Cold heading device for automobile auxiliary frame bolt sleeve

Abstract

The utility model relates to an automobile subframe bolt sleeve cold heading device which comprises a cutting mechanism, an ejection mechanism, a conveying mechanism and six dies, the cutting mechanism cuts off a blank, and the ejection mechanism ejects the blank; the conveying mechanism moves between the ejection mechanism and the six molds for feeding; the six dies comprise a first upsetting die used for punching concave holes in the two ends of an initial blank and chamfering the lower end, a second upsetting die used for extruding and stretching the lower end of a first blank and deepening an inner hole in the lower end, and a third upsetting die used for stretching and forming the upper end of a second blank and deepening an inner hole in the upper end. The four-upsetting die is used for enabling the overturned third blank to form a middle disc part and shortening two end hole parts; the five-upsetting die is used for deepening an inner hole in the lower end of the fourth blank; and the through hole die is used for enabling an inner hole in the upper end of the fifth blank to be communicated with the inner hole in the lower end of the fifth blank to form a through hole. By the adoption of the technical scheme, parts are rapidly formed through cold heading, and inner holes are free of tearing cracks; the production efficiency is high.

Description

Technical Field

[0001] The utility model belongs to the technical field of machinery, and in particular relates to a cold heading device for a bolt sleeve of an automobile auxiliary frame. Background Art

[0002] The automobile subframe is used to support and connect various parts of the automobile. Most of the parts and assemblies on the automobile are fixed by the subframe, such as the engine, transmission system, suspension, steering, cab and cargo box. The use of the subframe can reduce the transmission of road vibration and increase the connection stiffness of the suspension system.

[0003] Compared with the general straight-barrel bolt sleeve, the automobile subframe bolt sleeve has a larger protruding part in the middle, and the disc is used for welding the sleeve and the car body. The larger the supporting disc surface, the stronger the welding. The processing structure is complex. The original cold heading process cannot directly form the inner hole of the part. Subsequently, lathe processing is required to meet the corresponding size requirements. The excess material produced by lathe processing wastes materials, consumes working hours, has low production efficiency and high cost. Utility Model Content

[0004] In summary, in order to overcome the deficiencies of the prior art, the utility model provides a novel cold heading forming device for welding hexagonal flange nuts which saves cost and improves quality.

[0005] To achieve the above-mentioned purpose, the utility model provides the following technical solutions: a cold forging device for a bolt sleeve of an automobile subframe, comprising a cutting mechanism, an ejection mechanism, a conveying mechanism and six dies, wherein the cutting mechanism cuts off a blank, and the ejection mechanism lifts up the blank; the conveying mechanism moves and feeds between the ejection mechanism and the six dies; the six dies comprise: a first forging die for punching out recesses at both ends of an initial blank and chamfering the lower end, a second forging die for extruding and stretching the lower end of a first blank and deepening the inner hole at the lower end, a third forging die for stretching and forming the upper end of a second blank and deepening the inner hole at the upper end, and a third forging die for forming a middle forcing die for a flipped third blank. A four-upsetting die with a disc portion and shortened two end holes, a five-upsetting die for deepening the lower end inner hole of the fourth blank, and a through-hole die for connecting the upper end inner hole of the fifth blank with the lower end inner hole to form a through hole; the six dies all include a lower die and an upper die, the lower die includes a lower die shell, a lower die core, a lower die punch, a lower die locking nut and a lower die pad, the lower die core is arranged in the lower die shell, a lower model cavity is arranged in the lower die core, the lower die pad is arranged below the lower die core, and the lower die locking nut is connected to the lower die shell to fix the lower die pad and the lower die core; the upper die includes an upper die shell, an upper die pad and an upper die punch, and the upper die pad is arranged in the upper die shell.

[0006] By adopting the above technical scheme, large-diameter materials are stretched into small-diameter materials, and the inner hole is punched out for rapid cold heading forming, thereby improving production efficiency. The inner hole of large-size parts is formed by long cold heading, so that the cold heading material is fully utilized, saving materials and reducing costs, reducing the use of machining, and achieving the effect of cold heading rapid forming parts without tear marks on the inner hole; during the cold heading process, the metal material undergoes plastic deformation in a cold state, its internal structure is refined, and the grains become finer. This microstructure makes the cold heading parts have high mechanical strength, hardness and corrosion resistance; the production efficiency is high, and batch production can be achieved by using a mold on a cold heading machine, and the operation is simple, and workers only need to perform simple equipment operation and monitoring.

[0007] The utility model is further configured as follows: the main mold cavity of the first upsetting mold includes a first lower molding cavity for molding the chamfer of the lower end of the initial blank, the upper die punch of the first upsetting mold includes a first convex portion for punching the upper end of the initial blank out of the concave cavity, and the lower die punch of the first upsetting mold includes a second convex portion for punching the lower end of the initial blank out of the concave cavity; the main mold cavity of the second upsetting mold includes a second upper molding cavity for molding the upper cylinder, a second lower molding cavity for molding the lower cylinder, and a second middle molding cavity connecting the second upper molding cavity and the second lower molding cavity, and the second middle molding cavity is The inverted truncated cone is set up with a larger upper part and a smaller lower part. The inner diameter of the second upper forming cavity is larger than the inner diameter of the second lower forming cavity. The lower die punch of the second upsetting die passes through the lower die pad of the second upsetting die and extends into the second middle forming cavity to deepen the inner hole at the lower end of the first blank. The main mold cavity of the three-upsetting die has the same shape as the main mold cavity of the two-upsetting die. The length of the main mold cavity of the three-upsetting die is larger than the main mold cavity of the two-upsetting die. The lower die punch of the three-upsetting die passes through the lower die pad of the three-upsetting die and extends into the main mold cavity. A first die sleeve is arranged outside the upper die punch of the three-upsetting die. The upper die punch of the three-upsetting die passes through the first die sleeve and extends into the main mold cavity of the three-upsetting die to deepen the inner hole at the upper end of the second blank; the main mold cavity of the four-upsetting die includes a fourth upper forming cavity for preliminarily forming an intermediate disk at the middle end of the flipped third blank, and an upper die core is provided at one end of the upper die shell of the four-upsetting die corresponding to the fourth upper forming cavity, and the upper die core includes an upper forming cavity for stretching the upper segment of the third blank, the inner diameter of the upper forming cavity is smaller than the inner diameter of the fourth upper forming cavity, and the lower end of the upper forming cavity is in the form of a trumpet with a small upper portion and a large lower portion, and the upper forming cavity plus the fourth upper forming cavity are provided with a fourth upper forming cavity. The length of the four upper forming cavities is less than the length of the main model cavity of the three-heading mold; the shape of the main model cavity of the five-heading mold is the same as that of the four-heading mold, and the lower die punch of the five-heading mold passes through the lower die pad of the five-heading mold to the upper opening of the main model cavity of the five-heading mold; the shape of the main model cavity of the through-hole mold is the same as that of the five-heading mold, and the upper die punch of the through-hole mold passes through the upper forming cavity of the through-hole mold and punches down into the main model cavity of the through-hole mold, and the diameter of the upper die punch of the through-hole mold is smaller than the diameter of the upper die punch of the five-heading mold.

[0008] By adopting the above technical scheme, compared with directly forming the disk, a great punching force is required. During processing, the material is subjected to uneven stress and is prone to cracking and deformation. The reason why the original cold heading did not have a through hole is that the through hole caused cracks in the inner hole, which is not conducive to subsequent internal thread processing; multi-step forming optimizes material flow and forming quality, helps to guide the flow of materials during the cold heading process, reduces defects and internal stress, and at the same time, multi-step forming transfers the intermediate material to the protruding part in the middle to form a full shape; gradual through holes enhance the strength and stability of the mold, reduce the risk of wear and damage to the mold, and help improve the overall rigidity and stability of the mold; the diameter of the upper die punch of the through hole mold is smaller than the diameter of the upper die punch of the five-heading mold, and a reserved step is punched out to reduce the tear zone, increase the inner hole step, and reduce the waste of material in the inner hole processing part caused by the original cold heading.

[0009] The utility model is further configured as follows: the main model cavity of the four-upsetting mold also includes a fourth lower molding cavity for molding the lower section of the third blank, a fourth middle molding cavity is arranged between the fourth upper molding cavity and the fourth lower molding cavity, the fourth middle molding cavity is arranged in a truncated cone shape with a larger upper portion and a smaller lower portion, and a trumpet-shaped transition cavity with a larger upper portion and a smaller lower portion is also arranged between the fourth middle molding cavity and the fourth upper molding cavity, and the top angle of the transition cavity is greater than the top angle of the fourth middle molding cavity.

[0010] By adopting the above technical solution, it is helpful to guide the flow of materials during the cold heading process, so that the material can fill the mold cavity more evenly, reducing defects and internal stress. At the same time, the existence of the fourth forming cavity and the transition cavity can also play a certain guiding and restraining role on the material, which helps to improve the forming accuracy and surface quality of the bolt sleeve.

[0011] The utility model is further configured as follows: the chamfer of the first lower molding cavity is a1, 70°≤a1≤90°; the top angle of the second middle molding cavity is a2, 20°≤a2≤30°; the chamfer of the transition cavity is a3, 80°≤a3≤100°, the top angle of the fourth middle molding cavity is a4, 25°≤a4≤35°, a4>a2, and the top angle of the upper molding cavity is a5, 25°≤a5≤35°, a5=a4.

[0012] By adopting the above technical solution, the angle design helps to increase the stability of the forming of the lower end of the bolt sleeve, and can more effectively disperse the stress at the connection to avoid damage caused by stress concentration.

[0013] The embodiments describe the specific implementation of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the stepwise cold upsetting of a blank according to an embodiment of the utility model;

[0015] Figure 2 It is a cross-sectional view of a cold heading device according to an embodiment of the utility model;

[0016] Figure 3 It is a partial structural schematic diagram of an upsetting die according to an embodiment of the utility model;

[0017] Figure 4 It is a partial structural schematic diagram of the second upsetting die of the embodiment of the utility model;

[0018] Figure 5 It is a partial structural schematic diagram of a three-heading die according to an embodiment of the utility model;

[0019] Figure 6 It is a partial structural schematic diagram of a four-heading die according to an embodiment of the utility model;

[0020] Figure 7 It is a partial structural schematic diagram of a five-upsetting die according to an embodiment of the utility model;

[0021] Figure 8 It is a schematic diagram of the partial structure of the through-hole mold according to an embodiment of the utility model.

[0022] Figure numerals: 1. a forging die, 11. a lower die of a forging die, 111. a lower die shell of a forging die, 112. a main mold cavity of a forging die, 1121. a first lower molding cavity, 113. a lower die pad of a forging die, 114. a lower die punch of a forging die, 1141. a second convex portion, 115. a lower mold cavity of a forging die, 12. an upper die of a forging die, 121. an upper die shell of a forging die, 122. an upper die pad of a forging die, 123. an upper die punch of a forging die, 1231. a first convex portion; 2. a second forging die, 21. a lower die of a second forging die, 211. a lower die shell of a second forging die, 212. a main mold cavity of a second forging die, 2 121. The second upper forming cavity, 2122. The second middle forming cavity, 2123. The second lower forming cavity, 213. The lower die pad of the second upsetting die, 214. The lower die punch of the second upsetting die, 215. The lower mold cavity of the second upsetting die, 22. The upper die of the second upsetting die, 221. The upper mold shell of the second upsetting die, 222. The upper die pad of the second upsetting die, 223. The upper mold punch of the second upsetting die; 3. The third upsetting die, 31. The lower die of the third upsetting die, 311. The lower mold shell of the third upsetting die, 312. The main mold cavity of the third upsetting die, 313. The lower die pad of the third upsetting die, 314. The lower die punch of the third upsetting die, 315. The lower mold cavity of the third upsetting die, 32. The third upsetting die , 321. upper die shell of three-heading die, 322. upper die pad of three-heading die, 323. upper die punch of three-heading die; 324. first punch sleeve, 4. four-heading die, 41. lower die of four-heading die, 411. lower die shell of four-heading die, 412. main mold cavity of four-heading die, 4121. fourth upper forming cavity, 4122. transition cavity, 4123. fourth middle forming cavity, 4124. fourth lower forming cavity, 413. lower die pad of four-heading die, 414. lower die punch of four-heading die, 415. lower mold cavity of four-heading die, 42. upper die of four-heading die, 421. upper die shell of four-heading die, 4211. upper section forming cavity, 422. The upper die pad of the four-heading die, 423. The upper die punch of the four-heading die; 5. The five-heading die, 51. The lower die of the five-heading die, 511. The lower die shell of the five-heading die, 512. The main mold cavity of the five-heading die, 513. The lower die pad of the five-heading die, 514. The lower die punch of the five-heading die, 515. The lower mold cavity of the five-heading die, 52. The upper die of the five-heading die, 521. The upper die shell of the five-heading die, 5211. The second molding cavity, 522. The upper die pad of the five-heading die, 523. The upper die punch of the five-heading die; 6. The through-hole die, 61. The lower die of the through-hole die, 611. The lower die shell of the through-hole die, 612. The main mold cavity of the through-hole die, 613. The lower die pad of the through hole mold, 614. The lower die punch of the through hole mold, 615. The lower mold cavity of the through hole mold, 62. The upper die of the through hole mold, 621. The upper mold shell of the through hole mold, 6211. The final molding cavity, 622. The upper die pad of the through hole mold, 623. The upper die punch of the through hole mold. DETAILED DESCRIPTION

[0023] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

[0024] See attached Figure 1-8 The present embodiment discloses a cold forging device for a bolt sleeve of an automobile subframe, comprising a cutting mechanism, an ejection mechanism, a conveying mechanism and six dies, wherein the cutting mechanism cuts off a blank, and the ejection mechanism lifts up the blank; the conveying mechanism moves and feeds between the ejection mechanism and the six dies; the six dies comprise: a first forging die 1 for punching out recesses at both ends of an initial blank and chamfering the lower end, a second forging die 2 for extruding and stretching the lower end of a first blank and deepening the inner hole at the lower end, a third forging die 3 for stretching and forming the upper end of a second blank and deepening the inner hole at the upper end, and a third forging die 4 for forming a middle disk portion of a flipped third blank and chamfering the holes at both ends. A four-upsetting die 4 with a shortened portion, a five-upsetting die 5 for deepening the inner hole at the lower end of the fourth blank, and a through-hole die 6 for connecting the inner hole at the upper end of the fifth blank with the inner hole at the lower end to form a through hole; the six dies all include a lower die and an upper die, the lower die includes a lower die shell, a lower die core, a lower die punch, a lower die locking nut and a lower die pad, the lower die core is arranged in the lower die shell, a lower mold cavity is arranged in the lower die core, the lower die pad is arranged below the lower die core, and the lower die locking nut fixes the lower die pad and the lower die core by connecting with the lower die shell; the upper die includes an upper die shell, an upper die pad and an upper die punch, and the upper die pad is arranged in the upper die shell.

[0025] The present embodiment is further configured as follows: the main mold cavity 112 of the first upsetting mold 1 includes a first lower molding cavity 1121 for molding the chamfer of the lower end of the initial blank, the upper die punch 123 of the first upsetting mold 1 includes a first convex portion 1231 for punching the upper end of the initial blank out of a cavity, and the lower die punch 114 of the first upsetting mold 1 includes a second convex portion 1141 for punching the lower end of the initial blank out of a cavity; the main mold cavity 212 of the second upsetting mold 2 includes a second upper molding cavity 2121 for molding an upper cylinder, a second lower molding cavity 2123 for molding a lower cylinder, and a second middle molding cavity 2122 connecting the second upper molding cavity and the second lower molding cavity, and the second middle molding cavity 2122 is inverted with a larger upper portion and a smaller lower portion. The second upsetting die 2121 is arranged in a truncated cone shape, and the inner diameter of the second upper forming cavity 2121 is larger than the inner diameter of the second lower forming cavity 2123. The lower die punch 214 of the second upsetting die 2 passes through the lower die pad 213 of the second upsetting die 2 and extends into the second middle forming cavity 2122 to deepen the inner hole at the lower end of the first blank. The main model cavity 312 of the third upsetting die 3 has the same shape as the main model cavity 212 of the second upsetting die 2. The main model cavity 312 of the third upsetting die 3 is longer than the main model cavity 212 of the second upsetting die 2. The lower die punch 314 of the third upsetting die 3 passes through the lower die pad 313 of the third upsetting die 3 and extends into the main model cavity 312. The upper die punch 323 of the third upsetting die 3 is provided with a first die sleeve 324. The upper die punch 323 of the mold 3 passes through the first die sleeve 324 and extends into the main model cavity 312 of the three-upsetting mold 3 to deepen the inner hole at the upper end of the second blank; the main model cavity 412 of the four-upsetting mold 4 includes a fourth upper forming cavity 4121 that makes the middle end of the flipped third blank initially form an intermediate disk, and the upper mold shell 421 of the four-upsetting mold 4 is provided with an upper die core at one end corresponding to the fourth upper forming cavity 4121, and the upper die core includes an upper section forming cavity 4211 for stretching the upper section of the third blank, the inner diameter of the upper section forming cavity 4211 is smaller than the inner diameter of the fourth upper forming cavity 4121, and the lower end of the upper section forming cavity 4211 is in the form of a trumpet with a small upper part and a large lower part, and the upper section forming cavity 4211 plus the fourth upper forming cavity The length of cavity 4121 is less than the length of the main model cavity 312 of the three-heading die 3; the shape of the main model cavity 512 of the five-heading die 5 is the same as the main model cavity 412 of the four-heading die 4, and the lower die punch 514 of the five-heading die 5 passes through the lower die pad 513 of the five-heading die 5 and is pushed up to the upper opening of the main model cavity 512 of the five-heading die 5; the shape of the main model cavity 612 of the through-hole die 6 is the same as the main model cavity 512 of the five-heading die 5, and the upper die punch 623 of the through-hole die 6 passes through the upper forming cavity of the through-hole die 6 and punches down into the main model cavity 612 of the through-hole die 6, and the diameter of the upper die punch 623 of the through-hole die 6 is smaller than the diameter of the upper die punch 523 of the five-heading die 5.

[0026] The present embodiment is further configured as follows: the main model cavity 412 of the four-upsetting mold 4 also includes a fourth lower molding cavity 4124 for molding the lower section of the third blank; a fourth middle molding cavity 4123 is arranged between the fourth upper molding cavity 4121 and the fourth lower molding cavity 4124; the fourth middle molding cavity 4123 is arranged in a truncated cone shape that is larger at the top and smaller at the bottom; a trumpet-shaped transition cavity 4122 that is larger at the top and smaller at the bottom is also arranged between the fourth middle molding cavity 4123 and the fourth upper molding cavity 4121; the apex angle of the transition cavity 4122 is greater than the apex angle of the fourth middle molding cavity 4123.

[0027] This embodiment is further configured as follows: the chamfer of the first lower molding cavity 1121 is a1, 70°≤a1≤90°; the top angle of the second middle molding cavity 2122 is a2, 20°≤a2≤30°; the chamfer of the transition cavity 4122 is a3, 80°≤a3≤100°, the top angle of the fourth middle molding cavity 4123 is a4, 25°≤a4≤35°, a4>a2, and the top angle of the upper molding cavity 4211 is a5, 25°≤a5≤35°, a5=a4.

[0028] This embodiment further sets: a1 = 90°, a2 = 28°, a3 = 90°, a5 = a4 = 30°.

[0029] The above-mentioned "between" does not only refer to directions and positions, but also includes the interaction between different parts. The above-mentioned "upper", "middle" and "lower" are only relative positions for the convenience of explanation, and does not exclude the possibility of using other terms.

[0030] These terms are used only to more conveniently describe and explain the essence of the present invention; any additional limitations interpreted as these terms are contrary to the spirit of the present invention.

Claims

1. A cold heading device for a bolt sleeve of an automobile subframe, characterized in that: The invention comprises a cutting mechanism, an ejection mechanism, a conveying mechanism and six dies, wherein the cutting mechanism cuts the blank, and the ejection mechanism lifts the blank; the conveying mechanism moves and feeds between the ejection mechanism and the six dies; the six dies comprise: a first upsetting die for punching out recesses at both ends of the initial blank and chamfering the lower end, a second upsetting die for extruding and stretching the lower end of the first blank and deepening the inner hole at the lower end, a third upsetting die for stretching and forming the upper end of the second blank and deepening the inner hole at the upper end, a fourth upsetting die for forming a middle disk portion of the turned third blank and shortening the holes at both ends, and a fourth upsetting die for A five-upsetting die for deepening the inner hole at the lower end of the fourth blank and a through-hole die for connecting the inner hole at the upper end of the fifth blank with the inner hole at the lower end to form a through hole; the six dies each include a lower die and an upper die, the lower die includes a lower die shell, a lower die core, a lower die punch, a lower die locking nut and a lower die pad, the lower die core is arranged in the lower die shell, a lower model cavity is arranged in the lower die core, the lower die pad is arranged below the lower die core, and the lower die locking nut fixes the lower die pad and the lower die core by connecting with the lower die shell; the upper die includes an upper die shell, an upper die pad and an upper die punch, and the upper die pad is arranged in the upper die shell.

2. The cold heading device for a bolt sleeve of an automobile subframe according to claim 1, characterized in that: The main mold cavity of the first upsetting mold includes a first lower molding cavity for forming the chamfer of the lower end of the initial blank, the upper die punch of the first upsetting mold includes a first convex portion for punching the upper end of the initial blank out of the concave cavity, and the lower die punch of the first upsetting mold includes a second convex portion for punching the lower end of the initial blank out of the concave cavity; the main mold cavity of the second upsetting mold includes a second upper molding cavity for forming an upper cylinder, a second lower molding cavity for forming a lower cylinder, and a second middle molding cavity connecting the second upper molding cavity and the second lower molding cavity, and the second middle molding cavity is a rounded table with a larger upper portion and a smaller lower portion. The inner diameter of the second upper forming cavity is larger than the inner diameter of the second lower forming cavity, the lower die punch of the second upsetting die passes through the lower die pad of the second upsetting die and extends into the second middle forming cavity to deepen the inner hole at the lower end of the first blank; the main mold cavity of the three-upsetting die has the same shape as the main mold cavity of the two-upsetting die, the main mold cavity of the three-upsetting die is longer than the main mold cavity of the two-upsetting die, the lower die punch of the three-upsetting die passes through the lower die pad of the three-upsetting die and extends into the main mold cavity, the upper die punch of the three-upsetting die is provided with a first die sleeve, and the upper die of the three-upsetting die is provided with a first die sleeve. The punch rod passes through the first punch sleeve and extends into the main mold cavity of the three-upsetting mold to deepen the inner hole at the upper end of the second blank; the main mold cavity of the four-upsetting mold includes a fourth upper forming cavity for initially forming an intermediate disk at the middle end of the flipped third blank, and an upper mold shell of the four-upsetting mold is provided with an upper mold core at one end corresponding to the fourth upper forming cavity, and the upper mold core includes an upper forming cavity for stretching the upper segment of the third blank, the inner diameter of the upper forming cavity is smaller than the inner diameter of the fourth upper forming cavity, and the lower end of the upper forming cavity is in the form of a trumpet with a small upper portion and a large lower portion, and the upper forming cavity plus the fourth upper forming cavity are The length of the cavity is less than the length of the main model cavity of the three-heading mold; the shape of the main model cavity of the five-heading mold is the same as the main model cavity of the four-heading mold, and the lower die punch of the five-heading mold passes through the lower die pad of the five-heading mold and is pushed to the upper opening of the main model cavity of the five-heading mold; the shape of the main model cavity of the through-hole mold is the same as the main model cavity of the five-heading mold, and the upper die punch of the through-hole mold passes through the upper forming cavity of the through-hole mold and punches down into the main model cavity of the through-hole mold, and the diameter of the upper die punch of the through-hole mold is smaller than the diameter of the upper die punch of the five-heading mold.

3. The cold heading device for a bolt sleeve of an automobile subframe according to claim 2, characterized in that: The main model cavity of the four-upsetting mold also includes a fourth lower molding cavity for molding the lower section of the third blank, a fourth middle molding cavity is arranged between the fourth upper molding cavity and the fourth lower molding cavity, the fourth middle molding cavity is arranged in a truncated cone shape with a larger upper portion and a smaller lower portion, and a trumpet-shaped transition cavity with a larger upper portion and a smaller lower portion is also arranged between the fourth middle molding cavity and the fourth upper molding cavity, and the top angle of the transition cavity is greater than the top angle of the fourth middle molding cavity.

4. The cold heading device for a bolt sleeve of an automobile subframe according to claim 3, characterized in that: The chamfer of the first lower molding cavity is a1, 70°≤a1≤90°; the top angle of the second middle molding cavity is a2, 20°≤a2≤30°; the chamfer of the transition cavity is a3, 80°≤a3≤100°, the top angle of the fourth middle molding cavity is a4, 25°≤a4≤35°, a4>a2, and the top angle of the upper molding cavity is a5, 25°≤a5≤35°, a5=a4.

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