Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1984-12-07
1986-02-18
Godici, Nicholas P.
Metal founding
Process
Shaping liquid metal against a forming surface
164120, 164320, 164520, 164522, B22D 1900, B22C 108
Patent
active
045706930
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the manufacture of articles by the technique known variously as squeeze forming, squeeze casting or extrustion casting which for the sake of convenience throughout this specification and claims will be referred to as "squeeze forming". Basically the technique of squeeze forming comprises introducing liquid metal into a first part of a mould, closing the mould under pressure so that the liquid metal is displaced by the mould closure to fill a cavity within the mould without entrapping air, maintaining the metal under pressure whilst solidification takes place so as to ensure that any shrinkage cavities which may form are closed and filled, and then opening the mould and removing the formed article.
It is known to produce various squeeze formed articles, usually of aluminium or aluminium alloys, but such articles have generally been of a fairly simple shape. Thus where a more complex shape is required it would generally be necessary to achieve such shape by some form of machining operation subsequent to manufacture of the squeeze formed article.
It is an object of the present invention to provide an improved method of manufacturing an article by squeeze forming whereby a more complex shape may be provided to the article without the necessity of extensive subsequent machining.
In accordance with the invention there is provided a method of manufacturing a metal article by squeeze forming comprising locating a shaped compacted soluble salt core in a mould part of a squeeze forming press prior to the introduction of molten metal into the mould, the core being compacted to such a density and surface finish that it will retain its integrity during the squeeze forming operation and being of a shape required to be formed in the squeeze formed article; introducing molten metal into the mould; closing the mould under pressure so that molten metal is displaced by the mould closure to fill a cavity in the mould within which the shaped core is located; maintaining the metal under pressure whilst solidification thereof takes place; opening the mould; and dissolving the shaped core from the squeeze formed article.
Conveniently such a shaped soluble core can be utilised to provide a re-entrant recess or through bore in the squeeze formed article. By way of example, such core may be shaped to provide a re-entrant bowl in the crown of an internal combustion engine piston or, again, by way of example, such core may be shaped to provide a through bore in a link of an endless track assembly.
The said salt core is conveniently isostatically compacted either to the required shape or substantially to the required shape and is then machined. The molten metal conveniently comprises a light metal such as aluminium, magnesium or an alloy thereof.
The method of the invention is conveniently applicable to the manufacture of a light metal piston for an internal combustion engine wherein the piston is squeeze formed crown down in a squeeze forming press having a bottom mould part and a cooperating top punch vertically movable relative to one another, the shaped core being located in the bottom mould part and being so shaped as to form a bowl in the piston crown. Conveniently the core is so shaped as to provide a re-entrant bowl configuration in the piston crown.
In order to prevent pick-up of moisture in the salt core, it is preferable to add a desiccant thereto which will thus provide free-flowing characteristics to facilitate a closer packing of the salt during its isostatic compaction ensuring a dense compact. The desiccant may comprise magnesium carbonate or magnesium phosphate in a proportion of approximately 0.1 percent by weight of the core. Obviously a desiccant must be chosen which does not decompose at the forming temperature of the metal which, for aluminium, is within the range 680.degree. C. to 750.degree. C. The salt together with the desiccant is preferred to have all of the following properties: temperature and pressure requirements of the squeeze forming process. removal of the core from the forme
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patent: 4480681 (1984-11-01), Alexander et al.
Jones, W. D., Fundamental Priciples of Powder Metallurgy, pp. 337-339, 1960.
GKN Technology Limited
Godici Nicholas P.
Heinrich Samuel M.
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