JPH0745082B2 - Manufacturing method of neck cut bolt - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a neck cut bolt having a head that is broken by a certain tightening torque.

(Prior art) A neck-cutting bolt that is designed to break a neck-cutting portion when a constant tightening torque is applied to the bolt head is provided in the conventional neck-cutting bolt. Known from. Such neck-cutting bolts require that the breaking torque be adjusted to an accurate value that is as uniform as possible, but conventionally, the neck-cutting portion is formed by cutting the blank heads one by one. As a result, there have been problems such as large variations in breaking torque due to variations in dimensional accuracy of the necking portion, and high manufacturing costs due to cutting work one by one.

(Problems to be Solved by the Invention) An object of the present invention is to solve the above conventional problems and to provide a method for manufacturing a necking bolt that can manufacture a necking bolt with less variation in breaking torque at low cost. It has been completed.

(Means for Solving the Problem) The present invention cuts a round bar to a required size, and manufactures a blank composed of a bolt head having a relatively large diameter and a shaft portion having a relatively small diameter by cold forging, In addition to forming a cap-shaped collar portion on the bolt head and forming a hexagonal portion having a diagonal diameter of the same diameter as the bolt head portion, the bolt head portion is formed on the bolt head portion by a die equipped with a plate for supporting the shaft portion of the blank. It is characterized by rolling the neck cut portion and rolling a screw on the shaft portion by a conventional method.

Hereinafter, the present invention will be described in more detail with reference to the illustrated embodiments.

First, as shown in Fig. 1, a round bar (1) made of a material such as CH45K
Is cut into a required size, and the whole is annealed to be softened. Next, this round bar (1) is cold-pressed, and through the steps shown in FIGS. 2 and 3, a relatively thick bolt head (2) as shown in FIG. Blank consisting of a thin shaft (3)
(4) is manufactured. Next, a cap-shaped collar portion (7) is formed on the large-diameter bolt head (2), and a hexagonal portion (5) having a diagonal diameter of the same diameter as the bolt head (2) is formed into a cylindrical portion ( It is formed following 6).
Then, such a blank (4) is rolled using a die (8) as shown in FIG. 5, and the cylindrical portion (6) above the collar portion (7) is rolled as shown in FIG. A V-shaped neck cut (9) is formed. The die (8) is provided with a plate (10) for supporting the shank (3) of the blank (4), and a serration (not shown) for blank biting is provided at the starting end of the plate (10). Is engraved. Blank by this
(4) holds the shaft (3) securely without slipping, and the die
The gradually increasing height of the grooved part (11) and the lower surface of the collar part (7) slide along the stepped part with which it abuts without slipping and the neck part (9) rolls over the bolt head (2). Is built. In this way, the necking part (9) is rolled, and at the same time, the shaft part of the blank (4) is rolled.
In (3), the screw is rolled by a normal rolling die to obtain a finished product as shown in FIG.

As described above, in the present invention, the blank (4) has the large-diameter bolt head (2) formed with the cap-shaped brim (7) and has the same diagonal diameter as the bolt head (2). Since the hexagonal part (5) is formed, the forging ratio can be reduced when forming the collar part (7) and the hexagonal part (5), and the forging can be reasonably performed. Further, since the necking part (9) is rolled by using the die (8) provided with the plate (10) supporting the shaft part (3) of the blank (4), the cutting process is performed one by one. Compared with the conventional method, the processing accuracy of the necking part (9),
It is possible to obtain a necking bolt with a small variation in dimensional accuracy and a small variation in breaking torque. At this time, the plate (10) is blank.
Since the shaft (3) of (4) is securely supported and the lower surface of the collar (7) slides along the step of the plate (10), it is accurately positioned to roll the neck cut (9). In addition to being easy and accurate, the grooved part (11) has a cap-shaped brim (7).
Since the groove is squeezed along the slope of the blank, the blank (4) extends only toward the head side, and the metal fiber is not disturbed, and a stable breaking torque can be obtained. Furthermore, in the present invention, since the necking part (9) and the screw are both formed by rolling, the manufacturing cost can be significantly reduced as compared with the conventional method.

(Effects of the invention) As described above, the present invention is capable of manufacturing a neck-cutting bolt with less variation in breaking torque at low cost. Therefore, as a method of manufacturing a neck-cutting bolt that eliminates conventional problems, The contribution to the industry is extremely large.

[Brief description of drawings]

1 to 5 are front views for explaining the steps of the present invention, and FIG.
The figure is a front view of a neck-cutting bolt manufactured by the method of the present invention. (1): Round bar, (2): Bolt head, (3): Shaft part, (4): Blank, (5): Hexagonal part, (7): Collar part, (8): Die, (9 ): Neck cut, (10): Plate.

Claims (1)

[Claims] 1. A round bar is cut into a required size, and a blank including a bolt head having a relatively large diameter and a shaft portion having a relatively small diameter is manufactured by cold forging, and a cap-shaped blank is formed on the bolt head. In addition to forming a flange and forming a hexagonal part having a diagonal diameter of the same diameter as the bolt head, rolling the neck cutting part on the bolt head with a die equipped with a plate that supports the shaft of the blank, A method for manufacturing a neck-cutting bolt, which comprises rolling a screw on a shaft by a conventional method.