GB2193914A

GB2193914A - Casting using a metal core

Info

Publication number: GB2193914A
Application number: GB08620153A
Authority: GB
Inventors: Norman Brown; David Rastall
Original assignee: METAL CASTINGS
Current assignee: METAL CASTINGS
Priority date: 1986-08-19
Filing date: 1986-08-19
Publication date: 1988-02-24
Anticipated expiration: 2006-08-19
Also published as: GB8620153D0; GB2193914B; EP0257425A3; EP0257425A2

Abstract

In the diecasting of an aluminium magnesium or zinc alloy, there is used a core (14) of the same alloy. The core is formed by diecasting and is preferably discarded after a single use, though if it is assembled from interfitting parts it may be re-used. Any imperfect casting may be remelted with the core intact, facilitating recycling of the metal. In a particular embodiment, an aluminium alloy casting (16) is diecast in a mould comprising steel outer parts (10, 11) and a steel core (13) on which an annular aluminium alloy core (14) is mounted. The latter comprises parts held together by a circumferential band (15). <IMAGE>

Description

GB2193914A 1 SPECIFICATION core may be changed during removal of the core

from the casting. The shape of the core Casting may be changed by removal of material an d/or deforming the material of the core.

The present invention concerns casting of 70 The core preferably has a wall thickness bodies having shapes which are not simple over at least a majority of the area of the wall shapes, cores being used to achieve undercut which is not substantially less than, and is formations in the castings. By a core, we more preferably substantially greater than, the mean an element or assembly of elements wall thickness of a part of the casting which which is disposed in the cavity in which the 75 engages the core. This ensures that the core casting is to be formed, the core being does not receive from the molten metal suffi formed separately from the body which de- cient heat to melt the core. It will be under fines that cavity and the core defining a part stood that a core of particularly low mass of the surface of the casting but being sepa- may become fused to the casting, unless ar rated from the casting after the latter has solirangements are made to extract heat from the dified, for example, after the casting has been core whilst it is contact with the molten metal removed from the cavity which is formed. introduced into the cavity.

According to a first aspect of the present The method of the invention has been de- invention, there is provided a method of cast- vised for use in the diecasting of light metals ing wherein there is provided a body defining 85 and alloys thereof. These metals include alumi a cavity, a metal core is placed in the cavity, nium, magnesium and zinc.

the cavity is charged with molten metal, the According to a second aspect of the inven- molten metal cools to form a casting contain- tion, there is provided a method of diecasting ing the core, the casting is separated from the wherein a light metal core is mounted on or in body and the core is removed from the cast- 90 an open die, the die is closed with the core ing and wherein the core is formed at least inside, liquid metal, preferably having a com partly of a metal having a composition subposition which is substantially the same as stantially the same as that of the casting. that of the metal of which the core is formed, By reference to the metal of which the core is admitted to the die cavity, the die is is formed having a composition which is sub- 95 opened after the liquid metal has solidified to stantially the same as the composition of the form a casting, the casting is removed from casting, we mean that, in a case where the the die and the core is removed from the core is formed entirely of that metal, the com- casting.

position of the core is either identical with The method is useful in pressure diecasting, that of the casting or is sufficiently similar for 100 when the molten metal in the die is subjected the core and the casting to be remelted to- to a pressure in excess of 10, 000 psi (690 gether in a bulk supply of metal for making bar), although can be applied where the -die is further castings. It is common for a number of subjected to less than 10, 000 psi(690 bar)., imperfect castings to be produced during the for example dwon to 8000 psi (552 bar) or production of a large number of castings 105 even less.

which are intended to be identical one with An example of a method in accordance with another. Imperfect ca ' stings may be produced the invention will now be described, with ref at the beginning of a run, when a die in which erence to the accompanying drawing, wherein in all of the castings are to be produced and there is represented diagrammatically a cross associated ducts through which the molten 110 section through a two-part die, the parts of metal is supplied are below the normal workwhich are separated from each other, a cast ing temperature. It is desirable to remelt such ing which has been formed in the die and a imperfect castings so that the metal of which core in the casting.

they are formed is cast once more. If the The die illustrated in the drawing comprises casting contains a core having substantially 115 first and second parts 10 and 11 respectively the same composition as the casting itself, it which collectively define a die-cavity. For use, is unnecessary to remove the core from an the die parts are mounted in a die casting imperfect casting, before re-melting the cast- machine which may be of known construction ing. and the die part 11 is provided with a gated The core may be an assembly comprising a 120 runner system 12 through which molten metal plurality of components. Preferably, the core can be driven by means not shown from a or each component thereof is formed by die- bulk supply into the die- cavity, when the die casting. Even in a case where the core is is closed. The means for melting and storing removed from an acceptable casting, the core the bulk supply of molten metal and for driv may be re-melted after a single use. When all 125 ing portions of metal from that bulk supply of the cores are re-melted after use, it is un- into the die cavity form no part of the present necessary to carry out any maintenance of the invention and are therefore not described cores and no disadvantage arises from any herein or shown in the drawings.

damage caused to the cores, during removal The die part 10 is generally of hollow, and from the castings. Thus, the shape of the 130 in the example described generally cylindrical 2 GB2193914A 2 form and is open at one end only. The die after a single casting.

part 11 carries a core 13 which may be per- The arrangement of the core 14 may be manently fixed in the part 11 or removably such that one component thereof is readily mounted therein. When the die is closed, the moved relative to the other components in a core 13 extends along the interior of the die 70 radially inwards direction, once the core 13 part 10 to the closed end thereof. When the had been removed from the core 14. In this die is prepared for use, an annular core 14 is case, the core 14 may be removed from the mounted on the core 13 to lie within the die casting without substantial damage to the cavity, when the die is closed. The core 14 is components of the core 14. Alternatively, the so positioned on the core 13 that the core 14 75 shape of one or more components of the core is spaced from the closed end of the die part 14 may be modified during the removal proce and is also spaced from the die part 11, dure, by example by machining some material when the die is closed. When molten metal is away from the core 14 or by deforming that injected into the die cavity, it flows around the core. The components of the core 14 are pre core 14 and this core therefore establishes an 80 ferably re-melted, after a single use, so that undercut formation in the casting. Once the new core components are used for each cast casting has solidified, the die is opened and ing.

the casting is then ejected from the die part For some simple castings however, the core 10. After the casting has been ejected, the 14 may be easily extracted from the casting, core 14 is removed from the casting. 85 thereby enabling some re-use of the core 14, In a case where the core 13 is fixed with or at least some portions of the core 14, to respect to the die part 11, the core 13 is give economic advantage.

withdrawn from the core 14 when the die is The core 14 does not contribute greatly to opened or when the casting is ejected. Alter- the combined weight of the casting and core natively, if the core 13 is removably mounted 90 and therefor does not increase the difficulty of in the die part 11, the core 13 may remain in handling the casting. The core 14 and the the core 14, when the die is opened. In the casting have substantially the same co-efficient latter case, the die part 13 may be withdrawn of thermal expansion and so shrinkage of the from the core 14 after the casting has been casting onto the core during cooling, is at ejected from the die part 10 but in preparation 95 least reduced.

for removal of the core 14 from the casting. It will be appreciated that the temperature The core 14 is of generally annular shape difference between the core 14 and the cast and preferably comprises at least four arcuate metal helps prevent fusion of the core to the components which are assembled together casting.

prior to being mounted on the core 13. These 100 The molten metal is preferably subjected to components may have integral formations pressure whilst in the die cavity. A pressure in which are in mutual engagement to maintain excess of 50 psi (3.45 bar) is used preferably the assembled relation of the core parts until about 8000 psi (552 bar) or above. More pre the core is to be removed from the casting. In ferably, a pressure in excess of 10,000 psi this case, these formations may be deformed 105 (690 bar) is attained.

or removed, prior to removal of the core from The features disclosed in the foregoing de- the casting. Alternately, one or more addi- scription, or the accompanying drawings, ex tional elements may be used to maintain the pressed in their specific forms or in terms of core parts in assembled relation with one a means for performing the disclosed function, another. For example, there may be provided 110 or a method or process for attaining the dis a circumferential band 15. The parts of the closed result, as appropriate, may, separately core 14 may be assembled with one another or any combination of such features, be util on the core 13 or prior to mounting of the ised for realising the invention in diverse core 14 on the core 13. The core 14 may be forms thereof.

assembled on the core 13 prior to mounting 115

Claims

of the core 13 in the die part 11. CLAIMS

Typically, the casting 16 is formed of an 1. A method of casting wherein there is aluminium alloy. The components of the core provided a body defining a cavity, a metal 13 are formed of the same alloy. These comcore is placed in the cavity, the cavity is ponents may be formed by diecasting, by ex- 120 charged with molten metal, the molten metal trusion or by machining from suitable stock. cools to form a casting containing the core, The core 14 may be non-circular and can be the casting is separated from the body and asymmetrical, without inconvenience. The die the core is removed from the casting and parts 10 and 11 and the core 13 are formed wherein the core is formed at least partly of a of steel. Each of these is used repeatedly in 125 metal having a composition substantially the the making of further castings. same as that of the casting.

If desired core 13 could be made of alumi-
2. A method of diecasting wherein a light nium alloy or any other suitable material, and metal core is mounted on or in an opened die, where this is not fixed with respect to die the die is closed with the core inside, liquid part 11, may, like core 13, be disposable 130 metal is admitted to the die cavity, the die is - 3 GB2193914A 3 opened after the liquid metal has solidified to form a casting, the casting is removed from the die and the core is removed from the casting.
3. A method according to Claim 1 or Claim 2 wherein the core comprises a plurality of components assembled together.
4. A method according to any preceding Claim wherein the core is formed by diecast ing.
5. A method according to any preceding Claim wherein each core is melted after a sin gle use.
6. A method according to any preceding Claim wherein the molten metal is subjected in the cavity to a pressure of at least 50 psi (3.45 bar).
7. A method according to Claim 6 wherein the molten metal is subjected in the cavity to a pressure in excess of 10,000 psi (690 bar).
8. A method according to any preceding Claim wherein the core has a wall thickness over at least a majority of the area of the wall not substantially less than that of the part of the casting which engages the core.
9. A method according to Claim 8 wherein the core has a wall thickness over at least a majority of the area of the wall, which is sub stantially greater than that of the part of the casting which engages the core.
10. A method according to any preceding Claim wherein the shape of the core is changed by removal of material and/or by de formation during removal of the core from the casting.
11, A method according to any preceding Claim wherein the core is other than circular.
12. Any novel feature or novel combination of features disclosed herein or in the accom panying drawing.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3 RD.

Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.