Methods of Moulding and Mould Liners Therefor

This invention relates to methods of moulding and mould liners for use in same, with particular reference to the moulding of textured articles.

So called rapid prototyping processes are of increasing importance in many areas of design and manufacture. The desire is to quickly produce prototypes made according to a proposed design, in order to allow full and proper appreciation of the actual three-dimensional appearance of the proposed design. Prior art techniques which have been employed for rapid prototyping include stereolithography, Laminated Objective Manufacture (LOM), Selective Laser Sintering (SLS) and direct casting of glass fibre (GRP) models. Computer aided design (CAD) software may be used to generate the three dimensional (3D) prototype designs. A related area of interest is the field of rapid tooling, in which mould parts suitable for use in the production of moulded articles are rapidly produced from prototype models. A great many moulded articles are made with some form of textured surface finish which frequently has a major bearing on the appearance and saleability of the moulded article. Therefore, it is highly desirable that any rapid prototyping or rapid tooling process employed is able to faithfully reproduce the intended textured surface finish. However, this remains a problem in the art. International Publications WO 99/028113 and WO 00/058066, the contents of both of which are herein incorporated by reference, disclose highly advantageous methods in which texture can be applied to an essentially untextured prototype, and copies of the textured prototype made by rapid tooling. However, there is an ongoing desire for still improved techniques. In

particular there is considerable interest in the provision of a practical and flexible technique for rapid tooling.

The present invention, in at least some of its embodiments, addresses the above named problems and desires. Additionally, the present inventors have realised that the present invention, in at least some of its embodiments, can be applied to the moulding of textured articles perse.

According to a first aspect of the invention there is provided a method of producing copies of a textured prototype including the steps of: producing a textured prototype having a surface texture; bringing a hardenable material into contact with at least a portion of the textured prototype; causing the hardenable material to harden to produce a mould liner formed from the hardened material. providing a mould having at least one mould part; fixedly connecting, the mould liner to a portion of the mould part to provide the mould part with a textured moulding surface; and using the mould to produce said copies.

There are numerous advantages associated with the invention. For example, the texture of the moulded articles can be easily and quickly altered, enabling multiple choice options from a single tooling source. Also, any damage is easily repaired by insertion of a new mould liner, and tooling modifications can be conveniently made to the mould without affecting the moulding surface. Thus, modifications such as welding to the tooling 'A' surface do not affect the moulding surface provided by the mould liner, and modifications to the thickness

of the mould part can be conveniently made by producing a mould liner of a suitable thickness.

Preferably the textured prototype is produced by applying a textured skin to a prototype. In particularly preferred embodiments the textured skin includes a release backing having relief material attached thereto as a texture, and the release backing is peeled off the prototype to leave the relief material attached to the prototype, thereby producing the textured prototype. The textured skin may be burnished on to the prototype, and this may be done before and/or after removal of the release backing. The invention is particularly applicable to non-planar prototypes, especially prototypes having highly non-planar surfaces such as substantially curved or undulating surfaces. For the avoidance of doubt, the term 'prototype' includes within its scope tooling master models.

The mould part may be formed from a metal, such as steel, or a non- metallic material such as polymer and/or a hardened resin. An example of a non-metallic mould part is a polyurethane mould part.

Alternatively, the textured skin may be produced by methods such as the selective curing of a photopolymer, stereolithography, screen printing onto a substrate, thermo polymer printing, SLS and LOM techniques. Alternatively still, the prototype may be textured by a laser based procedure, a solid object printer, stereolithography, or by milling.

Advantageously, the mould liner comprises a ceramic material. The mould liner may consist essentially of a ceramic material, or may be a ceramic material reinforced hardened resin. The mould liner material may contain

another substance. For example, the mould liner may have metal particles dispersed therein.

Preferably the hardenable material includes a hardenable resin containing particles of one or more materials, and most preferably the hardenable material includes particles of a ceramic material, optionally in conjunction with metal particles.

Typically the texture is of a depth that exceeds 50 μm, preferably in the range 75 to 150 μm, although depths of greater than 1000 μm are possible. The texture may be a geometric pattern or a random pattern texture, such as a leather or woodgrain texture.

In preferred embodiments, the mould part is built up in a process which utilises the mould liner. This is a highly convenient way in which a mould part can be rapidly manufactured for production tooling.

In a preferred embodiment the mould part is produced by a slush moulding process in which a metal coating is electroformed onto a former.

Preferably, the metal coating is nickel.

In alternative preferred embodiments, the mould part is produced by in- mould graining (alternatively known as negative pressure forming or negative vacuum forming) or a spray moulding process in which a material, such as a metal or a polymeric material, polymeric precursor and/or a resinous material, is sprayed onto a former to form a shell. In a particular preferred embodiment polyurethane shell is produced.

In embodiments in which the mould part is produced by a slush moulding process, in-mould graining or a spray moulding process, it is particularly

preferred that the former includes the mould liner. In this way, the mould is conveniently built up utilising the mould liner.

An advantageous aspect of the invention is the ease with which alterations to the texture and/or the dimensions of the mould can be made. Thus, in one preferred embodiment: the mould is used to produce copies of the textured prototype; said production of copies is stopped; the mould liner is removed from the mould part; the mould liner is altered; the altered mould liner is fixedly reconnected to the mould part; and the mould is used to produce further moulded articles. In another preferred embodiment: the mould is used to produce copies of the textured prototype; said production of copies is stopped; the mould liner is removed from the mould part; a second mould liner formed from a hardened material is fixedly connected to the mould part; and the mould is used to produce further moulded articles. The second mould liner may be provided with a different texture to the first. In this way, limited production runs or even the production of "one off' personalised mouldings can be achieved. The dimensions (such as the thickness) of the second mould liner may differ from the dimensions of the first mould liner in order to, for example, alter the dimensions of the mould cavity. According to a second aspect of the invention there is provided a method of producing moulded articles having texture including the steps of: manufacturing a textured skin; applying the textured skin to a master to produce a textured master; bringing a hardenable material into contact with at least a portion of the

textured master; causing the hardenable material to harden to produce a mould liner formed from the hardened material; providing a mould having at least one mould part; fixedly connecting the mould liner to a portion of the mould part to provide the mould part with a textured moulding surface; and using the mould to produce said moulded articles.

The second aspect of the invention is not limited to the texturing of prototypes per se. The second aspect of the invention can incorporate any feature of the first aspect of the invention.

According to a third aspect of the invention there is provided a method of producing a mould part including the steps of: bringing a hardenable material into contact with at least a portion of a textured master; causing the hardenable material to harden to produce a mould liner formed from the hardened material; and building up a mould part is a process which utilises the mould liner, the mould part being compatible with the mould liner so that the mould liner can be fixedly connected to the mould part for use in a moulding process. The third aspect of the invention can incorporate any feature of the first aspect of the invention.

According to a fourth aspect of the invention there is provided a mould liner formed from a hardened material and having a texture imparted thereto, in which the mould liner is produced as part of a method according to any one of

the first, second or third aspects of the invention.

Whilst the invention has been described above, it extends to any inventive combination or sub-combination of the features set out above or in the following description or drawings or claims. Embodiments of methods and mould liners in accordance with the invention will now be described with reference to the accompanying drawings, in which:-

Figure 1 shows a prototype;

Figure 2 is a schematic diagram showing a) the application of a textured skin to the prototype of Figure 1 , b) the removal of a release backing, c) relief material and gossamer film on the prototype, d) sand-blasting of the gossamer film, e) relief material on the prototype, f) painting the relief material, and g) the painted textured prototype;

Figure 3 shows a) a textured prototype with a half-hardened layer thereon b) the layer removed from the prototype and c) the layer positioned in a mould; and

Figure 4 shows a) a textured prototype b) the textured prototype with a mould liner in place c) a nickel shell electroformed on the mould liner and d) a completed nickel shell mould tool. Figure 1 shows a prototype 10 which is to be textured according to the invention. The prototype might be produced by any convenient technique such as stereolithography, LOM, SLS, GRP techniques or moulding. Figure 2 depicts the application of a texture to a portion 12 of the prototype 10. The texture is present in the form of relief material 14 which is attached to a release backing 16

via a thin "gossamer" film 18. The relief material 14 is applied to the prototype 12 (Figure 2a) and the release backing 16 is peeled off (Figure 2b) to leave the relief material 14 on the prototype 12 with the gossamer film 18 still in place (Figure 2c). Next, the gossamer film 18 is removed by an abrasion, erosion or etching technique such as sandblasting (Figure 2d) to produce a prototype 12 having the relief material 14 only thereon (Figure 2e). The sandblasting also has the effect of firmly anchoring the relief material 14 onto the prototype 12. Finally, the prototype 12/relief material 14 is optionally painted (Figure 2f) to produce a textured prototype 20 having a paint layer 22 in which the texture has a soft, aesthetically pleasing appearance to the eye (Figure 2g). It will be apparent from the foregoing that the relief material can be, in the context of the invention, be considered to be attached to the release backing even if the attachment is indirect, via, for example, the gossamer film.

There are other techniques which might be used in order to produce the textured skin. It is possible to selectively cure a photopolymer, such as with UV radiation, by a number of methods. For example, a master template mask can be used, or a light source such as a laser can be manoeuvred with respect to the photopolymer so as to accomplish a spatially selective .cure. Such a procedure would be performed under computer control. It may be possible to use stereolithography to cure sheets of the photopolymer or to use systems such as SLS and fused deposition modelling (FDM). Another approach is selective deposition of, for example, a metal onto a carrier material. Another approach still is to produce textured carrier film via a thermopolymer printing process.

Yet another approach is to fill in a selectively engraved sheet or template with a relatively pliable material such as a resin or a wax, and to transfer the material to a carrier film. The selectively engraved sheet corresponds to a "negative" of the desired texture, and so the material used to fill the sheet corresponds to a "positive" of the desired texture. Other alternatives are to screen print a textured relief onto a substrate, and to employ cutting techniques whereby a material is cut and transferred to a carrier. LOM might be used in such a process. Further details concerning the application of texture to an item can be found in International Publications WO 99/028113 and WO 00/058066. An advantage associated with the techniques disclosed herein is the ease with which the production of the texture and the design corresponding to the texture can be controlled using software.

Next the preparation of a mould liner will be described. The mould liner is prepared using a hardenable material such as a ceramic, of, preferably, a resin such as an epoxy resin mixed with a ceramic whisker such as a whisker of S1O ₂ or AI ₂ O ₃ . The resin may be mixed with further particles such as metal particles. Figure 3a shows the application of a half-hardened resin sheet 24 to the paint layer 22 of the textured prototype 20 shown in Figure 2g. The layer 24 is pressed against the textured prototype 20 thereby imprinting the outline of the texture onto the layer 24. As shown in Figure 3b, after an appropriate period of time the now textured layer 24 is removed from the texture prototype 20. As shown in Figure 3c, the layer 24 can be applied to a mould part 26. The layer 24 is heated so as to harden the layer 24 to produce a hardened mould liner. The heat may be applied during any of the steps shown in Figures 3a, 3b and 3c.

Further exemplification of hardenable materials and methods for using hardenable materials to provide a textured surface can be found in US 4919388, the contents of which are herein incorporated by reference. The lined mould part 26 can be used in a moulding process to produce copies of the textured prototype. However, as exemplified below, there are other ways in which the mould part can be produced and lined with the mould liner.

It is particularly advantageous if a suitable mould part or parts are produced in a rapid tooling process after the ^production of the mould liner, the mould liner being used as part of the rapid tooling process. For example a spray process might be utilised in which a suitable material is sprayed onto the outer surface of the mould cavity. It is understood that the term "outer" refers to the surface of the mould liner which contacts its receiving mould part, as opposed to the inner surface of the mould liner, which is the surface that defines a mould cavity. The spray process may be a spray metal process which involves spraying metal plasma onto the surface of the mould liner. The metal hardens on contact with the surface, and is deposited in layers to produce a very stable substrate. The spray metal shell is then reinforced with resin to produce a moulding tool cavity. The core side of the tool is made by further processing of the mould so that a resultant metal tool can be quickly and cheaply produced for injection moulding. Non-limiting examples of suitable metals include nickel, copper and aluminium. In variants, the shell is formed from non-metallic materials. In a particularly preferred variant, a spray process is utilised to deposit a polyurethane skin onto the outer surface of the mould liner. The polyurethane skin is then reinforced using methods well known to one skilled in the art in order

to produce a mould tool which is particularly convenient for small to medium production runs.

Figure 4 shows process steps in another embodiment of an in situ mould part production technique of the invention. Figure 4a shows a textured prototype 40 which may be produced according to the principles described herein. Figure

4b shows the textured prototype with a mould liner 42 formed from a hardened material formed thereon. Next, as shown in Figure 4c, a slush moulding step is performed to produce a mould tool. In the slush moulding step, a metal shell is electroformed onto the former defined by the mould liner 42. The electroforming process produces a thin covering 44 of a metal, preferably nickel, on the mould liner 42. As shown in Figure 4d, a mould tool, shown generally at 46 is produced by adding bolstering materials 48 to the back of the nickel shell. Particles of a conductive material such as a metal or carbon may be dispersed in the mould liner in order to increase conductivity, thereby assisting in the electroforming. Alternatively, the mould tool can be produced by a more conventional slush moulding technique of the type described in WO 00/58066, in which the combined prototype and mould liner structure is cast in a mould forming material such as silicone rubber. This cast is used to produce a former such as a polyurethane or epoxy former which is used in the electroforming process.

The invention is highly convenient,, practical and flexible. In particular, it is easy to make alterations to a texture or even to completely change a texture by either altering the mould liner, or substituting a new mould liner for the previous one. Such changes can even be made during a production run.

Another advantage associated with the invention is the mould tools can be produced from relatively low grade steel, since it is the surface of the mould liner, rather than the metal mould part, that contacts the mouldable material during the moulding process.

The present invention has applications in many areas of commerce, such as vehicle interiors, furniture and luggage.