JPH0811263B2 - Method of manufacturing stepped tubular body having slits - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a stepped tubular body having a slit slit represented by a steering holder.

[0002]

2. Description of the Related Art Cutting is mainly used for manufacturing a stepped tubular body having a slit, but cutting is inefficient, and therefore, extrusion by forward extrusion has been attempted.
Taking the steering holder, which is one of the automobile parts, as an example, the forward extrusion molding is performed by a forming die having a protrusion 7 for forming a slit as shown in FIG.
At the same time that the outer periphery of the tip end portion is narrowed down, the slit 6 is also formed in the narrowed tip end portion, so that all can be completed in one step, which is perfect for mass production.

[0003]

However, according to the above-mentioned conventional molding method, the concentrated stress P acts on the tip of the protrusion 7 for forming the slit of the molding die (see FIG. 7), and the life of the molding die is shortened. And has problems such as damage. On the other hand, a product having no step is disclosed in, for example, JP-A-1-293936.
In the publication, there is disclosed a technique in which both the inner and outer peripheral surfaces of the tubular portion are constrained to form a vertical groove in the bottomed tubular material, and the central portion of the bottom portion is pierced and the vertical groove is formed by shaving. Although disclosed, when the technique is applied to a stepped tubular body,
The flow of meat in the small-diameter portion becomes faster, so that the load on the forming die is too large and the die life is significantly reduced.
Further, since the piercing is required, the constraint on the inner peripheral surface becomes incomplete during the piercing, and problems such as buckling in the axial direction and entrainment occur.

[0004]

SUMMARY OF THE INVENTION The present invention enables press forming without difficulty. First, the inner peripheral surface of the base end portion of a tubular material is constrained and the outer peripheral surface of the tubular material is first drawn. At the same time, the part corresponding to the slit slit is press-fitted inward without restraining the inner peripheral surface of the small diameter tip formed by the pre-drawing process to form the vertical groove, and then the press-fitting is performed to the inner side. The swelling part is scraped off and the vertical groove is finished into a slit shape.

[0005]

[Function] Since the inner peripheral surface is not constrained during the pre-drawing process, the flow of meat in the small diameter portion does not speed up, the load on the mold is reduced, and the inner peripheral surface of the base end is constrained. Since it does not exist, there is no concern about buckling or entrainment in the axial direction. Further, since the bulging portion is cut off, high accuracy is not required for the vertical groove, and it is possible to make the vertical groove a tapered surface shape so that concentrated load on the mold does not act. As a result, damage to the mold and shortening of the life can be prevented, and the load on the punch and the mold is small even when scraped off.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a method for manufacturing a stepped tubular body having a slit slit according to the present invention in forming a steering holder will be described with reference to the drawings. FIG. 1 shows a molding process. Reference numeral 1 denotes a molding die for forward extrusion, which is composed of two stages of a large diameter portion and a small diameter portion, and a ridge parallel to the shaft on the inner wall facing surface of the small diameter portion. 2 and 2 are formed.

First, when the inner peripheral surface of the straight cylindrical material 3 is pushed into the mold 1 while constraining the inner peripheral surface of the rear end portion of the straight cylindrical material 3 with the punch 5, the cylindrical material 3 is not constrained. Is pressed into the small diameter portion and a step is formed by the pre-drawing process.
The vertical grooves 4 and 4 corresponding to are formed. The protrusion 2 is thicker than the wall thickness of the tubular material 3, so that the vertical grooves 4 and 4 which are recessed have a depth such that the bottom surface thereof reaches the inner peripheral surface of the material. There is no angular edge portion, all the corner portions are formed into curved surfaces, and the vertical groove 4 has a shape that bulges inward in a curved shape (FIG. 2).

Next, the punch 5 is passed through the tip of the tubular material 3, and the protruding portion 4a which bulges inward of the vertical groove 4 is scraped off (FIG. 3). By doing so, it is possible to form the slit 6 by cutting the vertical groove 4 without applying an excessive force to the mold, and if it is necessary to improve the accuracy of the slit, the inner surface of the slit 6 can be formed in the die 8 protruding and retracting from the side. Then, the finished product of the steering holder M as shown in FIG. 5 is obtained by straightening (FIG. 4). On the other hand, the notch slit 6 with the vertical groove 4 that has been recessed cut off is
Since the outer circumference is a smooth surface, there is a merit that the fitting property is excellent unless it is straightened. It is also possible to keep the leg length unchanged by adjusting the wall thickness of the recessed portion.

In the embodiment, a type having two slits in the small diameter portion of a large and small cylindrical body has been described, but it can be applied to a cylindrical body having a cross section other than a circle.
The number of cut slits, the cut width, the length, and the like can be appropriately changed.

It is also possible to perform the formation of the vertical groove and the scraping off in the same mold, not in a continuous manner, but in separate steps.

[0011]

According to the present invention, a stepped tubular body having a slit slit can be efficiently manufactured from a straight tubular body with less burden on the molding die, and thus can be supplied at a low cost. Ideal for mass production.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a manufacturing method of the present invention.

FIG. 2 is an explanatory diagram of a material as seen from a section cut along the line AA.

FIG. 3 is an explanatory diagram of a material as seen from a section cut along a line BB.

FIG. 4 is an explanatory diagram of a material as seen from a section taken along line C-C.

FIG. 5 is an explanatory diagram of a finished product.

FIG. 6 is an explanatory view illustrating a conventional manufacturing method.

FIG. 7 is an explanatory diagram of a conventional slit formation example.

[Explanation of symbols]

1 ・ ・ Molding die, 2 ・ ・ Ridge, 3 ・ ・ Cylindrical material, 4 ・ ・ Vertical groove, 5 ・ ・ Punch, 6 ・ ・ Cutting slit, 7 ・ ・ Slit forming protrusion,
8 ... Die, M ... Steering holder.

Claims (1)

[Claims] 1. A distal end of the tubular body having a depth such that the inner peripheral surface of the base end portion of the tubular material is constrained and the outer peripheral surface of the tubular material is pre-drawn and at the same time the bottom reaches the inner peripheral surface. A first step of forming a vertical groove extending inwardly in parallel with the axial center from the inner peripheral surface of the small diameter tip portion formed by the predrawing without restraining the vertical groove; and a tube of the vertical groove. 2. A method for producing a stepped tubular body having a slit slit, which comprises the step of cutting off the portion that bulges inward to finish the vertical groove into a slit.