A method for manufacturing a rocket engine nozzle with a buffer cavity

Abstract

This invention relates to a method for manufacturing a rocket engine nozzle with a buffer cavity, belonging to the field of aerospace engine manufacturing technology. The manufacturing method includes: dividing the three-dimensional model of the nozzle circumferentially and axially into segments to form multiple sub-components; using laser selective melting technology to print the sub-components on a 650mm wide machine, and pre-setting a circumferentially extending buffer cavity communicating with an internal cooling channel on its axial mating surface; connecting the upper and lower segments into fan-shaped units by transverse welding, and then splicing multiple fan-shaped units into a complete nozzle by longitudinal welding. During welding, protective gas is introduced into the internal channel through a top protective gas shield and flows out from the bevel to form inner protection. The circumferentially extending buffer cavity can release thermal stress and enhance cooling turbulence during operation. This method utilizes conventional 650mm-class equipment to achieve low-cost, high-precision manufacturing of nozzles approaching 3 meters in size.

Description

Technical Field

[0001] This invention relates to the field of aerospace engine manufacturing technology, and in particular to a method for manufacturing a rocket engine nozzle with a buffer cavity. Background Technology

[0002] With the development of high-thrust reusable rocket engines, there is an urgent need for ultra-large diameter, variable-curvature thin-walled nozzles with internal cooling channels, ranging from 2 to 3 meters in diameter. These structures need to operate in extreme thermal environments, demanding extremely high manufacturing precision, structural integrity, and thermal protection performance. Current manufacturing technology faces two major bottlenecks.

[0003] Firstly, while integral additive manufacturing technologies (such as selective laser melting, SLM) can form complex internal cavities, they are limited by the size of the equipment. Commercial SLM equipment typically has a maximum forming area of ​​less than 1 meter x 1 meter. For meter-diameter components, expensive large or ultra-large specialized equipment is required, along with high toner filling costs and difficulties in controlling surface accuracy, resulting in high manufacturing costs for large-size nozzles. Furthermore, the thermal stress accumulated during the printing process of large components is difficult to release, easily leading to overall warping and deformation, as well as failure of internal surface accuracy, making yield and cost control difficult.

[0004] Secondly, to overcome size limitations, existing technologies employ a manufacturing path of circumferentially segmenting the nozzle, printing the segments, and then welding them. However, this method typically only involves unidirectional (e.g., circumferential) segmentation, leaving the welded joint area to directly bear the thermal load during engine operation, thus becoming a weak point in the structure. Furthermore, such structures lack effective buffering design for thermal expansion, resulting in a high concentration of circumferential thermal stress; their cooling channels are also continuous closed structures, with the coolant flow primarily laminar, leading to limited heat exchange efficiency.

[0005] Thirdly, in the implementation of the existing segmented welding scheme, controlling the deformation and maintaining the accuracy of the weld area after welding is a major challenge. It usually requires subsequent positioning, straightening and other processes, which are cumbersome. It is difficult to form effective protective measures when welding this structure, and the probability of welding defects is high. In addition, the process of digging and secondary welding results in excessive labor costs.

[0006] The above factors together result in excessive investment in the production of nozzle products, high production costs, easy overheating of the weld area, and easy generation of fatigue cracks, making it difficult to meet the stringent requirements of reusable engines for low cost and high reliability. Summary of the Invention

[0007] Based on the above analysis, the present invention aims to provide a low-cost method for manufacturing rocket engine nozzles, the nozzle assembly manufactured thereby, and a dedicated welding system, in order to at least solve one of the problems in the prior art, such as the limitation of equipment size and high cost in additive manufacturing of ultra-large components, as well as the problems of thermal stress concentration, insufficient cooling efficiency, and complex welding process in traditional segmented welding structures.

[0008] On one hand, embodiments of the present invention provide a method for manufacturing a rocket engine nozzle with a buffer cavity, wherein the nozzle is a thin-walled nozzle with an internal cooling channel, and the method includes the following steps:

[0009] S1. Dual segmentation: The three-dimensional model of the nozzle is divided into N equal parts along its circumference, and then into at least an upper sub-segment and a lower sub-segment along its axial direction, thereby forming multiple independent sub-components, where N is an integer greater than or equal to 4;

[0010] S2. Additive manufacturing: Using laser selective melting technology, the sub-components are printed separately on a device with a forming area smaller than the maximum diameter of the nozzle;

[0011] S3. Lateral assembly welding: The upper and lower segments belonging to the same petal are joined together and positioned by the first welding fixture to weld and form a fan-shaped petal unit;

[0012] S4. Longitudinal welding: Arrange the N fan-shaped units circumferentially and position them using a second welding fixture to weld the longitudinal welds between the fan-shaped units to form a complete nozzle;

[0013] In the docking area between the upper and lower sub-segments, corresponding cavity structures are pre-set, which, after docking, form a circumferentially extending buffer cavity that communicates with the internal cooling channel of the nozzle.

[0014] Furthermore, the cross-sectional shape of the circumferentially extended buffer cavity is rectangular or approximately rectangular.

[0015] Furthermore, the circumferentially extending buffer cavity is located at the interface between the upper and lower sub-segments, and after transverse welding, it forms a circumferential buffer structure located between the front weld and the back weld.

[0016] Furthermore, in the transverse welding step, a protective gas supply device is used to supply protective gas to the welding area.

[0017] The protective gas supply device includes a protective gas cover covering the top of the fan-shaped unit, the protective gas cover having a first air inlet and an air inlet chamber communicating with the first air inlet;

[0018] The protective gas cover is connected and fixed to the positioning structure at the top of the first welding fixture via its bottom connecting part.

[0019] Furthermore, the transverse welding step also includes a protective gas flow step:

[0020] After the protective gas enters the air inlet chamber through the first air inlet hole, it flows downward through the preset cooling channel inside the fan-shaped unit and flows out from the butt joint bevel formed at the transverse joint between the upper and lower sub-sections to cover and protect the weld pool in the butt joint bevel area.

[0021] Furthermore, the first welding fixture includes a clamping structure for accommodating and positioning the upper and lower sub-segments;

[0022] The inner wall of the fixture structure is provided with an inner welding gun window for the welding gun to be inserted during transverse welding.

[0023] The upper and lower sub-segments are respectively provided with additive manufacturing integrally formed positioning interfaces on their sides;

[0024] The first welding fixture is provided with a first positioning base that matches the shape of the positioning interface, and the positioning interface cooperates with the first positioning base to achieve precise positioning.

[0025] Furthermore, the second welding fixture is a rotating frame structure, and its outer surface is used to circumferentially install and fix N of the fan-shaped units; the second welding fixture has a second positioning base at both ends of its axial direction, which is used to cooperate with the corresponding positioning part of the fan-shaped unit.

[0026] On the other hand, the present invention proposes a variable curvature nozzle, which is manufactured using the manufacturing method described above. It includes a body composed of N fan-shaped units circumferentially spliced ​​together. Each fan-shaped unit is composed of an upper sub-segment and a lower sub-segment connected by a transverse weld. At the connection interface between the upper sub-segment and the lower sub-segment, a buffer cavity communicating with the internal cavity system of the body is formed.

[0027] Furthermore, the fan-shaped unit is provided with a longitudinally extending cooling channel, which forms a flow path for welding protective gas during manufacturing and a flow path for cooling medium when the rocket engine nozzle is working.

[0028] Furthermore, the present invention proposes a welding system for implementing the manufacturing method described above, comprising:

[0029] A protective gas supply device includes a protective gas cover for covering the top of a sub-component, the protective gas cover having an external gas source interface and a mounting and positioning part;

[0030] The first welding fixture is used to position and clamp the upper and lower segments for horizontal welding, and has an inner welding gun window on its inner side.

[0031] The second welding fixture, in the form of a rotating frame structure, is used for circumferential positioning and clamping multiple fan-shaped units for longitudinal welding.

[0032] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0033] 1) This invention combines axial segmentation and circumferential segmentation to form a dual splitting mechanism. This allows a nearly 3m-long nozzle assembly to be broken down into multiple sub-modules suitable for printing on conventional small-to-medium-sized additive manufacturing equipment (forming area ≤ 650mm). This enables the manufacture of ultra-large components on smaller equipment, avoiding the huge investment required for purchasing ultra-large, high-cost dedicated additive manufacturing equipment (each unit costing over 30 million RMB). The sub-modules can be stacked and printed simultaneously, improving material utilization and single-print output efficiency (from approximately 60% to over 85%), resulting in a 30%-40% reduction in overall manufacturing costs.

[0034] 2) The buffer cavity of this invention provides a buffer space for the thermal expansion of the nozzle during operation, effectively releasing circumferential thermal stress (approximately 30%-40%), thereby increasing the thermal fatigue life of the component to 1.7-3.1 × 10⁻⁶. 5 This is more than twice that of traditional structures. At the same time, the abrupt change in the cross-section of the cavity transforms the flow of cooling medium or gas from laminar to turbulent, enhancing the heat transfer process and increasing local heat transfer efficiency by 25%-30%, significantly improving the cooling rate of the welding area.

[0035] 3) This invention utilizes two sets of dedicated welding fixtures—one axial (lateral) and one circumferential (longitudinal)—combined with prefabricated positioning structures on the sub-segments, ensuring precise alignment (misalignment ≤ 0.5mm) during module assembly. The overall roundness error after welding is controlled within 0.15-0.25mm. During welding, the inherent cooling channel and longitudinal protective gas channel of the nozzle are reused for delivering welding protective gas, achieving direct protection of the weld area from within the component. This controls welding thermal deformation to within 0.3mm, ensuring the final product's forming accuracy and weld quality without the need for large, complex molds.

[0036] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0037] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0038] Figure 1 This is a three-dimensional structural schematic diagram of a rocket engine nozzle assembly manufactured using the method of this invention;

[0039] Figure 2 This is a three-dimensional structural schematic diagram of a fan-shaped unit according to an embodiment of the present invention;

[0040] Figure 3 yes Figure 2 A schematic diagram of the upper sub-segment in the fan-shaped unit shown;

[0041] Figure 4a This is a cross-sectional view of the buffer cavity taken along the circumferential direction according to the present invention;

[0042] Figure 4b This is a side view of the buffer cavity of the present invention;

[0043] Figure 5 This is a three-dimensional structural diagram of the first welding fixture used for transverse assembly welding;

[0044] Figure 6 This is a three-dimensional structural diagram of the second welding fixture used for longitudinal welding;

[0045] Figure 7 This is a three-dimensional structural diagram of the protective gas supply device;

[0046] Figure 8 This is a top view of the upper sub-segment installed on the first welding fixture;

[0047] Figure 9 This is a top view of the fan-shaped unit being installed on the second welding fixture;

[0048] Figure 10 yes Figure 9 The structure of the longitudinal weld groove (left) and the longitudinal protective gas channel (right).

[0049] Figure label:

[0050] 1. Nozzle assembly; 11. Fan-shaped unit; 12. Upper section; 13. Lower section; 14. Buffer cavity; 15. Cooling channel; 16. Positioning interface; 2. First welding fixture; 21. First positioning base; 22. Inner welding torch window; 23. Positioning structure; 3. Shielding gas supply device; 31. Connecting part; 32. First air inlet; 33. Air inlet cavity; 4. Second welding fixture; 41. Second positioning base; 42. Longitudinal shielding gas channel; 43. Second air inlet; 44. Longitudinal weld bevel; 45. First bevel; 46. Second bevel. Detailed Implementation

[0051] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0052] In aerospace and other fields, the manufacturing of large variable curvature thin-walled rotating structures (such as rocket engine nozzles) has long faced challenges: traditional integral molding relies on expensive large molds and equipment; while existing additive manufacturing combined with segmented welding can overcome equipment size limitations, it typically only performs circumferential segmentation. For ultra-large diameter, high-ratio structures, the axial stiffness and thermal compatibility are insufficient, and welding deformation and thermal stress control are difficult. Therefore, this invention proposes a new low-cost, high-precision manufacturing method and system.

[0053] On one hand, a specific embodiment of the present invention discloses a method for manufacturing a rocket engine nozzle with a buffer cavity, wherein the nozzle is a thin-walled nozzle with an internal cooling channel, and the method includes the following steps:

[0054] S1. Dual segmentation: The three-dimensional model of the nozzle is divided into N equal parts along its circumference, and then into at least an upper sub-segment and a lower sub-segment along its axial direction, thereby forming multiple independent sub-components, where N is an integer greater than or equal to 4;

[0055] S2. Additive manufacturing: Using laser selective melting technology, the sub-components are printed separately on a device with a forming area smaller than the maximum diameter of the nozzle;

[0056] During the printing process, a circumferentially extending buffer cavity is pre-set in the docking area between the upper and lower segments. This cavity is connected to the internal cooling channel of the nozzle and is used to provide a buffer space for thermal expansion during operation. When the coolant flows through it, the cross-sectional abrupt change promotes turbulence and enhances heat transfer.

[0057] S3. Lateral assembly welding: The upper and lower segments belonging to the same petal are joined together and positioned by the first welding fixture to weld and form a fan-shaped petal unit;

[0058] The first welding fixture includes a clamping structure for accommodating and positioning the upper and lower segments, with a welding torch window on the inner side of the clamping structure; the sides of the upper and lower segments are respectively provided with additively manufactured integral positioning interfaces, which cooperate with the positioning base on the first welding fixture to achieve precise alignment;

[0059] During welding, a protective gas supply device is used to supply protective gas to the welding area. The device includes a protective gas cover covering the top of the fan-shaped unit. The protective gas flows downward through the cooling channel inside the fan-shaped unit and flows out from the bevel formed at the transverse joint of the upper and lower segments, covering the weld pool.

[0060] Welding is performed using a fiber laser with a spot diameter of 0.3-0.5 mm and a welding speed of 6-10 mm / s. Welding is carried out in segments, and low-temperature stress relief treatment is performed after welding.

[0061] By precisely matching the positioning interface with the tooling positioning base, and combining segmented welding with low-temperature stress relief process, the misalignment of the upper and lower sub-segments can be strictly controlled within 0.5mm, laying the foundation for the overall accuracy of subsequent longitudinal welding.

[0062] S4. Longitudinal welding: N fan-shaped units are arranged circumferentially and positioned by a second welding fixture. The longitudinal welds between the fan-shaped units are welded to form a complete nozzle. In the docking area between the upper and lower sub-sections, corresponding cavity structures are pre-set. After docking, a circumferentially extending buffer cavity is formed that communicates with the internal cooling channel of the nozzle.

[0063] The second welding fixture is a rotating frame structure. Its outer surface is used for circumferential installation and fixing of each fan-shaped unit. The two ends of the axial direction are provided with positioning bases that cooperate with the positioning parts of the fan-shaped units.

[0064] During welding, shielding gas is introduced into the inner side of the longitudinal weld groove through the longitudinal shielding gas channel integrated in the second welding fixture to achieve protection (e.g., Figure 9 and Figure 10 );

[0065] Welding uses the same fiber laser as transverse welding, with a welding speed of 8-12 mm / s. After welding, low-temperature stress relief treatment is also performed. Finally, the tooling is removed, the process allowance is removed, and the nozzle manufacturing is completed.

[0066] The rotating frame structure of the second welding fixture, through circumferential positioning constraints and axial reference limits, combined with unified welding parameters and stress relief processes, can control the overall roundness error of the nozzle to below 0.2mm, meeting the high precision requirements of the aerospace field for thin-walled rotating structures.

[0067] It should be noted that the "rocket engine nozzle with buffer cavity" of the present invention refers to a thin-walled rotating structure with a regenerative cooling channel and a curved generatrix, and its typical structure is as follows: Figure 1 The rocket engine nozzle assembly shown.

[0068] The phrase "equipment with a forming area smaller than the maximum diameter of the nozzle" means that the present invention does not require the purchase of ultra-large additive manufacturing equipment that matches the final product size. For example, conventional SLM equipment with a maximum forming size of 650mm×650mm can be used to manufacture nozzles with a maximum diameter of 3m using this method.

[0069] The "circumferentially extended buffer cavity" is as follows: Figure 4a and Figure 4bAs shown, a circumferentially extending independent cavity is pre-set in the middle of the mating surface of the upper and lower segments during the model design stage. This cavity is directly connected to the internal cooling channel of the nozzle. Its core function is not for the mechanical connection or positioning of the segments, but rather to play a functional role in releasing the circumferential thermal stress during nozzle operation and disturbing the cooling medium flowing through it to enhance heat exchange.

[0070] During implementation, a machine such as Figure 1 The rocket engine nozzle assembly shown is an example, with a target large end diameter of approximately 3 meters. To clearly demonstrate the structure of this invention, Figure 1 The layout of the cooling channels distributed circumferentially and axially inside the nozzle is shown in cross-section.

[0071] First, in the 3D modeling software, the nozzle model is precisely divided into 6 equal segments along the circumference (N=6), such as... Figure 2 As shown, six fan-shaped units are obtained. Each fan-shaped unit is then cut into upper and lower sub-segments at specific locations along the axial direction, resulting in a total of 12 sub-components. The dimensions of the segments and lobes must be strictly calculated to ensure that the maximum profile dimension (e.g., width) of each sub-component is less than or equal to the effective forming dimension of the selected SLM equipment (e.g., 650mm format). Typically, the width of a single lobe is controlled below 250mm. This dual-segmentation strategy can overcome equipment size limitations.

[0072] Next, the 3D models of all 12 sub-components, along with their supporting structures, are arranged in one or more forming chambers using a "layered, vertically staggered placement" method. Using 316L stainless steel powder, all sub-components are printed in one go or in batches using the SLM process. After printing, post-processing includes support removal, sandblasting, and ultrasonic cleaning, and the mating edges are beveled.

[0073] The welding stage then begins. During transverse assembly welding, the upper and lower segments belonging to the same petal are assembled onto the first welding fixture. The integrated positioning interfaces on the sides of the upper and lower segments precisely engage with the first positioning base on the first welding fixture, achieving precise radial and circumferential positioning of the sub-components on the fixture, ensuring a misalignment of ≤0.5mm. Laser welding is used, with shielding gas introduced. During longitudinal welding, the six transversely welded fan-shaped units are assembled onto the outer ring of the second welding fixture. After precise positioning again, the longitudinal welds between the petals are welded. Finally, the fixture is removed, the process allowance reserved for positioning is removed, and leak detection and other verifications are performed, thus completing the manufacturing of the entire nozzle.

[0074] The manufacturing method provided in this embodiment transforms the manufacturing challenge from "relying on large equipment to print large parts" to "using small-to-medium-sized standardized equipment (e.g., 650mm format) to print small parts and then precisely assemble them" through a dual modular strategy combining "axial segmentation" and "circumferential segmentation." This not only allows conventional, low-cost additive manufacturing equipment to be applied to the manufacturing of ultra-large components, thereby reducing the equipment investment threshold and unit manufacturing cost; more importantly, through axial segmentation, the thermal expansion and deformation of the overall structure are decomposed into smaller sub-regions for management, while the pre-set circumferentially extended buffer cavities provide dedicated stress buffering and accommodation space for the thermal expansion differences between these sub-regions.

[0075] Specifically, during component operation, the circumferentially extending buffer cavity can absorb and accommodate the difference in axial and circumferential expansion caused by uneven heating, thereby actively releasing localized thermal stress concentrations that are difficult to avoid in traditional integral or single-segment structures. This improves the fatigue resistance of the structure under extreme thermal cycling loads.

[0076] It should be noted that the circumferentially extending buffer cavity is connected to the cooling channels inside the nozzle (the cooling channels of the upper and lower sub-sections) through multiple connecting holes (or slots) opened at its upper and lower ends. This makes the cavity essentially constitute an "intermediate transition channel" with a sudden change in cross-section, connecting the cooling channels of the upper and lower sub-sections after the nozzle is assembled.

[0077] This interconnected design ensures that, under operating conditions, the cooling medium (such as kerosene) flows continuously along the path from the upper sub-section cooling channel to the buffer cavity and then to the lower sub-section cooling channel, driven by system pressure, and finally exits from the nozzle outlet. Therefore, the medium within the cavity is in a state of continuous forced flow and displacement.

[0078] Meanwhile, since the cavity extends circumferentially and its cross-section is much larger than that of the connected conventional cooling channels, the flow velocity of the cooling medium decreases significantly after it flows into the cavity. The flow pattern changes from the restricted high-speed flow in the channel to the relatively slow flow in the cavity, forming a local slow flow zone or even micro-vortex in the cavity. Its main function is not to establish forced circulation, but to absorb the heat of the weld area by using the convection and thermal conduction of the medium in the cavity through the "liquid storage-heat exchange" mechanism, and then exchange heat with the main cooling flow through the cavity wall, thereby achieving auxiliary cooling and temperature homogenization of the high-temperature area.

[0079] Therefore, the method of the present invention not only successfully overcomes the physical manufacturing limitations of ultra-large components, but also significantly improves the service reliability and service life of the final product.

[0080] Furthermore, the buffer cavity is specifically designed as a cavity extending circumferentially, with multiple independent cavities distributed circumferentially within each fan-shaped unit. The cross-sectional shape of the cavity is as follows: Figure 4aThe longitudinal cross-sectional shape is as follows: Figure 4b As shown, it is preferably rectangular or approximately rectangular.

[0081] During the welding and assembly stage of segmented and segmented components, in order to ensure the strength, sealing and overall dimensional accuracy of the joint, the welding process needs to be optimized through bevel design: pre-processing bevels of specific shapes (such as transverse U-shaped bevels and longitudinal V-shaped bevels) at the butt joint edges to provide good accessibility for welding and ensure weld penetration and forming quality.

[0082] The buffer cavity is located between the first bevel and the second bevel in both the cross-section and longitudinal section. The first bevel is located on the side of the cavity closer to the outer side of the nozzle, forming the outer weld; the second bevel is located on the side of the cavity closer to the inner side of the nozzle, forming the inner weld. After the transverse welding is completed, the buffer cavity is enclosed between the outer and inner welds formed by the welding of the first and second bevels, creating a sealed but functionally independent stress buffer and flow field disturbance zone.

[0083] The cavities are independent and not connected, meaning that the circumferential cavities between different fan-shaped units are not directly connected in structure to maintain the independence of thermal management of each fan-shaped unit; however, within each fan-shaped unit, the cavity is still connected to the main cooling channel through the aforementioned connecting holes to achieve medium filling and heat transfer.

[0084] The "independent and non-connected" design between the circumferential cavities maintains the structural continuity of the nozzle axial direction and allows each cavity to independently buffer thermal expansion and cool flow disturbance to its respective fan-shaped area, achieving zoned and controllable thermal management, and matching the segmented manufacturing process of this invention.

[0085] Furthermore, after the transverse welding step is completed, the circumferentially extending buffer cavity is located precisely between the outer and inner weld seams between the upper and lower sub-segments (e.g., Figure 4b In the diagram, the first bevel is located on the outside of the cavity, forming an outer weld after welding; the second bevel is located on the inside of the cavity, forming an inner weld after welding.

[0086] In the transverse welding step, the welding is performed in the following order:

[0087] First, weld the inner weld: weld the second bevel through the inner welding gun window opened on the first welding fixture to form the inner weld.

[0088] Later welding of the outer side weld: After the inner side welding is completed and initially cooled, the first bevel is welded to form the outer side weld.

[0089] This welding sequence ensures that the external structure remains in a fine-tunable state when welding the inner side, which is beneficial for controlling overall deformation; while the outer side welding is carried out under the condition that the internal structure has been basically fixed, which further improves the centering and sealing of the weld.

[0090] This design encloses the cavity within two main weld seams, ensuring the integrity and sealing of the connection area while making the cavity a sealed but functionally independent stress buffer zone and flow field disturbance zone.

[0091] During implementation, the cross-sectional dimensions of the cavity can be designed based on the material's coefficient of thermal expansion and operating temperature to ensure it can effectively accommodate thermal deformation under operating conditions. For example, the radial width of the cavity can be designed within the range of 80-120 mm, and its axial wall thickness (i.e., the span of the cavity in the axial direction) can be designed to be at least 2 mm larger than the wall thickness of the adjacent nozzle, for example, within the range of 5-15 mm, thereby buffering and absorbing thermal expansion displacement on the order of 1-2 mm.

[0092] Furthermore, in the transverse welding step, the welding shielding gas is provided by a dedicated shielding gas supply device.

[0093] like Figure 5 and Figure 7 As shown, the protective gas supply device is aligned and fixedly connected to the positioning structure specially provided at the top of the first welding fixture through its bottom connecting part (e.g., Figure 8 (As shown). After the protective gas cover is installed, the outlet of its internal air inlet chamber automatically aligns with the inlet of the cooling channel at the top of the upper section, forming a sealed flow channel.

[0094] Specifically, after the protective gas (such as high-purity argon) is introduced into the gas inlet chamber inside the protective gas shield through the first gas inlet hole, the outlet of the gas inlet chamber is precisely aligned with the inlet of the cooling channel at the top of the upper segment. The gas flows into the cooling channel network and along these channels, eventually seeping out from the root area of ​​the butt groove between the upper and lower segments to be welded.

[0095] This method, which achieves rapid and sealed connection between the device and the component through a dedicated interface (connector), and allows the protective gas to flow into the internal channels of the component via an integrated cavity (inlet cavity), ultimately seeping out from the weld root, creates a protective gas environment with a controllable path from the inside out. This ensures excellent and stable inert gas protection even for narrow, deep bevels or inner welds, greatly avoiding defects such as weld oxidation and nitriding, and improving the quality of the weld joint.

[0096] To ensure the positioning accuracy of sub-components and control welding deformation during the welding process, this invention designs a matching special tooling system.

[0097] The first welding fixture not only provides clamping force, but also has an inner welding torch window on its inner side corresponding to the welding position, allowing the welding torch to extend in and weld the inner bevel (e.g. Figure 5 (As shown). Simultaneously, the upper segment has a positioning interface on its side, which closely engages with the corresponding first positioning base on the first welding fixture, enabling rapid and precise radial positioning of the segment on the fixture.

[0098] The second welding fixture is designed as a rotating frame structure (such as...). Figure 6 As shown, the outer surface profile of the fixture is adapted to the inner surface of the fan-shaped unit, and is used to circumferentially install and fix all N fan-shaped units. The second positioning base provided at both ends of the fixture is used to cooperate with the corresponding positioning interface of the fan-shaped unit, thereby constraining the axial position of all fan-shaped units during circumferential splicing and ensuring the accuracy of circumferential distribution.

[0099] This tooling system, by rigidly positioning and constraining the radial and circumferential degrees of freedom of the sub-components, combined with heat input control and stress management during the welding process, not only achieves precise cancellation of cumulative errors, but also directly controls the maximum misalignment within 0.5mm and the overall roundness error within 0.2mm, breaking through the technical bottleneck of the incompatibility between large size and high precision in traditional segmented welding.

[0100] To achieve the same high-quality protection during longitudinal welding, this invention integrates a dedicated gas protection structure into the second welding fixture. Specifically, (e.g.) Figure 9 and Figure 10 As shown in the diagram, the second welding fixture is provided with a longitudinal protective gas channel. The outlet of this channel is positioned adjacent to and directly opposite the root region of the longitudinal weld bevel formed by the adjacent edges of the two fan-shaped units after they are clamped and aligned on the fixture. The top of the longitudinal protective gas channel is provided with a second gas inlet hole that connects to an external gas source.

[0101] During welding, the shielding gas is introduced through the second inlet hole, then fills and flows through the longitudinal shielding gas channel on the second welding fixture, and is continuously ejected from its outlet, thereby forming a uniform, sufficient and stable inert gas shielding layer on the root and sidewall of the entire longitudinal weld groove.

[0102] This design integrates the protective gas channel into the positioning fixture, enabling the fixed-point and directional delivery of the protective gas. It simplifies the external gas supply device and completely avoids interference with the gas supply pipeline during welding operations, significantly improving the protection effect and ease of operation for longitudinal welding.

[0103] On the other hand, a specific embodiment of the present invention discloses a variable curvature nozzle, which is manufactured using the manufacturing method described above. It includes a body composed of N fan-shaped units circumferentially spliced ​​together. Each fan-shaped unit is composed of an upper sub-segment and a lower sub-segment connected by a transverse weld. At the connection interface between the upper sub-segment and the lower sub-segment, a circumferentially extending buffer cavity is formed that communicates with the internal cavity system of the body.

[0104] The nozzle inherits a unique internal structure formed during the manufacturing process, featuring a circumferentially extending buffer cavity. This cavity is not a hole created later in the manufacturing process, but rather a specific functional structure pre-formed during segmented design and printing, and permanently existing inside the product after welding.

[0105] by Figure 1 The rocket engine nozzle assembly shown is an example. This assembly consists of six identical fan-shaped units connected by six longitudinal welds. Each fan-shaped unit is further composed of an upper sub-segment and a lower sub-segment connected by a circumferential transverse weld. At the interface between the upper and lower sub-segments, along the circumference of the entire fan-shaped unit, is embedded a continuous, rectangular, circumferentially extending buffer cavity (such as...). Figure 3 (As shown in Figure 4). This cavity is connected to the cooling channel network of the nozzle through the edge conformal channels on the ribs, becoming part of the internal cavity system.

[0106] The variable curvature nozzle provided in this embodiment exhibits excellent resistance to thermal shock and thermal fatigue due to the introduction of a circumferentially extended buffer cavity. In traditional integral or simple segmented structures, the enormous thermal stress generated under high heat flux loads has nowhere to be released, easily leading to structural deformation or weld cracking. The circumferentially extended cavity in this structure provides a controllable "deformation buffer," allowing localized material to undergo slight displacement towards the cavity when heated, thereby reducing peak thermal stress by 30%-40% and significantly improving the structure's service life under extreme temperature alternation conditions.

[0107] The beneficial effects of this product structure stem from its unique internal configuration. The presence of the circumferentially extending buffer cavity firstly physically isolates the different thermal deformations from the upper and lower segments, avoiding stress concentration caused by rigid constraints. Secondly, the connection between the cavity and the cooling channel causes a sudden change and recovery of cross-sectional area when the working medium (such as fuel gas) flows through it, which effectively disrupts the laminar boundary layer and promotes turbulent mixing. For regenerative cooling nozzles, this means enhanced heat exchange between the coolant and the wall, with local heat exchange efficiency improved by 25%-30%, thereby reducing the operating temperature of critical areas (especially the heat-affected zone of the weld) and preventing overheating and ablation. Therefore, this structure achieves a synergistic improvement in both mechanical and thermal properties.

[0108] In a typical application embodiment, the variable curvature nozzle is a rocket engine nozzle assembly. The upper section features multiple longitudinally extending cooling channels. These cooling channels are designed with dual functions: during the manufacturing stage (welding), they serve as conduits for shielding gas, with gas introduced from the shielding gas supply device and flowing through them; during engine operation, they serve as cooling channels for the high-temperature exhaust gases, providing regenerative cooling or film cooling to the nozzle wall. This design significantly improves material utilization.

[0109] Furthermore, the dimensions of the circumferentially extending buffer cavity can be optimized. For example, its width can be selected between 80mm and 120mm, and its depth between 8mm and 15mm. A cavity that is too small will not provide sufficient buffering; a cavity that is too large may weaken the local structural strength. This dimensional range is an optimized range derived from thermo-fluid-structure interaction simulation analysis based on the thermal expansion of 316L stainless steel at typical engine operating temperatures (approximately 1.2mm) and the required cooling flow field disturbance intensity, achieving the best balance between stress relief and maintaining structural integrity.

[0110] Furthermore, in a specific embodiment of the present invention, a welding system for implementing the manufacturing method described above is disclosed, comprising: a shielding gas supply device, including a shielding gas cover for covering the top of a sub-component, the shielding gas cover having an external gas source interface and a mounting and positioning part; a first welding fixture for positioning and clamping an upper sub-segment and a lower sub-segment for transverse welding, the first welding fixture having a welding torch channel on its inner side; and a second welding fixture, having a rotating frame structure, for circumferentially positioning and clamping multiple single-lobed sub-components for longitudinal welding. This welding system is deeply integrated with the welding structure, welding sequence, and shielding gas supply method of the present invention.

[0111] The welding system provided in this embodiment simplifies the precision welding of complex components. It resolves the challenges of precise alignment, deformation control, and local protection that previously required advanced skills and repeated adjustments by establishing a mechanical interface and pre-defined procedures, thus ensuring the consistency and reliability of the manufacturing process.

[0112] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best implementation of the invention and do not limit the scope of the invention in any way.

[0113] Example 1

[0114] This embodiment manufactures a rocket engine nozzle assembly with a large end diameter of 3000mm, a small end diameter of 2000mm, and a height of 1200mm.

[0115] S1. Double Segmentation: The model is divided into 6 equal segments circumferentially (N=6), and axially into upper and lower segments 500mm from the small end. The pre-set circumferentially extended buffer cavity has a width of 100mm and a height of 10mm.

[0116] S2. Additive Manufacturing: Using a 650mm SLM machine and 316L stainless steel powder. Laser power 300W, scanning speed 1200mm / s, layer thickness 40μm. Twelve sub-component models are stacked and staggered, and printed in one go.

[0117] S3. Post-processing and beveling: Remove supports and sandblast clean. Process transverse U-shaped bevels and longitudinal 60° V-shaped bevels.

[0118] S4. Lateral Assembly Welding: The upper and lower sub-segments are placed on the first welding fixture and precisely positioned by engaging with the first positioning base through the positioning interface. A shielding gas supply device is installed and sealed onto the positioning structure of the first welding fixture. Before welding begins, 25 L / min of high-purity (≥99.99%) argon gas is introduced through this device as the welding shielding gas. The shielding gas flows through the inner cavity of the device into the cooling channel inside the sub-component and exits from the lateral U-shaped bevel, thereby forming an effective localized inert gas protective atmosphere in the weld pool area.

[0119] During welding, a fiber laser was used as the heat source, with a laser power of 2kW and a spot diameter of 0.3mm. Welding was performed in segments along the transverse U-shaped bevel at a welding speed of 6-8mm / s. Immediately after welding, a stress-relieving heat treatment was performed at 150℃ for 1 hour, followed by furnace cooling to room temperature, ultimately forming 6 independent fan-shaped units.

[0120] S5. Longitudinal welding: Arrange the 6 fan-shaped units circumferentially and install them on the second welding fixture. The second positioning base at both ends of the fixture cooperates with the corresponding positioning part of the fan-shaped unit and is clamped with bolts to ensure that all longitudinal V-shaped bevels are aligned and the misalignment is controlled within 0.1mm.

[0121] Argon gas at a rate of 15 L / min is introduced into the longitudinal protective gas channel through the second inlet, while nitrogen gas is continuously introduced into the circumferentially extending buffer cavity. Welding is performed using the same type of fiber laser as the transverse welding, with a welding speed set to 8-10 mm / s. The longitudinal V-grooves between each segment unit are welded sequentially to form a complete circumferential weld. Post-weld, a low-temperature stress-relief treatment at 150℃ for 1 hour is also performed.

[0122] S6. Final Processing: After the welded parts have cooled, remove all tooling. Remove the machining allowance reserved for positioning by machining. Finally, perform a hydrostatic test (30MPa, pressure held for 30min) on the manufactured nozzle to check for leaks. The leakage rate must meet the design requirements (e.g., ≤1×10⁻⁶). -9 Pa·m3 / s), thus completing the manufacturing of the entire nozzle.

[0123] Example 2

[0124] The manufacturing process, equipment, materials, and all process parameters except for the cavity width are exactly the same as in Example 1. The only difference is the width of the circumferentially extended buffer cavity. Three samples were prepared in total.

[0125] Sample 2A: Width of the circumferentially extended buffer cavity = 60mm.

[0126] Sample 2B: Width of the circumferentially extended buffer cavity = 100 mm. (This sample is identical to the product of Example 1)

[0127] Sample 2C: Width of the circumferentially extended buffer cavity = 120 mm.

[0128] Example 3

[0129] The only difference between this embodiment and Embodiment 1 is that:

[0130] S1. Dual Segmentation: Target diffuser large end diameter 1800mm. Use 450mm SLM equipment. Divide the model circumferentially into 8 equal segments (N=8) and axially into 3 segments (M=3). The pre-set circumferentially extended buffer cavity width is 80mm.

[0131] S2 to S6. Manufacturing and Welding: Following the process flow of Example 1, manufacturing was completed using a tooling system of appropriate dimensions. The result was the successful manufacturing of medium to large-sized components using small equipment.

[0132] Comparative Example 1

[0133] The same nozzle model, materials, and 650mm SLM equipment as in Example 1 were used. The nozzle model was divided into 6 equal segments circumferentially without any axial segmentation; therefore, the sub-components were complete fan-shaped segments, and the model did not include the circumferentially extending buffer cavity (14). The sub-components deformed significantly after printing (average warpage of approximately 1.8mm), requiring additional correction. Welding was performed using a conventional external gas shield protection.

[0134] Comparative Example 2

[0135] This comparative example uses the same model and equipment as Example 1. In terms of model design, the nozzle is divided into 6 equal segments along the circumference (N=6), but no axial segmentation (M=1) is performed. At the same time, a circumferentially extending buffer cavity (14) with the same size as that in Example 1 is pre-placed in the middle of the model. As a result, the size of the sub-component exceeds the limit and printing cannot be completed.

[0136] Comparative Example 3

[0137] This comparative example sets up two control groups. Their manufacturing process, equipment, materials, segmentation method (6 petals × 2 segments) and welding fixtures are exactly the same as those in Example 1. The only difference is the width of the circumferentially extended buffer cavity.

[0138] Comparative Example 3A: Width of the circumferentially extended buffer cavity = 40mm.

[0139] Comparative Example 3B: Width of the circumferentially extended buffer cavity = 150 mm.

[0140] Comparative Example 4

[0141] The same 12 printed sub-components as in Example 1 are used, but the first and second welding fixtures and their positioning system of the present invention are not used during welding assembly; only general-purpose fixtures and manual adjustments are used.

[0142] Characterization results and analysis

[0143] The samples obtained above were subjected to thermal cycling fatigue testing and critical dimension inspection. The results are shown in Table 1 below.

[0144] Table 1. Comparison of Key Performance Characterization Results for Different Manufacturing Schemes

[0145]

[0146] Characterization results show that all examples (Example 1, Example 2-A / C, and Example 3) exhibit excellent overall performance, with thermal cycling fatigue lives ranging from 1.7 to 3.1 × 10⁻⁶. 5 Secondly, the peak circumferential thermal stress is within a safe range of 170-280MPa, the maximum welding misalignment is ≤0.5mm, and the overall roundness error is at a high precision level of 0.15-0.25mm.

[0147] Comparative Examples 1-4 have serious deficiencies in at least one key performance indicator: Comparative Example 1 lags behind in all performance indicators (thermal cycling fatigue life is only 1.0-1.2 × 10⁻⁶). 5 The circumferential thermal stress reached 320-350 MPa, the welding misalignment reached 0.8-1.20 mm, and the overall roundness error reached 0.70-0.80 mm; Comparative Example 2 could not be manufactured; Comparative Example 3A / B, although improved in thermodynamic performance by introducing a segmented or buffer cavity structure (lifespan 1.3-2.3 × 10⁻⁶), still exhibited significant thermal stress. 5 The stress was 150-310MPa, but the welding misalignment was still 0.30-0.60mm, the accuracy fluctuated greatly, and the optimal balance was not achieved; the assembly accuracy of Comparative Example 4 was severely deteriorated, the welding misalignment was ≥1.00mm, the overall roundness error was ≥0.50mm, and it was not practical for engineering.

[0148] Furthermore, the solution adopted in Example 1 (divided into 6 segments × 2 sections, using 650mm format equipment) has significant advantages in equipment investment, labor time consumption, and material utilization compared to Comparative Example 1 (divided into 6 segments × 1 section, requiring larger equipment or incurring high deformation correction costs) and Comparative Example 4 (lack of dedicated tooling leading to increased scrap rate). Overall, the manufacturing cost of this embodiment is estimated to be approximately 30%-40% lower than traditional large-size integrated printing or low-precision welding solutions.

[0149] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing a rocket engine nozzle with a buffer cavity, characterized in that, The nozzle is a thin-walled nozzle with an internal cooling channel (15), and the method includes the following steps: S1. Dual segmentation: The three-dimensional model of the nozzle is divided into N equal parts along its circumference, and then into at least an upper sub-segment (12) and a lower sub-segment (13) along its axial direction, thereby forming multiple independent sub-components, where N is an integer greater than or equal to 4; S2. Additive manufacturing: Using laser selective melting technology, the sub-components are printed separately on a device with a forming area smaller than the maximum diameter of the nozzle; S3. Horizontal assembly welding: The upper sub-segment (12) and the lower sub-segment (13) belonging to the same petal are joined together and positioned by the first welding fixture (2) to weld and form a fan-shaped petal unit (11); S4. Longitudinal welding: N fan-shaped units (11) are arranged circumferentially and positioned by the second welding fixture (4). The longitudinal welds between each fan-shaped unit (11) are welded to form a complete nozzle. In the docking area between the upper sub-segment (12) and the lower sub-segment (13), corresponding cavity structures are pre-set, forming a circumferentially extending buffer cavity (14) that is connected to the internal cooling channel (15) of the nozzle after docking.

2. The manufacturing method according to claim 1, characterized in that, The cross-sectional shape of the circumferentially extended buffer cavity (14) is rectangular or approximately rectangular.

3. The manufacturing method according to claim 2, characterized in that, The circumferentially extending buffer cavity (14) is located at the interface between the upper sub-segment (12) and the lower sub-segment (13), and after transverse welding, it forms a circumferential buffer structure located between the front weld and the back weld.

4. The manufacturing method according to claim 1, characterized in that, In the transverse welding step, a protective gas supply device (3) is used to supply protective gas to the welding area; The protective gas supply device (3) includes a protective gas cover covering the top of the fan-shaped unit. The protective gas cover is provided with a first air inlet (32) and an air inlet chamber (33) communicating with the first air inlet (32). The protective gas cover is connected and fixed to the positioning structure (23) at the top of the first welding fixture (2) via the connecting part (31) at its bottom.

5. The manufacturing method according to claim 4, characterized in that, The transverse welding step also includes a protective gas flow step: After the protective gas enters the air inlet cavity (33) through the first air inlet hole (32), it flows downward through the preset cooling channel (15) inside the fan-shaped unit and flows out from the butt joint groove formed at the transverse butt joint between the upper sub-section (12) and the lower sub-section (13) to cover and protect the weld pool in the butt joint groove area.

6. The manufacturing method according to claim 1, characterized in that, The first welding fixture (2) includes a clamping structure for accommodating and positioning the upper sub-segment (12) and the lower sub-segment (13); The inner wall of the fixture structure is provided with an inner welding gun window (22) for the welding gun to be inserted during transverse welding; The upper sub-segment (12) and the lower sub-segment (13) are respectively provided with additive manufacturing integrally formed positioning interfaces (16); The first welding fixture (2) is provided with a first positioning base (21) that matches the shape of the positioning interface (16). The positioning interface (16) and the first positioning base (21) cooperate to achieve precise positioning.

7. The manufacturing method according to claim 1, characterized in that, The second welding fixture (4) is a rotating frame structure, and its outer surface is used to circumferentially install and fix N fan-shaped units (11); the second welding fixture (4) has a second positioning base (41) at both ends of its axial direction, which is used to cooperate with the corresponding positioning part of the fan-shaped unit (11).

8. A variable curvature nozzle, characterized in that, Made by the manufacturing method of any one of claims 1 to 7, comprising a body circumferentially spliced ​​together by N fan-shaped units (11), each of the fan-shaped units (11) being composed of an upper sub-segment (12) and a lower sub-segment (13) connected by a transverse weld, and at the connection interface between the upper sub-segment (12) and the lower sub-segment (13), a buffer cavity (14) communicating with the internal cavity system of the body is formed.

9. The variable curvature nozzle according to claim 8, characterized in that, The fan-shaped unit (11) has a longitudinally extending cooling channel (15) inside, which forms a flow path for welding protective gas during manufacturing and a flow path for cooling medium when the rocket engine nozzle is working.

10. A welding system for carrying out the manufacturing method according to any one of claims 1 to 7, characterized in that, include: The protective gas supply device (3) includes a protective gas cover for covering the top of the sub-component, the protective gas cover being provided with an external gas source interface and an installation positioning part; The first welding fixture (2) is used to position and clamp the upper sub-segment (12) and the lower sub-segment (13) for transverse welding, and its inner side is provided with an inner welding gun window (22). The second welding fixture (4) has a rotating frame structure and is used for circumferential positioning and clamping multiple fan-shaped units (11) for longitudinal welding.

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