Tapping screw

Abstract

To provide a tapping screw with high fatigue resistance.SOLUTION: A tapping screw (1) includes a shank (2) including an axis, a head (3), and a ridge (4) provided on an outer circumference of the shank (2). In a longitudinal section including the axis of the shank (2), the ridge (4) has at least a plurality of shaped ridges (41), and a plurality of fastening ridges (42) each having an outer diameter less than that of the shaped ridge (41). Between the shaped ridges (41), a flat root (43) is formed. The shaped ridges (41) each have a double flank (412). Between the fastening ridges (42), an outwardly recessed root (45) is formed. The fastening ridges (42) each have a double flank (422). In the longitudinal section including the axis of the shank (2), the root (45) formed between the fastening ridges (42) has an outwardly recessed arc-shaped portion.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a self-tapping screw. [Background technology]

[0002] Conventionally, tapping screws that can be fastened to a workpiece are known. For example, Patent Document 1 describes a tapping screw that can be screwed into a pilot hole formed in a workpiece, thereby entering the pilot hole and simultaneously forming an internal thread in the pilot hole. The tapping screw is fastened to the workpiece by being screwed into the internal thread formed in the pilot hole. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2021-527786 Summary of the Invention [Problem to be solved by the invention]

[0004] In order for a tapping screw to maintain a state in which it is fastened to a workpiece for a long period of time, a tapping screw having high resistance to fatigue is required.

[0005] The present disclosure has been made in consideration of the above circumstances, and has an object to provide a tapping screw with high resistance to fatigue. [Means for solving the problem]

[0006] A first aspect of the present disclosure is a tapping screw having a shank including an axis, a head, and a thread provided on the outer periphery of the shank, In a longitudinal cross section including the axis of the shaft portion, the thread has at least a plurality of forming threads located on the tip side of the shaft portion and a plurality of tightening threads located on the head side and having an outer diameter smaller than that of the forming threads, In a longitudinal cross section including the axis of the shank, a flat valley bottom is formed between the formed threads, and the formed threads have two side edges extending from the crest to the valley bottom, In a longitudinal cross section including the axis of the shank, a valley bottom that is concave outwardly is formed between the fastening threads, and the fastening threads have two side edges extending from a crest to the valley bottom, The thread is a tapping screw, and in a vertical cross section including the axis of the shank, the root formed between the fastening threads has an arc-shaped portion that is concave outward.

[0007] In a second aspect of the present disclosure, in the tapping screw according to the first aspect described above, the two side edges of the forming thread may extend linearly from the crest to the root.

[0008] In a third aspect of the present disclosure, in the tapping screw according to the first aspect or the second aspect described above, the diameter at the root of the forming thread may be smaller than the diameter at the root of the tightening thread.

[0009] In a fourth aspect of the present disclosure, in the tapping screw according to each of the first aspect to the third aspect described above, in a longitudinal cross section including the axis of the shank, the thread may further have a tip thread located on the tip side of the shank relative to the forming thread and having an outer diameter smaller than that of the tightening thread.

[0010] In a fifth aspect of the present disclosure, in the tapping screw according to each of the first aspect to the fourth aspect described above, the thread may have a double-start thread structure.

[0011] In a sixth aspect of the present disclosure, in each of the tapping screws according to the first aspect to the fifth aspect described above, the hardness of the surface of the tapping screw may be 1.2 times or less than the hardness of the core of the tapping screw. Effect of the Invention

[0012] According to the present disclosure, a tapping screw having high resistance to fatigue can be provided. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a perspective view showing an example of a tapping screw according to the present embodiment. [Diagram 2] FIG. 2 is a perspective view showing an example of a tapping screw according to the present embodiment. [Diagram 3] FIG. 4 is an enlarged partial cross-sectional view of a portion of the cross section of the tapping screw according to the embodiment. [Figure 4A] FIG. 4 is an enlarged longitudinal cross-sectional view including an axis of the formed thread of FIG. 3 . [Figure 4B] 4 is an enlarged longitudinal sectional view including an axis of the fastening screw thread of FIG. 3 and its surroundings. FIG. [Diagram 5] 5A to 5C are diagrams showing the operation of the tapping screw according to the embodiment; [Figure 6] 5A to 5C are diagrams showing the operation of the tapping screw according to the embodiment; [Figure 7] FIG. 4 is an enlarged partial side view of a tapping screw having a double-thread structure. [Figure 8] FIG. 4 is a partial side view showing an enlarged view of a portion of a tapping screw having only one thread. [Figure 9] 5A to 5C are diagrams showing the operation of the tapping screw according to the embodiment; [Figure 10] 5A to 5C are diagrams showing the operation of the tapping screw according to the embodiment; [Figure 11] 5A to 5C are diagrams showing the operation of the tapping screw according to the embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The tapping screw of this embodiment will be described with reference to Figs. 1 to 11. Fig. 1 is a perspective view showing the tapping screw 1. Fig. 2 is a perspective view showing the tapping screw 1 observed from a direction different from the observation direction in Fig. 1. As shown in Figs. 1 and 2, the tapping screw 1 includes a shank 2 including an axis LA, a head 3, and a thread 4 provided on the outer periphery of the shank 2. The thread 4 includes a plurality of formed threads 41 located on the tip side SA1 of the shank 2 in a longitudinal cross section including the axis LA of the shank 2, and a plurality of fastening threads 42 located on the head side SA2 and having a smaller outer diameter than the formed threads 41. The formed threads 41 and fastening threads 42 constituting the thread 4 will be described further below.

[0015] The tapping screw 1 is fastened to the workpiece 7 by being screwed into a pilot hole 71 of the workpiece 7, which will be described later.

[0016] In this specification, the direction in which the axis LA extends is referred to as the axial direction DA. In the axial direction DA, the side on which the tip 2a of the shank 2 is located, based on the position where the shank 2 and the head 3 are connected, is referred to as the tip side SA1 of the shank 2. In addition, in the axial direction DA, the side on which the head 3 is located, based on the position where the shank 2 and the head 3 are connected, is referred to as the head side SA2.

[0017] In the example shown in Figs. 1 and 2, the shank 2, head 3 and threads 4 that constitute the tapping screw 1 are integrally formed.

[0018] The tapping screw 1 is rotated about the axis LA when being screwed into a pilot hole 71 of the workpiece 7, which will be described later. In this specification, the direction going around the axis LA is referred to as the circumferential direction DB. Of the circumferential direction DB, the direction in which the tapping screw 1 is rotated when being screwed into the pilot hole 71 of the workpiece 7 is referred to as the screwing rotation direction SB1. Also, of the circumferential direction DB, the direction in which the tapping screw 1 is rotated when being loosened is referred to as the loosening rotation direction SB2. Also, the radial direction of the tapping screw 1 is the radial direction DC.

[0019] Next, each component of the tapping screw 1 will be further described.

[0020] First, the head 3 will be described. The head 3 forms an end of the head side SA2 of the tapping screw 1. In the example shown in Fig. 2, the head 3 has a portion that meshes with a tool for applying a rotational force to the tapping screw 1, for example, a head body 31, and a flange portion 32 that protrudes in the radial direction DC from the head body 31. The flange portion 32 is connected to the tip side SA1 of the head body 31. As an example, the flange portion 32 has a circular outline centered on the axis LA when viewed from the tip side SA1.

[0021] The head body 31 of the head 3 is a portion that meshes with a tool for rotating a general tapping screw, but the head 3 has a portion that meshes with, for example, a general wrench. The head 3 may have a portion that meshes with a general screwdriver. In this embodiment, as shown in FIG. 2, the head body 31 has a shape of a substantially hexagonal column extending in the axial direction DA. This allows the head body 31 to mesh with a hexagonal socket of a general socket wrench. Therefore, the tapping screw 1 can be rotated by using a socket wrench having a hexagonal socket and engaging the hexagonal socket with the head body 31 and operating the socket wrench. In the example shown in FIG. 2, a groove 33 in the shape of a "+" may be formed in the head body 31. Therefore, the tip of a general Phillips screwdriver is inserted into the groove 33, and the Phillips screwdriver is engaged with the head body 31 and operated. This also allows the tapping screw 1 to be rotated.

[0022] Next, the shaft portion 2 will be described. The shaft portion 2 includes an axis LA. The shaft portion 2 has a generally cylindrical shape extending in the axial direction DA. As an example, the shaft portion 2 has a shape that is rotationally symmetrical about the axis LA. The shaft portion 2 is connected to the tip side SA1 of the head portion 3. In the example shown in Figs. 1 and 2, the shaft portion 2 is connected to the tip side SA1 of the flange portion 32 of the head portion 3.

[0023] Next, the thread 4 will be described. The thread 4 is provided on the side surface 2b of the shaft portion 2. The thread 4 is provided so as to spirally go around the shaft portion 2. The tapping screw 1 has at least one thread 4, and preferably has a double thread structure as shown in FIG. 1 and FIG. 2. In this embodiment, the tapping screw 1 has two threads 4, a first thread 4a and a second thread 4b. In the example shown in FIG. 1 and FIG. 2, the first thread 4a and the second thread 4b are provided so as to spirally go around the shaft portion 2 in parallel with each other. Therefore, when the tapping screw 1 is observed along the axial direction DA, the first thread 4a and the second thread 4b appear alternately. Although not shown, the tapping screw 1 may have only one thread 4.

[0024] FIG. 3 is an enlarged view of a portion of the longitudinal section including the axis LA of the shank 2 of the tapping screw 1 shown in FIG. 1 and FIG. 2. In the longitudinal section including the axis LA of the shank 2 as shown in FIG. 3, the thread 4 has at least a plurality of formed threads 41 located on the tip side SA1 of the shank 2 and a plurality of fastening threads 42 located on the head side SA2 and having a smaller outer diameter than the formed threads 41. In the formed threads 41, fastening threads 42, and tip threads 44 described later, the outer diameter is the distance between the end of the formed threads 41, fastening threads 42, or tip threads 44 farthest from the axis LA and the axis LA. In the example shown in FIG. 3, each of the first thread 4a and the second thread 4b forms the formed thread 41 in a portion and the fastening thread 42 in another portion.

[0025] Next, the formed threads 41 will be described. The formed threads 41 are located closer to the tip side SA1 of the shank 2 than the fastening threads 42. As shown in FIG. 3, the formed threads 41 appear on the thread 4. FIG. 4A is an enlarged view of the formed threads 41 and its surroundings in FIG. 3. As shown in FIG. 3 and FIG. 4A, in a longitudinal section including the axis LA of the shank 2, a flat valley bottom 43 is formed between the formed threads 41. In the example shown in FIG. 3 and FIG. 4A, the flat valley bottom 43 is formed by the side surface 2b of the shank 2.

[0026] The end of the formed thread 41 farthest from the axis LA is called the crest 411. In the example shown in FIG. 3 and FIG. 4A, the crest 411 forms a surface parallel to the axis LA. In a longitudinal section including the axis LA of the shank 2 as shown in FIG. 3 and FIG. 4A, the formed thread 41 has two side edges 412 extending from the crest 411 to the root 43. One of the two side edges 412 forms a surface of the tip side SA1 of the formed thread 41. The other of the two side edges 412 forms a surface of the head side SA2 of the formed thread 41. The two side edges 412 of the formed thread 41 extend linearly from the crest 411 to the root 43.

[0027] 3, the portion of the thread 4 that forms the formed thread 41 goes around the outer periphery of the shank 2 at least one revolution. When the tapping screw 1 has a double-thread structure, each of the portions of the first thread 4a and the second thread 4b that form the formed thread 41 may go around the outer periphery of the shank 2 at least one revolution.

[0028] Next, the fastening thread 42 will be described. The fastening threads 42 are located closer to the head side SA2 than the forming threads 41. Fig. 4B is an enlarged view of the fastening threads 42 and its surroundings in Fig. 3. In Fig. 3, the outer diameter w2 of the fastening threads 42 is constant between the fastening threads 42. In Fig. 3, the outer diameter w21 of the fastening thread 42 formed by the first thread 4a is equal to the outer diameter w22 of the fastening thread 42 formed by the second thread 4b.

[0029] As shown in Fig. 3, a plurality of fastening threads 42 appear on the thread 4. In a longitudinal cross section including the axis LA of the shaft portion 2 as shown in Fig. 3 and Fig. 4B, a valley bottom 45 that is concave outward is formed between the fastening threads 42.

[0030] The end of the fastening thread 42 that is farthest from the axis LA is called the crest 421. In the example shown in FIG. 3, the crest 421 forms a surface parallel to the axis LA. In this case, in a longitudinal section including the axis LA of the shank 2 as shown in FIG. 3 and FIG. 4B, the fastening thread 42 has two side edges 422 extending from the crest 421 to the root 45. One of the two side edges 422 forms a surface of the tip side SA1 of the fastening thread 42. The other of the two side edges 422 forms a surface of the head side SA2 of the fastening thread 42. The two side edges 422 of the fastening thread 42 extend linearly from the crest 421 to the root 45 of the fastening thread 42.

[0031] As shown in FIG. 3 and FIG. 4B, in a longitudinal section including the axis LA of the shank 2, the valley bottom 45 formed between the fastening threads 42 has an arc-shaped portion that is concave toward the outside. The arc-shaped portion is a portion that appears as a curved line having a shape corresponding to a part of a circle in a longitudinal section including the axis LA of the shank 2 as shown in FIG. 3 and FIG. 4B. In the example shown in FIG. 3 and FIG. 4B, the valley bottom 45 formed between the fastening threads 42 does not have a flat portion. The valley bottom 45 is composed of an arc-shaped portion that is concave toward the outside. As a result, the valley bottom 45 is smoothly connected to the side edge 422 located on the head side SA2 of the fastening thread 42 located on the tip side SA1 of the valley bottom 45 without forming an angle. The valley bottom 45 is also smoothly connected to the side edge 422 located on the tip side SA1 of the fastening thread 42 located on the head side SA2 of the valley bottom 45 without forming an angle.

[0032] 3, the portion of the thread 4 that forms the fastening thread 42 goes around the outer periphery of the shank 2 at least one revolution. When the tapping screw 1 has a double-thread structure, each of the portions of the first thread 4a and the second thread 4b that form the fastening thread 42 may go around the outer periphery of the shank 2 at least one revolution.

[0033] The outer diameter w2 of the fastening thread 42 is smaller than the outer diameter w1 of the formed thread 41. As an example, the outer diameter w2 of the fastening thread 42 is 0.98 times or less the maximum value of the outer diameter w1 of the formed thread 41. Also, the diameter w4 of the formed thread 41 of the tapping screw 1 at the root 43 is smaller than the diameter w3 of the fastening thread 42 of the tapping screw 1 at the root 45. In FIG. 3, the diameter w4 of the formed thread 41 of the tapping screw 1 at the root 43 is smaller than the minimum value of the diameter w3 of the root 45 having an arc-shaped portion of the fastening thread 42 of the tapping screw 1. As an example, the diameter w4 of the formed thread 41 of the tapping screw 1 at the root 43 is 0.97 times or less the minimum value of the diameter w3 of the root 45 of the fastening thread 42 of the tapping screw 1.

[0034] The thread 4 of this embodiment further has a tip thread 44 located on the tip side SA1 of the shank 2 relative to the formed thread 41 in a longitudinal section including the axis LA of the shank 2 as shown in FIG. 3. In the example shown in FIG. 3, the tip thread 44 has a smaller outer diameter than the fastening thread 42. In the longitudinal section including the axis LA of the shank 2 shown in FIG. 3, a plurality of tip threads 44 appear. The outer diameter w10 of the tip thread 44 is smaller than the outer diameter w1 of the formed thread 41. In FIG. 3, the outer diameter w10 of the tip thread 44 is smaller than the outer diameter w2 of the fastening thread 42. As a result, the outer diameter w1 of the formed thread 41 is larger than the outer diameter w2 of the fastening thread 42 and the outer diameter w10 of the tip thread 44. In the example shown in FIG. 3, a valley bottom 46 is formed between the formed threads 41. The valley bottom 46 between the tip threads 44 is formed by the side surface 2b of the shank 2.

[0035] In the example shown in Fig. 3, the diameter w9 at the root 46 of the tip thread 44 of the tapping screw 1 becomes smaller toward the tip side SA1 in the axial direction DA. In the example shown in Fig. 3, the maximum value of the diameter w9 at the root 46 of the tip thread 44 of the tapping screw 1 is smaller than the diameter w4 at the root 43 of the forming thread 41 of the tapping screw 1.

[0036] The above-mentioned forming threads 41, the above-mentioned fastening threads 42, the tip thread 44, the root 43, the root 45 and the root 46 appear in at least one longitudinal cross section of the tapping screw 1 including the axis LA of the shank 2. The above-mentioned forming threads 41, the above-mentioned fastening threads 42, the tip thread 44, the root 43, the root 45 and the root 46 may appear in any longitudinal cross section of the tapping screw 1 including the axis LA of the shank 2.

[0037] The material of the tapping screw 1 is, for example, alloy steel or boron steel. The material of the tapping screw 1 may be chrome molybdenum steel. The material of the tapping screw 1 may be, for example, SCM435. The material of the tapping screw 1 may be a metal material similar to the material of a general tapping screw.

[0038] In this embodiment, when the tapping screw 1 is manufactured, the material of the tapping screw 1 is subjected to heat treatment. The heat treatment is performed on the material of the tapping screw 1 after the material is adjusted to the shape of the tapping screw 1. The heat treatment allows the tapping screw 1 to have desired characteristics, for example, desired hardness or toughness. Here, the inventors of the tapping screw 1 of this embodiment have found that it is particularly preferable to perform a thermal refining treatment as a heat treatment in the manufacture of the tapping screw 1 of this embodiment. The reasons why the thermal refining treatment is preferable will be described below.

[0039] In the manufacture of general tapping screws, the material of the tapping screw is subjected to a carburizing treatment as a heat treatment. In the carburizing treatment, carbon is added to the surface of the material of the tapping screw to harden only the surface area of ​​the material. In this case, the hardness of the surface area of ​​the manufactured tapping screw is increased, while the toughness of the surface area is decreased.

[0040] In contrast, in the present embodiment, in the manufacture of a tapping screw, a thermal refining treatment is performed on the material of the tapping screw as a heat treatment. Specifically, in the thermal refining treatment, the material of the tapping screw is quenched, and then tempered after quenching. In tempering, the material is heated to 400°C or higher. When the material of the tapping screw is subjected to the thermal refining treatment, the hardness near the surface of the tapping screw produced is smaller than when the material of the tapping screw is subjected to the carburizing treatment. On the other hand, the toughness near the surface of the tapping screw produced is greater. In addition, when the material of the tapping screw is subjected to the thermal refining treatment, it is considered that the difference between the hardness near the surface of the material and the hardness of the portion away from the surface is smaller than when the material of the tapping screw is subjected to the carburizing treatment.

[0041] In this embodiment, the tapping screw 1 is subjected to a thermal refining treatment, and the reason why the thermal refining treatment is preferable to the carburizing treatment is as follows. First, from the viewpoint of increasing the toughness near the surface of the tapping screw 1, the thermal refining treatment is preferable to the carburizing treatment. For this reason, the thermal refining treatment increases the toughness near the surface of the tapping screw 1, and the occurrence of cracks on the surface 1a of the tapping screw 1 can be suppressed. Furthermore, the thermal refining treatment reduces the difference in hardness between the surface and the portion away from the surface. This also makes it possible to suppress the occurrence of cracks on the surface 1a of the tapping screw 1. As a result, the occurrence of cracks on the surface 1a of the tapping screw 1 due to fatigue can be suppressed, and the fatigue resistance of the tapping screw 1 can be increased.

[0042] Also, from the viewpoint of increasing the hardness near the surface of the tapping screw 1, it can be considered that the carburizing treatment is more preferable than the thermal refining treatment. However, the inventors have found that the tapping screw 1 of this embodiment does not require a particularly high hardness near the surface. In particular, as described below, when the hardness of the workpiece 7 to which the tapping screw 1 is fastened is low, the inventors have found that the tapping screw 1 can be fastened to the workpiece 7 even if the tapping screw 1 does not have a particularly high hardness near the surface. From the above, in the manufacture of the tapping screw 1 of this embodiment, which does not particularly require an increase in hardness near the surface, it is preferable to subject the material to a thermal refining treatment rather than a carburizing treatment from the viewpoint of suppressing the occurrence of cracks.

[0043] We will now discuss the hardness of the tapping screw 1 obtained by subjecting the material to thermal refining treatment. The hardness of the surface 1a of the tapping screw 1 is 1.2 times or less the hardness of the core of the tapping screw 1. Here, hardness refers to Vickers hardness (HV).

[0044] The hardness of the surface 1a of the tapping screw 1 is measured using a Vickers hardness tester in accordance with JIS Z 2244:2009.

[0045] The core hardness of the tapping screw 1 is a value measured using a Vickers hardness tester in accordance with "Core Hardness Test" of JIS B 1122:2015. In other words, the core hardness of the tapping screw 1 is a value obtained by measuring the Vickers hardness at the midpoint between the root of a cross section obtained by cutting a portion of the tapping screw 1 sufficiently distant from the tip 2a perpendicularly to the axis LA and the axis LA in accordance with JIS Z 2244:2009.

[0046] As an example, the hardness of the surface 1a of the tapping screw 1 is 380 HV or less. The tapping screw 1 having the above-mentioned hardness can be obtained by subjecting the material to a thermal refining treatment. The tapping screw 1 having the above-mentioned hardness can stably suppress the occurrence of cracks. In particular, the occurrence of cracks on the surface 1a of the tapping screw 1 due to fatigue can be suppressed, and the resistance of the tapping screw 1 to fatigue can be increased.

[0047] (action) Next, the operation of the tapping screw 1 having such a configuration will be described. First, the operation of the tapping screw 1 when the tapping screw 1 is manufactured will be described. The tapping screw 1 of this embodiment can be manufactured by the following method. First, a material 100 for the tapping screw 1 is prepared, having a shape having a first portion 102 corresponding to the shaft portion 2 of the tapping screw 1 and a second portion 103 corresponding to the head portion 3 of the tapping screw 1, as shown in FIG. 5.

[0048] Next, the thread 4 is formed on the first portion 102 by rolling. FIG. 6 is an enlarged view of a part of a cross section including the axis of the first portion 102 when the thread 4 is formed on the first portion 102. When the thread 4 is formed by rolling, as shown in FIG. 6, a rolling die 9 is pressed against the first portion 102 to plastically deform the first portion 102. The rolling die 9 has a shape corresponding to the shape of the thread 4 of the tapping screw 1 to be manufactured. As a result, the thread 4 is formed on the first portion 102 as shown in FIG. 6. The tapping screw 1 is manufactured by subjecting the material 100 with the thread 4 formed on the first portion 102 to a thermal refining treatment.

[0049] Here, in the tapping screw 1 of this embodiment, a flat valley bottom 43 is formed between the formed threads 41 in a longitudinal section including the axis LA of the shank 2. The formed thread 41 has two side edges 412 extending from the crest 411 to the valley bottom 43. The two side edges 412 extend linearly from the crest 411 to the valley bottom 43. Such formed threads 41 and valley bottom 43 are formed by a rolling die 9 having a flat first surface 91 corresponding to the valley bottom 43 and a flat second surface 92 corresponding to the two linear side edges 412, as shown in FIG.

[0050] In the tapping screw 1 of this embodiment, as described above, a flat valley bottom 43 is formed between the formed threads 41 in a vertical cross section including the axis LA of the shank 2. Incidentally, the first surface 91 of the rolling die 9, which is a surface corresponding to the valley bottom 43, is flat. By using such a rolling die 9, the first portion 102 is pressed by the flat first surface 91 of the rolling die 9. As a result, the flat valley bottom 43 is formed between the formed threads 41. In addition, since the first surface 91 is flat, the portion of the first portion 102 corresponding to the valley bottom 43 can be pressed with a strong force. In addition, since the first surface 91 is flat, the portion of the first portion 102 corresponding to the valley bottom 43 can be pressed with a stronger force than when the first surface 91 is a curved surface, for example. As a result, the portion of the first portion 102 corresponding to the valley bottom 43 can be pressed deeper. As a result, the formed thread 41 can be made higher. That is, the outer diameter w1 of the formed thread 41 can be made larger. This allows the outer diameter w2 of the tightening thread 42 to be smaller than the outer diameter w1 of the forming thread 41, as described above. Also, by pressing the portion of the first portion 102 corresponding to the root 43 with a strong force, the diameter w4 of the forming thread 41 at the root 43 can be made smaller. This allows the diameter w3 of the tightening thread 42 at the root 43 to be larger than the diameter w4 of the forming thread 41 at the root 43, as described above.

[0051] In the tapping screw 1 of this embodiment, the two side edges 412 extend linearly from the crest 411 to the root 43. The second surface 92 of the rolling die 9 corresponding to the two side edges 412 is flat to match the shape of the two side edges 412 of the tapping screw 1. With such a rolling die 9, a part of the first portion 102 protruding due to the pressure of the second surface 92 is deformed to fit along the second surface 92, and the formed thread 41 having a large outer diameter w1 can be more stably formed.

[0052] Furthermore, in the tapping screw 1, the thread 4 may have a double-start thread structure. Next, the effect of the thread 4 having a double-start thread structure will be described with reference to Figs. 7 and 8. Fig. 7 is a partially enlarged side view of the tapping screw 1 in which the thread 4 has a double-start thread structure. Fig. 8 is a partially enlarged side view of the tapping screw 1 in which the thread 4 has only a single start. Note that the shape of the thread 4 in Figs. 7 and 8 is expressed more simply than in Figs. 1 and 2.

[0053] In FIG. 7, the tapping screw 1 has a double thread 4 consisting of a first thread 4a and a second thread 4b. When the tapping screw 1 is observed along the axial direction DA, the first thread 4a and the second thread 4b appear alternately. In FIG. 7, the pitch w5 of the first thread 4a and the pitch w6 of the second thread 4b are equal. The pitch w5 and the pitch w6 are twice as long as the distance w7 between the centers of the first thread 4a and the second thread 4b adjacent to each other in the axial direction DA. The pitch w8 of the thread 4 in FIG. 8 is equal to the pitch w5 and the pitch w6 in FIG. 7.

[0054] Comparing the thread 4 shown in Fig. 7 with the thread 4 shown in Fig. 8, the distance w7 between the centers of the first thread 4a and the second thread 4b adjacent in the axial direction DA of the thread 4 having the double-thread structure shown in Fig. 7 is half the length of the pitch w8 of the thread 4 shown in Fig. 8. For this reason, the width w11 in the axial direction DA of the valley bottom of the thread 4 shown in Fig. 7 is smaller than the width w12 in the axial direction DA of the valley bottom of the thread 4 shown in Fig. 8. In this way, when the pitch w8 is equal to the pitch w5 and the pitch w6, or the difference between the pitch w8 and the pitch w5 and the pitch w6 is small, the tapping screw 1 whose thread 4 has a double-thread structure is more likely to have a smaller valley bottom width of the thread 4 than the tapping screw 1 having only a single thread.

[0055] Here, the root of the thread 4 is formed by pressing and recessing a part of the first portion 102 using the rolling dies 9. The material of the part of the first portion 102 pressed by the rolling dies 9 moves in the axial direction DA to form the thread 4. If the width of the root of the thread 4 in the axial direction DA is large, it becomes necessary to use the rolling dies 9 to recess a wider area of ​​the first portion 102 and to move the material of the pressed part of the first portion 102 a larger distance.

[0056] In this regard, when the thread 4 is formed by plastically deforming the first portion 102 using the rolling die 9, if the thread 4 as shown in Fig. 7 is formed, the width of the root of the thread 4 to be formed can be made smaller than when the thread 4 as shown in Fig. 8 is formed. As described above, when the thread 4 is formed by plastically deforming the first portion 102 using the rolling die 9, it is easier to form the thread 4 into a desired shape with the thread 4 as shown in Fig. 7 than with the thread 4 as shown in Fig. 8.

[0057] Next, the action of the tapping screw 1 when the tapping screw 1 is fastened to the workpiece 7 having a plate-like shape as shown in FIG. 9 will be described. In particular, the action of the tapping screw 1 when the tapping screw 1 is fastened to the workpiece 7 to join the plate-like part 8 shown in FIG. 9 to the workpiece 7 will be described. First, the workpiece 7 and the part 8 are prepared. A pilot hole 71 into which the tapping screw 1 is screwed is formed in the workpiece 7. The material of the workpiece 7 is not particularly limited as long as the tapping screw 1 can be screwed into the pilot hole 71 of the workpiece 7. From the viewpoint of making it easy to screw the tapping screw 1 into the pilot hole 71 of the workpiece 7, it is preferable that the hardness of the workpiece 7 is small. At least a portion of the workpiece 7 that forms the wall surface 711 of the pilot hole 71 has a hardness smaller than the hardness of the surface 1a of the tapping screw 1. The material of the workpiece 7 is, for example, a resin. The material of the workpiece 7 is, for example, a resin. The material of the workpiece 7 may be a resin containing glass. The workpiece 7 may be aluminum die-cast or zinc die-cast. The part 8 has a hole 81 of a size that allows the shank 2 and threads 4 of the tapping screw 1 to pass through, but does not allow the head 3 of the tapping screw 1 to pass through.

[0058] Next, as shown in FIG. 9, the workpiece 7 and the component 8 are placed one on top of the other so that the pilot holes 71 and the holes 81 overlap each other.

[0059] Next, the shank 2 and thread 4 of the tapping screw 1 are passed through the hole 81 from the tip side SA1, and the tip 2a of the shank 2 is inserted into the pilot hole 71. This causes a part of the thread 4 provided on the shank 2 to come into contact with the wall surface 711 of the pilot hole 71.

[0060] Next, the tapping screw 1 is rotated in a screwing rotation direction SB1 while a part of the thread 4 is in contact with the wall surface 711 of the pilot hole 71. As a result, the tapping screw 1 is screwed into the pilot hole 71. At this time, as shown in FIG. 10, the tapping screw 1 advances deeper into the pilot hole 71 while forming an internal thread 712 on the wall surface 711 of the pilot hole 71. Here, in this embodiment, the outer diameter w1 of the forming thread 41 is larger than the outer diameter w2 of the fastening thread 42 and is also larger than the outer diameter w10 of the tip thread 44. Therefore, by rotating the tapping screw 1 in the screwing rotation direction SB1, the crest 411 of the forming thread 41 cuts the wall surface 711 of the pilot hole 71, thereby forming the internal thread 712. When rotating the tapping screw 1 in the screwing rotation direction SB1, for example, the tapping screw 1 can be rotated using a tool having a portion that meshes with the head 3 of the tapping screw 1. In the case of a tapping screw 1 having a head 3 shaped like a substantially hexagonal column as shown in FIG. 2, a tool for rotating the tapping screw 1 can be, for example, a socket wrench having a hexagonal socket.

[0061] By further rotating the tapping screw 1 in the screwing rotation direction SB1 from the state shown in Fig. 10, the workpiece 7 comes into contact with the component 8, and the flange portion 32 of the tapping screw 1 comes into contact with the component 8, as shown in Fig. 11. In Fig. 11, the tapping screw 1 is screwed into an internal thread 712 formed in a pilot hole 71. As a result, the tapping screw 1 is fastened to the workpiece 7. Also, in Fig. 11, the component 8 is sandwiched between the flange portion 32 of the tapping screw 1 and the workpiece 7, and the position of the component 8 relative to the workpiece 7 is fixed. As a result, the tapping screw 1 joins the component 8 to the workpiece 7.

[0062] Here, in the tapping screw 1 of this embodiment, the outer diameter w2 of the fastening thread 42 is smaller than the outer diameter w1 of the formed thread 41. This provides the following effects. As described above, by rotating the tapping screw 1 in the screwing rotation direction SB1, the crest 411 of the formed thread 41 cuts the wall surface 711 of the pilot hole 71, forming the internal thread 712. Since the outer diameter w2 of the fastening thread 42 is smaller than the outer diameter w1 of the formed thread 41, the crest 421 of the fastening thread 42 is less likely to come into contact with the internal thread 712 formed by the crest 411 of the formed thread 41. Therefore, when the tapping screw 1 is screwed into the pilot hole 71 of the workpiece 7, the contact area between the tapping screw 1 and the workpiece 7 is reduced. This reduces the friction generated between the tapping screw 1 and the workpiece 7 when the tapping screw 1 is screwed into the pilot hole 71 of the workpiece 7, thereby reducing the screwing torque of the tapping screw 1.

[0063] In this embodiment, the diameter w4 at the root 43 of the formed thread 41 of the tapping screw 1 is smaller than the diameter w3 at the root 45 of the fastening thread 42 of the tapping screw 1. Therefore, when the tapping screw 1 is screwed into the pilot hole 71 of the workpiece 7, the force with which the root 43 of the formed thread 41 is pressed against the wall surface 711 of the pilot hole 71 can be weakened. This further reduces the friction generated between the tapping screw 1 and the workpiece 7 when the tapping screw 1 is screwed into the pilot hole 71 of the workpiece 7, and reduces the screwing torque of the tapping screw 1.

[0064] In FIG. 11, the tapping screw 1 is fastened to the work 7. In addition, the part 8 is joined to the work 7 by the tapping screw 1. In order to maintain the state shown in FIG. 11, it is preferable that the resistance to fatigue of the tapping screw 1 is high. In particular, the fastening thread 42 is located on the head side SB2 rather than the forming thread 41 and the tip thread 44. For this reason, the external force is more likely to be transmitted to the part of the thread 4 that forms the fastening thread 42 and the part of the shank 2 that forms the valley bottom 45 between the fastening threads 42 through the head 3 of the tapping screw 1 and the surface of the work 7 than to the part of the thread 4 that forms the forming thread 41 and the tip thread 44. In particular, in FIG. 11, the part of the thread 4 of the tapping screw 1 that forms the fastening thread 42 is engaged with the part of the internal thread 712 that is formed near the opening 713 of the pilot hole 71. 11, external forces are likely to be transmitted to the portion of the thread 4 that forms the fastening thread 42 and the portion of the shank 2 that forms the valley bottom 45 between the fastening threads 42. For these reasons, it is particularly preferable that the portion of the thread 4 that forms the fastening thread 42 and the portion of the shank 2 that forms the valley bottom 45 between the fastening threads 42 have high resistance to fatigue.

[0065] Here, in the tapping screw 1 of this embodiment, in a longitudinal section including the axis LA of the shank 2, the valley bottom 45 formed between the fastening threads 42 has an arc-shaped portion that is concave outward. The effect of this will be explained. Let us consider a case where the valley bottom 45 formed between the fastening threads 42 is flat and is connected to the side edge 422 of the fastening threads 42 at an angle. In this case, since the valley bottom 45 is flat, external forces tend to concentrate and act on a part of the valley bottom 45. In particular, external forces tend to concentrate and act on the part of the flat valley bottom 45 that is connected to the side edge 422 at an angle. In contrast, since the valley bottom 45 has an arc-shaped portion that is concave outward, the force applied to the part of the shank 2 that forms the valley bottom 45 between the fastening threads 42 can be dispersed. In particular, the valley bottom 45 can be smoothly connected to the side edge 422 of the fastening threads 42 without forming an angle. This makes it possible to distribute the force applied to the portion of the thread 4 that forms the fastening thread 42, and the portion of the shank 2 that forms the valley bottom 45 between the fastening threads 42. As a result, it is possible to prevent external forces from concentrating on the portion of the thread 4 that forms the fastening thread 42, or on part of the portion of the shank 2 that forms the valley bottom 45 between the fastening threads 42, and to increase the resistance to fatigue of said portions.

[0066] The tapping screw 1 of the present embodiment described above includes a shank 2 including an axis LA, a head 3, and a thread 4 provided on the outer periphery of the shank 2. In a longitudinal section including the axis LA of the shank 2, the thread 4 has at least a plurality of formed threads 41 located on the tip side SA1 of the shank 2, and a plurality of fastening threads 42 located on the head side SA2 and having a smaller outer diameter than the formed threads 41. In a longitudinal section including the axis LA of the shank 2, a flat valley bottom 43 is formed between the formed threads 41, and the formed threads 41 have two side edges 412 extending from the crest 411 to the valley bottom 43. In a longitudinal section including the axis LA of the shank 2, a valley bottom 45 that is concave outward is formed between the fastening threads 42, and the fastening threads 42 have two side edges 422 extending from the crest 421 to the valley bottom 45. In a vertical cross section including the axis LA of the shaft portion 2, a root 45 formed between the fastening threads 42 has an arc-shaped portion that is concave outward.

[0067] According to such a tapping screw 1, the first surface 91, which is a surface of the rolling die 9 used to form the thread 4 in the manufacture of the tapping screw 1, is also formed flat in response to the valley bottom 43 between the formed threads 41 being flat. According to such a rolling die 9, the material 100 of the tapping screw 1 can be pressed with a strong force by the flat first surface 91. If the valley bottom 43 between the formed threads 41 is arc-shaped, the surface of the rolling die 9 corresponding to the valley bottom 43 will also be arc-shaped. In this case, it is difficult to make the arc-shaped surface of the rolling die 9 penetrate deep into the material 100 of the tapping screw 1. In contrast, according to this embodiment, a large force can be applied to the material 100 via the flat first surface 91 of the rolling die 9, and the first surface 91 can penetrate deep into the material 100 of the tapping screw 1. This allows the outer diameter w1 of the formed thread 41 to be large. In addition, the root 45 formed between the fastening threads 42 has an arc-shaped portion. As a result, when the tapping screw 1 is fastened to the workpiece 7, the force applied from the outside to the portion of the shank 2 that forms the root 45 between the fastening threads 42 can be dispersed by this arc-shaped portion. This increases the resistance of this portion to fatigue.

[0068] Furthermore, by making the outer diameter w2 of the fastening thread 42 smaller than the outer diameter w1 of the formed thread 41, the following effect is also obtained. When the tapping screw 1 is screwed into the pilot hole 71 of the workpiece 7, the crest 421 of the fastening thread 42 is less likely to come into contact with the internal thread 712 formed by the crest 411 of the formed thread 41. This reduces the friction generated between the tapping screw 1 and the workpiece 7 when the tapping screw 1 is screwed into the pilot hole 71 of the workpiece 7, thereby making it possible to reduce the screwing torque of the tapping screw 1.

[0069] In this embodiment, the two side edges 412 of the formed thread 41 extend linearly from the crest 411 to the root 43. This makes the second surface 92 corresponding to the two side edges 412 of the rolling die 9 used to form the thread 4 in the manufacture of the tapping screw 1 flat. With such a rolling die 9, the formed thread 41 having a large outer diameter w1 can be more stably formed.

[0070] In this embodiment, the diameter w4 at the root 43 of the forming thread 41 of the tapping screw 1 is smaller than the diameter w3 at the root 45 of the fastening thread 42 of the tapping screw 1. This further reduces the friction generated between the tapping screw 1 and the workpiece 7 when the tapping screw 1 is screwed into the pilot hole 71 of the workpiece 7, thereby making it possible to reduce the screwing torque of the tapping screw 1.

[0071] In this embodiment, in a vertical cross section including the axis LA of the shank 2, the thread 4 is located closer to the tip side SA1 of the shank 2 than the formed thread 41, and further has a tip thread 44 having an outer diameter smaller than the fastening thread 42. Therefore, the outer diameter w1 of the formed thread 41 is larger than the outer diameter w2 of the fastening thread 42, and is also larger than the outer diameter w10 of the tip thread 44. As a result, when the tapping screw 1 is screwed into a pilot hole 71 of the workpiece 7, the crest 411 of the formed thread 41 cuts the wall surface 711 of the pilot hole 71, so that an internal thread 712 can be formed on the wall surface 711.

[0072] In this embodiment, the hardness of the surface 1a of the tapping screw 1 is 1.2 times or less the hardness of the core of the tapping screw 1. Such a tapping screw 1 can be manufactured by subjecting the material of the tapping screw 1 to a thermal refining treatment. With such a tapping screw 1, the occurrence of cracks can be stably suppressed.

[0073] According to the tapping screw 1 of this embodiment, when the tapping screw 1 is screwed into the pilot hole 71 of the workpiece 7, the part of the thread 4 that forms the formed thread 41 can form an internal thread 712 on the wall surface 711 of the pilot hole 71. At this time, the above-mentioned characteristics of the tapping screw 1 allow the screwing torque of the tapping screw 1 to be kept small. On the other hand, from the viewpoint of maintaining the state in which the tapping screw 1 is fastened to the workpiece 7, it is preferable that the part of the thread 4 that forms the fastening thread 42 and the part of the shank 2 that forms the valley bottom 45 between the fastening threads 42 have high resistance to fatigue. In contrast, the above-mentioned characteristics of the tapping screw 1 allow the part of the thread 4 that forms the fastening thread 42 and the part of the shank 2 that forms the valley bottom 45 between the fastening threads 42 to have high resistance to fatigue. As described above, according to this embodiment, a tapping screw 1 can be provided in which the screwing torque is kept small when the tapping screw 1 is screwed into the pilot hole 71 of the workpiece 7, and the resistance to fatigue when the tapping screw 1 is fastened to the workpiece 7 is high.

[0074] It is also possible to combine the multiple components disclosed in the above embodiments as necessary, or to delete some of the components disclosed in the above embodiments. [Explanation of symbols]

[0075] 1 Tapping screw 1a surface 1b surface area 1c deep region 2 Shaft section 3 head 4 Threads 41 Formed Thread 42 Fastening thread 44 Tip Thread 7 Work 71 Pilot hole 8 parts 81 holes

Claims

1. A tapping screw having a shank including an axis, a head, and a thread provided on the outer periphery of the shank, In a longitudinal cross section including the axis of the shaft portion, the thread has at least a plurality of forming threads located on the tip side of the shaft portion and a plurality of tightening threads located on the head side and having an outer diameter smaller than that of the forming threads, In a longitudinal cross section including the axis of the shank, a flat valley bottom is formed between the formed threads, and the formed threads have two side edges extending from the crests to the valley bottom, In a longitudinal cross section including the axis of the shank, a valley bottom that is concave outwardly is formed between the fastening threads, and the fastening threads have two side edges extending from a crest to the valley bottom, a root formed between the fastening threads in a longitudinal cross section including the axis of the shank portion has an arc-shaped portion that is concave outwardly.

2. 2. The tapping screw according to claim 1, wherein the two side edges of the forming thread extend linearly from the crest to the root.

3. 3. The tapping screw according to claim 1, wherein the diameter of the forming thread at the root is smaller than the diameter of the tightening thread at the root.

4. 3. The tapping screw according to claim 1, wherein in a longitudinal cross section including the axis of the shank, the thread further includes a tip thread that is located closer to the tip of the shank than the forming thread and has an outer diameter smaller than that of the fastening thread.

5. The tapping screw according to claim 1 or 2, wherein the thread has a double-start thread structure.

6. 3. The tapping screw according to claim 1, wherein the hardness of the surface of the tapping screw is 1.2 times or less the hardness of the core of the tapping screw.

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