Method for integrally manufacturing an one-piece forged...

Metal deforming – By extruding through orifice – With metal-deforming other than by extrusion

Reexamination Certificate

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Details

C072S267000, C072S377000, C029S897200, C029S557000

Reexamination Certificate

active

06266990

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for integrally forming and manufacturing an one-piece forged hollow crank of a bicycle.
2. Description of the Related Art
A hollow crank of a bicycle made by a first conventional method includes multiple forged pieces which are assembled by a welding process. However, the hollow crank forged by multiple pieces is not integrally molded, thereby creating a weld effected zone in the material, so that the hollow crank has a worse stress tolerance. Therefore, the conventional hollow crank must use only alloys that are weldable and must design around the problems of the welding.
A second conventional method for making a hollow crank of a bicycle in accordance with the prior art shown in
FIGS. 1 and 2
comprises the following steps:
(a) melting a material;
(b) casting step;
(c) opening mold;
(d) removing sand core from a mold;
(e) clearing residue material;
(f) material surface treatment; and
(g) forming a screw hole in the rear end of a crank.
However, such a conventional method has complex steps, thereby greatly consuming time for making the hollow crank. In addition, by such a method, it is easy to produce a defective product which cannot be controlled by the steps. A major disadvantage to this method is the relatively lower strength of casting alloys to forging alloys.
In the casting process, it is necessary to make a blank
10
before machining the two ends of the hollow crank. The blank
10
is cast by the mold
11
in conjunction with the sand core
12
. After the mold is opened, the maker has to remove the cast duct
13
and the cast nozzle
14
by a cutter, and treating the originally rough surface (air vents, sand and mold lines) by a grinding machine so as to work the two ends of the blank
10
. Therefore, such a method greatly increases the cost of fabrication, and consumes a great deal of time.
SUMMARY OF THE INVENTION
The present invention has arisen to mitigate and/or obviate the disadvantage of the conventional method for manufacturing a hollow crank of a bicycle.
In accordance with one aspect of the present invention, there is provided a method for integrally forming and manufacturing an one-piece forged hollow crank of a bicycle comprising the steps of: (a) forging and molding a leading edge of a crank: forging and molding a stock of a hollow crank of a bicycle in a die by a forging machine to form a leading edge of a crank having a front end formed with a joint portion and a rear end formed with a preparing material; (b) extruding a crank body: moving a plunger into the preparing material to press and extrude the preparing material upward on the plunger to form an elongated hollow crank body on the plunger with a channel being formed in the hollow crank body; (c) forging and sealing a rear end of the crank body: after the plunger is removed from the hollow crank body, pressing the preparing material by a forging mold so that a material of a rear end of the preparing material is distorted and bent from all sides toward the channel to be embedded into the channel with a residue material being left on a rear end of the hollow crank body, and the material embedded into the channel alternating in an irregular shaped manner under the pressure exerted by the forging mold to seal a rear end of the channel of the hollow crank; and (d) cutting and piercing the rear end of the crank body: cutting the residue material left on the rear end of the hollow crank body by a cutting machine, and piercing a through hole in the hollow crank body by a pre-fitted machine so as to form a hollow crank.
In the step (b), the plunger is pressed into a central portion of the preparing material.
In the step (c), an irregular weldment is formed in the material embedded into the channel.
In such a manner, the hollow crank can be integrally forged and molded quickly by fewer manufacturing steps and out of better alloys than that of the conventional method. In addition, the product surface of the hollow crank is finished to have a fine and pretty appearance so that it is not easy to produce a defective product, thereby enhancing the aesthetics and quality and saving the manufacturing cost of hollow crank. Further, the method of the present invention can also save time of fabrication due to fewer manufacturing steps.
Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.


REFERENCES:
patent: 3940969 (1976-03-01), Princehouse
patent: 5197353 (1993-03-01), Trenerry et al.
patent: 5377518 (1995-01-01), Abbott
patent: 6085405 (2000-07-01), Kao
patent: 6195894 (2001-03-01), Mizobe et al.

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