A common base set circumference elastic control method and a welding method for welding a cylinder segment

Abstract

The application provides a circumference elastic control method for a common bottom set and a welding method for welding with a cylinder segment, and comprises the following steps: S1, common bottom locking groove machining and cylinder segment blanking welding are coaxially machined by being installed on a foundation, the circumference of the common bottom locking groove is first machined in place, the inner circumference of the cylinder segment locking welding side is blanked and welded according to the set gap, the circumference of the cylinder segment and the circumference of the common bottom locking groove are matched, and a negative interference assembly working condition is reached; S2, the common bottom and the cylinder segment are set and matched by using the circumference gap; S3, after the common bottom and the cylinder segment are set in place, the interference circumference of the cylinder segment welding side is tightened to reach a tight fit state by an external clamping tool. The circumference elastic control method for the common bottom set and the welding method for welding with the cylinder segment are provided, a common bottom locking frame assembly method for circumference elastic control is provided, and the problems that the assembly of a 3.35m large-diameter common bottom frame is difficult, the efficiency is low, and the assembly is out of tolerance and cannot be welded are solved.

Description

Technical Field

[0001] The invention belongs to the field of PMI sandwich common bottom production, and in particular relates to a circumference elasticity control method of a common bottom suit and a welding method for welding the common bottom suit to a cylinder section. Background Art

[0002] To meet the increased payload and higher orbital altitude requirements of Starlink satellite launch missions, my country's new generation of medium-sized carrier rockets has for the first time adopted a 3.35m diameter hydrogen-oxygen final stage. The core hydrogen-oxygen final stage tank, designed for weight reduction and efficient utilization, features the latest PMI sandwich common bottom structure. The common bottom is a key structural component connecting the liquid hydrogen and liquid oxygen tanks, separating the two chambers.

[0003] PMI sandwich common bottom is a new type of sandwich common bottom structure. High-density PMI foam is filled between the metal common bottom interlayers to replace the traditional double-layer honeycomb sandwich common bottom. The PMI foam filled in the common bottom interlayer plays the role of vacuum insulation, ensuring the rigidity of the structure while eliminating the need to evacuate the common bottom.

[0004] In the hydrogen and oxygen final stage tank, the weld quality requirements for the common bottom lock girth seam are stringent. It serves to seal and isolate the liquid hydrogen tank and liquid oxygen tank. The weld not only bears the internal pressure and bending moment of the tank, but also transmits the axial load of the rocket body. The difficulties in the assembly welding of the common bottom lock girth seam of the PMI sandwich include the following aspects:

[0005] Difficulty 1: The bottom and the box barrel are assembled horizontally, and the assembly accuracy is difficult to control.

[0006] The common bottom and the box barrel section are assembled horizontally on a frame. During assembly, the common bottom needs to be flipped vertically 90° and moved horizontally evenly to ensure that the common bottom lock weld is accurately docked and inserted into the box barrel section. After assembly, the fitting gap between the common bottom and the barrel section must be no more than 0.5mm. Due to the weak rigidity of the barrel section, the roundness deformation of the barrel section needs to be precisely controlled.

[0007] Difficulty 2: The structure of the common bottom lock ring seam joint is asymmetric, and the heat dissipation condition of the joint is complex

[0008] One side of the common bottom lock bottom welding joint is a box bottom fork ring variable cross-section structure, and the other side is a cylindrical section. The asymmetric structure of the welding joint increases the difficulty of implementing the welding process. In order to ensure that the welding heat input effectively acts on the joint, the lock bottom welding groove needs to be specially designed to determine the weld groove width, groove depth, groove thickness, etc. During welding, a more effective welding method needs to be used to control the arc shape and arc stiffness to ensure effective penetration and good formation of the weld.

[0009] Difficulty 3: The materials on both sides of the common bottom lock weld are of unequal strength

[0010] The base material on the common bottom side of the common bottom lock bottom weld is in the MCS (T6) heat treatment state with a theoretical tensile strength of 390 MPa. The base material on the barrel section side of the lock bottom weld is in the C10S (T8) heat treatment state with a theoretical tensile strength of 460 MPa. When welding materials in different heat treatment states, there are differences in the performance on both sides of the weld joint.

[0011] Difficulty 4: The common bottom PMI interlayer material is sensitive to heat input

[0012] The PMI interlayer material (full name: polymethacrylimide) used to fill the gap between two metal substrates is sensitive to heat input. When the critical temperature exceeds 400°C, it will decompose and damage the joint. During the welding of interlocking joints, the arc heat input directly acts on the upper surface of the metal substrate. Some of the heat is transferred to the PMI interlayer through metal heat conduction. Excessive heat input can indirectly cause the PMI interlayer to overheat and decompose. The use of PMI interlayer material places more stringent requirements on weld penetration depth and welding heat input.

[0013] The technical methods currently used for conventional common bottom lock bottom annular seam assembly welding are as follows: the common bottom assembly adopts a horizontal set mode. After the common bottom is flipped 90 degrees, it is horizontally inserted into the welding side of the barrel section. Due to the poor roundness of the barrel section deformation, tools such as crowbars are required to operate, so that the barrel section is locally deformed and the common bottom is squeezed into the barrel section; the common bottom lock bottom joint adopts a conventional Y-shaped groove form, and the traditional tungsten inert gas arc welding process method is used during welding. The heat input of the molten pool is controlled by adjusting parameters such as welding current to ensure the formation of the weld. The common bottom lock bottom joint usually adopts an equal thickness process design, that is, the thickness of the common bottom lock bottom groove after the groove is opened is consistent with the thickness of the barrel section. The traditional common bottom interlayer is a honeycomb structure. Unlike the PMI interlayer common bottom, the former has a layer of fiberglass cloth bonded to the bottom of the metal base material, which acts as a heat insulator and is less sensitive to heat input. Summary of the Invention

[0014] In view of this, the present invention aims to provide a method for controlling the circumference elasticity of a common bottom sleeve to solve the problem of poor weld formation caused by poor local assembly quality.

[0015] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0016] A method for controlling the circumference elasticity of a common bottom suit comprises the following steps:

[0017] S1. The processing of the common bottom lock groove and the blanking and welding of the barrel section are carried out coaxially by installing on the foundation. The circumference of the common bottom lock groove is first machined into place, and the inner circumference of the barrel section lock bottom welding side is blanked and welded according to the set clearance. By matching the circumference of the barrel section and the circumference of the common bottom lock groove, the negative interference assembly condition is achieved;

[0018] S2. When assembling on the foundation, use the perimeter gap to fit the common bottom and the cylinder section together;

[0019] S3. After the common bottom and the barrel section are in place, the external clamping tool is used to tighten the interference fit of the barrel section welding side to achieve a tight fit.

[0020] S4. Weld the annular seams of the common bottom and the barrel section.

[0021] Furthermore, the perimeter size matching formula is L1-2πδ1=L2+Δd×2π

[0022] L1-outer circumference of the barrel section welding area; δ1-thickness of the barrel section welding area; L2-circumference of the common bottom lock bottom groove fitting area; Δd-fitting clearance.

[0023] Compared with the prior art, the circumference elastic control method of the common bottom set described in the present invention has the following beneficial effects: a circumference elastic control common bottom lock chassis assembly method is proposed, which solves the problem of difficulty and low efficiency in assembling the 3.35m large diameter common bottom frame, and the problem of assembly out of tolerance and inability to weld.

[0024] Another object of the present invention is to propose a welding method for welding a common bottom and a barrel section to solve the process phenomenon of equal thickness and unequal strength on both sides of the weld joint and improve the reliability of the process performance of the weld joint.

[0025] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0026] A welding method for welding a common bottom to a barrel section calculates the axial stress borne by the weld joint using the tank internal pressure and tank diameter. Under tank operating conditions, the axial stress borne by the parent metal on both sides of the common bottom lock weld is the same. Due to the difference in nominal tensile strength of the parent metal, unequal thickness is used to compensate for this difference to ensure consistent allowable stress on both sides.

[0027] Furthermore, the axial stress calculation method of the welded joint is σaxis=PD / 4

[0028] σ axis: axial stress borne by the welded joint; P: internal pressure of the tank; D: diameter of the tank.

[0029] Furthermore, the formula for the unequal thickness joint is δ 叉形环 / δ 筒段 =σ 同段 / σ 叉形环

[0030] δ 叉形环 : effective joint thickness of the fork ring side of the common bottom lock groove; δ 筒段 : effective joint thickness on the barrel side; σ 筒段 : nominal allowable stress of the parent material on the side of the barrel; σ叉形环 : Nominal allowable stress of the parent material on the fork ring side

[0031] Compared with the existing technology, the welding method for welding the common bottom and the barrel section described in the present invention has the following advantages: it proposes a process design concept of strong matching such as the lock bottom ring seam joint of the 3.35m diameter common bottom assembly, which solves the problem of unequal performance of thick matching joints such as the traditional common bottom lock bottom ring seam joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0033] Figure 1 This is a schematic diagram of unequal thickness matching of the common bottom locking bottom joints according to an embodiment of the present invention.

[0034] Figure 2 This is a cross-sectional schematic diagram of the PMI interlayer common bottom according to an embodiment of the present invention.

[0035] Description of reference numerals:

[0036] 1- fork ring side; 2- barrel section side; 3- common bottom upper bottom; 4- common bottom lower bottom; 5- insulation layer. DETAILED DESCRIPTION

[0037] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0038] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0039] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0040] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0041] In order to solve the problem of difficulty in assembling the traditional common bottom lock chassis, the circumference elastic control assembly method of the common bottom lock chassis is proposed:

[0042] The steps include:

[0043] S1. The processing of the common bottom lock groove and the blanking and welding of the barrel section are carried out coaxially by installing on the foundation. The circumference of the common bottom lock groove is first machined into place, and the inner circumference of the barrel section lock bottom welding side is blanked and welded according to the set clearance. By matching the circumference of the barrel section and the circumference of the common bottom lock groove, the negative interference assembly condition is achieved;

[0044] S2. When assembling on the foundation, use the perimeter gap to fit the common bottom and the cylinder section together;

[0045] S3. After the common bottom and the barrel section are in place, the external clamping tool is used to tighten the interference fit of the barrel section welding side to achieve a tight fit.

[0046] S4. Weld the annular seams of the common bottom and the barrel section.

[0047] As mentioned in the above steps:

[0048] First, the processing of the common bottom lock groove and the blanking and welding of the barrel section follow the principle of serial processing. The circumference of the common bottom lock groove is first machined into place, and the inner circumference of the barrel section lock bottom welding side is blanked and welded according to the set clearance of 0.4mm-0.6mm. By matching the circumference of the barrel section and the circumference of the common bottom lock groove, a negative interference assembly condition is achieved. Circumference size matching formula:

[0049] L1-2πδ1=L2+Δd×2π (1)

[0050] Where: L1 is the outer perimeter of the barrel section welding area; δ1 is the thickness of the barrel section welding area; L2 is the perimeter of the common bottom lock bottom groove set area; Δd is the set clearance.

[0051] Secondly, when assembling on the rack, the circumference gap is used to smoothly fit the common bottom and the cylinder section together, avoiding the problems of uneven fitting and product damage caused by the extrusion fitting method.

[0052] Finally, once the assembly is in place, an external clamping fixture is used, leveraging the elastic perimeter control concept for thin-walled aluminum alloy parts. The interference fit on the weld side of the cylinder is tightened by 3-5mm (corresponding to a 0.4-0.8mm gap change). This ensures that the gap in the common bottom-lock weld is eliminated, achieving a tight fit. After welding, the interference fit is offset due to welding shrinkage, returning to a normal state.

[0053] To address the problem of different parent material properties due to different heat treatment conditions on the fork ring side 1 and the barrel section side 2 of the common bottom lock bottom joint, a welding method for the common bottom and barrel section is proposed. This is a process method for welding the joint with equal strength but unequal thickness. The axial stress borne by the weld joint is calculated based on the internal pressure and diameter of the tank. Under the operating conditions of the tank, the axial stress borne by the parent material on both sides of the common bottom lock bottom weld is the same. Due to the difference in nominal tensile strength of the parent material, unequal thickness is used to compensate for the difference to ensure the consistency of the allowable stress of the parent material on both sides.

[0054] The calculation method of the axial stress of the welded joint is σaxis = PD / 4

[0055] σ axis: axial stress borne by the welded joint; P: internal pressure of the tank; D: diameter of the tank.

[0056] The formula for unequal thickness joints is δ 叉形环 / δ 筒段 =σ 同段 / σ 叉形环

[0057] δ 叉形环 : effective joint thickness of the fork ring side of the bottom lock groove; δ 筒段 : effective joint thickness of barrel section side 2; σ 筒段 : nominal allowable stress of parent material on the barrel side 2; σ 叉形环 : Nominal allowable stress of base material on fork ring side 1.

[0058] The details are as follows:

[0059] The heat treatment state of the parent material on the common bottom lock fork ring side is MCS, and the nominal tensile strength is 390MPa; the heat treatment state of the parent material on the lock bottom barrel section side 2 is C10S, and the nominal tensile strength is 460MPa. The tank film stress formula is:

[0060] σ 轴 =PD / 4 (2)

[0061] Where σ 轴 : axial stress borne by the welded joint; P: internal pressure of the tank; D: diameter of the tank.

[0062] According to the tank film stress formula, under the tank operating conditions, the axial stress on the parent metal on both sides of the common bottom lock weld is the same. Due to the difference in the nominal tensile strength of the parent metal, in order to ensure the consistency of the allowable stress of the parent metal on both sides, the unequal thickness design method is adopted to compensate. The unequal thickness joint design formula is:

[0063] δ 叉形环 / δ 筒段 =σ 同段 / σ 叉形环 (3)

[0064] Where, δ 叉形环 : effective joint thickness of the fork ring side of the bottom lock groove; δ 筒段 : effective joint thickness of barrel section side 2; σ 筒段 : nominal allowable stress of parent material on the barrel side 2; σ 叉形环 : Nominal allowable stress of base material on fork ring side 1.

[0065] like Figure 1 As shown, by applying the formula, the thickness of the 2 welding joints on the cylinder side is 4mm, and the thickness of the bottom lock joint after equal strength design is 5.0mm.

[0066] In addition, this embodiment also proposes a binary gas bottom lock welding process method with a helium-argon mixed protective atmosphere, which combines the advantages of the helium arc's high arc stiffness, strong penetration, and high arc energy with the advantages of the argon arc's good arc stability. This can not only ensure good weld formation, but also achieve a low-arc fast welding process by finely controlling the welding heat input, thereby avoiding damage to the common-bottom PMI interlayer caused by excessive welding heat input.

[0067] Combining the helium-argon mixture binary gas lock bottom welding process method, the engineering iteration optimization of the welding process parameters was carried out to determine the optimal helium-argon mixture ratio. The determined welding process parameter window is as follows:

[0068] Table 1 Helium-argon mixed binary gas common bottom lock bottom welding parameters

[0069]

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for controlling the circumference elasticity of a common bottom suit, characterized by: The steps include: S1. The processing of the common bottom lock groove and the blanking and welding of the barrel section are carried out coaxially by installing on the foundation. The circumference of the common bottom lock groove is first machined into place, and the inner circumference of the barrel section lock bottom welding side is blanked and welded according to the set clearance. By matching the circumference of the barrel section and the circumference of the common bottom lock groove, the negative interference assembly condition is achieved; S2. When assembling on the foundation, use the perimeter gap to fit the common bottom and the cylinder section together; S3. After the common bottom and the barrel section are in place, the external clamping tool is used to tighten the interference fit of the barrel section welding side to achieve a tight fit. S4. Weld the annular seam of the common bottom and the barrel section; The axial stress on the weld joint is calculated based on the tank's internal pressure and diameter. Under tank operating conditions, the axial stress on the parent metal on both sides of the common bottom lock weld is the same. Due to differences in the nominal tensile strength of the parent metal, unequal thickness is used to compensate for this difference to ensure consistent allowable stress on both sides. The calculation method of the axial stress of the welded joint is σaxis=PD / 4 σ axis: axial stress borne by the welded joint; P: internal pressure of the tank; D: tank diameter; The formula for unequal thickness joints is δ 叉形环 / δ 筒段 =σ 同段 / σ 叉形环； δ 叉形环 : effective joint thickness of the fork ring side of the common bottom lock groove; δ 筒段 : effective joint thickness on the barrel side; σ 筒段 : nominal allowable stress of the parent material on the side of the barrel; σ 叉形环 : Nominal allowable stress of the parent material on the fork ring side.

2. The method for controlling the circumference elasticity of a common bottom suit according to claim 1, characterized in that: The circumference size matching formula is L1-2πδ1=L2+Δd×2π; L1-outer circumference of the barrel section welding area; δ1-thickness of the barrel section welding area; L2-circumference of the common bottom lock bottom groove fitting area; Δd-fitting clearance.

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