A method for forging a large taper cone shell forging

Abstract

The application provides a forging method of a large taper conical shell forging, and relates to the technical field of forging. In the application, during the process of forming the large head end and the small head end of the stepped cylinder preform by elongating and cutting the hollow cylinder blank, the outer diameter of the hollow cylinder blank is equal to the outer diameter of the large head end of the stepped cylinder preform, so that the end of the hollow cylinder blank for forming the large head end of the stepped cylinder preform does not need to be forged, and thus the concave core phenomenon does not occur in the large head end of the stepped cylinder preform. The core rod for elongating and cutting is provided with a blocking ring, and the end of the hollow cylinder blank for forming the small head end of the stepped cylinder preform abuts against the blocking ring during the process of elongating and cutting, so that the concave core phenomenon does not occur in the small head end of the stepped cylinder preform.

Description

A forging method for a large-tapered conical shell forging Technical Field

[0001] This invention relates to the field of forging technology, and more specifically, to a forging method for a large-tapered conical shell forging. Background Technology

[0002] Currently, the taper of conical shell forgings on the market is relatively small, generally less than 25 degrees. The common production methods are as follows: (1) For the taper of the conical shell forging, a hollow cylindrical blank is forged first, and then a special punch is used to punch it so that the blank and the lower die fit together. Due to the large number of product sizes, this method requires the use of special punches and lower dies of different sizes for different products, resulting in a large investment in auxiliary tools, and it cannot be applied to all sizes of conical shell forgings. (2) The blank is forged into a cylindrical shape, and the edge is forged by widening the hammer and electric rotary table, and the forging is gradually pressed down until the height of the forging is reached. This method is only suitable for small conical shell forgings; for conical shell forgings with large height and taper, a large amount of edge opening is required, which can easily cause damage to the outer circle and collapse of the waist. (3) A stepped cylinder preform is prepared by drawing, upsetting, punching, and drawing again from a steel ingot. Then, the stepped cylinder preform is expanded to obtain a conical shell forging. However, this method is currently mainly used for manufacturing conical forgings with a small taper (around 15 degrees). For the preparation of conical shell forgings with a large taper, such as a taper greater than 25 degrees, a length greater than 1500 mm, and a small end inner diameter less than 2000 mm, the stepped cylinder preform prepared by this method is prone to having a concave center at the small end, making it impossible to obtain a stepped cylinder preform of suitable size for subsequent expansion. Summary of the Invention

[0003] The problem solved by this invention is at least one of the following: how to avoid the occurrence of a concave center at the small end of the stepped cylinder preform when preparing a tapered shell forging with a taper greater than 25 degrees, a length greater than 1500 mm, and an inner diameter of less than 2000 mm at the small end by expanding the hole of the stepped cylinder preform.

[0004] To address the above problems, this invention provides a forging method for a large-tapered conical shell forging, comprising:

[0005] Step S1: The steel ingot is subjected to pressing, first upsetting, KD drawing, second upsetting and punching in sequence to obtain the first intermediate billet;

[0006] Step S2: The first intermediate billet is drawn with a mandrel to obtain a stepped cylinder preform; the stepped cylinder preform has a large end and a small end, the outer diameter of the large end being D; the mandrel used in the mandrel drawing process includes a mandrel body, a retaining ring, and a flange; one end of the mandrel body is provided with the flange, the retaining ring is sleeved on the mandrel body, the retaining ring is closely attached to the flange and located between the other end of the mandrel body and the flange; wherein, the mandrel drawing of the first intermediate billet includes: drawing the first intermediate billet into a hollow cylindrical billet with an outer diameter of D; drawing and cutting the hollow cylindrical billet to sequentially form the large end and the small end; during the drawing and cutting process, the end of the hollow cylindrical billet used to form the small end abuts against the retaining ring;

[0007] Step S3: The stepped cylinder preform is subjected to a first hole expansion, a small end closing, leveling, and a second hole expansion in sequence to obtain a conical shell forging.

[0008] Optionally, the design length L of the large-tapered conical shell forging is greater than 1500mm, the design taper θ is greater than 25 degrees, and the design inner diameter D1 of the small end is less than 2000mm.

[0009] Optionally, in step S2, the stepped cylinder preform includes a first hollow cylinder, a second hollow cylinder, a third hollow cylinder, a fourth hollow cylinder, and a fifth hollow cylinder connected in sequence with the same inner diameter; the outer diameters of the first hollow cylinder, the second hollow cylinder, the third hollow cylinder, the fourth hollow cylinder, and the fifth hollow cylinder decrease sequentially.

[0010] Optionally, in step S2, the outer diameters of the first hollow cylinder, the second hollow cylinder, the third hollow cylinder, the fourth hollow cylinder, and the fifth hollow cylinder are 3610mm, 3430mm, 3240mm, 3040mm, and 2820mm respectively, the inner diameter of each is 1180mm, and the length of each is 460mm.

[0011] Optionally, the design length L of the conical shell forging is 2000mm, the design taper θ is 30 degrees, the design inner diameter D1 of the small end is 1680mm, the design outer diameter D2 of the small end is 2895mm, the design inner diameter D3 of the large end is 3985mm, and the design outer diameter D4 of the large end is 5135mm.

[0012] In step S3, the pre-formed stepped cylinder blank undergoes a first reaming, a small end closing, leveling, and a second reaming process sequentially to obtain a conical shell forging, comprising:

[0013] Step S31: The stepped cylinder preform is expanded once using a lever with a diameter of 1120mm to obtain a second intermediate billet in the shape of a conical shell; the inner diameter of the small end of the second intermediate billet is 1850mm.

[0014] Step S32: The second intermediate billet is narrowed until the inner diameter of its small end is 1450mm, and then flattened to obtain the third intermediate billet; the length of the third intermediate billet is 2000mm.

[0015] Step S33: The third intermediate billet is expanded a second time to obtain a conical shell forging.

[0016] Optionally, in step S32, the seam is closed using an upper flat anvil and a lower V-shaped anvil with a width of 1200mm.

[0017] Optionally, in step S32, the closing is performed using a stepped closing method.

[0018] Optionally, in step S32, the amount of closing in a single pass during the closing process does not exceed 100mm.

[0019] Optionally, in step S33, the secondary reaming of the third intermediate billet to obtain the conical shell forging includes: heating the third intermediate billet to 1240°C to 1260°C, holding it at that temperature for 6 to 8 hours, and then cooling it down. When the temperature of the inner wall and end face of the small end of the third intermediate billet drops to 1000°C, the reaming forging is performed.

[0020] Optionally, the cooling process is carried out by spraying or misting.

[0021] Compared with the prior art, in the present invention, during the process of drawing and cutting a hollow cylindrical billet to form the large end and small end of the stepped cylinder preform, since the outer diameter of the hollow cylindrical billet is equal to the outer diameter of the large end of the stepped cylinder preform, the end of the hollow cylindrical billet used to form the large end of the stepped cylinder preform does not need to be forged, and thus the large end of the stepped cylinder preform will not have a concave center. Since the mandrel used for drawing and cutting is provided with a retaining ring, and the end of the hollow cylindrical billet used to form the small end of the stepped cylinder preform abuts against the retaining ring during the drawing and cutting process, the small end of the stepped cylinder preform can be prevented from having a concave center. Attached Figure Description

[0022] Figure 1 is a schematic diagram of the structure of the stepped cylinder preform in an embodiment of the present invention;

[0023] Figure 2 is a schematic diagram of the structure in an embodiment of the present invention;

[0024] Figure 3 is a schematic diagram of the drawing and blanking process using a mandrel in an embodiment of the present invention;

[0025] Figure 4 is a schematic diagram of the hollow cylindrical billet, which forms the small end, moving away from the retaining ring during the drawing and blanking process.

[0026] Figure 5 is a schematic diagram of the conical shell forging in an embodiment of the present invention;

[0027] Figure 6 is a schematic diagram of the conical shell forging being evenly divided along its length in an embodiment of the present invention;

[0028] Figure 7 is a schematic diagram of placing the stepped cylinder preform on the frame using a lever in an embodiment of the present invention.

[0029] Figure 8 is a schematic diagram of the pre-formed stepped cylinder blank after one hole enlargement by a lever in an embodiment of the present invention.

[0030] Figure 9 is a schematic diagram of the small end closing of the second intermediate blank in an embodiment of the present invention;

[0031] Figure 10 is a schematic diagram of leveling the second intermediate blank after it has been closed at the small end in an embodiment of the present invention;

[0032] Figure 11 is a schematic diagram before the third intermediate billet is placed on the horse rack.

[0033] Explanation of reference numerals in the attached figures:

[0034] 1. Stepped cylinder precast blank; 11. First hollow cylinder; 12. Second hollow cylinder; 13. Third hollow cylinder; 14. Fourth hollow cylinder; 15. Fifth hollow cylinder; 2. Mandrel; 21. Mandrel body; 22. Retaining ring; 23. Flange; 3. Second intermediate blank; 4. Third intermediate blank; 5. Rig; 6. Closing sleeve. Detailed Implementation

[0035] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0036] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0037] The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0038] It should be noted that, in this invention, the large end of the stepped cylinder preform refers to the end with the larger outer diameter, and the small end refers to the end with the smaller outer diameter. Similarly, the large end of the conical shell forging refers to the end with the larger outer diameter, and the small end refers to the end with the smaller outer diameter. The taper of the conical shell forging is the angle between the generatrix of the inner wall contour and the central axis of the forging. It should also be noted that in Figures 3, 4, and 9, A is the upper flat anvil, B is the lower V-anvil, C in Figure 7 is the anvil plate, D in Figure 10 is the cover plate, E in Figure 11 is the support frame, and F is the moving platform.

[0039] In related technologies, conical shell forgings can be prepared by the following method: a steel ingot is drawn, upset, punched, and drawn again to obtain a stepped cylinder preform, and then the stepped cylinder preform is enlarged to obtain a conical shell forging. However, this method is currently mainly used for manufacturing tapered forgings with a small taper (around 15 degrees). For the preparation of tapered shell forgings with a taper greater than 25 degrees, a length greater than 1500 mm, and an inner diameter of less than 2000 mm at the small end, the blank obtained by punching needs to have a large outer diameter and a small inner diameter to meet the size requirements of the overall inner diameter and outer diameter of the large end of the stepped cylinder preform. Therefore, the outer diameter of the blank obtained by punching is much larger than the inner diameter, and the side wall of the blank is thicker. During the process of drawing and cutting the mandrel, the material flow rate near the outer wall surface of the blank will be faster than that near the inner hole of the blank. In the process of forming the large end and small end of the stepped cylinder preform sequentially by drawing and cutting, the small end is prone to produce a very large flared mouth (as shown in Figure 4), that is, a concave core at the small end, which makes it impossible to obtain a stepped cylinder preform of suitable size for subsequent hole expansion.

[0040] To address the above problems, this embodiment provides a forging method for a large-tapered conical shell forging, comprising:

[0041] Step S1: The steel ingot is subjected to pressing, first upsetting, KD drawing, second upsetting and punching in sequence to obtain the first intermediate billet;

[0042] Step S2: The first intermediate billet is drawn with a mandrel to obtain a stepped cylinder preform 1; as shown in Figure 1, the stepped cylinder preform 1 has a large end and a small end, and the outer diameter of the large end is D; as shown in Figure 2, the mandrel 2 used in the mandrel drawing process includes a mandrel body 21, a retaining ring 22, and a flange 23; one end of the mandrel body 21 is provided with the flange 23, the retaining ring 22 is sleeved on the mandrel body 21, and the retaining ring 22 is set close to the flange 23 and located between the other end of the mandrel body 21 and the flange 23; In the process of drawing the first intermediate billet with a mandrel, the steps include: drawing the first intermediate billet into a hollow cylindrical billet with an outer diameter of D; drawing and cutting the hollow cylindrical billet to form the large end and the small end in sequence; as shown in Figure 3, during the drawing and cutting process, the end of the hollow cylindrical billet used to form the small end abuts against the retaining ring 22; as shown in Figure 4, if during the drawing and cutting process, the end of the hollow cylindrical billet used to form the small end moves away from the retaining ring 22, a concave small end situation will occur as shown in Figure 4.

[0043] Step S3: The stepped cylinder preform 1 is subjected to a first hole expansion, a small end closing, leveling, and a second hole expansion in sequence to obtain a conical shell forging.

[0044] In this embodiment of the invention, during the process of drawing and cutting a hollow cylindrical billet to form the large end and small end of the stepped cylindrical preform 1, since the outer diameter of the hollow cylindrical billet is equal to the outer diameter of the large end of the stepped cylindrical preform, the end of the hollow cylindrical billet used to form the large end of the stepped cylindrical preform does not need to be forged, and thus the large end of the stepped cylindrical preform will not have a concave center. Since the mandrel used for drawing and cutting is provided with a retaining ring 22, and during the drawing and cutting process, the end of the hollow cylindrical billet used to form the small end of the stepped cylindrical preform abuts against the retaining ring 22, thus preventing the small end of the stepped cylindrical preform 1 from having a concave center.

[0045] In some embodiments of the present invention, as shown in FIG5, the design length L of the large-tapered conical shell forging is greater than 1500mm, the design taper θ is greater than 25 degrees, and the design inner diameter D1 of the small end is less than 2000mm.

[0046] The conical shell forging obtained in this embodiment of the invention is shown in Figure 5. The shape of the conical shell forging can be considered as being obtained by rotating a parallelogram along its centerline, or it can be understood as being obtained by rotating the upper and lower bottom edges of a rectangular cross-section of unit area along the centerline after offsetting them radially by the same drop value. Therefore, the conical shell forging can be formed by expanding the hole in the stepped cylinder preform 1. As shown in Figure 1, exemplarily, the stepped cylinder preform 1 is composed of a first hollow cylinder 11, a second hollow cylinder 12, a third hollow cylinder 13, a fourth hollow cylinder 14, and a fifth hollow cylinder 15 connected in sequence with the same inner diameter; the outer diameters of the first hollow cylinder 11, the second hollow cylinder 12, the third hollow cylinder 13, the fourth hollow cylinder 14, and the fifth hollow cylinder 15 decrease sequentially, thereby forming 5 sets of outer steps; specifically, the process of expanding the hole of the preformed stepped cylinder preform 1 to form a conical shell forging includes: gradually reducing the difference between adjacent outer steps by partially expanding the hole of the stepped cylinder preform 1 until the outer contour of the stepped cylinder preform 1 is a smooth curved surface, and then synchronously expanding the hole.

[0047] In actual production, the dimensions of the stepped cylinder preform 1 need to be determined based on the design dimensions of the conical shell forging. As shown in Figure 6, the conical shell forging can be divided equally along its length, and each part of the forging can be considered as being obtained by rotating a parallelogram along its centerline. Since the conical shell forging is formed by expanding the hole of the stepped cylinder preform 1, the wall thickness of the billet gradually decreases radially during the expansion process, and both its inner and outer diameters increase, but it does not move material in the axial direction; therefore, the length of each hollow cylinder that makes up the stepped cylinder preform 1 is equal to the generatrix length of the outer contour of the forging obtained after dividing the conical shell forging equally.

[0048] For example, as shown in Figure 5, the design length L of the conical shell forging is 2000mm, the design taper θ is 30 degrees, the design inner diameter D1 of the small end is 1680mm, the design outer diameter D2 of the small end is 2895mm, the design inner diameter D3 of the large end is 3985mm, and the design outer diameter D4 of the large end is 5135mm. Correspondingly, as shown in Figure 1, the stepped cylinder preform 1 includes a first hollow cylinder 11, a second hollow cylinder 12, a third hollow cylinder 13, a fourth hollow cylinder 14, and a fifth hollow cylinder 15 connected in sequence with the same inner diameter. The outer diameters of the first hollow cylinder 11, the second hollow cylinder 12, the third hollow cylinder 13, the fourth hollow cylinder 14, and the fifth hollow cylinder 15 are 3610mm, 3430mm, 3240mm, 3040mm, and 2820mm respectively, the inner diameter of each is 1180mm, and the length of each is 460mm.

[0049] For the preparation of the high-specification conical shell forging, in step S3, the stepped cylinder preform 1 is subjected to a first reaming, a small end closing, a leveling, and a second reaming in sequence to obtain the conical shell forging, including:

[0050] Step S31: As shown in Figures 7-8, the stepped cylinder preform 1 is enlarged once using a lever 5 with a diameter of 1120mm to obtain a conical shell-shaped second intermediate blank 3; the inner diameter of the small end of the second intermediate blank 3 is 1850mm.

[0051] Step S32: As shown in Figures 9-10, the second intermediate blank 3 is narrowed until its inner diameter at the small end is 1450mm, and then flattened to obtain the third intermediate blank 4; the length of the third intermediate blank 4 is 2000mm.

[0052] Step S33, as shown in Figure 11, the third intermediate billet 4 is expanded twice to obtain a conical shell forging.

[0053] In the existing technology, during the reaming process using the lever 5, partial reaming is performed first. Therefore, the part that first contacts the anvil (the larger end of the billet) is reamed first. During the reaming process, the height difference between adjacent outer steps gradually decreases, and the taper of the forging gradually forms until there is no height difference between the various parts of the billet. Then, synchronous reaming is performed. During this process, the stepped cylinder preform 1 is constantly rotating. Because the inner diameter of the smaller end of the stepped cylinder preform 1 is small, the gap between the inner wall of the smaller end of the stepped cylinder preform 1 and the lever 5 is small. Throughout the reaming process, the smaller end of the stepped cylinder preform 1 is always subjected to the reaction force of the lever 5 for reaming. Since the reaming is only performed to the smaller end of the preform last, therefore... During the reaming process, the inner diameter of the small end of the preform continuously increases, resulting in an excessively large inner diameter of the small end of the forging. To address this issue, in this embodiment, the stepped cylinder preform 1 is first reamed using a lever 5 with a diameter of 1120mm, resulting in a second intermediate billet 3 with a conical shell shape and an inner diameter of 1850mm at the small end. The inner diameter of the small end of the second intermediate billet 3 is larger than the designed inner diameter of the small end of the conical shell forging (1680nm). Therefore, in this embodiment, the small end is further narrowed and flattened to obtain a third intermediate billet 4 with a smaller inner diameter of 1450mm at the small end. To ensure that the dimensions of the forging meet the requirements, a second reaming is performed, resulting in the final forging.

[0054] In some embodiments of the present invention, in step S32, the closing is performed using an upper flat anvil and a lower V-shaped anvil with a width of 1200mm. The manipulator inserts the lever 5 into the closing sleeve 6, clamping the lever 5 and inserting it from the large end of the second intermediate billet 3. The closing sleeve 6 is then pressed against the inner wall of the small end of the second intermediate billet 3, and the upper flat anvil and lower V-shaped anvil are used for closing, thereby preventing the billet from shifting during the closing process.

[0055] In some embodiments of the present invention, in step S32, the closing is performed using a stepped closing method.

[0056] In some embodiments of the present invention, in step S32, the amount of closing in a single pass during the closing process does not exceed 100 mm. This prevents cracks from forming on the end face due to excessive closing in a single pass.

[0057] In some embodiments of the present invention, step S33, which involves second-expanding the third intermediate billet 4 to obtain a conical shell forging, includes: heating the third intermediate billet 4 to 1240°C to 1260°C, holding it at that temperature for 6 to 8 hours, and then cooling it down. When the temperature of the inner wall and end face of the small end of the third intermediate billet 4 drops to 1000°C, the forging process is expanded.

[0058] In some embodiments of the present invention, the cooling process is carried out by spraying or misting. In this embodiment, the temperature of the inner wall and end face of the four small ends of the third intermediate billet is rapidly reduced by spraying, misting, or other measures, thereby increasing its deformation resistance.

[0059] The present invention will be further described below with reference to specific embodiments.

[0060] Example 1

[0061] As shown in Figure 5, the designed length L of the conical shell forging is 2000 mm, the designed taper θ is 30 degrees, the designed inner diameter D1 of the small end is 1680 mm, the designed outer diameter D2 of the small end is 2895 mm, the designed inner diameter D3 of the large end is 3985 mm, and the designed outer diameter D4 of the large end is 5135 mm. The fabrication process of the conical shell forging is as follows:

[0062] A1. Heat the steel ingot to 1250℃ and hold for 24 hours. Then, press the jaws and chamfer the edges. Cut the ingot body at the sprue end with gas cutting. Heat to 1270℃ and hold for 30 hours. Upset to an axial dimension of 1700mm and a radial dimension of 3730mm. Then, use the KD compaction method to draw to an axial dimension of 4690mm and a radial dimension of 2250mm. Heat to 1270℃ and hold for 30 hours. Upset to an axial dimension of 1700mm and a radial dimension of 3700mm. Then, punch holes to obtain the first intermediate billet. The inner diameter of the first intermediate billet is 1200mm.

[0063] A2. The first intermediate billet is heated to 1250℃ and held for 12 hours. Then, the first intermediate billet is drawn into a hollow cylindrical billet with an outer diameter of 3610mm. As shown in Figure 3, the hollow cylindrical billet is drawn and cut to form the large end and the small end of the stepped cylinder preform 1 in sequence, thus obtaining the stepped cylinder preform 1. The stepped cylinder preform 1 is composed of a first hollow cylinder 11, a second hollow cylinder 12, a third hollow cylinder 13, a fourth hollow cylinder 14, and a fifth hollow cylinder 15 connected in sequence with the same inner diameter. The outer diameters of the cylinder 14 and the fifth hollow cylinder 15 are 3610mm, 3430mm, 3240mm, 3040mm, and 2820mm respectively, their inner diameter is 1180mm, and their length is 460mm. As shown in Figure 2, the mandrel 2 used in the drawing and blanking process includes a mandrel body 21, a retaining ring 22, and a flange 23. The flange 23 is provided at one end of the mandrel body 21, and the retaining ring 22 is sleeved on the mandrel body 21. As shown in Figure 3, during the drawing and blanking process, the end of the hollow cylindrical blank used to form the small end of the stepped cylinder preform 1 abuts against the retaining ring 22.

[0064] A3. Heat the stepped cylinder preform 1 to 1250℃ and keep it at that temperature for 8 hours. As shown in Figures 7 and 8, use a lever 5 with a diameter of 1120mm, a frame and an anvil to expand the hole once to obtain a conical shell-shaped second intermediate blank 3. The inner diameter of the small end of the second intermediate blank 3 is 1850mm.

[0065] A4. As shown in Figures 9-10, the second intermediate billet 3 is heated to 1250℃ and kept at that temperature for 8 hours. The second intermediate billet 3 is then closed until the inner diameter of its small end is 1450mm. After that, it is flattened to obtain the third intermediate billet 4. The length of the third intermediate billet 4 is 2000mm. The closure is carried out in a stepped manner, and the closure is carried out using an upper flat anvil and a lower V anvil with a width of 1200mm.

[0066] A5. As shown in Figure 11, the third intermediate billet 4 is heated to 1250℃ and kept at that temperature for 6 hours. Then it is placed on a frame and left to stand for 20 to 30 minutes. During this period, a spraying method is used for cooling. When the temperature of the inner wall and end face of the small end of the third intermediate billet 4 drops to 1000℃, hole expansion forging is performed to obtain a conical shell forging.

[0067] Comparative Example

[0068] The difference from Example 1 is that, in step A2, during the drawing and blanking process, the end of the hollow cylindrical billet used to form the stepped cylinder preform 1 is away from the retaining ring 22; during the drawing and blanking process, the billet exhibits a concave end phenomenon.

[0069] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A forging method for a large-tapered conical shell forging, characterized in that, include: Step S1: The steel ingot is sequentially subjected to clamping, first upsetting, KD drawing, second upsetting and punching to obtain a first intermediate billet; Step S2: The first intermediate billet is drawn with a mandrel to obtain a stepped cylinder preform (1); The stepped cylinder preform (1) has a large end and a small end, and the outer diameter of the large end is D; The mandrel (2) used in the mandrel drawing process includes a mandrel body (21), a retaining ring (22) and a flange (23); The flange (23) is provided at one end of the mandrel body (21), the retaining ring (22) is sleeved on the mandrel body (21), the retaining ring (22) is set close to the flange (23) and is located at the other end of the mandrel body (21) and the flange (23). Between; wherein, the first intermediate billet is drawn by mandrel, including: drawing the first intermediate billet into a hollow cylindrical billet with an outer diameter of D; drawing and cutting the hollow cylindrical billet to form the large end and the small end in sequence; during the drawing and cutting process, the end of the hollow cylindrical billet used to form the small end abuts against the retaining ring (22); step S3, the stepped cylinder preform (1) is subjected to a first hole expansion, small end closing, flattening and a second hole expansion in sequence to obtain a conical shell forging; the design length L of the large taper conical shell forging is greater than 1500mm, the design taper θ is greater than 25 degrees, and the design inner diameter D1 of the small end is less than 2000mm; the stepped cylinder preform (1) includes sequentially connecting A first hollow cylinder (11), a second hollow cylinder (12), a third hollow cylinder (13), a fourth hollow cylinder (14), and a fifth hollow cylinder (15) with the same inner diameter are connected. The outer diameters of the first hollow cylinder (11), the second hollow cylinder (12), the third hollow cylinder (13), the fourth hollow cylinder (14), and the fifth hollow cylinder (15) decrease sequentially. The outer diameters of the first hollow cylinder (11), the second hollow cylinder (12), the third hollow cylinder (13), the fourth hollow cylinder (14), and the fifth hollow cylinder (15) are 3610mm, 3430mm, 3240mm, 3040mm, and 2820mm respectively, and the inner diameter of each is 1180mm. The length of each is also 1180mm. 460mm; The design length L of the conical shell forging is 2000mm, the design taper θ is 30 degrees, the design inner diameter D1 of the small end is 1680mm, the design outer diameter D2 of the small end is 2895mm, the design inner diameter D3 of the large end is 3985mm, and the design outer diameter D4 of the large end is 5135mm; In step S3, the step cylinder preform (1) is subjected to a first hole expansion, a small end closing, a flattening and a second hole expansion in sequence to obtain the conical shell forging, including: Step S31, the step cylinder preform (1) is subjected to a first hole expansion using a lever (5) with a diameter of 1120mm to obtain a second intermediate billet (3) in the shape of a conical shell; the inner diameter of the small end of the second intermediate billet (3) is 1850mm;Step S32: The second intermediate billet (3) is narrowed until its inner diameter at the small end is 1450mm, and then leveled to obtain the third intermediate billet (4); the length of the third intermediate billet (4) is 2000mm; Step S33: The third intermediate billet (4) is expanded a second time to obtain the conical shell forging.

2. The forging method for a large-tapered conical shell forging according to claim 1, characterized in that, In step S32, the closure is performed using an upper flat anvil and a lower V-shaped anvil with a width of 1200mm.

3. The forging method for a large-tapered conical shell forging according to claim 1, characterized in that, In step S32, the closing is performed using a stepped closing method.

4. The forging method for a large-tapered conical shell forging according to claim 1, characterized in that, In step S32, the amount of closing in a single pass during the closing process shall not exceed 100mm.

5. The forging method for a large-tapered conical shell forging according to claim 1, characterized in that, In step S33, the process of expanding the third intermediate billet (4) to obtain a conical shell forging includes: heating the third intermediate billet (4) to 1240°C to 1260°C, holding it at that temperature for 6 to 8 hours, and then cooling it down. When the temperature of the inner wall and end face of the small end of the third intermediate billet (4) drops to 1000°C, the forging process is expanded.

6. The forging method for a large-tapered conical shell forging according to claim 5, characterized in that, The cooling process is carried out by spraying or misting.

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