Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1997-09-26
1999-06-01
Pyon, Harold Y.
Metal founding
Process
Shaping liquid metal against a forming surface
164134, 164136, 164 63, 164254, 164319, 164321, 164337, B22D 1802, B22D 1106, B22D 2715, B22D 3900
Patent
active
059080655
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an apparatus and method for squeeze casting.
Two types of squeeze casting are known in the prior art end are referred to as direct squeeze casting and indirect squeeze casting. Both processes have been developed for the production of high integrity near net shape castings. However, in order to produce important casting conditions need to be satisfied:
(i) delivery of clean metal to the mould, usually involving filtration;
(ii) non-turbulent flow of metal into the die set after filtration;
(iii) accurate metering of metal into the die cavity;
(iv) full pressurisation of the metal during solidification.
When measured against these criteria, serious drawbacks and limitations are apparent in prior art techniques of both indirect and direct squeeze casting.
Indirect squeeze casting is generally considered to be a modification or development of high pressure die casting. Liquid metal is forced into a closed die cavity from a shot sleeve by a small piston. The piston, normally driven by a hydraulic ram continues to act on the metal in the die cavity during its solidification period. Squeeze pressures are limited by the bore of the piston and the rating of the hydraulic ram. In one method of indirect squeeze casting liquid metal is poured turbulently into a shot sleeve and the metal is non-turbulently displaced upwards into the die cavity by the piston through a gate, the width of the gate being many times larger than the gate used in conventional high pressure die casting. The die may open either vertically or horizontally to release the casting. In a second method of indirect squeeze casting, metal is injected turbulently at high velocity into the die cavity through a narrow gate and the metal is further consolidated in the mould by means of opening the gate wider to allow the piston to move forward to compensate for solidification shrinkage.
Indirect squeeze casting processes generally operate with short cycle times since they are generally based on high pressure die casting practice and hence they tend to be high productivity processes. By the same token, however, these processes are most suited to conventional casting alloys and it has been found difficult to manufacture consistently good castings from high strength aluminium wrought alloys. Even those indirect squeeze casting produced using conventional casting alloys may contain some remnant microporosity in regions remote from the action of the plunger which could be detrimental to the quality of the castings. Furthermore, in most indirect squeeze casting practices it is not feasible to filter the metal just prior to its entry into the die cavity and therefore the oxides present in the melt due to turbulent metal handling procedures inevitably become trapped in the cast article as non-metallic defects. Such defects undermine and diminish the quality of the cast metal product to an extent that cannot be easily quantified and which cannot be readily tolerated.
With regard to metering metal to produce castings of constant size and shape, indirect squeeze casting processes use a closed die to define the casting cavity. Opposing die halves are locked together rigidly by hydraulic cylinders and large toggle during the injection of metal from the shot sleeve and during the metal pressurisation period from the plunger. The only moving part of the equipment during casting is the plunger, which moves to inject metal into the fixed volume die cavity. Side cores may be used in the die to increase the complexity of the casting shape. Although the external form of the cast article may be accurately controlled, indirect due to the presence of microporosity, particularly in regions of the casting remote from the plunger. Excess metal comprising the runners and wad, which may constitute over fifty percent of the total shot mass, needs to be removed from the casting after ejection from the die.
Of the four casting conditions listed above as pre-requisites for the highest quality castings, indirect squeeze casting only satisfies the third req
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VDI Zeitschrift, vol. 133, No. 3, Mar. 1, 1991, pp. 127-128, 131-133, XP000219812 Schneider W: "Formgiessverfahren Fuer Innovative Aluminumgussteile".
Lin I.-H.
Papervision Limited
Pyon Harold Y.
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