The present invention relates to injection moulding.

Injection moulding processes are well known. They are commonly used for mass manufacture of plastic items, for example, but the process can also be used with other materials to be moulded. During such processes, the mould itself is reused many times. Typically, when moulding plastics for example, the mould itself will be made of metal. The creation of the mould or “tooling” involves precision manufacture of the moulding cavity, e.g. by milling the cavity out of a solid metal block, and thus represents a significant expense in the injection moulding process.

As a result, whilst injection moulding is a useful way of producing multiple identical items, it can be unviable where the total number of items required is relatively small. That is, the cost of creating the tooling can be prohibitive, and other methods must be used instead.

Further, when tooling is milled from solid blocks of metal, and despite the good thermal conductivity of metal, the ability to control the heat response of the tooling is limited by the bulk response of the insert.

Another issue with conventional injection moulding relates to the item shapes that can be formed. To be mouldable, an item must be formable in a way that allows the parts of the mould to be removed after the item is formed within the moulding cavity. Producing articles with holes that widen into the article, for example, provide challenges for being able to release the mould after the article has set. To a certain extent, these difficulties can be overcome by careful design and multi-part moulds but this introduces extra expense, and still does not allow complex shapes to be moulded.

The present invention is to at least partially address some of these problems.

According to the first aspect of the invention there is provided an injection moulding tooling formed from a heat conducting polymer, wherein the polymer has a thermal conductivity of 0.20 W m ¹ K ¹ or more. Optionally, the polymer has a thermal conductivity of 0.22 W m ¹ K ¹ or more, further optionally 0.24 W m ¹ K ¹ or greater, further optionally 0.30 W m ¹ K ¹ or more, further optionally 0.5 W m ¹ K ¹ or more, further optionally 1 W m ¹ K ¹ or more, further optionally 3 W m ¹ K ¹ or more, further optionally 5 W m ¹ K ¹ or more, further optionally 7 W m ¹ K ¹ or more, further optionally 10 W m ¹ K ¹ or more.

Optionally, the polymer has a melting point of 170°C or more, optionally 175°C or more, further optionally 185°C or more.

Optionally, the polymer is a thermoplastic

Optionally, the injection moulding tooling is formed by additive manufacturing.

Optionally, the heat conducting polymer comprises a filler.

Optionally, the filler comprises fibres, optionally carbon fibres.

Optionally, the heat conducting polymer comprises 5-30% w/w fibre, optionally 10-25% w/w fibre, and further optionally around 15-20% w/w fibre.

Optionally, the filler comprises metallic particles.

Optionally, the heat conducting polymer comprises up to 30% w/w metallic particles, optionally up to 20% w/w, and further optionally up to 15% w/w.

Optionally, the tooling comprises an induction coil for inductive heating.

Optionally, the induction coil is formed from an electrically conductive polymer.

Optionally, the injection moulding tooling comprises at least one cooling channel within the tooling. According to a second aspect of the invention there is provided an heat conducting polymer comprising a filler, wherein the filler comprises at least one of: fibres, optionally carbon fibres; and metallic particles.

Optionally, the polymer has a thermal conductivity of 0.20 W m ¹ K ¹ or more, optionally 0.22 W m ¹ K ¹ or more, further optionally 0.24 W m ¹ K ¹ or more, further optionally 0.30 W m ¹ K ¹ or more, further optionally 0.5 W m ¹ K ¹ or more, further optionally 1 W m ¹ K ¹ or more, further optionally 3 W m ¹ K ¹ or more, further optionally 5 W m ¹ K ¹ or more, further optionally 7 W m ¹ K ¹ or more, further optionally 10 W m ¹ K ¹ or more.

Optionally, the polymer has a melting point of 170°C or more, optionally 175°C or more, further optionally 185°C or more.

Optionally, the polymer is a thermoplastic.

Optionally, the heat conducting polymer comprises 5-30% w/w fibre, optionally 10-25% w/w fibre, and further optionally around 15-20% w/w fibre.

Optionally, the heat conducting polymer comprises up to 30% w/w metallic particles, optionally up to 20% w/w, and further optionally up to 15% w/w.

According to a third aspect of the invention there is provided the use of the heat conducting polymer according to any variation of the second aspect, to make an injection moulding tooling.

According to a fourth aspect of the invention there is provided a method of making an injection moulding tooling, the method comprising forming the injection moulding tooling from a heat conducting polymer by additive manufacture, wherein the polymer has a thermal conductivity of 0.20 W m ¹ K ¹ or more.

Optionally, the polymer has a thermal conductivity of 0.22 W m ¹ K ¹ or more, further optionally 0.24 W m ¹ K ¹ or more, further optionally 0.30 W m ¹ K ¹ or more, further optionally 0.5 W m ¹ K ¹ or more, further optionally 1 W m ¹ K ¹ or more, further optionally 3 W m ¹ K ¹ or more, further optionally 5 W m ¹ K ¹ or more, further optionally 7 W m ¹ K ¹ or more, further optionally 10 W m ¹ K ¹ or more.

Optionally, the heat conducting polymer comprises metallic particles, and the method further comprises a step of enriching the metallic particle concentration at the injection moulding surface of the tooling, after the step of additive manufacture, by polishing the injection moulding surface.

Optionally, the heat conducting polymer is a heat conducting polymer according to any to any variation of the second aspect.

Optionally, the injection moulding tooling is formed to comprise at least one cooling channel within the injection moulding tooling.

According to a fifth aspect of the invention there is provided a method of injection moulding, the method comprising using an injection moulding tooling according to the first aspect.

Optionally, the method comprises using an injection moulding tooling that comprises an induction coil for inductive heating, and the method further comprises a step of inductively heating the injection moulding tooling.

Optionally, the method further comprises using an injection moulding comprising at least one cooling channel within the tooling, and further comprises a step of cooling the injection moulding tooling during injection moulding by passing fluid through the cooling channel.

According to a sixth aspect of the invention there is provided an injection moulding tooling formed from a heat conducting polymer comprising a nanocellulose filler.

Optionally, the nanocellulose filler comprises cellulose nanocrystals, cellulose nanofibrils and/or cellulose whiskers.

Optionally, the nanocellulose filler comprises native and/or modified nanocellulose. Optionally, the nanocellulose filler comprises modified nanocellulose obtainable by lactic acid grafting, etherification, acylation or alkoxycarbonylation.

Optionally, the nanocellulose filler comprises modified nanocellulose obtainable by carbanilation, silylation, titanation and/or sulphonation.

Optionally, the polymer has a thermal conductivity of 0.20 W m ¹ K ¹ or more, optionally 0.22 W m ¹ K ¹ or more, further optionally 0.24 W m ¹ K ¹ or more, further optionally 0.30 W m ¹ K ¹ or more, further optionally 0.5 W m ¹ K ¹ or more, further optionally 1 W m ¹ K ¹ or more, further optionally 3 W m ¹ K ¹ or more, further optionally 5 W m ¹ K ¹ or more, further optionally 7 W m ¹ K ¹ or more, further optionally 10 W m ¹ K ¹ or more.

Optionally, the polymer has a melting point of 170°C or more, optionally 175°C or more, further optionally 185°C or more.

Optionally, the polymer is a thermoplastic

Optionally, the injection moulding tooling is formed by additive manufacturing.

Optionally, the filler comprises carbon fibres.

Optionally, the heat conducting polymer comprises 5-30% w/w fibre, optionally 10-25% w/w fibre, and further optionally around 15-20% w/w fibre.

Optionally, the filler comprises metallic particles.

Optionally, the heat conducting polymer comprises up to 30% w/w metallic particles, optionally up to 20% w/w, and further optionally up to 15% w/w.

Optionally, the tooling comprises an induction coil for inductive heating.

Optionally, the induction coil is formed from an electrically conductive polymer. Optionally, the injection moulding tooling comprises at least one cooling channel within the tooling.

According to a seventh aspect of the invention there is provided an heat conducting polymer comprising a filler, wherein the filler comprises at least one of: nanocellulose, and metallic particles.

Optionally, the nanocellulose comprises cellulose nanocrystals, cellulose nanofibrils and/or cellulose whiskers.

Optionally, the nanocellulose comprises native and/or modified nanocellulose.

Optionally, the nanocellulose has been modified by lactic acid grafting, etherification, acylation or alkoxycarbonylation.

Optionally, the nanocellulose has been modified by carbanilation, silylation, titanation and/or sulphonation.

Optionally, the polymer has a thermal conductivity of 0.20 W m ¹ K ¹ or more, optionally 0.22 W m ¹ K ¹ or more, further optionally 0.24 W m ¹ K ¹ or more, further optionally 0.30 W m ¹ K ¹ or more, further optionally 0.5 W m ¹ K ¹ or more, further optionally 1 W m ¹ K ¹ or more, further optionally 3 W m ¹ K ¹ or more, further optionally 5 W m ¹ K ¹ or more, further optionally 7 W m ¹ K ¹ or more, further optionally 10 W m ¹ K ¹ or more.

Optionally, the polymer has a melting point of 170°C or more, optionally 175°C or more, further optionally 185°C or more.

Optionally, the polymer is a thermoplastic.

Optionally, the heat conducting polymer comprises 5-30% w/w fibre, optionally 10-25% w/w fibre, and further optionally around 15-20% w/w fibre.

Optionally, the heat conducting polymer comprises up to 30% w/w metallic particles, optionally up to 20% w/w, and further optionally up to 15% w/w. According to an eighth aspect of the invention there is provided the use of the heat conducting polymer according to any variation of the seventh aspect, to make an injection moulding tooling.

According to a ninth aspect of the invention there is provided a method of making an injection moulding tooling, the method comprising forming the injection moulding tooling by additive manufacture from a heat conducting polymer comprising a nanocellulose filler.

Optionally, the heat conducting polymer further comprises metallic particles, and the method further comprises a step of enriching the metallic particle concentration at the injection moulding surface of the tooling, after the step of additive manufacture, by polishing the injection moulding surface.

Optionally, the heat conducting polymer is a heat conducting polymer according to any to any variation of the seventh aspect.

Optionally, the injection moulding tooling is formed to comprise at least one cooling channel within the injection moulding tooling.

According to a tenth aspect of the invention there is provided a method of injection moulding, the method comprising using an injection moulding tooling according to the sixth aspect.

Optionally, the method comprises using an injection moulding tooling that comprises an induction coil for inductive heating, and the method further comprises a step of inductively heating the injection moulding tooling.

Optionally, the method further comprises using an injection moulding comprising at least one cooling channel within the tooling, and further comprises a step of cooling the injection moulding tooling during injection moulding by passing fluid through the cooling channel.

The invention is described below by way of example, with reference to the accompanying figures, in which: Fig. 1 is a photograph of an injection moulding tooling;

Fig. 2 is a perspective view of mother form inserts for injection moulding;

Fig. 3 is a plan view of the inserts of Fig 2;

Fig. 4 is a plan view revealing the internal inductive heating coils within the inserts of Fig 2.

Fig. 5 is a plan view revealing the internal cooling channels within the inserts of Fig 2.

Fig. 6 is a perspective view of an example sacrificial insert for use in injection moulding;

Fig. 7 is a plan view of the moulding inserts of Fig 2, showing an example of how the sacrificial insert of Fig. 6 could be located.

Modern additive manufacturing techniques, also known as “3D printing”, allow for a variety of shapes to be created. In particular, 3D printing with polymers is a well-developed field, with various materials available with different properties for different purposes. Such polymer 3D printing processes allow for relatively rapid and cheap production of articles, certainly when compared to the cost of designing and milling an injection moulding tooling.

As explained in more detail below, it is possible to use such 3D printing methods to produce injection moulding tooling. Tooling produced in this way has obvious cost advantages in comparison to conventional metal toolings, and therefore makes injection moulding a more technically viable process for a wider range of products.

Fig 1 is a photograph of some example tooling 100. The tooling 100 includes faceplate frame 10 into which tooling inserts 20a and 20b (also referred to as “injection moulding inserts” in the text below, to distinguish from the “sacrificial inserts” discussed later) are inserted. The precise configuration of an injection moulding tooling varies from process to process. In some instances, the pieces of the tooling 100 are not created as separate face plate frame 10 with inserts 20, but instead the tool face plate consists completely of 3D printed tooling. Therefore, in this document, the term “tooling” can refer both to a combination of the inserts 20a, 20b and the faceplate frame 10 (whether provided integrally or separately), but can also refer to the individual parts themselves (i.e. the individual inserts 20a, 20b and faceplate frame 10).

In the arrangement of Fig 1, it can be seen that insert 20a is connected to the faceplate frame 10 by screws 26. Ejector pins 24, part of the injection moulding ejection package, can also be seen. These pins allow the moulded article to be removed from the mould once it has been formed.

Fig 2 shows a perspective view of the insert 20a and 20b. The inserts have moulding surfaces 21, forming the cavity within which the injection moulded material is retained and formed (and also forming the channels for the introduction of that material). Each insert 20a, 20b also has a contact surface 28 for contacting the other insert to form the overall mould cavity.

The skilled person will understand that more complicated moulded shapes may have more than the two separate parts shown in the Figures, and they will also understand that the discussion herein is equally applicable to such configurations.

Insert 20b is provided with an inlet 22b through which the material to be moulded is introduced to the moulding cavities. Opposite inlet 22b, in insert 20a, is provided an inlet channel 22a for receiving the material to be moulded and directing the material to the moulding cavities.

In Figure 2 it is also possible to see the ejector holes 23 in insert 20a, through which the ejector pins 24 (shown in Fig 1) access the moulding cavity. In use, during moulding, the ejector pins 24 of the ejection package are withdrawn to be level with the inner surface of the moulding surfaces 21 of the moulding cavity. Then, after the article has been formed and the inserts 20a and 20b separated, the ejector pins 24 can be advanced to push the moulded article out of the insert 20a.

Part or all of the tooling 100, e.g. the inserts 20a, 20b, can be formed by a 3D printed heat conducting polymer. By using a heat conducting polymer, the temperature of the moulding surfaces 21 can be controlled to ensure that the injection moulded material is at the right temperature as the article is moulded. It also allows for a rapid thermal response, e.g. allowing the inserts 20a, 20b to be heated during the introduction of the material and then subsequently cooled to set the article.

Suitable heat conducting polymers for use in the additively manufactured tooling 100 will depend on the particular application, and in particular the material to be moulded. For example, the material of the tooling 100 can be selected to have a higher melting point than the melting point of the injection moulded material. In general, any suitable polymer for a given process may be used to form the tooling 100. Such polymers may be thermoplastics, for example. The heat conducting polymer may include one or more additives bonded into the base polymer material.

The heat conducting polymer can have a thermal conductivity of 0.20 W m ¹ K ¹ or more, optionally 0.22 W m ¹ K ¹ or more, further optionally 0.24 W m ¹ K ¹ or more, further optionally 0.3 W m ¹ K ¹ or more, further optionally 0.5 W m ¹ K ¹ or more. Preferably, the heat conducting polymer can have a thermal conductivity of 1 W m ¹ K ¹ or more, 3 W m ¹ K ¹ or more, 5 W m ¹ K ¹ or more, 7 W m ¹ K ¹ or more, or 10 W m ¹ K ¹ or more. The thermal conductivity of plastics can be determined in accordance with ISO 22007. This can allow the tooling to have a suitably rapid thermal response to allow the forming and then cooling of articles being moulded.

The heat conducting polymer may also have a melting point of 170°C or more, optionally 175°C or more, further optionally 185°C or more. The melting point of polymers can be determined by differential scanning calorimetry (DSC) in accordance with ISO 11357.

In preferable arrangements, the heat conducting polymer further comprises a filler. The filler can be used to improve the heat transfer and/or mechanical properties of the tooling 100. The filler may be dispersed in the heat conducting polymer without physically interacting with the base polymer material.

By way of example, the filler may comprise a fibre, such as carbon fibre, natural bast, nanocellulose such as cellulose nanofibrils (CNF) or cellulose nanocrystals (CNC) for example. The presence of the fibre in the heat conducting polymer can provide structural reinforcement (as is conventionally understood with fibre reinforced plastics). The presence of the fibre can also improve the thermal properties, for example increase the melting point or thermal conductivity of the heat conducting polymer.

The heat conducting polymer can comprise 5-30% (by mass) fibre, optionally 10-25% fibre, and further optionally around 15-20% fibre. Providing smaller amounts of fibre can provide less improvement in the thermal properties, but overfilling the heat conducting polymer can lead to poor binding and reduced mechanical properties. The optimised values for the amount of fibre to include in the heat conducting polymer will vary from system to system (both in terms of the other materials constituting the heat conducting polymer, and the desired mechanical properties of the article being moulded).

As used herein, nanocellulose can mean cellulose material that has at least one dimension that is smaller than 100 nm, such as cellulose nanocrystals, cellulose nano fibrils or cellulose whiskers, both in native and modified state. For the avoidance of doubt, the term ‘nanocellulose fibre’ may be used cover all these forms of nanocellulose.

Nanocellulose, in particular, is potentially advantageous for use as a reinforcement filler as it has desirable mechanical properties, such as high strength and stiffness, but is less abrasive than other fibre materials such as carbon or glass fibre. As such, using nanocellulose as the filler can increase the lifetime of the components of the 3D printing system (e.g. such as the print head), compared to using other fillers.

Unmodified cellulose is natively hydrophilic and does not blend easily with hydrophobic polymer matrixes. Surface modification, including lactic acid grafting, etherification using acid oligomers of the target polymer matrix material, acylation (to form e.g. esters (acetate, nitrate), thioesters, imides, amides)), alkoxycarbonylation (carbonates) can significantly improve the dispersibility of the cellulose material in the matrix. Such modification can be tailored to a given polymer matrix, and methods for such tailoring are known in the field of cellulose modification.

Surface modification can also significantly improve the thermal stability of the nanocellulose material. This can be achieved with carbanilation (carbamates), silylation, titanation and sulphonation and can increase the thermal stability of the cellulose composite by 10 degrees Celsius or more. This is especially advantageous in fused filament fabrication where the material may need to be processed several times to produce the original filament, and then can be subsequently subjected to high nozzle heat during 3D printing. Improved thermal stability is also advantageous for recycling of material from 3D printing, which can include failed prints, failed filament production and recycling of 3D printed parts. Moreover, the recycling of cellulose based composites in other fields has been shown to be significantly more advantageous than glass or carbon fibre composites due to the reduced attrition of the cellulose material during reprocessing.

In addition, cellulose has a significantly lower bulk density weight compared with carbon and glass fibre. When the cellulose material has been properly compatibilized and dispersed in the polymer matrix, the strength reinforcement to weight ratio may be significantly higher for cellulose composites then for carbon or glass composites.

The fibre may be provided in lengths of 2 mm or less, optionally 1 mm or less. In the case of cellulose nano fibrils, the length may be 1000 nm or less, 600 nm or less, 400 nm or less..

The upper limit on the length will be dictated by the additive manufacturing nozzle size, as fibres that are two long could lead to clogging of the nozzle. As such larger nozzle sizes will allow for larger lengths of fibre.

Some examples of suitable materials for use in additively manufacturing the tooling 100 are provided in tables 1 and 2 below. Other materials being considered are polybutylene terephthalate [PolyOne (now Avient)]. Table 1 also indicates how the melting points of those materials are affected by the presence of 20% carbon fibre. Table 2 also indicates how the inclusion of nanocellulose filler and modification of the nanocellulose can affect the mechanical properties. In particular, the data shown comes from RSC Polymer Chemistry Series, Poly(lactic acid) Science and Technology: Processing , Properties, Additives and Applications, Chapter 9, and shows the effect of various fillers added to Poly(lactic acid), (PLA). Table 1

Table 2

The inserts 20a, 20b shown in Fig. 1 are made of the 20% carbon fiber / Poly( amide) (PA) 12 [DowDuPont] material.

The heat conducting polymer may also comprise metallic particles (alone or in combination with other fillers such as the carbon fibre mentioned above). As well as having a beneficial effect on the heat conducting abilities of the polymer, the use of metal particles also provides other benefits.

One advantage of using metal particles as a filler in the heat conducting polymer is that they can improve the release characteristics of the moulding surfaces 21. That is, once the article is moulded, it is easier to separate it from the moulding surfaces 21 without damaging the article (or, indeed, the tooling 100).

This effect can be enhanced by polishing the moulding surfaces 21 (including the inner surfaces of the inlet channel 22a) after the tooling 100 has been formed by additive manufacturing process. Polishing the tooling 100 formed from a heat conducting polymer comprising a metal particle filler results in the selective removal of the softer polymer material from the surface, leaving behind a surface enriched with the harder/less easily removed metallic particles. Such polishing leads to a moulding surface 21 which is enriched with the metallic component, and therefore behaves very similarly to a conventional metallic moulding surface. The polishing step can be performed manually or mechanically/automatically. For articles requiring precise moulding, the design of the moulding cavity produced by the additive manufacturing step can include an allowance to account for the removal of the material that occurs during the polishing step. That is, the moulding cavity as formed by the additive manufacturing process may be smaller than eventually desired in the product, to allow for the cavity being enlarged by the polishing. An allowance of around 10-20 microns may be made, for example, to be removed during the polishing step. The polishing step may use an abrasive paste, for example, as is well-known in conventional polishing techniques.

The metal particles themselves may have a variety of sizes and size distributions. For example, the particles may have a mean diameter (based on a spherical volume-equivalent diameter D of D = 2 (3K/4p), where V is the volume of the particle) of 1 mm or less, optionally 0.5 mm or less, further optionally 0.3 mm or less, further optionally 0.1 mm or less. The particles may have a mean diameter of 0.01 mm or more, optionally 0.03 mm or more, further optionally 0.05 mm or more. In general, smaller particles may be less likely to cause blockages in the additive manufacturing nozzle, and provide a smoother final surface, but particles that are too small are more easily (undesirably) removed during the polishing step.

The heat conducting polymer comprising metallic particles can comprise up to 30% (by mass) metallic particles, optionally up to 20%, and further optionally up to 15%.

When utilising both fibres and metal particles together as the filler, the heat conducting polymer cam comprise up to 40% (by mass) fibres and metal particles combined, optionally up to 30%, and further optionally up to 20%.

The metal particles can be of any suitable metal or alloy. However, ferrous metals have particular advantages. Firstly, conventional toolings are often made from ferrous metals, and thus existing mould release agents used with conventional toolings are also effective with toolings formed from a heat conducting polymer comprising a ferrous metal particle filler. A further advantage is that heat conducting polymers comprising a ferrous metal particle filler may be used for inductive heating. That is, for example as shown in Fig. 4, each insert 20a, 20b, could be provided with one or more inductive heating coils 28a, 28b. These coils 28a, 28b can be printed into the toolings 100 during the additive manufacture of the toolings 100. The coils 28a, 28b may be made from a different polymer to the surrounding material, being electrically conducting as well as heat conducting. Such materials are commercially available, such as for example conductive poly(lactide), PLA [ProtoPlant LLC]. The coils 28a, 28b can be provided with connective traces 29a, 29b of the same conductive material that can form connections to an external electrical circuit, to power the inductive coil 28a, 28b. When a coil is powered by an alternating current, an oscillating magnetic field is created in the coils. This then creates eddy currents in the surrounding material of the tooling 100, generating heat in the tooling 100, heating it up. Being able to apply heating directly in the tooling 100, and in whatever shape best suits the article being moulded, allows for a very responsive moulding process.

The precise form and number of the coils will depend on the shape of the article being moulded. However, in general, the present approach allows for such coils 28a, 28b to be easily included within the toolings 100, wherever they are needed, as they can be formed at the same time as the tooling is being manufactured. Such integrated and customised heating arrangements would be very much more difficult to create in conventional toolings, which start from a solid metal block.

Fig. 5 is a similar view to Fig. 4, but this time reveals cooling channels 27a and 27b which are formed within inserts 20a and 20b. The cooling channels can be formed in any desired shape/arrangement within the tooling during the 3D printing, allowing the cooling channels to be customised to the particular the tooling. Although the figures show the cooling channels in solid lines, it will be understood that the channels are embedded within the tooling, with ports connecting to a supply of external coolant that can be circulated through the tooling when needed during the moulding process.

As mentioned above, with conventional injection moulding processes, it can be difficult or impossible to create some shapes of items whilst also ensuring that the item can subsequently be released from the mould. To address this problem, a sacrificial insert can be used. Fig 6 is an example of such an insert. The sacrificial insert 200 has a main body 201. The body 201 has, in this example, cyclindrical holes 202 passing through it (that is, although it cannot be seen in Fig 6, the holes 202 are cylindrical passages extending to openings on the rear face of the body 201).

As shown in Fig 7, the sacrificial insert 200 can be positioned within the moulding cavity of an injection moulding tooling 100. Fig 7 indicates regions 203a in injection moulding insert 20a and region 203b in injection moulding 203b. Regions 203a and 203b represent the location at which the sacrificial insert is positioned when the two halves of the tooling 100 are positioned together. That is, the insert 200 fits into the moulding cavity between the parts of the exterior tooling 100.

In the illustrated example, injection moulding with the insert 200 positioned within the tooling 100 will result in the holes 202 becoming filled with the material being moulded, creating a set of five cylindrical columns which connect the two ends of the paddle or “dog bone” shape of that part of the injection moulding cavity.

Such an article cannot be produced by simple conventional injection moulding techniques due to the arrangement of the columns. The skilled person will immediately recognise other shapes and arrangements that are not easily formed by conventional injection moulding techniques could also be formed in this way.

In any case, the structure formed around the sacrificial insert 200 will be interlocked with the sacrificial insert 200 (i.e. in the example described above, the columns are initially formed within the body 201 of the sacrificial insert 200). Therefore, following the injection moulding, and ejection of the moulded article (with the sacrificial insert 200) from the tooling 100, the sacrificial insert 200 is removed to leave behind the final finished article. In some arrangements, it may alternatively be possible to integrate a mechanism for removing the sacrificial insert 200 with the tooling itself, before the article is ejected.

The sacrificial insert 200 is preferably water soluble. That allows the sacrificial insert 200 to be easily removed from the moulded article by dissolution - e.g. by immersing the sacrificial insert in water. As moulded articles are typically made of plastics that are not water soluble, this process easily removes the sacrificial insert without harming the moulded article. An example material that is suitable for use in the body 201 of the sacrificial insert 200 is poly(vinyl acetate), PVA.

Advantageously, sacrificial inserts 200 made of water-soluble polymers can be formed by additive manufacture, in the same way as the tooling 100 discussed above. This makes production of the inserts 200 technically viable, as the sacrificial inserts 200 are by design single-use items and therefore need to be producible simply, reproducibly and cheaply. Alternatively, the sacrificial inserts 200 could themselves be injection moulded from a tooling 100 as discussed above.

One advantage of manufacturing the sacrificial inserts 200 by additive manufacture is that inductive heating elements such as those discussed in connection with the tooling 100 can also be integrated into the sacrificial insert 200.

This can be useful, for example, when the sacrificial insert 200 defines a large cavity within an item to be moulded. The sacrificial insert 200 can therefore be used to heat from within the cavity, and ensure even distribution of heat within the item being moulded.

In such cases, the sacrificial insert 200 can be provided with an induction coil that is printed from an electrically conductive polymer during the additive manufacture of the overall sacrificial insert 200. In such cases, the coil may also be provided with electrically conducting traces that connect to contacts in the surrounding injection moulding inserts 20a, 20b, which in turn connects to the external source of power. That is, the injection moulding inserts 20a and 20b may be provided with electric traces for connecting the external source of power to the induction coil within the sacrificial insert 200.

When providing the sacrificial insert 200 with an induction coil, it is preferable to also include a metallic particle filler (preferably a ferrous metallic particle filler) in the water soluble polymer. This does not prevent the body 201 of the sacrificial insert 200 from being dissolved after use, although it may affect the speed at which the sacrificial insert 200 is dissolved compared to using an unfilled polymer for the sacrificial insert 200.

For some items, it can be possible to create a sacrificial insert 200 which is only partially destroyed following the creation of the moulded item. For example, considering the example of a large cavity to be formed within an item, this requires the sacrificial insert to have a corresponding large body around which the injection moulded material will be formed. However, whilst it may not be possible to remove the entire body from the cavity after the article has been moulded, it may be possible to remove a smaller body (e.g. if there are access holes into the cavity). Therefore, the sacrificial insert 200 may comprise an internal core that is not made of a sacrificial material, such that after the article has been moulded and the sacrificial material has been removed, the internal core element can be removed from inside the cavity. Such an arrangement would allow the internal core element to be re-used in producing further sacrificial cores. Such an arrangement might be desirable if, e.g. the re usable core incorporated more complex elements such as the induction heating coil mentioned above.

As such, the sacrificial insert 200 may be entirely made of a sacrificial material, but it may also include non-sacrificial materials. As such, in this document, a “sacrificial insert” covers inserts that can at least be partially “sacrifice” or dissolved to allow any remaining material to be removed from the moulded article, as well as inserts that are wholly degradable.

Whilst the invention has been discussed above by way of example, the skilled person will understand that the invention is not limited to these examples. The invention is defined in the claims.