Forming method of variable-thickness chromium bronze inner wall of liquid rocket engine combustion chamber expansion section

Abstract

The present invention provides a method for forming the variable-thickness chromium bronze inner wall of the expansion section of a liquid rocket engine combustion chamber. The type and number of forming dies are determined according to the forming process. The forming dies include fine-tuning bulging dies, multiple sets of progressive bulging dies, and correction dies, which are used sequentially. The progressive bulging dies are designed for their profiles. Each set of progressive bulging dies bulges a portion of the profile, while the remaining profile is extended tangentially. The increase in the diameter of the mouth after extension relative to the previous one is controlled within the process bulging range, maintaining the profile generatrix length unchanged. This determines the axial height of the profile for each bulge. The outer profile of the last progressive bulging dies is consistent with the inner profile of the target inner wall. The forming dies are placed in a QCr0.8 chromium bronze inner wall blank of the expansion section and bulged sequentially using the forming dies until the inner and outer walls are aligned. The method utilizes integral bulging of the dies to ensure good alignment of the inner and outer walls, without rib collapse, and with a gap of ≤0.3 mm between the inner and outer walls.

Description

Technical Field

[0001] The invention belongs to the technical field of metal forming, and in particular relates to a method for forming a variable-thickness chromium bronze inner wall of an expansion section of a liquid rocket engine combustion chamber. Background Art

[0002] The outer wall of a certain type of rocket engine combustion chamber is made of S-06 steel, and the inner wall is made of chrome bronze QCr0.8. The engine combustion chamber consists of a cylindrical section, a convergent section, and an expansion section. The expansion section ( Figure 1 The inner wall (arrows point in the direction of the arrow) features a variable wall thickness. The outer surface is spirally grooved with a uniform depth. The remaining wall thickness at the throat is 1.2mm, and the wall thickness at the large end is 4mm. The combustion chamber molding process involves bulging the inner wall until it conforms to the outer wall. The inner wall bulge reaches 48.97%, exceeding the maximum bulge coefficient of 43% for chrome bronze QCr0.8.

[0003] At present, the processing method is male die split-type bulging. The axial force generated during the stamping bulging process is small, and the limit bulging coefficient is increased, but the bulging is uneven. The uneven bulging will cause excessive local bulging, resulting in cracking, or the ribs are pressed and collapsed. Summary of the Invention

[0004] In order to overcome the deficiencies in the prior art, the inventors conducted intensive research and provided a method for forming the variable-thickness chromium bronze inner wall of the expansion section of a liquid rocket engine combustion chamber. The method adopts a male mold for overall bulging to ensure that the inner and outer walls fit well and there is no rib dumping phenomenon, thereby completing the present invention.

[0005] The technical solutions provided by the present invention are as follows:

[0006] A method for forming a variable-thickness chromium bronze inner wall of an expansion section of a liquid rocket engine combustion chamber comprises the following steps:

[0007] The type and quantity of forming dies are determined according to the forming process. The forming dies include fine-tuning bulging dies, multiple sets of progressive bulging dies, and correction dies, which are used in sequence. The fine-tuning bulging dies are used to expand the large end of the variable-wall-thickness chromium bronze inner wall to the same diameter as the throat before progressive bulging. The correction dies are used to correct the shape after progressive bulging.

[0008] The progressive bulging die is designed to bulge a portion of the die, with the remaining die extending tangentially. The length of the die's generatrix remains constant, and the increase in the diameter of the mouth after extension compared to the previous one is controlled within the process bulging range, thereby determining the axial height of the die for each bulging operation. The progressive bulging die is used to gradually bulge the die from the small end of the inner wall to the large end. The outer die surface of the final progressive bulging die is consistent with the inner die surface of the target inner wall.

[0009] The forming male die is placed in the inner wall blank of the chromium bronze QCr0.8 expansion section, and the forming male die is used to expand the blank in sequence until the inner and outer walls fit together.

[0010] The method for forming the variable-thickness chromium bronze inner wall of the expansion section of a liquid rocket engine combustion chamber provided by the present invention has the following beneficial effects:

[0011] (1) In the present invention, the forming method includes calculation of bulging times, design of progressive bulging male mold, and bulging process control. By optimizing the bulging die design parameters and controlling the bulging process parameters, the progressive bulging process is made stable and reproducible, and the gap between the inner and outer walls is ≤0.3 mm.

[0012] (2) In the present invention, although the bulging amount of the inner wall exceeds the maximum bulging amount of the material, the bulging amount is increased due to the progressive bulging, and no heat treatment is required between the two bulgings, which solves the problem that heat treatment is required due to large bulging amounts, improves processing accuracy and production efficiency, and reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the combustion chamber structure before and after bulging;

[0014] Figure 2 It is a schematic diagram of the bulging die structure;

[0015] Figure 3 This is a schematic diagram of the smooth transition structure of the bulging male die;

[0016] Figure 4 It is a schematic diagram of the design structure of the progressive bulging male die;

[0017] Figure 5 This is the finished product picture of the expansion section after bulging. DETAILED DESCRIPTION

[0018] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0019] The word "exemplary" is used exclusively herein to mean "serving as an example, example, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise indicated.

[0020] The present invention provides a method for forming a variable-thickness chromium bronze inner wall of an expansion section of a liquid rocket engine combustion chamber, comprising the following steps:

[0021] Step 1: Determine the type and quantity of the forming male mold according to the forming process, wherein the forming male mold types include fine-tuning bulging male molds, progressive bulging male molds and correction male molds.

[0022] The number of progressive bulge male dies, M, is determined based on the total bulge amount N and the single bulge amount n of the chrome bronze inner wall at the large end of the expansion section. If the single bulge amount n is a fixed value, then M = N / n. If the single bulge amount n is not a fixed value, the number of bulges required for each single bulge amount n to reach the total bulge amount N of the chrome bronze inner wall at the large end of the expansion section is the number of progressive bulge male dies, M.

[0023] For bulging the inner wall of chrome bronze (QCr0.8), the expansion amount per step is set to 3.5% to 4%, i.e., the diameter increase rate at the mouth is 3.5% to 4%. The chrome bronze inner wall of the expansion section is bulged until it fits the outer wall. The total expansion amount N at the large end is 48.97%. Assuming a single expansion amount n of approximately 4%, a total of 12 progressive bulging passes are required, requiring 12 sets of progressive bulging male dies.

[0024] The remaining wall thickness of the inner wall of the expansion section combustion chamber is variable wall thickness, and the initial inner diameter of the large end of the expansion section is smaller than the inner diameter of the throat. Two sets of fine-tuning bulging male dies are required as bulging dies for the first two times to expand the large end to the same diameter as the throat.

[0025] Considering that after the progressive bulging is completed, there is a possibility of surface rebound after bulging, a set of correction positive molds is required as the final bulging mold.

[0026] Step 2: Design the profile of the progressive bulging die. Each set of progressive bulging dies completes the bulging of a portion of the profile, and the remaining profile is extended tangentially. The length of the profile generatrix remains unchanged. The increase in the diameter of the mouth after extension compared to the previous one is controlled within the process bulging range, thereby determining the profile axial height of each bulge. Using such a progressive bulging die, the profile is gradually bulged from the small end (throat) of the inner wall to the large end of the inner wall. In other words, the outer diameter of the small end of each progressive bulge die is consistent, and the outer diameter of the large end increases step by step in the order of use until it is consistent with the target inner wall diameter. The first set of progressive bulging male molds calculates the profile of a certain axial height according to the above method, which is consistent with the inner profile at the corresponding height of the lower end of the inner wall of the finished product. The second set of progressive bulging male molds increases the height of the inner profile consistent with the target inner wall compared to the first set of progressive bulging male molds. Similarly, the outer profile of the last set of progressive bulging male molds is completely consistent with the inner profile of the target inner wall. Figure 2 shown.

[0027] To ensure uniform force on all parts of the inner wall and a smooth forming surface, the flatness of the upper and lower surfaces of the progressive bulging male mold should be better than 0.03, and the parallelism of the upper and lower surfaces should be better than 0.03 to ensure uniform force during the bulging process. The roughness of the outer surface should be better than Ra0.8 to reduce the friction between the bulging male mold and the part during the bulging process, making deformation uniform and reducing axial force. The roughness of other parts should be better than Ra1.6. Similarly, the fine-tuning bulging male mold and the shaping male mold should also meet the above requirements.

[0028] In order to ensure the smoothness of the inner wall surface after bulging, the leading edge of the small end of the progressive bulging male die (corresponding to the throat of the combustion chamber) has a straight line segment of 2.90 to 3.10 mm, such as 3.0 mm, extending toward the throat. It is mainly used to ensure a smooth transition between the bulging surface above the throat and the original surface below the throat, and a smooth transition between the straight line segment and the end face of the small end of the progressive bulging male die. Figure 3 Similarly, the small end of the fine-tuning bulging male die and the shaping male die (corresponding to the throat of the combustion chamber) has a straight line segment of 2.90 to 3.10 mm, such as 3.0 mm, extending toward the throat.

[0029] Step 3: Install a support tire in the cavity of the combustion chamber cylindrical section and the convergent section (non-target forming section) and fix it on the worktable of an 800-ton hydraulic press. Place the forming male mold in the inner wall blank of the expansion section (target forming section) and use the forming male mold to expand it in sequence until the inner and outer walls fit together.

[0030] To reduce friction, the inner wall of the blank is lubricated with lard before bulging, and each set of male molds is wiped clean with a silk cloth. The bulging force is controlled between 45 and 80 tons per cycle. After each set of male molds is bulged, the straight section of the male mold enters the straight groove reserved at the tire end.

[0031] Before bulging, measure the height difference between the upper edge of the inner wall blank and the upper edge of the outer wall to ensure that the height difference is ≤0.1mm. If it exceeds 0.1mm, reassemble the inner wall blank.

[0032] The interior of the support tire for the cylindrical section and convergent section of the combustion chamber cavity is provided with a push rod, and the end of the push rod has a boss, and a hole is provided at the bottom of the forming male mold to play a positioning and supporting role. The hydraulic press is provided with a push rod passing through the workbench, and the push rod in the support tire is located at the ejection position of the workbench push rod, and the two sections of the push rod are butted; before bulging, the push rod in the center of the support tire rises, and after the forming male mold is installed on the end of the push rod, the push rod drives the forming male mold to fall, and the forming male mold is automatically aligned, which can reduce the damage caused by the male mold to the inner wall of the chrome bronze QCr0.8. The hydraulic press slider presses downward on the forming male mold, and the bulging force is controlled between 45 and 80 tons; after the bulging is completed, the straight section of the forming male mold enters the straight groove reserved at the end of the support tire, and the push rod inside the support tire is driven to rise by the hydraulic press push rod to eject the forming male mold, see Figure 4 .

[0033] When calibrating the positive mold, expand it in directions perpendicular to each other in sequence. After the expansion is completed, measure the gap between the inner and outer walls. If the gap exceeds 0.3mm, stick white tape (thickness 0.1mm) around the outer surface of the positive mold. Expand it in directions perpendicular to each other in sequence to ensure uniform expansion. After expansion, the gap is ≤0.3mm.

[0034] In the present invention, the liquid rocket engine combustion chamber is manufactured with a product precision of a gap between the inner and outer walls of the large end of ≤0.3 mm, a smooth inner wall profile, and no tilting of ribs.

[0035] Example 1

[0036] The combustion chamber of a certain rocket engine is constructed from S-06 steel on the outer wall and QCr0.8 chrome bronze on the inner wall. The inner wall of the expansion section features a variable-thickness structure with spiral grooves of uniform depth. The remaining wall thickness at the throat is 1.2mm, and the wall thickness at the large end is 4mm. The combustion chamber forming process involves bulging the inner wall until it conforms to the outer wall. The bulging reaches 48.97%, exceeding the maximum bulging coefficient of 43% for QCr0.8 chrome bronze. The specific forming method includes the following steps:

[0037] (1) Determine the number of bulging times. The total bulging amount of the large end is 48.97%. Calculated based on a 4% bulging amount per time, a total of 12 bulging times are required, and the number of progressive bulging male dies is 12. Since the remaining wall thickness of the inner wall is variable, the inner diameter of the large end is smaller than the inner diameter of the throat. Two sets of fine-tuning bulging male dies are required to expand the large end diameter to the same diameter as the throat. After bulging, the mold surface rebounds, and a set of correction male dies is required for final correction. A total of 15 sets of molds are required.

[0038] (2) When designing the forming male mold, a 3.0mm straight section is included at the front end of the small end of each forming male mold to ensure a smooth transition between the bulging surface above the throat and the original surface below the throat. Each set of progressive bulging male mold surface is extended axially to a certain height from the previous set of progressive bulging male mold surface, and gradually bulges to the entire surface. The flatness of the upper and lower surfaces of the forming male mold is 0.03, the parallelism of the upper and lower surfaces is 0.03, the surface roughness is Ra0.8, and the roughness of the remaining surfaces is Ra1.6.

[0039] (3) When bulging with an 800-ton hydraulic press, the inner surface of the inner wall blank is lubricated with lard. Each set of bulging male molds is cleaned with silk cloth before use. The bulging force is controlled between 45 and 80 tons. Each set of molds is bulged, and no heat treatment is required in the middle. The last set of bulging male molds should be bulged once in the 90° direction. When the large end gap between the inner and outer walls is ≤0.3mm, tape is applied to the mold surface and bulged once in the 90° direction to ensure that the large end gap between the inner and outer walls is ≤0.3mm. Three products were bulged using this method. All of them met the requirements of the large end gap of the inner and outer walls after bulging ≤0.3mm. The products after bulging are shown in Figure 2. Figure 5 .

[0040] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

[0041] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for forming a variable-thickness chromium bronze inner wall of an expansion section of a liquid rocket engine combustion chamber, characterized in that: The steps include: The type and quantity of forming dies are determined according to the forming process. The forming dies include fine-tuning bulging dies, multiple sets of progressive bulging dies, and correction dies, which are used in sequence. The fine-tuning bulging dies are used to expand the large end of the variable-wall-thickness chromium bronze inner wall to the same diameter as the throat before progressive bulging. The correction dies are used to correct the shape after progressive bulging. The progressive bulging die is designed to bulge a portion of the die, with the remaining die extending tangentially. The length of the die's generatrix remains constant, and the increase in the diameter of the mouth after extension compared to the previous one is controlled within the process bulging range, thereby determining the axial height of the die for each bulging operation. The progressive bulging die is used to gradually bulge the die from the small end of the inner wall to the large end. The outer die surface of the final progressive bulging die is consistent with the inner die surface of the target inner wall. The forming male mold is placed in the inner wall blank of the chromium bronze QCr0.8 of the expansion section, and the forming male mold is used to expand in sequence until the inner and outer walls are fitted together. Specifically: a support tire is set in the cavity of the cylindrical section and the convergent section of the combustion chamber and fixed on the worktable of the hydraulic press. The interior of the support tire of the cylindrical section and the convergent section of the combustion chamber cavity is provided with a push rod, and the end of the push rod has a boss. A hole is set at the bottom of the forming male mold to play a positioning and supporting role. The hydraulic press is provided with a push rod passing through the worktable. The push rod in the support tire is located at the ejection position of the worktable push rod, and the two sections of the push rod are butt-jointed. Before expanding, the push rod in the center of the support tire rises. After the forming male mold is installed on the end of the push rod, the push rod drives the forming male mold to fall, and the forming male mold is automatically aligned. The hydraulic press slider is pressed downward on the forming male mold, and the expanding force is controlled between 45 and 80 tons. After the expanding is completed, the straight section of the forming male mold enters the straight groove reserved at the end of the support tire, and the push rod inside the support tire is driven to rise by the hydraulic press push rod to eject the forming male mold.

2. The method for forming the variable-thickness chromium bronze inner wall of the expansion section of the liquid rocket engine combustion chamber according to claim 1, characterized in that: The number M of progressive bulging male dies is determined based on the total bulging amount N and the single bulging amount n of the large end of the chrome bronze inner wall; if the single bulging amount n is a constant, then M=N / n; if the single bulging amount n is not a constant, then the number of bulging times when the cumulative single bulging amounts n reach the total bulging amount N of the large end of the chrome bronze inner wall is the number M of progressive bulging male dies.

3. The method for forming the variable-thickness chromium bronze inner wall of the expansion section of the liquid rocket engine combustion chamber according to claim 1, characterized in that: For the bulging of the inner wall of chromium bronze QCr0.8, the bulging amount each time, that is, the increase rate of the mouth diameter, is set to 3.5% to 4%.

4. The method for forming the variable-thickness chromium bronze inner wall of the expansion section of the liquid rocket engine combustion chamber according to claim 1, characterized in that: The upper and lower surface flatness of the fine-tuning bulging male die, multiple sets of progressive bulging male dies and correction male die are better than 0.03, the upper and lower surface parallelism are better than 0.03, the outer surface roughness is better than Ra0.8, and the roughness of other parts is better than Ra1.

6.

5. The method for forming the variable-thickness chromium bronze inner wall of the expansion section of the liquid rocket engine combustion chamber according to claim 1, characterized in that: The front edges of the small ends of the fine-tuning bulging male dies, the multiple sets of progressive bulging male dies and the correction male dies have a straight line section of 2.90 to 3.10 mm.

6. The method for forming the variable-thickness chromium bronze inner wall of the expansion section of the liquid rocket engine combustion chamber according to claim 1, characterized in that: Use the forming male mold to measure the height difference between the upper edge of the inner wall blank and the upper edge of the outer wall before bulging to ensure that the height difference is ≤ 0.1mm. If it exceeds 0.1mm, reassemble the inner wall blank.

7. The method for forming the variable-thickness chromium bronze inner wall of the expansion section of a liquid rocket engine combustion chamber according to claim 1, characterized in that: The forming male dies are expanded one by one without heat treatment in the middle.

8. The method for forming the variable-thickness chromium bronze inner wall of the expansion section of a liquid rocket engine combustion chamber according to claim 1, characterized in that: When using a positive mold for correction, bulge in directions perpendicular to each other in sequence; after bulging, measure the gap between the inner and outer walls. If the gap exceeds 0.3mm, stick white tape around the outer surface of the positive mold, and bulge in directions perpendicular to each other in sequence to ensure uniform bulging. After bulging, the gap is ≤0.3mm.

9. The method for forming the variable-thickness chromium bronze inner wall of the expansion section of the liquid rocket engine combustion chamber according to claim 1, characterized in that: The bulging amount of the chromium bronze inner wall exceeds the maximum bulging coefficient of chromium bronze by 43%.

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