GB2167444A - Electroforming - Google Patents

Abstract

A method of electroforming articles in a finish metal, comprising the steps of making a master model or replica of an article to be produced, making a working replica from the master model in a disposable material, electrodepositing a finish metal outer layer upon the working model to a required depth and removing the disposable working replica to leave a hollow electroform of finish material. Also claimed is a method of electroforming an article by electrodeposition of finish material upon the article which may be of the same material as the finish material and whereby the article as a whole is strengthened by increasing the overall metal wall thickness.

Description

SPECIFICATION Electroforming articles This invention relates to electroforming articles and is particufarly but not exclusively, concerned with the electroforming in high-purity, precious metal, such as gold reproductions of articles to be modelled in such precious material.

It is desirable in producing precious metal articles thatthe.fabrication process be economical in usage of precious material, and that the article has sufficient overall hardness and strength and thus durability when finished and yet be workable into a desired form and capable of reproducing fine detail and delicate features.

In mass production terms, it is also desirable that the article can be reproduced with consistency or uniformity and without undue cost. To this end, it is desirable that no undue amount of skilled labour is required in the fabrication process for multiple article reproduction.

Such requirements are especially relevant in the fabrication of jewellery, ornamental or decorative items, dental castings and specialised industrial components.

Accordingto one aspectofthe invention a method or process for modelling or reproducing articles in metal comprises the steps of coating by electroplating or electrodeposition a model of the article to be modelled with a desired finished material and removing the working model or replica to leave a hollow metal electroform reproducing the outer surface configuration of the article to be modelled.

According to another aspect of the invention a method or process for producing pure or high purity gold models by electroforming, comprises electrodeposition or electroplating of gold in an electroplating bath upon a working model or replica or mandrel of base material to a thickness to achieve sufficient overall strength and removing the mandrel or working replica [or base of matrix material] [ifthis is non-gold material].

Such a process of electrolytic deposition of gold is able to reproduce more intricate details even on complex shapes, in a single operation without difficuttyto a degree impossible ortoo costly to be achieved by conventional fabrication techniques such as casting, machining and hand-forming or cutting.

The electroforming gold process is applicable to high-purity gold electroforms orto control purity compositions to gold carat specification.

It is found thatelectrodeposited pure gold coatings are much harderand strongerthan, say, wrought gold formed by conventional (jewellery) processes. Accor dingly the process can advantageously be applied to harden orstrengthen pure gold items. For example, in the setting of gem stones on jewellery where the stones can be embedded initially in soft pure gold or other locating features of an intermediate base or matrix material and then electrocoated or electroplated with a layer of gold to strengthen or secure the gemstone mounting, followed by removal of all non-gold material.

Aworking model or replica or mandrel for subse- quentelectroforming or fabrication can be obtained by making a master model or replica ofthe article to be reproduced or modelled. Working models or replicas ofthese master models or replicas are then repro duced from the master in wax or metal alloys by casting. By choice of suitable casting materials, working models or replicas can be made of fragile or delicate natural objects such as flowers, leaves, fruits, eggs etc., reproducing the fine natural detail so that the final electroform will be very real or lifelike in appearance.

The working model or replica on which gold isto be electrodeposited or electroplated or coated can be of electriallyconductive material such as metal, in particular alloys such as copper, tin, nickle, fusible alloy or pure metal such as iron or gold simpliciter.

Alternatively, electrically non-conductive material such as wax, plastic or even suitably selected plant material may be used, in which case the preliminary metal conductive plating or coating must be applied for subsequent electroforming by electrodeposition of gold.

The choice of working replica material takes account ofthe nature of the articleto be produced and the ease of making and removingtheworking replica after electroforming. Removal in some cases may require destruction ofthe working replica; forexample by chemical etching or decomposition. Holes may be left in the outer electroform to facilitate such removal by solvent etching or dissolving or even by heating and melting out at a lowertemperaturethanthegold electroform itself would melt. Alternatively, the working replica or model or mandrel may be re-used.

The plating or metalising of nonconductive working replicas or models or mandrels can be effected by coating with chemicals containing conductive pigments, by chemical vapour deposition, by sputtering molten metal or chemical metallisation processes such as mirroring.

Electroplating or electrodepositing with gold can be carried out on most metal surfaces or metallised non-conductive materials, but is usually carried out directly only if the surface finish oftheworking replica is flawless, otherwise gold is consumed in eveningaut the surface imperfections in ordertoachieve the desired surface finish. Itis preferableto achieve such a preliminarysurfaceevening-outorfinishing byelec- trodepositing a thin even coat of a relatively inexpensive base material such as nickel or copper priorto gold deposition. This intermediate plating step may be particularly advantageous for metalised nonconductive working replicaswhere the metallising process itself yields small imperfections, for example surface roughness on plated areas and holes with contaminants.

Priorto electrodeposition of gold, any areas not to be coated with gold may be masked with a suitable coating, such as a lacquer, andforsuch selective electrodeposition of gold the application of a base metal priorto application of masking material coating may be advantageous.

The gold electrodepositional plating itself is desirably performed in an electroplating bath capable of yielding a strong deposit of consistentthickness at both high and low current density regions of the working replica.The electrolyte itself must be stable, easy to control and capable of plating outsubstantial quantities of gold in strong coherent deposits.

Afterelectrodepositing gold, minor surface finishing may be carried out before non-gold constituents are removed.

The surfacefinishing may includethe mounting or incorporation of gemstones, i.e. precious or semiprecious stones, onthe preliminaryelectrodeposited gold surface and the assembly returned to the gold plating bathforfurtherelectrodeposition in orderto finish and securethe gemstone mounting.

There nowfollows a description of some particular embodiments oftheinvention, byway of example only: A master model or replica is made ofthe article which is to be reproduced as a gold electroform. For example, an ornament such as a miniature animal e.g.

a horse, might be selected as a model whose intricate and delicate detail must be reproduced or modelled.

Themastermodel orreplicamayitselfberepro- duced by moulding or casting and the material used forthe master model or replica must allowsubse- quentproduction ofworking models or replicas, which may themselves be destroyed in the fabrication process or maybe re-used.

Working models or replicas of a master model or replica maybe produced by casting in wax or metal alloys such as pewter, so thatthe encapsulated working replica may be melted out afterthe gold electroform has been produced.

The working replica isfinished to a desiredstan dard, for example by polishing, possibly afterfurther plating with copper or nickel.

In the case of wax, which is non-electrically conduc- tive, a preliminarysurface metallising step is per formed, for example with copper.

Formetal plating of non-conductive materials a conductive wire may be embedded in such material to provide a return path forthe plating curent The plating path forthe preliminary metal coating must give a good throwing powerandevennon- porous deposits, so thatthe working model or replica or mandrel canbefinishedtothedesiredstandard.

Atthis stage any parts of the replica notto be plated with gold are masked with a (nonconductive) coating, for example a suitable lacquer. Such non-coated areas resultin apertures in the electroform which may advantageously allow removal oftheworking replica afterthe electroform has been produced.

After any preliminary metallisingand masking,the working replica is cleaned and placed in an electro plating gold bathto produce a gold electroform-to a desiredsurfacethickness. In particular, itis necessary thatthe gold electroform shell produced has sufficient inherrentstrength and coherenceto support itself when theworking replica is removed. Typically a gold bath capable of depositing bright strong ductile gold coatings ofthickness up to 0.5 mm is chosen. An even gold depositis desirableforappearance, strength and economyof gold usage.

Minorsurfacefinishing ofthegold electroform may be performed if there is any plating roughness during electroforming Selective drilling ofthe electroform with small holes, which can be plugged unobtrusively at a later date, may be performed in orderto removethe non-goldworking replica or mandrel by etching or melting. Afinal checkforthe complete removal ofthe working replica may be performed application of an acid which will not adversely affectthe gold itself.

The electroform is cleaned and flushed outsuitably with water, of any residual chemicals, and if necessary forfurtherstrength returned to the gold plating bath to increase the electroform wall thickness.

Furtherfinishing and decoration maybe performed on the gold electroform,for example other precious metal finishing, enamelling or gemstone setting.

In some applications,theworking model or replica may itself be a precious metal article,for example gold, [and thus remains an inherentpartofthe electroform and is not separated, removed and discardedjasina preformedjewelleryitemwhose strength isfurtherincreased by subsequentelectrodeposition.

Alternatively, jewellery items may be made initially from a brasscastingwhichisreadilygivena good surfacefinish bytumbling and buffing,furthercopper ornickle platingto improvethefinish and chemical and heat-resistant gemstones, such as sapphires, rubies etc. setinthe brassfixture priorto electroforming. Goldfixturesthemselves may also be mounted in the brass casting.

In orderto remove the discardable working replica completely, a combination of chemical etching and heat melting may be employed.

Furtherstrengthening ofthe electroform is readily achieved and because the electroformed gold is hard and strong the overall article strength can be improved byfurtherelectroforming.

Claims (9)

1. Amethod of producing or modelling articlesina finish metal, comprisingthe steps of making a master model or replica of an article to be produced, making a working replicafrom the mastermodel-in a disposable material, electrodepositing afinish metal outer layer upontheworkingmodeltoa required depth and removing the disposable working replica to leave a hollow electroform offinish material.

2. Amethod of electroforming metal articles as claimed in Claim 1,whereintheworking replica is of non-electroconductive material and including the additional step ofmetallising or metal plating said working replica priorto electrodepositionwithfinish material.

3. A method of electroforming asclaimed in either ofthepreceedingclaims, includingthestep of electroplating theworking replica with a intermediate base material p ortofinish electrodeposition.

4. A method of electroplating as claimed in any of the preceding claims, including the step of masking off any areas ofthe working replica notto be platedwith finish material.

5. A method of electroforming as claimed in any of thepreceeding claimsJincludingfurther electroplat- ingwithfinish material aftertheworking replica has been removed in orderto increasethe overall electroform wall thickness and therebystrengthen the electroformed article as awhole.

6. Amethodofelectroformingasclaimedin any of the preceeding claims, wherein precious or semiprecious stones are set into the electroform by mounting in the working model priorto electrodeposition.

7. A method of electroforming as claimed in any of the preceeding claims, comprising the steps of reproducing the article in gold by making a master model or replica of the article to be reproduced in gold, producing a working replica of the master model or replica in a suitable matrix material such as wax or brass, meatallising if necessary the working replica model surface ifthe matrix material is non-conductive electrically, electrically plating the working model or replica with a non-precious metal base layer such as copper, applying if necessary a masking coating on areas not to be further electroplated or coated with gold, electroplating the thus treated working model or replica with gold to the required thickness to achieve a gold electroform outer layer, removing any non-gold material completely, including the working replica if non-gold, strengthening the gold electroformed mod elfurtherbyfurtherelectrodepositionto increase the wall thickness thereof.

8. A method of electroforming an article by electrodepositionoffinish material upon the article which may be ofthesame material as the finish material and whereby the article as a whole is strengthened by increasingthe overall metal wall thickness.

9. Anelectroformed article produced by the method according to any ofthe preceeding claims