12, Example 2 has higher tensile strength and elongation, indicating that the outer wall of the expansion section of the liquid rocket engine in Example 2 has better performance. This may be because the dimensional stability of the formed blank is the best under the spinning finishing parameters of Example 2. Therefore, the spinning finishing parameters selected in Example 2 are optimal.

[0099] Experiment Example 7: Investigating the effect of the value of k on the performance of the outer wall of the expansion section of a liquid rocket engine.

[0100] Using Examples 2, 13, and 14 as comparative experiments, the performance of the outer wall of the expansion section of the liquid rocket engine under different values ​​of k is shown in Table 7 below:

[0101] Table 7 shows the performance of the outer wall of the expansion section of a liquid rocket engine under different values ​​of k.

[0102] Group Tensile strength / MPa elongation Example 2 687 44.8％ Example 13 672 42.8％ Example 14 676 43.0％

[0103] As shown in Table 7, compared with Examples 2, 13, and 14, Example 2 has higher tensile strength and elongation, indicating that the outer wall of the expansion section of the liquid rocket engine in Example 2 has better performance. This may be because the emulsion spraying amount is most suitable under the value of k in Example 2, and the plastic deformation performance of the billet is the best. Therefore, the value of k selected in Example 2 is the optimal.

[0104] Experiment Example 8: Investigating the effect of emulsion concentration on the outer wall performance of the expansion section of a liquid rocket motor.

[0105] Using Examples 2, 15, 16 and Comparative Example 1 as experimental comparisons, the performance of the outer wall of the expansion section of the liquid rocket engine at different emulsion concentrations is shown in Table 8 below:

[0106] Table 8 Performance of the outer wall of the expansion section of a liquid rocket engine at different emulsion concentrations

[0107]

[0108]

[0109] As shown in Table 8, compared with Examples 2, 15, and 16, Example 2 has higher tensile strength and elongation, indicating that the outer wall of the expansion section of the liquid rocket engine in Example 2 has better performance. This may be because the lubrication performance of Example 2 is optimal at the emulsion concentration. Therefore, the emulsion concentration selected in Example 2 is optimal.

[0110] Compared with Comparative Example 1, in Example 2, after the amount of emulsion sprayed was kept constant during the first and second spinning processes, the tensile strength and elongation of the outer wall of the expansion section of the liquid rocket engine both decreased. This may be because the internal dendrites could not be fully broken during the billet forming process. Therefore, the emulsion spraying method selected in Example 2 is optimal.

[0111] Experiment Example 9: Investigating the effect of the composition of the base fluid on the performance of the outer wall of the expansion section of a liquid rocket engine.

[0112] Using Examples 2, 17, 18 and Comparative Example 2 as experimental comparisons, the performance of the outer wall of the expansion section of the liquid rocket engine with different base fluid compositions is shown in Table 9 below:

[0113] Table 9 Performance of the outer wall of the expansion section of a liquid rocket engine with different base fluid compositions.

[0114] Group Tensile strength / MPa elongation Example 2 687 44.8％ Example 17 672 43.4％ Example 18 670 43.1％ Comparative Example 2 662 40.8％

[0115] As shown in Table 9, compared with Examples 2, 17, and 18, Example 2 has higher tensile strength and elongation, indicating that the outer wall of the expansion section of the liquid rocket engine in Example 2 has better performance. This may be because the emulsion has the best lubrication performance under the base liquid composition of Example 2. Therefore, the base liquid composition selected in Example 2 is the optimal one.

[0116] Compared with Comparative Example 2, Example 2 showed that the tensile strength and elongation of the outer wall of the expansion section of the liquid rocket engine decreased after using a commercially available emulsion. This indicates that the emulsion in Example 2 has better performance and can effectively improve the performance of the outer wall of the expansion section of the liquid rocket engine. Therefore, the emulsion composition selected in Example 2 is superior.

Claims

1. A method for spin forming the outer wall of the expansion section of a liquid rocket engine, characterized in that, Includes the following steps: S1. Cut the stainless steel sheet to obtain a circular blank; S2. Perform a heat treatment on the billet. The heat treatment method is as follows: hold the billet at 1020-1040℃ for 1-2 hours, and then cool it rapidly. S3. Perform a first spinning on the billet after heat treatment to obtain a first-spun billet. The first spinning is performed in the forward direction, the heating temperature is 650~750℃, the rotation speed is 20~40rpm, the feed ratio is 10~20mm / min, the thinning rate is 30~40%, and the spinning thrust is 300-600kN. S4. Perform a second heat treatment on the blank after one spinning. The second heat treatment method is to keep the blank after one spinning at 1020~1040℃ for 1~2h, and then cool it rapidly. S5. Perform secondary spinning on the blank after secondary heat treatment to obtain the shaped blank. The secondary spinning is performed in reverse spinning. The heating temperature is 650-750℃, the rotation speed is 20-40rpm, the feed ratio is 20-40mm / min, the thinning rate is 40-60%, and the spinning thrust is 400-800kN. S6. Spin finishing is performed on the formed blank to obtain the finished formed blank. The heating temperature during spin finishing is 650~750℃, the rotation speed is 20~40rpm, the feed ratio is 100~150mm / min, the thinning rate is ≤5%, and the spin thrust is 300-500kN. S7. The finished blank is subjected to solution treatment to obtain the outer wall of the expansion section of the liquid rocket engine.

2. The method for spin forming of the outer wall of the expansion section of a liquid rocket engine according to claim 1, characterized in that, During the first spinning, second spinning, and spinning finishing processes, the radius of the spinning wheel fillet is R38~R42mm.

3. The method for spin forming of the outer wall of the expansion section of a liquid rocket engine according to claim 1, characterized in that, The solution treatment method is as follows: the finished molded blank is kept at 1050-1150℃ for 1-2 hours, and then cooled to room temperature by water.

4. The method for spin forming of the outer wall of the expansion section of a liquid rocket engine according to claim 1, characterized in that, Each of the first spinning, second spinning, and spinning finishing processes involves 1 to 2 passes.

5. The method for spin forming of the outer wall of the expansion section of a liquid rocket engine according to claim 1, characterized in that, The cooling rate during the first heat treatment is 60-80℃ / s, and the cooling rate during the second heat treatment is 100-120℃ / s.

6. The method for spin forming of the outer wall of the expansion section of a liquid rocket engine according to claim 5, characterized in that, During the first spinning, second spinning, and spinning finishing processes, an emulsion is sprayed onto the surface of the billet. The spraying rate Q of the emulsion conforms to the following relationship: Where Q is the spraying rate of the emulsion, retained to two decimal places, in L / s; k is a coefficient, with a value of 4 to 6; V is the cooling rate during the previous heat treatment, in ℃ / s; T2 is the temperature during the previous heat treatment, in ℃; T1 is the heating temperature during this spinning, in ℃; and ρ is the mass concentration of the emulsion, in g / L.

7. The method for spin forming of the outer wall of the expansion section of a liquid rocket engine according to claim 6, characterized in that, The emulsion is prepared by mixing 10-20g of base liquid with 1L of water. The base liquid consists of the following components by weight: 30-40 parts of paraffin oil, 10-15 parts of sulfurized castor oil, 10-20 parts of sodium dodecylbenzene sulfonate, 5-10 parts of borate ester, 3-6 parts of polysiloxane, 1-5 parts of triethanolamine, and 6-12 parts of sorbitan monooleate.

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