JP2000345367A - Gear surface treatment method - Google Patents

Abstract

(57) [Summary] [Problem] To manufacture a compacted electrode at a low cost, can be used also for a gear having a different number of teeth, and can be used without any problem even if the electrode is worn to some extent. Disclosed is a gear discharge surface treatment method that can significantly reduce the treatment cost, can easily control the position of a work with respect to an electrode, and can perform surface treatment only on the side where the gear meshes. SOLUTION: A green compact electrode E formed in a rack shape is used instead of a compact green compact electrode having a gear-shaped hollow portion.
To rotate the gear W to be processed and the gear W
And the rack-shaped electrode E are discharged relative to each other while relatively moving, so that a hard coating is formed on the tooth surface of the gear W to be processed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for modifying the surface of a gear, and more particularly, to preventing the occurrence of pitting and extending the life of the gear by coating a hard coating on the surface of the gear. The present invention relates to a possible discharge surface treatment method.

[0002]

2. Description of the Related Art For example, in a constantly meshing gear of an automatic transmission, pitting occurs particularly in the vicinity of the root of the gear at the side where meshing starts, and the gear may be damaged starting from the pitting. To prevent breakage accidents, the gear life is extended by coating the tooth profile surface with a hard coating such as TiN or TiC. Coating of such a hard coating is performed, for example, by PVD (Physic) using a vacuum furnace.
al Vapor Deposition), an electric discharge surface treatment method using an electric discharge machine, and the like.

[0003] Among them, in the electric discharge surface treatment method, as shown in FIG. 3, a gear having a size slightly larger than a gear (work) W to be coated by using, for example, Ti powder. Using the green compact Ec formed into a compact shape having a hollow part H as the electrode, the target gear W is inserted into the hollow part H of the green compact electrode Ec in a discharge liquid such as white kerosene. In this state, a pulse voltage is applied between the electrode Ec and the gear W while oscillating the electrode Ec to generate a discharge between them.
As a result, Ti in the electrode Ec reacts with C, which is a constituent element of the discharge liquid, to generate TiC, which is deposited on the tooth surface of the gear W to be processed to form a hard coating.

[0004]

However, in the above-mentioned discharge surface treatment, a green compact electrode having a gear-shaped cavity is used, so that the manufacturing cost of the electrode is high. In addition, the gap between the electrode and the gear to be processed (workpiece) is determined by the dimensions at the time of manufacture of the electrode, making it difficult to control the gap. If the number of gear teeth changes, the same electrode cannot be used, so it is necessary to prepare an electrode for each type of work. . In addition, there is a problem that it is difficult to perform surface treatment only on the start side of gear engagement where the tendency of pitting is particularly remarkable, and solving these problems is a problem in such a discharge surface treatment of gears. It was.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems in the conventional electric discharge surface treatment of a gear, and has a low manufacturing cost of a green compact electrode and is applicable to a gear having a different number of teeth. It can be used without any problem even when the electrodes are worn out to some extent, greatly reducing the cost of gear surface treatment, and making it easy to control the position of the workpiece with respect to the electrodes. It is an object of the present invention to provide a method of surface treatment for electric discharge of a gear which can be subjected to surface treatment only.

[0006]

According to a first aspect of the present invention, there is provided a method for treating a discharge surface of a gear, comprising the steps of generating a discharge between the gear to be treated and the green compact electrode to form a hard coating on the surface of the gear to be treated. In the discharge surface treatment of the gear forming the above, the green compact electrode is formed into a rack shape, the gear to be processed is rotated, and a discharge is generated between the gear and the rack electrode while relatively moving the gear and the rack electrode. In the method for treating the electric discharge surface of a gear according to claim 2 of the present invention, the meshing start side of the gear to be processed is brought close to the rack-shaped electrode, and the meshing is started. It is characterized in that it is configured to discharge only to the side, and such a configuration in the method for treating the electric discharge surface of a gear is a means for solving the above-mentioned conventional problems.

[0007]

According to the method for treating the surface of a discharge of a gear according to the first aspect of the present invention, instead of the green compact electrode having a gear-shaped cavity, the compact compacted in a rack shape is used. Since the body electrode is used, the shape of the electrode is simplified, and the manufacturing cost of the green compact electrode is reduced to about one tenth of that of the gear-shaped female electrode.
Also, since the gear to be processed is relatively moved while being rotated on the rack-shaped green compact electrode without being inserted into the gear-shaped cavity of the female type electrode, the number of teeth of the gear to be processed has changed. Even if the modules are the same, the same electrodes are shared.

[0008] Since the gap between the green compact electrode and the gear to be processed can be easily controlled, even if the electrode is consumed by the discharge, the distance between the compact electrode and the target gear is controlled by reducing the distance from the electrode. Can be further used, and the service life of the electrode is extended.

Also, since the position of the gear to be processed with respect to the green compact electrode can be easily controlled, the starting side of the gear to be processed is brought closer to the rack-shaped electrode. By causing the electric discharge only at the engagement start side, a hard coating is formed only at the engagement start side of the gear where the tendency of pitting is remarkable, and the pitting resistance of the portion is improved. Will be.

FIG. 1 is a perspective view for explaining the positional relationship between the green compact electrode and the gear to be processed at this time. As shown in FIG. The process start side of the workpiece gear W, which is a workpiece, approaches the tooth shape of the body electrode E and engages in a non-contact manner. A discharge is generated between the powder electrodes E to perform a surface treatment. When the electrode E is consumed by the discharge, the electrode E is driven in the radial direction of the gear W, the distance between the two is controlled, and the discharge surface treatment is continued.

When the compacted electrode E is further consumed, the same discharge surface treatment can be continued by moving the electrode E in the axial direction of the gear W as shown in FIG. it can. At this time, even if the meshing position is shifted in the axial direction, the front end portion of the green compact electrode E remains
As shown in (b), since the surface is sufficiently consumed by the previous discharge and the distance to the gear to be processed W is maintained at a certain value or more, the discharge surface treatment is performed only on the side where the gear W starts to mesh. Therefore, a hard coating is not formed on the tip side portion that does not require coating.

[0012]

According to a first aspect of the present invention, there is provided a method for treating a discharge surface of a gear according to the first aspect of the present invention. The structure is such that a hard coating is formed by generating a discharge between the electrodes while relatively moving the electrodes. In other words, since the rack-shaped green compact electrode is used, the manufacturing cost of the green compact electrode can be significantly reduced as compared with a conventional female electrode having a gear-shaped cavity. Even if the number of teeth of the gear to be processed is changed, the same electrode can be used as long as the module is the same, so that the number of types of compacted electrodes can be reduced, and the manufacturing cost and management cost of the electrode Can be reduced. Furthermore, since the distance between the rack-shaped green compact electrode and the gear to be processed can be easily controlled, even if the electrode is consumed by electric discharge, by controlling the distance between the electrode and the electrode, the use period of the electrode can be reduced. This makes it possible to extend the length of the gear, thereby achieving an extremely excellent effect that a significant reduction in the cost of the electric discharge surface treatment of the gear can be achieved.

[0013] In the method for treating the electric discharge surface of a gear according to the second aspect of the present invention, the meshing start side of the gear to be processed is brought close to the rack-shaped electrode so that only the meshing start side is discharged. That is, in the method for treating the electric discharge surface of the gear according to the present invention, the rack-shaped green compact electrode is used, and the position of the gear to be processed with respect to the green compact electrode is easily controlled. As shown in the figure, the starting side of the gear to be processed is brought close to the rack-shaped electrode so that only the starting side of the gear can be discharged. , And the pitting resistance of this portion can be greatly improved.

[0014]

EXAMPLES The present invention will be described below more specifically based on examples.

SCM defined in JIS G 4052
Using 420H steel (chromium molybdenum steel), the gear was forged into a gear shape, finished, and then carburized and quenched according to a conventional method. The tooth surface of the gear W (work) to be processed thus obtained had a surface hardness of about 850 in Vickers hardness.

On the other hand, using Ti alloy powder, FIG.
As shown in the figure, a rack-shaped green compact electrode E as shown in FIG. 1 is formed, and only the meshing start side of the gear W to be carburized and quenched in a discharge liquid (white kerosene) is formed. Non-contact meshing with the green compact electrode E, rotating the gear W, and moving the green compact electrode E while applying a pulse voltage between these electrodes E and the gear W to cause discharge, Ti on the side where the gear W to be processed starts meshing
A hard coating made of C was formed. At this time, the surface hardness of the coating portion of the gear W to be processed was about 2500 in Vickers hardness.

The gear W thus subjected to the discharge surface treatment is assembled into an actual automatic transmission and subjected to a durability test to investigate the pitting life of the gear W. A comparison was made with a comparative gear in which only carburizing and quenching was performed.

The result is as shown in FIG.
Compared to the comparative gears that were carburized and quenched, TiC
It has been confirmed that the pitting life of the invention gears subjected to the electric discharge surface treatment was significantly improved.

[Brief description of the drawings]

FIG. 1 (a) is a perspective view for explaining a method of performing a surface treatment of a hard coating only on a side where a gear meshes with a gear in a method of treating a discharge surface of a gear according to the present invention. FIG. 2B is a perspective view illustrating a surface treatment procedure after one side of the rack-type electrode illustrated in FIG. 1A has been consumed.

FIG. 2 is a graph showing the pitting life of an example gear subjected to a discharge surface treatment according to the present invention in comparison with a case of a conventional gear not subjected to a discharge surface treatment.

FIG. 3 is a perspective view showing a conventional method for treating a discharge surface of a gear.

[Explanation of symbols]

 E Green compact electrode W Gear to be processed (work)

Claims (2)

[Claims] In a discharge surface treatment of a gear for forming a hard coating on a surface of a gear to be processed by generating a discharge between the gear to be processed and a green compact electrode, the green compact electrode is formed into a rack shape. A method of treating a discharge surface of a gear, comprising: rotating a gear to be processed and generating a discharge between the gear and the rack-shaped electrode while relatively moving the gear and the rack-shaped electrode to form a hard coating. 2. The method according to claim 1, wherein the meshing start side of the gear to be processed is brought close to the rack-shaped electrode to discharge only to the meshing start side.