Flow drill screw and fastening structure using the same

Abstract

To provide a flow drill screw that has excellent fastening workability and in which looseness is less likely to occur, and a fastening structure using the flow drill screw.SOLUTION: A flow drill screw 1 has a head 10 and a shaft part 20, and the shaft part 20 is provided with a fully threaded region 22 that continues to a tip region 21. A thread height of a low-profile thread part 32 in an under-neck region 23 of the shaft part 20 formed between a bearing surface of the head 10 and the fully threaded region 22 is from 10 percent to 50 percent inclusive of a thread height of a fully threaded part 30 in the fully threaded region 22.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a flow drill screw for forming a through hole and a female thread in a plate material for fastening work, and a fastening structure using the same. [Background technology]

[0002] Conventionally, a flow drill screw has been disclosed that is composed of, for example, a head, a threaded portion connected to the head and having a thread formed on its outer periphery, and a drill portion connected to the threaded portion and having a conical tip, in which the threaded portion is composed of a circular threaded portion connected to the head and a non-circular threaded portion that is continuous with the circular threaded portion and connected to the drill portion, and the non-circular threaded portion has a cross section perpendicular to the axis that is a rounded, approximately polygonal shape (see Patent Document 1). As shown in Figures 6 to 8 of Patent Document 1, when a flow drill screw 1 is fastened to a workpiece 50, 50', the flow drill screw 1 is rotated at high speed while being pressed against the workpiece 50, 50' using a screwdriver (not shown) or the like, generating frictional heat at the pressure contact portion 51 between the hole forming portion 42 and the workpiece 50, 50'. This frictional heat partially softens and plastically deforms the periphery of the pressure contact portion 51 of the workpiece 50, 50', forming a pilot hole 52 that is continuous with the hole forming portion 42 and has the same diameter as the circumscribing circle of the pilot portion 41. At this time, the hole forming portion 42 bites into the workpiece 50, 50', and the excess material expands, forming an annular protrusion 54 on the top surface of the workpiece 50. Furthermore, the workpiece 50' is deformed by being pressed against the hole forming portion 42, forming an annular protrusion 55 on the bottom surface of the workpiece 50'. Another conventional flow drill screw has a polygonal cross section consisting of a threaded portion 5 and a non-threaded portion 7 that extends from the threaded portion 5 to a rounded forward thread tip 8. The side line of the non-threaded portion 7 extends continuously and smoothly with a constant curvature from the threaded portion 5 to the tip 8. This flow drill screw is used to attach an element to a panel part, and the screw itself drills a hole in the panel part and forms a thread (see Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-106063 [Patent Document 2] US2011 / 0289752A1 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, when a complete thread portion is formed in the under-neck region located directly below the head 20, the complete thread portion and the female thread formed in the workpiece 50 are threaded together. As a result, after the workpiece 50 is temporarily lifted as the flow drill screw 1 rotates, the head 20 presses the workpiece 50 down again, preventing smooth fastening operations. Furthermore, since the workpiece 50 is lifted and then pushed down again to be fastened together, there is a problem that a gap is likely to occur between the workpiece 50 and the workpiece 50'. Furthermore, Patent Document 2 also has the same problems as Patent Document 1. In view of the above problems, an object of the present invention is to provide a flow drill screw that is easy to fasten and is less likely to produce gaps, and a fastening structure using the same. [Means for solving the problem]

[0005] In order to solve the above problems, the flow drill screw according to the present invention has the following features: In this fastening structure, multiple overlapping plate materials are fastened together by forming a female thread with a flow drill screw. The flow drill screw has a head and a shank, and The shank portion comprises a tip region, a fully threaded region continuous with the tip region, and a neck region formed between the bearing surface of the head and the fully threaded region, In the shank, the thread height of the low-profile thread portion in the under-neck region formed between the bearing surface of the head and the fully threaded region is 10% or more and 50% or less of the thread height of the fully threaded portion in the fully threaded region. can be, The length of the under-neck region is equal to or greater than the thickness of the uppermost plate material among the multiple plate materials to be fastened together.The structure is as follows. [Effects of the Invention]

[0006] According to the present invention, the female thread formed in the upper plate material to be fastened together is less likely to interfere with the low-profile thread portion formed in the under-neck region. As a result, the upper plate material to be fastened together is less likely to be temporarily lifted and is less likely to be pushed down again, making it possible to perform the fastening work smoothly and improving the fastening workability. Furthermore, since the upper plate material is less likely to be pushed down again after being lifted, gaps are less likely to occur between the plate materials that are fastened together. In particular, a part of the female thread formed in the uppermost plate does not interfere with the low-profile thread formed in the under-neck region, allowing for smooth fastening work.

[0007] As an embodiment of the present invention, The root diameter of the low-profile thread portion in the under-neck region may be equal to the root diameter of the full thread portion.

[0008] According to this embodiment, the low-profile thread portion formed in the under-neck region and the female thread formed in the upper plate material to which they are fastened together are less likely to interfere with each other, making it possible to perform the fastening operation smoothly.

[0009] Another embodiment of the present invention is The thread height of the low-profile thread portion in the under-neck region may have a uniform height. According to this embodiment, there is an effect that a desired mechanical strength can be obtained by ensuring a predetermined moment of inertia.

[0010] The fastening structure using the flow drill screw according to the present invention includes: The flow drill screw described above has a configuration in which through holes are formed in a plurality of plate materials and female threads are formed therein to fasten them together.

[0011] According to the present invention, the female thread formed on the plate material to be fastened together is less likely to interfere with the low-profile thread portion formed in the under-neck region, which reduces the amount of temporary lifting of the upper plate material to be fastened together and reduces the amount of pressing down again, making it possible to perform the fastening work smoothly and improving the efficiency of the fastening work. Furthermore, since the upper plate material is less likely to be pushed down again after being lifted, there is an effect that gaps are less likely to occur between the plate materials that are fastened together. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a front view of a flow drill screw according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view of the flow drill screw shown in FIG. 1. [Figure 3] FIG. 3 is a partially enlarged view of the cross-sectional view shown in FIG. 2. [Figure 4] FIG. 1 is a graph comparing the tightening torques according to Example 1 and Comparative Example 1. [Figure 5] 1 is a photograph showing a cross-sectional view according to Example 1. [Figure 6] 1 is a photograph showing a cross section according to Comparative Example 1. [Figure 7] 10 is a photograph showing a cross-sectional view according to Example 2. [Figure 8] 10 is a photograph showing a cross section according to Comparative Example 2. [Figure 9] 10 is a photograph showing a cross-sectional view according to Example 3. [Figure 10] This is a reference photo comparing the fastening states. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of a flow drill screw according to the present invention will be described with reference to FIGS. 1 to 3. As shown in FIGS. 1 and 2, the flow drill screw 1 according to this embodiment is made up of a head portion 10 and a shank portion 20.

[0014] The head 10 may have any shape that can be held by a fastening machine during fastening work, and examples of the head shape include a hexagonal shape, a hexalobular shape, etc. These may have or may not have a flange, and various shapes can be selected as needed. The bearing surface of the head 10 is formed with an annular recess 11 that can accommodate a portion of the upper plate material that is pushed out during the fastening work.

[0015] The shank 20 is formed with a tip region 21 , a fully threaded region 22 , and a neck region 23 formed between the bearing surface of the head 10 and the fully threaded region 22 .

[0016] In the tip region 21, the hole forming portion 25 rotates while being pressed against the plate material to be fastened together, softening the plate material with frictional heat and forming a through hole.

[0017] The fully threaded region 22 is screwed onto the inner peripheral surface of the through hole formed by the hole forming portion 25, with the fully threaded portion 30 forming a female thread.

[0018] The shape of the complete thread portion 30 is not limited to a triangular thread, but may be, for example, a trapezoidal thread, a buttress thread, or a round thread. Furthermore, the triangular thread and trapezoidal thread do not need to be symmetrical and may be asymmetrical, for example, may have a cross section that is approximately a right triangle.

[0019] As shown in Figure 3, the under-neck region 23 is formed between the seat surface of the head 10 and the fully threaded region 22, and has a low-profile thread portion 32 formed to be continuous with the fully threaded portion 30 at the same pitch. The thread height of the low-back thread portion 32 is uniform, and is preferably 10 to 50 percent, and particularly 10 to 40 percent, of the thread height of the fully threaded portion 30. If the thread height of the low-back thread portion 32 is less than 10%, the desired mechanical strength cannot be ensured, and if it exceeds 50%, the low-back thread portion will interfere with the female thread portion formed in the upper plate material, hindering smooth fastening operations. The cross-sectional shape of the low-profile thread portion 32 is not limited to a trapezoid, but may be, for example, a triangular cross-section. Furthermore, the low-profile thread portion 32 does not necessarily have to be symmetrical, but may be asymmetrical, for example, may have a cross-sectional shape of a substantially right-angled triangle. Furthermore, the cross-sectional shape of the low-profile thread portion 32 does not necessarily have to be the same as that of the full thread portion 30 of the full thread region, but may be different as needed.

[0020] The inner diameter (root diameter) N of the under-neck region 23 is preferably equal to the root diameter N of the complete thread portion 30. If the inner diameter (root diameter) N of the low back thread portion 32 is larger than the root diameter N of the complete thread portion 30, the female thread formed in the upper plate material will interfere with the low back thread portion 32, hindering smooth fastening work.

[0021] The length of the underhead region 23 is preferably equal to or greater than that of the plate material positioned above. If the length of the underhead region 23 is shorter than the thickness of the plate material positioned above, part of the female thread formed in the upper plate material will interfere with the complete thread portion 30, hindering smooth fastening work.

[0022] The flow drill screw 1 may be manufactured by, for example, rolling, cutting, forging, or a combination of these methods. In particular, the neck region 23 and the full thread region 22 may be manufactured in a continuous process, or may be manufactured in separate processes. Example 1

[0023] Next, a fastening test in which two plate materials are fastened together using the flow drill screw 1 will be described. The sample flow drill screw used had a total length of 20 mm, a nominal diameter of 5.0 mm, and a thread pitch of 0.8 mm. In particular, the tip region 21 was approximately 8 mm. The length of the fully threaded region 22 was approximately 9 mm, the major diameter M was 5.07 mm, the thread height of the fully threaded portion 30 was 0.49 mm, and the root diameter N was 4.09 mm. The length of the under-neck region 23 was 3 mm, the outer diameter L was 4.45 mm, the thread height of the low-back thread portion 32 was 0.18 mm, and the root diameter N was 4.09 mm.

[0024] The lower plate 2 to be fastened together was made of a 5000 series aluminum plate having a thickness of 3.0 mm, and the upper plate 3 was made of a 780 MPa class steel plate having a thickness of 1.4 mm.

[0025] The tightening work was carried out by setting the rotation speed and load of the tightening machine according to the tightening work stage of the flow drill screw. The change in fastening torque is shown in Figure 4. A cross-sectional photograph of the fastened and integrated sample is shown in Figure 5. (Comparative Example 1)

[0026] The flow drill screw sample used in the comparative example did not have a low-profile thread portion like in Example 1, and the outer diameter from the bearing surface to the fully threaded region 22 was the same height and shape as the fully threaded portion 30. A make-up test was conducted on a sample with the same shape as in Example 1 described above, under the same conditions as in Example 1. The change in fastening torque is shown in Figure 4. A cross-sectional photograph of the fastened and integrated sample is shown in Figure 6.

[0027] As is clear from Figure 4, Example 1 was found to be able to achieve fastening integration with a make-up torque that was approximately 35% lower than that of Comparative Example 1. This not only makes it less likely that the female thread formed during the make-up operation will be damaged, but also has the advantage of preventing melting of the flow drill screw 1 as shown in Figure 10.

[0028] 5 relating to Example 1, the low-profile thread portion 32 in the under-neck region 23 formed directly below the bearing surface was not fully threaded with the female thread portion formed in the upper plate 3, and a slight gap existed. In contrast, as shown in FIG. 6 relating to the comparative example, the male thread portion of the complete thread portion formed in the under-neck region 23 was fully threaded with the female thread portion formed in the upper plate 3.

[0029] As shown in Figure 5 of the Example, of the gaps that occurred between the lower plate 2 and the upper plate 3, the largest gap that occurred at the base of the shank 20 of the flow drill screw 1 was 0.863 mm. On the other hand, as shown in Figure 6 of the Comparative Example 1, the largest gap that occurred at the base of the shank 20 of the flow drill screw 1 was 1.001 mm. Therefore, it was found that the flow drill screw 1 of the present invention can reduce the gap by approximately 14% compared to the conventional flow drill screw 1. Example 2

[0030] The sample flow drill screw used had a total length of 20 mm, a nominal diameter of 4.0 mm, and a thread pitch of 0.7 mm. In particular, the tip region 21 was approximately 8 mm. The length of the fully threaded region was approximately 9 mm, the major diameter M of the fully threaded portion 30 was 4.07 mm, the thread height was 0.45 mm, and the root diameter N was 3.17 mm. The length of the under-neck region 23 was 3 mm, the outer diameter L was 3.38 mm, the thread height of the low-back thread portion 32 was 0.11 mm, and the root diameter N was 3.17 mm.

[0031] The same plate materials as those in Example 1 were used for the lower plate material 2 and the upper plate material 3 which were fastened together.

[0032] The rotation speed and load of the fastening machine were set in the same manner as in Example 1 according to the stage of the fastening work of the flow drill screw, and the fastening work was carried out. A cross-sectional photograph of the fastened and integrated sample is shown in FIG. (Comparative Example 2)

[0033] The sample of flow drill screw 1 used in Comparative Example 2 did not have a low-profile thread portion like in Example 2, and the outer diameter from the bearing surface to the fully threaded region 22 was the same height and shape as the fully threaded portion 30. A make-up test was conducted on a sample with the same shape as in Example 2 described above, under the same conditions as in Example 2. A cross-sectional photograph of the fastened and integrated sample is shown in FIG.

[0034] According to FIG. 7 relating to Example 2, the low-profile thread portion 32 in the neck region 23 formed directly below the seat surface and the female thread portion formed in the upper plate material 3 were not sufficiently threaded together, and a slight gap existed. 8 relating to Comparative Example 2, the male thread portion consisting of the fully threaded portion formed in the underhead region 23 was deeply engaged with the female thread portion formed in the upper plate 3. For this reason, it was found that the make-up operation of Comparative Example 2 required a larger make-up torque than that of Example 2. Example 3

[0035] The sample flow drill screw used had a total length of 20 mm, a nominal diameter of 4.5 mm, and a thread pitch of 0.75 mm. In particular, the tip region 21 was approximately 8 mm. The length of the fully threaded region was approximately 9 mm, the major diameter M of the fully threaded portion 30 was 4.56 mm, the thread height was 0.49 mm, and the root diameter N was 3.58 mm. The length of the under-neck region 23 was 3 mm, the outer diameter L was 3.95 mm, the thread height of the low-back thread portion 32 was 0.19 mm, and the root diameter N was 3.58 mm.

[0036] The same plate materials as those in Example 1 were used for the lower plate material 2 and the upper plate material 3 which were fastened together.

[0037] The rotation speed and load of the fastening machine were set in the same manner as in Example 1 according to the stage of the fastening work of the flow drill screw, and the fastening work was carried out. A cross-sectional photograph of the fastened and integrated sample is shown in FIG.

[0038] 9 relating to Example 3, there was a slight gap between the low-profile thread portion 32 in the under-neck region 23 formed directly below the bearing surface and the female thread portion formed in the upper plate 3. For this reason, it was found that fastening was possible with a small fastening torque.

[0039] Furthermore, the fastening structure according to the present invention has the advantage that the flow drill screw can be removed even after fastening, unlike when the fastening structure is integrated by welding.

[0040] In this embodiment, the case where two different types of plate materials are fastened together has been described, but this is not necessarily limited to this, and plate materials of the same type may also be fastened together, or three or more plate materials may also be fastened together. Furthermore, although the case where the fastening is performed without providing a pilot hole has been described, the present invention is not limited to this, and the fastening operation may be performed by providing a pilot hole or a blind hole as necessary. [Industrial Applicability]

[0041] The flow drill screw according to the present invention is not limited to applications in which a plurality of plate materials are fastened together, but may also be applied to a fastening structure in which a plate material is fastened together to a base such as an automobile chassis, for example. [Explanation of symbols]

[0042] 1 Flow Drill Screw 2 Lower plate material 3 Upper plate material 10 head 11 Recess 20 Shaft 21 Tip area 22 Full thread area 23 Lower neck area 25 Hole forming part 30 Fully threaded 31 Valley 32 Low-profile thread section

Claims

1. A flow drill screw having a head and a shank, the shank having a fully threaded region that continues to a tip region, A flow drill screw characterized in that the thread height of a low-profile thread portion in an under-neck region of the shank formed between the bearing surface of the head and the fully threaded region is 10 percent or more and 50 percent or less of the thread height of the fully threaded portion in the fully threaded region.

2. 2. The flow drill screw according to claim 1, wherein the root diameter of the low-profile thread portion in the under-neck region is equal to the root diameter of the full thread portion.

3. 2. The flow drill screw according to claim 1, wherein the length of the underhead region is equal to or greater than the thickness of the uppermost plate material among the multiple plate materials to be fastened together.

4. 2. The flow drill screw according to claim 1, wherein the thread height of the low-profile thread portion in the under-neck region has a uniform height.

5. A fastening structure using a flow drill screw according to any one of claims 1 to 4, characterized in that through holes are formed in a plurality of plate materials, and female threads are formed in the plate materials to fasten them together.

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