ZA200605259B

ZA200605259B - Casting of metal artefacts

Info

Publication number: ZA200605259B
Application number: ZA200605259A
Authority: ZA
Inventors: Raffle Marie Thomas Gilles
Original assignee: Raffle Marie Thomas Gilles; Price James Cairns
Priority date: 2003-11-26
Filing date: 2006-06-26
Publication date: 2007-10-31
Also published as: DE602004007162T2; EA200601051A1; ES2293361T3; PL1704008T3; EA009004B1; EP1704008A1; AU2004292502A1; ATE365088T1; KR20060109961A; US20070102131A1; EP1704008B1; BRPI0416225A; WO2005051571A1; CA2546742A1; IL175653A0; JP2007512144A; CN1882404A; DE602004007162D1

Abstract

The invention provides a process, casting assembly ( 10 ) and casting apparatus for charging a mould ( 12 ) with molten metal and solidifying it in the mould to form an artefact, the process including, prior to charging the mould, heating the mould by induction heating to an elevated temperature at which the charging takes place. The assembly ( 10 ) includes a mould ( 12 ) for casting he artefact and an induction heating arrangement ( 14 ), which includes at least one induction coil surrounding the mould, for heating it to an elevated temperature prior to the casting. The apparatus ( 20 ) includes the assembly ( 10 ) and a melting apparatus ( 4 ) for forming a molten charge of metal, the apparatus ( 40 ) including a heating arrangement ( 44 ) for heating a precursor of the molten charge to melt it.

Description

CASTING OF METAL ARTEFACTS

THIS INVENTION relates to the casting of a metal awmtefact. More particularly, the invertion relates to a process for casting a metal artefact, to a casting assembly for casting metal artefacts, and to a casting apparatus or installation for casting a metal artef"act, all being particularly suitable for casting light rmetal artefacts.

As used herein, the t-ermm light metal encompasses both light metals as sch, and alloys thereof in which one or more light metals form the major proportion of over 50% by mass, light metals beeing those having a density of less than 2.7g/lcm™. Light metals usually have low melting points of 660°C or less.

According to a first aspect of the invention, there is prowided a process for casting a metal artefact by charging a die or mould with molten me=tal and causing or allowing the met=al to solidify in the die or mould to form the artefaxct, the process including the step, perior to charging the die or mould with the molten metal, of heating the die or mould by induction heating to an elevated temperature, the charging taking place with the die oer mould at the elevated temperature.

The process may include the step of purging the die or maould, prior to the heating, so that c asting of the artefact takes place under a desired atmosphere.

Instead or in additieon, the purging may be carried out during the heatting of the die or mould. Thus, in otker words, the process may include the step, prior to the charging of the die or mould, of purging the die or mould with a purging gas, the ch arging taking place under an atrmosphere provided by the purging gas. Preferably, he purging is carried out both pri or to and during the heating of the die or mould, the gpourging being discontinued before the charging takes place. The purging gas may be selected from the group consisting of argon, carbon dioxide and mixtures thereof. Instead said purging may be by means of a gas, such as sulphur hexafluoride (SF), “which can act as a flux.

The process may include the step, prior to charging the die or mould with molten metal, of sealing off or locking the die or mould. In addition theret-o, the process may include the step of disconnecting the supply of purging gas to the die or mould, prior to charging the die or mould with the molten metal. Typically, the supply of purging gas is dis continued when the die or mould attains its operating temperature.

Charging the die or mould will typically be carried out to fill the die or nnould to its full capacity. oo

The charging may be carried out under pressure, acting to fill the die or mould to its full capacity. In particular, and preferably, the filling of the die or mould with the molten charge is under an intermediate pressure, being neither what is known in the art as low pressure injection moulding nor what is known in the art as high pressure injection moulding. More particularly, the charging may be carried out by injection moulding, at an intermediate pressure in the range 50KPa - 30M Pa. It will be appreciated that routine experimentation can be employed to determine a desired or an optimum intermediate pressure wander which the die or mould should be filled with the molten charge.

The process may irclude using, as the metal, a metal selected from the group consisting of aluminium, meagnesium, lithium, zinc and alloys thereo¥. Preferably the process includes using, as the metal, a light metal selected frormn the group consisting of magnesium, alumin@ium and alloys thereof.

The process is expected to be useful, in particular, in the casting of light metal or alloy products selected from the group consisting of wheel riems, such as aluminium- or magnesium-alloy- wheel rims, automotive gearbox casirgs, steering wheels, steering column houssings, brake auxiliary parts or components, and automotive engine, marine and anircraft parts or components. Typically, the process will be used in the casting of alumminium- and magnesium-alloy wheel rimss. Thus, the casting may be of a light metal artefact in the form of a motor vehicle wheel rim.

In particular, the porocess is expected to be useful in casting artefacts having cross-sectional thicknesses in the range 1.5 — 30mm, usually 2 — 27mm, with respective masses of 0.25 - 3-Okg, usually 0.5 — 20kg. In other worcds and more particularly, the casting may be of a metal artefact in which all parts of the solidified artefact are spaced from the closest part of the surface of the artefact by a spacing of 0.75 — 15mm, the artefact having a mass of 0.25 — 30 kg.

Importantly, the process may include the step of providing the die or mould with a desired temperature profile, by selective application of the ineduction heating thereto, to promote solidification at desired rates of different parts of the molten light metal charged into the die or mould. Thus, the induction heating may be employed to provide the surface of the interior of the die or mould with a desired temperature profile whereboy the interior surface of the die or mould has d ifferent parts or zones at different temperatures from each other or one another, in &ontact with the molten metal charged into the die or mould, thereby to promote clesired cooling and solidification rates in different parts of the metal charged into thes die or mould.

Charging the die or mould may be from a melting apparatus having a capacity to produce a full change of molten metal which is matched in volurme with the capacity or volume or the die or mould, the charging of the die or mould being with sufficient molten metal to produce a single artefact and the charging acting entirely to consume a full molten charge produced by the melting apparatus.

Furthermore, charging the: die or mould may be from a melting apparatus vahich is reciprocably movable relative to the die or mould, the process including recip-rocably moving the melting apparatus between a charging position where it is charged with a precursor of the molten charge, and a filling position where the melten chaarge is transferred from the meltink g apparatus to the casting assembly. The casting may be carried out in a plurality ©f dies or moulds each associated with a single melting apparatus from which it is charged, each melting apparatus being associated with a single die or mould and boeing electrically heated by induction heating, a common electrical power supply being used to supply electrical power to the dieses or moulds for the induction heating thereof, and &a common electrical power suppl vy being used to supply electrical power to the meltirng apparatuses. The process maay be carried out by using a casting apparatus or installation as defined hereunder. 5

According to another aspect of the invention, there is proviaded a casting assembly for casting a metal artefact, th e assembly including a die or mould for casting the artefact and including also an induction heating arrangement, the induction heating arrangement including at least one incluction coil surrounding the die or mould, for heating the die or mould to an elevated £emperature prior to the casting of the artefact.

The induction heating arrangement may be in the form «of a variable- frequency induction heater.

The assembly may includ e a purging gas supply connectecd to the die or mould for supplying a purging gas to the interior of the die or mould.

The die or mould may bes a disposable die, for example sLich as a sand casting die or mould. Instead, the die ox mould may comprise a re-usable die or mould.

The re-usable die or mould may be a metal die or mould, preferably a steel die or mould. In particular, the die or mould nnay be a re-usable multi-core seg mented metal die or mould.

In the case of a re-usable die or mould, the die or mould may thus be a multi- core or segmented die or mould, comprising two or more coress or segments. In particular, the die or mould may comprise a top core or segment to which the solidified artefact remains removably attached at the end of the casting. The top core or segment may include ©r be associated with release means for re=leasing the artefact therefrom. In this cases the die or mould will typically also comprise2 a bottom — or face core, and a ring of sides cores associated with pistons, which side cares or segments give the die or mould it=s segmented character. In particular, the re—usable die or mould may be hydraulically operable, with regard to the pistons of the sside cores and with regard to lifting of the top core and casting from the remaining coress to bring the casting into contact with pins forming the release means. The die or mould will typically have a charging opening for usse in filling or charging the die or mould witlih molten light metal.

In one embodiment of the invention, the die or mould has its chargimng opening provided through its bottom or faace core for charging or filling the die or mosiiid from below. In a 16 preferred embodiment , the re-usable die or mould is hydraulically operable and has a bottom- or face core porovided with a metal-charging opening for- charging the die or mould with molten me=tal from below. :

The indwuction heating arrangement may include two or more induction coils, operable indepe=ndently of one another in achieving a desire«d temperature profile in the die or mould. | n other words, the induction heating arrangement may include a plurality of at least two induction coils which are operable incdependently of each other or one another to heat the die or mould to said elevate-d temperature while providing the surface of the intemrior of the die or mould with a desired temperature profile.

The casting assemably may be of permanent construction as part of an installation, being constructed to remain more or less permanent] y in situ, at a production facility for casting ligh® metal artefacts. Instead, and prefer=bly, the casting assembly is not of permanent cconstruction, being moveable as part eof an apparatus from one said production facility tc another. —10 The invention thus extends to a casting apparatus or installation for casting metal artefacts, the apparatus or installation including a castirng assembly for casting a metal artefact as defined above, and a melting apparatus for forming a molten charge of metal for use in casting the metal artefact in the casting assembly, the melting apparatus including a heating arrangement for heating a precursor of the 45 molten charge to a temperature at which the molten charge is formed from the precursor.

Preferably the melting apparatus is sized to melt charges of wmetal which are matched in size with the size of —the die or mould, so that casting of tree artefact in the <0 die or mould consumes an entire charge. More particularly, the melting apparatus may have a capacity to produce a fumll charge of molten metal having a \wvolume which is matched with the capacity or v olume of the die or mould so that the casting of a single artefact in the die or mould entirely consumes a full molten charge produced by the melting apparatus when the melting apparatus is operated at full capacity.

The heating arrangement of the melting apparatus cer installation may be an induction heating arrangement comprising at least one inductiosn coil. In each case where the die or mould arrangement, on the one hand, and, the reiting apparatus on the other hand, inclLude one or more induction heating coils, the ineduction coils may be electrically connectexd to an electrical power supply therefor.

The rmelting apparatus may be reciprocably mov-able relative to the casting assembly between a charging position where charging of tie melting apparatus with a precursor of ~the molten charge takes place, and a filling pomsition where transfer of a molten charge from the melting apparatus or installation to tlhe casting assembly takes place. Thus, the casting apparatus or installation may incliade rails, the melting apparatus being mounted via wheels on the rails, the wheels beirg rollable along the rails during reciproecating movement of the melting apparatus re=lative to the casting assembly.

The casting apparatus or installation may include two or more of the casting assemblies and the same number of the melting appa.ratuses, the casting assemblies sharing a common heating power supply and the ameiting apparatuses sharing a common heating power supply, for the casting of artefacts in respective casting cycles which are sufficiently out of phase to permit sucsh sharing. In other words, the casting apparatus or installation may include a plumrality of the casting assemblies and tBhe same plurality of the melting apparatiises, each casting assembly being asssociated with a single said melting apparatums and each melting apparatus being associated with a single said casting assermbly, the casting assemblies sharing a commoen electrical heating power supply and the melting apparatuses sharing a common electrical heating power supply.

The arrangement of the facility is particularly suitable f~or the case where the heating arrangement for -the melting apparatuses or install=ations is also an induction heating arrangement , the heating power supplies being electrical power supplies.

The invention will now be described, by way of a non—limiting illustrative example, with reference to the amccompanying diagrammatic drawings.

In the drawings,

Figure 1 shows an exploded schematic side elevatiory of the various components of a casting assenmbly according to the invention for camsting a light metal artefact in accordance with the process of the invention;

Figure 2 shows an exploded schematic side elevatior of the various components of a melting apparatus for use with the casting assembly, for forming a molten charge of light metal, for use in the process of the invention;

Figure 3 is a three-dimeznsional view of a casting apparatuss or installation in accordance with the invention, #or casting light metal artefacts, in acccordance with the method of the invention;

Figure 4 is a three-dimensional view of a casting facility according to the #nvention and comprising two casting apparatuses or installations of Figure 3, for «casting light metal artefacts in accordance with the method of the invention;

Figure 5 shows a series of simplified schematic side elevations of the casting aapparatus or installation of Figure 3, illustrating the method of casting a light metal artefact in the form of a magnesium alloy wheel rim, in accordance with the invention, wising the casting apparatus or installation of Figure 3; and

Figure 6 is another series of simplified schematic side elevation of the casting apparatus or installation of Figure 3, further illustrating the me=thod of casting a light Imetal artefact in the form of a magnesium alloy wheel rim illustrated by Figure 5.

Referring first to Figure 1 of the drawings, referenc-e numeral 10 generally refers to a casting assembly for casting a light metal artefact, in accordance with the invention. The casting assembly 10 comprises a die or mould 12 for casting a light metal artefact in the form of a magnesium alloy wheel rim, and comprises also an induction heating arrangement 14 surrounding the die or mould “12.

The die or mould 12 is a multi-core or segmented re-useable steel die or mould, comprising a top core 16 to which a solidified artefact remains removably attached at the end of the casting process, a bottom — or face core 18 having a centrally located charging opening or passage 20 provided theresthrough for charging or filing the die or mould 12 from below, and a segmented ringm of four side cores 22 associated with respective pistons 24, the side cores 22 giving the die or mould 12 its segmented character. The die or mould 12 is hydraulically oper-ated, with regard to the pistons 24 of the side cores 22 and with regard to lifting of the top ceore 16 and any attached light metal casting (not shown), upwardly and away from the remaining cores.

The top core 16 is associated with release means ( not shown) for releasing the artefact therefrom at the end of the casting process.

The heating arrangement 14 comprises six windings respectively forming induction coils 25, 26, 27, 28, 29 and 30, operable independently of cone another, for achieving a desired temperature profile in the die or mould 12.

The casting assembly 10 also includes a purging gas supply shown schematically by broken line 31, for supplying SFe/CO2 purging gas to tFe die or mould 12 prior to and during the casting process.

Referring now to Figure 2 of the drawings, reference numeral 40 generally refers to a melting app aratus for forming a molten charge of light metal, in : accordance with the invention. The melting apparatus or installation 10 comprises a hollow low carbon — or mild steel cylinder or sleeve 42 of circular cross-section for holding a molten charge of light metal and also for facilitating heating o=F a precursor of the charge of light metal, an induction heating arrangement 44 comprisimng an induction coil 46 for heating contents of the cylinder or sleeve 42 to form a molter charge, and a molten metal transfer assembly 4-8 for transferring a molten charge of | ight metal from the cylinder or sleeve 42 to the die or mould 12 in which an artefact is cast.

The melting apparatus 40 aiso in cludes an inert gas supply 50 for supplying argon gas to the interior of the cylinder wor sleeve 42 such that melting of the light metaal charge takes place under a substan-tially inert atmosphere, and also to provide ceooling to the lower end or base of thme cylinder or sleeve 42 to form a 5S secondan. seal therefor as described hereunder.

In use, the induction coil 46 is mourted on the metal transfer assembly 48, the coll 46 being connected to the barrel 62 armd surrounding the cylinder or sleeve 42 to heat the contents thereof.

The transfer assembly 48 compriseas a telescopically moveable muilti- stage piston arrangement 52 for use in elevating ®&he cylinder or sleeve 42 fo engage lockingly waith the periphery of the charging openineg 20 of the die or mould 12, prior to filling the cdie or mould 12 with a molten charge from the cylinder or sleeve 42. The multi-stage piston arrangement 52 incorporates a central piston comprising three telescopic piston rods 54, 55, 56 with the central rod 56 having a piston head 58 provided wwith a conical sealing surface 59 for seal ingly engaging the periphery of the opening 20) into the die or mould 12 when an entiire molten charge in the cylinder or sleeve 42 has been transferred from the cylinder or sleeve 42 into the die or mould 12. The wmmulti-stage piston arrangement 52 includes a variable force and speed controller {not shown) for controlling the rate of movement thereof and also for controlling the upward force exerted by the piston head 58 on a molten charge in the cylinder or sleeve 42 and in the die or mould 12, “when the piston head 58 sealingly engages thme periphery of the charging opening 20 of the die or mould 12.

Thus, in use, the cyl inder or sleeve 42 is supported on the transsfer assembly 48, such that the multi-steage piston arrangement 52 is moveable within the interior of the cylinder or sleeve 42 in sliding and sufficiently sealing engagement therewith so as to enable a molten charge in the cylinder or sleeve 42 to be puslihed upwardly and out of the cylinder or sleeve 42 upon the upward movement of the pisston rods 54, 55, 56, to transfer and inject the molten charge into the die or mould 12.

The transfer assembly~ 48 also comprises a plurality of concentric barrels { 0 60, 61, 62, 63 and 64 of different cliameters. The barrels 60, 61, 62, 63 and 64 are telescopically vertically displaceable », relative to one another and nest in one another—.

The barrel 80 is the bottom barrel and has wheels 66 for running on rails 87 forming part of the casting instal lation of Figures 4 - 6 for reciprocating the mel ting £5 apparatus or installation 40 betweera a charging position where charging of the cylirder or sleeve 42 with a precursor of a molten charge takes place, and a filling posi:tion where the melting apparatus 40 is ir alignment with the charging opening 20 of the - die or mould 12 of the casting assembly 10, to enable a molten charge formed by meBting of a precursor thereof in the cylinde=r or sleeve 42 to be transferred therefrom into said =0 die or mould 12, thereby typically fil ling it with the molten charge. The barrel 64 is the top barrel and provides a circumferentially extending upwardly facing support ring having a groove (not shown) for se=alingly engagingly the lower end of the cylindest or sleeve 42 therein. The barrel 6:2 in tum provides a circumferentially extencding upwardly facing support ring on which the induction coil 46 is supported when placzed over the cylinder or sleeve 42 to surround it.

In addition to the seal provicled by the groove on the bamel 64, the arcgon gas supplied via the gas supply 50 provid es cooling to the lower end of the cylinder— or sleeve 42 during melting of the precursoer of the molten charge, allowing part of the molten charge formed to solidify in a zone= between the piston arrangement 52 and “the top barrel 64 and at the lower end of thee cylinder or sleeve 42, thereby providing a secondary seal which is formed of solidifie-d light metal from the molten charge.

Referring now to Figure 3 of the drawings, reference numeral 70 generally refers to a casting apparatus of installation for casting light metal artefactss, in accordance with the invention. The samme parts are assigned the same refererce numerals as in Figures 1 and 2, unless otlnerwise specified.

The casting apparatus or installation 70 comprises a casting assembly~ 10 as described above and a melting appara tus 40 also as described above. The casting apparatus or installation 70 also includes a die or mould hydraulic controller 72 aned a melting apparatus 40 hydraulic controller #4.

The top core 16 is associated with release means (not shown) for releasing the artefact therefrom at the endl of the casting process.

Thee casting apparatus or installation 70 also includes a ce-=ntral processing unit (CPU) 76 for monitoring the heating of the induction heating arrangement 14 to achieve the desired temperature profile, and also for providing feedback control to respective power supplies 92 and 94 (Figure 4) therefor.

Thee casting apparatus or installation 70 also includes rails (not showr but see 67 in Figure= 2) on which the wheels 66 of the metal transfer assembly 48 off the melting apparatuis 40 can run. Thus, the melting apparatus 40 is reciprocable rel=ative to the die arranggement 12 between a charging position (=as shown in Figure 3) w-here charging of the melting apparatus 40 with a precursor of thee molten charge takes pRB ace, and a filling position (see Figures 5 and 6) where transfer of a molten charge fromm the melting apparatus 40 to the die or mould 12 of the casting &ssembly 10 takes place=.

Re=ferring now to Figure 4 of the drawimgs, reference numera I 90 generally refers “to a development of the apparatus or installation 70 in the form of a casting facility. The casting facility 90 comprises twvo casting apparatusess or installations 70, each comprising a casting assembly 10 having a die or mould 12 in which the castineg of the artefact is carried out, and having a melting apparatus 4%0 for induction melting a charge of light metal. The casting faecility 90 also includes a melt induction heatingg power supply 92, for example of 100k<W, for separately supplying power to each off the two melting apparatuses 40, a die incduction heating power stuapply 04, also for example of 100kw, for separately supplyving power to each cassting assembly 10, a cooling tower (not shown) for providing ccaoaling fluid, and a gas supply control unit 96 for sLipplying purging gases to the casting assembly 10 and also to the melting apparatuses 40.

It will Boe appreciated that the casting facility 80 permits two artefacts to be cast simultaneo usly using casting cycles which are out= of phase, the melting apparatuses 40 sharing the common induction heating power supply 92 and the casting facilities 10 sharing the common induction heating power supply 94. The casting of the arte=facts then takes place in respective caasting cycles which are sufficiently out of pHhase to permit such sharing. It will thus be appreciated that the casting facility 90 can be operated in quasi-continuous fastion, in that the casting apparatuses or installations 70 can be used on an altematzing basis, with the one having its melting apoparatus 40 in its filling position and being umsed for casting while the other has its meltimg apparatus 40 in its charging position and is charged with a precursor of the ligh t metal, and being prepared to be reciprocsated to its filling position, as soon as the cassting process in the other casting apparaatus or installation 70 is completed.

Referring now to Figures 5 and 6 of the drawi:ngs, use of the casting apparatus or installation 70 described above is illustrated witHh reference to casting a light metal artefact ian the form of a magnesium alloy wheel rin 100, using a precursor in the form of a pres-formed billet or ingot 102 of a magnesimum-aluminium-zinc alloy known in the art as AZ91. The billet or ingot 102 is placed on the piston arrangement 52, with the associated melting apparatus or 40 in its charging goosition. The cylinder or sleeve 42 is placed over the billet or ingot 102, such that the leower end of the cylinder or sleeve 42 sealingly engages said graove on the top barrel 64 of the metal tramsfer assembly 48. The induction coil 46 is connected to the barrel 62 of the metal tramsfer assembly 48, so that placing the cylinder or sleeve 42 and the billet or ingot 132 in position, acts to have them surrounded by the coil 46.

The casting assembly 10 &s prepared for casting by lowering the top «core 16 such that it engages with the bottom- or face core 18. The ring of side ~core segments are then placed in position, using their pistons 24, to close the die. Purging gas in the form of SF¢/CO- fluxing gas mixture comprising 0.2% by volume SF iss fed -10 into the die or mould 12 and the die or rmould 12 is heated using the induction coils 25, 26, 27, 28, 29 and 30 by electrical power fed from the induction heating power suapply 94 using a pre-selected frequency, until the die or mould 12 achieves a required operating temperature, and has a desired temperature profile. The rate of heating can be altered by changing the power input from the power supply 84 and/or by chan ging the frequency thereof, with a higher frequency resulting in a higher heating rate; and the coils 25, 26, 27, 28, 29 and 30 can be selectively operated with different pOwer supplies thereto, to achieve said temperature profile.

The melting apparatus 40 is reciprocated with the aid of the wheels 6 6 on the rails 67 of the casting apparatus or installation 70, from the charging position were charging of the cylinder or sleeve 42 with the billet or ingot 102 of a molten charge of

AZ91 alloy takes place, to a filing position where the melting apparatus 40 3s in alignment with the charging opening 20 through the bottom- or face core 18 of thes die or mould 12. The cylinder or sleeve 42 is sealingly engaged with the lower surface of tlhe bottom- or face core 18, by raising the barrel 684 hydraulically, which also seals the cylinder or sleeve 42 to the barrel 64. The cyl inder or sleeve 42 is purged by a

SF/CO, purging gas. The billet or ingot 102 is me=lted under an atmosphere provided bey the purging gas introduced to the cylinder or slexeve 42 by the gas supply 50, until a rnolten charge of AZ91 alloy is formed. Argon is then used to provide a cooling amtmosphere for cooling of the molten charge at the lower end of the cylinder or sleeve 4-2 to form a secondary seal in the form of a more or less semi-solid or solidified portion omer sprue of the light metal (not shown).

Once the desired operating temperaature and temperature profile have beeen achieved in the die or mould 12, and the die or mould 12 has been pressure locked with the aid of the pistons 24 by means of the hydraulic controller 72, the gas s upply to the cylinder or sleeve 42 is cut off and thea molten charge is transferred under p ressure from the cylinder or sleeve 42 into the die or mould 12 by means of the piston a rrangement 52, thereby filling the die or mould 12 ~with the molten charge. Prior to and d uring injection of the molten charge into the die or mould 12, the die or mould 12 is p urged with the abovementioned SFs /CO2 purging./fluxing gas by means of gas supply ceontrol unit 96, which gas also protects the molten surface off the molten charge both in tie sleeve 42 and when it enters the die or mould 12. The pisten head 58 locks seealingly against the periphery of the charging o-pening 20 and partially enters the chharging opening 20 to increase the pressure on th_e molten charge in the die or mould 1=2. The die or mould 12 is allowed to cool dow~n and the melting apparatus 40 is diisengaged from the die or mould 12. The melting apparatus 40 is then reciprocated baack to its charging position.

The die or mould 12 is then opened by hydraulically disengamging the ring of side core segments 22 from one another with the aid of the pistons 24 _, and the top c-ore 16 with the solidified wheel rim 100 attached thereto, is lifted, using fhe controller 7 2. The wheel rim 100 is then detached or released from the top core 16S by allowing d ownwardly directed pins forming part of the release means (not shown) to push the wheel rim 100 downwardly during the raising of the top core 16.

The piston arrangement 52 is lowered and then the baamels of the a ssembly 20 are retracted, releasing the cylinder or sleeve 42 and the solidified portion o r sprue (not shown) of the molten charge which formed the secondary seal for the cylinder or sleeve 42. The used cylinder or sleeve 42 is then cleaned and wre-positioned b ack on the transfer assembly 48 in preparation for the casting of a new wieel rim 100.

It will be appreciated, however, that a different cylinder or sleeve 42 ma~y instead be u:=sed to avoid waste of production time and also to minimise the possibi lity of cross- ceontamination.

It is an advantage of the invention that the casting aspparatus or inn stallation 70 need not necessarily to be of a permanent construction, beirng moveable from one production facility to another with ease. Thus the casting &apparatus or irmstallation 70 may be inexpensively set up close to an end user of the artefacts to be cast, thereby reducing transportation costs, and the like.

It is also a further particular advanatage of the invention that the induction heating of the die or mould 12 by the heating arrangement comprising the six induction coils 25, 26, 27, 28, 29 and 30, operable independently of one another, enables a desired temperature profile to be obtained in thse die or mould 12, prior to the casting step, thereby having a desirable consequential effect on the solidification rate of the various portions of the artefact, such as the wheel rim 100, thereby reducing stresses in the solidified artefact (wheel rim 100). The at®ainment of desired flow distances for complete filling of the die or mould 12 are also peamitted.

It is yet a further advantage of the present invention that the casting apparatus or installation 70 does not require rmuch space for it to be erected. For example, the casting apparatus or installation 770 as described above only requires a floor space of about 20 - 30m2 The present p rocess also offers other costs benefits such as the fact that power supply only has to be fed to the casting apparatus or instalation 70 immediately prior to casting and caan be switched off at the end of casting a single artefact, without adversely affecting the process or the efficiencies thereof. In the case of a power failure during the casting process using the method and casting apparatus or installation 70 of the present invertion, it will be appreciated that losses need be no greater than loss of the molten charge in the cylinder or sleeve 42, comprising the single billet or ingot 102, as cormpared to a typical foundry where the process is continuous and large amounts of met=al have to be molten at any given point "in time, all of which can solidify in the event of za power failure. Indeed, losses can in principle be avoided completely by simply re-nmelting the contents of the cylinder or sleeve 42, when the power supply is restored.

It is a yet a further advantage of the process in accordance with the present invention, that the die or mould 12 of the casting assembly 0 does not require running-in in order ®o achieve the optimum process conditions.

T he desired casting temperature profile ray be easily obtained by selectively controlling power fed to each of the coils 25, 26, 27, 28, 29 and 30. The fact that the process «does not require a running-in cycle or cycles means that a particular number of bill ets or ingots 102, barring any power failures, should yield an equivalent number of wiheel rims 100, with reduced wastage arising from reject artefacts and enhanced quality control.

Claims

CLAIMS:

1. A process for «casting a metal artefact by charging a die a»r mould with molten metal and causing oF allowing the metal to solidify in the die o r mould to form the artefact, the process being characterized in that it includes the step, prior to charging the die or mould with tke molten metal, of heating the die or rmould by induction heating to an elevated temperature, the charging taking place» with the die or mould at the elevated temperature.

2. A process as claimed in Claim 1, characterized in that it includes the step, prior to the charging of the die or mould, of purging the die or renould with a purging gas, the charging tak ing place under an atmosphere provided by the purging gas.

3. A process as claimed in Claim 2, characterized in that the purging is carried out both prior to and during the heating of the die or mould , the purging being discontinued before t he charging takes place.

4. A process as claimed in any one of the preceding claims, characterized in that the charging is carried out under pressure, acting to fill the die or mould to its full capacity.

5. A process as «claimed in Claim 4, characterized in that the charging is carried out by injection moulding, at an intermediate pressure in the range 50 KPa -30MPa. .

6. A processs as claimed in any one of the preceding claims, characterized in that it includes usi ng, as the metal, a metal selected from the group corsisting of aluminium, masgnesium, lithium, zinc and alloys thereof.

7. A process as claimed in Claim 6, characterized in that it includes using, as the metal, a light metal selected from the group consisting of magnesium, aluminium and alloys thereof.

8. A proce sss as claimed in any Claim 7, characterized in that the cas®ing is of a light metal arte-fact in the form of a motor vehicle wheel rim.

S. A proce sss as claimed in any one of the preceding claims, characterized in that the casting is ©f a metal artefact in which all parts of the solidified artefact are spaced from the closest part of the surface of the artefact by a spacing of 0.75 — =15mm, the artefact havinge a mass of 0.25 — 30 kg.

10. A proce ss as claimed in any one of the preceding claims, characteri zed in that the induction heating is employed to provide the surface of the interior of the die or mould with a desired temperature profile whereby the interior surface of the die or mould has different parts or zones at different temperatures from each ot her or one another, in cortact with the molten metal charged into the die or mould, thereby to promote desired cooling and solidification rates in different parts of the metal : charged into the die or mould.

11. A process as claimed in any one «of the preceding claims, characterized in that chargirg the die or mould is from a melting apparatus having a capacity to produce a full charge of molten metal which is matched in volume with the capacity or volume or the die or mould, the charging of th e die or mould being with sufficieent molten metal to produce a single artefact and tlhe charging acting entirely to consume a full molten charge produced by the melting apparatus.

12. .A process as claimed in any one of the preceding claims, characterg&zed in that the chaarging of the die or mould is frorm a melting apparatus which is reciprocably movab le relative to the die or mould, thee process including reciprocably roving the melting apparatus between a charging position where it is charged with aa precursor of the molten charge, and a filling position where the molten charge is Eransferred from thm e melting apparatus to the casting assembly.

13. _Aprocess as claimed in any one ef the preceding claims, characterized in that the cassting is carried out in a plurality of dies or moulds, each associauted with a single melting apparatus from which it is charged, each melting apparatus being associzated with a single die or mould and being electrically heated bys induction heating, a common electrical power supply being used to supply electrical power to the die=s or moulds for the induction heamting thereof, and a common electmrical power supply being used to supply electrical power to the melting apparatuses.

14. A casting assembly (10) for cassting a metal artefact (100), the assembly including a die or mould (12) for cassting the artefact and the assembly bei ng characterized in that it includes an induction heating arrangerment (14), the induction heating arrangement including at least one induction coil (25=, 26, 27, 28, 29, 30) surrounding the die or mould, for heating the die or mould to ar elevated temperature prior to the casting of the artefact.

15. An assembly as claimed in Claim 14, characterized in that the inductison heating arrangement is in the form of a wariable-frequency induction heater (16).

16. An assembly as claimed in Clairm 14 or Claim 15, which includes a purging gas supply line (31) connected to the die or mould for supplying a purging gas to the interior of the die or mould.

17. An assembly as claimed in any ome of Claims 14 — 16 inclusive, characterizeed in that the die or mould is a re-usable multi-core segmented metal die or mould.

18. An assembly as claimed in Claim 17, characterized in that the re-usable die or mould is hydraulically operable and haas a bottom- or face core provided with a metal-charging opening for charging the die or mould with molten metal from below.

19. An assembly as claimed in any cone of Claims 14 — 18 inclusive, in which tlhe induction heating arrangement includess a plurality of at least two induction comils which are operable independently of eacch other or one another to hexat the die or mould to said elevated temperature while providing the surface of the Rinterior of the die or mould with a desired temperature pmrofile.

20. A casting apparatus or installation for casting metal artefacts, tlhe apparatus being characterized in that it includes a casting assembly (10) as clairrmed in Claim 14, arad a melting apparatus (40) for form ing a molten charge of metal ~for use in the castineg of a metal artefact in the casting amssembly, the melting apparatus including a heatin g arrangement (44) for heating a precursor of the molten charge to a tempe=rature at which the molten charge iss formed from the precursor.

21. An apparatus or installation as clafimed in Claim 20, characteriz=ed in that the meltin g apparatus has a capacity to prod uce a full charge of molten metal having a volum_e which is matched with the capacity or volume of the die or mound so that the castin g of a single artefact in the die or meould entirely consumes a full rmolten charge produ ced by the melting apparatus wher the melting apparatus is operated at full capacity.

22, An apparatus or installation as clai med in Claim 20 or Clam 21, characterized in theat the heating amangement of the melting apparatus is an induction heating arrangement comprising at least one indu: ction coil (46).

23. An apparatus or installation as clai@med in any one of Claims 20 — 22 inclusive, chara cterized in that the melting appara tus is reciprocably movable relative to the casting asssembly between a charging position where chargingi of the melting apparatus vith a precursor of the molten charge takes place, and a filling position where transsfer of a molten charge from the melting apparatus to the casting assembly tamkes place.

24. An apparatus or installation as claimed in Claim 23, characterized in that it includes raills (67), the melting apparatus being mounted via wheels (66) on the rails, the wheels being rollable along the rails during reciprocating nmovement of the melting app=aratus relative to the casting assembly.

25. An a pparatus or installation as claimed in any one of Claims 20 — 24 inclusive, characterizead in that it includes a plurality of the casting assemblies and the same plurality of the melting apparatuses, each casting assembly being associated with a single said melting apparatus and each melting apparatus being associated with a single said casting assembly, the casting assemblies sharing a common electrical heating power supply (94) and the melting apparatuses sharing a common electrical heating powver supply (92).