A blind hole welding nut and a forming device and method thereof

Abstract

The application provides a blind hole welding nut and a forming device and method thereof, relates to the technical field of metal plastic forming and automobile fastener manufacturing, and comprises a head flange and a rod part. The nut is in a blind hole structure. A projection welding point for projection welding connection is arranged on a welding surface of the head flange. The application is used for providing a blind hole welding nut with reasonable structure, good sealing performance and high connection strength. Another purpose is to provide a special forming device and manufacturing method for manufacturing the nut. The device and the method can realize one-time precision cold upsetting forming of all features except threads, thereby greatly improving production efficiency and material utilization rate while guaranteeing excellent performance of the product.

Description

Technical Field

[0001] This invention relates to the fields of metal plastic forming and automotive fastener manufacturing technology, specifically to a blind hole welding nut for vehicle body connection, and a forming apparatus and manufacturing method for efficiently and precisely forming the nut. Background Technology

[0002] In automotive body-in-white manufacturing, a large number of nuts need to be welded to the body sheet metal to provide threaded connection points for subsequent components. Currently, the commonly used through-hole weld nuts are prone to contamination and blockage during welding and subsequent electrophoresis and spraying processes. This significantly impacts assembly efficiency and connection reliability, especially in areas such as the body floor assembly where the strength and cleanliness requirements for connection points are even higher. Therefore, there is an urgent need for a weld nut solution that can effectively seal and provide high-strength connection performance. Summary of the Invention

[0003] The present invention aims to overcome the shortcomings of the prior art and provide a blind hole welded nut with reasonable structure, good sealing performance and high connection strength. Another objective of the present invention is to provide a special forming device and manufacturing method for manufacturing the nut. The device and method can realize one-time precision cold heading forming of all features except threads, which can greatly improve production efficiency and material utilization while ensuring the excellent performance of the product.

[0004] This invention provides the following technical solution: A blind hole welded nut and its forming device are disclosed, comprising a head flange and a rod, wherein the nut has a blind hole structure; the welding surface of the head flange is provided with a projection weld point for projection welding connection.

[0005] The technical advantage lies in the fact that the blind hole structure fundamentally eliminates the possibility of foreign matter such as welding slag and liquid entering the threaded hole during welding, electrophoresis, and spraying, ensuring the cleanliness of the threads. This improves the reliability of subsequent assembly and the torque consistency of the connection pair. Furthermore, the projection weld allows the nut to form a high-strength metallurgical bond with the body sheet metal through the projection welding process, providing torsional resistance and connection reliability far exceeding those of planar welding. The combination of these two effects solves the industry pain points of easy contamination of through-hole nuts and insufficient reliability of connection points in the background technology.

[0006] Preferably, the protrusion is an annular protrusion or a plurality of point-like protrusions distributed in a circle.

[0007] The technical advantages lie in the fact that the annular protrusions provide a continuous and uniform current path and welding contact surface, forming an annular weld nugget with high and stable connection strength. Multiple dot-like protrusions can disperse welding stress, reducing welding deformation and improving adaptability under specific plate thicknesses or materials.

[0008] Preferably, the depth of the blind hole is greater than or equal to the depth of its internal thread.

[0009] Its technical effect is to ensure the absolute effectiveness of the seal. Only when the depth of the blind hole completely covers the entire thread area can 100% sealing be achieved under any working condition, preventing foreign objects from remaining at the root of the thread, thereby completely achieving the anti-fouling design purpose of this invention.

[0010] Preferably, it includes a cold heading machine, a cutting mechanism, a conveying mechanism, and a plurality of dies disposed on the cold heading machine, wherein the plurality of dies sequentially include, along the feeding direction: The first mold is a bundled rod mold, used to shape the cut wire blanks; The second mold is a pre-upsetting mold, which is used to axially upset the shaped blank to pre-form the head material accumulation area and the rod prototype; The third mold is an upsetting flange mold, whose cavity structure is capable of simultaneously forming the shape of the head flange and the protruding weld point in one forming action; The fourth mold is a drawing die, equipped with a first punch, which is used to perform the first reverse extrusion on the material from the end face of the rod to form a rough blind hole; The fifth mold is a small hole drawing mold, which is equipped with a second punch with a diameter smaller than that of the first punch. It is used to perform a second reverse extrusion finishing process on the rough-machined blind hole to form a blind hole that meets the final size requirements. The sixth mold is a trimming mold, used to remove the burrs from the outer edge of the head flange.

[0011] Its core lies in defining the specific types and strict sequence of six mold stations (bundle rod, pre-upsetting, flange upsetting, drawing large holes, drawing small holes, and trimming). The technical effect is to achieve a highly efficient and precise automated production process. This sequence is a carefully designed plastic processing flow that ensures reasonable material flow and gradual deformation, forming the basis for the stable, mass production of high-quality blind hole weld nuts.

[0012] Preferably, the bottom of the punch working surface or the main mold cavity of the third mold is provided with a groove or protrusion structure corresponding to the shape of the weld point.

[0013] The specific structure of the third mold (upsetting flange mold) is defined, namely, its cavity with formed weld points. Its technical advantage lies in achieving "feature integration" and "one-time forming." This design allows the head flange shape and weld points to be completed simultaneously in the same stroke, bringing two major advantages: 1: The projection weld and the flange body are integrally formed by plastic flow, with continuous metal flow lines, no weak joint surfaces, and excellent mechanical properties. 2: It eliminates the need for separate processing of the weld points, greatly improving production efficiency and reducing costs.

[0014] Preferably, the first punch of the fourth mold and the second punch of the fifth mold are coaxially arranged.

[0015] Its technical advantages lie in ensuring the machining accuracy of blind holes. The coaxial design ensures that the finishing punch and the roughing hole have perfect guidance during the secondary drilling process, resulting in blind holes with high straightness, accurate diameter, and smooth hole walls. This provides a high-quality foundation for subsequent tapping and reduces tap wear and thread defects.

[0016] A method for manufacturing blind hole weld nuts using the apparatus described above includes the following forming steps performed in sequence: S1, Bundle rod step: Shape the wire blank using the first mold; S2, Pre-upsetting step: The shaped billet is upset using the second mold to pre-form the head material accumulation area and the rod part; S3, Upsetting flange step: Simultaneously and precisely forming the head flange and the protruding weld points on its welding surface using the third mold; S4, enlarging hole step: using the fourth mold and the first punch, reverse extrusion is performed from the end face of the workpiece rod to form a rough-machined blind hole; S5, Draw small hole step: Using the fifth mold and the second punch, the rough blind hole is finely machined to form a final blind hole with accurate dimensions; S6, Edge trimming step: Use the sixth mold to trim the flash on the outer edge of the head flange to obtain a cold heading blank for the nut.

[0017] The sequence of these six steps reflects the logical operation of the device, and its core effects include: 1. "Outside first, inside later": First form the complex external features (flanges and weld points), and then process the internal blind holes. This ensures the dimensional stability of the external features and provides a stable positioning reference for internal processing. 2. "Step-by-step hole forming": Blind holes are completed in two steps: enlarging the hole (removing excess material) and enlarging the hole (finishing). This breaks down the difficulty of deformation and improves the quality of the hole and the life of the mold. 3. Process control: This method defines a repeatable and controllable standardized production process, which is the fundamental guarantee for obtaining consistent high-quality products.

[0018] Preferably, after obtaining the nut cold-forging blank in step S6, the process further includes steps of sequentially performing heat treatment, tapping internal threads, and surface anti-corrosion treatment on the blank.

[0019] The beneficial effects of this invention are: 1. The nut of this invention integrates the sealing and anti-fouling function of the "blind hole" with the high-strength connection function of the "protruding weld point", which fundamentally solves the contamination problem of through-hole welded nuts and ensures the torque performance of the connection point. It is particularly suitable for critical automotive connection parts with strict requirements for cleanliness and reliability. 2. The "outer-to-inner, feature-synchronized, step-by-step hole forming" process route and dedicated device proposed in this invention are scientific and reasonable. The simultaneous forming of the projection weld point at the flange upsetting station ensures the continuity of the metal flow line between the projection weld point and the flange body, resulting in high strength and efficiency far exceeding that of secondary processing. The use of two stations for forming blind holes (large hole drawing and small hole drawing) effectively decomposes the deformation amount, reduces the processing difficulty, and significantly improves the dimensional accuracy, coaxiality, and hole wall quality of the blind hole, providing an excellent foundation for subsequent tapping. 3. This invention achieves near-net-shape forming of all features except threads through multi-station cold heading, resulting in high material utilization, complete metal flow lines, and superior part strength compared to machined parts. The production process is highly automated with a fast production cycle, significantly reducing production costs and yielding remarkable economic benefits compared to traditional CNC machining methods. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is an axial sectional view of the finished blind hole welded nut of the present invention.

[0021] Figure 2 This is a top view of the finished blind hole welded nut of the present invention.

[0022] Figure 3 Product drawing for the first station's tie rod forming process; Figure 4 A drawing of the product pre-forged at the second workstation; Figure 5 Product drawing for flange upsetting at the third workstation; Figure 6 Product drawing for enlarged hole forming at the fourth workstation; Figure 7 A product drawing for the fifth station's small hole forming process; Figure 8 This is a schematic diagram of the first mold rod forming process; Figure 9 A schematic diagram of pre-upsetting using the second mold; Figure 10 A schematic diagram of flange upsetting using the third mold; Figure 11 A schematic diagram for forming a larger hole using the fourth mold; Figure 12A schematic diagram of the fifth mold for forming small holes; Figure 13 This is a schematic diagram of the edge-cutting process of the sixth mold; Markings in the diagram: 10. Head flange; 11. Rod; 12. Projection weld; 13. Blind end; 14. Central blind hole; 15. Internal thread; 31. Main mold cavity; 32. Die; 321. Annular protrusion; 41. First punch; 51. Second punch. Detailed Implementation

[0023] Example 1 Regarding product structure: such as Figure 1 and Figure 2 As shown, in this embodiment of the blind hole welded nut of the present invention, the diameter D and thickness H of the head flange 10 can be varied according to the design requirements of the connection point. The projection weld 12 is illustrated as an annular boss, the height h and width of which must ensure that a sufficient weld nugget can be formed during projection welding. The shank 11 is a cylinder, and its end is a closed blind end 13. The depth H1 of the central blind hole 14 must be greater than the length H2 of the internal thread 15 to achieve an effective seal. The product is used after heat treatment and surface treatment (such as galvanizing).

[0024] Example 2 Regarding the manufacturing apparatus and method: The manufacturing process is carried out on a multi-station cold heading machine. In this embodiment, the coiled wire is straightened, fed, and cut to a fixed length by a scissor-type cutting mechanism. The blank is ejected and gripped by a mechanical clamp (transfer mechanism) and sequentially fed into six mold stations.

[0025] First station (S1, binding rod): Under the constraint of the first mold, the blank is micro-upset to obtain an initial blank (A) with flat ends and precise dimensions, providing a volume reference for subsequent deformation, such as... Figure 3 and Figure 8 As shown.

[0026] Second station (S2, pre-upsetting): The billet (A) undergoes forward upsetting in the second die. The punch pushes the billet, shortening its length within the die cavity and expanding its head diameter, forming a distinct head (B1) and a relatively slender rod (B2), completing the initial material distribution, such as... Figure 4 and Figure 9 As shown.

[0027] Third station (S3, upsetting flange, assembly) Figure 4This is the decisive step. The pre-forged part (B) is placed into the third mold. The main mold cavity 31 of this mold precisely defines the shape of the flange. As the punch 32 advances, the annular protrusion 321 (corresponding to the annular weld point) on its front end face is pressed into the head of the workpiece. Under high pressure, the metal flows plastically, simultaneously and fully filling the flange shape cavity and the weld point forming cavity, resulting in a head flange 10 with regular weld points 12 in one step. This step produces a semi-finished product (C), such as... Figure 5 and Figure 10 As shown.

[0028] Fourth station (S4, enlarging the hole): Position the workpiece (C) so that the end face of the rod faces the fourth mold. The first punch 41 is forcefully driven into the center of the rod, and the metal flows upwards (towards the head) along the circumference of the punch, forming a rough-machined blind hole of sufficient depth. This process undertakes the main "material removal" task, such as... Figure 6 and Figure 11 As shown.

[0029] Fifth station (S5, drawing small holes, joining) Figure 5 The workpiece is moved to the fifth mold. The second punch 51 (slightly smaller in diameter than the first punch 41) finishes the rough-machined blind hole along the same axis. This process is similar to reaming, further correcting the hole wall to machine the hole diameter to within the design tolerance, forming a smooth final blind hole, producing a semi-finished product (D), such as... Figure 7 and Figure 12 As shown.

[0030] Sixth station (S6, trimming): The workpiece (D) is placed into the precision cavity of the sixth mold. The punch descends and shears against the cavity opening, cleanly removing the flash from the outer circumference of the flange, obtaining the final cold-headed blank (E), as shown. Figure 1 and Figure 13 As shown.

[0031] Subsequent processing: The obtained cold-headed blanks (E) are collected and subjected to continuous heat treatment (such as carburizing and quenching in a mesh belt furnace + tempering) to achieve the required hardness and toughness on the surface and core. Subsequently, an internal thread 15 is machined in the blind hole using a special tap on a precision tapping machine. Finally, according to corrosion protection requirements, electroplating treatments such as galvanizing or zinc-nickel alloy plating are performed to complete the finished product manufacturing.

[0032] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A blind hole welded nut, characterized in that, It includes a head flange and a rod, the nut has a blind hole structure, and the welding surface of the head flange is provided with a projection weld point for projection welding and fixing to the body sheet metal.

2. The blind hole welded nut according to claim 1, characterized in that, The weld point is a ring-shaped protrusion or multiple point-like protrusions distributed in a circle.

3. The blind hole welded nut according to claim 1, characterized in that, The depth of the blind hole is greater than or equal to the depth of its internal thread.

4. A forming apparatus for manufacturing the blind hole weld nut as described in claim 1, characterized in that, It includes a cold heading machine, a cutting mechanism, a conveying mechanism, and multiple molds mounted on the cold heading machine, wherein the multiple molds sequentially include, along the feeding direction: The first mold is a bundled rod mold, used to shape the cut wire blanks; The second mold is a pre-upsetting mold, which is used to axially upset the shaped blank to pre-form the head material accumulation area and the rod prototype; The third mold is an upsetting flange mold, whose cavity structure is capable of simultaneously forming the shape of the head flange and the protruding weld point in one forming action; The fourth mold is a drawing die, equipped with a first punch, which is used to perform the first reverse extrusion on the material from the end face of the rod to form a rough blind hole; The fifth mold is a small hole drawing mold, which is equipped with a second punch with a diameter smaller than that of the first punch. It is used to perform a second reverse extrusion finishing process on the rough-machined blind hole to form a blind hole that meets the final size requirements. The sixth mold is a trimming mold, used to remove the burrs from the outer edge of the head flange.

5. The multi-station cold heading forming apparatus according to claim 4, characterized in that, The bottom of the punch working surface or main mold cavity of the third mold is provided with a groove or protrusion structure corresponding to the shape of the weld point.

6. The multi-station cold heading forming apparatus according to claim 4, characterized in that, The first punch of the fourth mold and the second punch of the fifth mold are coaxially arranged.

7. A method for manufacturing blind hole weld nuts using the apparatus as described in any one of claims 4-6, characterized in that, This includes the following molding steps performed in sequence: S1, Bundle rod step: Shape the wire blank using the first mold; S2, Pre-upsetting step: The shaped billet is upset using the second mold to pre-form the head material accumulation area and the rod part; S3, Upsetting flange step: Simultaneously and precisely forming the head flange and the protruding weld points on its welding surface using the third mold; S4, enlarging hole step: using the fourth mold and the first punch, reverse extrusion is performed from the end face of the workpiece rod to form a rough-machined blind hole; S5, Draw small hole step: Using the fifth mold and the second punch, the rough blind hole is finely machined to form a final blind hole with accurate dimensions; S6, Edge trimming step: Use the sixth mold to trim the flash on the outer edge of the head flange to obtain a cold heading blank for the nut.

8. The forming method of the blind hole welded nut according to claim 7, characterized in that, After obtaining the nut cold heading blank in step S6, the process further includes sequentially performing heat treatment, internal thread tapping, and surface anti-corrosion treatment on the blank.

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