JP3148742U - Self-tapping screw for high-tensile steel plate - Google Patents

Abstract

To provide a self-tapping screw that can be screwed into an ultra-high-strength steel sheet while forming a female thread, and that hardly causes delayed fracture. The shaft portion is composed of a constant diameter portion 3c from the head side to the tapered portion 3b on the tip side, and the male screw 4 is arranged in order from the tip side toward the head side, the introduction screw portion 4a, The internal thread forming screw portion 4b and the normal thread portion 4c are formed. The introduction screw portion 4a is formed on the tapered portion 3b of the shaft portion, and the outer shape of the thread is formed in a triangle. The internal thread forming screw portion 4b is formed on the shaft portion and the like. On the side of the tapered portion 3b in the diameter portion 3c, a triangular shape is formed so that the outer shape of the thread is in contact with the outer periphery of the equal diameter portion 3c at three positions, and the normal screw portion 4c is the head of the equal diameter portion 3c of the shaft portion. It is formed on the part 2 side so that the outer shape of the screw thread is circular, and the material is low carbon steel with C of 0.15% or less, and the hardness of the surface portion is Hv550 or more, the internal hardness Is set to Hv380 or less. [Selection] Figure 1

Description

  The present invention relates to a self-tapping screw for a high-strength steel plate that can be screwed into the high-strength steel plate.

  In recent automobiles, the use of materials has been diversified in order to promote weight reduction. Steel plates are the most common materials used in automobiles. Among them, high-strength steel plates have high tensile strength and sufficient strength even when they are thin. I think that.

  In automobiles, many parts are assembled with bolts and nuts, but fastening with self-tapping screws is also actively used because no nuts are required. However, even among high-strength steels, when they become super high-tensile steels with a tensile strength of 980 MPa class, the hardness is considerably high, so the threads are easily crushed. It becomes difficult to screw in while forming. Therefore, conventionally, a method has been used in which a nut is fixed to a steel plate side in advance by welding or the like, and a component is assembled by screwing a normal bolt into the nut.

Where a self-tapping screw can be used, welding a nut is wasteful and expensive.
Even if a self-tapping screw for ultra-high-strength steel sheet is provided, a large torque is required to screw the self-tapping screw into the ultra-high-strength steel sheet. It is expected that a large stress remains on the screw, causing a problem of delayed fracture. This delayed fracture is due to the embrittlement phenomenon of the material, which is believed to be due to hydrogen embrittlement.

  Accordingly, an object of the present invention is to provide a self-tapping screw for a high-strength steel sheet that can be screwed into an ultra-high-strength steel sheet while forming a female thread, and that hardly causes delayed fracture.

  The present invention provides a self-tapping for high-strength steel sheet that has a male screw on the outer periphery of a shaft portion provided with a head on one end, and is screwed while forming a female screw in a pilot hole formed in the high-tensile steel sheet. In the screw, the shaft portion has a tapered shape at the distal end side, and is an equal diameter portion from the head side to the tapered portion on the distal end side, and the male screw is formed by forming an internal thread on the inner peripheral surface of the pilot hole. An introduction screw portion for forming a shallow guide groove, a female screw forming screw portion for forming the female screw on the inner peripheral surface of the pilot hole by deepening the guide groove, and forming on the inner peripheral surface of the pilot hole The introduction screw portion is configured so that a thread is formed on the tapered portion of the shaft portion and the outer shape of the thread is a triangle. The female thread forming screw portion is formed with the same diameter of the shaft portion. The thread portion is formed on the side of the tapered portion in the minute so that the outer shape of the screw thread is a triangle that is in contact with the outer periphery of the equal diameter portion at three positions, and the normal thread portion is the portion of the shaft portion. On the head side in the equal diameter portion, a screw thread is formed so that the outer shape of the screw thread is circular, and the material is a low carbon steel having a C of 0.15% by mass or less, and the surface The hardness of the portion is Hv550 or higher, and the internal hardness is Hv380 or lower.

  In the self-tapping screw for high-tensile steel plate having this configuration, the outer shape of the thread of the introduction screw portion and the female screw forming portion is a triangle, and in particular, in the female screw forming portion, the outer shape of the screw thread is in contact with the shaft portion at three points. Therefore, the length of the portion of the prepared hole that contacts the inner peripheral surface is shortened, and the resistance when forming the female screw can be reduced. In addition, since the hardness on the surface side of the thread is Hv550 or higher, even if it is a hard ultra-high strength steel sheet, the thread is not crushed and can be screwed in while forming the female thread. And since the hardness of the center part of a self-tapping screw is Hv380 or less, it is excellent in toughness and can prevent delayed fracture effectively.

  Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a self-tapping screw (hereinafter simply referred to as a self-tapping screw) 1 for a high-strength steel sheet according to the present invention. The self-tapping screw 1 is formed by forming a male screw 4 on the outer periphery of a shaft portion 3 provided with a head 2 with a hook on one end side.

  The shaft portion 3 has a tapered shape on the tip side, and a constant diameter portion 3c is formed between the neck lower portion 3a on the head 2 side and the tapered portion 3b on the tip side. As shown in FIG. 3, the male screw 4 includes an introduction screw portion 4a, a female screw forming screw portion 4b, and a normal screw portion 4c from the distal end side. The introduction screw portion 4a is formed in the tapered portion 3b of the shaft portion 3, and the screw thread is formed in a triangular shape as shown in FIGS. 2 (d) and 2 (e), as shown in FIGS. ing. The thread having a triangular outer shape in the introduction screw portion 4a is formed at three positions, that is, the center of the portion corresponding to each side of the triangle is in contact with the outer peripheral surface of the tapered portion 3b. Further, the height h1 of the portion corresponding to the triangular corner of the thread is gradually increased toward the female thread forming screw portion 4b side.

  The female thread forming screw portion 4b is formed continuously with the introduction screw portion 4a on the tapered portion 3b side of the constant diameter portion 3c of the shaft portion 3, and the thread has an outer shape corresponding to one round when viewed from the axial direction. It is formed in a triangle as shown in (b) and (c). The external thread forming screw part 4b has a triangular outer thread shape that is in contact with the outer peripheral surface of the equal-diameter portion 3c at three positions, like the thread of the introduction screw part 4a. In addition, the height h2 of the portion corresponding to the triangular corner of the thread in the female screw forming screw portion 4b gradually increases toward the normal screw portion 4c. In the present embodiment, the number of screw threads of the female thread forming screw portion 4b is three. However, the number of mountains is not limited to three, but may be three or more.

The normal thread portion 4c is formed continuously to the female thread forming screw portion 4b on the head 2 side of the constant diameter portion 3c of the shaft portion 3, and the outer shape of the screw thread for one round viewed from the axial direction is circular. The protrusion height h3 from the equal-diameter portion 3c is constant. In this normal thread portion 4c, the thread on the female thread forming screw portion 4b side gradually changes from the triangle of the female thread forming screw portion 4b to a circular shape.
The triangular threads of the introduction screw portion 4a and the internal thread forming screw portion 4b are formed such that the protruding height of the rounded corner portion gradually increases toward the normal screw portion 4c. The height of the screw thread is constant.

  The self-tapping screw 1 is manufactured from a low carbon steel, particularly a low carbon steel having C of 0.15% by mass or less. In addition to C, Si is contained in an amount of 0.1% by mass or less and Mn is contained in an amount of 0.6% by mass. The head 2 and the shaft 3 are formed by header processing from the above-mentioned low carbon steel rod, and then a male screw is formed on the shaft 3 by a rolling die. The tapered portion 3b of the shaft portion 3 is formed in a cross-sectional triangle when the header is processed, and becomes a circular cross-section when the male screw 4 is rolled. For this reason, the tapered portion 3b is not a perfect circle, and there is a portion where a remnant of the original cross-sectional triangle exists.

  Then, after the male screw 4 is formed on the shaft portion 3 by rolling, it is carburized and quenched and further tempered. By this quenching and tempering, the self-tapping screw 1 is hardened so that the hardness of the surface becomes Hv550 or more, and the radius from the center of the shaft portion 3 inside, specifically, in the equal-diameter portion 3c of the shaft portion 3 Curing is controlled so that the hardness of the portion that is closer to the outer peripheral surface side by half the length is less than Hv380.

  Next, the operation of the self-tapping screw 1 having the above configuration will be described. FIG. 4 shows a state in which a component 6 as a fastening target member is fixed to the high-tensile steel plate 5 by the self-tapping screw 1. In this case, the high-tensile steel plate 5 is an 980 MPa class ultra-high-strength steel plate, and a pilot hole 7 (see FIG. 5) for screwing the self-tapping screw 1 is formed in the high-tensile steel plate 5. Further, a through hole 8 for the self-tapping screw 1 is formed in the component 6.

  In order to fix the component 6 to the high-tensile steel plate 5 with the self-tapping screw 1, the component 6 is stacked on the high-tensile steel plate 5, and the through hole 8 of the component 6 is aligned with the lower hole 7 of the high-tensile steel plate 5. Then, the self-tapping screw 1 is passed through the through hole 8 of the component 6, and the introduction screw portion 4 a of the self-tapping screw 1 is inserted into the prepared hole 7.

  In this state, a screwdriver (not shown), which is a screwdriver, is applied to the head 2 and rotated in the screwing direction. Then, the thread of the male screw 4 of the introduction screw portion 4a is applied to the inner peripheral surface of the pilot hole 7, and this triggers the formation of a shallow guiding groove 9a in the inner peripheral surface of the pilot hole 7 in a spiral shape (FIG. 5). (See (a)). When the driver is further rotated, the thread of the female thread forming screw part 4b gradually forms the shallow guiding groove 9a formed on the inner peripheral surface of the pilot hole 7 by the thread of the introduction screw part 4a while gradually forming the pilot hole It will begin to enter into 7. In this way, initially, the shallow guiding groove 9a formed by the introduction screw portion 4a on the inner peripheral surface of the prepared hole 7 is deeply formed by the female screw forming screw portion 4b to form the female screw 9 (FIG. 5). (See (b)).

  When the internal thread 9 is formed by the threads of the introduction thread portion 4a and the internal thread forming thread portion 4b, the external shape of the thread is a triangle. Therefore, the thread is entirely on the inner peripheral surface of the pilot hole 7. Rather than making contact at the periphery, the female thread is formed by contacting locally at three positions. For this reason, when the introduction screw portion 4a and the female screw forming screw portion 4b form the female screw 9, the resistance acting on the screw thread becomes relatively small. And since the hardness of the surface of a screw thread is Hv550 or more and it is very hard, even if a counterpart material is a super high-strength steel plate, the thread of the introduction screw part 4a and the female screw forming screw part 4b is not crushed, and the female screw 9 can be screwed into the inner peripheral surface of the pilot hole 7 while being molded.

  In particular, in the female thread forming screw portion 4b, the portions corresponding to the three sides of the triangular thread are in contact with the outer peripheral surface of the equal-diameter portion 3c of the shaft portion 3, so that the contact length of the pilot hole 7 with respect to the inner peripheral surface The length can be shortened. That is, FIG. 6 shows the thread of the female thread forming screw portion 4b, the solid line shows this embodiment, and the broken line has a height in which the three sides of the triangular thread are not in contact with the equal-diameter portion 3c. Shows the case. As can be understood by comparing the solid thread and the broken thread in FIG. 6, the length L of the thread contacting the inner peripheral surface of the pilot hole 7 is shorter in this embodiment. For this reason, it becomes possible to make resistance at the time of forming the internal thread 9 smaller.

  When the female screw 9 is formed on the inner peripheral surface of the pilot hole 7 by the female screw forming screw portion 4b, the normal screw portion 4c is then screwed into the female screw 9 (see FIG. 5C). Then, as shown in FIG. 4, the component 6 is fastened and fixed to the high-tensile steel plate 5 by tightening the self-tapping screw 1 until the flange 2 a of the head 2 is seated on the component 6. At this time, as shown in FIG. 5 (c), the internal thread 9 formed in the pilot hole 7 and the thread of the normal thread portion 4c of the self-tapping screw 1 are in close contact with each other, so that the tightening force is increased. It is also possible to prevent looseness.

  As described above, according to the self-tapping screw 1 of the present embodiment, the female screw 9 can be formed without causing a problem that the screw thread is crushed even if the counterpart material is an ultra-high-strength steel plate. Moreover, since the material of the self-tapping screw 1 is a low carbon steel having C of 0.15% by mass or less, it is difficult to absorb hydrogen, and since the internal hardness is Hv380 or less, the inside does not lose toughness. For this reason, delayed fracture based on hydrogen embrittlement can be prevented as much as possible.

  FIG. 7 shows a second embodiment of the present invention. This embodiment differs from the first embodiment described above in the form of the introduction screw portion 4a of the male screw 4 of the self-tapping screw 1. That is, in this embodiment, the thread of the introduction screw portion 4a has a triangular outer shape, but the portion corresponding to the three sides does not contact the tapered portion 3b of the shaft portion 3, but has a height. Different from the first embodiment.

  FIG. 8 shows a third embodiment of the present invention. This embodiment is different from the above-described embodiment in how the self-tapping screw 1 is used. That is, in this embodiment, the self-tapping screw 1 is screwed into the pilot hole 11 of the high-tensile steel plate 10 made of a 980 MPa class ultra-high-strength steel plate, and the self-tapping screw 1 is fixed to the high-tensile steel plate 10.

  The component 12 fixed to the high-tensile steel plate 10 has a through hole 13. The self-tapping screw 1 fixed to the high-tensile steel plate 10 is passed through the through-hole 13, and the component 12 is attached to the high-tensile steel plate 10. Overlay on. Thereafter, the nut 14 is screwed onto the normal thread portion 4 c of the self-tapping screw 1 protruding from the component 12, and the component 12 is fastened and fixed to the high-tensile steel plate 10.

The present invention is not limited to the embodiment described above and shown in the drawings, and can be expanded or changed as follows.
The material of the self-tapping screw 1 may include components other than C and the content other than those shown in the first embodiment.
Of course, it is possible to use a metal plate other than the 980 MPa class ultra-high-strength steel plate.
The prepared hole formed in the high-tensile steel plate may be burring processed.

Side view of the self-tapping screw showing the first embodiment of the present invention 1 shows cross-sectional shapes of each part of a self-tapping screw, where (a) is a cross-sectional view taken along line AA in FIG. 1, (b) is a cross-sectional view taken along line BB in FIG. 1, and (c) is a cross-sectional view taken along line CC in FIG. (D) is DD sectional drawing of FIG. 1, (e) is EE sectional drawing of FIG. Perspective view of self-tapping screw Sectional view showing the state of component mounting with self-tapping screws The process of screwing the self-tapping screw into the pilot hole is shown. (A) is a cross-sectional view showing the state of forming the guiding groove with the male screw, (b) is a cross-sectional view showing the formed state of the female screw with the male screw, (c) Sectional drawing which shows the screwing state with respect to the internal thread of the external thread Cross section of female thread forming thread FIG. 2 shows a second embodiment of the present invention, where (a) is a diagram corresponding to (d) of FIG. 2, and (b) is a diagram corresponding to (e) of FIG. FIG. 4 equivalent view showing a third embodiment of the present invention

Explanation of symbols

  In the figure, 1 is a self-tapping screw for high-tensile steel plate, 2 is a head, 3 is a shaft portion, 3b is a tapered portion, 3c is an equal diameter portion, 4 is a male screw, 4a is an introduction screw portion, and 4b is a female screw forming screw. 4c is a normal thread part, 5 and 10 are high-tensile steel plates, 7 and 11 are pilot holes, and 9 is a female thread.

Claims (2)

In the self-tapping screw for high-strength steel sheet that has a male screw on the outer periphery of the shaft part provided with a head on one end side and is screwed in while forming a female screw in a pilot hole formed in the high-tensile steel sheet by the male screw.
The shaft portion has a tapered shape on the tip side, and is a constant diameter portion from the head side to the tapered portion on the tip side,
The male screw is formed by forming a shallow guiding groove for forming a female screw on the inner peripheral surface of the pilot hole, and forming the female screw on the inner peripheral surface of the pilot hole by deepening the guiding groove. A female thread forming screw part, and a normal thread part screwed to the female thread formed on the inner peripheral surface of the pilot hole,
The introduction screw portion is formed on the tapered portion of the shaft portion such that a screw thread is formed such that the outer shape of the screw thread is a triangle,
The female thread forming screw portion has a thread on the tapered portion side of the constant diameter portion of the shaft portion, and a triangular shape in which the outer shape of the screw thread contacts the outer periphery of the constant diameter portion at three positions. Formed,
The normal threaded portion is formed on the head side in the equal-diameter portion of the shaft portion so that the outer shape of the thread is circular,
The material is a low carbon steel with C of 0.15% by mass or less, the surface portion has a hardness of Hv550 or higher, and the internal hardness is Hv380 or lower. Tapping screw.   The self-tapping screw for high-tensile steel sheets according to claim 1, wherein the female thread forming portion includes at least three threads.

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