Manufacturing process for ring-shaped parts

Details Manufacturing process for ring-shaped parts Manufacturing process for ring-shaped parts

1992-04-07

1994-03-01

Nelson, Peter A.

Powder metallurgy processes

Powder metallurgy processes with heating or sintering

Plural heating steps including sintering

419 25, 419 50, 419 55, B22F 700

Patent

active

052905080

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a manufacturing process for ring-shaped parts, which is suitable for the production of all kinds of ring-shaped machine parts which have sliding face of irregular shape at the inner or outer surface thereof, such as a sprocket, a pulley, a race of a one-way clutch, which is one component forming the auto-transmission of a car, a cam, etc.


PRIOR ART

In general, when manufacturing the aforementioned types of ring-shaped parts by powder sintering, a method wherein the raw material powder is first compacted and then sintered and is subsequently forged into a predetermined shape and sintered for a second time; the resulting sintered body then undergoes machine processing such as cutting and grinding, and is shaped into a predetermined ring shape; high frequency hardening is then carried out for the inner or outer surfaces of the ring-shaped part in order to increase the hardness of the aforementioned surface and improve the abrasion resistance, then the hardened body undergoes tempering at a relatively low temperature (at approximately 180.degree. C. for 30 min.), a so-called "temper process".
However, although it is possible in the aforementioned manufacturing process for ring-shaped parts to obtain a predetermined hardness at the inner and outer periphery by high frequency hardening, the degree of hardness at the middle layer of the aforementioned parts in particular becomes too high; a moderate hardness (in other words, a great toughness) is difficult to obtain, and therefore there is a disadvantage in that it is difficult to manufacture machine parts with high radial crushing strength constant which have came into demand in recent years.
For this reason, one may think of a manufacturing process for increasing the hardness of the aforementioned surfaces, in which, in contrast to the aforementioned powder sintering method, a prototype is first produced by previous forging, and after various machine processes have been performed thereon and a predetermined shape of the aforementioned ring-shaped part is obtained, high frequency hardening is performed at the inner peripheral layer or outer peripheral layer which has to be hardened, as necessary.
However, in the aforementioned manufacturing process through forging, there is in particular the problem that if the inner or outer peripheral layers are of irregular shape, a great amount of labor is required in all the machine processes in order to produce the aforementioned shaped parts, causing a complication of the process and increasing the cost of manufacturing.


DISCLOSURE OF THE INVENTION

Here, the inventors decided to utilize the powder sintering techniques used in the production of general machinery parts, and carried out energetic research with the purpose of manufacturing ring-shaped mechanical parts having radial crushing strength constants not inferior to those made by forging. As a result the following manufacturing process was discovered. In the process, sintering and forging were carried out after compacting of a raw powder material which is composed of a composition containing (weight %) C at 0.4-0.9%, Ni at 1.5-4.0%, Mo at 0.2-0.6%, and a remainder consisting of Fe and unavoidable impurities. A sintered body superior with respect to its utilization as a mechanical part was obtained by using the abovementioned raw powder material. After hardening the obtained sintered body at a temperature within the range of 800.degree.-950.degree. C., high temperature tempering at a temperature within the range of 570.degree.-700.degree. C. for 20-60 minutes is carried out. Then the surface layer of the inner and/or outer periphery, which requires a high degree of hardness, of said sintered body is hardened. By this method we can obtain ring-shaped parts which have a high radial crushing strength constant for the entire body, because the middle layer has a desirable hardness in a rang of HRC 25-40, and a high hardness which is required for the inner and/or outer peripheral surface is obtained. By carrying

REFERENCES:
patent: 2637671 (1948-03-01), Pavitt
patent: 2842471 (1958-07-01), Koehler
patent: 4492671 (1985-01-01), Ruano et al.
patent: 4976916 (1990-12-01), Shimomura
patent: 5049183 (1991-09-01), Saka et al.
patent: 5067979 (1991-11-01), Kiyota et al.

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