JPS6111699B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention was developed primarily for the purpose of improving the initial screwing torque of self-tapping screws and increasing the screw holding force after screwing, and further for the purpose of improving the plastic working rate of female screws. This invention relates to the structure of a self-tapping screw, which is characterized mainly by the screw material, and to a method of forming a thread-forming screw.

Conventionally, various shapes of this type of tuft pin screw have been proposed and used, but the current situation is that the needs of users have not yet been completely met.
The user's request is to provide a tapping screw that can maximize the two objectives of having a smaller initial screw-in torque and a high holding force after screw-in to prevent loosening.

The present invention reduces the initial screwing torque as much as possible, increases the screw holding force after screwing, and
It is characterized by perfecting the locking effect and improving the female thread plastic working rate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing one embodiment of the invention.

In the drawing, 1 is a screw material main body, and this screw material main body 1 has a cylindrical shaft portion 2 and a cylindrical shaft portion 2.
It is composed of a head 4 having an engagement groove 3 for a screwdriver tool such as a screwdriver formed at its rear end, and a truncated conical shaft 5 connected to the tip of a cylindrical shaft 2. , furthermore, the cylindrical shaft portion 2 of this screw material main body 1
Three first plane parts 6 are formed at equal intervals in the circumferential direction and parallel to the axial center line in a region covering approximately the entire length of the truncated conical shaft part 5 and a part of the truncated conical shaft part 5. Part 5
in the region reaching the cylindrical shaft portion 2 leaving a truncated conical shaft end portion 7 at its tip, and the first flat portion 6
forming three second flat portions 8 that are equally spaced in the circumferential direction and parallel to the axial center line with a phase difference of 60° to
Thus, the truncated conical shaft portion 5 forming the second plane portion
As shown in FIG. 5A, the cross-sectional shape of the truncated conical shaft portion 5 is formed into a triangular shape with arcuate corners, and the first and second flat portions 6 and 8 are formed. As shown in Figure B, the cross-sectional shape of the cylindrical shaft part 2 is formed into a hexagonal shape with arced corners, and the first flat part 6 is formed, as shown in Figure C. It is formed into a triangular shape having an arcuate surface and a phase difference of 60° with respect to the triangular shape of the truncated conical shaft portion 5. Next, an external thread 9 is rolled over the entire area of the cylindrical shaft portion 2 and the truncated conical shaft portion 5 of the screw main body 1 thus formed. Through this thread rolling, a first preliminary internal thread forming external thread 10 having a triangular cross-sectional shape and a rounded shape is formed on the truncated conical shaft part 5 having only the second flat part 8, As shown in FIG.
A second male screw thread 11 for forming a second preliminary female screw having a rounded hexagonal cross-sectional shape as a whole is rolled, and the first
A normal male screw thread 12 having a triangular cross-sectional shape that is rounded and nearly circular is rolled on the cylindrical shaft portion 2 having the flat portion 6.

According to the present invention, by forming the first and second preliminary female thread forming male thread portions 10 and 11, the initial torque for screwing in is extremely small, the female thread can be formed smoothly and easily, and the first preliminary female thread forming is possible. The cross-sectional shape of the male thread portion 10 for use is formed into a substantially triangular shape, the male thread portion 11 for carving the second preliminary female thread is formed into a substantially hexagonal shape close to a circle, and the cross-sectional shape of the normal thread portion 1 is formed. Since the cross-sectional shape is formed into a rounded triangular shape with a phase difference of 60 degrees with respect to the triangular shape of the male thread portion 10 for carving the first preliminary female thread, the screw holding force after screwing is increased. Various advantages can be obtained, such as being strong enough to not loosen even with slight vibrations.

In particular, at the transition portion from the truncated conical shaft portion 5 to the cylindrical shaft portion 2, the first flat portion 6 and the second flat portion 8 are approximately intersected with each other at a phase of 60° at the boundary portion. Since it is formed into a hexagonal shape close to a circle, a spare female thread that is as close as possible to the normal female thread formed by the male thread 9 of the cylindrical shaft portion 2 can be formed at the same place with extremely reduced screwing torque. Since the normal female thread is formed from the male thread of the cylindrical shaft portion 2, the transition is extremely smooth without any resistance, and the female thread can be formed with extremely high accuracy.

According to the present invention, perfect screw holding force and loosening effect can be obtained.
According to the product of the present invention, even if a 3 mm forming screw is used instead, it can be expected to have the same holding power and locking force as a 4 mm forming screw. Therefore, when using a large number of screws, there is an advantage that the total weight can be significantly reduced.

In addition, as another embodiment, when considering the ideal thread build-up during male thread rolling, the first flat portion 6
It is preferable that the second plane part 8 has a large arcuate radius of curvature in the circumferential direction as shown in an enlarged view in FIG.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is a side view showing the shape of the main thread material, FIG. 2 is a plan view of the same, FIG. 3 is a side view showing the shape after thread rolling, and FIG. The figure is the same plan view as above, and Figure 5 A, B, and C are Figure 1 A.
-A cross-sectional view taken along lines A, B-B, and C-C; Figure 6 is a partially cutaway exploded view of the main screw material; Figure 7 is a cross-sectional view showing the first and second plane parts enlarged. It is a diagram. In the figure, 1 is the screw material main body, 2 is the cylindrical shaft part, and 5
1 is a truncated conical shaft portion, 6 is a first plane portion, 8 is a second plane portion, 10 is a male thread portion for carving a first preliminary female thread,
Reference numeral 11 indicates a male thread portion for carving a second preliminary female thread, and 12 indicates a normal male thread portion.

Claims (1)

[Claims] 1. In a screw material body consisting of a cylindrical shaft portion and a frusto-conical shaft portion connected to the tip of the cylindrical shaft portion, the cylindrical shaft portion and the frusto-conical shaft portion of the screw material are Three first plane parts are formed in a part of the area at equal intervals in the circumferential direction and parallel to the axis, and are cut from the continuous part of the cylindrical shaft part and the truncated conical shaft part. The first region extends near the tip of the conical shaft.
Three second flat parts having a phase difference of 60° with respect to the flat part and parallel to the axis are molded, and then the first,
An external thread is rolled over the entire area of the cylindrical shaft portion and the frustoconical shaft portion including the second plane portion, and by this thread rolling, the region of the frustoconical shaft portion forming the second plane portion is formed. The first male screw thread part for forming a preliminary internal thread is molded in a generally triangular shape with a rounded outer shape, and the region of the truncated conical shaft part in which the first and second flat parts are molded has a roughly triangular outer shape with a rounded shape. A hexagonal second male thread portion for forming a preliminary female thread is molded, and the outer shape of the area of the cylindrical shaft portion forming the first plane portion is modeled after the outer shape of the male thread portion for forming the first preliminary female thread. A method for forming a thread forming screw, characterized by forming a normal male screw thread in a nearly circular triangular shape having a phase difference of 60 degrees with respect to a substantially triangular shape.