A low-friction rotary shrinking forming die

Abstract

The present invention discloses a low-friction rotary necking forming die, which relates to the field of plastic processing technology of light metal materials. The die comprises a clamping mechanism and a necking die, wherein a tube billet is driven to rotate under the clamping of the clamping mechanism, the necking die is driven to move vertically under the axial feed drive, and the necking mold cavity is equipped with multiple rows of rollers, and the rollers are arranged along the form of the necking part generatrix; the necking die descends, and when the upper end of the tube billet contacts the first circle of rollers of the necking die, the rollers are driven to rotate under the drive of the tube billet, and the rollers synchronously extrude the tube billet to begin shrinking and deforming. As the necking die descends, the contact area between the tube billet and the rollers gradually increases, more rollers are driven to rotate, and the deformation of the material becomes larger and larger until the necking is completed. The present invention can break through the limit necking coefficient and manufacture conical or quasi-conical components with large diameter differences and difficult-to-deform materials in a short process and high efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of plastic processing of light metal materials, in particular to a low-friction rotary necking forming die. Background Art

[0002] Radial necking equipment is a processing machine designed specifically for metal pipes and similar circular cross-section materials. Its operating principle is based on strong radial compression technology, aiming to precisely reduce the diameter of the material's ends, often accompanied by a moderate increase in pipe wall thickness. Therefore, as a vital tool in fields such as metalworking and automotive manufacturing, radial necking equipment is continuously driving the manufacturing industry towards higher levels and higher quality with its unique processing capabilities, advanced CNC technology, broad adaptability, and environmentally friendly production philosophy.

[0003] Traditional necking forming technologies include die-cut necking, which refers to a forming process that uses a die to reduce the diameter of the mouth of a cylindrical or tubular part. It is one of the basic stamping processes. The advantages of this process are simple die structure, high forming efficiency, easy mechanization, and both partial and overall forming. Depending on the product requirements, products with straight or curved busbars can be formed. Depending on whether the necking process is supported, it can be divided into three forming methods: internal support, external support, and no support. Depending on whether heating is used, it can be divided into normal temperature necking and heated necking. Although a variety of forming methods have been derived from die-cut necking, die-cut necking still has the problem of a large limit necking coefficient.

[0004] The shrinkage coefficient k, that is, the ratio of the minimum diameter d after deformation to the original blank diameter d0, is expressed as k=d / d0. The size of the shrinkage coefficient directly affects the difficulty of shrinkage. For example, the maximum shrinkage coefficient of aluminum alloy components without support is about 0.8. In the case of external support, the shrinkage coefficient is about 0.62. Under the premise of internal and external support, the shrinkage coefficient can be reduced to about 0.5. The maximum shrinkage coefficient of steel components is larger than that of aluminum. It can be seen that the smaller the shrinkage coefficient, the greater the difficulty of forming.

[0005] While existing technologies can produce high-quality conical or quasi-conical components with widely varying diameters and difficult-to-deform materials, the forming process remains cumbersome and the shrinkage coefficient that can be achieved in a single forming step is significantly limited. These technologies often 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 can also lead to inconsistent forming quality, especially when processing complex shapes or high-strength materials. Summary of the Invention

[0006] The purpose of the present invention is to provide a low-friction rotary necking forming die for manufacturing conical or conical-like components with large diameter differences and difficult-to-deform materials in a short process and high efficiency.

[0007] To achieve the above object, the present invention provides the following technical solutions: a low-friction rotary necking forming die, comprising an upper die plate, a rotary worktable, a clamping mechanism and a necking die;

[0008] The clamping mechanism includes a square limit block, a turntable, a screw, a driven gear, a driving gear, an outer clamp, an inner clamp, a base, and a rotating rod;

[0009] The turntable and the base are coaxially arranged one above and one below, and the multiple inner clamps are evenly distributed on the base in a ring-shaped manner with the center of the base as the center, and the multiple inner clamps are respectively slidably arranged along the radial direction of the base. The multiple outer clamps are fixedly arranged on the base and correspondingly located on the outer sides of the multiple inner clamps, and a clamping space is left between adjacent inner clamps and outer clamps for placing the tube blank;

[0010] The turntable is provided with an arc-shaped slot at a position corresponding to the inner clamp. The arc-shaped slot is a slot with one end radially inclined in an arc shape relative to the other end. A screw is axially passed through each arc-shaped slot. One end of each screw is fixedly connected to an inner clamp, and the other end of the screw passes through the arc-shaped slot and is tightened by a nut.

[0011] The plurality of driven gears and a driving gear are evenly distributed on the base in a circular manner with the center of the base as the center. The base is provided with a plurality of recessed grooves for the driven gears and the driving gears to be respectively embedded and pivotally connected therein. The rotating rod is cooperatively connected with the driving gear to drive the driving gear to rotate in the recessed groove. The end surface of the turntable is provided with gear teeth at positions corresponding to the driven gears and the driving gear. The gear teeth are engaged with the driven gear and the driving gear to make the turntable rotate around its own center. As the turntable rotates, the screw slides along the arc-shaped through groove, driving the inner clamp to slide radially closer to or away from the outer clamp to control the size of the clamping space.

[0012] The turntable and the base are coaxially provided with square limiting holes. When the square limiting holes of the two coincide with each other, the square limiting blocks are fitted into the square limiting holes to limit the relative rotation of the turntable and the base.

[0013] The upper template is connected to the axial feeding mechanism, the base is fixedly installed on the rotating workbench, the tube blank is clamped between the upper template and the rotating workbench through the clamping mechanism, the upper template is installed with the shrinking die, the shrinking die is provided with a cavity, the cavity is provided with a die entry for the tube blank to be axially placed into the cavity, the cavity gradually shrinks from the die entry to the inside, a plurality of rollers are distributed on the inner wall of the cavity, and the rollers are engaged in rolling friction with the outer surface of the tube blank.

[0014] Preferably, the distribution of the rollers on the inner wall of the cavity of the necking mold is as follows: a plurality of evenly spaced roller belts are provided on the inner wall of the cavity of the necking mold from the mold inlet to the inside, and each roller belt is composed of a plurality of rollers continuously combined into a row.

[0015] Preferably, the inner wall of the cavity of the necking mold is designed with multiple semi-cylindrical roller grooves and roller grooves. The roller is a cylinder with a center hole, and the roller is built-in in the center hole. The roller is half-fitted in the roller groove, and a screw hole is opened in the roller groove. The roller is pivotally connected to the roller groove. The rollers extend out of both ends of the roller. The extended parts are milled with flat surfaces, and shaft holes are opened on the flat surfaces. Set screws are passed through the shaft holes. The set screws lock the two ends of the roller in the screw holes, so that the roller is fixed in the roller groove and semi-protrudes from the inner wall surface of the cavity.

[0016] Preferably, both ends of the roller are provided with arc-shaped transition angles.

[0017] Preferably, the base is provided with an inverted T-shaped slide groove at the position of the inner clamp, the inverted T-shaped slide groove is radially provided along the base, the inner surface of the inner clamp is convexly provided with an inverted T-shaped slide that slides in cooperation with the inverted T-shaped slide groove, a fixing hole is provided on the inverted T-shaped slide, and one end of each screw is screwed into the fixing hole of the inverted T-shaped slide of the corresponding inner clamp.

[0018] Preferably, a gear shaft is passed through the middle of the driven gear, and the gear shaft is pivotally connected in the groove; different from the driven gear, the middle of the driving gear is a through hole with a slot, and a clamping platform is provided at the end of the rotating rod, which passes through the slot and is connected to the through hole of the driving gear, and the clamping platform cooperates with the slot.

[0019] Preferably, the number of the inner clamps and the outer clamps are four respectively, and they are evenly distributed in a circular shape with the center of the base as the center.

[0020] Preferably, the inner clamp and the outer clamp are both arc-shaped.

[0021] Preferably, the inner wall surface of the outer clamp and the outer wall surface of the inner clamp are both designed with anti-slip grooves.

[0022] Preferably, a hanging ring is provided on the top of the square limit block.

[0023] Compared with the prior art, the beneficial effects of the present invention are: 1. Reducing the risk of buckling instability in the force transmission area of ​​the tube blank during the forming process. In the traditional die shrinking process, the friction force generated by the large-area contact between the tube blank and the shrinking die is transmitted to the undeformed area, reaching the support limit and causing buckling instability. The low-friction rotary shrinking forming method proposed by the present invention, on the one hand, greatly reduces the contact area between the tube blank and the roller, and the friction force is also reduced accordingly. On the other hand, the tube blank drives the roller to rotate, which changes the direction of the friction force in real time, so that the axial pressure transmitted to the undeformed area of ​​the tube blank is reduced, thereby reducing the risk of shrinking instability; 2. Reducing height difference. In traditional die shrinking, the friction force varies greatly due to uneven lubricant application, resulting in greater height differences in the shrinking parts. However, in the present invention, the tube blank and the roller are basically in line contact during the deformation process, and are less affected by friction. In the actual forming process, no lubricant needs to be applied or a small amount of lubricant can be applied, thereby reducing the impact of uneven application and reducing the height difference of the shrinking parts; 3. Reducing the risk of mouth deformation and wrinkling. During the forming process of traditional die compression, the material in the mouth area deforms too much and does not have enough time to deform, which easily leads to material accumulation and wrinkling. However, during the forming process of the present invention, the roller contacts and deforms locally with the tube billet, reducing the material deformation and thus reducing the risk of deformation and wrinkling at the mouth. ④ Breaking through the limit shrinkage coefficient. The buckling instability of the tube billet in the undeformed area during the shrinkage forming process is the main factor limiting the shrinkage coefficient. The present invention reduces the risk of instability in the undeformed area and wrinkling at the mouth, thus breaking through the limit shrinkage coefficient of traditional die compression. For example, using traditional die compression technology at home and abroad, the limit shrinkage coefficient of a tube billet made of aluminum alloy is 0.8 when there is no support inside or outside. However, the low-friction rotary shrinkage forming proposed by the present invention can reduce the shrinkage coefficient to 0.45, improving the forming limit. ⑤ Both local shrinkage and overall shrinkage can be achieved, and it is only necessary to design the arrangement and number of rollers according to the product busbar form. ⑥ Reducing the difficulty of forming, one-time forming, improving forming efficiency, shortening the time, and forming conical or conical-like components with large diameter differences and difficult-to-deform materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the overall structure of the mold of the present invention;

[0025] Figure 2 Schematic diagram of the exploded view of the clamping mechanism of the present invention;

[0026] Figure 3 Schematic diagram of the top surface structure of the turntable of the present invention;

[0027] Figure 4 This is a schematic diagram of the back structure of the turntable of the present invention;

[0028] Figure 5 Schematic diagram of the structure of the driven gear of the present invention;

[0029] Figure 6 This is a schematic structural diagram of the driving gear of the present invention;

[0030] Figure 7 It is a structural schematic diagram of the outer clamp of the present invention;

[0031] Figure 8 It is a structural schematic diagram of the inner clamp of the present invention;

[0032] Figure 9 It is a structural schematic diagram of the base of the present invention;

[0033] Figure 10 It is a structural schematic diagram of the rotating rod of the present invention;

[0034] Figure 11 Schematic diagram of the changing process of the clamping mechanism of the present invention;

[0035] Figure 12 Schematic diagram of the internal structure of the necking die of the present invention;

[0036] Figure 13 for Figure 12 Enlarged view of part A in the middle;

[0037] Figure 14 It is a structural schematic diagram of the roller of the present invention;

[0038] Figure 15 It is a schematic cross-sectional view of the assembly of the roller of the present invention in the roller groove;

[0039] Figure 16 This is a schematic diagram of the forming process of the tube blank under the action of the necking die of the present invention.

[0040] In the figure: 1. square limit block; 2. turntable; 3. screw; 4. driven gear; 5. driving gear; 6. outer clamp; 7. inner clamp; 8. base; 9. turning rod; 10. inverted T-shaped slide; 11. inverted T-shaped slide; 12. arc-shaped through groove; 13. nut; 14. countersunk groove; 15. gear shaft; 16. clamping groove; 17. through hole; 18. clamping table; 19. gear teeth; 20. anti-slip groove; 21. square limit hole; 22. lifting ring; 23. cavity; 24. die entry; 25. roller; 26. tube blank; 27. roller groove; 28. roller groove; 29. ​​roller; 30. screw hole; 31. shaft hole; 32. set screw; 100. upper template; 200. rotating worktable; 300. clamping mechanism; 400. shrinking die; DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0042] See also Figures 1-16 The present invention provides a low-friction rotary necking forming die, comprising an upper die plate 100, a rotary worktable 200, a clamping mechanism 300 and a necking die 400;

[0043] like Figure 2 As shown, the clamping mechanism 300 includes a square limit block 1, a turntable 2, a screw 3, a driven gear 4, a driving gear 5, an outer clamp 6, an inner clamp 7, a base 8, and a rotating rod 9;

[0044] The turntable 2 and the base 8 are coaxially arranged one above and one below. The base 8 is designed with a mounting hole and a keyway on the back. The rotating workbench 200 is designed with corresponding key positioning. The base 8 and the rotating workbench 200 are fixed through the mounting holes. Since this is a common design of the mold, it will not be repeated here.

[0045] The plurality of inner clamps 7 are evenly distributed on the base 8 in a circular pattern with the center of the base 8 as the center, and the plurality of inner clamps 7 are respectively arranged to slide radially along the base 8. The specific structure is as follows: the base 8 is provided with an inverted T-shaped slide 10 at the position of the inner clamp 7, and the inverted T-shaped slide 10 is radially opened along the base 8. The inner surface of the inner clamp 7 is convexly provided with an inverted T-shaped slide 11 that slides with the inverted T-shaped slide 10. An assembly gap is reserved between the inverted T-shaped slide 10 and the inverted T-shaped slide 11 to ensure that the inner clamp 7 can slide back and forth along the inverted T-shaped slide 10;

[0046] The plurality of outer clamps 6 are fixedly mounted on the base 8 (specifically, fixing holes can be designed at the bottom of the outer clamps 6 and fixed with screws), and are correspondingly located on the outside of the plurality of inner clamps 7. A clamping space is left between adjacent inner clamps 7 and outer clamps 6 for placing the tube blank 26. The inner clamps 7 and outer clamps 6 are both arc-shaped. The outer diameter of the inner clamp 7 is the same as the inner diameter of the tube blank 26, but the inner diameter of the outer clamp 6 is about 5 mm larger than the outer diameter of the tube blank 26 to facilitate the placement of the tube blank 26 in the preparation stage.

[0047] An arc-shaped through groove 12 is provided at the position corresponding to the inner clamp 7 of the turntable 2. The arc-shaped through groove 12 is a through groove with one end radially inclined in an arc shape relative to the other end. A screw 3 is axially passed through each arc-shaped through groove 12, and one end of each screw 3 is fixedly connected to an inner clamp 7. Specifically, a fixing hole is provided on the inverted T-shaped slide 11 of the inner clamp 7. One end of each screw 3 is screwed into the fixing hole of the inverted T-shaped slide 11 of the corresponding inner clamp 7, and the other end of the screw 3 is tightened by a nut 13 after passing through the arc-shaped through groove 12. The number of the inner clamp 7 and the outer clamp 6 is not limited. In the preferred embodiment, the number of the inner clamp 7 and the outer clamp 6 are four respectively, and they are evenly distributed in a ring with the center of the base 8 as the center. The four-piece design provides more stable and balanced clamping.

[0048] The plurality of driven gears 4 and the driving gear 5 are evenly distributed on the base 8 in a circular pattern with the center of the base 8 as the center. Similarly, the present preferred embodiment designs three driven gears 4, and a plurality of recessed grooves 14 are provided on the base 8 for the driven gears 4 and the driving gear 5 to be respectively embedded and pivoted therein. Specifically, a gear shaft 15 is passed through the middle of the three driven gears 4, and the gear shaft 15 is pivotally connected in the recessed groove 14; the difference from the driven gear 4 is that the middle part of the driving gear 5 is a through hole 17 with a slot 16, and a clamping platform 18 is provided at the end of the rotating rod 9. The end of the rotating rod 9 passes through the slot 14 and is connected to the through hole 17 of the driving gear 5, and the clamping platform 18 cooperates with the slot 16, and the rotating rod 9 cooperates with the driving gear 5 to drive the driving gear 5 to rotate in the slot 14. The end face of the turntable 2 is provided with gear teeth 19 at positions corresponding to the driven gear 4 and the driving gear 5. Specifically, the gear teeth 19 are designed in the interval area of ​​the arc-shaped through groove 12. The gear teeth 19 are engaged with the driven gear 4 and the driving gear 5, so that the turntable 2 rotates around its own center of circle. While the turntable 2 rotates, the four screws 3 slide along the arc-shaped through groove 12, driving the inner clamp 7 to slide radially closer to or away from the outer clamp 6 to control the size of the clamping space. The inner wall surface of the outer clamp 6 and the outer wall surface of the inner clamp 7 are both designed with anti-slip patterns 20. The anti-slip patterns 20 can specifically be cross twill patterns, which can have a good anti-slip effect.

[0049] The turntable 2 and the base 8 are coaxially defined with square limiting holes 21 of equal size, preferably located in the center of the turntable 2 and the base 8. When the square limiting holes 21 of the two coincide, the square limiting block 1 fits into the square limiting hole 21 to limit the relative rotation of the turntable 2 and the base 8. To facilitate mechanized operation, a lifting ring 22 is provided on the top of the square limiting block 1.

[0050] The upper template 100 is connected to the axial feeding mechanism, and the tube blank 26 is clamped between the upper template 100 and the rotating worktable 200 through the clamping mechanism 300. The upper template 100 is installed with the shrinking die 400. The upper template 100 and the shrinking die 400 are fixed with bolts and cylindrical pins, driving the shrinking die 400 to complete vertical up and down movement.

[0051] The shrinking die 400 opens a cavity 23, and the cavity 23 is provided with a die inlet 24 for the tube blank 26 to be axially placed into the cavity 23. The cavity 23 gradually reduces in diameter from the die inlet 24 to the inside. A plurality of rollers 25 are distributed on the inner wall of the cavity 23, and the rollers 25 are engaged with the outer surface of the tube blank 26 by rolling friction.

[0052] In a preferred embodiment, the distribution of the rollers 25 on the inner wall of the cavity 23 of the necking mold 400 is as follows: a plurality of evenly spaced roller belts are provided on the inner wall of the cavity 23 of the necking mold 400 from the mold inlet 24 to the inside, and each roller belt is composed of multiple rollers 25 continuously combined into a row. The inner wall of the cavity 23 of the shrinking mold 400 is designed with multiple semi-cylindrical roller grooves 27 and roller grooves 28. The roller 25 is a cylinder with a center hole, and the center hole has a built-in roller 29. The two ends of the roller 25 are provided with arc-shaped transition angles to facilitate the entry of the tube blank 26 into the mold and the transition between the two adjacent rollers 25 during the shrinking process. The roller 25 is semi-fitted in the roller groove 27, and a screw hole 30 is provided in the roller groove 27. The roller 29 is pivotally connected to the roller groove 28. Both ends of the roller 29 extend out of the roller 25. The protruding parts are milled with planes, and an axial hole 31 is provided on the plane. A set screw 32 is passed through the axial hole 31. The set screw 32 locks the two ends of the roller 29 in the screw hole 30, so that the roller 25 is fixed in the roller groove 27 and semi-protrudes from the inner wall surface of the cavity 23.

[0053] like Figure 15 As shown, to ensure that the profile formed by each row of rollers 25 conforms to the product generatrix, the design must ensure that the tangent to the outer generatrix of the tube 26 is parallel to the axis of the rollers 25, and that the perpendicular to the tangent at the point of tangency remains perpendicular to the axis of the rollers 25. The number of rollers 25 in the circumferential and axial directions can be designed based on the material characteristics. For example, if the material is soft, the number of rollers 25 can be appropriately reduced, while if it is soft, the number of rollers 25 can be increased. However, the spacing between rollers 25 in both the axial and circumferential directions should be limited to prevent deformation of the tube 26 between the two rollers 25 due to the material being too soft during the necking process.

[0054] The present invention also provides a low-friction rotary necking forming method, comprising the following steps:

[0055] S1 clamping: see Figure 11, first place the tube blank 26 in the clamping space between the inner clamp 7 and the outer clamp 6, then rotate the rotating rod 9. The rotation of the rotating rod 9 will drive the rotation of the driving gear 5, and then drive the turntable 2 to rotate through the engagement with the gear teeth 19. The turntable 2 designed with an arc-shaped through groove 12 drives the screw 3 to move outward, and at the same time drives the inner clamp 7 to move outward, so that the inner clamp 7 and the outer clamp 6 clamp the tube blank 26 together. At this time, the square limiting holes 21 of the turntable 2 and the base 8 coincide with each other, and the square limiting block 1 is placed in the square limiting hole 21 to achieve the purpose of locking. Since the inner diameter of the outer clamp 6 is larger than the outer diameter of the tube blank 26, the outer clamp 6 can cause a slight deformation of the tube blank 26 when it is combined, thereby clamping the tube blank 26, and the outer surface of the inner clamp 7 and the inner surface of the outer clamp 6 are designed with cross twill to prevent slipping;

[0056] S2 Neck reduction: First, the rotary table 200 is driven to start, and the clamped tube 26 is rotated through the base 8. Then, the upper template 100 drives the necking die 400 to feed axially. When the upper end of the tube 26 contacts the first circle of rollers 25 of the die inlet 24 of the necking die 400, the rollers 25 are driven to rotate under the drive of the tube 26, and the rollers 25 synchronously extrude the tube 26 to start shrinking and deforming. As the necking die 400 descends, the contact area between the tube 26 and the rollers 25 gradually increases, more rollers 25 are driven to rotate, and the deformation of the material becomes larger and larger until the necking is completed.

[0057] S3 Demolding: The tube 26 continues to rotate, while the necking die 400 returns. The square stopper 1 is then removed using auxiliary tooling. The rotating rod 9 is then rotated in the opposite direction, releasing the inner clamp 7. Finally, the tube 26 is removed, completing demolding. The necking die 400 with rollers 25 also avoids the difficulty of demolding. The tube 26 can be heated or not depending on the material characteristics. Whether the tube 26 is heated or cold does not change the mold structure. However, using a heated tube requires selecting a more heat-resistant mold material for the rollers 25 and 29.

[0058] The technical advantages of the clamping mechanism proposed in the present invention are: ① The diameter of the inner circle of the outer clamp is about 5 mm larger than the outer diameter of the tube blank, so that the tube blank will produce slight deformation when clamped, thereby ensuring that the tube blank is clamped; ② By rotating the rotating rod, the inner clamps in four directions move simultaneously and the movement distance is consistent, thereby ensuring that the four inner clamps clamp the tube blank with the same tightness, avoiding the generation of additional stress inside the tube blank during the necking forming process due to different tightness; ③ The square limit hole and the square limit block can ensure that problems such as clamp loosening caused by vibration during necking deformation are avoided, thereby improving safety; ④ The gear transmission structure has high torque output efficiency, is safe and reliable.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the design of this case. Any equivalent changes made based on the key design of this case shall fall within the scope of protection of this case.

Claims

1. A low-friction rotary necking forming die, characterized in that: It includes an upper template, a rotating workbench, a clamping mechanism and a shrinking die; The clamping mechanism includes a square limit block, a turntable, a screw, a driven gear, a driving gear, an outer clamp, an inner clamp, a base, and a rotating rod; The turntable and the base are coaxially arranged one above and one below, and the multiple inner clamps are evenly distributed on the base in a ring-shaped manner with the center of the base as the center, and the multiple inner clamps are respectively slidably arranged along the radial direction of the base. The multiple outer clamps are fixedly arranged on the base and correspondingly located on the outer sides of the multiple inner clamps, and a clamping space is left between adjacent inner clamps and outer clamps for placing the tube blank; The turntable is provided with an arc-shaped slot at a position corresponding to the inner clamp. The arc-shaped slot is a slot with one end radially inclined in an arc shape relative to the other end. A screw is axially passed through each arc-shaped slot. One end of each screw is fixedly connected to an inner clamp, and the other end of the screw passes through the arc-shaped slot and is tightened by a nut. The plurality of driven gears and a driving gear are evenly distributed on the base in a circular manner with the center of the base as the center. The base is provided with a plurality of recessed grooves for the driven gears and the driving gears to be respectively embedded and pivotally connected therein. The rotating rod is cooperatively connected with the driving gear to drive the driving gear to rotate in the recessed groove. The end surface of the turntable is provided with gear teeth at positions corresponding to the driven gears and the driving gear. The gear teeth are engaged with the driven gear and the driving gear to make the turntable rotate around its own center. As the turntable rotates, the screw slides along the arc-shaped through groove, driving the inner clamp to slide radially closer to or away from the outer clamp to control the size of the clamping space. The turntable and the base are coaxially provided with square limiting holes. When the square limiting holes of the two coincide with each other, the square limiting blocks are fitted into the square limiting holes to limit the relative rotation of the turntable and the base. The upper template is connected to the axial feeding mechanism, the base is fixedly installed on the rotating workbench, the tube blank is clamped between the upper template and the rotating workbench through the clamping mechanism, the upper template is installed with the shrinking die, the shrinking die is provided with a cavity, the cavity is provided with a die entry for the tube blank to be axially placed into the cavity, the cavity gradually shrinks from the die entry to the inside, a plurality of rollers are distributed on the inner wall of the cavity, and the rollers are engaged in rolling friction with the outer surface of the tube blank.

2. A low-friction rotary necking forming die according to claim 1, characterized in that: The rollers are distributed on the inner wall of the cavity of the necking die as follows: a plurality of roller belts with even intervals are arranged on the inner wall of the cavity of the necking die from the die inlet to the inside, and each roller belt is composed of a plurality of rollers continuously combined into a row.

3. The low-friction rotary necking forming die according to claim 1, characterized in that: The inner wall of the cavity of the necking mold is designed with multiple semi-cylindrical roller grooves and roller grooves. The roller is a cylinder with a center hole. The center hole has a built-in roller. The roller is half-fitted in the roller groove. A screw hole is provided in the roller groove. The roller is pivotally connected to the roller groove. The rollers extend out of both ends of the roller. The extended parts are milled with planes, and shaft holes are provided on the planes. Set screws are passed through the shaft holes. The set screws lock the two ends of the roller in the screw holes, so that the roller is fixed in the roller groove and semi-protrudes from the inner wall surface of the cavity.

4. The low-friction rotary necking forming die according to claim 1, characterized in that: Both ends of the roller are provided with arc-shaped transition bevels.

5. The low-friction rotary necking forming die according to claim 1, characterized in that: The base is provided with an inverted T-shaped slide at the position of the inner clamp, and the inverted T-shaped slide is provided radially along the base. The inner surface of the inner clamp is convexly provided with an inverted T-shaped slide that slides in cooperation with the inverted T-shaped slide. A fixing hole is provided on the inverted T-shaped slide, and one end of each screw is screwed into the fixing hole of the inverted T-shaped slide of the corresponding inner clamp.

6. The low-friction rotary necking forming die according to claim 1, characterized in that: A gear shaft is passed through the middle of the driven gear, and the gear shaft is pivotally connected in the sink groove. Unlike the driven gear, the driving gear has a through hole with a slot in the middle, and a clamping platform is provided at the end of the rotating rod. The end of the rotating rod passes through the sink groove and is connected to the through hole of the driving gear, and the clamping platform cooperates with the slot.

7. The low-friction rotary necking forming die according to claim 1, characterized in that: The number of the inner clamps and the number of the outer clamps are four respectively, and they are evenly distributed in a circular shape with the center of the base as the center.

8. The low-friction rotary necking forming die according to claim 1, characterized in that: The inner clamp and the outer clamp are both arc-shaped.

9. The low-friction rotary necking forming die according to claim 1, characterized in that: The inner wall surface of the outer clamp and the outer wall surface of the inner clamp are both designed with anti-slip grooves.

10. The low-friction rotary necking forming die according to claim 1, characterized in that: A hanging ring is provided on the top of the square limiting block.

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