A method for forming an extra-large thick-wall stepped cylinder with flanges

Abstract

The present application relates to a kind of forging forming methods, specifically, a kind of forming method of thick-walled stepped cylinder with super large flange, comprising the following steps: S1: based on the structure of the stepped cylinder to be formed, blank, die and variable-diameter mandrel are designed respectively;S2: according to the design of step S1, machining is carried out, to obtain blank;S3: the blank obtained in step S2 is subjected to multi-pass necking free forging, so that the size of inner diameter and outer diameter is reduced;S4: the cylinder precursor obtained in step S3 is subjected to multi-pass local free forging, to form small diameter section;S5: the cylinder intermediate body obtained in step S4 is expanded and lengthened by variable-diameter mandrel, to expand the inner diameter difference and increase the length of blank.Compared with the prior art, the present application solves the problem that the prior art cannot form forgings with extreme variable-diameter structure in the field of super large forgings, and realizes the forming of super large forgings with an inner diameter change of nearly 50%.

Description

Technical Field

[0001] This invention belongs to the field of extra-large forgings, specifically relating to a method for forming an ultra-large thick-walled stepped cylindrical body with an inner flange. Background Technology

[0002] Nuclear power pressure vessels are typically welded from multiple ring components and end caps, and their quality is affected by the quality of the welds. If they could be integrally formed, the number of welds could be reduced. Integral forming is particularly challenging for ultra-large, thick-walled stepped cylinders with internal flanges (outer diameter exceeding 4m and wall thickness exceeding 400mm), as it involves the integral forming of two stepped sections with a significant dimensional abrupt change between them. Furthermore, an internal flange is located at the abrupt change point, making it an extra-large, complex, irregularly shaped forging.

[0003] Its extreme structural dimensions present several challenges to the forming process, including but not limited to the following:

[0004] (1) The inner diameter of the forging changes drastically, shrinking by nearly half. Combined with its large size, this poses a significant challenge to the forming process.

[0005] (2) Unlike traditional variable cross-section cylinders, the cross-section of this type of cylinder changes abruptly without size transition, which makes it impossible to form such cylinders by traditional hole expansion forming methods. Therefore, innovation in forming process is required.

[0006] (3) As an extra-large forging, its extra-large size itself means a great deformation resistance during the forging process, which places strict requirements on the capabilities of the forging equipment.

[0007] (4) The wall thickness of the two sections of the forging is different. The uneven wall thickness means that the forming process of the forging needs to be adjusted based on the traditional process.

[0008] CN112692223A discloses a transition section with varying diameters, a forming method, an auxiliary tool, and a hydrogenation reactor. The method includes pre-treating a steel ingot to obtain a billet; sequentially performing upsetting, mandrel drawing, and pre-expansion treatments on the billet; flattening and pre-forming the pre-expansioned billet; and using an auxiliary tool in conjunction with forging to obtain transition sections with different inner diameters. This technology can only form cylinders with small variations in inner diameter; it cannot form structures with large variations in inner diameter.

[0009] Therefore, there is a need to provide a forming method to better form ultra-large thick-walled stepped cylinders with inner flanges. Summary of the Invention

[0010] The purpose of this invention is to provide a forming method for an ultra-large thick-walled stepped cylindrical body with an inner flange, in order to solve at least one of the above-mentioned problems. This method addresses the shortcomings of existing technologies in forming forgings with extreme diameter variations in the field of extra-large forgings, enabling the forming of extra-large forgings with an inner diameter variation of nearly 50%. Furthermore, by designing a reasonable billet structure, the method reduces the reduction and load required for the closing process, lowers the requirements for equipment, and increases the stability of the billet during the closing process, thereby reducing the occurrence of instability.

[0011] The objective of this invention is achieved through the following technical solution:

[0012] A method for forming an ultra-large thick-walled stepped cylindrical body with an inner flange, used for forming stepped cylindrical bodies with an outer diameter of not less than 4m and a wall thickness of not less than 400mm.

[0013] The forming method includes the following steps:

[0014] S1: Design the blank, mold and variable diameter mandrel based on the structure of the stepped cylinder to be formed;

[0015] S2: Perform machining according to the design in step S1 to obtain the blank;

[0016] S3: Perform multiple passes of free forging on the billet obtained in step S2 to reduce the size of the inner and outer diameters;

[0017] S4: Perform multiple passes of local free forging on the cylinder precursor obtained in step S3 to form a small diameter section.

[0018] S5: The intermediate cylindrical body obtained in step S4 is enlarged and lengthened by using a variable diameter mandrel to increase the inner diameter difference and length of the blank.

[0019] Preferably, the stepped cylindrical body comprises a small-diameter section and a large-diameter section of integral structure. The small-diameter section is connected to one end of the large-diameter section, with the inner surface of the connection continuously changing and the outer surface of the connection being an arc connection. Here, the small-diameter section refers to a section of the cylinder with a smaller diameter at the opening, and the inner diameter of the small-diameter section is approximately 50% smaller than the inner diameter of the large-diameter section.

[0020] Preferably, in step S1, the design of the billet is optimized by finite element numerical simulation; the finite element numerical simulation includes the simulation of the free forging process of closing, the simulation of the local free forging process, and the simulation of the hole expansion and drawing process by using a variable diameter mandrel.

[0021] Preferably, in step S2, the machining includes upsetting and punching, mandrel drawing, lever reaming and mechanical thinning performed sequentially.

[0022] Preferably, the upsetting and punching process involves: upsetting the billet and then punching a hole in the center to form a through hole; the mandrel drawing process involves: inserting a mandrel into the through hole for drawing; the mandrel enlarging process involves: inserting an enlarging mandrel into the through hole to uniformly enlarge the hole and upsetting it to form a cylindrical billet with a flat end face; and the mechanical thinning process involves: removing material from the outer side of the billet to reduce the wall thickness and shape.

[0023] Preferably, in step S3, during the free forging process of closing the die: before pressing down, the bottom surface of the closing die is not lower than the end face of the billet, and the zero position of the pressing amount is calibrated.

[0024] Preferably, in step S4, during the local free forging process, a symmetrical pressing method is adopted, and after each pressing of the anvil, the cylinder precursor is rotated by a certain angle, and then pressed down again.

[0025] Preferably, the rotation angle is 30°.

[0026] Preferably, in step S5, the variable diameter mandrel is inserted into the through hole of the intermediate body of the cylinder, and the intermediate body of the cylinder abuts against the variable diameter step of the variable diameter mandrel, and then the hole is enlarged and lengthened.

[0027] Preferably, during the reaming and drawing process, a small anvil is used to press the cylinder from the diameter change point along the axial direction to the end. After each pass is completed, the cylinder is rotated before proceeding to the next pass. Between each pass, the cylinder should be kept in contact with the diameter change step of the diameter change mandrel.

[0028] In all the above processes, the materials need to be heated and kept warm according to the forging temperature requirements.

[0029] The working principle of this invention is as follows:

[0030] This invention employs a localized free forging process based on a narrowing technique. Through narrowing, localized free forging, and mandrel expansion and elongation, it enables the formation of forgings with extreme diameter variations that are impossible to achieve with traditional processes, particularly in the field of extra-large forgings. By initially reducing the end dimensions of the forging through narrowing forging of a relatively small, thick-walled cylinder, combined with localized upsetting and shaping processes, the inner diameter of the material is further reduced, the wall thickness increased, and a stepped structure is formed during localized upsetting. Finally, the minimum inner diameter of the forging and the difference between the inner diameters of the cylinder and the mandrel are further increased through expansion and elongation. This allows for the formation of stepped, thick-walled cylinders with internal flange structures in the field of extra-large forgings. The forging process preserves the metal fiber flow lines to the greatest extent possible, ensuring the mechanical and fatigue properties of the forging and improving its service stability. This invention utilizes localized free forging and mandrel expansion and elongation, enabling the forging to be formed under existing forging equipment conditions, reducing the equipment requirements for forgings with extreme structures.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] This invention addresses the forming of ultra-large, thick-walled stepped cylindrical bodies with internal flanges, proposing a solution involving localized deformation after necking, combined with a reaming and elongation process using a variable-diameter mandrel. This solution can form forgings with the aforementioned extreme dimensional structures, and unlike conventional necking processes, this invention offers the following advantages:

[0033] (1) Traditional closing process has requirements on the size of closing deformation, and cannot form forgings with large size differences. By adopting the hole expansion and drawing process of variable diameter mandrel and combining it with the local deformation process after closing, it is possible to form extra-large forgings with an inner diameter change of nearly 50%.

[0034] (2) By introducing the mandrel expansion process and local deformation process, the present invention reduces the diameter of the blank required for the closing process, reduces the forming load, and at the same time reduces the amount of pressing and load required for the closing process, thus reducing the equipment requirements.

[0035] (3) The blank shape and size used in this invention have a thicker cylinder wall than the blank shape and size used in the traditional closing process, which increases the stability of the blank during the closing process and reduces the occurrence of instability. Attached Figure Description

[0036] Figure 1 A schematic diagram of the structure of an ultra-large thick-walled stepped cylindrical body with an inner flange;

[0037] Figure 2 This is a schematic diagram of the target forging in an embodiment of the present invention;

[0038] Figure 3 This is a process flow diagram of the forming method of the present invention.

[0039] Figure 4 This is a process flow diagram of the blank machining in the forming method;

[0040] Figure 5 This is a schematic diagram of the structural changes during the forming process of the present invention;

[0041] Figure 6 This is a diagram showing the dimensional envelope of the forming dimensions of the ultra-large thick-walled stepped cylindrical body with an inner flange obtained by the present invention.

[0042] In the diagram: 1-part; 2-forging. Detailed Implementation

[0043] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. This embodiment is based on the technical solution of the present invention and provides detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following embodiments.

[0044] In the following embodiments, unless otherwise specified, the functional components or structures are conventional components or structures used in the art to achieve the corresponding functions; unless otherwise specified, the processing techniques are also conventional processing techniques used in the art.

[0045] An ultra-large, thick-walled stepped cylindrical body with an inner flange; the conventional structural shape of such forgings is as follows: Figure 1 As shown, it encompasses all such cylindrical structures, which consist of two segments with different diameters. The smaller diameter segment is connected to one end of the larger diameter segment. The inner surface of the connection is continuously changing, while the size changes abruptly. The outer surface can be varied according to different structural requirements.

[0046] Example

[0047] like Figure 2 The diagram shows a schematic of an ultra-large thick-walled stepped cylindrical body with an inner flange, which is the target forging actually produced in this embodiment. It consists of an upper small-diameter section (with an inner flange) and a lower large-diameter section, which are essentially a single unit. The inner wall of the stepped cylindrical body changes continuously at the connection between the large-diameter and small-diameter sections, while the outer wall forms an arc structure at the same connection. The free end of the small-diameter section tapers, and the inner flange is located at the free end of the small-diameter section. The large-diameter section is essentially a straight cylindrical structure; therefore, the inner diameter of the free end of the small-diameter section is approximately 50% of the outer diameter of the large-diameter section, and the inner diameter changes drastically at the inner flange.

[0048] This embodiment provides a forming technology for an ultra-large, thick-walled stepped cylindrical body with an inner flange (cylinder outer diameter reaches 5.5m, cylinder wall thickness reaches 500mm), such as... Figure 3 , 5 As shown in Figure 6, the overall steps are as follows:

[0049] (1) Design the blank: Based on the shape of the ultra-large thick-walled stepped cylindrical part 1 with an inner flange, design the blank size and shape;

[0050] (2) Mold design: Based on the inner diameter difference requirement of the ultra-large thick-walled stepped cylindrical part 1 with inner flange, design the mold shape for each pass of the closing process.

[0051] (3) Design of local free forging die: Based on the structural characteristics of the small diameter section of the ultra-large thick-walled stepped cylindrical part 1 with inner flange, design the die shape used in the local free forging process;

[0052] (4) Design of variable diameter mandrel: Based on the shape of the ultra-large thick-walled stepped cylindrical part 1 with inner flange, design the variable diameter mandrel used in the process of mandrel expansion and elongation.

[0053] (5) Billet preparation:

[0054] (a) Upsetting and punching: After upsetting the billet, a hole is punched in the center to form a through hole;

[0055] (b) Mandrel drawing: The mandrel is inserted into the through hole of the punched billet for drawing;

[0056] (c) Hole enlargement by mandrel: Insert the mandrel into the through hole to enlarge the hole evenly, and then upset to form a cylindrical blank with flat end faces;

[0057] (d) Machining: Based on the designed blank shape, the blank after hole expansion is machined on the outside to remove local material and reduce the wall thickness;

[0058] (6) Multi-pass free forging with narrowing: The heated and heat-preserved billet is forged with narrowing to initially reduce the inner and outer diameters;

[0059] (7) Local free forging process: The reheated billet is subjected to multiple local free forging passes, and symmetrical downward pressing is used to form a small diameter section of cylindrical structure;

[0060] (8) Mandrel expansion and lengthening process of variable diameter mandrel: Place the partially free forged billet on the mandrel, and use a small anvil to expand and lengthen the hole at the same time, further increasing the inner diameter difference of the billet while increasing the length of the billet.

[0061] In all the above processes, the materials need to be heated and kept warm according to the forging temperature requirements.

[0062] More specifically, it includes the following steps:

[0063] (1) Blank Design: When designing the blank shape and dimensions, based on the shape and dimensions of the ultra-large thick-walled stepped cylindrical part 1 with an inner flange, the forging 2 is divided into a small-diameter section and a large-diameter section. Based on the principle of constant volume, the blank design reduces the inner and outer diameters and height of the cylindrical part, increases the wall thickness, reduces the diameter reduction required for the closing process, and lowers the load. Based on the shape and dimensions of the thick-walled cylindrical part 1 with abrupt changes in inner diameter and uneven wall thickness, and considering the estimated deformation, a blank with smaller inner and outer diameters and shorter length is designed. The blank shape is improved and optimized using the plastic forming finite element numerical simulation software FORGE. The specific design process is as follows:

[0064] S101: Based on the outline and size requirements of the ultra-large thick-walled stepped cylindrical part 1 with an inner flange, the cylindrical part is divided into two parts: a small diameter section and a large diameter section. The volume of each part is calculated according to the principle of constant volume. Combined with the requirements of the forging drawing 2 and subsequent processes, the deformation is estimated, the inner and outer diameters of the billet are initially determined, and the total height is calculated based on the calculated volume.

[0065] S201: Import the billet design results obtained in S101 into the finite element software, preliminarily design the mold dimensions, simulate the forging process, determine whether the load in the simulation results exceeds the limit of the available press, and determine whether the shape of forging 2 conforms to the estimated deformation. Specifically: the first forging load should be within the nominal pressure of the press (since the load of forging is relatively large, it is necessary to ensure that the load required in the design process is less than the maximum pressure (nominal pressure) that the press can output), and minimize the diameter of forging 2 as much as possible. The final forging should be straightened to make the forging material into a straight wall to reduce the bulging at the cylinder diameter change point during subsequent deformation. If the simulation results show that the shape of forging 2 meets the requirements, then simulate the local free forging process on this basis, and extract the overall strain and temperature distribution of forging 2 during the simulation. If the shape of forging 2 does not meet the requirements, then take the forming defects in S201 into account, return to S101, and redesign the billet shape.

[0066] S301: Based on the simulation results of the closing process obtained in S201, design the anvil for the local free forging process and import it into the finite element software to simulate the local free forging process. Determine whether the simulation results meet the two-stage cylinder size requirements of the forging 2 with abrupt change in inner diameter and uneven wall thickness. Specifically, pay attention to the bulging of the outer material during the local pressing process to avoid folding or exclude folding from the range of forging 2. If the simulation results show that the shape of forging 2 meets the requirements, then perform the variable diameter mandrel expansion process based on this model, and extract the overall strain and temperature distribution of forging 2 during the simulation. If forging 2 does not meet the requirements, then take the forming defects of S301 into account, return to S101 to redesign the billet shape, closing forging process, and local free forging process;

[0067] S401: Based on the billet design results obtained in S301, design the variable diameter mandrel and anvil for the variable diameter expansion and drawing process, and import them into finite element software to perform finite element simulation of the variable diameter mandrel expansion and drawing. Based on the simulation results of the inner and outer diameters and length of forging 2, determine whether it meets the outline, dimensions, and subsequent machining requirements of the thick-walled cylindrical part 1 with abrupt changes in inner diameter and uneven wall thickness. If the simulation results show that the shape of forging 2 meets the requirements, then extract the overall strain and temperature distribution of forging 2 during the forging process. If the shape of forging 2 does not meet the requirements, then take into account the forming defects in S401, return to S101 to redesign the billet shape and the forging process and local free forging process;

[0068] Furthermore, in step (5), the blank shape and size designed in step (1) are machined, such as... Figure 4 As shown.

[0069] Furthermore, in step (6), the diameter-changing portion of the thick-walled cylindrical part 1, which has a sudden change in inner diameter and uneven wall thickness, is forged to narrow its opening. The specific operation process is as follows:

[0070] S601: Multi-pass free forging with closing: Install the closing die and the billet in place, and calibrate the zero position of the pressing amount by confirming that the lower end face of the die is flush with the upper end face of the billet (or the bottom face of the die is slightly higher than the end face of the billet). According to the pressing amount determined in step (2), ensure that the pressing amount of each pass is accurate.

[0071] S701: Local upsetting: Use a small anvil, rotate the billet a certain angle after each press, and then press down again. Avoid excessive pressure in a single press, which could lead to large localized deformation.

[0072] S702: Local shaping: Forging is carried out using a mold designed in step (3) that is similar to the structure of the small-diameter section of the cylinder. The billet is rotated 30° after each pressing of the anvil to avoid large local deformation. Until the inner material of the billet is pressed onto the lower mold. The forging process requires that the upper end of the billet and forging 2 should be well formed.

[0073] S801: Mandrel Expansion and Lengthening: Remove the excess material at the inner diameter of the forging 2 obtained above, pass the variable diameter mandrel designed in step (4) through the cylinder, and hold the cylinder against the variable diameter step. Use a small anvil to press the billet axially from the variable diameter step to the cylinder end. After each pass, rotate the billet by a certain angle. When the forging meets the process requirements, the wall thickness of the billet is uniform and the length meets the standard.

[0074] Figure 5 This is an envelope diagram of the simulation results of the forging implementation scheme. The diagram shows that the present invention can effectively enclose the ultra-large thick-walled stepped cylinder with an inner flange. The final forging result closely resembles the target forging 2, with intact metal flow lines. Forging 2 exhibits good mechanical properties. Furthermore, it requires less machining allowance, reducing costs.

[0075] In summary, this solution has the following advantages:

[0076] (1) Traditional closing process has requirements on the size of closing deformation, and cannot form forgings with large size differences 2. By adopting the hole expansion and drawing process of variable diameter mandrel and combining it with the local deformation process after closing, it is possible to form extra-large forgings 2 with an inner diameter change of up to 50%.

[0077] (2) By introducing the mandrel expansion process and local deformation process, the present invention reduces the diameter of the blank required for the closing process, reduces the forming load, and at the same time reduces the amount of pressing required for the closing process and reduces the requirements in the height direction of the equipment.

[0078] (3) The blank shape and size used in this invention have a thicker cylinder wall than the blank shape and size used in the traditional closing process, which increases the stability of the blank during the closing process and reduces the occurrence of instability.

[0079] This invention, by forming an ultra-large, thick-walled stepped cylindrical body with an inner flange in two parts—a small-diameter section and a large-diameter section—can produce forgings with abrupt diameter changes that are impossible to form using traditional processes, particularly in the field of extra-large forgings. This forming method employs a combination of a diameter-changing mandrel expansion and elongation process with a closing-off local forming method. Unlike typical integral forming methods for extra-large cylindrical parts, this invention not only reduces the maximum load required during the forming process and maximizes the preservation of metal flow lines, improving material utilization, but also lowers the hardware requirements for forging equipment. Furthermore, it ensures the mechanical properties of the forging and the properties of the billet, improving the service stability of the forging. This invention can be used for forming large forgings with abrupt changes in inner diameter, improving the yield of such forgings.

[0080] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for forming an ultra-large thick-walled stepped cylindrical body with an inner flange, characterized in that, This is used for forming stepped cylindrical bodies with inner flanges, having an outer diameter of not less than 4m and a wall thickness of not less than 400mm. The stepped cylindrical body includes a small-diameter section and a large-diameter section with an integral structure. The small-diameter section is connected to one end of the large-diameter section. The outer surface of the connection is an arc connection, and the inner surface of the connection is continuously changing. The stepped cylindrical body has uneven wall thickness and abrupt changes in inner diameter. An inner flange is provided at the abrupt change point, and the inner flange is located in the small-diameter section. The forming method includes the following steps: S1: Design the blank, mold and variable diameter mandrel based on the structure of the stepped cylinder to be formed; S2: Perform machining according to the design in step S1 to obtain the blank; S3: Perform multiple passes of free forging on the billet obtained in step S2 to reduce the size of the inner and outer diameters; S4: Perform multi-pass local free forging on the cylinder precursor obtained in step S3 to form a small-diameter segment; during the local free forging process: a symmetrical pressing method is adopted, and after each pressing of the anvil, the cylinder precursor is rotated 30°, and then pressed down again; the mold for local free forging is designed based on the structural characteristics of the small-diameter segment. S5: The intermediate cylindrical body obtained in step S4 is enlarged and lengthened by a variable diameter mandrel to increase the inner diameter difference and the length of the blank. The variable diameter mandrel is inserted into the through hole of the intermediate cylindrical body, and the intermediate cylindrical body is pressed against the variable diameter step of the mandrel. Then, the enlargement and lengthening are performed. During the enlargement and lengthening process, a small anvil is used to press the intermediate cylindrical body axially from the variable diameter point to the end. After each pass is completed, the intermediate cylindrical body is rotated before the next pass is performed.

2. The method for forming an ultra-large thick-walled stepped cylindrical body with an inner flange according to claim 1, characterized in that, In step S1, the design of the billet is optimized by finite element numerical simulation; the finite element numerical simulation includes the simulation of the free forging process of closing, the simulation of the local free forging process, and the simulation of the hole expansion and drawing process by using a variable diameter mandrel.

3. The method for forming an ultra-large thick-walled stepped cylindrical body with an inner flange according to claim 1, characterized in that, In step S2, the machining process includes upsetting and punching, mandrel drawing, lever reaming and mechanical thinning performed sequentially.

4. The method for forming an ultra-large thick-walled stepped cylindrical body with an inner flange according to claim 1, characterized in that, In step S3, during the free forging process of closing the die: before pressing down, ensure that the bottom surface of the closing die is not lower than the end face of the billet, and calibrate the zero position of the pressing amount.

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