Screw for fastening different materials

Abstract

To provide a more improved screw for fastening different materials.SOLUTION: A cross-sectional shape of a pointed head part 20 of a screw 1 for fastening different materials has three vertices, sides connecting the vertices are each curved outwardly and convexly, and ridge parts 21, 22, 23 connecting the vertices of the pointed head part 20 are spirally oriented in the same direction as a spiral direction of a screw groove 11 of a main screw part 10 as they approach a tip.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a screw for fastening different materials, which can melt a thermoplastic resin by heat when being screwed into a predetermined portion of a thermoplastic resin as a base material, form a screw groove in the predetermined portion, and fix it, and can fasten a material different from the base material to the base material.

Background Art

[0002] For example, like the screw disclosed in Patent Document 1, a tapered pointed portion is provided at the tip of the screw portion, the cross-sectional shape of the pointed portion has three vertices, and the sides connecting between the vertices each have an outward convex curved shape, and the pointed portion has a substantially triangular pyramid shape. In such a screw, the base material is heated by friction and plastically deformed to form a hole by screwing in the pointed portion, and then a screw groove is formed by the screw portion and the screw is screwed onto the base material. In order to heat and plastically deform the base material, it has been considered desirable that the pointed portion has a substantially triangular pyramid shape as described above rather than a simple conical shape.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The above-mentioned pointed portion requires a predetermined length to generate frictional heat sufficient to plastically deform the base material. However, the pointed portion exists only for plastically deforming the base material, and in the state where the screw is fastened to the base material, the pointed portion is not involved in the fastening to the base material. Here, in recent years, in the automotive industry and the like, the demand for weight reduction of parts has been increasing, and it has been desired to reduce the weight of screws as much as possible.

[0005] Therefore, an object of the present invention is to provide a more improved screw for fastening different materials.

Means for Solving the Problems

[0006] The present invention is provided with a main screw portion that is located in a fastening state of a fastening target made of different materials from each other, has a constant outer diameter, and has a screw groove formed on its outer peripheral surface, and is continuously formed from the tip of the main screw portion. , a pointed tip portion whose diameter decreases toward the tip, and in the pointed tip portion, the fastening target is not located in the fastening state, and further, the cross-sectional shape of the pointed tip portion has three vertices, and the sides connecting between the vertices are respectively convex curved shapes facing outward, and three ridge line portions formed by connecting the vertices on the outer peripheral surface of the pointed tip portion are spiral-shaped in the same direction as the spiral direction of the screw groove of the main screw portion toward the tip. It is a screw for fastening different materials characterized by being

[0007] In such a configuration, the ridge line portion of the pointed tip portion is not linear but curved in a spiral shape, whereby the surface area of the pointed tip portion is larger than that of the conventional one, and the frictional heat with the base material becomes larger. Therefore, the required length of the pointed tip portion can be shorter than that of the conventional one, contributing to the weight reduction of the screw. The inclination angle (spiral inclination) of the ridge line portion with respect to the axis is preferably about 5° to 20°. If it is less than 5°, it is difficult to obtain an effect compared with the conventional screw, and if it exceeds 20°, there is a concern that the heating efficiency due to friction will decrease.

Effects of the Invention

[0008] The screw for fastening different materials of the present invention can shorten the overall length compared with the conventional one, and has an excellent effect of contributing to weight reduction.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0010] Embodiments of the present invention will be described according to examples. It should be noted that the present invention is not limited to the examples shown below, and design changes can be made as appropriate. Also, for the sake of convenience, in the examples, the head side of the screw for fastening different materials is defined as the rear, and the tip side of the screw for fastening different materials is defined as the front for explanation, but the present invention is not limited by this.

[0011] As shown in FIG. 1 and the like, the screw 1 for fastening different materials (hereinafter, also simply referred to as screw 1) has a main screw portion 10 having a constant outer diameter and a cylindrical shape, and is continuously formed from the front (tip side) of the main screw portion 10. It includes an introduction reduced-diameter portion 15 having a diameter smaller than that of the main screw portion 10, and a pointed head portion 20 that is continuously formed from the front of the introduction portion 15 and whose diameter is reduced toward the tip. Further, a screw head 30 is formed behind the main screw portion 10.

[0012] A screw groove 11 is formed on the outer peripheral surface of the main screw portion 10. In this embodiment, the screw direction of the screw groove 11 is a right-handed screw direction.

[0013] The outer diameter of the introduction reduced-diameter portion 15 is set to be substantially equal to the diameter of the valley portion of the screw groove 11 of the main screw portion 10. To explain earlier, the inner peripheral surface of the hole in the base material W1 drilled by the pointed head portion 20 is adjusted by the introduction reduced-diameter portion 15, and a screw shape is formed on the inner peripheral surface of the hole by the screw groove 11 of the main screw portion 10, and the screw 1 is screwed on.

[0014] As shown in Fig. 3(b), the cross-sectional shape of the tip portion 20 has three vertices 21a, 22a, and 23a, and the sides connecting between the vertices 21a, 22a, and 23a each have an outwardly convex curved shape. Each of the vertices 21a, 22a, and 23a is the point farthest from the axis L in the radial direction, and it does not have a sharp shape with corners. Instead, as shown in Fig. 3(b), the tip is rounded and curved so that it is convex outward.

[0015] And the ridge lines 21, 22, and 23 connecting the vertices 21a, 22a, and 23a in the tip portion 20 are in a spiral shape inclined in the right-handed direction as they go towards the tip. This is in the same direction as the spiral direction of the thread groove 11. That is, when comparing Fig. 3(b) showing the cross-sectional shape of the rear end portion of the tip portion 20 and Fig. 3(c) showing the cross-sectional shape at the substantially middle portion of the tip portion 20, the positions of the vertices 21a, 22a, and 23a are shifted around the axis of the screw 1.

[0016] As shown in Fig. 2, the deviation angle α of the ridge lines 21, 22, and 23 from the axis in this embodiment is 10°.

[0017] In the figure, for ease of understanding, the ridge lines 21, 22, and 23 are drawn as two-dot chain lines. However, since the outer peripheral surface portion near the vertices 21a, 22a, and 23a is rounded as described above, the outer shape of the ridge lines 21, 22, and 23 also becomes a convex curved line shape on the outside.

[0018] Such a screw 1 is used when bonding the work piece W2 to the base material W1 made of a thermoplastic resin as shown in Fig. 4. Since the base material W1 is a thermoplastic resin, it is melted by the frictional heat generated between the tip portion 20 as the screw 1 rotates around its axis, and the screw 1 bites in.

[0019] When the screw 1 bites into the base material W1 to a certain extent, corresponding thread grooves are formed in the base material W1 by the thread groove 11 of the main thread portion 10 of the screw 1, and the screw 1 is screwed onto the base material W1.

[0020] At this time, as shown in FIG. 5, in the fastened state X where the screw 1 is screwed onto the base material W1, a bulging portion 50 is formed around the screw 1 on the back surface of the base material W1, which is the opposite side of the base material W1 through which the screw 1 passes. A thread groove is also formed on the inner peripheral surface of the bulging portion 50, further increasing the screwing strength between the base material W1 and the screw 1.

[0021] In addition, in the fastened state X shown in FIG. 5, the base material W1 to be fastened and the material W2 to be fastened are located at the main screw portion 10 of the screw 1, and the pointed head portion 20 is located in the back side direction penetrating from the base material W1. That is, the pointed head portion 20 is not involved in the fixation of the base material W1 or the material W2 to be fastened in the fastened state X.

[0022] In this way, since the ridge lines 21, 22, 23 of the pointed head portion 20 are configured to be helical and deviated from the axis, the outer surface area of the pointed head portion 20 is larger than that of a conventional screw with the ridge lines along the axis, increasing the contact area with the base material W1 and generating more frictional heat. The greater the generation of frictional heat, the easier the plastic deformation of the base material W1 due to heat, so the total length of the pointed head portion 20 can be made shorter than that of the conventional one. The pointed head portion 20 becomes an unnecessary part after the fastening of the base material is completed, and the shorter the total length of the pointed head portion 20, the more it contributes to the weight reduction of the screw 1.

[0023] In the above embodiment, the dimensional shapes of each part can be freely selected as appropriate. In order to eliminate the problem that the screw 1 cannot be properly screwed due to the bulge on the surface side of the base material W1, for example, a concave portion may be formed at the boundary between the main screw portion 10 and the screw head portion 30 to absorb the bulge on the surface side of the base material W1.

Explanation of symbols

[0024] 1 Screw for fastening different materials 10 Main screw portion 11 Thread groove 15 Introduction portion 20 Pointed head portion 21, 22, 23 Ridge lines 21a, 22a, 23a Vertices 30 Screw head 50 Bulge W1 Base material (object to be fastened) W2 Material to be fastened (object to be fastened) X Fastening state α Deviation angle

Claims

[Claim 1] A threaded portion having a constant outer diameter and a thread groove formed on an outer peripheral surface thereof, in which the fastening objects are positioned in a fastening state of the fastening objects being made of different materials; a pointed head portion formed continuously from the tip of the main screw portion and tapering toward the tip; Equipped with At the pointed portion, a fastening object is not located in a fastening state, Furthermore, the cross-sectional shape of the pointed portion has three vertices, and the sides connecting the vertices are each outwardly convexly curved, Furthermore, three ridges formed by successive vertices on the outer peripheral surface of the pointed head are spirally oriented in the same direction as the spiral direction of the thread groove of the main screw portion as they approach the tip. A screw for fastening dissimilar materials.

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