Technical Field of the Invention

The present invention relates to a method for manufacturing a component. The method is particularly, but not exclusively, directed at producing a net shape or near net shape metallic and/or ceramic component. The invention also relates to a housing for use in the method and to apparatus for manufacturing a component.

Background to the Invention

It is known to produce components using an injection moulding (IM) process. In a conventional IM process, the material from which the component is to be formed is injected into a hollow mould using an injection moulding machine. The material injected is commonly referred to as a "feedstock" and may comprise a homogeneous mixture of different materials. The feedstock is solidified in the mould to form a moulded part which is then taken out of the mould in a process known as "de- moulding". The moulded part may be subject to further processing to result in the final component. The IM process can be used to form components from a range of materials including, for example, polymers and resins.

More recently has seen the development of a powder injection moulding (PIM) process. In a conventional PIM process, the feedstock is produced by mixing a polymeric binder with metal and/or ceramic powders and other ingredients. The feedstock is injected into a hollow mould using an injection moulding machine similar to those used for injection moulding plastics. Once the material has cooled and solidified, it is de-moulded and the resultant moulded part is known as a "green part". A portion of the binder material is removed from the green part using solvent, thermal furnaces, catalytic process, or a combination of methods to produce a so-called "brown part". The brown part is sintered to condense the material resulting in a component which may be net shape or near net shape.

As an alternative to injection moulding, it is also known to press a feedstock into the mould.

The known IM, PIM, and press moulding processes use a hard mould which can withstand high pressure without deforming or breaking. Such hard moulds are typically made from metallic and/or ceramic materials. However, the use of hard moulds limits the potential geometry of the components that can be produced due to difficulties in de-moulding.

A further known method of manufacturing components uses a soft mould. The process involves the manufacture of a master mould and the production of a mirrored soft mould from the master mould. In one known method, the soft mould is formed from low-cost polymers such as polydimethysiloxane (PDMS). Moulded parts are formed in the soft moulds by filling them with feedstock in flowable form and allowing the feedstock to solidify. Once the feedstock has solidified, the soft mould material is peeled-off to reveal the moulded part. This method has been used in particular to manufacture ceramic components from a ceramic powder which is incorporated with a binder and other ingredients to form a feedstock in the form of a slurry. The slurry consolidates in the mould to form the green part. Once removed from the mould, the green part is subjected to a de-binding and sintering process resulting in a net shape or near net shape component.

Use of a soft mould method overcomes some of the disadvantages of a hard mould, allowing for de-moulding from more complex geometries. Nevertheless, it has drawbacks. Filling and de-moulding are often carried out manually and individually, resulting in a low speed process which is more suitable for research than commercial application. The soft moulds cannot withstand high pressure during the filling process, which tends to result in less dense components, and the soft moulds are not suitable for use with injection moulding machines.

There is then a need for an alternative method of manufacturing a component which overcomes, or at least mitigates, some or all of the drawbacks of the known methods.

There is a need in particular for an alternative method of moulding a net shape or near net shape component which overcomes, or at least mitigates, some or all of the drawbacks of the known methods. There is also a need for alternative apparatus for manufacturing a component which overcomes, or at least mitigates, some or all of the drawbacks of the known apparatus.

Summary of the Invention According to a first aspect of the invention, there is provided a method of manufacturing a component, the method comprising: a. providing a mould in a meltable material; b. supporting the mould in a housing; c. filling the mould with a feedstock under pressure whilst the mould is supported in the housing; d. allowing the feedstock to solidify in the mould to form a moulded part; and e. subsequently melting the mould to release the moulded part.

The mould may define a mould cavity into which the feedstock is introduced when the mould is filled. In an embodiment, the mould defines the mould cavity in a first exterior surface and has at least one further exterior surface, the housing contacting and supporting mould on the at least one further exterior surface of the mould whilst the mould cavity is filled. The mould may have at least two further exterior surfaces, the housing contacting and supporting mould on each further exterior surface whilst the mould cavity is filled.

The housing may define at least one internal cavity within which a mould located. The mould may have a cylindrical peripheral side wall and the, or each, internal cavity of the housing may have a cylindrical portion within which the peripheral side wall is a close fit. The mould may be an interference fit in the housing cavity and be pressed into the cavity. In this case, the method may comprise heating the housing to soften an exterior surface of the mould as the mould is pressed into the housing cavity. The housing may have rigid support surfaces which engage the mould so that the housing is operative to support the mould whilst it is filled under pressure to prevent the mould deforming and/or breaking outwardly.

In an embodiment, the housing comprises at least two parts which define at least one internal cavity for receiving a mould, the two parts being movable between an open configuration in which a mould can be inserted into/removed from the housing and a closed configuration in which the at least one internal cavity is enclosed between the parts, at least one of the parts defining an inlet for directing feedstock into a mould held in the at least one internal cavity when the two parts are in the closed configuration.

The feedstock is flowable and may be a liquid, a slurry, or a powder.

The feedstock may comprise a polymer or a resin.

The feedstock may comprise a metallic and/or ceramic powder. The feedstock may comprise binder mixed with the metallic and/or ceramic powder. The moulded part may be a green part when initially demoulded and the method may further comprise sintering the green part. Where the feedstock comprises a binder, the method may comprise removing at least a portion of the binder from the moulded part prior to the step of sintering.

The mould may be produced using a 3D printer. The meltable material may be a polymeric material, which may be a wax or resin.

The meltable material may contain Sulphonamide Derivatives, or a combination of Sulphonamide Derivatives with Polyester Resin and/or Benzoate Derivatives. The meltable material has a lower melting point than the moulded part. The melting point of the meltable material is preferably sufficiently below that of the moulded part that the moulded part can be de-moulded by melting the mould without damaging the moulded part or adversely affecting its mechanical properties beyond acceptable limits. The meltable material may have a melting point in the range of 50 to 600 degrees Celsius, or a melting point in the range of 60 to 500 degrees Celsius, or a melting point in the range of 70 to 400 degrees Celsius, or a melting point in the range of 80 to 300 degrees Celsius, or a melting point in the range of 80 to 200 degrees Celsius, or a melting point in the range of 80 to 150 degrees Celsius.

The step of filling the mould with the feedstock whilst the mould is supported in the housing may comprise injecting the feedstock into the mould. Alternatively, the step of filling the mould with the feedstock whilst the mould is supported in the housing method may comprise pressing the feedstock into the mould in the housing. The method may comprise subjecting the filled mould to a vacuum prior to the feedstock solidifying. The housing may fully enclose the mould whilst it is filled and may have an inlet through which the feedstock is introduced into the mould cavity.

In accordance with a second aspect of the invention, there is provided a housing for use in the method of the first aspect, wherein the housing comprises at least two parts which define at least one internal cavity for receiving a mould of meltable material, the two parts being movable between an open configuration in which a mould can be inserted into/removed from the housing and a closed configuration in which the at least one internal cavity is enclosed between the parts, at least one of the parts defining an inlet through which a feedstock can be injected to a mould located in the at least one cavity when the parts are in the closed configuration. The housing may have a system for heating and/or cooling at least those surfaces of the housing which contact the mould.

In accordance with a third aspect of the invention, there is provided a housing for use in the method of the first aspect, wherein the housing comprises a pair of plates having mating surfaces, a plurality of internal cavities for receiving and supporting moulds made from a meltable material being defined in a first one of said plates, each internal cavity opening on to the mating surface of said one of the plates, the plates being movable between an open configuration in which their mating surfaces are separated to enable a mould to be inserted in and/or removed from each cavity and a closed configuration in which the mating surfaces are in abutment, at least one of the mating surfaces defining channels forming runners for directing feedstock towards each of the internal cavities, and at least one of the plates having an inlet fluidly connected with the runners when the plates are in the closed configuration through which feedstock can be injected into the runners.

The housing may have a system for heating and/or cooling at least those surfaces of the housing which contact the moulds. The heating system may be an electronic heating system or a fluid heating system.

In accordance with a fourth aspect of the invention, there is provided apparatus for manufacturing a component, the apparatus comprising: a housing having at least two parts, the housing defining at least one internal cavity for receiving and supporting a mould of meltable material, the two parts being movable between an open configuration in which a mould can be inserted into/removed from the at least one internal cavity and a closed configuration in which a mould located in the at least one internal cavity is enclosed within in the housing; a mould for location in the at least one internal cavity, the mould made from a meltable material and defining a mould cavity; the housing further defining an inlet for injection of a feedstock into the housing to fill the mould cavity of a mould located in an internal cavity of the housing when the housing is in the closed configuration.

The housing may define more than one internal cavity and the apparatus include a corresponding number of moulds. The housing inlet may comprise passages fluidly connected with each of the internal cavities.

In an embodiment, the housing comprises a pair of plates having mating surfaces which abut one another in the closed configuration and which are separated in the open configuration. The apparatus may comprises a system for heating and/or cooling the housing, or at least a part of the housing in which the at least one internal cavity is located.

The mould may be produced using a 3D printer. The meltable material may be a polymeric material which may be a wax or resin. The meltable material may contain Sulphonamide Derivatives, or a combination of Sulphonamide Derivatives with Polyester Resin and/or Benzoate Derivatives.

The meltable material may have a melting point in the range of 50 to 600 degrees Celsius, or a melting point in the range of 60 to 500 degrees Celsius, or a melting point in the range of 70 to 400 degrees Celsius, or a melting point in the range of 80 to 300 degrees Celsius, or a melting point in the range of 80 to 200 degrees Celsius, or a melting point in the range of 80 to 150 degrees Celsius.

A fifth aspect of the invention comprises use of the housing in accordance with either of the second or third aspects or the apparatus in accordance with the fourth aspect of the invention in the method according to the first aspect.

Detailed Description of the Invention

In order that the invention may be more clearly understood embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 is a perspective view of a turbine wheel produced using a method in accordance with an aspect of the invention;

Figure 2 is a perspective view of a mould for use in a method in accordance with an aspect of the invention; Figure 3 is a perspective view of an assembly comprising a first part of a housing in which the mould of Figure 2 has been inserted prior to filling the mould as part of a method in accordance with an aspect of the invention;

Figure 4 is a view similar to that of Figure 3 but showing the assembly after the mould has been filled and the feedstock allowed to solidify to form a green part; Figure 5 shows the mould and green part removed from the housing prior to de-moulding;

Figure 6 shows the green part after the mould has been melted in a de-molding step of a method in accordance with an aspect of the invention; and Figure 7 is a perspective view of an alternative embodiment of a housing for supporting a plurality of moulds suitable for use in an injection moulding process as part of a method in accordance with an aspect of the invention.

A method of manufacturing a ceramic turbine wheel 10 in accordance with an embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings. However, it should be appreciated that the method in accordance with the invention can be adapted to produce a wide range of components from a range of materials including: polymers, resins, metallic/ceramic powders. The method is particularly suited to the manufacture of a net shape or near net shape component having a relatively complex geometry but is not limited to this application. The turbine wheel 10 is illustrated in Figure 1.

The primary steps in a method of manufacturing the turbine wheel in accordance with an embodiment of the present embodiment include:

1. producing a mould 12 of the turbine 10 in a meltable material;

2. supporting the mould 12 in a housing 14 whilst it is filled under pressure with a feedstock 16, which in this embodiment is in the form of a slurry comprising ceramic powder and binder;

3. allowing the feedstock 16 to consolidate in the mould to form a moulded green part 18; and

4. melting the mould 12 to release the moulded green part 18.

In this embodiment, the moulded part 18 when released from the mould is a so called "green part" and the method further comprises the steps of de-binding the green part to remove at least a portion of the binder and sintering the part after de-binding.

The mould 12, as illustrated in Figure 2, can be produced from a meltable material using any suitable method but, advantageously, the mould 14 is produced using a 3D printer. Conveniently, a Computer Aided Design (CAD) model of the mould is produced and used by the 3D printer to form the mould 12. Alternatively, the mould could be shaped from a solid block of meltable material.

The term "meltable material" as used herein should be understood as referring to a material that has a lower melting point than the moulded part, so that the moulded part can be de-moulded by melting the mould without damaging or adversely affecting the mechanical properties of the moulded part. The meltable material should be solid and capable of retaining its shape at the temperatures at which the mould is filled and held whilst the feedstock solidifies. A material with a melting point in the range of 80 to 150 degrees Celsius is suitable for many applications. However, materials having a higher or lower melting point can be used depending on the melting point of moulded part and the temperatures the mould will be subjected to prior to de-moulding. If necessary, the temperature of the working environment can be controlled to ensure the mould does not unintentionally melt before de-moulding, or at least before the feedstock has solidified sufficiently to retain its shape independently of the mould. The meltable material could have a melting point in the range of 50 to 600 degrees Celsius, or a melting point in the range of 60 to 500 degrees Celsius, or a melting point in the range of 70 to 400 degrees Celsius, or a melting point in the range of 80 to 300 degrees Celsius, or a melting point in the range of 80 to 200 degrees Celsius, or a melting point in the range of 80 to 150 degrees Celsius.

A wide range of meltable of materials can be used to form the mould including polymeric materials such as wax or resin. Where the mould is to be produced using a 3D printer, the meltable material should be compatible for use with the printer. The meltable material may, for example, contain Sulphonamide Derivatives, or a combination of Sulphonamide Derivatives with Polyester Resin and/or Benzoate Derivatives. In an embodiment, the mould 12 is made from Solidscape ® 3Z Model which has a melting point of between 95 to 115 degrees Celsius and is manufactured by Solidscape, Inc. of 316 Daniel Webster Highway, Merrimack, H 03054 USA. The mould 12 in this embodiment is generally cylindrical having a cylindrical side wall 20 and first and second end faces 22, 24. A mould cavity 26 is defined in the first end face 22, whilst the second end face 24 is generally planer. The mould cavity 26 is profiled to define the negative of the shape of the desired component, in this case the turbine wheel 10. Typically the materials from which the mould 12 are made will be solid and capable retaining their shape prior to the de-moulding stage but tend not to be hard or strong and so would be liable to deform and/or break, typically outwardly, if filled under pressure without support. The housing 14 encloses the mould 12 and supports it during the filling stage so that the mould does not deform and/or break as it is filled with the feedstock 16 under pressure. The housing 14 according to the present embodiment is made from steel but the housing 14 could be made from any material suitable for withstanding the required pressure and for rigidly supporting the mould. The housing will generally be made from materials that have sufficient hardness and strength to resist deformation of the mould as it is filled under pressure. Suitable materials include, as examples only, metallic materials such as steel, aluminium, beryllium-copper alloy, and/or composite materials.

The housing 14 as illustrated in Figures 3 and 4 has two parts, a first part 14A with an internal cavity 30 for receiving a mould and a second part (not shown) which is releasably mountable to the first part so that the mould 12 is encapsulated within the assembled housing 14. The second part may be in the form of a lid which can be attached to the first part to form a sealed enclosure. The internal cavity is configured so that the mould is a close fit to prevent the mould deforming outwardly as it is filled under pressure At least one of the parts has an inlet including one or more fluid passages through which the feedstock can be injected into the mould cavity 26 whilst the mould is encapsulated in the housing. Alternatively, at least one of the parts can incorporate, or have an inlet adapted to receive, a mechanism for pressing feedstock into the mould cavity 26.

The internal cavity 30 in the first part 14A of the housing has a cylindrical side wall portion 32 within which the cylindrical side wall 20 of the mould 12 is a close fit. In practice, the outer diameter of the side wall 20 of the mould 12 may be slightly larger than the internal diameter of cylindrical side wall portion 32 of the housing cavity 30 and the exterior surface of the mould where it engages with the housing may be softened (partially melted) to allow the mould to be pressed into the cavity with an interference fit to ensure that the mould is tightly engaged by the surface(s) of the housing which define the internal cavity 30 and support the mould. The housing can be heated in order to soften the outer surface of the mould where it engages the internal surface of the cavity 30 as the mould is pressed into the cavity. The first part 14A of the housing 14 is in the form of a cylindrical tube having bore which defines the cylindrical side wall portion 32 and which is closed at one end by a planar end wall (not shown). The mould 12 is placed in the bore with its second end face 24 directed toward and supported by the planar end wall at the closed end of the bore.

Figure 3 illustrates the empty mould 12 in the first part 14A of the housing 14 prior to second part being assembled. At least those parts of the housing 14 which support the mould 12 are rigid and strong so as to prevent the mould from deforming outwardly and/or breaking when it is filled under pressure. However, it will be appreciated that not every part of the housing 14 need be rigid, provided that as a whole the housing 14 is able to support the mould 12 and contain the pressure as the mould 12 is filled. References to the housing being rigid should be understood accordingly.

In the present embodiment, the feedstock is injected into the mould cavity 26 whilst the mould is enclosed in the assembled housing 14 at a pressure in region of 30 MPa until the mould is full. An injection moulding machine similar to that used in conventional IM processes can be used. It will be appreciated the injection pressure can vary depending on the nature of the feedstock material and the size and geometry of the component being produced. Typically, the housing 14 is closed with the mould 12 inside and placed in an injection machine where the feedstock is injected into the mould cavity through the housing inlet. The feedstock is then allowed to solidify (consolidate) within the mould cavity whilst the mould is supported by the housing to form the moulded part 18. This process can be aided by opening the housing after the mould cavity has been filled to expose the top of the injected feedstock to air until it becomes solid as illustrated in Figure 4.

In an additional optional step, the filled mould 14 can be subject to a vacuum before the feedstock solidifies so as to eliminate any air bubbles that may be trapped in the feedstock in the mould cavity. This can be achieved by placing the housing with the filled mould in a vacuum environment where the mould is subjected to a vacuum. The housing 14 may be opened prior to applying a vacuum. Once the feedstock has consolidated in the mould 12 to form the moulded part 18, the mould 12 containing the moulded part 18 is removed from the housing 14. The housing may be heated to release the mould. After the mould has been released from the housing, the mould is heated in order to order to melt the mould and release the moulded part 18, which is illustrated in Figure 6. The mould may be heated in an oven or on a hot plate, for example. In one embodiment, the mould 12 is loaded into a tray or similar receptacle and placed in an oven where it is heated to just above the melting point for the mould material. The filled mould 12 may be placed on a raised support in the tray, such as a mesh through which the mould material can flow when it melts, so that mould material drains away from the moulded part below the support to leave the moulded part 18 on the raised support mesh. The meltable material may be collected to be reused.

The moulded part 18 in this embodiment is a green part and once it has been released from the mould it is subjected to a de-binding process and is sintered. De- binding may typically comprise heating the part 18 to a few hundred degrees whilst sintering may typically comprise heating the part 18 to a temperature of around 1000 degrees C for metals, and over 1500 degrees C for ceramics. After sintering, the turbine wheel 10 is a largely finished component, though it can be subject to further process steps such as machine finishing where required. In an alternative arrangement which may be suitable in some applications, the mould could be melted whilst in the housing to de-mould the moulded part 18.

Example 1

A specific example using the above method will now be described.

1. A CAD model of a mould was produced. 2. A mould made from Solidscape ® 3Z Model was produced from the CAD model using a 3D printer.

3. The mould was placed in the internal cavity of a first part of a steel housing and a second part of the housing secured to the first part to enclose the mould inside the assembled housing. 4. A feedstock in the form of an alumina slurry was prepared in the following way:

High purity A1203 powder with an average particle size of 1.5 μιη (Dynamic Ceramic Corp. UK) was used. Duramax ® D-3005 (Rohm and Haas, PA, USA) was used as the dispersant, Duramax ® B-1000 and B-1007 (Rohm and Haas) was used as the binder, NaOH and HCl were used to adjust the pH of slurries in all processes, and distilled water was used as the solvent. All samples were weighed to ±0.001 g in accuracy and typical batch size was 27 g. The mixing process consisted of the following steps: (a) 0-1.0 g/ml Duramax® D-3005 was added to distilled water and under constant magnetic stirring for 30 min. Afterward, alumina powder was slowly poured into the solution and then stirred for 3 h;

(b) 0.75 wt.% (B-1000+B-1007) was added as binder, with pH adjusted and then stirred for 2 h; (c) the slurry was poured into a plastic bottle, covered, and sealed. The bottle was then put on a shaking machine and shaken for 7 h, and then left overnight to make the slurry more uniform;

(d) before use, the slurry was placed in a vacuum condition until all residual bubbles were removed. 5. The prepared ceramic slurry was injected into the mould at 30 MPa pressure via an inlet port in the removable end closure.

6. After the mould was filled, the metal housing was taken out of the injection machine and the end closure opened to expose the top of the injected slurry component to air over night until the slurry became solid to form a consolidated green ceramic moulded part within the mould;

7. The filled mould was removed from the housing by placing the first part of metal housing half way into boiling water but avoiding submerge it completely in the water to release the mould and then taking the mould out of the housing; 8. The filled mould was placed in a petri dish and the loaded dish left in an oven preheated to 150 degrees C for 30 mins to allow the mould material to melt away from the green ceramic moulded part.

9. The green moulded part was subject to a de-binding and sintering process by placing it on a 99.9% alumina substrate in a high-temperature furnace. The furnace heated to 600°C at a low ramping rate at 75°C/h to decompose the binder and dispersant in the component in a de-binding stage and then heated to 1,600°C at a high ramping rate of 200°C/h for sintering. The temperature remained at 1,600°C for 2 h before the furnace was cooled down to room temperature.

The above described method can be adapted to produce a range of components from different materials as will be appreciated by those skilled in the art, provided that the moulded part can withstand the temperature used for demoulding. Where a component is formed from a feedstock comprising metallic and/or ceramic binder, the moulded part will be a green part which is typically subject to a de-binding process and sintered to form the final component. However, parts moulded from other materials, such as polymers and resins, need not be subject to these further process steps and may be the finished component or close to the finished component. Parts could be moulded using the method according to an aspect of the invention from a polymeric slurry for example, provided the cured polymer can withstand the demoulding temperature.

It should also be noted that the shape of the mould 12 and the design of the housing 14 can be varied. Typically, the shape of the mould 12 will be determined, or at least influenced by, the shape of the component 10 being moulded and the housing 14 designed accordingly to support the mould 12 so that it does not break or deform when the feedstock is introduced into the mould cavity under pressure.

It should also be appreciated that a housing 14 can be configured to support more than one mould 12 so that multiple components can be moulded at the same time. An example of such a housing 14' for use in a largely conventional injection moulding machine is illustrated in Figure 7. The housing 14' in this embodiment comprises a first part 14 A' and a second part 14B' in the form of a pair of plates with mating planar faces 34, 36. The two plates 14A', 14B' are similar in construction to the plates used to form a mould in a conventional injection moulding machine, except that the plates 14A', 14B' define a number of internal cavities 30' for supporting a corresponding number of moulds 12 made of a meltable material. In the housing 14' as shown, there are six internal 30' cavities but the number of internal cavities can be varied. The parts 14A', 14B' can be made of any suitable material such as steel, aluminium, and beryllium-copper alloy, for example.

The first part 14 A' has a number of guide pins 38 which project from its mating face 34 and which are received in corresponding holes 40 in the second part 14B' in order to aligned the parts when they are assembled together. Other arrangements for aligning the parts can be used. The internal cavities 30' for the moulds 12 are defined in the first part 14 A' and open at its mating face 34. The cavities 30' in this case are in the form of blind cylindrical bores similar to that described above in relation to the first embodiment of the housing 14 but the shape of the cavities can be varied to suit the shape of the moulds 12. The internal cavities 30' are arranged in a circle on a common pitch circle dimeter about a centre of the plate. A number of channels or runners 42 are defined in the mating face 34 of the first part 14 A' connecting each internal cavity 30' with a sprue bush 44 at the centre of the second part 14B' which forms an inlet through which the feedstock is injected into the housing. In use, moulds 12 of a meltable material are located in each of the internal cavities 30' in the first part 14 A' and the two parts 14A', 14B' of the housing are assembled together with their mating faces 34, 36 in tight contact. Feedstock is injected through sprue bush 44 and travels along the runners 42 to fill each of the moulds 12. Once the feedstock has solidified, the two parts of the housing 14' are separated and the moulds 12 with the moulded parts inside are ejected from the cavities. The first part 14 A' could be provided with ejector pins or the like to press the moulds 12 out. Given the relatively soft nature of the mould material, the ejector pins may be of relatively large cross sectional area and could take the form of pistons which define all or part of the closed ends of the cavities 30. The housing 14' could include heating means to partially melt or soften the moulds 12 when they are inserted in and/or removed from the cavities and/or the housing could include a cooling system to help in controlling solidification of the feedstock. For use in an injection moulding machine, the second part 14B' may be a fixed part which is connected with an injection unit and the first part 14 A' may be a movable part which can be clamped to the second part to close the housing 14' and moved away from the second part for insertion of empty moulds 12 and the removal of filled moulds. The housing 14' in accordance with the second embodiment is particularly suited to use in a commercial manufacturing arrangement where it is more cost effective to be able to mould a number of components at the same time.

The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.