ZA200605260B

ZA200605260B - Casting of metal artefacts

Info

Publication number: ZA200605260B
Application number: ZA200605260A
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: EA200601050A1; PL1704007T3; CA2546630A1; US20070102132A1; AU2004292503A1; EA009003B1; ES2291961T3; ATE364463T1; CN1882403A; WO2005051570A1; EP1704007A1; DE602004007044D1; BRPI0416224A; KR20070007035A; DE602004007044T2; EP1704007B1; IL175656A0; JP2007512145A

Abstract

The invention provides a process and apparatus ( 50 ) for casting an artefact by forming a molten charge of metal, charging a mould with the charge to fill it sufficiently to form a single artefact, the charge solidifying in the mould. The size of the charge is selected to match the capacity of the mould so that charging the mould consumes substantially the whole charge. The apparatus ( 50 ) has a container ( 12 ) in which a molten charge of metal is held and a mould ( 54 ) into which the charge is transferred. The container and mould have matched capacities so that filling the mould with sufficient metal to form a single artefact consumes substantially the whole charge and leaves the container empty.

Description

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CASTING OF ME TAL ARTEFACTS

THIS INVENTION relates to the casting of a metal artefact. More particularlyw, the invention relates to a process for casting a metal artefact and to a casting apgparatus or installation for casting a metal artefact, the process andl apparatus or installation being particularly suitable -for casting light metal artefacts. As used herein, the= term light metal encompasses oth light metals as such, and alleys thereof in which light metals form the major proportion of over 50% by mass th ereof, light metals being those having a density of lesss than 2.7 g/cm®. Light metals usually have low melting points of 660°C or less.

According to a first aspect off the invention, there is provided a process for castings a metal artefact, by forming a molten charge of metal from aa precursor thereof, cBharging a die or mould with the molten charge to fill the die or mould sufficiently to form a single metal artefaect and causing or allowing the charge to solidify in the die or mould to form the artefact, the process including the step of selecting he size of the molten charge to match the capacity of the die o r mould so that the charging of the die or mould consumes substantially the wheole molten charge.

Although the process may include the step of forming £he molten charge from a precursor thereof which #is a mixture of one or more or-es, fluxes, alloying e=lements and the like, the mo Iten charge is preferably form ed from a precursor thereof wshich is a metal billet or ingot or a compact of metal particles, such as shavings ow granules, or the like. Thus, the process may includes the step of pre-forming a bil let or ingot of the metal or pre-forming a compact off particles such as shavings or- granules of the metal.

The p rocess may include heating the metal of the molte n charge, after forming the rmnolten charge, to raise the temperature of the molte=n charge, prior to filling the die or mould with the molten charge at the raised termperature.

The step of filling the die or mould with the molten charge may be at a predetermined rate . Preferably, the filling of the die or mould with the molten charge is under pressure, for example by injection moulding. 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 pa rticularly, the charging may be carried out by injection moulding at an intermediate psressure in the range 50KPa - 30MPa. It will be apprec=iated that routine experimentation can be employed to determine a desired or an optimum intermediate pressure under which the die or mould should be filled with the molten charge.

The p-rocess may include the step of purging the environment in which the molten ¢ harge is formed with a purging gas, prior to forming the molten charge. Instead or im addition, the purging may be carried out during the forming of the moltem charge: Preferably, the purging is car-ried out both prior to and curing the formimg of the molten charge. The purgings gas may be a passive or" inert purging gaas and may be a noble gas selected fromm the group consisting of &rgon, helium, n eon and mixtures thereof. Instead, thee purging gas may be an active purging gas and may be selected from the group consisting of SFs, CO®2 and mixtures thereof. In particular, the process may> include the step of purgirg the environmeent in which the molten charge is forrmed with an active purgirmg gas selected —from the group consisting of SFs, CO2 sand SFe/CO2 mixtures, preferably

SFe/CO2 mixtures comprising 0.1 — 0.3% by vol ume of SFe , prior to and during the formi ng of the molten charge. In addition, the process may include, at onset of formirmg the molten charge, the step of sealimg the molten charge in place by passing & passive or inert gas selected from the group consisting of argon, Helium, neon and mixtures thereof, preferably argon, past the molten charge and in contact therewith, to provide a solidified light m etal seal formed from part of the molten ckarge.

The process may include using, as the metal, a metal selecteed from the grougp consisting of aluminium, magnesium, lithium, zinc and alloys thnereof.

Preferably the process includes using, as the met=al, a light metal selected freom the group consisting of magnesium, aluminium and alloys thereof. By alloys of the light metals are meant alloys, as indicated above,. in which one or more of tie light metals form the major proportion of over 50% byw mass thereof.

The process is expected to be useful, in particular, in the casting of licght metal or light metal alloy products sel-ected from the group consisting of wheel rirmns, such as aluminium- or magnesium-aclioy wheel rims, automotive gearbox casinegs, steering wheel housings, braké auxiliamy parts or components, and automotive engimne, marine and aircraft parts or componemis. Typically, the process will be used in the casting of aluminium- and magnesium—alloy wheel rims, sO that the casting may be &fa light metal artefact in the form of motor vehicle wheel rim.

The process is expected to be useful in casting artefacts having cromss- sectional thicknesses in the range 1. 5 — 30mm, usually 2 — 27mm, with respecitive masses of 0.25 -30kg, usually 0.5 — 20kg. Thus, in particular, the casting may be ofa metal artefact in which all the parts of the solidified artefact are spaced from the closest part of the surface of the arte=fact by a spacing of 0.75 ~ 15mm, the artefact having a mass of 0.25 — 30 kg.

The process may be useed with any type of die or mould, for examples, a disposable die or mould such as a szand die or mould, or a re-useable die or mould such as a metal die or mould. In partiecular, the process in accordance with the present invention is particularly suited for use with a metal die or mould forming a re-usable die ormould. Preferably, the metal die or mould is a steel die or mould.

The process mayy include forming the molten charge by induc=tion heating of the precursor, the induction heating being such as to provide the moslten charge with a temperature profile, for example to ensure that the part of the moolten charge which first enters the die or mould is hotter than thaat which enters the die or mould later. Howeaver, any desired profile can in principle be achieved.

According to another aspect of the invention there is provided a casting apparatus or installation for casting a metal artefact in a die or mould, the casting apparatus or installation including a die or mould and a melting apparatus which includes a contaimner for holding a precursor of a molten charge of metal, a heating arrangement for heating the precursor in the container to form a molten charge of metal, and a mo Hen metal transfer assembly for transfesring a molten charge of metal from the container to the die or mould, the container and die or mould having capacities which =are matched so that charging of the die or mould from the container to fil the die or mould with a charge sufficient to form a single metal artefact consumes substaantially the whole charge of molten metal from the container and leaves the contaimer empty.

The= heating arrangement may be mounted om the molten metal transfer assembly. The pmelting apparatus may be reciprocable re lative to the die or mould between a charging position where charging of the melti ng apparatus takes place and a filing posit-ion where transfer of a molten charge frorm the melting apparatus to the die or mould takes place.

Thee apparatus or installation may include an inert gas supply for supplying inert amas to the container, to permit forming of the molten charge to take place under an irsert atmosphere. :

The co ntainer may have a hallow cylindrical interior, for example being in the form of a hollow cylinder or sleeve. The container may be re-usabele. Instead and preferably, the cont-ainer is disposable, being for single use and boeing discarded thereafter. In the czase where the container is disposable, it will be appreciated that cross-contamination from one metal or alloy charge to another is rediaced, particularly in cases where the apparatus or installation is used successively to cast artefacts comprising different metals or alloys.

In a pearticular construction, the container may be a hollow cylinder or sleeve, the transfer assembly being a telescopic piston arrangement for elevating the cylinder or sleeve Ento engagement with the die or mould and into communication with a charging ope=ning in the die or mould. More particularly, the transfer assembly may comprise a te lescopic multi-stage piston arrangement for use in elevating the container to engages lockingly with a die or mould prior to filling the die or mould with a molten charge from the container. in a particular embodiment of the in: vention, in which the transfer assemboly comprises said telescopic multi-stage piston arrangement, the container is a saicd hollow cylinder, the cylinder being supported on the transfer assembly with its heollow interior in a more or less upright attitude, sumch that a central piston of the multi-stage arrangement is upwardly moveable within t7he interior of the cylinder in sliding aand more or less sealing engagement therewith seo as to enable a molten charge in thze cylinder to be pushed upwardly and out of the cylinder upon the upward movement cof the central piston, to transfer the molten charge fto a die or mould, a peripheral piston, surrounding the central piston, being upwardly ranoveable to urge the cylinder upward ly to cause its upper end to seat sealingly against & lower surface of the die or mould, zaround a charging opening into the die or mould.. Thus, in other words, the piston arrangement may have . central piston for enterimng the cylinder or sleeve and for sliding upwardly therein in sealing engagement therewith, the piston arrangement having a peripheral piston, surrounding the central pisston, for urging the cylinder or sleeve upwardly into sealing engagement with the die= or mould around the charging opening of the die or mould.

In particular, the central piston may have a piston he=ad provided with a sealing surface for sealingly engaging the periphery of the charging opening of the die or mould, preferably when all the molten charge in the cylinder hams been transferred from the cylinder into the die or mould. Thus, in use, the step of caus=sing or allowing the molten charge to solidify in the die or mould to form the artefact will typically take place while the piston head sexalingly engages the periphery of the opening.

The casting apparatus or installation may be of esssentially immovable construction, being constructed in situ, at a production facility for casting light metal artefacts, in which case it can be regarded as an installation. Inste=ad, and usually, the casting apparatus or installation is expected not to be of immovable: construction, being moveable from one said production facility to another, in which cases it can be regarded as an apparatus.

The melting apparatus may be provided with wheels . for running on rails forming part of the casting apparatus or installation, the wheels being for pemitting reciprocating movement of the melting apparatus between the chamrging position where charging of the container with a precursor of a molten charge in usee takes place, and a filling position where the melting apparatus is in alignment with time charging opening into trme die or mould, to enable the container to be brought upwardly into sealing contact with the die or mould and in communication therewith, and to enable a molten charges formed by melting of the precursor in thes container to be transferred farom the contai ner into the die or mould, thereby filling the die or mould with the molten ciarge. ‘ it will be appreciated that, whether= or not the container and die cor mould have capacities which are matched as defined and described above, the irvention conte mplates a casting apparatus or installation for casting a metal artefact in a die or mould, the casting apparatus or installation including, in combination, a die or mould and = melting apparatus which includes a container for holding a precurssor of a molten charge of metal, a heating arrangem_ent for heating the precursosr in the container to form a molten charge of metal, ancl a molten metal transfer asse=mbly for transferring a molten charge of metal from the container to the die or mould, the heati ng arrangement being mounted on the mestal transfer assembly.

An important sub-assembly of th is combination is a melting a pparatus including a container for holding a precursor of a molten charge of metal, aa heating arrargement for heating the precursor in the container to form a molten c=harge of metal, and a molten metal transfer assembly far transferring the molten chaarge from a coentainer into a die or mould, the container and the heating arrangermment both being mounted on the molten metal transfer asssembly.

Similarly, it will be appreciated hat, whether or not the container and die or mould have capacities which are matched as described above, the invention contemplates a casting apparatus or installation for casting a metal artefact in a die or mould, the casting apparatus or installation including, in combination, a die or mould and a melting appawratus which includes a container for holdirmg a precursor of a molten charge of metal , a heating arrangement for heating the precursor in the container to form a molten charge of metal, and a molten metal transsfer assembly for transferring a molten cha rge of metal from the container to the die or mould, the melting apparatus being reciprocable relative to the die our meould between a charging position where charging of the melting apparatus takes place and a filling position where transfer of” a molten charge from the melting apparatus to the die or mould takes place.

In turn, an i mportant sub-assembly of this combination is a container for holding a precursor ©f a molten charge of metal, a heating arrangement for heating the precursor in tine container to form a molten charge of meatal, and a molten metal transfer assembly for transferring the molten charge from a container into a die or mould, the melting apparatus being reciprocable between a «charging position where charging of the melting apparatus takes place and a fillinug position where transfer of a molten cha rge from the melting apparatus into a die or mould takes place.

It is to be ewnphasized, as indicated above, that it is arm important aspect of the present invention that the capacity of the container is no larger than, and is at least roughly matched with, the size of a molten charge required to fll the die or mould to produce a single artefact. This means that, each time the die or- mould is charged with a molten charge from the melting apparatus sufficient to form a single artexfact, the container of the melting apparatus or installation will be emptied.

The die or mould arrangeament may comprise a re-usable die or mould.

In particular, 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 may be a re-usable multi-core se=gmented die or mould.

The die or mould arrangsement may include a heating arrangement for heating the die or mould arrangemeent to a casting temperature. The= heating arrangement may be an induction haeating arrangement comprising one or more heating coils.

In each case where the rnelting apparatus, on the one hand, ard the die or mould arrangement, on the other haand, include one or more induction heating coils, the heating coils may be electrically connected to an electrical power supply therefor.

In particular, the die or mould may be gorovided with a heating arrangement imcluding a plurality of at least two induction coils, =which are independently operable to pmrovide the surface of the interior of the die or mou%d with a desired temperature profile.

The invention makes pcoossible the provision of a casting facility, which includes two or more casting apparatuses or installations, the facility includiing two or more melting apparatuses as defined above for melting charges of metal, tthe casting facility also including the same numioer of die or mould arrangements in “which the casting of the artefacts is carried owt, the melting apparatuses sharing aa common heating paswer supply and the die or mould arrangements sharineg a common heating power sup ply, for the casting of artefacts in respective casting cyclees which are typically sufficiently out of phase to permit such sharing, while permittincy he use of common heating psower supplies which are not much larger, if at all, than those needed respectively for a single melting apparatus or a single casting apparatus or installation.

The arrangement of the facility is particularly suitab le for the case where each heating amangement is an induction heating arangemernt, the heating power supplies >eing electrical power supplies. | a

During the use of a casting facility as defined albovs, the process of the preseent invention may include using one of the shamred power supplies successiwely to form molten charges in the respective containers of the melting apparatuses, and using the other of the shared power supmplies successively to heat the respective die or mould arrangements, in casting cycles which are out of phase.

The invention will now be described, by way of a mnon-limiting illustrative example, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 shows an exploded schematic side elevation of the various componernts of a melting apparatus in accordance with the in—vention, for forming a molten charge of light metal, in accordance with the process of the invention;

Figure 2 is a three-dinmensional view of a casting apparatus or installation in accordance with the invention , for casting light metal artefacts, in accordance with the method of the invention;

Figure 3 is a three-dimeensional view of a casting facility comprising two casting apparatuses or installations of Figure 2, in accordance with the inveantion, for casting light metal artefacts in accordance with the method of the invention;

Figure 4 shows a series of simplified schematic side elevations of the casting apparatus or installation of Figure 2, illustrating the method of cassting a light metal artefact in the form of a magresium alloy wheel rim, in accordance with the invention, using the casting apparatus ow installation of Figure 2; and

Figure 5 is another se=ries of simplified schematic side elevation of the casting apparatus or installation of Figure 2, further illustrating the method of casting a light metal artefact in the form of a magnesium alloy wheel rim illustrated ky Figure 4.

Referring first to Figure 1 of the drawings, referesnce numeral 10 generally refers to a meltingg apparatus for forming a molten char-ge of light metal, in accordance with the invent&on.

The melting apparatus 10 comprises a container 122 in the form of a hollow cylinder or sleeve 14 of circular cross-section for holding a mowlten charge of light metal and also for facilitating heating of a precursor of the charge= of light metal, an induction heating arrangememnt 16 comprising an induction coil 18 for heating contents of the cylinder or sleeve 14- to form a molten charge, and a molten metal transfer assembly 20 for transferring a molten charge of light metal from the= cylinder or sleeve

14 to a die or mould (not shown in Figure 1, but see Figures 3 to 5) in “which an artefact is cast.

The meltirmg apparatus 10 also includes an inert g=as supply 22 for supplying argon gas to the interior of the cylinder or sleeve 14 such that melting of the light metal charge take-s place under a substantially inert atmosptoere, and also to provide cooling to the lower end or base of the cylinder or sleeve 14 to form a secondary seal therefor as described hereunder.

The cylincler or sleeve 14 is re-useable. The cylinde=r or sleeve 14 is made of mild- or low ca_rbon steel. In other embodiments, the cylind er or sleeve 14 is optionally made of cast fron or stainless steel.

In use, thee induction coil 16 is mounted on the metal Transfer assembly 20, the coil 16 being comnnected to the barrel 62 and surrounding the cylinder or sleeve 14 to heat the contents ®&thereof.

The transsfer assembly 20 comprises a telescopicallw moveable multi- stage piston arrangeme=nt 24 for use in elevating the cylinder or sleseve 14 to engage lockingly with the periprery of a downwardly facing charging opening of a die or mould, prior to filling the die or mmould with a molten charge from the cylinder or sleeve 14. The multi-stage piston arraangement 24 incorporates a central piston comprising three telescopic piston rods 28, 27, 28 with the central rod 28 having a piston head 30 provided with a conical sealing surface 31 for sealingly engaging the periphery of an opening into a die or mould when an entire molten charge in the cylinder or sleeve 14 has been transferred from the cylinder or sleeave 14 into said die or mould. The multi-stage piston arrangement 24 include=s a variable force and speed controller (mot shown) for controlling the rate of movement thereof and also for controllingy the upward force exerted by the pistaan head 30 on a molten charge in the cylimder or sleeve 14 and in a die or mould , when the piston head 30 sealingly engagyes the periphery of the charging openirmg of the die or mould.

Thus. in use, the cylinder or sleeve 14 is stipported on the transfer assembly 20, such that the multi-stage piston arrangement 224 is moveable within the interior of the cylimnder or sleeve 14 in sliding and sufficie ntly sealing engagement therewith so as to enable a molten charge in the cylinder or sleeve 14 to be pushed upwardly and out of the cylinder or sleeve 14 upon the upwar-d movement of the piston rods 26, 27, 28, to ®transfer and inject the molten charge into a die or mould. :

The ®ransfer assembly 20 also comprises a pluzrality of concentric barrels 32, 34, 35, 36 ancl 37 of different diameters. The barrels 32, 34, 35, 36 and 37 are telescopically vertically displaceable, relative to one another a_nd nest in one another.

The Marvel 32 is the bottom barrel and has whe=els 38 for running on rails 39 forming part of the casting installation of Figures 3 to 5 fom reciprocating the melting apparatus 10 between a charging position where charging off the cylinder or sleeve 14 with a precursor of a molten charge takes place, and a filling mposition where the melting apparatus 10 is in alignment with the charging opening of a die or mould of a casting apparatus or installation, to enable a mo-lten charge formed by melting of a precursor: thereof in the cylinder or sleeve 14 to be= transferred therefrom into said die or mould. thereby typically filling it with the molten charge. The barre! 37 is the top barrel andl provides a circumferentially extending u pwardly facing support ring having a groove (not shown) for sealingly engagingly the Mower end of the cylinder or sleeve 14 therein -

The barrel 35 in turn provides a circurmferentially extending upwardly facing support ring on which the induction coil 18 is supported when placed over the cylinder or sleeve 14 to surround it. in addition to the seal provided by the groove on the barrel 37, argon gas supplied via the gas supply 22 provide=s cooling to the lower end of the cylinder or sleeve 14 at the onset of melting of the precursor of the molten charge, allowing part oof the molten charge formed to solidify in a zone between the piston arrangement 24 and the top barrel 37 and at the lower end of the cylinder or sleeve 14, thereby providing & secondary seal which is formed of solidified light metal from the molten charge.

Referring now to Figure 2 of the drawings, reference numeral 50 generally refers to a casting apparatus o~f installation for casting light metal artefacts, im accordance with the invention. The szame parts are assigned the same reference numerals as in Figure 1, unless otherwise specified.

The casting apparatus or imstallation 50 comprises the melting apparatus 10 as described above and a die or mowuld arrangement 52 comprising a die or mould 54 and a heating arrangement 56.

The die or mould 54 is a multi-core or segmented re-useabMlle steel die or mould, comprising a top core 58 to which the solidified artefact remairs removably attached at the end of the casting process, a bottom — or face core 60 having a centrally located charging opening or passage 62 provided therethrough fcr charging or filing the die or mould 54 from below, and a segmented ring of four sside cores 64 associated with respective pistons 686, the side cores 64 giving the die or mould 54 its segmented character. The die or mould 54 is hydraulically operated, with. regard to the pistons 66 of the side cores 64 and with regard to lifting of the top cores 58 and any attached light metal casting (not shown), upwardly and away from the renmnaining cores.

The casting apparatus or installation 50 also includes a die or moeuld hydraulic controller 67 and a melting apparatus or installation 10 hydraulic controlier— 6S.

The top core 58 is associated with release means (not shown) for releasing the artefact therefrom at the end of the casting process. :

The heating arrangement 56 comprises six inductCon windings respectively forming induction coils, operable independently of one another, for achieving a desired temperature profile in the die or mould 564. Thus, the casting apparatus or installation 50 also includes a central processing unit CPU) 70 for monitoring the heating of the heating arrangement 56 to achieve the desired temperature profile, and also for providing feedback control to respeective power supplies 82 and 84 (Figure 3) therefor.

The casting apparatus or installation 50 also includes rails (rot shown) on which the wheels 38 of the metal transfer assembly 20 forming part of the melting apparatus or installation 10 can run. Thus, the melting apparatus 10 is reciprcocable relative to the die arrangement 52 between a chaarging position (as shown in Figure 2) where charging of the melting apparatus 10 w ith a precursor of the molten charge takes place, and a filling position (see Figures 4 and 5) where transfer of a smolten charge from the melting apparatus10 to the die 54 of the die or mould arrangement 52 takes place.

Referring now to Figure 3 of the drawings, reference nume=ral 80 generally refers to a casting facility according toe the invention. The casting faczility 80 comprises two casting apparatuses or installations 50 each comprising a reiting apparatus 10 for induction melting a charge of light metal and a die or mould arrangement 52 in which the casting of the artefact is carried out. The casting facility 80 also includes a melt induction heating power supply 82, for example of 100<W, for separately supplying power to each of the two melting apparatuses 10, a die induction “15 heating power supply 84, also for example of 10@0KW, for separately supplying power to the die or mould arrangements 52, a cooling tower (not shown) for providing ecooling fluid, and a gas supply control unit 86 for su pplying purging gases to the melting apparatuses 10 and also to the die or mould arremngements 52. =20 It will be appreciated that the casting facility 80 permits two artef~acts to be cast simultaneously using casting cycles =which are out of phase, the mmelting apparatuses 10 sharing the common induction eating power supply 82 and thes die or mould arrangements 52 sharing the common in=duction heating power supply 8«4. The casting of the artefacts then takes place in respective casting cycles whi ch are —5 sufficiently out of phase to permit such sharing. It will thus be appreciated tlhat the casting facility 80 «can be operated in quasi-continuous fashieon, in that the casting apparatuses or installations 50 can be used on an altematirg basis, with the one having its melting a pparatus 10 in its filling position and being ussed for casting while the other has its meltimg apparatus or installation in its charging osition and is charged with a precursor of the light metal, and being prepared to be reciprocated to its filling position, as soon eas the casting process in the other casting =apparatus or installation 50 is completed.

Referring now to Figures 4 and 5 of the drawirgs, use of the casting apparatus or instal lation 50 described above is illustrated withn reference to casting a light metal artefact in the form of a magnesium alloy wheel rim 90, using a precursor in the form of a pre-formed billet or ingot 82 of a magnesium-alurninium-zinc alloy known in the art as AZ91. The billet or ingot 92 is placed on the pistcon arrangement 24, with the associated mel ting apparatus 10 in its charging position. T! he cylinder or sleeve 14 is placed over the billet or ingot 92, such that the lower end of t-he cylinder or sleeve 14 sealingly engages said groove on the top barrel 37 of the metal transfer assembly 20.

The induction coil 18 is connected to the barrel 35 of the metal transfer assembly 20, so that placing thes cylinder or sleeve 14 and the billet or ingcot 92 in position acts to have them surroun:ded by the coil 18.

The «die arrangement 52 is prepared for casting Hoy lowering the top core 58 such that it eng ages with the bottom- or face core 60. The ring side core segments 64 are then placed in position, using their pistons 66, to close the die. Purging gas in the form of a SF/«CO; fluxing gas mixture comprising 0.2% bywy volume SF is fed into the die or mould 54 and the die or mould 54 is heated using the induction coil 64 by electrical power fed from the inducticon heating power supply 84 wusing a pre-selected frequency, until the die or mould 54- achieves a required operatimng temperature, and has a desired temperature profile. Tine rate of heating can be altered by changing the power input from the power supply 84 and/or by changing the freqruency thereof, with a higher frequency resulting in a higher heating rate; and loopss of coil 64 can be selectively operated with different poswer supplies thereto, to achiesve said temperature profile.

The melting apparatus 10 is reciprocated with the ai of the wheels 38 on the rails (not shown) on the casting apparatus or installation 5+0, from the charging position where charging of the cylitder or sleeve 14 with the Dillet or ingot 92 of a charge of AZ91 alloy precursor talkkes place, to a filing positiomn where the melting apparatus or installation 10 is in ali-gnment with the charging op ening 62 through the bottom- or face core 60 of the die o»r mould 54. The cylinder or =sleeve 14 is sealingly engaged with the lower surface of tine bottom- or face core 60, bwy raising the barrel 37 hydraulically, which also seals the cylinder or sleeve 14 to the barrel 37. The cylinder or sleeve 14 is purged by a SFe/C02 purging atmosphere. Th: e billet or ingot 92 is melted under the purging atmospheere introduced to the cylinder or sleeve 14 by the gas supply 22, until a molten charge of AZ91 alloy is formed. aArgon is then used to provide a cooling atmosphere for cooling of the molten charge aat the lower end of the cylinder or sleeve 14 to form a secondary seal in the form of a nore or less semi-solid or solidified portion or sprue of the light metal (not shown).

Once the desired operating temperature and temperature profile have een achieved in the die or mould 54, and the dilie or mould 54 has been pressure locked with the aid of the pistons 66 by means of the hydraulic controller 67, the gas ssupply to the cylinder or sleeve 14 is cut off and thea molten charge is transferred under pressure from the cylinder or sleeve 14 into the die or mould 54 by means of the piston arrangement 24, thereby filling the die or mould 54 with the molten charge. Prior to and during the injection of the molten charge into the die or mould 54, the die or mould 54 is purged with the abovementioned SF¢/CO. purginegfiuxing gas by means of the gas supply control unit 86, which gas also protects the molten surface of the molten charge

Poth in the sleeve 14 and when it enters the die or rmould 54. The piston head 30 locks ssealingly against the periphery of the charging ospening 62 and partially enters the charging opening 62 to increase the pressure on tree molten charge in the die or mould 54, The die or mould 54 is allowed to cool down and the melting apparatus or i nstallation 10 is disengaged from the die or mo-uld 54. The melting apparatus or i nstallation 10 is then reciprocated back to its charg’ ing position.

The die or mould 54 is then opened oy hydraulically disengaging the ring of side core segments 64 from one another with the aid of the pistons 66, and the top core 58 with the solidified wheel rim 90 attached thereto, is lifted, using the controller 37. The wheel rim 90 is then detached or released from the top core 58 by allowing edownwardly directed pins forming part of the rele=ase means (not shown) to push the wnheel rim 90 downwardly during the raising of the teop core 58.

The piston arrangement 24 is lowwered and then the barrels of the assembly 20 are retracted, releasing the cylinder o r sleeve 14 and the solidified portion or sprue (not shown) of the molten charge which formed the secondary seal for tre cylinder or sleeve 14. The used cylinder or sleeve 14 is then discarded and a new cylinder or sleeve 14 used for casting a new wheel vim 80. It will be appreciated trmat the discardin g of the used cylinder or sleeve 14 and muse of a new cylinder or sleeve 14 to cast a neew wheel rim 90, allows for the substantially uninterrupted casting of artefacts orme after the other from billets or imngots comprising different all-oy compositions, taking no longer than casting from the same alloy composition, using tthe same casting cycle but, naturally, with different temperatures and temperature profiles, if appropriates. In one embodiment of the invention, the melting apparatus or installati- on 10 allows ca sting of alloy wheel rims comprising the ®ollowing alloys one after the oth-er, without fear «of cross-contamination: AMG0B (aluminimum-magnesium-manganese allosy),

Galsi12dv (aluminium-silicon alloy), AZ91 (magreesium-aluminium-manganese-zlinc alloy) and Gaaisi7 (aluminium-silicon alloy)

It is an advantage of the present invemtion that the size of the precursor for the molten charge, for example the billet or ingot 92, is matched with the volume= of molten metal charge required to charge or fill the die or mould 54 to produce a sinegle artefact, for example a single wheel rim 80. Thus , metal wastage is reduced, if ot eliminated, iin comparison to the casting of light metal artefacts or wheel rims 90- in accordance with casting processes generally knowsn in the art, wherein substantiaaly more light maetal is melted, than is required for one wheel rim.

It is a further advantage of the inventio-n that the melting apparatus10 aZand also the cassting apparatus or installation 50 are expected not necessarily to be osf a permanent «construction, being moveable from one production facility to another with ease, thus the casting apparatus or installation 50 may be inexpensively set up close to an end user of the artefacts to be cast, thereby reducing transportation costs, amd the like. it is a further Advantage of the present invention that the casting apparatus or installation 50 des not require much space for it to be erected. For example, the casting apparatu s or installation 50 as described above only requires a floor space of about 23m2. Thae present process also offers other costs benefit-s such as the fact that power supply aenly has to be fed to the casting apparatus or inst=allation 50 immediately prior to casting and can be switched off at the end of casting a_ single artefact, without adversely affe cting the process or the efficiencies thereof. In th _e case of a power failure during the c-asting process using the method and casting apfoaratus or installation 50 of the presen t invention, it will be appreciated that losses need be no greater than loss of the molten charge in the cylinder or sleeve 14, comprising the single billet or ingot 92, as compared to a typical foundry where the process is continuous and large amounts of metal have to be molten at any given point in t7ime, all of which can solidify in the eveant of a power failure. Indeed, losses can in principle be avoided completely, by simplsy re-melting the contents of the cylinder or sleeve 14, when the power supply is restored.

It is yet a further advantage of the process in accordance with the gporesent invention, that it does not requuire running-in in order to achieve the optimum forocess conditions. Precursors of the light metal such as the billet or ingot 92 are ma-de to a required composition and me-tallography. Thus, the precursors such as the billet or ingot 92 can be a stock item. Itwill be appreciated that wheel rims 90 produced from a stock of bilets or ingots 92 will exhibit similaar metallography and hermce similar propertiess, so that quality control is enhanced.

The fact that the processs does not require a running-in cycle or cycles means that == particular number of billet=s or ingots 92, barrineg any power failures, should yield an ecguivalent number of wheel rimms 90.

Claims

CLAIMS:

1. A process for casting a metal artefact by forming a molten charge of metal from a precursor thereof, charging a die or mould with tre molten charge to fill the die or mould sufficiently to form a single metal artefact amnd causing or allowing the charge to solidify in the die or mould to form the artefact, t he process being characterized in that it includes the step of selecting the size of the molten charge to match the capacity of the die or mould so that the charging of the die or mould consumes substantially the whole molten charge.

2. A process as claimed in Claim 1, characterized in that forming the molten charge is from a precursor thereof which is a metal billet or ingot or a compact of metal particles.

3. A process as claimed in Claim 1 or Claim 2, characterized in that it includes heating the metal of the molten charge, after forming the molten charge, to raise the temperature of the molten charge, prior to filling the die or mould with the molten charge at the raised temperature.

4. A process as claimed in any one of Claims 1 — 3 inclusive, characterized in that the charging is carried out by injection moulding at san intermediate pressure in the range 50 KPa - 30MPa.

5. A process as claimed in any one of the preceding claims, characterized &in that itincludes the step of purging the environment in which the molten charge is formed with a purging gas, prior to and during the forming of the molten charge.

6. A process as claimed in any one of the preceding claims, characterized in that it includes using, as the metal, a metal selected from the group consisting of aluminium, magnesium, lithium, zinc ard 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 g roup consisting of magnesium, aluminiumm and alloys thereof.

8. A process as claimed in Claim #, characterized in that the casting is of a light metal artefact in the form of a motor ve hicle wheel rim.

9. A process as claimed in any one of the preceding claims, characterized in that the casting is of a metal artefact in which all the 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.

10. A casting apparatus or installati on (50) for casting a metal artefact in &a die or mould, the casting apparatus or installation including a die or mould (54) and a melting apparatus (10) which includes a container (12) for holding a precurssor of a molten charge of metal, a heating arrangement (16) for heating the precursom in the container to form a molten charge of metal, and a molten metal transfer as=sembly

(20) for transferring a molten charge of rnetal from the container to the die or mould, “the casting apparatus or installation beineg characterized in that “the container and die or mould have cagpacities which are matched so that charging of the die or mould from the container to fill the die or mould with a charge sufficient to form a single metal artefact consumees substantially the whole charge of molten metal from the container and leaves the container empty.

11. An apparatus or installation as claimed in Claim 10, characterized in that the heating arrangement is mounted on the molten metal transfer assembly.

12. An apparatus or installation as claimed in Claim 10 or Claim 11, characterized in that the melting apparatus is reciproacable relative to the die or mould between a charging position where charging of thes melting apparatus takes place and a filling position where transfer of a molten charge from the melting apparatus to the die or mould takes place.

13. An apparatus or installation as c laimed in any one of Claims 10 -12 inclusive, characterized in that it includes an inert: gas supply (22) for supplying inert gas to the container, to permit forming of the molten charge to take place under an inert atmosphere.

14. An apparatus or installation as cslaimed in any one of Claims 10 -13 inclusive, characterized in that the container has sa hollow cylindrical interior.

15. An apparatus as claimed in any one of Claims 10 -14 inclusive, characterized in that the container is a hollow cylinder ©r sleeve (14), the transfer assembly being & telescopic piston amrangement (24) For elevating the cylinder or sleeve into engagement with the die or mould and into communication with a charging opening (62) in the die or mould.

16. An apparatus or installation as claimed in Claim 15, characterized in that the piston arrangement has a central pistor (28, 30) for entering the cylinder or sleeve and for sliding upwardly therein in sealing engagement therewith, the pistor arrangement having a peripheral piston (37), surrounding the central piston, fo r urging the cylinder or sleeve upwardly irato sealing engagement with the die or mould around the charging opening of the die or mould.

17. An apparatus or installation as cl aimed in Claim 16, characterized in that the 156 central piston has a piston head (30) provided with a sealing surface (31) for sealingly engaging the periphery of the charging opening of the die or mould.

18. An apparatus or installation as claimed in any one of Claims 10 — 17 inclusive characterized in that the heating arrangement includes at least one induction coil surrounding the container.