A rivet nut processing device and processing method

Abstract

This invention discloses a rivet nut processing device and method, relating to the field of metal assembly processing. The processing method includes the following steps: S1, pre-treating aluminum alloy wire with warm upsetting; S2, processing the wire sequentially through four stations to obtain a semi-finished rivet nut; S3, stress-relieving annealing the semi-finished rivet nut and furnace cooling; S4, tapping the inner hole of the annealed semi-finished rivet nut using a tap; S5, performing solution treatment and aging treatment on the tapped semi-finished rivet nut to obtain the rivet nut. By employing a three-stage stepped necking structure with specific tapers, the deformation rate and shear stress peak in local areas are effectively reduced, preventing internal tearing or surface cracks caused by severe material flow obstruction in the necking area of ​​the rod, thereby improving the stability of the necking dimensional accuracy, significantly reducing the scrap rate, and achieving crack-free forming of the rivet nut.

Description

Technical Field

[0001] This invention relates to the field of metal assembly processing technology, and more particularly to rivet nut processing, specifically a rivet nut processing device and processing method. Background Technology

[0002] Rivet nuts, as a high-efficiency fastener, are widely used in high-end manufacturing fields such as aerospace, rail transportation, and new energy vehicles. They achieve integrated forming of metal materials through plastic forming processes such as cold heading and extrusion, offering advantages such as high connection strength, fast assembly efficiency, lightweight design, and good adaptability. With the increasing demands for lightweight and reliable structures in modern industry, high-strength aluminum alloys (such as 7075-T6) are becoming increasingly popular due to their low density (2.8 g / cm³). 3 With its high specific strength (tensile strength ≥ 560 MPa), it has gradually replaced traditional steel materials as the mainstream base material for rivets and nuts.

[0003] However, 7075-T6 aluminum alloy has poor plasticity at room temperature, with an elongation of only 10%~12%, and is highly sensitive to work hardening. In the traditional cold heading process, especially for complex shapes such as hexagonal or dodecagonal heads and necking of rods, the stress concentration coefficients at the corners can be as high as 3.2 and 2.5, respectively, due to the dodecagonal head containing 12 30° acute angles and the hexagonal head containing 6 60° angles. When the material undergoes severe plastic deformation, the excessive radial flow resistance at the corners easily leads to stress concentration and shear microcracks, resulting in a high scrap rate and severely restricting its large-scale application in the field of high-end equipment.

[0004] Therefore, it is necessary to improve upon the shortcomings of existing technologies in order to solve the above problems. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a rivet nut processing device and processing method. By precisely controlling the plasticity of the material, optimizing the stress distribution of the mold, and releasing the forming load in stages, it achieves crack-free forming of 7075 aluminum alloy rivet nuts, while ensuring that the mechanical properties of the product are comparable to those of the raw material. This provides a new technical path for the efficient manufacturing of high-strength aluminum alloy fasteners.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Firstly, the present invention provides a method for processing rivet nuts, the method being applicable to hexagonal or dodecagonal rivet nuts made of 7075-T6 aluminum alloy, comprising the following steps:

[0007] S1. The aluminum alloy wire is subjected to warm forging pretreatment to obtain pretreated wire;

[0008] S2. The wire is cut to a fixed length, pre-upset, stepped necking, and head and inner hole forming are carried out in sequence through four stations to obtain semi-finished rivet nuts.

[0009] a. The first station uses a V-shaped anvil to apply back pressure and cut the wire to a fixed length;

[0010] b. The second station uses a flat punch with an end face radius of R0.2~0.5 mm and a three-lobed combined die to pre-upset the cut wire at a compression ratio of 20~25%.

[0011] c. The third station uses a three-stage tapered die to perform stepped necking with a diameter reduction of 12-16%.

[0012] d. The fourth station presses out a shallow hexagonal profile with a 60° transition angle, then finely presses it into a dodecagonal shape, while simultaneously performing inner hole pre-punching and flange forming, and head forming;

[0013] S3. Stress-relief annealing of the semi-finished rivet nuts, followed by furnace cooling;

[0014] S4. Use a tap to tap the inner hole of the annealed semi-finished rivet nut.

[0015] S5. The tapped semi-finished rivet nuts are subjected to solution treatment and aging treatment respectively to obtain rivet nuts.

[0016] In a preferred embodiment of the present invention, in step S1, the warm upsetting pretreatment specifically involves holding the temperature at 220~240 ℃ for 100~140 s.

[0017] In a preferred embodiment of the present invention, in step S2, the included angle of the V-shaped anvil is 55°~65°, and the back pressure is 0.4~0.6 MPa.

[0018] In a preferred embodiment of the present invention, in step S2, the inlet cone angle of the die is 10°~14°, the transition cone angle is 18°~22°, and the sizing cone angle is 6°~10°.

[0019] In a preferred embodiment of the present invention, in step S3, the annealing temperature is 230~270 ℃ and the holding time is 1.5~2.5 h.

[0020] In a preferred embodiment of the present invention, in step S5, the solution treatment temperature is 470~490℃ and the water quenching time is 0.5-1.5 h; the aging treatment temperature is 110~130℃ and the treatment time is 20~28 h.

[0021] In another aspect, the present invention provides a processing apparatus for a rivet nut processing method, comprising: a cold heading machine, and a mold mechanism mounted on the cold heading machine;

[0022] The mold mechanism includes: a first mold for step necking of the pre-upset wire, a second mold for pre-forming the hexagonal profile of the head, a third mold for forming the dodecagonal profile of the head, a fourth mold for forming the upper inner hole, a fifth mold for forming the lower inner hole, and a sixth mold for forming the head flange.

[0023] The diameter of the upper inner hole is larger than the diameter of the lower inner hole.

[0024] In a preferred embodiment of the present invention, the first mold, the second mold, the third mold, the fourth mold, the fifth mold, and the sixth mold each include a corresponding main mold and a die punch.

[0025] The main mold includes: a main mold shell, a main mold pad, a main mold ejector pin, a main mold core, and a main mold spring disposed inside the main mold shell, and a main mold cavity formed inside the main mold core; the main mold pad is installed at the bottom of the main mold shell, the main mold core is installed at the top of the main mold shell, one end of the main mold ejector pin is fixed on the main mold pad, and the other end passes through the bottom of the main mold core into the interior of the main mold cavity;

[0026] The mold includes: a mold shell, and a mold pad, a mold ejector pin, and a mold chuck disposed inside the mold shell; the mold pad is installed on the top of the mold shell, the mold chuck is installed on the bottom of the mold shell, one end of the mold ejector pin is fixed on the mold pad, and the other end passes through the mold chuck and corresponds to the main mold cavity.

[0027] In a preferred embodiment of the present invention, the main cavity cross-section of the first mold is a stepped necking structure, which includes, from top to bottom, an inlet, a transition, and a sizing section; the necking cone angle of the inlet is 10°~14°, the necking cone angle of the transition is 18°~22°, and the necking cone angle of the sizing section is 6°~10°.

[0028] In a preferred embodiment of the present invention, the die of the fourth mold and the fifth mold further includes: a die top block, a die ejector rod, and a die sleeve; the die top block is installed inside the die shell located on top of the die pad block, one end of the die ejector rod is fixed to the bottom of the die top block, and the other end is fixed to the top of the die sleeve, and the inner side of the die sleeve is sleeved on the side of the die ejector pin.

[0029] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0030] (1) The present invention provides a rivet nut processing device and processing method. By adopting a three-stage specific taper stepped necking structure, the stepped transition allows the atoms inside the material to migrate along the tapered surface gradient during deformation, and the dislocation movement path is dispersed. This avoids the accumulation and blockage of atoms at the abrupt interface in traditional single-stage necking, effectively reducing the deformation rate and shear stress peak in the local area, preventing internal tearing or surface cracks caused by severe obstruction of material flow in the necking area of ​​the rod, thereby improving the stability of the necking dimension accuracy, significantly reducing the scrap rate, and realizing crack-free forming of rivet nuts.

[0031] (2) In this invention, the aluminum alloy wire is preheated to a specific sub-recrystallization temperature range and kept at that temperature before forming. This preheating process keeps the aluminum alloy wire below the recrystallization temperature, thus preventing grain growth and preserving the cold work hardening effect and fine grain structure. The subsequent solution treatment causes the strengthening phase to redissolve and form a supersaturated solid solution. The aging treatment promotes the uniform precipitation of fine and dispersed strengthening phases (such as GP zone and η' phase), thereby enabling the tensile strength and yield strength of the material to be restored to the level of the raw material. Compared with the traditional processing method that relies solely on cold work hardening, this method can further ensure that the product maintains high strength performance while eliminating forming cracks, thereby meeting the structural load-bearing capacity and reliability requirements of rivet nuts in high-end equipment.

[0032] (3) In this invention, a step-by-step forming process is adopted for the twelve-cornered head. First, a shallow hexagonal outline is pressed out to distribute the basic stress. Then, the twelve-cornered structure is precision pressed. This allows the material to undergo step-by-step loading during the complex shape forming process, avoiding stress superposition caused by one-time severe deformation. This reduces the stress concentration coefficient at the head corners. Compared with the high stress concentration problem caused by the traditional direct forming of twelve corners, this significantly reduces shear cracks in the acute angle area, thereby further improving the forming quality of the complex head structure. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the twelve-cornered rivet nut structure of a preferred embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the mold mechanism structure of the rivet nut processing device according to a preferred embodiment of the present invention;

[0036] Figure 3This is a schematic diagram of the first mold structure according to a preferred embodiment of the present invention;

[0037] Figure 4 This is a schematic diagram of the fourth mold structure according to a preferred embodiment of the present invention;

[0038] Figure 5 This is a schematic diagram of the half-section structure of the main mold core in the first mold of a preferred embodiment of the present invention;

[0039] In the diagram: 1. First mold; 2. Second mold; 3. Third mold; 4. Fourth mold; 5. Fifth mold; 6. Sixth mold; 11. Main mold; 111. Main mold shell; 112. Main mold pad; 113. Main mold ejector pin; 114. Main mold core; 115. Main mold spring; 116. Main mold cavity; 1161. Entrance section; 1162. Transition section; 1163. Sizing section; 12. Mold punch; 121. Punch shell; 122. Punch pad; 123. Punch ejector pin; 124. Punch chuck; 125. Punch ejector block; 126. Punch ejector rod; 127. Punch sleeve; 7. Dodecagonal rivet nut; 71. Rod body; 72. Upper inner hole; 73. Lower inner hole; 74. Inner hole thread; 75. Flange. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0042] In the description of this application, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0043] In the description of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "setup," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0044] It should be noted that the rivet nut processing method of the present invention is preferably applicable to hexagonal or dodecagonal rivet nuts made of 7075-T6 aluminum alloy.

[0045] A method for machining rivet nuts includes the following steps:

[0046] S1. The aluminum alloy wire is subjected to warm forging pretreatment to obtain pretreated wire;

[0047] It should be noted that the pre-treatment of warm upsetting is specifically: holding at 220~240 ℃ for 100~140 s.

[0048] Specifically, by pre-treating 7075 aluminum alloy wire by heating it to 220~240 ℃ and holding it at that temperature for 100~140 s, the room temperature plastic deformation capacity of the material is significantly improved. The thermal activation effect at this temperature enhances atomic diffusion capacity and reduces grain boundary slip resistance. Dislocation density can be partially eliminated through dynamic recovery during deformation, effectively reducing the deformation resistance of the material and delaying the work hardening process. This allows the material to withstand more drastic shape changes without brittle cracking during subsequent extrusion molding, thus overcoming the inherent defects of 7075 aluminum alloy, such as poor room temperature plasticity and sensitivity to work hardening, further reducing the risk of cracking during molding, and avoiding grain coarsening caused by high temperature.

[0049] S2. The wire is cut to a fixed length, pre-upset, stepped necking, and head and inner hole forming are carried out in sequence through four stations to obtain semi-finished rivet nuts.

[0050] a. The first station uses a V-shaped anvil to apply back pressure and cut the wire to a fixed length;

[0051] It should be noted that the included angle of the V-shaped anvil is 55°~65°, and the back pressure is 0.4~0.6 MPa.

[0052] b. The second station uses a flat punch with an end face radius of R0.2~0.5 mm and a three-lobed combined die to pre-upset the cut wire at a compression ratio of 20~25%.

[0053] c. The third station uses a three-stage tapered die to perform stepped necking with a diameter reduction of 12-16%.

[0054] It should be noted that the entrance cone angle of the die is 10°~14°, the transition cone angle is 18°~22°, and the sizing cone angle is 6°~10°.

[0055] Specifically, by adopting a three-stage stepped necking structure with specific tapers, the stepped transition allows the atoms inside the material to migrate along the gradient of the cone surface during deformation, and the dislocation movement path is dispersed. This avoids the accumulation and blockage of atoms at the abrupt interface in traditional single-stage necking, effectively reducing the deformation rate and peak shear stress in the local area. It also prevents internal tearing or surface cracks caused by severe obstruction of material flow in the necking area of ​​the rod, thereby improving the stability of the necking dimensional accuracy, significantly reducing the scrap rate, and achieving crack-free forming of rivet nuts.

[0056] d. The fourth station presses out a shallow hexagonal profile with a 60° transition angle, then finely presses it into a dodecagonal shape, while simultaneously performing inner hole pre-punching and flange forming, and head forming;

[0057] S3. Stress-relief annealing of the semi-finished rivet nuts, followed by furnace cooling;

[0058] It should be noted that the annealing temperature is 230~270 ℃ and the holding time is 1.5~2.5 h.

[0059] S4. Use a tap to tap the inner hole of the annealed semi-finished rivet nut.

[0060] Specifically, by feeding the annealed semi-finished rivet nut into a tapping machine, a tapping tap is used to tap it to form threads on the inner hole wall, thus forming a functional part on the hole wall that can be fastened to the bolt according to the specifications. At the same time, because the stress-relief annealing treatment before tapping reduces the hardness of the semi-finished product, the threads are easier to form during the inner hole tapping process, while reducing the wear of the tapping tap and improving the processing efficiency of the tapping process.

[0061] S5. The tapped semi-finished rivet nuts are subjected to solution treatment and aging treatment respectively to obtain rivet nuts.

[0062] It should be noted that the solution treatment temperature is 470~490 ℃ and the water quenching time is 0.5~1.5 h; the aging treatment temperature is 110~130 ℃ and the treatment time is 20~28 h.

[0063] Specifically, by employing solution treatment and aging treatment after forming and tapping, the solution treatment fully dissolves the reinforcing phase to form a supersaturated solid solution, while the subsequent artificial aging promotes the uniform precipitation of fine, dispersed, and reinforced precipitates, effectively hindering dislocation movement and thus endowing the material with excellent mechanical strength. Compared with the traditional processing method that relies solely on cold work hardening, this not only eliminates the softening effect that may be caused by warm upsetting, but also restores the tensile strength and yield strength of the material to a level comparable to that of the raw material. This further ensures that the product maintains high strength performance while eliminating forming cracks, thereby meeting the structural load-bearing capacity and reliability requirements of rivets and nuts in high-end equipment.

[0064] To further simplify and make the present invention achieve its objectives and effects, the present invention will be further illustrated in conjunction with the following specific embodiments and comparative examples, but the present invention is not limited to the scope of the embodiments described herein.

[0065] It should be noted that the 7075-T6 aluminum alloy wire was purchased from Jiangsu Giraffe Aluminum Industry.

[0066] Example 1:

[0067] A method for machining rivet nuts includes the following steps:

[0068] S1. A Ø8 mm 7075 aluminum alloy wire is subjected to warm upsetting pretreatment at 230 ℃ for 120 s to obtain pretreated wire.

[0069] S2. The wire is cut to a fixed length, pre-upset, stepped necking, and head and inner hole forming are carried out in sequence through four stations to obtain semi-finished rivet nuts.

[0070] a. The first station uses a V-shaped anvil with an included angle of 60°, applies a back pressure of 0.5 MPa, and cuts 25 mm wire at a fixed length;

[0071] b. The second station uses a flat punch with a diameter of Ø7.0 mm and an end face radius of R0.3 mm, with a three-lobed combined die with an inner diameter of Ø7.2 mm, to pre-upset the cut wire at a compression ratio of 22%.

[0072] c. The third station uses a three-stage tapered die with an entrance cone angle of 12°, a transition cone angle of 20°, and a sizing cone angle of 8°, to perform stepped necking with a 14% reduction in diameter (Ø8-Ø6.9 mm);

[0073] d. At the fourth station, a shallow hexagonal profile is pressed out with a 60° transition angle, and then finely pressed into a twelve-sided shape. Simultaneously, an inner hole pre-punch and flange forming are performed using a Ø5.95 mm punch, and the head is formed.

[0074] S3. Anneal the semi-finished rivet nuts at 250 ℃ for 2 h, and then cool them in the furnace.

[0075] S4. Use a tap to tap the inner hole of the annealed semi-finished rivet nut, forming an M6×1.0 thread on the inner hole wall.

[0076] S5. For the semi-finished rivet nut after tapping, first perform solution treatment by water quenching at 480 ℃ for 1 h, and then place it at 120 ℃ for aging treatment for 24 h to obtain a twelve-cornered rivet nut.

[0077] Example 2:

[0078] This embodiment is basically the same as embodiment 1, except that the temperature of the warm upsetting pretreatment is different; the specific steps of S1 are as follows: the Ø8 mm 7075 aluminum alloy wire is subjected to warm upsetting pretreatment at 240 ℃ for 120 s to obtain the pretreated wire.

[0079] Example 3:

[0080] This embodiment is basically the same as embodiment 1, except that the temperature of the warm upsetting pretreatment is different; the specific steps of S1 are as follows: the Ø8 mm 7075 aluminum alloy wire is subjected to warm upsetting pretreatment at 220 ℃ for 120 s to obtain the pretreated wire.

[0081] Example 4:

[0082] This embodiment is basically the same as embodiment 1, except that the solution treatment temperature is different; step S5 is as follows: the semi-finished rivet nut after tapping is first water-quenched at 490 ℃ for 1 h for solution treatment, and then placed at 120 ℃ for aging treatment for 24 h to obtain a twelve-cornered rivet nut.

[0083] Example 5:

[0084] This embodiment is basically the same as embodiment 1, except that the solution treatment temperature is different; step S5 is as follows: the semi-finished rivet nut after tapping is first water-quenched at 470 ℃ for 1 h for solution treatment, and then placed at 120 ℃ for aging treatment for 24 h to obtain a twelve-cornered rivet nut.

[0085] Example 6:

[0086] This embodiment is basically the same as embodiment 1, except that the aging treatment temperature is different; the specific steps of S5 are as follows: the semi-finished rivet nut after tapping is first quenched in water at 480 ℃ for 1 h for solution treatment, and then placed at 130 ℃ for aging treatment for 24 h to obtain a twelve-cornered rivet nut.

[0087] Example 7:

[0088] This embodiment is basically the same as embodiment 1, except that the aging treatment temperature is different; the specific steps of S5 are as follows: the semi-finished rivet nut after tapping is first quenched in water at 480 ℃ for 1 h for solution treatment, and then placed at 110 ℃ for aging treatment for 24 h to obtain a twelve-cornered rivet nut.

[0089] Comparative Example 1:

[0090] This comparative example is basically the same as Example 1, except that: no stepped necking is performed; step b in step S2 is specifically: the third station uses a single-stage tapered die with a taper angle of 8° to perform necking with a 14% reduction in diameter (Ø8-Ø6.9 mm).

[0091] Comparative Example 2:

[0092] This comparative example is basically the same as Example 1, except that: no warm upsetting pretreatment was performed; specifically, step S1 was omitted.

[0093] Comparative Example 3:

[0094] This comparative example is basically the same as Example 1, except that the temperature of the warm upsetting pretreatment is different; the specific steps of S1 are as follows: the Ø8 mm 7075 aluminum alloy wire is subjected to warm upsetting pretreatment at 250 ℃ for 120 s to obtain the pretreated wire.

[0095] Comparative Example 4:

[0096] This comparative example is basically the same as Example 1, except that the temperature of the warm upsetting pretreatment is different; the specific steps of S1 are as follows: the Ø8 mm 7075 aluminum alloy wire is subjected to warm upsetting pretreatment at 230 ℃ for 120 s to obtain the pretreated wire.

[0097] Comparative Example 5:

[0098] This comparative example is basically the same as Example 1, except that: the head forming does not have a hexagonal transition; step d in step S2 is: the fourth station directly presses out the twelve-corner profile with a 30° transition angle, and simultaneously uses a Ø5.95 mm punch to pre-punch the inner hole and form the flange to form the head.

[0099] Comparative Example 6:

[0100] This comparative example is basically the same as Example 1, except that: no post-tapping treatment was performed; specifically, step S5 is omitted.

[0101] Comparative Example 7:

[0102] This comparative example is basically the same as Example 1, except that: no solution treatment was performed; step S5 is as follows: the semi-finished rivet nut after tapping is placed at a temperature of 120 ℃ and aged for 24 h to obtain a twelve-cornered rivet nut.

[0103] Comparative Example 8:

[0104] This comparative example is basically the same as Example 1, except that the solution treatment and aging treatment process steps are different; the specific steps of S3 are as follows: the semi-finished rivet nut is first water-quenched at 480 ℃ for 1 h for solution treatment, and then placed at 120 ℃ for aging treatment for 24 h to obtain the post-treated semi-finished rivet nut.

[0105] The specific steps of S4 are as follows: anneal the post-processed semi-finished rivet nuts at 250 ℃ for 2 h, and then cool them in the furnace.

[0106] The specific steps of S5 are as follows: using a tap to tap the inner hole of the annealed semi-finished rivet nut, forming an M6×1.0 thread on the inner hole wall to obtain a twelve-corner rivet nut.

[0107] Performance testing: The twelve-corner rivet nuts obtained in Examples 1-7 and Comparative Examples 1-8 were subjected to performance tests on scrap rate and mechanical property retention rate, respectively. The results are shown in Table 1.

[0108] Scrap rate: According to the processing methods of Examples 1-7 and Comparative Examples 1-8, 60 dodecagonal rivet nuts were processed respectively, and they were immersed in red penetrant for 10 min. The surface was cleaned and a developer was sprayed. The necking area of ​​the rod and the head corner were observed through an optical microscope. When the crack was ≥0.1 mm, it was judged as a scrap. Scrap rate = (number of scraps / 60) × 100%.

[0109] Mechanical property retention rate: 30 pieces were randomly selected from the processed twelve-cornered rivet nuts as the experimental group, and 7075-T6 aluminum alloy wire as the control group. The tensile strength and yield strength were tested using a universal testing machine according to GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Test at room temperature". The average mechanical properties of the experimental group and the control group were calculated respectively. Mechanical property retention rate = (average value of experimental group / average value of control group) × 100%.

[0110] Table 1: Performance test results of the twelve-cornered rivet nuts obtained in Examples 1-7 and Comparative Examples 1-8

[0111]

[0112] As shown in Table 1:

[0113] A comparison of Examples 1-7 with Comparative Example 1 reveals that: Comparative Example 1 uses a traditional single-stage tapered die for necking, which causes the material to undergo severe shear deformation at the abrupt cross-section. During the necking process, atomic migration paths are concentrated, and the deformation rate and peak shear stress are significantly increased. The necking area of ​​the rod experiences internal tearing due to excessive flow resistance, and the scrap rate increases from 1.21% in Example 1 to 15.43%. At the same time, single-stage deformation leads to uneven work hardening, and the dispersion of the strengthening phase after subsequent heat treatment is reduced, resulting in a decrease in the mechanical property retention rate to 93.57%.

[0114] A comparison of Examples 1-7 with Comparative Example 2 reveals that: without pre-treatment by warm upsetting, the stacking fault energy of 7075-T6 aluminum alloy at room temperature is low, the dislocation slip system is sensitive to work hardening, the material has high resistance to deformation and dislocations are difficult to dynamically recover, the stress concentration factor at the acute angle is high during dodecagonal forming of the head, resulting in a large number of shear cracks and a scrap rate that surges to 18.76%; in addition, room temperature forming does not enhance atomic diffusion capability through thermal activation, and the amount of strengthening phase precipitated after subsequent solution aging is reduced, resulting in a mechanical property retention rate of only 89.34%.

[0115] A comparison of Examples 1-3 and Comparative Examples 3-4 reveals that: Examples 1-3, by preheating the aluminum alloy wire to a specific sub-recrystallization temperature range before forming, can both enhance the material's plasticity through thermal activation (reducing deformation resistance) and prevent grain growth, thus preserving the foundation for precipitation strengthening in subsequent processing; Comparative Example 3, by increasing the temperature to 250 ℃, resulted in grain coarsening, increased grain boundary slip resistance, and a scrap rate of 5.62%; Comparative Example 4, by lowering the temperature to 210 ℃, suffered from insufficient atomic diffusion and inadequate dislocation dynamic recovery, leaving the material in a highly work-hardened state, with a scrap rate of 4.89%.

[0116] A comparison of Examples 1-7 with Comparative Example 5 reveals that directly pressing the dodecagonal head at a 30° transition angle, without the step-by-step molding of the shallow hexagonal contour, resulted in the acute angles being subjected to extremely high hydrostatic pressure. The intense radial flow caused shear bands to form at the grain boundaries, increasing the scrap rate from 1.21% in Example 1 to 8.37%. Although subsequent heat treatment could partially alleviate the stress, the dislocation accumulation caused by the lack of step-by-step loading could not be completely eliminated, and the mechanical property retention rate slightly decreased to 94.26%.

[0117] A comparison of Examples 1-7 with Comparative Example 6 reveals that the unaged semi-finished product retains only the warm-forged supersaturated solid solution, lacks a reinforcing phase, has low dislocation movement resistance, high elongation but insufficient load-bearing capacity, and the internal stress generated during the molding process is not released through heat treatment, resulting in a mechanical property retention rate of only 82.54%. Although the scrap rate is 1.75% due to the lack of high-temperature treatment, the strength cannot meet the requirements of high-end equipment.

[0118] A comparison of Examples 1-7 with Comparative Example 7 shows that: Comparative Example 7 only underwent aging treatment without solution treatment. The undissolved coarse reinforcing phase could not reform into a supersaturated solid solution. After aging, only a small amount of GP zone precipitated, resulting in insufficient reinforcing effect and a mechanical property retention rate of 85.42%. At the same time, the non-solid solution caused the microstructure inhomogeneity, which disrupted the internal stress distribution and slightly increased the scrap rate to 1.52%.

[0119] A comparison of Examples 1-7 with Comparative Example 8 shows that when solution treatment and aging are performed before annealing and tapping, the hardness of the heat-treated and strengthened material increases, tap wear is aggravated during tapping, and subsequent annealing treatment can easily coarsen the precipitated strengthening phase, reducing the mechanical property retention rate to 88.79%.

[0120] like Figure 1 and Figure 2 As shown, the present invention provides a processing apparatus for a rivet nut processing method, comprising: a cold heading machine, and a mold mechanism mounted on the cold heading machine; the mold mechanism comprises: a first mold 1 for step-neck forming of a rod body 71 from pre-headed wire, a second mold 2 for pre-forming a hexagonal head contour, a third mold 3 for forming a dodecagonal head contour, a fourth mold 4 for forming an upper inner hole 72, a fifth mold 5 for forming a lower inner hole 73, and a sixth mold 6 for forming a head flange 75; the diameter of the upper inner hole 72 is larger than the diameter of the lower inner hole 73.

[0121] It should be noted that the proposed processing device is specifically applicable to steps c and b in step S2 of the proposed method; the wire material is 7075-T6 aluminum alloy; the processing device also includes a material transfer mechanism, which is preferably a three-jaw pneumatic clamp driven by a servo motor, used to transfer the wire between the mold mechanisms to ensure the continuity and accuracy of the processing flow; the inner thread 74 inside the lower inner hole 73 of the dodecagonal rivet nut 7 is formed separately by a tapping machine.

[0122] Specifically, the mold mechanism of the present invention uses the first to sixth molds 6 arranged in sequence to realize the continuous processing of pre-forged wire on a cold heading machine, including stepped necking, head contour forming, inner hole processing and flange 75 forming, thereby obtaining a twelve-cornered rivet nut 7, which can significantly improve the degree of production automation and product consistency, and reduce the product scrap rate.

[0123] like Figure 3 As shown, in some specific embodiments, the first mold 1, the second mold 2, the third mold 3, the fourth mold 4, the fifth mold 5 and the sixth mold 6 each include a corresponding mold main mold 11 and a mold punch 12;

[0124] The main mold 11 includes: a main mold shell 111, a main mold pad 112, a main mold ejector pin 113, a main mold core 114 and a main mold spring 115 disposed inside the main mold shell 111, and a main mold cavity 116 formed inside the main mold core 114; the main mold pad 112 is installed at the bottom of the main mold shell 111, the main mold core 114 is installed at the top of the main mold shell 111, one end of the main mold ejector pin 113 is fixed on the main mold pad 112, and the other end of the main mold core 114 penetrates into the main mold cavity 116 from the bottom of the main mold core 114;

[0125] The die 12 includes a die shell 121, and a die pad 122, a die ejector pin 123, and a die chuck 124 disposed inside the die shell 121. The die pad 122 is installed on the top of the die shell 121, the die chuck 124 is installed on the bottom of the die shell 121, one end of the die ejector pin 123 is fixed on the die pad 122, and the other end passes through the die chuck 124 and corresponds to the main die cavity 116.

[0126] Understandably, the mold mechanism is installed and fitted on the cold heading machine. The mold punches 12 in the first mold 1, second mold 2, third mold 3, fourth mold 4, fifth mold 5 and sixth mold 6 move as a whole under the drive of the drive device. The ejector pins 123 push the wire to be processed into the main mold cavity 116, and according to the principle of material plastic deformation, it is formed into the preset shape and size in the main mold cavity 116.

[0127] Specifically, the main mold 11 and the die 12 are tightly fitted together by a mechanical structure. The main mold pad 112, main mold ejector pin 113, main mold core 114 and main mold spring 115 inside the main mold shell 111 together form a stable support structure. The main mold cavity 116 has a shape corresponding to the wire processing. The die 12 moves as a whole under the action of the driving device. The die ejector pin 123 accurately pushes the wire into the main mold cavity 116. Through the synergistic action of the die pad 122, die ejector pin 123 and die chuck 124, the accurate positioning and stable deformation of the wire in the mold are ensured. The corresponding structure of the main mold cavity 116 and the die ejector pin 123 enables the wire to accurately enter the mold and withstand the preset plastic deformation, thereby producing rivet nuts with accurate shape and stable dimensions, improving the precision and consistency of product processing.

[0128] like Figure 4 As shown, in some specific embodiments, the die 12 of the fourth die 4 and the fifth die 5 further includes: a die ejector block 125, a die ejector rod 126, and a die sleeve 127; the die ejector block 125 is installed inside the die shell 121 located on top of the die pad block 122, one end of the die ejector rod 126 is fixed to the bottom of the die ejector block 125, and the other end is fixed to the top of the die sleeve 127, and the inner side of the die sleeve 127 is sleeved on the side of the die ejector pin 123.

[0129] It should be noted that in the die punch 12 structure of the fourth die 4 and the fifth die 5, in order to solve the demolding problem after the upper inner hole 72 and the lower inner hole 73 are formed, a die punch 125, a die punch 126 and a die punch sleeve 127 structure are specially added to ensure that the product (semi-finished rivet nut) can be smoothly removed from the die punch pin 123.

[0130] Specifically, when the die completes the inner hole machining and returns, driven by the cold heading machine, the die 12 pushes the die ejector pin 123 into the main mold cavity 116. The die sleeve 127 stabilizes the path of the die ejector pin 123, and the die ejector rod 126 transmits controllable pressure through the die ejector block 125, so that the material is formed stepwise into the upper inner hole 72 or the lower inner hole 73. When the die completes the inner hole machining and returns during the drive, the die ejector block 125, the die ejector rod 126 and the die sleeve 127 reset together, and with the ejection action of the main mold ejector pin 113, the product is automatically unloaded from the die ejector pin 123, thereby avoiding manual intervention, reducing the risk of scratches on the product at sharp corners or inner hole walls, ensuring a smooth inner hole surface and improving processing efficiency.

[0131] like Figure 5 As shown, in some specific embodiments, the main cavity 116 of the first mold 1 has a stepped necking structure. The stepped necking structure includes, from top to bottom, an inlet 1161, a transition 1162, and a sizing section 1163. The necking cone angle of the inlet 1161 is 10°~14°, the necking cone angle of the transition 1162 is 18°~22°, and the necking cone angle of the sizing section 1163 is 6°~10°.

[0132] It should be noted that, based on the plasticity of 7075-T6 aluminum alloy wire, the inlet section 1161 has a relatively gentle necking cone angle of 10°~14° to reduce initial flow resistance, allowing the material to flow in slowly during initial deformation and reducing abrupt stress; the transition section 1162 has a necking cone angle of 18°~22° to promote gradient deformation, accelerate radial migration of the material, disperse dislocation paths, and prevent atomic accumulation at abrupt interfaces; the sizing section 1163 has a necking cone angle of 6°~10° to ensure final dimensional stability.

[0133] Specifically, the main cavity 116 of the first mold 1 adopts a stepped necking structure. Through the different necking cone angles of the inlet 1161, transition 1162 and sizing 1163, the wire is gradually deformed during the necking process, which effectively reduces the deformation rate and shear stress peak in the local area, prevents internal tearing and surface cracking, and significantly improves the stability of the necking dimensions and the product qualification rate.

[0134] The above description is based on the preferred embodiments of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the invention is defined by the appended claims rather than the foregoing description, and all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0135] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for processing rivet nuts, characterized in that, The processing method is applicable to twelve-corner rivet nuts made of 7075-T6 aluminum alloy, and includes the following steps: S1. The aluminum alloy wire is subjected to warm upsetting pretreatment at 220~240 ℃ for 100~140 s to obtain pretreated wire; S2. The wire is cut to a fixed length, pre-upset, stepped necking, and head and inner hole forming are carried out in sequence through four stations to obtain semi-finished rivet nuts. a. The first station uses a V-shaped anvil to apply back pressure and cut the wire to a fixed length; b. The second station uses a flat punch with an end face radius of R0.2~0.5 mm and a three-lobed combined die to pre-upset the cut wire at a compression ratio of 20~25%. c. The third station uses a three-stage tapered die with an entrance cone angle of 10°~14°, a transition cone angle of 18°~22°, and a sizing cone angle of 6°~10°, and performs step necking with a reduction of 12~16%; d. The fourth station presses out a shallow hexagonal profile with a 60° transition angle, then finely presses it into a dodecagonal shape, while simultaneously performing inner hole pre-punching and flange forming, and head forming; S3. Stress-relief annealing of the semi-finished rivet nuts, followed by furnace cooling; S4. Use a tap to tap the inner hole of the annealed semi-finished rivet nut. S5. The tapped semi-finished rivet nuts are subjected to solution treatment and aging treatment respectively to obtain rivet nuts.

2. The rivet nut processing method according to claim 1, characterized in that: In step S2, the included angle of the V-shaped anvil is 55°~65°, and the back pressure is 0.4~0.6 MPa.

3. The method for processing rivet nuts according to claim 1, characterized in that: In step S3, the annealing temperature is 230~270 ℃, and the holding time is 1.5~2.5 h.

4. A method for processing rivet nuts according to claim 1, characterized in that: In step S5, the solution treatment temperature is 470~490 ℃ and the water quenching time is 0.5~1.5 h; the aging treatment temperature is 110~130 ℃ and the treatment time is 20~28 h.

5. A method for processing rivet nuts according to any one of claims 1-4, characterized in that, The processing apparatus of the processing method includes: a cold heading machine, and a mold mechanism installed on the cold heading machine; The mold mechanism includes: a first mold for step necking of the pre-upset wire, a second mold for pre-forming the hexagonal profile of the head, a third mold for forming the dodecagonal profile of the head, a fourth mold for forming the upper inner hole, a fifth mold for forming the lower inner hole, and a sixth mold for forming the head flange. The diameter of the upper inner hole is larger than the diameter of the lower inner hole.

6. A method for processing rivet nuts according to claim 5, characterized in that: The first mold, the second mold, the third mold, the fourth mold, the fifth mold, and the sixth mold each include a corresponding main mold and a die. The main mold includes: a main mold shell, a main mold pad, a main mold ejector pin, a main mold core, and a main mold spring disposed inside the main mold shell, and a main mold cavity formed inside the main mold core; the main mold pad is installed at the bottom of the main mold shell, the main mold core is installed at the top of the main mold shell, one end of the main mold ejector pin is fixed on the main mold pad, and the other end passes through the bottom of the main mold core into the interior of the main mold cavity; The mold includes: a mold shell, and a mold pad, a mold ejector pin, and a mold chuck disposed inside the mold shell; the mold pad is installed on the top of the mold shell, the mold chuck is installed on the bottom of the mold shell, one end of the mold ejector pin is fixed on the mold pad, and the other end passes through the mold chuck and corresponds to the main mold cavity.

7. A method for processing rivet nuts according to claim 6, characterized in that: The main cavity of the first mold has a stepped necking structure, which includes, from top to bottom, an inlet, a transition section and a sizing section; the necking cone angle of the inlet is 10°~14°, the necking cone angle of the transition section is 18°~22°, and the necking cone angle of the sizing section is 6°~10°.

8. A method for processing rivet nuts according to claim 6, characterized in that: The fourth mold and the fifth mold further include: a die top block, a die ejector rod, and a die sleeve; the die top block is installed inside the die shell located on top of the die pad block, one end of the die ejector rod is fixed to the bottom of the die top block, and the other end is fixed to the top of the die sleeve, and the inner side of the die sleeve is sleeved on the side of the die ejector pin.

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