JPH0762497B2 - Gear manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a gear.

2. Description of the Related Art FIG. 3 is a flowchart showing a conventional method for manufacturing a gear, which is used for each step of primary blanking, normalizing, secondary blanking, gear cutting, carburizing and tempering. It is sequentially transferred, and finally polished.

Problems to be Solved by the Invention In order to improve the durability of a gear, the empirical rule that the surface hardness increases as the depth of the carburized layer increases, and the depth of the carburized layer is increased to increase the number of tooth surfaces. It is possible to increase the wear resistance. However, since the carburizing and quenching are performed while the tooth surface and the tooth bottom corners have substantially the same surface roughness by the gear cutting, the carburizing layer 1 by the carburizing and quenching is formed as shown in FIG. and the effective depth t ₂ of the effective depth t ₁ and tooth bottom corner 3 tooth surface 2 is in substantially the same. Therefore, an attempt to increase the wear resistance of the tooth surfaces 2 and deepening the effective depth t ₁ of the tooth surface two carburized layer 1, the tooth bottom corner 3 of the carburized layer 1 of the effective depth t ₂
Since the tooth bottom corner portion 3 becomes fragile and the impact strength of this portion 3 is reduced, it is difficult to employ it suddenly.

By the way, Fig. 5 shows an outer diameter of 20 mm, an inner diameter of 12 mm, and an axial height of 2.
Obtained by making a ring-shaped sample of 1 mm and material SCM420H, changing the surface roughness (center line average roughness) of the sample in the range of 0.2 to 0.6 μm, carburizing and tempering this sample. It is an experimental result which shows the relationship between the obtained surface roughness and surface hardness.

Therefore, the present invention provides a method for manufacturing a gear that can improve the wear resistance of the tooth surface and enhance the durability of the gear without impairing the impact strength at the tooth bottom corners.

Means for Solving the Problems First, after gear cutting, the root corners are ground to make the surface roughness smaller than the surface roughness of the tooth surface, and then carburizing and quenching.

Action Effective depth of carburized layer by carburizing and quenching, deep on tooth surface,
Shallow at the bottom of the tooth.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, by attaching the same reference numerals to only the same portions as those of the conventional structure.

As shown in FIG. 1, the material is sequentially transferred to the steps of primary blanking, normalizing, secondary blanking, and gear cutting, and then the tooth bottom 4 and the tooth bottom corner 3 are ground and the surface thereof is polished. The roughness (centerline average roughness) Ra (bottom) is made smaller than the surface roughness (centerline average roughness) Ra (pitch) of the tooth flank 2 (R
a (pitch) -Ra (bottom)> 0), then carburizing and tempering, and finally polishing finish.

Specifically, in the manufacturing of the module 5.5 differential gear with the material SNCM420H, the total surface roughness of the teeth at the time of finishing the gear cutting is set to 0.7 μm or more, and the bottom corners are formed by the subsequent polishing. After the surface roughness between the tooth bottom and the tooth bottom is 0.2 μm or less,
When carburized and tempered, a carburized layer 1A as shown in FIG. 2 was obtained. In the carburization layer 1A is a valid depth t ₁ of the tooth surface 2 is 0.8 mm, the effective depth t ₂ of the tooth bottom corner 3 and the tooth base 4 was 0.4 mm. This differential gear is installed in the differential gear of automobile, and the torque of both shafts is 400kgf ・ m.
When a durability test was carried out on the rapid start table, the life was more than double that of the conventional differential gear.

In the embodiment, the difference between the surface roughness Ra (pitch) of the tooth flank 2 and the surface roughness Ra (bottom) of the tooth bottom corner 3 is Ra (pitc).
h) −Ra (bottom)> 0.5 μm, but the difference in surface roughness between them satisfies Ra (pitch) −Ra (bottom) ≧ 0.25 μm, so that the wear resistance of the tooth surface 2 is improved. It was possible to obtain a durable gear having sufficient impact strength with which damage to the tooth bottom corner portion 3 was prevented.

As described above, according to the present invention, by carburizing and quenching,
By increasing the effective depth of the carburized layer on the tooth surface and shallowing the effective depth of the carburized layer on the root corner, only the surface hardness of the tooth surface can be improved. There is a novel effect that the wear resistance of the tooth surface of the gear can be improved without impairing the strength, and thus the durability of the gear can be improved.

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of the present invention,
FIG. 3 is a structural diagram showing a main part of a gear manufactured in the same embodiment, FIG. 3 is a flowchart showing a conventional gear manufacturing method, and FIG.
FIG. 5 is a structural diagram showing a main part of a gear manufactured by the conventional method, and FIG. 5 is a graph showing a relationship between surface roughness before carburizing and quenching and surface hardness after carburizing and quenching. 1,1A ... Carburized layer, 2 ... Tooth surface, 3 ... Root corner, t ₁ , t ₂
…… Effective depth.

Claims (1)

[Claims] 1. A method for manufacturing a gear, comprising first grinding a tooth bottom after grinding to form a surface roughness smaller than a surface roughness of a tooth surface, and then carburizing and quenching.