Flow drill screw and fastening structure using same

Abstract

The present invention provides a flow drill screw that has excellent fastening workability and does not readily loosen and a fastening structure that uses the flow drill screw. A flow drill screw 1 has a head part 10 and a shaft part 20. The shaft part 20 has a full thread region 22 that is continuous with a tip end region 21. The thread height of low-profile thread parts 32 at an underhead region 23 of the shaft part 20 that is formed from a seat surface for the head part 10 to the full thread region 22 is 10%–50% of the thread height of full thread parts 30 at the full thread region 22.

Description

Flow drill screw and fastening structure using same

[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.

[0002] Conventionally, a flow drill screw has been disclosed that includes, 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, wherein the threaded portion includes a circular threaded portion connected to the head and a noncircular threaded portion connected to the head and continuing from the circular threaded portion and connected to the drill portion, and the noncircular threaded portion has a rounded, generally polygonal cross section perpendicular to the axis (see Patent Document 1). As shown in Figures 6 to 8 of Patent Document 1, when the flow drill screw 1 is fastened to a workpiece 50, 50', frictional heat is generated at the pressure contact portion 51 between the hole forming portion 42 and the workpiece 50, 50' when 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. This frictional heat partially softens and plastically deforms the periphery of the press-fit portion 51 of the workpieces 50, 50', forming a pilot hole 52 with the same diameter as the circumscribed circle of the pilot portion 41, which is continuous with the hole forming portion 42. At this time, the hole forming portion 42 bites into the workpieces 50, 50', causing excess material to be expanded on the upper surface of the workpiece 50, forming an annular protrusion 54. The lower surface of the workpiece 50' is deformed by being pressed against the hole forming portion 42, forming an annular protrusion 55. Another conventional flow drill screw has a polygonal cross-section consisting of a threaded portion 5 and a non-threaded portion 7 extending from the threaded portion 5 to a rounded forward thread tip 8. The side line of the non-threaded portion 7 extends smoothly and continuously 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 component, drilling a hole in the panel component and forming a thread (see Patent Document 2).

[0003] JP 2020-106063 A

[0004] However, in Patent Document 1, if a complete thread portion is formed in the under-neck region located directly below the head 20, the complete thread portion will thread into the female thread formed in the workpiece 50. 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, because the workpiece 50 is lifted and then pressed down again to be fastened together, there is a problem that a gap is likely to form between the workpiece 50 and the workpiece 50'. 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 a gap, and a fastening structure using the same.

[0005] In order to solve the above-mentioned problems, the flow drill screw according to the present invention is a flow drill screw having a head and a shank, and wherein the shank is provided with a fully threaded region that continues to a tip region, and wherein 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 between 10 percent and 50 percent of the thread height of the fully threaded portion in the fully threaded region.

[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 less likely to be pushed down again, allowing for smooth fastening work and improving fastening workability. In addition, because 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 to be fastened together.

[0007] In 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. 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 be fastened together are less likely to interfere with each other, allowing for smooth fastening work.

[0008] In another embodiment of the present invention, the length of the underhead region may be equal to or greater than the thickness of the uppermost plate among the multiple plate materials to be fastened together. According to this embodiment, a part of the female thread formed in the uppermost plate material does not interfere with the low-profile thread formed in the underhead region, enabling smooth fastening work.

[0009] In another embodiment of the present invention, the thread height of the low-profile thread portion in the under-neck region may be uniform, which has the effect of ensuring a predetermined moment of inertia and thereby obtaining a desired mechanical strength.

[0010] A fastening structure using a flow drill screw according to the present invention has a configuration in which through holes are formed in a plurality of plate materials using the above-mentioned flow drill screw, and female threads are formed in the plate materials 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. As a result, the upper plate material to be fastened together is less likely to be temporarily lifted and less likely to be pushed down again, which enables smooth fastening work and improves fastening workability. In addition, 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 fastened plate materials.

[0012] Fig. 2 is a front view of a flow drill screw according to the present invention; Fig. 3 is a cross-sectional view of the flow drill screw shown in Fig. 1; Fig. 4 is a partially enlarged view of the cross-sectional view shown in Fig. 2; Fig. 5 is a graph comparing the make-up torques of Example 1 and Comparative Example 1; Fig. 6 is a photograph showing a cross-sectional view of Example 1; Fig. 7 is a photograph showing a cross-sectional view of Comparative Example 1; Fig. 8 is a photograph showing a cross-sectional view of Example 2; Fig. 9 is a photograph showing a cross-sectional view of Comparative Example 2; Fig. 10 is a photograph showing a cross-sectional view of Example 3; Fig. 11 is a reference photograph comparing make-up states;

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

[0014] The head 10 may have any shape as long as it 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 part 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 FIG. 3 , the under-neck region 23 is formed between the bearing surface of the head 10 and the fully threaded region 22. The low-back thread portion 32 is 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, preferably 10 to 50 percent, and particularly preferably 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. If it exceeds 50%, the low-back thread portion will interfere with the female thread portion formed in the upper plate, hindering smooth fastening operations. The cross-sectional shape of the low-back thread portion 32 is not limited to a trapezoid and may be, for example, a triangular cross section. Furthermore, the low-back thread portion 32 does not need to be symmetrical and may be asymmetrical, for example, a substantially right-angled triangular cross section. Furthermore, the cross-sectional shape of the low-profile thread portion 32 does not necessarily have to be the same as the cross-sectional shape of the fully threaded portion 30 of the fully threaded 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 fully threaded portion 30. If the inner diameter (root diameter) N of the low-profile thread portion 32 is larger than the root diameter N of the fully threaded portion 30, the female thread formed in the upper plate material will interfere with the low-profile 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 located above. If the length of the underhead region 23 is shorter than the thickness of the plate material located above, part of the female thread formed in the plate material located above 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 will be described in which two plates are fastened together using the flow drill screw 1. 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 outer 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, and the thread height of the low-profile 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 operation was performed by setting the rotation speed and load of the tightening machine according to the tightening stage of the flow drill screw. The change in tightening torque is shown in Figure 4. A cross-sectional photograph of the tightened 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 make-up torque is shown in Figure 4. A cross-sectional photograph of the make-up integrated sample is shown in Figure 6.

[0027] As is clear from Figure 4, Example 1 was found to be able to achieve integral fastening with a fastening 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 fastening operation will be damaged, but also has the advantage of being able to avoid 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, and the outer 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 neck region 23 was 3 mm, the outer diameter L was 3.38 mm, and the thread height of the low-profile 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 tightening operation was carried out by setting the rotation speed and load of the tightening machine according to the tightening operation stage of the flow drill screw in the same manner as in Example 1. A cross-sectional photograph of the tightened and integrated sample is shown in Figure 7. (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 that of 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 sample with the same shape as Example 2 described above was subjected to a make-up test under the same conditions as Example 2. A cross-sectional photograph of the made-up sample is shown in Figure 8.

[0034] As shown in Figure 7 relating to Example 2, 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. As shown in Figure 8 relating to Comparative Example 2, the male thread portion consisting of the fully threaded portion formed in the under-neck region 23 was deeply threaded with the female thread portion formed in the upper plate 3. For this reason, it was found that a greater tightening torque was required for the tightening operation of Comparative Example 2 than for Example 2. (Example 3)

[0035] The sample flow drill screw 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, and the outer 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 neck region 23 was 3 mm, the outer diameter L was 3.95 mm, and the thread height of the low-profile 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 tightening operation was carried out by setting the rotation speed and load of the tightening machine according to the tightening operation stage of the flow drill screw in the same manner as in Example 1. A cross-sectional photograph of the tightened and integrated sample is shown in Figure 9.

[0038] 9 relating to Example 3, 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. 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. Also, while the case where pilot holes are not provided has been described, this is not necessarily limited to this, and pilot holes or blind holes may be provided as needed for the fastening work.

[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.

[0042] REFERENCE SIGNS LIST 1 Flow drill screw 2 Lower plate 3 Upper plate 10 Head 11 Recess 20 Shank 21 Tip region 22 Full thread region 23 Neck region 25 Hole forming portion 30 Full thread portion 31 Root portion 32 Low-profile thread portion

Claims

1. A flow drill screw having a head and a shank, the shank being provided with a fully threaded region that continues to a tip region, wherein the thread height of a low-profile thread portion in the under-neck region of the shank, which is formed between the bearing surface of the head and the fully threaded region, is between 10 percent and 50 percent of the thread height of the fully threaded portion in the fully threaded region.

2. The flow drill screw according to claim 1, characterized in that 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. A flow drill screw as set forth in claim 1 or 2, characterized in that the length of the under-neck region is equal to or greater than the thickness of the uppermost plate among the multiple plates to be fastened together.

4. A flow drill screw according to any one of claims 1 to 3, characterized in that 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 multiple plate materials, and female threads are formed in the plate materials to fasten them together.

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