Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Heat and pressure simultaneously to effect sintering
Patent
1992-10-30
1995-05-16
Walsh, Donald P.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Heat and pressure simultaneously to effect sintering
419 42, B22F 100
Patent
active
054158320
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method of manufacturing mouldings from powder material wherein the powder material is filled into preformed capsules, which are thereafter evacuated and gas-tightly sealed before being compacted into essentially dense bodies by isostatic pressing. The invention is especially applicable to the manufacture of mouldings with small individual weights or in large series.
When compacting powder material by means of isostatic pressing, the powder material is enclosed in a deformable, gas-tight capsule before the isostatic pressure is applied to the body from a surrounding pressure medium.
The body is formed, for example by filling powder into a preformed capsule, but the powder may also be preformed into a green body from which binder (if any) is driven off before the body is coated with a dense, encapsulating layer.
In the manufacture of metallic bodies by isostatic pressing, the metal powder is usally filled into a preformed thin sheet capsule. The costs of manufacturing the sheet metal capsule limits the application of isostatic pressing since the relative importance of the mould costs for the total cost of the mouldings increases with decreased individual weight, with reduced alloying content, and with an increasingly complex shape, but remains essentially unaffected by the length of the series. The cost picture which arises when each moulding requires a seal-welded and pressure-tested capsule restricts the possibilities of using isostatic pressing, especially when manufacturing mouldings with small individual weights, a complex shape, or low material costs.
SUMMARY OF THE INVENTION
When manufacturing mouldings by isostatic pressing of powdered material in a deformable capsule, according to the present invention at least one sub-element is preformed by compression moulding of thin sheet, with recesses. The capsule is joined, by means of welding, from the preformed sub-elements into a capsule, at least one of the recesses in the preformed sub-element forming a mould for a moulding part and at least one additional recess in the preformed sub-element forming an inlet channel for the powder material. The capsule is filled with powder material and is evacuated and sealed in an essentially gas-tight manner, after which the capsule with powder material enclosed therein is isostatically compacted into an essentially dense body.
After the compaction, the capsule is removed and the moulding parts are separated from each other and cleaned from the inlet channels.
Since the sub-elements are preformed and joined together by mechanizable technique, compression moulding of thin sheet and welding, possibilities are provided for manufacturing considerably more complex capsules which, in addition to the mould for the mouldings, may also contain inlet channels for the powder. This makes it possible to manufacture a large number of mouldings in the same capsule. In addition, the application of mechanizable technique results in a reduction of the costs of the capsule with increasing lengths of series.
The manufacture of capsules according to the invention in which compression moulding of sheet is utilized for forming the capsule means that the lower economic limit to the individual weight is removed and that capsules can now be manufactured which contain a large number of moulds, that more complicated shapes can be manufactured in an economic way, that the fact that the costs per capsule decrease with increasing series lengths can be taken advantage of, and that the testing cost per capsule, for capsules containing several moulds, can be spread over a larger number of parts.
For example, the invention makes it possible to manufacture blanks for turbine blades, the properties of which have been improved by isostatic pressing, without the high costs associated with conventional capsule manufacture.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained in greater detail with reference to the accompanying drawings, wherein FIG. 1 schematically shows the manufac
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patent: Re31355 (1983-08-01), Rozmus
patent: 2725288 (1955-11-01), Dodds et al.
patent: 2943933 (1960-07-01), Lenhart
patent: 4389362 (1983-06-01), Larsson
patent: 4601878 (1986-07-01), Aslund et al.
Friborg Sigurd
Lill Kurt
Torssell Krister
Asea Brown Boveri AB
Chi Anthony R.
Walsh Donald P.
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