JP3418159B2 - Gear manufacturing method - 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 gear used in an electric assist unit of an electric assist bicycle.

[0002]

2. Description of the Related Art A gear 1 shown in FIG. 3 is used for an electric assist unit of an electric assist bicycle. The gear 1 in which the teeth 12 are formed on the outer peripheral surface of the shaft portion 11 at one end is cup-shaped, and since the inner peripheral surface is related to power transmission, the cylindrical portion 10 has no center runout, and the cylindrical portion 10 has And shaft 11
It is required that the coaxial precision with the and is high, and for this reason, the cylindrical portion 10 and the shaft portion 11 are formed by cutting.

[0003]

However, in the manufacturing by cutting, the cost is very high, which is one of the reasons that the manufacturing cost of the electric assist unit cannot be reduced, and the teeth provided on the shaft portion 11 are also reduced. When the 12 is formed by cutting, the total length of the teeth 12 of the shaft portion 11 becomes considerably longer than the required complete tooth portion length, which is small in the total length of the gear and the axial size of the electric assist unit. This is one of the factors that limit the conversion.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of manufacturing a gear which has a high accuracy, a low manufacturing cost, and a short axial length. To provide.

[0005]

SUMMARY OF THE INVENTION The present invention is, however, a method of manufacturing a gear in which a tooth is formed on the outer peripheral surface of a shaft portion which is cup-shaped and protrudes from one end. While holding the outer peripheral surface of the disc part of the protruding material with a die,
By pressing the other end of the disk portion with a punch guided by a stripper that keeps a predetermined position with respect to the die, the disk portion is forged into a cup shape, and the surplus is located on the outer periphery of the shaft portion. It is characterized in that the tooth is forged into the outer peripheral surface of the shaft portion by being pushed into the tooth forming portion. The cup-shaped part and the teeth of the shaft part are simultaneously formed by forging of a material having a disk part and a shaft part, and the teeth do not forge the shaft part itself, but the surplus of the disk part. It is formed by pouring meat on the shaft side.

As a material to be used for forging, if the surface of the disk portion on the shaft side is a tapered surface having a receding angle of about 8 °, the flow of meat to the tooth portion during forging is used. You can get better.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on an example of an embodiment. FIG. 3 shows a gear 1 manufactured by a manufacturing method according to the present invention.
A tooth 12 is formed on the outer peripheral surface of a shaft portion 11 having a shape of 0 and protruding from one end. The gear 1 is formed by forging molding of the material 15 shown in FIG. 2, and FIG. 1 shows a die used for forging molding. The material 15 has a shape in which the shaft portion 11 projects from one end of a solid disk portion 16, and the surface of the disk portion 16 on the shaft portion 11 side is a tapered surface having a receding angle α. The material 15 may be manufactured by any method such as cold forging, hot forging, and cutting.

On the other hand, the die for forging includes a die 21 on the die plate 20 and a punch 25, and
The die 21 is provided with a stripper 27 for keeping the punch 25 coaxial, and the die 21 has a small-diameter hole portion 23 extending downward from the bottom center of the hole portion 22 into which the material 15 is fitted.
It has a tooth forming part 24. The stripper 27
Has a tubular portion 28 that fits into the inner surface of the hole portion 22 of the die 21, and guides the punch 25 on the inner surface of the tubular portion 28 so that the hole portion 22 of the die 21 and the punch 25 are coaxial. keep.

Here, it is assumed that the shaft portion 11 of the material 15 has an outer diameter equal to or smaller than the inner diameter of the tooth forming portion 24 of the die 21.

At the time of forging, the hole 22 of the die 21
Set the material 15 inside and set the shaft 11 to the small diameter hole 23.
Located inside. Then, the punch 25 is lowered while being guided by the stripper 27, so that the disc portion 16 is provided between the inner surface of the hole portion 22 of the die 21 and the outer surface of the punch 25.
Is forged into a cup shape to form the cylindrical portion 10, and the excess thickness of the disk portion 16 is caused to flow to the shaft portion 11 side so that the shaft portion 11
The teeth 12 are formed by pushing into the tooth forming portion 24 of the die located on the outer periphery of the tooth. Instead of molding the outer peripheral portion of the shaft portion 11 itself, the teeth 12 are molded by using the extra thickness flowing from the disk portion 16 to the shaft portion 11 side.

At this time, since the surface of the disk portion 16 of the material 15 on the side of the shaft portion 11 is a tapered surface having a receding angle α, the flow of meat to the portion where the teeth 12 are formed is improved during the forging. Therefore, the load applied to the die 21 is reduced, and the life of the die 21 is improved. The receding angle α is preferably about 8 °. If it is smaller than this, the load applied to the die 21 becomes large, and if it is larger than 8 °, the overall axial length of the gear 1 becomes long.

The formation of the cylindrical portion 10 from the disc portion 16 of the material 15 and the formation of the teeth 12 on the outer periphery of the shaft portion 11 are simultaneously performed by one forging, and the shaft portion 11 is also formed. Since the tooth 12 provided in the tooth is formed by the meat flowing from the disk portion 16, one end of the tooth 12 in the axial direction is completely connected to the cylindrical portion 10 side, and for this reason, the predetermined length L The above complete tooth portion can be formed at a position close to the cylindrical portion 10, and therefore the cylindrical portion 1
The overall length in the axial direction including 0 can be kept short.

When the forging and forming are completed, the punch 1 is pulled up and the knockout 29 is raised to take out the gear 1 which has been formed. After that, the gear 1 finishes the inner peripheral surface of the cylindrical portion 11 and the like to a required size by an NC lathe.

[0014]

As described above, according to the present invention, when manufacturing a gear having a cup-shaped outer peripheral surface of a shaft portion protruding from one end, the shaft portion protrudes from one end of the disk portion. While holding the outer peripheral surface of the disk part of the, by pressing the other end of the disk part by a punch guided by a stripper that keeps a predetermined position with respect to the die, while forging the disk part into a cup shape The extra thickness is pushed into the tooth forming portion of the die located on the outer periphery of the shaft portion to forge the teeth on the outer peripheral surface of the shaft portion, which can be manufactured by forging, and the cylindrical portion and the shaft portion can be manufactured. Since the teeth of the mold are formed at the same time, the manufacturing cost can be greatly reduced, and furthermore, since the punch is guided and forged by the stripper that keeps the predetermined position with respect to the die, it has high coaxial precision. It is possible to obtain. In addition, the teeth are formed not by molding the outer circumference of the shaft portion but by flowing the surplus of the disk portion toward the shaft portion, so the tooth can be formed near the cylindrical portion. Therefore, the overall length in the axial direction can be shortened.

Further, if a material whose surface on the shaft portion side of the disk portion is a taper surface having a receding angle of about 8 ° is used as the material, the flow of meat to the teeth forming portion of the shaft portion is good. Therefore, the load on the mold can be reduced and the life of the mold can be extended.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a mold used for manufacturing according to the present invention.

FIG. 2 is an explanatory diagram showing a manufacturing procedure.

FIG. 3 is a sectional view of a manufactured gear.

[Explanation of symbols]

1 gear 10 Cylindrical part 11 Shaft 12 teeth 15 Material 16 discs 21 die 24 Tooth forming part 25 punch 27 strippers

Continuation of the front page (56) Reference JP-A-7-214227 (JP, A) JP-A-2-211924 (JP, A) JP-A-58-167050 (JP, A) JP-A-1-258840 (JP , A) JP 62-9737 (JP, A) JP 3-90243 (JP, A) JP 2000-71046 (JP, A) JP 3-90244 (JP, A) JP 8 -132169 (JP, A) JP 11-300447 (JP, A) JP 7-223033 (JP, A) Actual flat 6-70937 (JP, U) (58) Fields investigated (Int.Cl) . ⁷ , DB name) B21J 5/06 B21J 5/12 B21K 1/30 F16H 55/17

Claims (2)

(57) [Claims] 1. A method of manufacturing a gear, which is cup-shaped and has teeth formed on the outer peripheral surface of a shaft portion protruding from one end, wherein the outer peripheral surface of the disk portion is made of a material having the shaft portion protruding from one end of the disk portion. While the die is held by the die, the other end of the disc portion is pressed by a punch guided by a stripper that keeps a predetermined position with respect to the die. A method for manufacturing a gear, characterized in that the tooth is forged on the outer peripheral surface of the shaft by being pushed into the tooth forming portion of the die located on the outer periphery of the portion. 2. The method for manufacturing a gear according to claim 1, wherein a material having a taper surface having a receding angle of about 8 ° is used as a surface of the disk portion on the shaft side.