JP2000334524A - Bolt hole working method of wheel disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a tool wear life and to dispense with a tool change due to a different plate thickness of a stock in piercing a bolt hole of a wheel disk. SOLUTION: A bolt hole forming part in the bulged part 2 of a wheel disk is pressed to be thinned to a prescribed thickness beforehand, a prepared hole having a diameter corresponding to a bolt diameter is punched to the thinned part, a nut seat 5 is formed by pressing the inner periphery of the prepared hole, at the same time, the prepared hole is extruded downward while maintaining the prepared hole diameter, the tip part extruded is formed to a radius shape, thus, the bolt hole is finished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a bolt hole for mounting an axle in an automobile wheel disc.

[0002]

2. Description of the Related Art As a method of machining a bolt hole of an automobile wheel disc, there are those disclosed in Japanese Patent Application Laid-Open No. Hei 2-254001 and Japanese Patent Publication No. Hei 7-108424.

[0003] These prior arts, as shown in FIG.
In the bulging portion 2 of the wheel disk 1 formed by drawing, a pilot hole 3 having a diameter smaller than a required bolt hole diameter is punched in advance by using a punch 5 and a punching die 6, as shown in FIG. Using the coining punch 7 and the coining die 8, the pilot hole 3 is burred at the burring portion 7 a of the coining punch 7, so that the hole 3 is pushed out to the bolt hole 4 having a required diameter, and the nut is formed at the coining portion 7 b of the coining punch 7. The seat is molded.

[0004]

However, in the above-mentioned prior art, since a pilot hole is burred with a coining punch and pushed up to a required diameter of a bolt hole, the coining punch and a coining die (hereinafter, referred to as a coining die) are used. However, there is a problem that the wear of the coining tool is fast and the replacement life due to the wear of the coining tool is short.

[0005] Punching of a prepared hole and burring of expanding a prepared hole are performed by punching a punch, a punching die (hereinafter referred to as a punching tool) and a coining tool in accordance with the difference in the thickness of the material. Must be replaced each time.

Further, there is a problem that burrs are formed on the back side of the bolt holes due to the burring of the prepared holes, and the appearance is poor. An object of the present invention is to provide a new method for machining a bolt hole of a wheel disc that has solved the above-mentioned problems.

[0007]

According to the present invention, in order to achieve the above object, a first aspect of the present invention is to form a bulging portion by drawing in a bolt hole forming portion. Before drilling a bolt hole, a first step of reducing the thickness of the bulged portion by pressing a portion corresponding to the diameter of the bolt hole, and reducing the diameter of the bolt hole from the front side of the bulged portion to the thinned portion. A second step of punching a corresponding pilot hole, and simultaneously forming a nut seat around the front side of the pilot hole by pressing the front side of the inner peripheral portion of the pilot hole, while maintaining the diameter of the pilot hole while maintaining the diameter of the pilot hole. A third step of extending a peripheral surface portion downward and forming a tip end surface of the extended portion into an R-shape to finish a bolt hole.

[0008]

According to the above means, the bulging portion for drilling the bolt hole of the wheel disk is thinned in advance, and a pilot hole having a diameter corresponding to the diameter of the bolt hole is punched in the thinned portion, and the pilot hole is punched. Since the bolt holes are finished by the coining tool while keeping the diameter, the wear of the coining tool is reduced, and the wear life of the coining tool is extended.

[0009] The bulging portion for drilling the bolt hole is
By reducing the wall thickness to the required thickness in advance, the same punching tool and coining tool can be used even if the thickness of the wheel disc material is different.

[0010] Further, since the periphery of the pilot hole is extended downward and its tip end surface is formed in an R shape, it does not appear as a burr on the back side of the bolt hole.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the embodiments shown in FIGS.

FIG. 1 shows a cross section of a main part of a wheel disk before a first step, and FIGS. 2 and 3 show a first step of the present invention. As a first step, first, as shown in FIG. 2, a conical drawing die 10 is applied to a position where a later-described bolt hole is formed in the material 1a of the wheel disc 1, and the opposite of the drawing die 10. A forming punch 11 having a convex portion 11a formed on the front end surface is set at a corresponding position on the side.

Next, as shown in FIG.
1 rises toward the drawing die 10 side to form a conical bulging portion 2 along the shape of the drawing die 10 at a position where a bolt hole is formed in the material 1a, and a convex portion 11a of the forming punch 11 is formed. Pressurizes the back side of the bulging part 2,
A portion where a bolt hole to be described later is drilled is thinned to a required thickness as indicated by reference numeral 2a. In this case, the ratio of the reduction in thickness depends on the thickness of the material 1a, but is preferably in the range of 30% to 50% of the thickness.

As shown in FIG. 3, the peripheral portion 2b is made thicker on the contrary to the thinned portion 2a, which is advantageous when a high-strength nut seat described later is formed. Next, FIGS. 5 and 6 show a second step of the present invention.

As shown in FIG. 5, the thinned bulging portion 2 of the wheel disc 1 formed in the first step is set on a punching die 12 having an inner diameter 12a slightly larger than the diameter of a bolt hole. Then, a punch 13 having an outer diameter A corresponding to the diameter of the bolt hole is set vertically above the punching die 12 (vertically above the thinned portion 2a).

In FIG. 5, reference numeral 14 denotes a die holder for holding the punching die 12;
This is a lower mold auxiliary plate for fixing the die holder 2 and the die holder 14.

Next, as shown in FIG. 6, the inner punch 13 is lowered toward the punching die 12, and the first punch 13 is lowered.
The thinned portion 2a of the bulging portion 2 formed in the process is punched.
As a result, a pilot hole 3 having a diameter corresponding to the diameter of the bolt hole is punched in the bulging portion 2. In FIG. 6, 3a
Is a punched piece of the prepared hole 3.

Next, FIGS. 7 and 8 show a third step of the present invention. As shown in FIG. 7, a hole 16a having an inner diameter slightly larger than the diameter of the bolt hole is provided.
The swollen portion 2 perforated in the second step is set on a coining die 16 having an R-shaped groove 16b formed in an R shape in the axial direction, and the coining die 16
The coining punch 17 is set vertically upward. The coining punch 17 has a tapered insertion portion 17a at the tip and a punch 1 at its base.
3, having a straight portion 17b having the same outer diameter B as the outer diameter A,
Furthermore, a tapered coining portion 17c whose diameter increases upward is provided at the base of the straight portion 17b.

The coining die 16 is held by the die holder 14 as in the case of the second step, and the coining die 16 and the die holder 14 are fixed by the lower auxiliary plate 15.

Next, as shown in FIG. 8, the coining punch 17 is lowered toward the coining die 16 and the coining punch 17 is inserted into the prepared hole 3 of the bulging portion 2 punched in the second step. In this case, since the coining portion 17c of the coining punch 17 presses the inner peripheral surface of the pilot hole 3, the tapered nut seat 5 is formed along the tapered shape of the coining portion 17c. Here, as shown in FIG. 4, the peripheral portion 2b of the pilot hole 3 is thickened and has high rigidity, so that deformation in the horizontal direction is restrained, and the peripheral surface of the pilot hole 3 is pushed downward. Will be prolonged. At the same time, the distal end face 2c of the extended portion is formed into an R shape along the R groove 16b formed in the coining die 16. Therefore, burrs do not occur at the front end portion extended below the inner peripheral portion of the pilot hole 3.

The inner peripheral surface of the pilot hole 3 has a straight portion 17a of the coining punch 17 corresponding to the diameter of the bolt hole.
To form a bolt hole 4 having a diameter corresponding to the outer diameter B of the straight portion 17a. Therefore, the abrasion of the coining punch 17 and the coining die 16 is reduced as compared with the conventional method of expanding the prepared hole by burring. According to the comparative experiment, the replacement life due to the wear of the coining punch 17 and the coining die 16 was improved about twice as compared with the conventional method.

The thickness of the pilot hole 3 formed in the bulging portion 2 is previously reduced to a required thickness. Therefore, even if the material 1a has a different thickness, the punching tools 12, 13
The same tools 16 and 17 for coining can be used.

Further, as shown in FIG. 4, the portion of the nut seat 5 formed in the third step is thickened in the first step and has high rigidity. Even when used, a nut seat 5 with high strength can be obtained.

In this embodiment, the formation of the thinned portion 2a of the bulging portion 2 is performed simultaneously with the drawing of the bulging portion 2. The molding of the portion 2a may be performed.

In the present embodiment, the thinner portion 2a is formed by pressing the back side of the bulging portion 2 with a forming punch 11 provided with a convex portion 11a on the front end surface. A convex portion may be provided on the inner surface, and the thinner portion 2a may be formed by pressing the front side of the bulging portion 2; To form a thinned portion.

[0026]

As described above, the present invention has the following effects as compared with the conventional method for boring a hole in a wheel disk.

(1) The wear life of a tool for coining is greatly improved, and the frequency of changing the tool is greatly reduced. (2) It is not necessary to replace a punching tool or a coining tool each time according to the difference in the thickness of the material.

(3) No burr is formed on the back side of the bolt hole, and the appearance is improved.

[Brief description of the drawings]

FIG. 1 is an essential part cross-sectional view showing a wheel disc in a state before a first step of the present invention.

FIG. 2 is a cross-sectional view of a main part showing a state before a bulging portion is formed in a first step of the present invention.

FIG. 3 is a sectional view of an essential part showing a state after the formation of the bulging portion.

FIG. 4 is a cross-sectional view of the bulge formed in the same manner.

FIG. 5 is a sectional view of a main part showing a state before punching a prepared hole in a second step of the present invention.

FIG. 6 is a sectional view of an essential part showing a state after punching a prepared hole.

7A is a cross-sectional view of a main part showing a state before forming a bolt hole in a third step of the present invention, and FIG. 7B is an enlarged cross-sectional view of the main part.

8A is a cross-sectional view of a main part showing a state after forming a bolt hole, and FIG. 8B is an enlarged cross-sectional view of the main part.

FIG. 9 is a sectional view of a main part showing a state after punching a conventional pilot hole.

FIG. 10 is a cross-sectional view of a main part showing a state after a conventional bolt hole is formed.

[Description of Signs] 1 Wheel disc 2 Swelling portion 2a Thinned portion 2c Tip surface 3 Prepared hole 4 Bolt hole 5 Nut seat 16 Coining die 16a Hole 16b Annular groove 17 Coining punch 17a Tip portion 17b Straight portion 17c Coining portion

Claims (1)

[Claims] 1. A method for forming a bulging portion by drawing in a forming portion of a bolt hole, wherein a portion corresponding to a diameter of the bolt hole in the bulging portion is added before the bolt hole is formed in the bulging portion. A first step of pressing to reduce the thickness, a second step of punching a pilot hole corresponding to the diameter of the bolt hole from the front side of the bulging part in the thinning part, and pressing the front side of the inner peripheral part of the pilot hole. At the same time, the nut seat is formed around the front side of the prepared hole, and at the same time, the peripheral surface portion of the prepared hole is extended downward while maintaining the diameter of the prepared hole, and the tip end surface of the extended portion is formed into an R shape. And a third step of finishing the bolt holes to form bolt holes in the wheel disc.