Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Post sintering operation
Utility Patent
1999-02-17
2001-01-02
Mai, Ngoclan (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Post sintering operation
C425S078000, C072S343000, C072S359000, C029S893340
Utility Patent
active
06168754
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to post-sintering densification of powder metal preforms such as gears and the like.
2. Related Prior Art
Powder metal gears and other powder metal components have long offered a low cost alternative for many wrought components. Powder metal forming eliminates the high cost of machining association with wrought gears. However, applications where high strength components are required, such as transmission gears and the like, traditional powder metal components have not exhibited sufficient strength and dimensional tolerances necessary to serve as low cost alternatives to high strength wrought components.
A technique commonly used to densify sintered powder metal gear components is roll forming. The sintered gear preform is enmeshed with a rotating roll forming gear with sufficient force to displace and densify the surface of the preform teeth. U.S. Pat. No. 5,711,187 shows the general arrangement. An inherent disadvantage with such roll forming processes is that greater force is exerted on the driven side of the preform teeth than on the opposite coast side, leading to non-uniform densification and strength of the preform teeth. Some of the problem can be alleviated by reverse roll forming in the opposite direction, but the additional forming step adds cost and complexity to the manufacture of the gears and may not eliminate the problem entirely.
Powder metal gear preforms are also densified by impact forging the sintered preform in closed dies. See for example U.S. Pat. Nos. 2,542,912 and 5,009,842. The closed die process involves loading the preform into one end of the die and then forcing it past a forming ring which shapes the part. At the end of the stroke, the preform is compressed against an opposing punch or a bottom wall of the die to impart densification. The part is then ejected back through the same open end. The process does not lend to high production rate manufacturing of powder metal components.
It is an object of the present invention to advance the art of powder metal preform densification to provide high strength high precision powder metal components such as transmission gears that are comparable in strength and precision to corresponding wrought gears in a cost effective manner.
SUMMARY OF THE INVENTION AND ADVANTAGES
A method of producing powder metal articles is provided comprising compacting and sintering a powder metal preform having an outer perimeter portion thereof to be densified, providing a multi-stage forming tool according to the invention having a plurality of forming die plates disposed in axially spaced succession defining a series of progressively smaller sized die openings corresponding generally in shape to the portion of the preform to be densified, but being relatively and progressively smaller in size than that of the portion of the preform to be densified, and forcing the preform axially through the dies from largest to smallest and plastically and elastically deforming the preform portion in stepped progression through the die openings to achieve densification and sizing of the preform portion and imparting compressive stresses to the preform, with the spacing between adjacent dies being sufficient to allow elastic springback of the preform material between successive die plates.
The invention is advantageous in that it provides a cost effective means of forming high density, high precision powder metal components using a simple, but highly effective multi-stage forming tool and densificiation method. The outer peripheral surface of the forming portions contact the preform material at each stage and induce elastic and plastic deformation in the preform. The preform may be displaced in a quasi-static fashion, or with very high speed, ensuring an impact on the preform leading to rapid plastic deformation. The result of the deformation of the forming tool densifies the preform at and in the vicinity of the inner peripheral walls contacted by the forming tool This densification leads to a graduation of density and hence material properties. The density is greater at the peripheral walls and gradually decreases. Such a variation of material properties causes incomplete elastic recovery of the material, resulting in compressive residual stresses. At each successive stage, more deformation and less elastic recovery occurs resulting in an increase of compressive residual stresses. The spacing between successive die plates enables the preform to recover elastically in preparation for further deformation by the next die plate. Recovery of the elastic deformation between die plates is beneficial in maximizing the compressive stresses introduced to the preform at each stage to contribute to the strengthening of the preform.
REFERENCES:
patent: 2542912 (1951-02-01), Ensign
patent: 3756062 (1973-09-01), Merola
patent: 3842646 (1974-10-01), Kuhn
patent: 3851512 (1974-12-01), Zhuravlev et al.
patent: 4111031 (1978-09-01), Vennemeyer et al.
patent: 4693864 (1987-09-01), Lloyd
patent: 4712411 (1987-12-01), Goodwin
patent: 5009842 (1991-04-01), Hendrickson et al.
patent: 5325698 (1994-07-01), Nagpal et al.
patent: 5368629 (1994-11-01), Kondo et al.
patent: 5390414 (1995-02-01), Lisowsky
patent: 5403544 (1995-04-01), Adrian et al.
patent: 5409662 (1995-04-01), Hirai
patent: 5453242 (1995-09-01), Knoess
patent: 5613180 (1997-03-01), Kosco
patent: 5659955 (1997-08-01), Plamper
Riley Eric
Woolf Richard Mark
Federal-Mogul World Wide Inc.
Mai Ngoclan
Reising Ethington, Barnes, Kisselle, Learman & McCulloch, P.C.
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