Launch vehicle box bottom and method of forming same

Abstract

The application provides a launch vehicle box bottom and a forming method thereof, and comprises the following steps: S1, calculating stress distribution of the box bottom under the action of internal pressure by using a film stress method and a moment-free theory; S2, determining a tensile-compressive stress demarcation line in the weft direction according to the stress distribution of the box bottom under the action of internal pressure; S3, respectively forming the top and the bottom; and S4, splicing and welding the formed top and the bottom according to the tensile-compressive stress demarcation line in the weft direction, so as to obtain a final formed box bottom. The forming method of the launch vehicle box bottom provided by the application solves the problems of wrinkle elastic buckling of the bottom and cracking instability of the top of the box bottom under the action of internal pressure.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aerospace technology, in particular, to a launch vehicle box bottom and a forming method thereof. BACKGROUND

[0002] The diameter of a launch vehicle directly determines the carrying capacity of the launch vehicle. With the development of space activities, the demand for high-reliability manufacturing of rocket body structures is becoming more and more urgent. The design and service reliability of the structure of the box bottom, as a key component of the rocket body structure, are the top priority of the launch vehicle.

[0003] The forming technology and equipment manufacturing technology of the rocket box bottom component have always been the focus of the rocket manufacturing technology field at home and abroad. Foreign countries have developed the overall forming manufacturing technology and method of the box bottom since the 1970s. The super-thick plate spinning + machining technology developed by military enterprises such as Mitsubishi Heavy Industries in Japan, MT Aerospace Technology Company in Germany, and Boeing Company in the United States represents the leading level in the last century. Typical products include the H2 whole bottom in Japan, with a diameter of 5.2 meters; the whole bottom of Ariane, with a diameter of 5.6 meters; and the external hanging tank box bottom of the space shuttle in the United States, with a diameter of 5.5 meters. The materials are all 2195 aluminum lithium alloy and 2219 aluminum alloy. The plate blanks are spliced by friction stir welding technology, and the spinning process adopts hot spinning technology. The plate blank thickness reaches more than 70 mm. The reliability of the spliced bottom weld is still a difficulty in limiting the flight application of 5-meter whole bottom. Therefore, the 5-meter whole bottom spinning manufacturing technology has not been applied in batch production. Since the 21st century, China has also carried out research on spinning technology. Enterprises represented by the 211 Factory, 7102 Factory, 706 Institute, and 800 Institute of the Aerospace Science and Technology Group have successively carried out research on whole bottom forming technology and have made breakthrough progress. The 2250 diameter box bottom made of 5A06 material has passed the flight verification. The 3350 aluminum lithium alloy box bottom and the 3800 whole bottom box bottom developed by the 800 Institute have passed the ground test and are expected to complete the first flight by the end of 2024.

[0004] The super-thick plate material used in the above spinning technology has a plate blank thickness of 70 mm for the 5-meter whole bottom product abroad, and the material utilization rate is only 5.7%, resulting in extremely high material cost and processing cost. Therefore, domestic thin plate whole bottom liquid-filled deep drawing forming technology is proposed, which realizes the batch production of 3350 whole bottom and realizes the application verification of multiple materials. The material utilization rate is increased to more than 30%, and the processing efficiency is also greatly improved. However, under the background of space activity scheduling, high-reliability manufacturing of manned spaceflight, and manned deep space exploration, the whole bottom forming technology has been unable to meet the manufacturing requirements of 4-meter or even 10-meter whole bottom in the future.

[0005] To this end, the application provides a lightweight thin-wall box bottom design and manufacturing method, which solves the lightweight and high-reliability manufacturing requirements of future large-diameter box bottom components, and meets the low-cost and high-quality manufacturing of 4-meter or larger box bottom structures. SUMMARY

[0006] In view of the defects in the prior art, the application aims to provide a launch vehicle box bottom and a forming method thereof.

[0007] According to the application, a launch vehicle box bottom forming method is provided, which comprises the following steps:

[0008] Step S1: calculating the stress distribution of the box bottom under the action of internal pressure by using the thin film stress method and the moment-free theory;

[0009] Step S2: determining the tensile-compressive stress demarcation line in the latitudinal direction according to the stress distribution of the box bottom under the action of internal pressure;

[0010] Step S3: respectively forming the top and the bottom;

[0011] Step S4: according to the tensile-compressive stress demarcation line in the latitudinal direction, splicing and welding the processed top and bottom to obtain the final formed box bottom.

[0012] Preferably, the step S1 comprises:

[0013]

[0014]

[0015]

[0016]

[0017]

[0018]

[0019] wherein a represents the long axis of the ellipse, b represents the short axis of the ellipse, t represents the shell thickness, and p represents the acting force.

[0020] Preferably, the step S2 comprises:

[0021]

[0022]

[0023] m=a / b

[0024] wherein y is the short axis direction of the box bottom ellipse, x is the long axis direction of the box bottom ellipse, a is the long semi-axis of the ellipsoid equation, and b is the short semi-axis of the ellipsoid equation.

[0025] Preferably, step S3 includes:

[0026] The top is an integral thin-walled shell structure, which is a seamless curved surface component formed from a single plate.

[0027] The bottom is a circumferential welded structure, which is constructed by a welding manufacturing method.

[0028] Preferably, the forming process of the top includes: cutting the raw material into a circular blank, annealing or solution treating the circular blank; then processing the treated circular blank into a part blank using the top forming method, artificially aging the part blank, and finally obtaining the top through machining.

[0029] Preferably, the forming method of the top includes: hydraulic bulging method, liquid-filled deep drawing method, cryogenic deep drawing method, spin forming method, or additive forming method.

[0030] Preferably, the bottom forming process includes: using a flat blank to roll-bend in an annealed or solution-treated state to obtain a cylindrical or conical section, and then welding it into a complete ring using a bottom welding manufacturing method; if the roll-bending is performed in an annealed state, the welded complete ring is subjected to solution heat treatment; after obtaining the solution-treated complete ring, it is then formed by necking or bulging to obtain a rotating ring shell with a specific generatrix; then the ring shell is subjected to artificial aging treatment, and finally machining.

[0031] Preferably, the bottom welding manufacturing method includes: welding a cylindrical necking forming, welding a conical bottom expansion forming, ring additive manufacturing, or welding a cylindrical spin forming.

[0032] Preferably, the process of welding the top and bottom together includes welding the top and bottom together to form the bottom of the box using any one of the following welding methods: friction stir welding, arc welding, and laser welding.

[0033] The launch vehicle box bottom provided by the present invention is prepared by the launch vehicle box bottom forming method described above.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. This invention uses a latitudinal tensile and compressive stress dividing circle as a combined structure box bottom. The top cover is a thin-walled integral shell and the bottom is a thick-walled annular shell, thereby improving the ability of large-module box bottoms to resist wrinkling and cracking defects, and providing a reliable design and manufacturing method for the design and manufacturing of box bottoms of 4 meters and above.

[0036] 2. The present invention provides a method for forming the bottom of a launch vehicle box, which solves the problems of bottom wrinkling and elastic buckling and top cracking and instability that are prone to occur under internal pressure.

[0037] 3. The weld of this invention is located at the point of internal stress tension-compression transition. The weld area and bottom adopt a thickened structure, which enhances the anti-wrinkling ability of this area under compressive stress. At the same time, the weld's influence is eliminated under the tensile stress conditions in the warp and weft directions at the top, thereby improving the ability to resist cracking and instability under internal pressure at the top.

[0038] 4. This invention uses theoretical calculations to determine the stress distribution characteristics under internal pressure at the bottom of the tank. For tank bottoms with a modulus greater than 1, it calculates the intersection of latitudinal tensile and compressive stresses and designs the weld seams connecting the tank bottoms at these locations. The top adopts an integral component, and the bottom adopts a circumferential welded structure, thus realizing a highly reliable manufacturing method for the bottom of storage tanks of 4 meters and above. Attached Figure Description

[0039] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0040] Figure 1 This is a schematic diagram of the welded bottom of a traditional launch vehicle.

[0041] Figure 2 This is a schematic diagram of a box bottom structure with anti-wrinkling and anti-cracking instability capabilities provided by an embodiment of the present invention.

[0042] Figure 3 This is a schematic diagram of the stress element analysis at the bottom of the ellipsoidal box.

[0043] Figure 4 This is a schematic diagram of the ellipse equation for the meridian section.

[0044] Figure 5 This is a schematic diagram of the latitudinal stress distribution.

[0045] Figure 6 This is a structural diagram of the top section when the bottom diameter of the storage tank is 4200mm and the module is 1.6.

[0046] Figure 7 This is a schematic diagram of the bottom ring structure when the bottom diameter of the storage tank is 4200mm and the module is 1.6.

[0047] Figure 8 This is a flowchart of the box bottom structure forming process provided in an embodiment of the present invention. Detailed Implementation

[0048] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0049] Embodiment 1

[0050] According to the application, a method for forming a box bottom of a launch vehicle is provided, comprising:

[0051] Step S1: calculating stress distribution of the box bottom under the action of internal pressure by using a film stress method and a moment-free theory;

[0052] Step S2: determining a tensile-compressive stress demarcation line in the latitudinal direction according to the stress distribution of the box bottom under the action of internal pressure; in this embodiment, the tensile-compressive stress demarcation line in the latitudinal direction is used as a boundary to design the structure of the box bottom; the box bottom is divided into a top seamless part and a bottom thick area;

[0053] Step S3: respectively forming the top and the bottom;

[0054] Step S4: splicing and welding the formed top and bottom according to the tensile-compressive stress demarcation line in the latitudinal direction, so as to obtain a final formed box bottom.

[0055] Specifically, the step S1 comprises:

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062] Wherein, a represents a long axis of the ellipse, b represents a short axis of the ellipse, t represents a shell thickness, and p represents an acting force.

[0063] Specifically, in this embodiment, the step S2 comprises: the tensile-compressive stress demarcation line refers to a region with zero latitudinal stress, the latitudinal stress is compressive stress towards an opening region, and the latitudinal stress is tensile stress towards a bottom region. The demarcation line is related to a module of the box bottom. Taking an elliptic equation on a normal section passing through an axis of the box bottom as an example, the position coordinates of the critical line are:

[0064]

[0065]

[0066] m=a / b

[0067] Wherein, y is the coordinate of the bottom of the box in the direction of rotation, that is, the short axis direction of the bottom of the box ellipse, x is the long axis direction of the bottom of the box ellipse; a is the long semi-axis of the ellipsoid equation, b is the short semi-axis of the ellipsoid equation, and m is the modulus of the ellipsoid equation;

[0068] Specifically, the step S3 comprises:

[0069] The top is an overall thin-walled shell structure, adopts an overall seamless curved surface component formed by a plate blank, and the plate blank is free from welding and additive processes.

[0070] The cross-sectional curve of the longitudinal section of the bottom of the box, which can be a circle, an ellipse or a conic line.

[0071] The bottom is a ring-shaped welding structure and is formed by a welding manufacturing method. The bottom ring has a thick wall structure and a larger wall thickness than the top region. In this embodiment, the wall thickness of the bottom ring is 20-35 mm, and the wall thickness of the bottom region is 5-12 mm.

[0072] Specifically, the forming process of the top comprises: cutting a raw material into a circular plate blank, annealing or solid solution treatment of the circular plate blank, processing the treated circular plate blank into a part blank by a forming method of the top, artificial aging treatment of the part blank, and finally machining the top.

[0073] Specifically, the forming method of the top comprises: a hydraulic bulging method, a liquid-filled drawing method, an ultra-low temperature drawing forming method, a spinning forming method or an additive forming method.

[0074] Specifically, the forming process of the bottom comprises: roll bending forming of a flat blank in an annealed or solid solution state to obtain a cylindrical segment or a conical cylindrical segment, and then welding the formed whole ring by a welding manufacturing method of the bottom; when the roll bending forming is performed in the annealed state, the whole ring after welding is subjected to solid solution heat treatment; the whole ring in the solid solution state is subjected to necking or bulging forming to obtain a rotary ring shell with a specific generatrix; then the ring shell is subjected to artificial aging treatment, and finally subjected to mechanical machining.

[0075] Specifically, the welding manufacturing method of the bottom comprises: (1) wall plate roll bending + welding straight cylinder + hard die necking forming; (2) wall plate roll bending + welding straight cylinder + spinning necking; (3) wall plate roll bending + welding conical cylinder + bulging; (4) friction stir welding additive forming.

[0076] Specifically, the welding of the machined top and bottom comprises: welding the top and the bottom by any one of a friction stir welding, an electric arc welding and a laser welding to form the bottom of the box.

[0077] In the embodiment, for non-strengthenable aluminum alloy or stainless steel and the like, the above-mentioned parts (top and bottom members) are bent, roll-bent, expanded, and necked in an annealed state (solution treatment state). The forming process considers the regulation of uniform deformation to achieve control of the strength of the member, that is, the forming process needs to control the uniformity of the deformation amount of each region of the part. For example, the top part can adopt a liquid-filled drawing process method, and the size of the deformation amount is adjusted by regulating the back expansion amount of the blank.

[0078] According to the application, a box bottom of a launch vehicle is provided, which is prepared by the forming method of the box bottom of the launch vehicle.

[0079] Embodiment 2

[0080] Embodiment 2 is a preferred example of embodiment 1

[0081] According to the application, a box bottom of a launch vehicle is provided, which is prepared by the forming method of the box bottom of the launch vehicle.

[0082] Step S1: theoretical calculation of the meridional stress demarcation line of the box bottom, as shown in Figures 3 to 5 ;

[0083] Stress element column differential equation:

[0084]

[0085] wherein σ1 is the meridional stress; σ2 is the latitudinal stress; r1 is the meridional area radius; r2 is the latitudinal area radius; ds1 is the element radial arc length; ds2 is the element latitudinal arc length; dθ1 is the element radial angle; dθ2 is the element latitudinal angle; t is the shell thickness; and p is the acting force.

[0086] Substitute ds1=r1dθ1 and ds2=r2dθ2 into formula (1), and substitute sinθ=θ into it. When the angle is very small, formula (1) is simplified as

[0087] σ2tr1+σ1tr2=pr1r2 (2)

[0088] Formula (2) is further converted into

[0089]

[0090] r1 is the meridional area radius; r2 is the latitudinal area radius; r1 is obtained by using an elliptic equation and differential calculation as follows:

[0091]

[0092]

[0093] Wherein, x represents the long axis direction of the bottom of the ellipse, y represents the short axis direction of the bottom of the ellipse, is the first derivative of y with respect to x, is the second derivative of y with respect to x, a and b are the long axis and the short axis of the ellipse respectively.

[0094] The ellipse equation can be converted to

[0095]

[0096] Therefore

[0097]

[0098]

[0099] The above reciprocal formula (4) is introduced into the expression of the meridional curvature radius as follows:

[0100]

[0101] The normal of the plane used, define l is the vertical component of r2, then

[0102] r2=[l 2 +x 2 ] 1 / 2 (10)

[0103]

[0104]

[0105]

[0106]

[0107] The ratio of r1 and r2 is

[0108]

[0109] Simplify by applying the equation:

[0110] pπx 2 -σ1(2πx)tsinθ=0(16)

[0111] Since Substitute and combine

[0112]

[0113] Substitute the above formula into formula (3), and get

[0114]

[0115] The stress calculation equation of the ellipsoid bottom configuration box bottom is as follows:

[0116]

[0117]

[0118]

[0119]

[0120]

[0121]

[0122]

[0123]

[0124] This embodiment takes the ellipsoid bottom with a box bottom diameter of 4200 mm and a modulus of 1.6 as an example, the major axis of which is 2100 mm, and the coordinates of the stress demarcation circle thereof are x=1908 mm and y=556 mm obtained by substituting formula (19) and formula (20). The box bottom structure forming flowchart provided by the embodiment is shown in Figure 8 The diagram is a process route for a heat-treated strengthened aluminum alloy, a top component is formed by a liquid-filled deep drawing method, and a bottom part is formed by an expansion method.

[0125] S2, top integral part

[0126] Figure 6 is a top structure schematic diagram of the embodiment, the top is designed as an integral component, the opening diameter of the component is 3816 mm, the height is 765 mm, the wall thickness is designed according to internal pressure, and the wall thickness is 4.0 mm; the top is an ellipsoid crown, the major axis of the generatrix is 2100 mm, and the minor axis is 1312.5 mm. The generatrix of the revolving shell can also be designed as a circle, a cone or an arbitrary curve.

[0127] S3, bottom ring part

[0128] Figure 7 is a bottom ring structure schematic diagram, the bottom ring is designed as a tailor-welded structure component or an integral structure component, the large opening diameter of the component is 4200 mm, the small opening diameter is 3816 mm, the height is 549 mm, the wall thickness is designed according to internal pressure, the wall thickness is thicker than that of the top, the wall thickness at this position is designed according to the loss coefficient of welding reinforcement, generally according to a strength coefficient of 0.6, and then the wall thickness is 1.7 times thicker than that of the top region. According to the top region wall thickness of 4200 mm, the wall thickness is designed to be 7 mm. The ring part is equally divided into three segments in the ring direction, or is designed as an integral structure by using a stirring additive method.

[0129] S4, top member forming process

[0130] The forming process of the top member adopts a thin plate liquid-filled deep drawing process method, which can integrally stamp and form the top member. The overall blank diameter used is 4000-4500 mm, and the blank is integrally rolled or integrally forged.

[0131] After the top member is formed by the above process, a mirror milling method is used for thinning processing, and the initial thickness of the blank is 8 mm, and the thickness of the blank after machining is 4 mm.

[0132] S5, bottom member forming process

[0133] The forming process of the bottom member adopts a flat sector plate roll bending and welding to form a conical cylinder, and then expands to form an elliptical shell with an elliptical generatrix. The expansion forming can be hydraulic expansion or steel die expansion. The above process forms an ellipsoidal member, which is processed by turning to obtain an equal-thickness box bottom.

[0134] S6, welding of top and bottom rings

[0135] The box bottom top cover and the bottom ring are welded by the assembling method, and the welding adopts the friction stir welding method. After the box bottom member is welded, stress relief heat treatment or shape correction is performed according to needs.

[0136] While Figure 1 The figure shows a traditional launch vehicle tailor-welded box bottom schematic diagram; Figure 2 The figure shows a box bottom structure schematic diagram provided by the embodiment of the application, which has anti-wrinkling and cracking instability capacity.

[0137] The launch vehicle box bottom structure design and manufacturing method provided by the application is not only suitable for box bottom parts in the field of aerospace, but also suitable for other closed or semi-closed structural members; not only suitable for parts after sheet forming, but also suitable for components obtained by additive manufacturing, forging, casting and machining processes.

[0138] Those skilled in the art know that, in addition to implementing the system provided by the present application and each device, module and unit thereof in the form of pure computer readable program code, the system provided by the present application and each device, module and unit thereof can also be implemented in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers and embedded microcontrollers, etc. by logically programming the method steps to achieve the same functions. Therefore, the system provided by the present application and each device, module and unit thereof can be considered as a hardware component, and the devices, modules and units included therein for achieving various functions can also be considered as structures within the hardware component; the devices, modules and units for achieving various functions can also be considered as both software modules for implementing methods and structures within hardware components.

[0139] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0140] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be arbitrarily combined with each other without conflict.

Claims

1. A method for forming the bottom of a launch vehicle container, characterized in that, include: Step S1: Calculate the stress distribution at the bottom of the box under internal pressure using the membrane stress method and moment-free theory; The method for calculating the stress distribution at the bottom of the box under internal pressure in step S1 is as follows: in, ; ; in, Represents the major axis of the ellipse. Denotes the minor axis of the ellipse. Indicates shell thickness. Represents the applied force; (x, y) are the coordinates of a point on the cross-section. Radial stress; It is latitudinal stress; The radius of the region in the meridional direction; The radius of the region in the latitudinal direction; Step S2: Determine the tensile and compressive stress boundary line in the latitudinal direction based on the stress distribution at the bottom of the box under internal pressure; The tension-compression stress boundary line is the region where the latitudinal stress is zero. The latitudinal stress towards the opening region is compressive stress, and the latitudinal stress towards the bottom region is tensile stress. The tension-compression stress boundary line is related to the module of the bottom of the box. Based on the equation of the ellipse on the normal section passing through the bottom axis of the box, the position coordinates of the tension-compressive stress boundary line are: Where y is the direction of the minor axis of the box-bottom ellipse, x is the direction of the major axis of the box-bottom ellipse; a is the semi-major axis of the ellipsoid equation, and b is the semi-minor axis of the ellipsoid equation. Step S3: Perform shaping processing on the top and bottom respectively; Step S4: Based on the tensile and compressive stress boundary line in the weft direction, weld the processed top and bottom together to obtain the final shaped box bottom.

2. The method for forming the bottom of a launch vehicle container according to claim 1, characterized in that, Step S3 includes: The top is an integral thin-walled shell structure, which is a seamless curved surface component formed from a single plate. The bottom is a circumferential welded structure, which is constructed by a welding manufacturing method.

3. The method for forming the bottom of a launch vehicle container according to claim 1, characterized in that, The forming process of the top includes: cutting the raw material into a circular blank, annealing or solution treating the circular blank; then processing the treated circular blank into a part blank through the top forming method, artificially aging the part blank, and finally obtaining the top through machining.

4. The method for forming the bottom of a launch vehicle container according to claim 3, characterized in that, The forming methods for the top include: hydraulic bulging, liquid-filled deep drawing, cryogenic deep drawing, spin forming, or additive forming.

5. The method for forming the bottom of a launch vehicle container according to claim 1, characterized in that, The bottom forming process includes: using a flat blank to roll-bend in an annealed or solution-treated state to obtain a cylindrical or conical section, and then welding it into a complete ring using a bottom welding manufacturing method; if the roll-bending is performed in an annealed state, the welded complete ring is subjected to solution heat treatment; after obtaining the solution-treated complete ring, it is then formed by necking or bulging to obtain a rotating ring shell with a specific generatrix; then the ring shell is subjected to artificial aging treatment, and finally machined.

6. The method for forming the bottom of a launch vehicle container according to claim 5, characterized in that, The bottom welding manufacturing method includes: welding a cylindrical necking forming, welding a conical bottom expansion forming, ring additive manufacturing, or welding a cylindrical spinning forming.

7. The method for forming the bottom of a launch vehicle container according to claim 1, characterized in that, The process of welding the top and bottom together includes welding the top and bottom together to form the bottom of the box using any one of the following welding methods: friction stir welding, arc welding, or laser welding.

8. A launch vehicle box bottom, characterized in that, It is prepared by the method for forming the bottom of a launch vehicle box as described in any one of claims 1 to 7.

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