A hot melt self-piercing connector, a hot melt connection structure and a connection process

Abstract

The application discloses a hot-melt self-tapping connecting piece, a hot-melt connecting structure and a connecting process. The hot-melt self-tapping connecting piece comprises a screw head and a screw rod, the screw rod comprises a threaded area, the threaded area is sequentially provided with a sealing section, a retaining section and a tapping section from the screw head to the screw rod, the tapping section is configured to have a tapping thread for forming an internal thread on a connecting base material, the retaining section is configured to keep a thread cooperation state with the internal thread formed by the tapping section on the connecting base material, and the sealing section is configured to keep a thread interference cooperation state with the internal thread formed by the tapping section on the connecting base material. The application solves the problem that the traditional hot-melt self-tapping connecting piece needs to rely on a sealing glue for sealing.

Description

Technical Field

[0001] This invention relates to the field of vehicle fastening technology, and in particular to a thermofusion self-tapping connector, a thermofusion connection structure, and a connection process. Background Technology

[0002] Flow Drill Screw (FDS) is a fastening process for joining thin metal sheets. It utilizes high-speed rotation and friction to generate heat, locally softening the sheet metal and causing the connector to self-tap its internal threads and tighten, achieving efficient connections even with unilateral operation. This technology is particularly suitable for joining lightweight materials such as aluminum alloys and magnesium alloys, as well as for connecting multiple layers of dissimilar metal sheets.

[0003] However, traditional FDS connectors only provide mechanical connection functionality and lack sealing capabilities. In practical applications, to ensure the airtightness and watertightness of the connection points, it is usually necessary to apply sealant after connection. This step not only increases the complexity of the process and material costs, but also introduces long-term reliability risks such as sealant aging, cracking, and peeling, hindering the widespread application of FDS technology in scenarios with high sealing requirements. Summary of the Invention

[0004] Therefore, this invention proposes a self-sealing hot-melt self-tapping connector, a hot-melt connection structure, and a connection process that can achieve self-sealing without the need for applying sealant.

[0005] To address the aforementioned technical problems, the present invention provides the following technical solution: A thermoplastic self-tapping connector, comprising: The screw includes a head and a shank, the shank comprising a threaded section, which, from near the screw head to away from the screw head, consists of a sealing section, a retaining section, and a tapping section. The tapping section is configured with a tapping thread for forming an internal thread on the connecting base material. The retaining section is configured with a tapping thread for maintaining a threaded fit with the internal thread formed by the tapping section on the connecting base material. The sealing section is configured with a sealing thread for maintaining an interference fit with the internal thread formed by the tapping section on the connecting base material.

[0006] In some embodiments of the present invention, the envelope surface of the major diameter of the thread of the sealing section is constructed as a conical surface that gradually expands from the screw shank to the screw head, and the taper of the sealing section relative to the longitudinal axis is between 1°25′ and 1°50′.

[0007] In some embodiments of the present invention, the longitudinal length of the sealing section is greater than or equal to the thickness of the connecting base material.

[0008] In some embodiments of the present invention, the longitudinal length of the sealing section is 150%-200% of the thickness of the connecting base material.

[0009] In some embodiments of the present invention, the threaded area and the screw head are transitioned by a smooth section, which is constructed as a conical surface that gradually tapers from the screw shank to the screw head, and the taper of the smooth section relative to the longitudinal axis is between 13° and 16°.

[0010] In some embodiments of the present invention, the screw head has an annular recessed area formed in the region facing the screw shank, the annular recessed area extending smoothly in an arc from the end face of the screw head to the smooth section.

[0011] In some embodiments of the present invention, the screw head includes a flange section and a drive section, the flange section being close to the screw shank and having an outer diameter 1.5-2 times that of the screw shank, and the drive section being configured to mate with a fastening tool.

[0012] In some embodiments of the present invention, the screw shank further includes a drilled portion, which is configured as a rod-shaped body with a conical end, and the drilled portion smoothly transitions to the tapping section of the screw thread area.

[0013] In some embodiments of the present invention, the pitch of the sealing section and the retaining section are the same.

[0014] The present invention also provides a thermoplastic self-tapping connector, comprising: The screw includes a head and a shank, the shank comprising a threaded area, which is divided into a first sealing section, a retaining section, a second sealing section, and a tapping section along its length from near the screw head to away from the screw head. The tapping section is configured with a tapping thread for forming an internal thread on the connecting base material. The retaining section is configured with a tapping thread for maintaining a threaded fit with the internal thread formed by the tapping section on the connecting base material. The first and second sealing sections are configured with sealing threads for maintaining an interference fit with the internal thread formed by the tapping section on the connecting base material.

[0015] In some embodiments of the present invention, the envelope surface where the major diameter of the threads of the first sealing section and the second sealing section are located is constructed as a conical surface that gradually expands from the screw shank to the screw head, and the taper of the first sealing section and the second sealing section relative to the longitudinal axis is between 1°25′ and 1°50′.

[0016] The present invention also provides a thermoplastic self-tapping connection structure, including a connecting base material and a thermoplastic self-tapping connector as described in any of the above embodiments.

[0017] In some embodiments of the present invention, the connecting base material includes a first plate and a second plate stacked together, and the hot-melt self-tapping connector passes through the first plate and the second plate in sequence to form a threaded connection; in the connected state, the sealing section is interference-fitted with at least a portion of the internal threads of the connecting base material to form a sealing ring.

[0018] The present invention also provides a connection process for the hot-melt self-tapping connector according to any of the above embodiments, comprising the following steps: The connecting base material is fixedly connected to the clamp, the area to be connected is pressed and the flatness is less than the first threshold. The control fastening tool picks up the hot melt self-tapping connector and aligns the end of the screw rod of the hot melt self-tapping connector with the preset connection point. The control fastening tool drives the hot melt self-tapping connector to rotate and feed at 3000rpm-8000rpm. The hot melt self-tapping connector generates heat through friction with the surface of the connecting base material, causing the metal in the contact area to soften. The compressed connecting base material flows to the bottom, eventually forming a bushing structure. The control fastening tool drives the hot melt self-tapping connector to rotate continuously at 600rpm–1000rpm. The tapping section of the hot melt self-tapping connector contacts the inner wall of the bushing of the connecting base material, and forms a matching internal thread on the connecting base material by rolling. When the entire bushing area of ​​the connecting base material forms an internal thread, the fastening tool is controlled to drive the hot melt self-tapping connector to rotate continuously at 400rpm–800rpm. The retaining section of the hot melt self-tapping connector is threaded with the connecting base material; the sealing section of the hot melt self-tapping connector is interference-fitted with the internal thread of the connecting base material to form a sealing ring. Once the clamping torque meets the set torque requirement, the fastening tool is stopped.

[0019] The present invention also provides a vehicle including the above-described heat-fusion connection structure.

[0020] The technical solution of the present invention has the following technical effects compared with the prior art: The self-sealing connector provided by this invention achieves a self-sealing function at the connection interface by setting a sealing section in the threaded area of ​​the connector that maintains an interference fit with the connecting base material. This interference fit directly forms a sealing ring within the threaded pair. Compared to traditional self-sealing connectors that rely on applying sealant, this invention completely eliminates the sealant application process, simplifying the process, reducing costs, and eliminating long-term reliability issues such as sealant aging, cracking, and peeling. Attached Figure Description

[0021] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, which will help to understand the purpose and advantages of the present invention, wherein: Figure 1 This is a schematic diagram of the structure of the hot-melt self-tapping connector according to Embodiment 1 of the present invention; Figure 2 This is a cross-sectional view of the hot-melt self-tapping connector according to Embodiment 1 of the present invention; Figure 3 This is a partially enlarged view of the sealing section in the hot-melt self-tapping connector of Embodiment 1 of the present invention; Figure 4 The results of tensile and shear tests on the hot-melt self-tapping connector of Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the structure of the hot-melt self-tapping connector according to Embodiment 2 of the present invention; Figure 6 This is a schematic diagram of the heat fusion connection structure according to Embodiment 3 of the present invention; Figure 7 This is a schematic diagram of some steps in the connection process of the hot-melt self-tapping connector in Embodiment 4 of the present invention. Detailed Implementation

[0022] 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 a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0024] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0025] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; 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; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0026] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0027] Example 1 like Figure 1 As shown, this embodiment provides a thermofusion self-tapping connector. This thermofusion self-tapping connector has an overall slender, rotating structure, integrally formed from metal material, preferably high-strength steel or alloy steel, such as SCM435 or equivalent strength alloy steel. The surface is coated with a zinc-aluminum coating to ensure sufficient strength, hardness, and wear resistance under high-speed rotation and frictional heat conditions. The thermofusion self-tapping connector includes a screw head 100 and a screw shank 200. The screw shank 200 extends downwards along the longitudinal axis from the lower end face of the screw head 100. The overall length of the screw shank 200 is determined according to actual connection requirements, typically 5 to 15 times the diameter of the screw shank 200.

[0028] The screw shank 200 includes a threaded section, which is divided sequentially into a sealing section 210, a retaining section 220, and a tapping section 230 along the direction from near the screw head 100 to far away from the screw head 100. In other words, viewed from the screw head 100 towards the end of the screw shank 200, the sections are, in sequence, the sealing section 210, the retaining section 220, and the tapping section 230. The tapping section 230 is located at the lowermost end of the threaded section (i.e., the end furthest from the screw head 100), the retaining section 220 is located between the tapping section 230 and the sealing section 210, and the sealing section 210 is located between the retaining section 220 and the screw head 100. These three sections of the threaded section are arranged continuously along the longitudinal axis, with smooth transitions between adjacent sections, without obvious steps or discontinuities.

[0029] The tapping section 230 is configured with a tapping thread. This tapping thread has a complete thread profile and a sharp crest, and is used to form a matching internal thread on the connecting base material 600 by rolling. The outer diameter (i.e., the major diameter) of the thread of the tapping section 230 is basically the same as the outer diameter of the thread of the retaining section 220, but the crest of the thread of the tapping section 230 may be provided with a slightly sharp edge to facilitate cutting into the inner wall of the bushing of the connecting base material 600 during the initial tapping stage.

[0030] The retaining section 220 is configured with a connecting thread, which is continuous with the tapping thread of the tapping section 230 and has the same pitch and thread profile. This thread is used to maintain a normal thread fit with the internal thread on the connecting base material 600 formed by the tapping section 230. A "normal thread fit" means that the thread of the retaining section 220 and the internal thread of the connecting base material 600 are in a clearance fit or transition fit. That is, there is a normal thread pair clearance between the thread teeth of the retaining section 220 and the internal thread teeth of the connecting base material 600, ensuring low frictional resistance during screwing in and out of the retaining section 220, allowing the connector to smoothly screw into the connecting base material 600.

[0031] The sealing section 210 is configured with a sealing thread that is continuous with the thread of the retaining section 220 and has the same pitch and thread profile. However, the thread profile dimension of the sealing section 210 is larger than that of the retaining section 220. Specifically, the pitch diameter and / or major diameter of the thread of the sealing section 210 is larger than the corresponding dimension of the retaining section 220. The sealing section 210 is used to maintain an interference fit with the internal thread of the connecting base material 600 formed by the tapping section 230. The so-called "thread interference fit" means that there is an interference in the radial direction between the thread of the sealing section 210 and the internal thread of the connecting base material 600, that is, the pitch diameter of the thread of the sealing section 210 is larger than the pitch diameter of the internal thread of the connecting base material 600. When the sealing section 210 is screwed into the internal thread of the connecting base material 600, the thread of the sealing section 210 is subjected to radial compression, while the internal thread of the connecting base material 600 is subjected to radial expansion, generating a stable contact pressure between the two.

[0032] In an interference fit configuration, the thread flank of the sealing section 210 and the internal thread flank of the connecting base material 600 form a tight contact along the entire helical engagement length. Due to the inherent surface roughness and microscopic unevenness of the thread flank, under contact pressure, the microscopic protrusions on the thread flank surface undergo elastoplastic deformation, increasing the actual contact area and ultimately forming a continuously extending sealing ring at the engagement interface of the threaded pair. This sealing ring macroscopically exhibits impermeability to both liquid and gaseous media, thus providing a sealing function.

[0033] It should be noted that the thread interference of the sealing section 210 needs to be determined comprehensively based on factors such as the material and thickness of the connecting base material 600, the sealing requirement level, and the size of the connecting parts. If the interference is too small, the contact pressure will be insufficient, and an effective sealing ring cannot be formed; if the interference is too large, the screwing resistance will increase sharply, which may cause plastic yielding or damage to the internal thread of the connecting base material 600, and also place excessive demands on the torque output capacity of the fastening tool. After extensive experimental verification, the interference of the thread pitch diameter of the sealing section 210 relative to the internal thread pitch diameter of the connecting base material 600 is preferably 0.02mm to 0.08mm. Within this range, a reliable sealing effect can be obtained without causing unacceptable damage to the internal thread.

[0034] like Figure 3 As shown, the envelope surface of the major diameter of the thread in the sealing section 210 is a conical surface. Specifically, the diameter of the sealing section 210 gradually increases from the end near the retaining section 220 to the end near the screw head 100, that is, the sealing section 210 is generally truncated cone in shape, with its small end facing the end of the screw shank 200 (i.e., near the retaining section 220) and its large end facing the screw head 100.

[0035] The taper of the conical surface of the sealing section 210 relative to the longitudinal axis of the thermoplastic self-tapping connector is set between 1°25′ and 1°50′. This taper range was determined through extensive theoretical analysis and experimental verification. From the perspective of the sealing mechanism, the interference fit between the sealing section 210 and the internal thread of the connecting base material 600 needs to generate sufficient contact pressure to allow the microscopic protrusions on the thread flank surface to undergo sufficient elastoplastic deformation, forming a continuous sealing ring. The magnitude of the contact pressure is positively correlated with the interference amount. By setting the sealing section 210 to have the aforementioned specific taper range, the interference amount between the sealing section 210 and the internal thread of the connecting base material 600 is gradually distributed along the axial direction: at the end near the retaining section 220 (small end), the interference amount is small or even zero, allowing the sealing section 210 to smoothly enter the internal thread of the connecting base material 600 without generating excessive initial resistance; as the sealing section 210 gradually screws in, the interference amount gradually increases along the axial direction, reaching its maximum value near the screw head 100 (large end). From the perspective of screwing resistance, if the taper is too large (e.g., exceeding 2°), the rate of change of the interference fit along the axial direction is too large. This causes the interference fit of the sealing section 210 to increase rapidly within a very short axial stroke, resulting in a sharp increase in screwing resistance. This not only places excessive demands on the torque output capability of the fastening tool but may also generate excessive circumferential stress on the internal thread of the connecting base material 600, leading to plastic expansion or even cracking of the internal thread. If the taper is too small (e.g., less than 1°), the rate of change of the interference fit along the axial direction is too small. The sealing section 210 needs a very long axial length to accumulate sufficient interference fit to form an effective seal. This not only increases the total length of the connector and material consumption but may also result in insufficient sealing area of ​​the sealing section 210, failing to cover the entire thickness range of the connecting base material 600. Experimental verification shows that when the taper is within the range of 1°25′ to 1°50′, the sealing section 210 can establish sufficient interference fit within a moderate axial length, while the screwing resistance is controlled within an acceptable range, resulting in optimal overall performance.

[0036] like Figure 1 As shown, the length of the sealing section 210 along the longitudinal axis of the heat-fused self-tapping connector is defined as L, and the thickness of the connecting base material 600 is defined as T (the connecting base material 600 may include a single layer of sheet material or multiple layers of stacked sheet material, the thickness of which is the sum of the thicknesses of all sheet material). In this embodiment, the longitudinal length L of the sealing section 210 is not less than the thickness T of the connecting base material 600, i.e., L≥T. Preferably, the longitudinal length L of the sealing section 210 is set to 150% to 200% of the thickness T of the connecting base material 600, i.e., 1.5T ≤ L ≤ 2.0T.

[0037] When the longitudinal length L of the sealing section 210 is at least equal to the thickness T of the connecting base material 600, the sealing section 210 can essentially cover the entire axial range of the internal thread of the connecting base material 600, ensuring an interference fit between the internal thread of the connecting base material 600 and the sealing section 210 in all thickness directions. However, during the actual heat-sealing process, the connecting base material 600 undergoes compressive deformation under the clamping force of the screw head 100, resulting in an axial length actually involved in the threaded fit exceeding the thickness of the plate. Setting the longitudinal length of the sealing section 210 to 1.5 to 2 times the thickness of the connecting base material 600 ensures that the sealing section 210 can completely cover the entire thickness range of the bushing formed by the connecting base material 600, guaranteeing the reliability of the seal. At this point, the sealing ring exists continuously in the entire thickness direction of the connecting base material 600, completely blocking the leakage path.

[0038] like Figure 2 As shown, the threaded section and the screw head 100 are connected by a smooth section 240. The smooth section 240 is a smooth conical surface without threads. Its construction involves a conical surface that gradually tapers from the screw shank 200 towards the screw head 100. Specifically, the smooth section 240 has a larger outer diameter at the end near the threaded section (lower end) and a smaller outer diameter at the end near the screw head 100 (upper end), forming an overall truncated cone shape. The larger end faces the screw shank 200, and the smaller end faces the screw head 100. The taper of the smooth section 240 relative to the longitudinal axis of the thermoplastic self-tapping connector is set between 13° and 16°.

[0039] Because thermoplastic self-tapping fasteners bear complex loads during use, stress concentration can easily occur in the connection area between the screw head 100 and the screw shank 200 due to the abrupt change in geometry. By incorporating a smooth conical section 240 with a taper between 13° and 16°, the geometric change in this area becomes gentler, allowing for a smooth transition of stress flow lines. This effectively disperses stress and significantly improves the fatigue strength and load-bearing capacity of the fastener. Simultaneously, the smooth conical surface of the smooth section 240 does not contact or interfere with the internal threads of the connecting base material 600 during the fastener's insertion, ensuring smooth screwing into place.

[0040] like Figure 2 As shown, the screw head 100 has an annular recessed area 100a formed in the region facing the screw shank 200 (i.e., the lower end face region of the screw head 100). The annular recessed area 100a extends smoothly in an arc shape from the lower end face of the screw head 100 inward (i.e., inward towards the inside of the screw head 100) to a smooth section 240.

[0041] More specifically, the annular recessed region 100a has a concave arc-shaped cross-sectional profile. That is, starting from the middle region of the lower end face of the screw head 100, the annular recessed region 100a extends into the interior of the screw head 100 in the form of a concave arc surface. The inner end (i.e., the radially inner end) of the annular recessed region 100a is smoothly connected to the upper end of the smooth section 240, so that the entire transition region from the smooth section 240 to the lower end face of the screw head 100 is a smooth arc-shaped surface.

[0042] The depth of the annular recess 100a (i.e., the axial distance from the lower end face of the screw head 100 to the innermost point of the annular recess 100a) is preferably 0.5 mm to 2.0 mm, and the specific value is determined according to the size of the connector and the material of the connecting base 600. The radial width of the annular recess 100a is preferably 5% to 15% of the diameter of the screw head 100.

[0043] When the hot-melt joining process enters the final tightening stage, the annular recessed area 100a acts as a buffer zone for stress and deformation when the middle area of ​​the screw head 100 is subjected to the downward axial clamping force of the fastening tool. At this time, a small amount of elastic bending deformation occurs in the area outside the annular recessed area 100a. After the connection is completed and the fastening tool is removed, this elastic deformation is converted into a continuous rebound force (axial residual stress). This dynamically compensates for the preload loss that may occur in the connecting base material 600 under hot-melt cooling shrinkage, material creep, or vibration environments, thereby significantly improving the relaxation resistance and fatigue life of the connection structure. Furthermore, since hot-melt joining is usually used for stacking multi-layer sheet metal, the surface of the connecting base material 600 often has micro-irregularities due to the influence of stamping accuracy and stacking gaps. The outer edge deforms as the clamping force increases, closely conforming to the actual surface contour of the base material, thus improving the connection stiffness. At the same time, after the connector is screwed into place, the annular recessed area 100a forms an annular space (i.e., cavity) between itself and the surface of the connecting base material 600. This space can accommodate a small amount of metal chips, oxide particles or other impurities that may be generated during the screwing of the connector, ensuring that the lower end face of the screw head 100 can fit tightly against the surface of the connecting base material 600.

[0044] like Figure 1 As shown, the screw head 100 includes a flange section 110 and a drive section 120. The flange section 110 is located near the screw shank 200, and the drive section 120 is located on the side of the flange section 110 away from the screw shank 200. The flange section 110 and the drive section 120 are integrally formed by forging or cold heading processes.

[0045] The flange section 110 has a disc-shaped structure, and its outer diameter is 1.5 to 2.0 times the diameter of the screw shank 200. The lower end face of the flange section 110 is an annular plane (with an annular recessed area 100a in the central region). After the connector is screwed into place, the lower end face of the flange section 110 fits against the surface of the connecting base material 600, forming a surface contact. After the connector is screwed into place, the axial preload is transmitted to the surface of the connecting base material 600 through the lower end face of the flange section 110. Setting the outer diameter of the flange section 110 to more than 1.5 times the diameter of the screw shank 200 ensures a sufficiently large bearing area, controls the compressive stress below the allowable contact stress of the connecting base material 600, and avoids damage to the surface of the connecting base material 600.

[0046] The drive section 120 is configured to mate with a fastening tool. The drive section 120 can have various shapes, including but not limited to standard drive shapes such as external hexagonal, internal hexagonal, star-shaped, slotted, and cross-shaped, or it can be designed as a non-standard shape according to the requirements of a specific fastening tool. The outer circumferential surface or inner bore surface of the drive section 120 is provided with a force-bearing surface that matches the working head of the fastening tool, used to receive the torque and axial force applied by the fastening tool during assembly, driving the entire connector to rotate and feed. The axial height of the drive section 120 needs to be sufficiently high to ensure that the fastening tool can stably clamp and drive the connector, preventing slippage or disengagement during high-speed rotation. The axial height of the drive section 120 is preferably 0.5 to 1.0 times the diameter of the screw shank 200.

[0047] like Figure 1 As shown, the screw shank 200 also includes a drilled portion 250, which is located at the end of the screw shank 200 (that is, the side of the tapping section 230 away from the screw head 100). The drilled portion 250 is constructed as a rod-shaped body with a conical end, and its overall shape is similar to the tip of a drill bit.

[0048] Specifically, the end of the drilled portion 250 is a conical tip, the apex angle of which is preferably 30° to 60°. Behind the conical tip (i.e., towards the screw head 100), the diameter of the drilled portion 250 gradually increases until it smoothly transitions into the starting end of the tapping section 230. The transition between the drilled portion 250 and the tapping section 230 in the threaded area is smooth; that is, the outer diameter of the upper end of the drilled portion 250 (the end closest to the tapping section 230) is substantially the same as the minor or pitch diameter of the thread of the tapping section 230, and the connection area between them is stepless and edgeless, forming a continuous and smooth geometric profile.

[0049] The drilling portion 250 performs the initial penetration function during the thermal self-piercing tapping connection process. At the initial stage of the connection process, the thermal self-piercing tapping connector rotates at high speed and advances axially driven by the fastening tool, and the conical end of the drilling portion 250 first comes into contact with the surface of the connected base material 600. Under the combined action of frictional heat generated by high-speed rotation and axial pressure, the temperature of the area on the surface of the connected base material 600 that is in contact with the drilling portion 250 rises rapidly, and the metal material softens. The conical end of the drilling portion 250 pierces into the softened metal under the action of axial force to form an initial perforation. As the connector continues to rotate and advance, the conical surface of the drilling portion 250 gradually expands the diameter of the perforation until the diameter of the perforation is large enough to allow the tapping section 230 to enter.

[0050] In the watertight test (IPX7 grade), the specific procedure is: place the tooling in a 1m water column for 30 minutes, and the tooling is qualified if there is no water inside it after being taken out. After testing, no water seepage is observed at the connection points of the tooling using the above-mentioned thermal self-piercing tapping connector.

[0051] Meanwhile, as shown in Figure 4 , the tensile and shear test results of the thermal self-piercing tapping connector of this embodiment show that the average breaking load is only about 3% lower than that of the standard FDS, which is still within the safety margin range.

[0052] Embodiment 2 This embodiment provides another structure of the thermal self-piercing tapping connector. As shown in Figure 5 , the thermal self-piercing tapping connector includes a screw head 100 and a screw shank 200, and the screw shank 200 includes a threaded zone. The difference from the threaded zone in Embodiment 1 is that the threaded zone in this embodiment is composed of four sections.

[0053] Specifically, the threaded zone is sequentially divided into a first sealing section 210a, a retaining section 220, a second sealing section 210b, and a tapping section 230 along the direction from approaching the screw head 100 to moving away from the screw head 100. In other words, when viewed from the end of the screw shank 200 toward the screw head 100, the order is the tapping section 230, the second sealing section 210b, the retaining section 220, and the first sealing section 210a. The tapping section 230 is located at the lowermost end of the threaded zone, the second sealing section 210b is located between the tapping section 230 and the retaining section 220, the retaining section 220 is located between the second sealing section 210b and the first sealing section 210a, and the first sealing section 210a is located between the retaining section 220 and the screw head 100.

[0054] The tapping section 230 is configured with tapping threads to form internal threads on the connecting base material 600. The retaining section 220 is configured to maintain a normal thread fit with the internal threads formed by the tapping section 230 on the connecting base material 600. The first sealing section 210a and the second sealing section 210b are respectively configured to maintain an interference fit with the internal threads formed by the tapping section 230 on the connecting base material 600.

[0055] The outer contours of both the first sealing section 210a and the second sealing section 210b are constructed as conical surfaces that gradually widen from the screw shank 200 towards the screw head 100; that is, both are truncated cones, with the smaller end facing the end of the screw shank 200 and the larger end facing the screw head 100. The taper of both the first sealing section 210a and the second sealing section 210b relative to the longitudinal axis is between 1°25′ and 1°50′.

[0056] By setting up a dual sealing structure with a first sealing section 210a and a second sealing section 210b, two independent sealing rings are formed, achieving a redundant sealing design and significantly improving sealing reliability and fault tolerance. This is particularly suitable for connections where the connecting base material 600 has three layers or a large thickness. In the connected state, the first sealing section 210a and the second sealing section 210b each form two independent interference fit areas with the internal threads of the connecting base material 600, i.e., two independent sealing rings. These two sealing rings are separated axially by a retaining section 220 and operate independently. Even if the sealing performance of one sealing ring deteriorates or fails for some reason, the other sealing ring can still function independently, maintaining the overall sealing function.

[0057] Example 3 This embodiment provides a thermoplastic self-tapping connection structure. For example... Figure 6 As shown, the thermoplastic self-tapping connection structure includes a connecting base material 600 and a thermoplastic self-tapping connector as described in any of the aforementioned embodiments. The connecting base material 600 and the thermoplastic self-tapping connector are fixed together by a threaded connection, forming a connection structure that integrates load-bearing and sealing.

[0058] The connecting base material 600 includes a first plate 610 and a second plate 620 stacked together. The first plate 610 and the second plate 620 can be metal plates of the same material, such as both being aluminum alloy plates, both being magnesium alloy plates, or both being steel plates; they can also be metal plates of different materials, for example, the first plate 610 is an aluminum alloy plate and the second plate 620 is a steel plate, or the first plate 610 is a magnesium alloy plate and the second plate 620 is an aluminum alloy plate. The first plate 610 and the second plate 620 can be in a tightly fitted state, or there can be an intermediate layer, which can be an adhesive layer, a sealing layer, or other functional layer. During the thermosetting self-tapping connection process, the screw shank 200 of the thermosetting self-tapping connector passes sequentially through the first plate 610 and the second plate 620, forming an internal thread on the connecting base material 600 through the thermosetting self-tapping process, and forming a threaded connection with the connector. The length and taper parameters of the sealing area of ​​the hot melt self-tapping connector can be flexibly adjusted according to different application scenarios, and it is suitable for a variety of typical body structures such as 1.0+1.2mm steel-aluminum laminate and 2.0+1.5mm thick plate combination.

[0059] In the connected state, the threaded connection relationship between the hot-melt self-tapping connector and the connecting base material 600 is as follows: the tapping section 230 has completed its tapping function and formed an internal thread on the connecting base material 600; the retaining section 220 maintains a normal thread fit with the internal thread of the connecting base material 600, providing the main load-bearing and connection functions; the sealing section 210 (or the first sealing section 210a and the second sealing section 210b) is interference-fitted with the internal thread of the connecting base material 600, forming a sealing ring at the meshing interface of the threaded pair.

[0060] A sealing ring is formed between the threads of the sealing section 210 and the internal threads of the connecting base material 600. Under the action of the interference fit, radial contact pressure is generated between the thread sides of the sealing section 210 and the internal thread sides of the connecting base material 600. The contact pressure causes the micro-protrusions on the two contact surfaces to undergo elastoplastic deformation, increasing the actual contact area and ultimately forming a continuous, gapless contact interface. This sealing ring extends from one end of the sealing section 210 to the other along the helical path of the threads, macroscopically exhibiting impermeability to liquid and gaseous media.

[0061] During the thermoforming self-tapping process, the plate 610 (i.e., the first plate 610) closest to the screw head 100 is tightly fitted to the lower end face of the flange section 110 under the clamping force of the flange section 110 of the screw head 100. Simultaneously, the metal material squeezed and flowing to the bottom during the thermoforming self-tapping process forms a bushing structure on the back of the second plate 620. This bushing structure wraps around the outer periphery of the threaded portion of the connector, increasing the length and load-bearing area of ​​the threaded connection, and improving the connection strength and fatigue resistance.

[0062] The hot-melt self-tapping connection structure of this embodiment is particularly suitable for applications with high sealing requirements, such as battery pack enclosure connections in electric vehicles, aluminum alloy sheet connections in vehicle body structures, and cooling system piping connections in hybrid vehicles. The seal is formed directly within the threaded pair through the interference fit between the sealing section 210 and the internal thread, eliminating the need to apply sealant or use additional gaskets between the connector head and the surface of the connecting base material 600. This simplifies the assembly process of the connection structure and avoids long-term reliability issues caused by sealant aging or gasket failure.

[0063] Example 4 This embodiment provides a connection process for a thermoplastic self-tapping connector. This connection process is used to connect the thermoplastic self-tapping connector described in Embodiment 1 to the connecting base material 600. The connection process includes the following steps: Step S1: Secure the connecting base material 600 to the fixture, pressing the area to be connected and ensuring the flatness is less than a first threshold. The first threshold is determined based on the material and thickness of the connecting base material 600. For aluminum alloy sheets, the first threshold is typically set to 0.1 mm; for steel sheets, the first threshold is typically set to 0.2 mm to 0.3 mm. The fixture can be a pneumatic fixture, a hydraulic fixture, or a mechanical quick clamp. The clamping force of the fixture needs to be large enough to overcome the axial reaction force and torque generated during the connection process, preventing the connecting base material 600 from moving or vibrating during processing.

[0064] Step S2: Control the fastening tool to pick up the thermoplastic self-tapping connector and align the end of the screw shank 200 (i.e., the conical tip of the drilled portion 250) of the thermoplastic self-tapping connector with the preset connection point. The fastening tool can be an automatic tightening gun, an electric screwdriver, or a robotic tightening system, with a drive head at its front end adapted to the connector drive section 120. When picking up the connector, the drive head of the fastening tool inserts into or fits onto the drive section 120, holding the connector on the fastening tool by means of vacuum adsorption, magnetic adsorption, or mechanical clamping.

[0065] Step S3: Control the fastening tool to drive the thermoplastic self-tapping connector to rotate at a speed of 3000 rpm to 8000 rpm. In this step, the drilled portion 250 of the thermoplastic self-tapping connector first contacts the surface of the connecting base material 600. Under the combined action of high-speed rotation and axial feed, intense friction is generated between the drilled portion 250 and the surface of the connecting base material 600. The frictional work is converted into heat, causing the metal temperature in the contact area to rise rapidly to near or reach its softening point.

[0066] For the aluminum alloy connecting base material 600, its softening temperature is approximately 300°C to 400°C. At a rotation speed of 3000 rpm to 4000 rpm, the contact area typically reaches this temperature range within 1 to 3 seconds. After the metal softens, its yield strength decreases significantly. Under the action of axial force, the drilled portion 250 penetrates the softened metal, forming an initial perforation. As the connector continues to rotate and feed, the compressed connecting base material 600 flows towards the bottom (i.e., the back side of the second plate 620), ultimately forming an annular bushing structure on the back side of the second plate 620. This bushing structure provides sufficient material volume for subsequent internal thread forming, ensuring that the internal thread has sufficient tooth height and strength.

[0067] The final choice of rotation speed depends on the material and thickness of the connecting base material 600. For softer aluminum alloy sheets, a lower rotation speed (e.g., 3000 rpm to 4000 rpm) can be selected; for harder steel sheets or thicker sheets, a higher rotation speed (e.g., 7000 rpm to 8000 rpm) is required to generate sufficient heat. If the rotation speed is too low, the heat generated by friction will be insufficient, the metal will not soften sufficiently, drilling resistance will be high, and it may lead to breakage of the connector or overload of the fastening tool; if the rotation speed is too high, excessive heat generated by friction may cause localized overheating or even melting of the connecting base material 600, affecting the connection quality.

[0068] Step S4: At the moment of penetrating the connecting base material 600, the conical tip of the drilled part 250 passes through the lower surface of the first plate 610 and the second plate 620, and the axial resistance suddenly decreases. The pressure sensor on the fastening tool detects this sudden drop in clamping force, and the control system determines that it has entered the tapping stage.

[0069] If a sudden drop in clamping force is detected, the fastening tool is controlled to continuously rotate the hot-melt self-tapping connector at a speed of 600 rpm to 1000 rpm for feeding.

[0070] During the tapping stage, the tapping section 230 of the thermoplastic self-tapping connector contacts the inner wall of the bushing of the connecting base material 600. Since the material of the bushing inner wall has softened in step S3, the tapping section 230 forms a matching internal thread on the connecting base material 600 through roll forming. Roll forming does not cut the fibrous structure of the metal, and the formed internal thread has higher strength, better surface quality, and better fatigue resistance.

[0071] The tapping speed is reduced to 600 rpm to 1000 rpm because the tapping process requires more precise control and more stable machining conditions. Excessive speed may lead to a decrease in the quality of internal thread forming, such as incomplete thread profile, rough thread surface, or tearing defects.

[0072] Step S5: After determining that the tapping section 230 has completed the connection of the entire bushing area of ​​the base material 600 to form an internal thread through the detection of the position sensor and pressure sensor, control the fastening tool to drive the hot melt self-tapping connector to rotate continuously at a speed of 400 rpm to 800 rpm for feeding.

[0073] In this step, the retaining segment 220 first enters the internal thread area of ​​the connecting base material 600, forming a normal threaded fit with the internal thread. The thread of the retaining segment 220 and the internal thread have a clearance fit or transition fit, resulting in low frictional resistance, allowing the connector to continue screwing in smoothly. Subsequently, the sealing segment 210 enters the internal thread area. Since the thread profile of the sealing segment 210 is larger than the corresponding size of the internal thread, an interference fit begins to form between the sealing segment 210 and the internal thread. As the sealing segment 210 continues to screw in, the interference gradually increases, and the contact pressure between the thread flanks gradually builds up. Under the action of the contact pressure, the microscopic protrusions on the thread flank surface undergo elastoplastic deformation, increasing the actual contact area, and ultimately forming a continuous sealing ring at the meshing interface between the sealing segment 210 and the internal thread. As the sealing segment 210 continues to screw in, the sealing ring gradually expands axially until the sealing segment 210 completely enters the internal thread area, and the sealing ring covers the entire axial length of the sealing segment 210.

[0074] In this step, the rotational speed is further reduced to 400 rpm to 800 rpm to ensure that the sealing section 210 does not generate excessive frictional heat and wear due to excessive speed when entering the interference fit. The contact pressure generated by the interference fit is already relatively large. If it is screwed in at high speed, the frictional heat will increase sharply, which may lead to the destruction of the lubricating film on the thread surface, surface scratches, or fretting wear, affecting the quality and long-term reliability of the sealing ring.

[0075] Step S6: Control the fastening tool to drive the hot melt self-tapping connector to rotate continuously at a speed of 400 rpm to 800 rpm until the clamping torque meets the set torque requirement, then control the fastening tool to stop.

[0076] The set torque is predetermined based on the size, material, and connection requirements of the connector. When the thermoplastic self-tapping connector is screwed into place, the lower end face of the flange section 110 of the screw head 100 is in contact with the surface of the connecting base material 600. As it continues to screw in, the torque increases sharply. The torque sensor on the fastening tool monitors the torque value in real time. When the torque value reaches the set torque, the control system sends a stop signal, and the fastening tool stops rotating and feeding, completing the connection operation.

[0077] Example 5 This embodiment provides a vehicle including the hot-melt self-tapping connection structure described in Embodiment 3 above. This vehicle can be a conventional fuel-powered vehicle, an electric vehicle, or a hybrid vehicle.

[0078] The hot-melt self-tapping connection structure is specifically applied to various connection scenarios in vehicles. For example, in one embodiment, a 1.8mm thick high-strength steel shock absorber tower bracket and a 2.5mm thick die-cast aluminum alloy chassis are connected by hot-melt drilling using the hot-melt self-tapping connectors described in Embodiments 1 or 2 above, to achieve a waterproof and sealed connection.

[0079] In another embodiment, when manufacturing the battery pack shell of a pure electric SUV, 1.5mm thick DC01 low carbon steel and 2.0mm thick 6061-T6 aluminum alloy are connected by hot-melt drilling using the hot-melt self-tapping connectors described in Embodiment 1 or 2 above, so as to achieve a waterproof and sealed connection.

[0080] The hot-melt self-tapping connection structure of the present invention forms a sealing ring inside the threaded pair through the interference fit between the sealing section 210 and the connecting base material 600. The sealing requirements can be met without additional glue, eliminating the risk of sealant aging and failure, and improving safety and reliability in long-term use.

[0081] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A thermoplastic self-tapping connector, characterized in that, include: The screw includes a head and a shank, the shank comprising a threaded section, which, from near the screw head to away from the screw head, consists of a sealing section, a retaining section, and a tapping section. The tapping section is configured with a tapping thread for forming an internal thread on the connecting base material. The retaining section is configured with a connecting thread for maintaining a threaded fit with the internal thread formed by the tapping section on the connecting base material. The sealing section is configured with a sealing thread for maintaining an interference fit with the internal thread formed by the tapping section on the connecting base material.

2. The self-tapping connector according to claim 1, characterized in that, The envelope surface of the major diameter of the thread of the sealing section is constructed as a conical surface that gradually expands from the screw shank to the screw head, and the taper of the sealing section relative to the longitudinal axis is between 1°25′ and 1°50′.

3. The self-tapping connector according to claim 1, characterized in that, The longitudinal length of the sealing section is greater than or equal to the thickness of the connecting base material.

4. The self-tapping connector according to claim 3, characterized in that, The longitudinal length of the sealing section is 150%-200% of the thickness of the connecting base material.

5. The self-tapping connector according to claim 1, characterized in that, The threaded area and the screw head are connected by a smooth section, which is a conical surface that gradually tapers from the screw shank to the screw head. The taper of the smooth section relative to the longitudinal axis is between 13° and 16°.

6. The self-tapping connector according to claim 5, characterized in that, The screw head has an annular recessed area formed in the region facing the screw shank, the annular recessed area extending smoothly in an arc from the end face of the screw head to the smooth section.

7. The self-tapping connector according to claim 1, characterized in that, The screw head includes a flange section and a drive section. The flange section is close to the screw shank and its outer diameter is 1.5-2 times that of the screw shank. The drive section is configured to mate with a fastening tool.

8. The self-tapping connector according to claim 1, characterized in that, The screw shank also includes a drilled section, which is configured as a rod-shaped body with a conical end, and the drilled section smoothly transitions to the tapping section of the screw thread area.

9. The self-tapping connector according to claim 1, characterized in that, The pitch of the sealing section and the retaining section are the same.

10. A thermoplastic self-tapping connector, characterized in that, include: The screw includes a head and a shank, the shank comprising a threaded area, which is divided into a first sealing section, a retaining section, a second sealing section, and a tapping section along its length from near the screw head to away from the screw head. The tapping section is configured with a tapping thread for forming an internal thread on the connecting base material. The retaining section is configured with a connecting thread for maintaining a threaded fit with the internal thread formed by the tapping section on the connecting base material. The first and second sealing sections are configured with sealing threads for maintaining an interference fit with the internal thread formed by the tapping section on the connecting base material.

11. The self-tapping connector according to claim 10, characterized in that, The envelope surface where the major diameter of the threads of the first sealing section and the second sealing section are located is a conical surface that gradually expands from the screw shank to the screw head. The taper of the first sealing section and the second sealing section relative to the longitudinal axis is between 1°25′ and 1°50′.

12. A hot-melt self-tapping connection structure, characterized in that, Includes the connecting base material and the thermoplastic self-tapping connector as described in any one of claims 1-11.

13. The thermoplastic self-tapping connection structure according to claim 12, characterized in that, The connecting base material includes a first plate and a second plate stacked together. The hot-melt self-tapping connector passes through the first plate and the second plate in sequence to form a threaded connection. In the connected state, the sealing section is interference-fitted with at least a portion of the internal threads of the connecting base material to form a sealing ring.

14. A connection process for a self-tapping thermoplastic connector according to any one of claims 1-9, characterized in that, Includes the following steps: The connecting base material is fixedly connected to the clamp, the area to be connected is pressed and the flatness is less than the first threshold. The control fastening tool picks up the hot melt self-tapping connector and aligns the end of the screw rod of the hot melt self-tapping connector with the preset connection point. The control fastening tool drives the hot melt self-tapping connector to rotate and feed at 3000rpm-8000rpm. The hot melt self-tapping connector generates heat through friction with the surface of the connecting base material, causing the metal in the contact area to soften. The compressed connecting base material flows to the bottom, eventually forming a bushing structure. The control fastening tool drives the hot melt self-tapping connector to rotate continuously at 600rpm–1000rpm. The tapping section of the hot melt self-tapping connector contacts the inner wall of the bushing of the connecting base material, and forms a matching internal thread on the connecting base material by rolling. When the entire bushing area of ​​the connecting base material forms an internal thread, the fastening tool is controlled to drive the hot melt self-tapping connector to rotate continuously at 400rpm–800rpm. The retaining section of the hot melt self-tapping connector is threaded with the connecting base material; the sealing section of the hot melt self-tapping connector is interference-fitted with the internal thread of the connecting base material to form a sealing ring. Once the clamping torque meets the set torque requirement, the fastening tool is stopped.

15. A vehicle, characterized in that, Includes the thermal fusion connection structure as described in claim 12 or 13.

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