Precision gear, its gear mechanism, and production method of precision gear

Abstract

A metal-made high-precision gear and a gear mechanism are disclosed. The precision gear is made of a novel material which does not exist in conventional materials for precision gears, including resins and tool steels, has high hardness, strength and excellent surface smoothness, and is superior in workability. In the precision gear which is formed of an amorphous metal alloy having a ternary, quaternary or higher composition containing iron group elements, such as Fe, Co, Ni, and Cu, Ti, Zr, Hf, as the principal elements, the precision gear whose module is 0.2 or less is made of the amorphous metal alloy having a disordered structure which does not have a fixed regularity and whose XRD pattern is a halo pattern, namely exhibits a broad peak.

Description

TECHNICAL FIELD [0001] The present invention relates to a precision gear which is small-sized, subjected to a heavy load and required to have a long life-span, a gear mechanism employing the precision gear, and a method for manufacturing the precision gear. BACKGROUND OF THE INVENTION [0002] In the field of precision gears which are used in precision devices requiring high accuracy, such as watches and micro-geared motors, metal-made precision-gears whose modules exceed 0.2 and which have excellent properties and accuracy are manufactured by various methods including pressing and forming by rolling, as well as electro-discharge forming, cutting, etc. [0003] However, regarding forming of a metal-made gear whose module is 0.2 or less, it is difficult to practically employ the electro-discharge forming, cutting, pressing, and forming by rolling, since there are problems in terms of accuracy of the gear, manufacturing cost and the like. For this reason, resin-made precision-gears whose ...

AI Technical Summary

Benefits of technology

[0014] In view of the foregoing problems of the prior art gears, it is an object of the present invention to provide a metal-made, high precision gear and a gear mechanism, the high precision gear being made of novel material providing excellent workability, and having a unique combination of high hardness, high strength, and excellent surface smoothness, as compared to the prior art gears which are made of resin or tool steel.

[0015] The inventors of the present invention have discovered that a precision gear whose module is 0.2 or less can be made from an amorphous metal alloy which has a ternary, quaternary or higher composition, for example, a composition comprising ferrous elements, such as Fe, Co, Ni, and Cu, Ti, Zr, Hf, as the principal elements, and which provides, to the full, strength comparable to that of tool steel, excellent workability, mechanical properties and dynamic properties. The amorphous metal alloy of which the gear according to the present invention is formed is characterized by a disordered structure which does not have a fixed regularity whose XRD pattern is a halo pattern, namely exhibits a broad peak.

[0016] The gear of the present invention which is made of the amorphous metal alloy having the above-mentioned structure can be manufactured such that its surface roughness is at least 2 μm Ry and its dimensional accuracy is at least the range of + / −5 μm. This is extremely advantageous for producing with good accuracy, a precision gear whose module is 0.2 or less and which facilitates workability and has excellent mechanical properties and dynamic properties.

Problems solved by technology

However, regarding forming of a metal-made gear whose module is 0.2 or less, it is difficult to practically employ the electro-discharge forming, cutting, pressing, and forming by rolling, since there are problems in terms of accuracy of the gear, manufacturing cost and the like.

However, as compared to metal-made products, resin-molded integrated products are considerably inferior to the metal-made products in mechanical strength and hardness, tend to change in size and configuration thereof according to change in environmental temperature, and have creep properties.

Therefore, the resin-molding is completely unsatisfactory for forming an ultra-high-precision gear whose module is 0.2 or less and which is highly reliable.

In addition, as compared to the surface hardness and tensile strength of metallic material, those of resinous material are considerably low.

Moreover, the resinous material is inferior to the metallic material in heat resistance.

These properties of the resinous material have great adverse-effects on the durability and lifespan of the resin-molded product.

However, the present situation in the filed of the resinous materials does not yet reach the level of practical use of the metallic materials including tool steels.

However, the tensile strength of the alloys is about 750 MPa and is low like that of the resin materials.

In addition, the surface roughness of products made from the alloys is about 5 μm Ry and uneven shrinkage of the alloy products occurs due to crystal particles in the alloys and there are sharp convex regions on the surfaces of the alloy products.

Therefore, the alloys are unsuitable as materials for precision gears whose modules are 0.2 or less.

Incidentally, precision gears of tool steels are generally made by machining, so that it is difficult to mass-produce the precision gears at low cost.

In addition, it is considerably hard to get a machining accuracy and, even if the hardness of the finished products is high, the surface roughness of the products has a great effect on wear of the product materials which is brought about by sliding of the products in use, and consequently lifespan of the products is reduced.

However, a gear whose module is 0.2 or less and which has surface smoothness of 2 μm Ry or less and is to be made by a manufacturing method in which mass-production is taken into consideration, has not been proposed yet.

However, in this case, it is difficult to get a dimensional accuracy of the gear-shaped component, since the volume of metal powders used for sintering is shrunk by a quantity equivalent to spaces between adjacent particles of the metal powders at the time of the sintering.

In addition, there are vacancies in the component that has been made by the sintering, and the vacancies are easy to produce cracks.

In addition, the pin itself is extremely small, so that it is hard to easily and efficiently carry out the press-fitting of the pin.

Therefore, this requires a great deal of skill.

Images