Self-tapping fastener and connecting assembly

Abstract

The invention discloses a self-tapping fastener and a connecting assembly. The self-tapping assembly comprises a driving part, a thread part, a repairing part, an avoiding part, a stretching part, a hole flanging part and a tail part which are sequentially connected from top to bottom. The self-tapping fastener can realize the connection of dissimilar materials, and is particularly suitable for the connection of magnesium and aluminum alloys with poor ductility; metal plate pre-trepanning and thread pre-machining are not needed, and the cost is low; the assembly connection efficiency is high; the pollution to the working environment is small; the connection strength is high, and the shearing strength is high due to the rotation of threads; the thread is good in quality and smoothness, can be repeatedly disassembled and repaired for use, is high in yield, and reduces failure and scrap of sheet metal structural parts; the noise is low, the friction area is small, and less heat and chippings are generated, so that the working noise is low.

Description

Technical Field

[0001] The present invention relates to the field of fasteners, and in particular to a self-tapping fastener and a connection assembly. Background Art

[0002] With the development of the automotive industry, in order to improve fuel economy and increase battery life, lightweighting of vehicle bodies has become a major development direction. More and more lightweight materials such as aluminum, magnesium alloys, and carbon fiber are being used in vehicle body structures, but the connection between these materials has become a problem that needs to be solved urgently.

[0003] Traditional joining methods, such as resistance spot welding, while mature, are inapplicable when joining tubular structures or other structures with limited space. Furthermore, when joining dissimilar materials, significant differences in physical and chemical properties such as melting points, coefficients of expansion, and thermal conductivity make it difficult to form a stable weld nugget.

[0004] In particular, for the connection of thin plates, since threads cannot be produced on thin plates, bolts and nuts are usually needed for locking, and pre-drilling and tapping are required. The connection structure and process are complex and the production efficiency is low. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects or problems in the background technology or provide a material basis for overcoming the above-mentioned defects or problems in the background technology, and to provide a self-tapping fastener and a connection assembly.

[0006] To achieve the above objectives, the present invention and its preferred embodiments adopt the following technical solutions, but the embodiments are not limited to the following solutions:

[0007] Solution 1: A self-tapping fastener comprises a driving portion, a threaded portion, a finishing portion, an avoidance portion, a stretching portion, a flanging portion and a tail portion connected in sequence from top to bottom;

[0008] The threaded portion is provided with an external thread;

[0009] The size of the horizontal cross section of the middle portion of the trimming portion is larger than the sizes of the horizontal cross sections at both ends thereof and smaller than the maximum size of the external thread, and the sizes of the horizontal cross sections at both ends of the trimming portion are equal;

[0010] The size of the horizontal cross section of the middle portion of the avoidance portion is smaller than the sizes of the horizontal cross sections at both ends thereof, and the sizes of the horizontal cross sections at both ends thereof are equal;

[0011] The size of the horizontal cross section of the middle portion of the stretching portion is larger than the sizes of the horizontal cross sections of the two ends thereof and is smaller than or equal to the size of the horizontal cross section of the middle portion of the trimming portion; the size of the horizontal cross section of the upper end of the stretching portion is larger than the size of the horizontal cross section of the lower end thereof;

[0012] The horizontal cross-section of the middle portion of the punching portion is larger than the horizontal cross-sections of the two ends thereof and smaller than the horizontal cross-section of the middle portion of the stretching portion. The horizontal cross-section of the upper end of the punching portion is larger than the horizontal cross-section of the lower end thereof.

[0013] The size of the tail gradually decreases from top to bottom and converges into a tip.

[0014] Solution 2: Based on Solution 1, the contours of the horizontal cross sections of the trimming portion and the avoidance portion are circular.

[0015] Solution three, based on solution one, the contours of the horizontal cross sections of the stretching portion, the hole-turning portion, and the tail portion are polygons formed by connecting multiple convex arcs.

[0016] Option 4, based on Option 1, the tail has a thread.

[0017] Solution 5: Based on Solution 1, the curvature radius of the front outer contour of the stretching portion is smaller than the curvature radius of the front outer contour of the hole-turning portion.

[0018] Option six, based on option one, the threaded portion includes a functional portion and an attacking portion connected from top to bottom, and the horizontal cross-section of the functional portion is circular; the outer diameter of the attacking portion gradually decreases from top to bottom and is a triangular rod thread.

[0019] Option seven, based on Option six, the striking part includes complete teeth, guide teeth and smooth teeth connected from top to bottom, the thread size of the smooth teeth is smaller than the size of the horizontal cross-section of the middle part of the finishing part, the thread size of the guide teeth is larger than the size of the horizontal cross-section of the middle part of the finishing part, and the thread size of the complete teeth is the same as the thread size of the functional part.

[0020] Option 8, based on Option 6, the thread crest angle of the functional part is smaller than that of ordinary metric threads, and the thread root width, thread root diameter, and thread root arc are larger than those of ordinary metric threads.

[0021] Option 9, a connection assembly, including sheet metal and a self-tapping fastener as described in any one of Options 1 to 8, wherein the self-tapping fastener cooperates with the sheet metal thread.

[0022] Solution 10, based on Solution 9, further includes a gasket, which is clamped between the sheet metal and the driving part.

[0023] From the above description of the present invention and its preferred embodiments, it can be seen that compared with the prior art, the technical solution of the present invention and its preferred embodiments have the following beneficial effects due to the adoption of the following technical means:

[0024] 1. In solution 1 and its preferred embodiment, a self-tapping fastener comprises a driving portion, a threaded portion, a trimming portion, a relief portion, a stretching portion, a flanging portion, and a tail portion connected in sequence from top to bottom;

[0025] The size of the tail gradually decreases from top to bottom and converges into a tip. The sharp tip penetrates into the sheet metal to play a guiding role, preventing the sheet metal from being stretched and thinned prematurely, especially for materials with poor ductility such as magnesium and aluminum alloy. After the tip penetrates, it can reduce the deformation resistance and effectively prevent the occurrence of defects such as bursting around the hole. Bursting around the hole will affect the process of drilling and stretching.

[0026] The horizontal cross-section of the middle portion of the punching section is larger than that of its ends, and the horizontal cross-section of the upper end of the punching section is larger than that of the lower end. This allows the hole pierced by the tail to begin to turn up, forming a bulge, preparing for the formal stretching and hole expansion. The horizontal cross-section of the middle portion of the punching section is smaller than that of the middle portion of the stretching section. The punching section serves as the initial punching, while the stretching section is the main stretching and hole expansion area, gradually expanding the hole to facilitate the formation of a high-quality hole.

[0027] The horizontal cross-section of the middle portion of the stretching portion is larger than that of the two ends, and the horizontal cross-section of the upper end of the stretching portion is larger than that of the lower end. The stretching portion is the main end for stretching and hole expansion, and is also the area with the largest force and contact (friction) area. It is used for gradual stretching, gradually expanding the hole diameter, and forming the basic structure and size of the hole. The horizontal cross-section of the middle portion of the stretching portion is smaller than or equal to that of the middle portion of the trimming portion, so that the trimming portion can perform hole wall trimming.

[0028] The horizontal cross-section of the middle of the relief is smaller than that of its two ends, which are equal in size. After forming in the stretching section, a large amount of frictional heat has already been generated on the hole wall surface. Furthermore, due to the large deformation of the hole during the stretching section, the frictional resistance is relatively large, which also results in a certain amount of metal debris accumulation. If the frictional heat and debris are not discharged smoothly, "cold welding" will occur, affecting the quality of the hole and subsequent self-tapping and tightening. Therefore, the relief section (forming a relief groove) is designed to accommodate chips and dissipate heat. In this area, the hole wall and the relief section do not contact each other, reducing friction. At the same time, the debris is discharged into the groove to prevent cold welding caused by excessive extrusion.

[0029] The horizontal cross-section of the middle section of the trimming section is larger than that of its ends and smaller than the maximum dimension of the external thread. The horizontal cross-sections of the ends of the trimming section are equal. After stretching and reaming in the stretching section, the hole's size and shape are essentially achieved, but the hole wall finish is still insufficient (rough). Self-tapping threads have very high requirements for hole wall roughness and aperture dimensional accuracy, especially for magnesium and aluminum alloys with poor ductility. Therefore, a narrow convex ring (the trimming section) is required to trim (finish) the hole wall to improve dimensional and surface accuracy and prevent adhesion abnormalities caused by insufficient hole precision during subsequent self-tapping and tightening. The lower end to the middle section of the trimming section facilitates introduction after reaming, gradually stretching and expanding the hole diameter, making deformation more gradual. Since the hole wall shrinks after finishing, the middle section to the upper end of the trimming section can reserve shrinkage and shrinkage space, reducing scratches on the hole wall caused by secondary contact. During the hole trimming process, the center of the trimming section is primarily in line contact with the hole wall, which can reduce frictional resistance.

[0030] The multi-stage variable diameter parts realize the functions of each hole forming process to form holes of high quality.

[0031] The driving portion is suitable for being driven by a tool (such as a wrench, an electric screwdriver, etc.) to realize the rotation of the self-tapping fastener; the threaded portion is provided with an external thread for tapping the thread and connecting with the sheet metal thread.

[0032] This self-tapping fastener can connect dissimilar materials and is particularly suitable for connecting magnesium and aluminum alloys with poor ductility; it does not require pre-drilling of sheet metal, pre-processing of threads, and is low in cost; it has high assembly and connection efficiency; it has little pollution to the working environment; it has high connection strength, and the thread is transformed, and has high shear strength; the thread is of good quality and good finish, and can be repeatedly disassembled and repaired, with a high yield rate and reduced failure and scrapping of sheet metal structural parts; it has low noise, a small friction area, and generates less heat and debris, so the working noise is low.

[0033] 2. In the second solution and its preferred embodiment, the contours of the horizontal cross sections of the trimming portion and the avoidance portion are circular, which is convenient for processing, and the trimming portion can be easily trimmed to form a circular hole.

[0034] 3. In Scheme 3 and its preferred embodiment, the contours of the horizontal cross-sections of the stretching portion, the hole-turning portion, and the tail portion are polygonal shapes formed by connecting a plurality of convex arcs, so that only the convex arcs at the farthest end from the center axis of the self-tapping fastener are in contact with the hole wall, thereby increasing stress and making the hole wall easier to deform (stretch, expand), while reducing friction and preventing premature adhesion due to large frictional resistance.

[0035] 4. In the fourth solution and its preferred embodiment, the tail portion has threads to facilitate drilling.

[0036] 5. In Scheme 5 and its preferred embodiment, the curvature radius of the front outer contour of the stretching portion is smaller than the curvature radius of the front outer contour of the punching portion. The curvature radius of the stretching portion is smaller than that of the punching portion, the degree of curvature is reduced, and it is smoother, so as to facilitate the gradual downward stretching and elongation of the hole, increase the subsequent thread length, and guide the material flow; and the punching portion uses a larger degree of curvature to provide sufficient interference, so that the sheet metal is squeezed and stretched.

[0037] 6. In Scheme 6 and its preferred embodiment, the threaded portion includes a functional portion and a striking portion connected from top to bottom. The horizontal cross-section of the functional portion is circular to ensure a stable connection; the outer diameter of the striking portion gradually decreases from top to bottom, thereby gradually guiding the tapping. The striking portion is a triangular rod thread, which reduces the contact area with the through hole and reduces friction.

[0038] 7. In the seventh solution and its preferred embodiment, the tapping portion includes a complete thread, a guide thread, and a stable thread connected from top to bottom. The thread size of the stable thread is smaller than the horizontal cross-section size of the middle portion of the finishing portion, that is, the outer diameter of the stable thread is smaller than the aperture. On the one hand, it is used for guidance and to prevent deflection and vibration during the temperature tightening process. On the other hand, because it is smaller than the aperture, it can further dissipate heat (reduce friction) and discharge debris from the self-tapping thread, prevent the self-tapping thread from sticking, and ensure smooth final tightening. The thread size of the guide thread is larger than the horizontal cross-section size of the middle portion of the finishing portion, that is, larger than the aperture size, to guide the tapping; the thread size of the complete thread is the same as the thread size of the functional portion, and the complete thread is used for finishing size.

[0039] 8. In Option 8 and its preferred embodiment, the crest angle of the thread of the functional part is smaller than that of ordinary metric threads, and the root width, root diameter, and root arc are larger than those of ordinary metric threads. The purpose of this design is to increase the fitting clearance between the internal and external threads to a certain extent, and reduce the risk of scratching the internal thread, prevent abnormal tightening, and make the internal thread reusable.

[0040] 9. In scheme nine and its preferred embodiment, a connection assembly includes sheet metal and the above-mentioned self-tapping fastener, the self-tapping fastener cooperates with the sheet metal thread to achieve connection, and has the beneficial effects brought by the above-mentioned self-tapping fastener.

[0041] 10. Option 10 and its preferred embodiment further include a gasket, which is clamped between the sheet metal and the driving part to achieve installation of the gasket. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0043] Figure 1 It is a front view of the self-tapping fastener in Example 1;

[0044] Figure 2 Schematic diagram of the attacking portion in Example 1;

[0045] Figure 3 This is a schematic diagram of the threads of the functional portion in Example 1;

[0046] Figure 4 Schematic diagram of the connection components in Example 2;

[0047] Figure 5 This is a schematic diagram of the cooperation between the tail and the sheet metal in the second embodiment;

[0048] Figure 6 Schematic diagram of the cooperation between the punching part and the sheet metal in the second embodiment;

[0049] Figure 7 Schematic diagram of the cooperation between the stretching portion and the sheet metal in the second embodiment;

[0050] Figure 8 Schematic diagram of the coordination between the avoidance portion, the finishing portion and the sheet metal in the second embodiment;

[0051] Description of main reference numerals:

[0052] 1 driving part; 2 threaded part; 21 functional part; 22 striking part; 221 complete thread; 222 guide thread; 223 stable thread; 3 finishing part; 4 avoidance part; 5 stretching part; 6 drilling part; 7 tail part;

[0053] 8 sheet metal; 81 through hole; gasket 9; DETAILED DESCRIPTION

[0054] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are preferred embodiments of the present invention and should not be regarded as excluding other embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0055] In the claims, description and drawings of the present invention, unless otherwise clearly defined, the use of terms such as "first", "second" or "third" is for the purpose of distinguishing different objects rather than for describing a specific order.

[0056] In the claims, specification and the above-mentioned drawings of the present invention, unless otherwise expressly defined, directional words such as the terms "center", "transverse", "longitudinal", "horizontal", "vertical", "top", "bottom", "inside", "outside", "up", "down", "front", "back", "left", "right", "clockwise", "counterclockwise" and the like indicating directions or positional relationships are based on the directions and positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction or be constructed and operated in a specific direction, and therefore cannot be understood as limiting the specific scope of protection of the present invention.

[0057] In the claims, description and above-mentioned drawings of the present invention, unless otherwise expressly defined, the terms "fixed connection" or "fixed connection" should be understood in a broad sense, that is, any connection method without displacement relationship and relative rotation relationship between the two parties, that is, including non-detachable fixed connection, detachable fixed connection, integral connection and fixed connection through other devices or elements.

[0058] In the claims, description and drawings of the present invention, if the terms "include", "have" and their variations are used, they are intended to mean "including but not limited to".

[0059] Example 1

[0060] refer to Figure 1 A self-tapping fastener comprises a driving portion 1, a threaded portion 2, a finishing portion 3, an avoidance portion 4, a stretching portion 5, a flanging portion 6 and a tail portion 7 which are sequentially connected from top to bottom;

[0061] The driver 1 is adapted to be driven by a tool (such as a wrench, electric screwdriver, etc.) to achieve rotation of the self-tapping fastener. It can be driven externally, internally, or a combination of both. Externally, the tool engages the outer wall of the driver 1 to prevent rotation. Internally, the driver 1 is provided with an upward-facing drive slot, which prevents rotation between the tool and the slot. In this embodiment, the external drive is employed. When mounted on the sheet metal 8, the driver 1 also abuts against the gasket 9 or the sheet metal 8.

[0062] The threaded portion 2 is provided with an external thread for tapping a thread on the through hole 81 of the sheet metal 8 and cooperating with the internal thread on the through hole 81 to achieve the connection between the self-tapping fastener and the sheet metal 8. The threaded portion 2 includes a functional portion 21 and a tapping portion 22 connected from top to bottom. Figure 3 The profile of the horizontal cross section of the functional part 21 is circular, and the thread size of the functional part 21 remains unchanged. Compared with the ordinary metric thread of the same level, the thread of the functional part 21 has a smaller tooth crest angle than the ordinary metric thread, and the tooth root width, tooth root diameter, and tooth root arc are larger than the ordinary metric thread, so as to form a narrow-body arc mechanical thread specially used for magnesium and aluminum alloys.

[0063] refer to Figure 2 The outer diameter of the attacking part 22 gradually decreases from top to bottom, and it is a triangular rod thread (i.e., triangular tooth). The attacking part 22 includes a complete tooth 221, a guide tooth 222 and a smooth tooth 223 connected from top to bottom. Accordingly, the thread size gradually decreases along the arrangement order of the complete tooth 221, the guide tooth 222 and the smooth tooth 223.

[0064] refer to Figure 1 、 Figure 2 The thread size of the smooth thread 223 is smaller than the size of the through hole 81 in the sheet metal 8 before tapping. The thread size of the guide thread 222 is larger than the size of the through hole 81 in the sheet metal 8 to facilitate tapping. The thread size of the complete thread 221 is the same as the thread size of the functional part 21.

[0065] The trimming portion 3 has no threads on its surface and is roughly drum-shaped, symmetrical from top to bottom. Its horizontal cross-section is circular. The horizontal cross-section of the middle portion of the trimming portion 3 (at its maximum dimension, not necessarily in the center) is larger than that of its ends and smaller than the maximum dimension of the external thread (the thread dimension of the functional portion 21). In this embodiment, the horizontal cross-section of the middle portion of the trimming portion 3 is larger than the thread dimension of the smooth teeth 223 and smaller than the thread dimensions of the guide teeth 222, the full teeth 221, and the functional portion 21. The horizontal cross-sections of the ends of the trimming portion 3 are equal in size. The upper end of the trimming portion 3 is connected to the lower end of the smooth teeth 223, and the lower end of the trimming portion 3 is connected to the upper end of the avoidance portion 4.

[0066] The relief portion 4 has no threads on its surface and is generally rod-shaped. Its ends transition into the trimming portion 3 and the stretching portion 5 in an arc-shaped manner, and its horizontal cross-section is circular. The horizontal cross-section of the middle portion of the relief portion 4 is smaller than that of its ends, and the horizontal cross-sections at both ends are equal. The upper end of the relief portion 4 is connected to the lower end of the trimming portion 3, so the horizontal cross-section of the upper end of the relief portion 4 is equal to the horizontal cross-section of the lower end of the trimming portion 3. The lower end of the relief portion 4 is connected to the upper end of the stretching portion 5, so the horizontal cross-section of the lower end of the relief portion 4 is the same as the flat cross-section of the upper end of the stretching portion 5.

[0067] The stretching portion 5 has no threads on its surface and is roughly bowl-shaped. The outer contour of the horizontal cross-section of the stretching portion 5 is a polygon formed by a plurality of connected convex arcs, which is a triangle in this embodiment. The convex arc refers to an arc that protrudes outward from the central axis of the self-tapping fastener. The horizontal cross-section of the middle portion of the stretching portion 5 (referring to the largest dimension) is larger than the horizontal cross-sections at its ends and smaller than or equal to the horizontal cross-section of the middle portion of the trimming portion 3. The horizontal cross-section of the upper end of the stretching portion 5 is larger than the horizontal cross-section of the lower end, and the distance from the upper end of the stretching portion 5 to the middle is smaller than the distance from the lower end of the stretching portion 5 to the middle, to facilitate stretching. The lower end of the stretching portion 5 is connected to the upper end of the hole-turning portion 6, so the horizontal cross-section of the lower end of the hole-turning portion 6 is the same as the horizontal cross-section of the upper end of the hole-turning portion 6.

[0068] The folding portion 6 is rounded, and the horizontal cross-section of the folding portion 6 is a polygon formed by connecting multiple convex arcs. In this embodiment, the horizontal cross-section of the folding portion 6 is triangular and close to a complete circle. The horizontal cross-section of the middle portion of the folding portion 6 (at its maximum dimension) is larger than the horizontal cross-sections at its ends and smaller than the horizontal cross-section of the middle portion of the stretching portion 5. The horizontal cross-section of the upper end of the folding portion 6 is larger than the horizontal cross-section of the lower end. The radius of curvature of the front outer contour of the folding portion 6 is larger than the radius of curvature of the front outer contour of the stretching portion 5, that is, the folding portion 6 has a greater degree of curvature, while the stretching portion 5 has a more stable curvature.

[0069] The tail portion 7 gradually decreases in size from top to bottom and converges into a pointed tip. The horizontal cross-section of the tail portion 7 is a polygon formed by connecting multiple convex arcs. In this embodiment, the horizontal cross-section of the tail portion 7 is a triangle. Preferably, the tail portion 7 has threads to facilitate drilling. Of course, in other embodiments, the outer surface of the tail portion 7 can also be smooth.

[0070] Example 2

[0071] refer to Figure 4 A connection assembly includes a sheet metal 8 and the above-mentioned self-tapping fastener, the self-tapping fastener being threadedly matched with the sheet metal 8.

[0072] The gasket 9 is clamped between the sheet metal 8 and the driving part 1. The gasket 9 can be the sheet metal 8 or a flexible product to increase the sealing performance.

[0073] Specifically, refer to Figure 4-Figure 8Initially, the sheet metal 8 is not provided with a through hole 81. During the self-tapping process of the self-tapping fastener, the tail portion 7 first contacts the sheet metal 8 and penetrates the sheet metal 8, preparing for subsequent stretching and hole expansion. The hole-turning portion 6 squeezes and stretches the sheet metal 8, causing the hole pierced by the tail portion 7 to begin to rise, forming a bulge. The stretching portion 5 is the main end for stretching and hole expansion. It is also the area with the largest force and the largest contact (friction) area, which is used for gradual stretching and gradually expanding the hole diameter. Since a large amount of frictional heat has been generated on the surface of the hole wall after being formed by the stretching portion 5, and since the hole is greatly deformed during the stretching portion 5, the friction resistance is relatively large, and a certain amount of metal debris will also accumulate. If the frictional heat and debris are not discharged smoothly, "cold welding" will occur, affecting the quality of the hole and the subsequent self-tapping and tightening. Therefore, the avoidance portion 4 (forming an avoidance groove) is designed to accommodate chips and dissipate heat. The hole wall in this area does not contact the avoidance portion 4, reducing friction. At the same time, the debris is discharged into the groove to prevent excessive extrusion and cold welding. After stretching and reaming by the stretching section 5, the size and shape of the hole are basically in place, but the hole wall finish is still insufficient (rough). Self-tapping threads have very high requirements for hole wall roughness and aperture dimensional accuracy, especially for magnesium and aluminum alloys with poor ductility. Therefore, it is necessary to use a narrow convex ring (trimming section 3) to trim (repair and finish) the hole wall to improve dimensional accuracy and surface accuracy, and prevent adhesion abnormalities caused by insufficient hole accuracy during subsequent self-tapping and tightening processes. Among them, the lower end of the trimming section 3 to the middle of the trimming section 3 is conducive to introduction after reaming. Since the hole wall shrinks after finishing, the shrinkage and shrinkage space can be reserved from the middle of the trimming section 3 to the upper end of the trimming section 3, reducing scratches on the hole wall caused by secondary contact. During the hole trimming process, the convex ring at the most convex point in the middle of the trimming section 3 is mainly in line contact with the hole wall, which can reduce friction resistance.

[0074] The outer diameter of the stabilizing teeth 223 is smaller than the aperture. This serves as a guide and reduces runout and vibration during the tightening process. Furthermore, its smaller size allows for further heat dissipation (reducing friction) and debris removal from the self-tapping thread, preventing sticking and ensuring a smooth final tightening. The guiding teeth 222 guide the tapping, while the full-thread teeth 221 adjust the dimensions. Finally, the functional portion 21 threads into the through-hole 81, and the driving portion 1 abuts against the gasket 9 (some self-tapping fasteners also have flanges, in which case the flange abuts against the gasket 9), completing the tapping process.

[0075] Compared with the prior art, this embodiment has the following beneficial effects:

[0076] In an exemplary embodiment, a self-tapping fastener includes a driving portion 1, a threaded portion 2, a finishing portion 3, an avoidance portion 4, a stretching portion 5, a hole-turning portion 6, and a tail portion 7 connected sequentially from top to bottom;

[0077] The size of the tail 7 gradually decreases from top to bottom and converges into a pointed tip. The sharp tip penetrates into the sheet metal 8 to play a guiding role, preventing the sheet metal 8 from being stretched and thinned prematurely, especially for materials with poor ductility such as magnesium and aluminum alloy. After the tip penetrates, the deformation resistance can be reduced, and the occurrence of defects such as bursting around the hole can be effectively prevented. Bursting around the hole will affect the process of drilling and stretching.

[0078] The horizontal cross-section of the middle portion of the punching portion 6 is larger than that of its ends, and the horizontal cross-section of the upper end of the punching portion 6 is larger than that of the lower end. This allows the hole pierced by the tail portion 7 to begin to rise, forming a bulge, preparing for the actual stretching and hole expansion. The horizontal cross-section of the middle portion of the punching portion 6 is smaller than that of the middle portion of the stretching portion 5. The punching portion 6 serves as the initial punching, while the stretching portion 5 is the main stretching and hole expansion area, gradually expanding the hole to facilitate the formation of a high-quality hole.

[0079] The horizontal cross-section of the middle portion of the stretching portion 5 is larger than that of the ends, and the horizontal cross-section of the upper end of the stretching portion 5 is larger than that of the lower end. The stretching portion 5 is the primary end for stretching and hole expansion, and is also the area subject to greater force and the largest contact (friction) area. It is used for gradual stretching, gradually expanding the hole diameter, and forming the basic structure and size of the hole. The horizontal cross-section of the middle portion of the stretching portion 5 is smaller than or equal to that of the middle portion of the trimming portion 3, so that the trimming portion 3 can perform hole wall trimming.

[0080] The horizontal cross-section of the middle portion of the avoidance portion 4 is smaller than that of the two ends, which are equal in size. Since a large amount of frictional heat has already been generated on the hole wall surface after being formed by the stretching portion 5, and since the hole deforms significantly during the stretching portion 5, the frictional resistance is relatively large, which also produces a certain amount of metal debris accumulation. If the frictional heat and debris are not discharged smoothly, "cold welding" will occur, affecting the quality of the hole and subsequent self-tapping and tightening. Therefore, the avoidance portion 4 is designed (forming an avoidance groove) to accommodate chips and dissipate heat. In this area, the hole wall and the avoidance portion 4 do not contact each other, reducing friction. At the same time, the debris is discharged into the groove to prevent excessive extrusion and cold welding.

[0081] The horizontal cross-section of the middle portion of the trimming section 3 is larger than that of its ends and smaller than the maximum dimension of the external thread. The horizontal cross-sections of the ends of the trimming section 3 are equal. After stretching and expanding the hole by the stretching section 5, the hole size and shape are basically achieved, but the hole wall finish is still insufficient (rough). Self-tapping threads have very high requirements for hole wall roughness and hole diameter dimensional accuracy, especially for magnesium and aluminum alloys with poor ductility. Therefore, a narrow convex ring (trimming section 3) is required to trim (finish and finish) the hole wall to improve dimensional accuracy and surface precision, and prevent sticking caused by insufficient hole precision during subsequent self-tapping and tightening. Among them, the lower end of the trimming part 3 to the middle part of the trimming part 3 is conducive to the introduction after hole expansion, gradual stretching and gradually expanding the hole diameter, making the deformation smoother; since the hole wall shrinks after finishing, the middle part of the trimming part 3 to the upper end of the trimming part 3 can reserve shrinkage and shrinkage space, reducing the scratches on the hole wall caused by secondary contact. In the process of trimming the hole, the middle part of the trimming part 3 is mainly in line contact with the hole wall, which can reduce friction resistance.

[0082] The multi-stage variable diameter parts realize the functions of each hole forming process to form holes of high quality.

[0083] The driving portion 1 is suitable for being driven by a tool (such as a wrench, an electric screwdriver, etc.) to realize the rotation of the self-tapping fastener; the threaded portion 2 is provided with an external thread for tapping the thread and being threadedly connected to the sheet metal 8.

[0084] This self-tapping fastener can realize the connection of dissimilar materials, and is particularly suitable for the connection of magnesium and aluminum alloys with poor ductility; it does not require pre-drilling of sheet metal 8, pre-processing of threads is unnecessary, and the cost is low; it has high assembly and connection efficiency; it has little pollution to the working environment; it has high connection strength, and the thread is transformed, and has high shear strength; the thread is of good quality and good finish, and can be repeatedly disassembled and repaired, with a high yield rate, reducing the failure and scrapping of sheet metal structural parts; it has low noise, a small friction area, and generates less heat and debris, so the working noise is low.

[0085] In an exemplary embodiment, the contours of the horizontal cross sections of the trimming portion 3 and the avoidance portion 4 are circular, which is convenient for processing, and the trimming portion 3 can be easily trimmed to form a circular hole.

[0086] In an exemplary embodiment, the contours of the horizontal cross-sections of the stretching portion 5, the hole-turning portion 6, and the tail portion 7 are polygonal shapes formed by connecting a plurality of convex arcs, so that only the convex arcs at the farthest end from the center axis of the self-tapping fastener are in contact with the hole wall, thereby increasing stress and making the hole wall easier to deform (stretch, expand), while reducing friction and preventing early adhesion due to large friction resistance.

[0087] In an exemplary embodiment, the tail portion 7 has threads to facilitate drilling.

[0088] In an exemplary embodiment, the curvature radius of the front outer contour of the stretching portion 5 is smaller than the curvature radius of the front outer contour of the punching portion 6. The curvature radius of the stretching portion 5 is smaller than the curvature radius of the punching portion 6, the degree of curvature is reduced, and it is smoother, so as to facilitate the gradual downward stretching and elongation of the hole, increase the subsequent thread length, and guide the flow of material; and the punching portion 6 uses a larger degree of curvature to provide sufficient interference, so that the sheet metal 8 is squeezed and stretched.

[0089] In an exemplary embodiment, the threaded portion 2 includes a functional portion 21 and a striking portion 22 connected from top to bottom. The horizontal cross-section of the functional portion 21 is circular to ensure a stable connection; the outer diameter of the striking portion 22 gradually decreases from top to bottom, thereby gradually guiding the tapping. The striking portion 22 is a triangular rod thread, which reduces the contact area with the through hole 81 and reduces friction.

[0090] In an exemplary embodiment, the tapping portion 22 includes a complete thread 221, a guide thread 222, and a smooth thread 223 connected from top to bottom. The thread size of the smooth thread 223 is smaller than the horizontal cross-section size of the middle portion of the finishing portion 3, that is, the outer diameter of the smooth thread 223 is smaller than the aperture. On the one hand, it is used for guidance and to prevent deflection and vibration during the temperature tightening process. On the other hand, because it is smaller than the aperture, it can further dissipate heat (reduce friction) and discharge debris from the self-tapping thread, prevent the self-tapping thread from sticking, and ensure smooth final tightening. The thread size of the guide thread 222 is larger than the horizontal cross-section size of the middle portion of the finishing portion 3, that is, larger than the aperture size, to guide tapping. The thread size of the complete thread 221 is the same as the thread size of the functional portion 21, and the complete thread 221 is used for finishing.

[0091] In an exemplary embodiment, the thread of the functional part 21 has a smaller crest angle than that of an ordinary metric thread, and the thread root width, thread root diameter, and thread root arc are larger than those of an ordinary metric thread. The purpose of this design is to increase the fitting clearance between the internal and external threads to a certain extent, and to reduce the risk of scratching the internal thread, prevent abnormal tightening, and make the internal thread reusable.

[0092] In an exemplary embodiment, a connection assembly includes a sheet metal 8 and the above-mentioned self-tapping fastener, wherein the self-tapping fastener is threadedly engaged with the sheet metal 8 to achieve connection and has the beneficial effects brought by the above-mentioned self-tapping fastener.

[0093] In an exemplary embodiment, a gasket 9 is further included, and the gasket 9 is clamped between the sheet metal 8 and the driving part 1 to achieve the installation of the gasket 9.

[0094] The above description and embodiments are intended to explain the scope of protection of the present invention, but do not constitute a limitation thereto. Modifications, equivalent substitutions, or other improvements to the embodiments of the present invention or portions thereof that can be obtained by a person of ordinary skill in the art through logical analysis, reasoning, or limited experimentation based on the teachings of the present invention or the above embodiments, combined with common knowledge, ordinary technical knowledge in the field, and / or prior art, should all be included within the scope of protection of the present invention.

Claims

1. A self-tapping fastener, characterized in that: It includes a driving part, a threaded part, a trimming part, an avoidance part, a stretching part, a hole-turning part and a tail part which are connected in sequence from top to bottom; The threaded portion is provided with an external thread; The size of the horizontal cross section of the middle portion of the trimming portion is larger than the sizes of the horizontal cross sections at both ends thereof and smaller than the maximum size of the external thread, and the sizes of the horizontal cross sections at both ends of the trimming portion are equal; The size of the horizontal cross section of the middle portion of the avoidance portion is smaller than the sizes of the horizontal cross sections at both ends thereof, and the sizes of the horizontal cross sections at both ends thereof are equal; The size of the horizontal cross section of the middle portion of the stretching portion is larger than the sizes of the horizontal cross sections of the two ends thereof and is smaller than or equal to the size of the horizontal cross section of the middle portion of the trimming portion; the size of the horizontal cross section of the upper end of the stretching portion is larger than the size of the horizontal cross section of the lower end thereof; The horizontal cross-section of the middle portion of the punching portion is larger than the horizontal cross-sections of the two ends thereof and smaller than the horizontal cross-section of the middle portion of the stretching portion. The horizontal cross-section of the upper end of the punching portion is larger than the horizontal cross-section of the lower end thereof. The size of the tail gradually decreases from top to bottom and converges into a tip.

2. A self-tapping fastener according to claim 1, characterized in that: The contours of the horizontal cross sections of the trimming portion and the avoiding portion are circular.

3. The self-tapping fastener according to claim 1, wherein: The horizontal cross-sections of the stretching portion, the punching portion, and the tail portion are in the form of polygons formed by connecting a plurality of convex arcs.

4. The self-tapping fastener according to claim 1, wherein: The tail portion has threads.

5. The self-tapping fastener according to claim 1, wherein: The curvature radius of the front outer contour of the stretching portion is smaller than the curvature radius of the front outer contour of the punching portion.

6. The self-tapping fastener according to claim 1, wherein: The threaded portion includes a functional portion and an attacking portion connected from top to bottom, and the horizontal cross section of the functional portion is circular; the outer diameter of the attacking portion gradually decreases from top to bottom and is a triangular rod thread.

7. A self-tapping fastener according to claim 6, characterized in that: The striking part includes complete teeth, guide teeth and smooth teeth connected from top to bottom, the thread size of the smooth teeth is smaller than the size of the horizontal cross-section of the middle part of the finishing part, the thread size of the guide teeth is larger than the size of the horizontal cross-section of the middle part of the finishing part, and the thread size of the complete teeth is the same as the thread size of the functional part.

8. The self-tapping fastener according to claim 6, wherein: The thread crest angle of the functional portion is smaller than that of an ordinary metric thread, and the thread bottom width, thread bottom diameter and thread bottom arc are larger than those of an ordinary metric thread.

9. A connection assembly, characterized in that: It comprises a sheet metal and a self-tapping fastener according to any one of claims 1 to 8, wherein the self-tapping fastener cooperates with the sheet metal thread.

10. A connection assembly according to claim 9, characterized in that: A gasket is also included, and the gasket is clamped between the sheet metal and the driving part.

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