Patent Description:
Prior art methods of short run production of metal parts may be expensive or slow.

Where such parts are used for Research and Development (R&D) or prototyping it may be desirable for such parts to be produced cheaply, quickly, repeatably, reliably, with a wide range of shapes, with a wide range of metals or alloys, or scalably. <CIT> pertains to a system for curing thermo-sensitive materials in molds. <CIT> relates to investment casting core-shell mold components and processes utilizing these components. <CIT> elates to casting core components and processes utilizing these core components. <CIT> relates to a method of forming a shell for use as a mould in investment casting.

The scope of the present invention is defined by independent claims <NUM> and <NUM>, and further embodiments of the invention are specified in dependent claims <NUM>-<NUM>.

It is acknowledged that the terms "comprise", "comprises" and "comprising" may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, these terms are intended to have an inclusive meaning - i.e., they will be taken to mean an inclusion of the listed components which the use directly references, and possibly also of other non-specified components or elements.

Reference to any document in this specification does not constitute an admission that it is prior art, validly combinable with other documents or that it forms part of the common general knowledge.

The accompanying drawings which are incorporated in and constitute part of the specification, illustrate embodiments of the invention and, together with the general description of the invention given above, and the detailed description of embodiments given below, serve to explain the principles of the invention, in which:.

<FIG> illustrates a system <NUM> for casting according to an example embodiment. In general terms there may be stages to the casting process, or stages may be combined or carried out in a different order according to the requirements of any given application. A mould is designed <NUM> for a specific part specification. Then an inorganic semi-permanent mould is printed on a 3D printer <NUM> using the mould design. The mould is filled with appropriate feedstock <NUM>. The filled mould is energised by a wireless power source to in situ melt the feedstock <NUM>. Alternatively, the feedstock could be melted by heating the filled mould using conventional means, for example a combustion furnace. The mould is cooled and removed from the wireless power source <NUM>. The part within the mould can then be removed <NUM> and the mould can then be reused for subsequent casting if the application calls for reusability.

One or more embodiments may have the advantage that a mould may be quicker to 3D print, than the part in question. In any case, once printed, the mould can be used to quickly cast two or more parts.

In any embodiment where the moulds can be reused two or more times, the typical production time of each part may be reduced from <NUM> hours (or much longer for some methods) to as low as <NUM>-<NUM> minutes. An example system, such as shown in <FIG>, may have a small footprint, operate stably, may be more efficient, provide an acceptable finish, may be fast and simple to train on and/or is low maintenance. One or more embodiments may be advantageous for the automotive, consumer goods, construction, equipment and machine, mining, aerospace, ship building and military industries.

The following terminology will be used throughout:.

The step of Mould design <NUM> in <FIG>, may be implemented using a Multipart Mould <NUM> as shown in <FIG>, or a single-use complex design (or Investment Mould) which cannot be made with split moulds. In this case the Mould is broken after cooling and the part removed. The Mould may be designed in CAD software or according to the requirements of the application.

Another possibility is to make tools for the plastic injection moulding (PIM) market. An advantage of one or more embodiments over CNC machining may be to make metal tools with integral internal conformal cooling channels. The ability to cool the metal tools may reduce turnaround time, allows rapid or controlled cooling of the plastic, improved part quality and / or production volumes. PIM moulds could be cast by the System or copper could be cast to make electrodes for spark erosion of tooling steel Moulds both of which may be made more easily than CNC machining.

The 3D Printer will be able to print using multiple print heads to print binder, susceptor, ink and possibly release agent, or using a single print head capable of printing multiple materials. The printed material may include a Mould Identifier on the Mould which will inform a user of those details when scanned by a suitable reader which may include: ID tag, specific Feedstock, volume/mass of Feedstock required, instructions for the Furnace, how many times the Mould has been used, where in the process the Mould is, and what the current condition of the Mould is.

The step of Mould printing <NUM> in <FIG>, may be implemented using a local 3D printer. The Printer may use the binder jetting technique. Alternatives may depend on the application, for example Digital Light Processing (DLP) printed or Selective Laser Sintering (SLS). This may be implemented according to the disclosure in <CIT>, or <CIT> the contents of which are incorporated herein by reference.

In some embodiments the Printer may print the mould out of a powder which is able to retain its integrity by withstanding multiple melts at different melt temperatures for a range of Feedstocks. Gypsum with a powdered PVA binder that is activated by spraying with water through the print heads is one option for the moulds. Another option is silica powder with a grain size of between <NUM> and <NUM> mesh. Spherically shaped grains may flow better on the print table, but irregular shaped grains may perform well too. Alumina powder and others are possible depending on the requirements of the application. Silica may be more compatible with a wider range of molten metals (resists wetting and is non-reactive). Silica powder/binder blend is hydroscopic the powder may need to be kept in airtight containers or otherwise protected from water absorption. In some embodiments the Printer will avoid using nano aluminium powder, which may be undesirable in some applications.

Other examples of ceramics include: Zircon/Zirconia-based, Graphite, Silicon nitride, or Boron nitride.

In order to hold the ceramic powder in the desired shape we may use a binder. These are typically in a dry, powdered form and are mixed into the ceramic powder. Liquid binder may be printed rather than using it in the powdered form on the print bed.

Other Binders may include an inorganic colloidal solutions or high temperature inorganic binders such as sodium silicate potassium silicate, aluminium-phosphate, silicone resins and hydraulic-setting cements.

In some embodiments the Printer prints a susceptor <NUM> in the Mould parts <NUM> as shown in <FIG>. In an embodiment, a susceptor can be painted, sprayed, sputtered, dipped or deposited directly onto the Inner Surface of the Mould. Susceptor could be directly printed through the print heads by using nano scale particles similar to pigments in ink. The susceptor generates temperatures able to melt Feedstock when exposed to wireless energy delivered by the Wireless Power Source. In addition, the susceptor may also keep the heating surface in contact with the metal allowing the Mould to perform as an excellent insulator (for safety and faster, more efficient melting etc), avoid the risk of the metal particles arcing and damaging the Furnace (e.g., in case of Microwave) and/or the Mould. Ideally the susceptor is printed in a way that reduces the amount necessary and that it does not heat up in a way that damages the Mould or the Feedstock. The susceptor <NUM> may be spread evenly throughout the Mould as shown in <FIG> or varying the susceptor distribution <NUM> as shown in <FIG>, so that it is concentrated near the internal surface of the Mould and decreasing in density as it gets closer to the exterior surface to allow controlled heating of the Mould body and avoid thermal shock or printed in a more complex way to provide a shield around the part. There may be a susceptor layer at different depths (compared to the Interior Surface of the Mould) at different locations in the Mould as shown in <FIG>, to minimise thermal shock or thermal stress in complex part of the Mould, such as crevices. In a further alternative as shown in <FIG>, the Mould <NUM> may be completely formed by a susceptor material or the ceramic and/or binder may have susceptor characteristics (either at certain temperatures or in general).

In another alternative example, shown in <FIG>, the mould <NUM> is printed with one or more voids <NUM> in it. Susceptor material <NUM> can then be placed into the voids. The susceptor <NUM> may be in particulate form that is poured into the voids <NUM> or may be a solid preformed shape that is inserted into the voids <NUM>. In the example shown in <FIG> the susceptor <NUM> is in the form of rods. In this example, the mould <NUM> does not need to include any other susceptor or be printed from a susceptor material. This means that the choice of materials for the mould <NUM> is greater so that the base material for making the mould <NUM> can be selected for optimal compatibility with the feedstock. It may also allow the use of lower cost base materials for the mould <NUM>. This arrangement may also have improved resistance to thermal shock.

The susceptor materials may include Graphite, magnetite, ferrite, silicon carbide, metal oxides, zirconia, Alumina, metallised film, water, molybdenum, stainless steel or any conductive material, depending on the requirements of the application.

In some embodiments a Release Agent maybe provided on the inner most surface of the Mould. This allows easy extraction of the part but may also provide a barrier if certain alloys react to the susceptor/ceramic. This may be printed, similar to the susceptor, coated post printing or mixed with a liquid susceptor to give a hybrid coating. Graphite powder may work well for some metals. Mould life may improve with the use of a release agent applied over the susceptor, as this can protect against any chemical reaction between some metals and the susceptor.

A dehumidifier / heater may be added to control the temperature and humidity in the printer.

After printing the Mould may be cured to set the binder and expel moisture. This may be done with the application of heat (or UV in the case of DLP). The Mould cure may impact on its integrity which may be useful for a Reuseable Mould.

The step of Feedstock filling <NUM> in <FIG>, may be implemented using a Feedstock hopper, vibration platform and a weigh scale.

An alternative tube feed arrangement may be used as shown in <FIG>. In this arrangement the Mould <NUM> may be filled while in the Microwave <NUM>. A high temperature resistant tube <NUM> (which may also be microwave reflective or absorbing) is affixed to an aperture in the roof of the Microwave <NUM>. The Mould <NUM> is positioned in the Microwave <NUM> under the tube <NUM> for filling and then subsequent heating. A waveguide <NUM> beyond the aperture cut-off ensures no radiation leaks. The tube <NUM> can be removeable and/or slidable so that different height moulds can be placed underneath it. Inert gas such as Argon gas may also be dispensed into the tube <NUM> to reduce oxidation. Additionally, an IR sensor may be directed down the tube <NUM> axis to measure the temperature of the melt directly.

The ability to flow will depend on the shape of the Feedstock particles (e.g., spherical, rough or flat are all possible) and the size of the particles from nano, to micro to pellets. With Ingots, the cold Feedstock will not flow into the Mould Impression. Ingots may be loaded into the hopper instead. Once the ingots in the hopper become molten, the feedstock will flow into the cavity and fill it. Susceptor around the Mould Impression may continue to heat the Feedstock so that it is remains molten until all sections are filled. Keeping the Feedstock molten until the Mould Impressions is filled may have advantages over the prior art which must rapidly fill the cavity before the feedstock solidifies. This may provide greater control of the Feedstock flow and/or improved quality of the Part. One or more Mould designs may help address an uneven fill, including the addition of a vibration table and designing a larger hopper in the mould to hold additional Feedstock to provide gravity assistance. Different Feedstocks will have different melting characteristics under different Wireless Power Sources and other factors including the shape and size of the particles. Spherical powder shapes of a certain size work well for most metal alloys. Aluminium may require a different approach due to its exceptionally high oxidation characteristics. A blend of different sizes and shapes of particles may be used to balance flow with meltability. Trace additives may act as a melt and/or flow catalyst or inhibit oxidization. An electronic scale may ensure the Mould is filled with the correct amount of Feedstock.

The step of Melting the Feedstock <NUM> in <FIG>, may be implemented using a Furnace, such as a Microwave.

The filled Mould is placed into the microwave. The internal metal shape of the Microwave may be used to ensure radiation is focused on an optimal melt and to ensure safe use. We can also employ a 'stirrer' that ensures an even spread of microwaves. The Mould's External Surface temperature may be measured which lets the Operator know if the Part is solidified and can be removed.

The Mould may be clamped during heating and cooling. After cooling the Operator may be able to open, easily release the Part and then close the Mould and secure the clamping system repeatedly (two or more times).

The clamping system could be either part of the Mould <NUM> as shown in <FIG> e.g., with ceramic bolts <NUM> going through specific holes <NUM>), be independent as shown in <FIG> e.g., using a silicone band <NUM> which would be reusable, or as shown in <FIG> e.g., using pins <NUM> such as spring steel (with rounded ends) and be slightly tensioned, or be ceramic, or disposable e.g., high temp tape.

Also, it could be completely external like a feature in the floor of the Furnace, or a wedged box that holds the Mould together.

For metal Parts, the way Feedstock cools in the Mould may impact how the metal molecules are aligned and this may impact its strength characteristics i.e. tensile, shear, torsional, compression and hardness. Controlling the cooling of the metal part will allow parts of a desired strength profile. Conformal cooling in the Mould <NUM> could be used to control cooling as shown in <FIG>. Alternatively, selectively melting areas of the Mould and then moving the melt zone to another area may provide additional control. Forced air cooling may quickly cool the Mould while still in the Microwave. Forced air extraction and filtering (likely to be activated carbon) to remove any noxious fumes that may be released during the melt cycle may be useful.

Once the part has been cast it is allowed to cool to a safe temperature before being handled.

The step of Removing the Part from the Mould <NUM> in <FIG>, may be implemented using an inspection station.

The clamping system is removed, and the Mould parts are separated. If the Mould is an Investment Mould - in which case it is physically removed (e.g. with a hammer or vibratory tool). The part is then pulled out of the Mould.

The funnel and any other casting artefacts are cut off - normally a hacksaw or bandsaw. If required, the part is then sanded, filed, finished or polished to an acceptable surface finish. It may then be coated, painted or treated in some way. The Mould is inspected (by eye or machine or with some calibration device) for damage. It is then closed (manually) and fastened together again and refilled with Feedstock before being placed back into the Furnace. If a long period of time has passed since the Mould was used, then it may require another cure cycle to remove any moisture that may be present. If the Mould fails the inspection, it is removed from production.

Claim 1:
A casting mould (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>) for casting a metal part, the casting mould comprising:
an inorganic mould configured to receive feedstock; and
a susceptor (<NUM>; <NUM>; <NUM>; <NUM>) on or in the mould, the susceptor being configured for heating in-situ to melt the feedstock,
wherein the mould is 3D printed and the susceptor is a 3D printed susceptor.