Hollow and lining core double-die composite drawing device and method for thin-wall special-shaped pipe
The thin-walled special-shaped tube hollow and liner core dual-die composite drawing device and method solves the problems of dimensional accuracy and uneven wall thickness in traditional drawing methods, and realizes high-precision forming and efficient production of ultra-thin-wall special-shaped tubes.
Patent Information
- Application Number
- CN202510878676.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-27
- Publication Date
- 2025-09-23
AI Technical Summary
When processing ultra-thin-wall special-shaped tubes with complex cross-sectional shapes, traditional hollow drawing or core-lined drawing methods have disadvantages such as insufficient dimensional accuracy, uneven tube wall thickness, and excessive cross-sectional shrinkage leading to drawing fracture.
A thin-walled special-shaped tube hollow and liner core dual-die composite drawing device and method is adopted. Through the combined use of the first and second dies, different transition sections, diameter reduction areas and sizing areas are designed respectively. In combination with an automatic oiling device, the deformation amount and friction force are controlled, and the forming process is decomposed into two steps.
It improves the dimensional accuracy and wall thickness uniformity of key parts of the pipe, reduces the risk of pipe defects, increases the yield rate, simplifies the forming process, and reduces friction resistance.
Smart Images
Figure CN120679857A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a composite drawing device and method, belonging to the technical field of thin-wall special-shaped tube processing. Background Art
[0002] Special-shaped ultra-thin-wall metal pipes are widely used in high-tech fields such as aviation, aerospace, and nuclear power plant equipment due to their thin walls, light weight, high metal utilization, and high thermal conductivity. Traditional drawing technology is widely used in the processing and production of metal pipes. It can not only process rectangular pipes, elliptical pipes, and special-section pipes of different sizes, but also has the advantages of high shape and size accuracy, good surface quality, and high material utilization. However, due to the complexity of the forming process and the limitations of processing technology and traditional analysis methods, for ultra-thin-wall special-shaped pipes with more complex cross-sectional shapes, traditional hollow drawing or core-lined drawing methods still have shortcomings such as insufficient dimensional accuracy, uneven pipe wall thickness, and excessive cross-sectional shrinkage leading to drawing fracture. Summary of the Invention
[0003] The present invention aims to solve the problems of insufficient dimensional accuracy, uneven pipe wall thickness and excessive cross-sectional shrinkage leading to drawing fractures in traditional hollow drawing or liner core drawing methods, and further proposes a thin-walled special-shaped pipe hollow and liner core dual-die composite drawing device and method.
[0004] The technical solution adopted by the present invention to solve the above problems is: the thin-walled special-shaped tube hollow and core-lined double-die composite drawing device described in the present invention includes a first die sleeve and a second die sleeve coaxially arranged from left to right, a first drawing die is fixedly embedded in the first die sleeve, and a second drawing die is fixedly embedded in the second die sleeve. The blank passes through the first drawing die and the second drawing die from left to right in sequence, a core head is provided in the blank, and a connecting rod is provided at the left end of the core head.
[0005] Furthermore, the first drawing die is provided with a first transition section, a first diameter reducing area, a first intersecting area, a first sizing area and a first outlet area from left to right.
[0006] Furthermore, the second drawing die is provided with a second transition section, a second diameter reducing area, a second intersecting area, a second sizing area and a second exit area from left to right.
[0007] Furthermore, the outer walls of the first drawing die and the second drawing die are both provided with positioning pins.
[0008] Furthermore, the entrance cone angle α1 of the first drawing die is 18-25°, and the entrance cone angle α1 of the second drawing die is 12-20°.
[0009] Furthermore, the lengths of the first sizing zone and the second sizing zone are both 2 mm to 5 mm.
[0010] Furthermore, an automatic oil injection device is provided at the entrance of the first drawing die and the second drawing die.
[0011] Furthermore, there are gaps between the core head and the blank, between the blank and the first drawing die, and between the blank and the second drawing die, and the gaps are less than 0.15 mm.
[0012] The steps of the double-die composite drawing method for hollow and liner core of thin-walled special-shaped tubes described in the present invention include: Step 1: Coaxially arrange the first drawing die and the second drawing die, embed the first drawing die in the first die sleeve, embed the second drawing die in the second die sleeve, and fix the first die sleeve and the second die sleeve on the frame of the drawing device, and mirror-polish the first drawing die, the second drawing die, and the core head; Step 2: Install one end of the stainless steel tube into the first drawing die and add lubricating oil through the automatic oiling device; Step 3: The shape of the preformed inner mold of the first drawing die is petal-shaped, and the inlet cone angle α1 is set to 18-25°; Step 4: During the drawing process, the blank passes through the first transition section and contacts the first diameter reduction zone, begins to reduce the diameter and enters the first sizing zone through the first intersecting zone, ensuring a smooth transition at the junction of the first diameter reduction zone and the first sizing zone; Step 5: The first drawing die is designed as a hollow drawing die. No core head is added in the first sizing area. The length of the first sizing area is 2mm~5mm. The automatic oil injection device at the entrance ensures the lubrication of the blank surface during the drawing process. Step 6: After the pre-drawing, the blank enters the second drawing die from the first drawing die, passes through the second transition zone and enters the second diameter reduction zone. Since the blank has been formed into a certain petal shape, the entrance cone angle of the second drawing die is smaller than the entrance cone angle of the first drawing die. The additional cone angle α2 is 12-20°, which increases the contact time of the blank in the second diameter reduction zone, smoothes the diameter reduction process, and avoids defects caused by transition deformation. The second intersection zone of the second drawing die transitions in a circular arc, making the transition at the junction of the second diameter reduction zone and the second sizing zone in the second drawing die smoother, thereby reducing the generation of defects in the tube deformation process. Step 7: The forming process of the second drawing die is liner core drawing. The core head is a contoured structure. The cross-sectional shape of the core head is consistent with the shape of the inner hole of the special-shaped tube and is connected to the connecting rod to ensure that the core head is always in the center position of the inner die of the second drawing die 12; in order to prevent the blank, the core head and the die from locking during drawing, a gap should be left between the core head and the inner surface of the blank. The gap does not exceed 0.15mm to ensure that the core head plays a stable supporting role in the forming of the blank. The outer edges of the front and rear end faces of the core head are rounded to prevent scratching the inner surface of the blank; Step 8: While ensuring the forming quality, the second sizing zone of the second drawing die is reduced in length by reducing the sizing zone 17. The length of the second sizing zone is 2-4 mm, which can not only ensure the quality of the final product of the pipe, but also reduce the contact area between the pipe and the inner and outer dies, thereby reducing friction resistance. Step 9: The diameter reduction of the first drawing die is less than the diameter reduction of the second drawing die, and the cross-sectional shrinkage rate of the first drawing die does not exceed 50% of the total.
[0013] The beneficial effects of the present invention are: 1. The present invention provides a dual-die composite drawing method for hollow and liner tubes, particularly for multi-lobed ultra-thin-wall cladding tubes. This method not only improves the dimensional accuracy of key tube parts but also improves the uniformity of tube wall thickness. Furthermore, the present invention avoids the high friction resistance disadvantage of dual-die drawing by controlling the length of the dual-die sizing belts, the deformation amount during hollow and liner drawing, and an automatic oiling device. 2. The present invention is suitable for drawing and forming ultra-thin-wall special-shaped metal pipes. Compared with the traditional single-pass core-lined and hollow-core forming drawing methods, the dual-die composite drawing method is easier to control the finished pipe dimensional accuracy and wall thickness uniformity, and greatly reduces the risk of pipe defects and improves the pipe yield rate; 3. For thin-walled multi-lobed special-shaped tubes, the present invention decomposes one-pass forming into two continuous drawing processes, reducing the diameter reduction in each process. When drawing a round tube into a simple preformed shape in the first process, the deformation is relatively small, and the forming process is relatively simple. When drawing the preformed shape through the second die into the final finished shape, the diameter reduction is small, the forming process is simplified, and the quality of the finished tube and the uniformity of the tube wall thickness and cross-sectional shape and size are better guaranteed. 4. The present invention is more suitable for the drawing and forming of ultra-thin-wall special-shaped metal pipes. Compared with the traditional single-pass core lining and hollow forming drawing method, the double-die composite drawing method is easier to control the finished product size accuracy and wall thickness uniformity of the pipe, and greatly reduces the risk of pipe defects and improves the pipe yield. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Figure 1 It is a structural diagram of a thin-walled special-shaped tube hollow and liner core double-die composite drawing device; Figure 2 is a front view of the first drawing die; Figure 3 It is a partial enlarged schematic diagram of the intersection area of the first drawing die; Figure 4 is a front view of the second drawing die; Figure 5 It is a partial enlarged schematic diagram of the intersection area of the second drawing die; Figures 1 to 5In the figure, 1-first mold sleeve, 2-first drawing die, 3-first transition section, 4-first diameter reducing area, 5-first intersection area, 6-first sizing area, 7-first outlet area, 8-automatic oiling device, 9-connecting rod, 10-blank, 11-second mold sleeve, 12-second drawing die, 13-second transition section, 14-core head, 15-second diameter reducing area, 16-second intersection area, 17-second sizing area, 18-second outlet area, 19-locating pin. DETAILED DESCRIPTION
[0015] Specific implementation method 1: Figures 1 to 5 As shown, a thin-walled special-shaped tube hollow and core-lined dual-die composite drawing device includes a first die sleeve 1 and a second die sleeve 11 coaxially arranged from left to right, a first drawing die 2 is fixedly embedded in the first die sleeve 1, and a second drawing die 12 is fixedly embedded in the second die sleeve 11. The blank 10 passes through the first drawing die 2 and the second drawing die 12 from left to right in sequence, a core head 14 is provided in the blank 10, and a connecting rod 9 is provided at the left end of the core head 14.
[0016] The first drawing die 2 is provided with a first transition section 3, a first diameter reduction zone 4, a first intersecting zone 5, a first sizing zone 6 and a first outlet zone 7 from left to right. The second drawing die 12 is provided with a second transition section 13 , a second diameter reducing zone 15 , a second intersecting zone 16 , a second sizing zone 17 and a second exit zone 18 in sequence from left to right.
[0017] The outer walls of the first drawing die 2 and the second drawing die 12 are both provided with positioning pins 19 .
[0018] In some embodiments, the entrance cone angle α1 of the first drawing die 2 is 18-25°, and the entrance cone angle α1 of the second drawing die 12 is 12-20°.
[0019] In some embodiments, the lengths of the first sizing zone 6 and the second sizing zone 17 are both 2 mm to 5 mm.
[0020] In some embodiments, an automatic oil injection device 8 is provided at the entrance of the first drawing die 2 and the second drawing die 12 .
[0021] In some embodiments, there are gaps between the core head 14 and the blank 10 , between the blank 10 and the first drawing die 2 , and between the blank 10 and the second drawing die 12 , and the gaps are less than 0.15 mm.
[0022] Specific implementation method 2: Figures 1 to 5 As shown, a thin-walled special-shaped tube hollow and liner core dual-die composite drawing method, the specific steps include: Step 1: Coaxially arrange the first drawing die 2 and the second drawing die 12. The first drawing die 2 is embedded in the first die sleeve 1, and the second drawing die 12 is embedded in the second die sleeve 11. The first die sleeve 1 and the second die sleeve 11 are fixedly mounted on the frame of the drawing device. The first drawing die 2, the second drawing die 12 and the core head 14 are mirror polished. Step 2: The core head 14 installs one end of the stainless steel tube into the first drawing die 2 and lubricating oil is added through the automatic oiling device; Step 3: The shape of the preformed inner mold of the first drawing die 2 is petal-shaped, and the inlet cone angle α1 is set to 18-25°; Step 4: During the drawing process, the blank 10 passes through the first transition section 3 and contacts the first diameter reduction zone 4, begins to reduce in diameter, and enters the first sizing zone 6 through the first intersecting zone 5, ensuring a smooth transition at the junction of the first diameter reduction zone 4 and the first sizing zone 6; Step 5: The first drawing die 2 is designed as a hollow drawing die. No core head 14 is added in the first sizing area 6. The length of the first sizing area 6 is 2 mm to 5 mm. The automatic oiling device 8 at the entrance ensures lubrication of the surface of the blank 10 during the drawing process. Step 6: After pre-drawing, the blank 10 enters the second drawing die 12 from the first drawing die 2, passes through the second transition zone 13 and enters the second diameter reduction zone 15. Since the blank 10 has been formed into a certain petal shape, the entrance cone angle of the second drawing die 12 is smaller than the entrance cone angle of the first drawing die 2. The additional cone angle α2 is 12-20°, which increases the contact time of the blank in the second diameter reduction zone 15, smoothes the diameter reduction process, and avoids defects caused by transition deformation. The second intersection zone 16 of the second drawing die 12 transitions in an arc, making the transition at the junction of the second diameter reduction area and the second sizing area in the second drawing die 12 smoother, thereby reducing the generation of defects in the tube deformation process. Step 7: The forming process of the second drawing die 12 is liner core drawing. The core head 14 is a contoured structure. The cross-sectional shape of the core head 14 is consistent with the shape of the inner hole of the special-shaped tube and is connected to the connecting rod 9 to ensure that the core head 14 is always in the center position of the inner mold of the second drawing die 12; in order to prevent the blank 10, the core head 14 and the die from locking during drawing, a gap should be left between the core head 14 and the inner surface of the blank 10. The gap does not exceed 0.15mm to ensure that the core head 14 plays a stable supporting role in the forming of the blank 10. The outer edges of the front and rear end faces of the core head are rounded to prevent scratching the inner surface of the blank; Step 8: The second sizing zone of the second drawing die 12 is designed to reduce the length of the sizing zone 17 while ensuring the forming quality. The length of the second sizing zone is 2-4 mm, which can not only ensure the quality of the final product of the pipe, but also reduce the contact area between the pipe and the inner and outer dies, thereby reducing friction resistance. Step 9: The diameter reduction of the first drawing die 2 is smaller than the diameter reduction of the second drawing die 12, and the cross-sectional shrinkage rate of the first drawing die 2 does not exceed 50% of the total.
[0023] Example like Figure 1 As shown, the material used is stainless steel, the length is 2000 mm, the billet diameter is 10 mm, and the wall thickness is 0.20 mm.
[0024] The specific process is: Step 1: Double mold pulling device, such as Figure 1 As shown, the first drawing die 2 and the second drawing die 12 are coaxially distributed along the axial direction. In order to ensure the coaxiality, the first drawing die 2 and the second drawing die 12 are designed as an embeddable die, wherein the outer die and the inner die are transitionally matched, and the first die sleeve 1 and the second die sleeve 11 are fixed on the frame, and the first drawing die 2 and the second drawing die 12 are embedded in the center position. The first drawing die 2 and the second drawing die 12 are positioned and fixed by the positioning pin 19; the surfaces of the first drawing die 2, the second drawing die 12 and the core head 14 are mirror polished; after mirror polishing, the roughness of the surface of the outer die and the core head can be more effectively controlled, and the friction coefficient between the outer die and the outer wall of the pre-stainless steel tube and the friction coefficient between the core head and the inner wall of the pre-stainless steel tube can be controlled in combination with lubricating oil; Step 2: Install one end of the stainless steel tube into the mold cavity with the core head 14 and add lubricating oil. Step 3: The shape of the preformed inner mold of the first drawing die 2 is a petal shape, such as Figure 1 and Figure 2 As shown, it mainly consists of a first transition zone 3, a first diameter reduction zone 4, a first intersection zone 5, a first sizing zone 6 and a first outlet zone 7. The size of the inlet part is relatively large, the inlet end is circular, and the inlet cone angle α1 is reasonably customized, and the cone angle is 18-25°; Step 4: During the drawing process, the blank 10 passes through the first transition section 3 and contacts the first diameter reduction zone 4, begins to reduce the diameter and enters the first sizing zone 6 through the first intersection zone 5. The blank is subjected to a large force at the junction of the diameter reduction zone and the sizing zone, and the deformation is uneven, which is very likely to cause defects such as wrinkles and fractures. Therefore, the intersection zone must adopt an arc transition, such as Figure 2 As shown, a smooth transition process is ensured at the junction of the first diameter reducing zone 4 and the first sizing zone 6.
[0025] Step 5. The first drawing die 2 is designed as a hollow drawing, that is, no core rod is added in the sizing section. Since this section is far away from the pulling end, the friction between the blank and the die should be reduced. The length of the sizing section should not be too long, generally 2mm-5mm, and an automatic oiling device 8 is designed at the die entrance to always ensure the lubrication of the blank during the drawing process.
[0026] Step 6: After pre-drawing, the blank 10 enters the second drawing die 12 from the first drawing die 2. The tube passes through the second transition section 13 and enters the second diameter reduction zone 15. Since the tube has been formed into a certain petal shape, the entrance cone angle of the second drawing die 12 can be slightly smaller than the entrance cone angle of the first drawing die 2. The cone angle α2 is 12-20°, which increases the contact time of the tube in the diameter reduction zone 15, smoothes the diameter reduction process, and avoids defects caused by transition deformation. The second intersection zone 16 of the second drawing die 12 has a larger arc transition, which makes the transition at the junction of the diameter reduction zone and the sizing zone in the second drawing die 12 smoother, thereby reducing the defects caused by the tube deformation process. Step 7: The forming process of the second drawing die 12 is liner core drawing, and the core head 14 is a contoured structure, such as Figure 4 As shown, the cross-sectional shape of the core head is consistent with the shape of the inner hole of the special-shaped tube, and is connected to the connecting rod 9 to ensure that the core head 14 is always in the center of the inner mold of the second drawing die 12; in order to prevent the blank, the core head and the die from locking during drawing, an appropriate gap should be left between the core head and the inner surface of the blank; but the gap should not be too large, generally not exceeding 0.15mm, to ensure that the core head plays a stable supporting role in the forming of the blank; the outer edges of the front and rear end surfaces of the core head are rounded to prevent scratching the inner surface of the blank; Step 8: While ensuring the forming quality, the length of the sizing zone 17 of the second drawing die 12 should be minimized. In this case, the length of the sizing zone of the second drawing die 12 is 2-4 mm. This can not only ensure the quality of the final pipe product, but also reduce the contact area between the pipe and the inner and outer dies, thereby reducing frictional resistance. Step 9: Design of double-die drawing: the first drawing die 2 is hollow core drawing, which has a certain degree of wall thickness increase while reducing the diameter; the second drawing die 12 is core-lined drawing, which controls the gap between the core and the die, generally not exceeding 0.15mm, and reduces the diameter while reducing the wall thickness to control the cross-sectional dimensional accuracy and wall thickness uniformity of the finished pipe; Step 10: The diameter reduction of the first drawing die 2 is less than that of the second drawing die 12, and the cross-sectional shrinkage rate of the first drawing die 2 does not exceed 50% of the total. In this embodiment, the cross-sectional shrinkage rate of the first drawing die 2 is 30% of the total.
[0027] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement of the above embodiments made according to the technical essence of the present invention, within the spirit and principles of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the scope of protection of the technical solution of the present invention.
Claims
1. A thin-walled special-shaped tube hollow and liner core double-die composite drawing device, characterized in that: The invention comprises a first die sleeve (1) and a second die sleeve (11) which are coaxially arranged from left to right, wherein a first drawing die (2) is fixedly embedded in the first die sleeve (1), and a second drawing die (12) is fixedly embedded in the second die sleeve (11), and a blank (10) passes through the first drawing die (2) and the second drawing die (12) from left to right in sequence, a core head (14) is provided in the blank (10), and a connecting rod (9) is provided at the left end of the core head (14).
2. A thin-walled special-shaped tube hollow and liner core dual-die composite drawing device according to claim 1, characterized in that: The first drawing die (2) is provided with a first transition section (3), a first diameter reduction zone (4), a first intersecting zone (5), a first sizing zone (6) and a first outlet zone (7) in sequence from left to right.
3. A thin-walled special-shaped tube hollow and liner core dual-die composite drawing device according to claim 1, characterized in that: The second drawing die (12) is provided with a second transition section (13), a second diameter reduction zone (15), a second intersecting zone (16), a second sizing zone (17) and a second outlet zone (18) in sequence from left to right.
4. A thin-walled special-shaped tube hollow and liner core dual-die composite drawing device according to claim 1, characterized in that: The outer walls of the first drawing die (2) and the second drawing die (12) are both provided with positioning pins (19).
5. A thin-walled special-shaped tube hollow and liner core dual-die composite drawing device according to claim 1, characterized in that: The inlet cone angle α1 of the first drawing die (2) is 18-25°, and the inlet cone angle α1 of the second drawing die (12) is 12-20°.
6. A thin-walled special-shaped tube hollow and liner core dual-die composite drawing device according to claim 2 or 3, characterized in that: The lengths of the first sizing zone (6) and the second sizing zone (17) are both 2 mm to 5 mm.
7. A thin-walled special-shaped tube hollow and liner core dual-die composite drawing device according to claim 1, characterized in that: Automatic oil injection devices (8) are provided at the entrances of the first drawing die (2) and the second drawing die (12).
8. A thin-walled special-shaped tube hollow and liner core dual-die composite drawing device according to claim 1, characterized in that: There are gaps between the core head (14) and the blank (10), between the blank (10) and the first drawing die (2), and between the blank (10) and the second drawing die (12), and the gaps are less than 0.15 mm.
9. A thin-walled special-shaped tube hollow and liner core double-die composite drawing method, characterized in that: The specific steps include: Step 1: The first drawing die (2) and the second drawing die (12) are coaxially arranged, the first drawing die (2) is embedded in the first die sleeve (1), the second drawing die (12) is embedded in the second die sleeve (11), the first die sleeve (1) and the second die sleeve (11) are fixedly mounted on a frame of the drawing device, and the first drawing die (2), the second drawing die (12) and the core head (14) are mirror-polished; Step 2: The core head (14) installs one end of the stainless steel tube shrinkage head in the first drawing die (2), and lubricating oil is added through the automatic oiling device; Step 3: The shape of the preformed inner mold of the first drawing die (2) is petal-shaped, and the inlet cone angle α1 is set to 18-25°; Step 4: During the drawing process, the blank (10) passes through the first transition section (3) and contacts the first diameter reduction zone (4), begins to reduce the diameter and enters the first sizing zone (6) through the first intersecting zone (5), ensuring a smooth transition at the junction of the first diameter reduction zone (4) and the first sizing zone (6); Step 5: The first drawing die (2) is designed as a hollow drawing die, and no core head (14) is added in the first sizing zone (6). The length of the first sizing zone (6) is 2 mm to 5 mm. The automatic oiling device (8) at the entrance ensures lubrication of the surface of the blank (10) during the drawing process. Step 6: After the blank (10) is pre-drawn and formed, it enters the second drawing die (12) from the first drawing die (2), passes through the second transition zone (13) and enters the second diameter reduction zone (15). Since the blank (10) has been formed into a certain petal shape, the entrance cone angle of the second drawing die (12) is smaller than the entrance cone angle of the first drawing die (2). The additional cone angle α2 is 12-20°, which increases the contact time of the blank in the second diameter reduction zone (15), smoothes the diameter reduction process, and avoids defects caused by transition deformation. The second intersection zone (16) of the second drawing die (12) transitions in an arc, so that the transition at the junction of the second diameter reduction zone and the second sizing zone in the second drawing die (12) is smoother, thereby reducing the generation of defects in the tube deformation process. Step 7: The forming process of the second drawing die (12) is core drawing. The core head (14) is a contoured structure. The cross-sectional shape of the core head (14) is consistent with the shape of the inner hole of the special-shaped tube and is connected to the connecting rod (9) to ensure that the core head (14) is always in the center position of the inner die of the second die. In order to prevent the blank (10), the core head (14) and the die from locking during drawing, a gap should be left between the core head (14) and the inner surface of the blank (10). The gap does not exceed 0.15 mm to ensure that the core head (14) plays a stable supporting role in the forming of the blank (10). The outer edges of the front and rear end faces of the core head are rounded to prevent scratching the inner surface of the blank. Step 8: The second sizing zone of the second drawing die (12) is designed to reduce the length of the sizing zone 17 while ensuring the forming quality. The length of the second sizing zone is 2-4 mm, which can not only ensure the quality of the final product of the pipe, but also reduce the contact area between the pipe and the inner and outer dies, thereby reducing friction resistance. Step 9: The diameter reduction of the first drawing die (2) is less than the diameter reduction of the second drawing die (12), and the cross-sectional shrinkage rate of the first drawing die (2) does not exceed 50% of the total.