A radial shrinking forming method that breaks through the shrinking coefficient limitation

Abstract

The present invention discloses a radial shrinking forming method that breaks through the limitation of shrinking coefficient, including a fixing mechanism, a working mechanism and a power mechanism; the fixing mechanism includes a shell, the shell is provided with a feed port and a cavity, the feed port is for the tube blank to be placed and fed along the axial direction of the cavity, the working mechanism includes a plurality of shrinking petal dies, the shrinking petal dies are installed in the cavity and connected to the power mechanism, the plurality of shrinking petal dies are surrounded at equal angles around the outer circumference of the tube blank, the power mechanism drives the shrinking petal dies to reciprocate in a short distance along the normal direction of the cavity, and during the axial feeding of the tube blank, the short-range reciprocating motion of the shrinking petal dies hits the tube blank, causing the tube blank to produce plastic deformation. This case can effectively realize the cold and hot deformation of the tube blank, and is not limited by the shrinking coefficient, and will not cause defects such as instability of the force transmission area, wrinkling of the mouth and height inconsistency; by controlling the frequency of opening and merging of the shrinking petal dies to adapt to materials of different hardness and softness, the process flow is simplified and production efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of plastic processing of light metal materials, in particular to a radial shrinkage forming method that breaks through the limitation of shrinkage coefficient. Background Art

[0002] Radial shrink forming is a processing technology used for metal pipes or other circular cross-section materials. It reduces the end diameter of the material by radial compression, which may be accompanied by an increase in wall thickness. This technology is widely used in fields such as metal processing and automobile manufacturing.

[0003] Traditional shrinking forming technologies include spinning shrinking, differential rolling shrinking and die shrinking, etc. However, there are many problems. For example, in the process assisted by the radial shrinking forming device, the spinning shrinking process has many spinning passes, large wall thickness difference, uneven grain refinement, cracking, back extrusion, bulging and annular peeling. The differential rolling process needs to be welded at the joints after rolling, which has a great impact on the overall performance of the component. In addition, due to the uneven friction between the rollers, the dimensional accuracy error is large, and one machine cannot be used for multiple purposes, making it difficult to achieve the purpose of fast and efficient forming. In the die shrinking process, when the material deformation is too large or the material is too soft, it is easy to cause instability in the force transmission area or wrinkling at the mouth, and the uneven friction is easy to cause large height differences in the shrinking parts, as well as large limit shrinking coefficients.

[0004] The so-called shrinkage coefficient k is the ratio of the minimum diameter d after deformation to the original tube diameter d0. The formula is k=d / d0. The size of the shrinkage coefficient k directly affects the difficulty of shrinkage. The smaller the shrinkage coefficient k, the greater the difficulty of forming. Although the existing technology can form conical or quasi-conical components with various diameter differences and difficult-to-deform materials with high quality, its forming process is still cumbersome, and the shrinkage coefficient of one-time forming is greatly limited. These technologies usually rely on multi-step forming processes, resulting in low production efficiency and high requirements for equipment and operators. This not only increases production costs, but may also lead to instability in forming quality, especially when dealing with complex shapes or high-strength materials. In order to solve these problems, it is urgent to develop a more efficient and reliable forming technology to simplify the process, improve production efficiency, and expand the range of shrinkage coefficients for one-time forming. Summary of the invention

[0005] The purpose of the present invention is to provide a radial necking forming method that breaks through the necking coefficient limitation, so as to solve the problems raised by the above-mentioned background technology.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a radial shrinkage forming method that breaks through the limitation of shrinkage coefficient, the method relates to a forming device, the forming device includes a fixing mechanism, a working mechanism and a power mechanism; the fixing mechanism includes a shell, the shell is provided with a feed port and a cavity, the feed port is for the tube blank to be placed and fed along the axial direction of the cavity, the working mechanism includes a plurality of shrinkage split-flap molds, the shrinkage split-flap molds are installed in the cavity, and the plurality of shrinkage split-flap molds are arranged around the outer circumference of the tube blank at equal angles, the power mechanism includes a motor, a fixing plate, a reset spring, a sleeve, a top block and a fixing sleeve, the shell is provided with a mounting port coaxial with the cavity on the other side relative to the feed port, one end of the sleeve coaxially extends into the mounting port, and the other end The end is externally fixed on a plane; the fixing plate is installed and fixed on the end surface of one end of the sleeve extending into the installation opening, the fixing plate is placed on the outside of the shrinking and splitting mold, and the fixing plate is provided with a through hole at the position corresponding to the shrinking and splitting mold, each shrinking and splitting mold is fixedly connected to the top block through the through hole, the top block is arranged on the other side of the fixing plate relative to the shrinking and splitting mold, a return spring is sleeved between the top block and the fixing plate, and the top block and the shrinking and splitting mold constitute a whole that moves relative to the fixing plate; the sleeve extends into the cavity from the installation opening and is rotatably sleeved between the top block and the inner wall of the cavity, the sleeve part is coaxially sleeved on the outer wall of the fixing sleeve, the inner wall of the sleeve is provided with a convex block at a position relative to each top block, and a gap is provided between adjacent convex blocks, and the sleeve is connected to a motor; the method is:

[0007] Step 1: The tube billet is fed, and the motor drives the sleeve to rotate. When the convex block of the sleeve rotates to the position of the top block, the reset spring is compressed between the top block and the fixed plate, and the shrinking and split dies merge toward the center at the same time, causing the mouth of the original tube billet to deform for the first time;

[0008] Step 2: The motor drives the sleeve to continue rotating. When the convex block of the sleeve continues to rotate, the reset spring is released, driving the top block and the shrinking and splitting mold to open;

[0009] Step 3: The tube billet continues to be fed, the motor drives the sleeve to continue to rotate, and the shrinking and split molds merge toward the center to complete the second deformation. This is a forming cycle that is repeated continuously until the tube billet is fed to the far right to complete the deformation.

[0010] Preferably, the power mechanism also includes a clutch, a transmission rod, a transmission, a transmission belt and a pulley, the output end of the motor is connected to a clutch, and the clutch is connected to the transmission through the transmission rod, the transmission is connected to the pulley, and the pulley is connected to the sleeve through the transmission belt.

[0011] Preferably, the fixing mechanism is a split structure and also includes a front cover, a rear cover, a first circular gasket, a first bearing, a second circular gasket, a second bearing, a third circular gasket and screws. The front cover and the rear cover are respectively covered on the left and right sides of the outer shell and fixed by screws. The first circular gasket, the first bearing, the second circular gasket, the second bearing and the third circular gasket are arranged in sequence from left to right inside the outer shell, wherein the first bearing and the second bearing are interference fit on the inner wall of the outer shell, and the first circular gasket, the second circular gasket and the third circular gasket are clearance fit with the inner wall of the outer shell.

[0012] Preferably, the first circular gasket, the first bearing, the second circular gasket, the second bearing and the third circular gasket are sleeved between the inner wall of the outer shell and the sleeve, the sleeve and the first bearing and the second bearing are interference fit, and the sleeve and the first circular gasket, the second circular gasket and the third circular gasket are clearance fit.

[0013] Preferably, a plurality of top blocks are installed corresponding to each shrinking and splitting mold, and the number and position of the protrusions are consistent with those of the top blocks.

[0014] Preferably, the cross-section of the top block is triangular.

[0015] Preferably, the edge of the protrusion smoothly transitions to the inner wall of the sleeve.

[0016] Compared with the prior art, the beneficial effects of the present invention are: by adopting the method of feeding the tube billet and the radial high-frequency reciprocating motion of the petal-type shrinking die to impact the tube billet, the hot and cold deformation of the tube billet can be effectively realized, and it is not limited by the shrinking coefficient, and there will be no defects such as instability in the force transmission area, wrinkling at the mouth and height inconsistency; and by controlling the frequency of opening and merging of the shrinking petal die to adapt to materials of different hardness and softness, the present invention has universal applicability, thereby simplifying the process flow, improving production efficiency, and expanding the shrinking coefficient range of one-time forming, so that when the radial shrinking forming method is used, it plays a role in breaking through the shrinking coefficient limitation and improving work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the three-dimensional structure of the present invention;

[0018] Figure 2 This is a schematic diagram of radial shrinkage forming of the present invention;

[0019] Figure 3 It is a schematic diagram of local shrinkage of the present invention;

[0020] Figure 4 It is a schematic diagram of the overall necking of the present invention;

[0021] Figure 5 It is a schematic diagram of the radial shrinkage deformation process of the tube blank in the mold cavity of the present invention;

[0022] Figure 6It is a schematic diagram of the main cutaway structure of the necking and split-petal mold in the combined state of the present invention;

[0023] Figure 7 It is a schematic diagram of the cross-section structure of the necking and split-flap mold of the present invention in a merged state from the left side;

[0024] Figure 8 It is a schematic diagram of the main cutaway structure of the necking and splitting mold of the present invention in an open state;

[0025] Fig. 9 It is a schematic diagram of the cross-section structure of the necking and splitting mold of the present invention in an open state from the left side;

[0026] Fig.10 It is a structural schematic diagram of the working process of the radial shrinkage forming device of the present invention.

[0027] In the figure: 1. motor; 2. clutch; 3. transmission; 4. pulley; 5. transmission belt; 6. sleeve; 7. fixed sleeve; 8. rear cover; 9. housing; 10. front cover; 11. first circular gasket; 12. first bearing; 13. second circular gasket; 14. second bearing; 15. third circular gasket; 16. fixing plate; 17. top block; 18. return spring; 19. shrinking and splitting mold; 20. feed port; 21. cavity; 22. installation port; 23. perforation; 24. bump; 25. tube blank. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] See also Figure 1-Figure 10 The present invention provides a radial shrinkage forming device that breaks through the shrinkage coefficient limitation, including a fixing mechanism, a working mechanism and a power mechanism;

[0030] The fixing mechanism includes a shell 9, which is provided with a feed port 20 and a cavity 21. The feed port 20 is for the tube blank 25 to be placed and fed along the axial direction of the cavity 21. The working mechanism includes a plurality of shrinking and split dies 19. The shrinking and split dies 19 are installed in the cavity 21 and connected to a power mechanism. The plurality of shrinking and split dies 19 are arranged around the outer periphery of the tube blank 25 at equal angles. The power mechanism drives the shrinking and split dies 19 to perform short-range reciprocating motion along the normal direction of the cavity 21. During the axial feeding of the tube blank 25, the short-range reciprocating motion of the shrinking and split dies 19 hits the tube blank 25, causing the tube blank 25 to undergo plastic deformation.

[0031] Specifically, the power mechanism includes a motor 1, a clutch 2, a transmission rod, a transmission 3, a pulley 4, a transmission belt 5, a sleeve 6, a fixed sleeve 7, a fixed plate 16, a reset spring 18, and a top block 17. The housing 9 is provided with a mounting port 22 coaxial with the cavity 21 on the other side relative to the feed port 20. One end of the sleeve 6 coaxially extends into the mounting port 22, and the other end is externally fixed on a plane; the fixed plate 16 is installed and fixed on the end surface of the end of the sleeve 6 extending into the mounting port 22, and the fixed plate 16 is placed on the outside of the shrinking and splitting mold 19. The fixed plate 16 has a through hole 23 at the position corresponding to the shrinking and splitting mold 19. Each shrinking and splitting mold 19 is fixedly connected to the top block 17 through the through hole 23. The top block 17 is arranged on the other side of the fixed plate 16 relative to the shrinking and splitting mold 19. The top block 17 and the fixed plate 16 are fixedly connected to the top block 17 through the through hole 23. A return spring 18 is sleeved between the fixed plates 16, and the top block 17 and the shrinking and splitting mold 19 form a whole that moves relative to the fixed plate 16; the sleeve 6 extends into the cavity 21 from the installation port 22 and is rotatably sleeved between the top block 17 and the inner wall of the cavity 21, and the sleeve 6 is partially coaxially sleeved on the outer wall of the fixed sleeve 7, and the inner wall of the sleeve 6 is provided with a protrusion 24 at a position relative to each top block 17, and there is a gap between adjacent protrusions 24, the sleeve 6 is connected to the motor 1, so that the motor 1 drives the sleeve 6 to rotate, and then the protrusions 24 on the inner wall of the sleeve 6 reciprocate and push the top block 17 and the shrinking and splitting mold 19 to hit the tube blank 25, and the output end of the motor 1 is connected to a clutch 2, and the clutch 2 is connected to a transmission 3 through a transmission rod, the transmission 3 is connected to a pulley 4, and the pulley 4 is connected to the sleeve 6 through a transmission belt 5.

[0032] The fixing mechanism is a split structure and also includes a front cover 10, a rear cover 8, a first circular gasket 11, a first bearing 12, a second circular gasket 13, a second bearing 14, a third circular gasket 15 and screws. The front cover 10 and the rear cover 8 are respectively covered on the left and right sides of the outer shell 9 and are tightened and fixed by screws. The first circular gasket 11, the first bearing 12, the second circular gasket 13, the second bearing 14, and the third circular gasket 15 are arranged in sequence from left to right inside the outer shell 9, wherein the first bearing 12 and the second bearing 14 are interference fit on the inner wall of the outer shell 9, and the first circular gasket 11, the second circular gasket 13, the third circular gasket 15 are clearance fit with the inner wall of the outer shell 9.

[0033] The outer wall of the sleeve 6 is sleeved with the rear cover 8, and there are four fixing plates 16. The four fixing plates 16 are fixed to the front cover 10 at one end by screws, and are fixed to the fixing sleeve 7 at the other end; a plurality of top blocks 17 are installed corresponding to each shrinking and flapping mold 19, and the number and position of the protrusions 24 correspond to the top blocks 17. In the present embodiment, there are eight top blocks 17, which are fixed to the shrinking and flapping mold 19 by screws; a 2mm gap is reserved on one side between the top block 17 and the through hole 23 of the fixing plate 16 to ensure that the top block 17 can move freely along the normal direction of the shrinking and flapping mold 19; there is an interference fit between the sleeve 6 and the first bearing 12 and the second bearing 14, and a 2-4mm assembly gap is reserved on one side with the first circular gasket 11, the second circular gasket 13 and the third circular gasket 15 to avoid interference.

[0034] In specific implementation, during the operation of the radial shrinking forming device, the rear cover 8, the housing 9 and the front cover 10 are assembled in advance, and the first bearing 12, the second bearing 14 and the housing 9 are interference fit to prevent the first bearing 12, the second bearing 14 and the housing 9 from sliding during operation, and the first circular gasket 11, the second circular gasket 13, the third circular gasket 15 and the housing 9 are clearance fit, and an assembly clearance of about 1 mm is left with the first bearing 12 and the second bearing 14 to avoid friction;

[0035] See also Figure 2 , Figure 3 and Figure 4 The shrinking mold cavity 21 needs to be designed and processed in advance according to the product shape. It is composed of 4 shrinking split molds 19, and the split mold can reciprocate in a short distance along the black bidirectional arrow in the normal direction diagram, and the movement frequency remains the same. The tube blank 25 is fed along the black unidirectional arrow in the axial diagram; the short-range reciprocating motion of the shrinking split mold 19 can hit the tube blank 25 at a high frequency, causing the tube blank 25 to produce plastic deformation, and the tube blank 25 is continuously fed by manual or auxiliary equipment until the forming is completed. The shrinking mold is in the form of a split mold, which also avoids the problem of difficult demoulding; the tube blank 25 can be heated or not according to the deformation characteristics of the material, and the cold or hot tube blank 25 will not change the mold structure;

[0036] Since the sleeve 6 is evenly distributed with four identical protrusions, the cross section of the top block 17 is triangular, and the edge of the protrusion 24 smoothly transitions to the inner wall of the sleeve 6 .

[0037] The present invention also provides a radial shrinkage forming method that breaks through the shrinkage coefficient limitation, combined with Figure 8 , Fig. 9 and Fig.10 , the method is:

[0038] Step 1: The tube blank 25 is fed, and the motor drives the sleeve 6 to rotate. When the protrusion 24 of the sleeve 6 rotates to the position of the top block 17, the return spring 18 is compressed between the top block 17 and the fixed plate 16, and the shrinking and splitting molds 19 merge toward the center at the same time, so that the mouth of the original tube blank undergoes initial deformation;

[0039] Step 2: The motor drives the sleeve 6 to continue rotating. When the convex block 24 of the sleeve 6 continues to rotate, the reset spring 18 is released, driving the top block 17 and the shrinking and splitting die 19 to open. Then, when the power mechanism drives the sleeve 6 to rotate at a high speed, the shrinking and splitting die 19 realizes a high-frequency closing-opening action, exerting a radial force on the tube blank 25, thereby causing deformation and realizing radial shrinking forming.

[0040] Step 3: The tube blank continues to be fed. At this time, the tube blank can be fed manually or by auxiliary devices. The motor drives the sleeve 6 to continue to rotate, and the shrinking and splitting mold 19 merges toward the center to complete the second deformation. This is a forming cycle that is repeated continuously.

[0041] Step 4: The shrinking and splitting die 19 opens radially, and the tube blank 25 continues to be fed;

[0042] Step 5: The shrinking and splitting dies 19 merge toward the center to complete the third deformation until the tube blank 25 is fed to the far right to complete the deformation;

[0043] Step 6: The shrinking and splitting mold 19 is radially opened to facilitate material withdrawal.

[0044] Before forming, the forming method needs to be determined according to the hardness and softness characteristics of the material. If the material is too hard to be deformed, the feeding of the tube blank 25 can be stopped at the difficult forming stage, so that the shrinking and splitting die 19 can reciprocate to hit the tube blank 25 until the material is deformed, or the reciprocating motion frequency of the shrinking and splitting die 19 can be increased to hit the tube blank 25, so that the tube blank 25 is deformed; if the material is soft, the movement frequency of the shrinking and splitting die 19 can be reduced to prevent the impact energy from being too high to cause damage to the surface of the component;

[0045] See also Figure 1 , Figure 6 and Figure 7 It can be seen that in the power mechanism, the motor 1, the clutch 2 and the transmission 3 are connected in series, the transmission belt 5 connects the sleeve 6 and the pulley 4, the power output of the motor 1 can drive the sleeve 6 to rotate, and the transmission 3 can conveniently control the speed of the sleeve 6;

[0046] When the material of the tube 25 is relatively hard, the speed of the sleeve 6 can be increased by controlling the transmission 3, so that the shrinking and splitting die 19 hits the tube 25 at high speed, thereby causing deformation. The feeding of the tube 25 can also be stopped at the difficult forming stage, so that the shrinking and splitting die 19 hits the tube for a long time, causing deformation. Alternatively, the sleeve 6 can be replaced, and the four protrusions can be changed to more to increase the movement frequency of the sleeve 6. When the material of the tube 25 is relatively soft, the speed of the sleeve 6 can be reduced or the sleeve 6 can be replaced to reduce the number of protrusions, thereby reducing the frequency of the shrinking and splitting die 19 hitting the tube 25, and preventing the surface of the tube 25 from being damaged due to excessive impact energy.

[0047] Ultimately, the process is simplified, production efficiency is improved, the limitation of the shrinkage coefficient is broken, and the range of the shrinkage coefficient for one-time forming is expanded.

[0048] The radial shrinkage forming method has the following advantages:

[0049] First, buckling instability will not occur; Different from the conventional die shrinking forming, the undeformed area of ​​the tube blank 25 is not subjected to force during the radial shrinking forming process, that is, there is no force transmission area, so buckling instability of the tube blank 25 will not occur;

[0050] Second, break through the limit of the shrinkage coefficient; radial shrinkage forming will not be unstable, so it can break through the limit of the shrinkage coefficient and expand the range of the shrinkage coefficient;

[0051] Third, reduce the height difference; the traditional die shrinking part has a large height difference due to the uneven friction between the die and the tube blank 25, while the radial shrinking part belongs to local high-frequency loading and local deformation, and the influence of friction on the forming is small, so the height difference of the shrinking part can be greatly reduced;

[0052] Fourth, no wrinkles will be generated at the mouth. In the traditional shrinking forming process, when the tube blank 25 is thin and the shrinkage coefficient is small, the shrinking mouth material has no time to deform, and it is easy to cause material accumulation and wrinkles. The radial shrinking forming is completed under the high-frequency impact of the mold. The deformation caused by each impact of the split mold on the tube blank 25 is very small, so the generation of wrinkles at the mouth can be avoided.

[0053] Fifth, design the corresponding shrinking mold to achieve local shrinking (such as Figure 3 ) and overall shrinkage (such as Figure 4 ).

[0054] The above description is only a preferred embodiment of the present invention and is not a limitation on the design of this case. Any equivalent changes made based on the design key of this case shall fall within the protection scope of this case.

Claims

1. A radial necking forming method that breaks through the necking coefficient limitation, characterized in that: The method relates to a forming device, which includes a fixing mechanism, a working mechanism and a power mechanism; the fixing mechanism includes a shell, the shell is provided with a feed port and a cavity, the feed port is for a tube blank to be placed and fed along the axial direction of the cavity, the working mechanism includes a plurality of shrinking and split-flap dies, the shrinking and split-flap dies are installed in the cavity, and the plurality of shrinking and split-flap dies are arranged around the outer circumference of the tube blank at equal angles, the power mechanism includes a motor, a fixing plate, a reset spring, a sleeve, a top block and a fixing sleeve, the shell is provided with a mounting port coaxial with the cavity on the other side relative to the feed port, one end of the sleeve coaxially extends into the mounting port, and the other end is externally fixed on a plane; the sleeve extends into the mounting port The fixing plate is fixedly installed on the end surface of one end, the fixing plate is placed on the outer side of the shrinking and splitting mold, and the fixing plate is provided with a through hole at the position corresponding to the shrinking and splitting mold, and each shrinking and splitting mold is fixedly connected to the top block through the through hole, and the top block is arranged on the other side of the fixing plate relative to the shrinking and splitting mold, and a return spring is sleeved between the top block and the fixing plate, and the top block and the shrinking and splitting mold constitute a whole that moves relative to the fixing plate; the sleeve extends into the cavity from the installation port and is rotatably sleeved between the top block and the inner wall of the cavity, and the sleeve part is coaxially sleeved on the outer wall of the fixing sleeve, and the inner wall of the sleeve is provided with a protrusion at a position relative to each top block, and a gap is provided between adjacent protrusions, and the sleeve is connected to a motor; the method is: Step 1: The tube billet is fed, and the motor drives the sleeve to rotate. When the convex block of the sleeve rotates to the position of the top block, the reset spring is compressed between the top block and the fixed plate, and the shrinking and split dies merge toward the center at the same time, causing the mouth of the original tube billet to deform for the first time; Step 2: The motor drives the sleeve to continue rotating. When the convex block of the sleeve continues to rotate, the reset spring is released, driving the top block and the shrinking and splitting mold to open; Step 3: The tube billet continues to be fed, the motor drives the sleeve to continue to rotate, and the shrinking and split molds merge toward the center to complete the second deformation. This is a forming cycle that is repeated continuously until the tube billet is fed to the far right to complete the deformation.

2. A radial necking forming method that breaks through the necking coefficient limitation according to claim 1, characterized in that: The power mechanism also includes a clutch, a transmission rod, a transmission, a transmission belt and a pulley. The output end of the motor is connected to a clutch, and the clutch is connected to the transmission through the transmission rod. The transmission is connected to the pulley, and the pulley is connected to the sleeve through the transmission belt.

3. A radial necking forming method that breaks through the necking coefficient limitation according to claim 1, characterized in that: The fixing mechanism is a split structure and also includes a front cover, a rear cover, a first circular gasket, a first bearing, a second circular gasket, a second bearing, a third circular gasket and screws. The front cover and the rear cover are respectively covered on the left and right sides of the shell and are tightened and fixed by screws. The first circular gasket, the first bearing, the second circular gasket, the second bearing and the third circular gasket are arranged in sequence from left to right inside the shell, wherein the first bearing and the second bearing are interference fit on the inner wall of the shell, and the first circular gasket, the second circular gasket and the third circular gasket are clearance fit with the inner wall of the shell.

4. A radial necking forming method that breaks through the necking coefficient limitation according to claim 3, characterized in that: The first circular gasket, the first bearing, the second circular gasket, the second bearing and the third circular gasket are sleeved between the inner wall of the shell and the sleeve. The sleeve has an interference fit with the first bearing and the second bearing, and the sleeve has a clearance fit with the first circular gasket, the second circular gasket and the third circular gasket.

5. A radial necking forming method that breaks through the necking coefficient limitation according to claim 1, characterized in that: Each shrinking and splitting mold is correspondingly equipped with a plurality of top blocks, and the number and position of the protruding blocks are consistent with those of the top blocks.

6. A radial necking forming method that breaks through the necking coefficient limitation according to claim 1, characterized in that: The cross section of the top block is triangular.

7. A radial necking forming method that breaks through the necking coefficient limitation according to claim 1, characterized in that: The edge of the protrusion transitions smoothly with the inner wall of the sleeve.

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