Reverse rivet nut and forming device thereof

Abstract

The utility model discloses a reverse rivet nut and a forming device thereof. The reverse rivet nut comprises a flange, a step and a conical rod part which are sequentially arranged along the axis, and is provided with a threaded hole penetrating through each part; the step is convexly arranged on the flange end face around the threaded hole, and a plurality of tendons surrounding the step are arranged on the flange end face; the conical rod part is arranged on the side, away from the flange, of the step, and the outer wall inclines in the axis direction to form a groove structure. The forming device comprises a cold header and a die assembly matched with the cold header, and a die sequentially carries out multi-station plastic machining on the nut and sequentially completes forming of a rod part straight section, a flange step, a chamfer, a tendon, a groove and a through hole. By means of the structure and the device, efficient one-time forming of the reverse rivet nut can be achieved, the pulling resistance and the torque holding capacity of the nut are improved, material waste and machining errors are reduced, the controllability of product quality and the automatic integration capacity of the technological process are remarkably enhanced, and good practicability and popularization value are achieved.

Description

Technical Field

[0001] This utility model belongs to the field of fastener technology, and in particular relates to a reverse rivet nut and its forming device. Background Technology

[0002] Fastening and connection technology plays an irreplaceable role in thin-plate structures such as automotive bodies, rail transportation, home appliance sheet metal, and energy storage shells. With the accelerating trend of lightweighting and process integration, rivet nuts, which can be assembled from one side, are widely used because they do not require double-sided operation and can simultaneously achieve hole expansion and thread insertion. However, common forward rivet nuts require applying tension from one side of the surface during installation, and the riveting deformation direction is the same as that of the operating end. When assembly space is limited, damage to the outer appearance surface is not allowed, or the sheet metal can only obtain clamping force from the back, traditional structures often cannot meet the application requirements of "reverse force application and forward riveting," resulting in limited assembly processes or the need for additional auxiliary fixtures, significantly increasing manufacturing costs and on-site operation difficulty.

[0003] On the other hand, to reduce unit costs and improve material utilization in mass production, the fastener manufacturing industry has widely adopted cold heading instead of multi-machine machining. However, the shapes of rivet nuts are increasingly characterized by complex geometries such as multi-step flanges, tendons, anti-slip teeth, and thin-walled tapered shanks. Conventional two- to four-station cold heading machines cannot complete the fine forming in one go, forcing companies to adopt a compromise of "cold heading blank + secondary machining." This approach not only weakens the near-net-shape advantage of cold heading but also increases unit energy consumption and manufacturing costs due to increased scrap and tool wear. Meanwhile, due to the hardening characteristics of difficult-to-machine materials such as high-strength steel, stainless steel, or aluminum-magnesium alloys, problems such as localized stress concentration in molds, reduced mold life, and fluctuations in the quality of internal threads in parts are becoming increasingly prominent, hindering product consistency and production cycle time.

[0004] Existing dedicated rivet guns and nut systems face the challenge of installation load curves being significantly affected by operator hand force, air pressure fluctuations, and the dispersion of substrate hardness, making it difficult to control riveting quality. Simultaneously, the torque transmission and pull-out resistance between the nut and the base material must balance high strength and long lifespan, making loosening and failure prone to occur under high-speed vibration conditions. With the development of intelligent manufacturing, fastener production lines are upgrading towards integrated digital quality inspection, online screening, and automated packaging, highlighting the increasing limitations of traditional discrete processing flows in terms of information loop and production line cycle time.

[0005] In summary, the field of high-strength thin-plate joining urgently needs an improved rivet nut solution that can complete reverse-force riveting in confined spaces, has near-net-shape forming capability for complex geometric features, and is equipped with an efficient multi-station cold heading device, in order to solve the prominent problems of existing technologies in terms of installation adaptability, manufacturing efficiency, forming accuracy, and assembly reliability. Utility Model Content

[0006] To solve the above-mentioned technical problems, this utility model provides a reverse rivet nut and its forming device.

[0007] Specifically, the technical solution provided by this utility model is as follows:

[0008] A reverse rivet nut includes a flange, a step, and a tapered shank arranged sequentially along an axis, and a threaded hole penetrating the flange, step, and shank along the axial direction; the step protrudes from the threaded hole on the end face of the flange, and its circumscribed circle radius is smaller than that of the flange; multiple tendons are also provided on the end face of the flange around the step; the tapered shank protrudes from the threaded hole on the end face of the step, and its radius gradually increases with distance from the step, and the outer wall of the tapered shank forms a groove with the end face of the step, the groove being inclined towards the center of the axis along the outer wall of the tapered shank.

[0009] Preferably, the flange and the step are in the shape of a regular hexagon, and the tendons are evenly distributed around the step to connect the edges of the step.

[0010] Preferably, the end face of the tapered rod is further provided with a smooth bevel for enhancing the pushing force.

[0011] A forming apparatus for manufacturing the aforementioned reverse rivet nut includes a cold heading machine and a mold assembly mounted on the cold heading machine, the mold assembly comprising:

[0012] A first mold is used to shape the blank so that the blank is formed into a straight section for forming a rod.

[0013] The second mold is used to shape the blank formed by the first mold in order to preform the flange and step;

[0014] The third mold is used to shape the blank formed by the second mold to form the chamfer at the end of the flange;

[0015] The fourth mold is used to shape the blank formed by the third mold in order to form tendons, rods and screw holes;

[0016] The fifth mold is used to shape the blank formed by the fourth mold in order to form the groove between the rod and the step;

[0017] The sixth mold is used to process the blank formed by the fifth mold in order to remove waste material from the screw holes.

[0018] Furthermore, the first mold, the second mold, the third mold, the fourth mold, the fifth mold, and the sixth mold each include a main mold and a punch die corresponding to the main mold;

[0019] The main mold includes a main mold shell, a main mold pad, a main mold ejector pin, and a main mold core disposed within the main mold shell. The main mold core has an opening facing the main mold cavity of the die. The main mold ejector pin passes through the main mold cavity from the bottom of the main mold core. The die includes a die shell, a die pad, and a die ejector pin disposed within the die shell. One end of the die ejector pin is connected to the die pad, and the other end passes through the die shell and is opposite to the main mold cavity.

[0020] Preferably, the forming device further includes a shearing mechanism for cutting the wire into nut blanks.

[0021] Preferably, the molding device further includes a feeding mechanism for feeding materials between multiple molds.

[0022] This invention overcomes the prominent problems of existing technologies, such as the inability to achieve single-sided assembly in confined spaces, low forming efficiency, complex structures requiring multiple machining operations, low material utilization, and short mold life, through a comprehensive innovation in the reverse riveting nut structure and its forming device. The adopted reverse riveting structure not only allows the nut to be inserted from the back and achieve stable riveting, improving adaptability and assembly reliability, but also allows its tapered rod, tendons, and multi-step structure to be formed in one step during cold heading, eliminating the need for subsequent machining and significantly improving production efficiency and batch consistency. The matching multi-station mold assembly, combined with cold heading equipment, enables high-precision, progressive plastic flow for complex geometric features, reducing material waste and processing errors, while extending mold life and further reducing maintenance costs. The overall solution not only improves the nut's pull-out resistance and torque retention capacity but also significantly enhances product quality control and the automation integration capabilities of the process, demonstrating good practicality and promotional value. Attached Figure Description

[0023] The accompanying drawings are provided to further understand the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention and do not constitute a limitation thereof.

[0024] Figure 1 This is a three-dimensional structural diagram of a reverse rivet nut provided in an embodiment of the present invention;

[0025] Figure 2 This is a three-dimensional half-sectional schematic diagram of a reverse rivet nut provided in an embodiment of the present invention;

[0026] Figure 3 This is a half-sectional view of a reverse rivet nut provided in one embodiment of the present invention;

[0027] Figure 4 This is a top view of a reverse rivet nut provided in an embodiment of this utility model;

[0028] Figure 5 This is a bottom view of a reverse rivet nut provided in an embodiment of this utility model;

[0029] Figure 6 This is a schematic diagram of the first mold structure provided in an embodiment of the present invention;

[0030] Figure 7 This is a schematic diagram of the second mold structure provided in one embodiment of the present invention;

[0031] Figure 8 This is a schematic diagram of the third mold structure provided in one embodiment of the present invention;

[0032] Figure 9 This is a schematic diagram of the fourth mold structure provided in one embodiment of the present invention;

[0033] Figure 10 This is a schematic diagram of the fifth mold structure provided in one embodiment of the present invention;

[0034] Figure 11 This is a schematic diagram of the sixth mold structure provided in one embodiment of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0036] Example 1

[0037] This embodiment provides a reverse rivet nut, such as Figures 1-5 As shown, the nut includes a flange 1, a step 2 and a rod 3 arranged sequentially along the axis, and is provided with a threaded hole that passes through the flange 1, the step 2 and the rod 3 along the axial direction.

[0038] To facilitate clamping and tightening, the flange 1 is polygonal in shape (e.g., a regular hexagon) with flat clamping surfaces on its sides. A step 2 protrudes from the threaded hole onto the end face of the flange 1, with its circumscribed circle radius smaller than that of the flange 1. The step shape can be the same as the flange 1 or other shapes. In some embodiments, multiple tendons 5 are also provided around the step 2 on the end face of the flange 1. A tapered rod 3 protrudes from the threaded hole onto the end face of the step 2, its radius gradually increasing with distance from the step 2. The outer wall of the tapered rod 3 forms a groove 4 with the end face of the step 2, and this groove 4 slopes towards the center of the axis along the outer wall of the tapered rod 3.

[0039] With the above structure, the tapered rod 3 can be pressed into the plate to be fastened, and the nut can be prevented from falling out of the plate through the snap-fit ​​of the oblique groove 4. To facilitate easy embedding of the rod 3 into the plate and improve the pushing force, the end face of the rod 3 is also provided with a smooth bevel through chamfering. The end face of the step 2 contacts the plate, and through multiple tendons 5 connected to the flange 1, the rotational torque is improved, ensuring its stability after assembly.

[0040] In some embodiments, the tapered rod portion 3 has a thinner wall thickness, which allows for riveting and press-fitting deformation to achieve a tight connection with the sheet metal, thereby improving the connection strength of the product.

[0041] Example 2

[0042] The nut described in Example 1 is produced using a cold heading process. The CBP-136L cold heading machine is used to harden the material and shape the main dimensions of the product. The manufacturing process includes wire (coil), cold heading, tapping, heat treatment, surface treatment, and final inspection. The wire needs to be purchased and cut into blanks using a shearing mechanism. These blanks are then fed into the mold assembly via a feeding mechanism for cold heading. The tendons and steps on the flange are also directly cold-headed, eliminating the need for slow machining. Cold heading increases production efficiency several times, meets higher performance requirements, and is more suitable for mass production.

[0043] In this embodiment, the mold assembly for cold heading includes six molds, such as... Figures 6-11 As shown, each mold includes a punch and a main mold (103, 203, 303, 403, 503, 603). The punch consists of a punch shell (101, 201, 301, 401, 501, 601), a punch pad, and punch ejector pins (102, 202, 302, 402, 502, 602). The main mold consists of a main mold shell (103, 403), a main mold core (604), a main mold pad, and main mold ejector pins (104, 204, 303, 404, 504). The molds are assembled on a cold heading machine, and the die passing is completed by a feeding mechanism such as clamps.

[0044] (1) After the wire is cut, the blank is passed through the mold to the first mold. The punch moves with the slide block of the equipment. The ejector pin of the punch pushes the blank into the main mold cavity. According to the principle of material plastic forming, the blank flows in the cavity to form the tail rod straight section. After the forming is completed, the equipment ejector mechanism drives the ejector pin of the main mold to push the part out of the main mold cavity.

[0045] (2) The blank processed by the first mold is passed through the second mold, and the part enters the punch and the main mold cavity. The material flows with the shape of the mold cavity to preform the hexagonal flange, hexagonal steps and anti-slip teeth. After the forming is completed, the equipment ejector mechanism drives the main mold ejector pin to push the part out of the main mold cavity.

[0046] (3) The blank processed by the second mold is passed through the third mold, and the part enters the punch and main mold cavity. The material flows with the shape of the mold cavity, and the bottom of the hexagonal flange is formed. R Corner. After molding is completed, the equipment's ejector mechanism drives the main mold ejector pin to push the part out of the main mold cavity.

[0047] (4) The blank processed by the third mold is passed to the fourth mold. The part is pushed into the movable main mold cavity by the movable die ejector pin. The material flows with the shape of the mold cavity. The main mold forms the hexagonal flange and the depth of the center screw hole. The die forms the anti-slip ribs on the hexagonal flange surface, the hexagonal steps and the thin-walled shape of the rod. After the forming is completed, the equipment ejector mechanism drives the main mold ejector pin to push the part out of the main mold cavity.

[0048] (5) The blank processed by the fourth mold is passed through the fifth mold, and the part enters the punch and main mold cavity. The material flows with the shape of the cavity, and the thin wall of the rod presents an inverted "V" shape (conical shape). After the forming is completed, the equipment ejector mechanism drives the ejector pin of the main mold to push the part out of the main mold cavity.

[0049] (6) The blank processed by the fifth mold is passed through the sixth mold, and the part enters the die and the main mold cavity; during the movement of the punch, the intermediate waste is removed to achieve the through hole state of the product. After the forming is completed, the equipment ejector mechanism drives the die ejector to push the part out to the equipment discharge port slide.

[0050] The entire process described above utilizes the relative movement between molds to form the product and ensure that the cold heading dimensions of the product are met. This process makes the most of the special characteristics of the product's shape and size, and, combined with the characteristics of the molding technology, controls material utilization and mold life to the optimal level.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and not to limit it; under the concept of this utility model, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of different aspects of this utility model as described above. For the sake of brevity, they are not provided in detail; although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A reverse-pull rivet nut, characterized in that, The device includes a flange, a step, and a tapered rod arranged sequentially along an axis, and has a threaded hole that passes through the flange, step, and rod along the axial direction. The step protrudes from the end face of the flange around the threaded hole, and its circumscribed circle radius is smaller than that of the flange. Multiple tendons are also provided around the step on the end face of the flange. The tapered rod protrudes from the end face of the step around the threaded hole, and its radius gradually increases as it moves away from the step. The outer wall of the tapered rod forms a groove with the end face of the step, and the groove is inclined towards the center of the axis along the outer wall of the tapered rod.

2. The reverse rivet nut as described in claim 1, characterized in that, The flange and step are in the shape of a regular hexagon, and the tendons are evenly distributed around the step to connect the edges of the step.

3. The reverse rivet nut as described in claim 1, characterized in that, The end face of the tapered rod is also provided with a smooth bevel to enhance the pushing force.

4. A forming apparatus for manufacturing a reverse rivet nut as described in any one of claims 1 to 3, comprising a cold heading machine and a mold assembly mounted on the cold heading machine, characterized in that, The mold assembly includes: A first mold is used to shape the blank so that the blank is formed into a straight section for forming a rod. The second mold is used to shape the blank formed by the first mold in order to preform the flange and step; The third mold is used to shape the blank formed by the second mold to form the chamfer at the end of the flange; The fourth mold is used to shape the blank formed by the third mold in order to form tendons, rods and screw holes; The fifth mold is used to shape the blank formed by the fourth mold in order to form the groove between the rod and the step; The sixth mold is used to process the blank formed by the fifth mold in order to remove waste material from the screw holes.

5. The molding apparatus as described in claim 4, 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 main mold and a punch die corresponding to the main mold; The main mold includes a main mold shell, a main mold pad, a main mold ejector pin, and a main mold core disposed within the main mold shell. The main mold core has an opening facing the main mold cavity of the die. The main mold ejector pin passes through the main mold cavity from the bottom of the main mold core. The die includes a die shell, a die pad, and a die ejector pin disposed within the die shell. One end of the die ejector pin is connected to the die pad, and the other end passes through the die shell and is opposite to the main mold cavity.

6. The molding apparatus as described in claim 4, characterized in that, The forming device also includes a shearing mechanism for cutting the wire into nut blanks.

7. The molding apparatus as described in claim 4, characterized in that, The molding apparatus also includes a feeding mechanism for feeding materials between multiple molds.

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