Background

The present invention is concerned with an improved apparatus and method for use in the manufacture of components using additive manufacturing (AM) techniques. Particularly, but not exclusively, the apparatus and method may be used as part of an electron beam melting (EBM) manufacturing process.

A typical additive manufacturing process such as EBM uses a metallic powder as the forming material for the desired component. Progressive layers of metallic powder are melted using an electron beam in predetermined paths to form the desired component’s 3-D shape.

The part is formed in a build tank which is used to contain and support the successive layers of metallic powder and, importantly, the melted 3-D component which has been formed by melting the powder together in predetermined paths. Once the process is complete a 3-D component is surrounded by un-melted metallic powder within the build tank.

In order to release the component from the surrounding powder within the build tank (also known as a build cake) the conventional approach is to hand blast the residual powder away from the outside of the cake to leave the formed component or part which is contained within the cake. Careful blasting using an abrasive entrained in a gas flow (for example compressed air) is used to remove the excess un-melted powder from the part leaving a clean and finished 3-D component.

Because of the cost of the metallic powder using in additive manufacturing processes such as EBM the removed powder is collected and sieved before being recycled and re-used to form the next component. This reduces waste material and also reduces the costs of manufacturing parts. It is also environmentally desirable.

Conventional techniques allow for intricate components to be formed and cleaned of excess powder whilst simultaneously reducing the environmental impact of the manufacturing process and of course manufacturing cost. AM techniques such as EBM allow for intricate 3- D components to be formed with complex external and internal geometries. The conventional processes allow powder to be thoroughly removed from such internal spaces of components to leave a net shape. Typically the excess powder is removed by placing the cake into a sealed housing. Inside the housing a gas jet or nozzle is provided which can be manipulated by an operator using sealed rubber gloves which extend into the housing. As described above complex components can be cleaned of excess powder to leave the desire net-shape component. Metallic powder can then be conveniently collected at the bottom of the housing using a suitable filter and the metallic powder recycled accordingly.

Whilst existing approaches to EBM offer very reliable and accurate cleaning of AM formed components the inventors have established an alternative approach to handling build tank contents and furthermore to recovery of metallic powder. Still further the inventors have devised an apparatus and method that advantageously allows for increases in production rates and component integrity by control of the metallic powder recycling process. Specifically the inventors have established a way in which the integrity of a subsequent build can be monitored before a recycled powder is re-used for a subsequent build. This is particularly advantageous in the aerospace industry where some components require very high levels of structural integrity before they can be certified for aircraft use.

The apparatus and method described herein is particularly useful in EBM processes but is also applicable to other AM techniques including laser melting processes and other processes using a metallic powder in which excess powder must be removed and recycled.

Summary of the Invention

Aspects of the invention are set out in the accompanying claims.

Viewed from a first aspect there is provided an additive manufacturing metallic powder recovery apparatus comprising a powder removal chamber in communication with one or more powder recovery modules, each module arranged in use to recover metallic powder from a gas flow passing through the module(s); and wherein the or each module comprises a weight detector arranged in use to determine the weight of powder recovered by the module.

Thus, an arrangement is provided with may be used to recover excess metallic powder as part of an additive manufacturing (AM) process in a controlled and accountable manner. Not only is the excess powder recovered but it is further collected and weighted allowing for precise determinations to be made as to the location of any and all powder that has been used in the manufacturing process.

Conventionally a component is formed by melting a metallic powder according to a predetermined profile to form a three dimensional component. Generally such parts are formed from a series of layers where the heat source may for example be an electron beam/laser or other heat source. Powder is then manually chipped away or blown away within a blast chamber to release the final product. Waste powder (which may include partially or fully melted powder) settles within the chamber and can finally be disposed of.

According to an invention described herein the gas forming the atmosphere within the blast chamber can be processed and the excess powder removed in a series of processing steps. Importantly, the powder recovered by each step is determined so as to provide an indication of the amount and location of powder within the system.

To determine the weight or mass of powder each or a sub-set of the plurality of modules which are arranged to recover the metallic powder may be provided with an associated weight detector arranged in use to determine the weight of the powder recovered from the module. The weight may be detected in a number of ways, for example using a calibrated force transducer or other suitable weighing apparatus which has been calibrated to establish the mass of the powder which has been collected in the, or each, module. The gas forming the atmosphere within the blast chamber may be processed in a number of ways to remove or collect the metallic powder which is carried by the gas. The modules may for example be selected from one of a cyclonic separator, a dust filter or a mechanical sieve. These may be used in series or parallel and may be arranged to receive multiple passes of the gas.

Each module may be selected and placed in sequence such that the cyclonic separator, dust filter or mechanical sieve are each arranged to remove metallic powder from the gas flow having predetermined average particle/agglomerate sizes.

Advantageously, the powder removal chamber and one or more modules may be arranged as a closed loop and arranged to output powder for introduction into a vessel for an additive manufacturing machine. Thus, the recovered powder may be re-used in a subsequent manufacturing process instead of being discarded as potentially hazardous waste.

The powder removal chamber may be in any suitable form such as a blast chamber arranged to cause an abrasive powder to impact against a metallic powder body containing a component to be removed and further arranged to communicate all or some of the released metallic powder to the one or more modules. The chamber thereby acts as the releasing mechanism for the un-melted or partially melted powder using the manufacturing process. The chamber may then communicate the recovered powder to the modules for processing and‘cleaning’.

The excess metallic powder around the component which has been formed by the AM process may be removed in a number of ways. Advantageously an abrasive material contained within a high velocity gas flow may be caused to impact against the outer body of the part removed from the additive manufacturing machine.

Advantageously the abrasive material may be selected so as to correspond to the metallic powder which was utilised in the AM manufacturing process. Thus, cross-contamination of powders within the system can be avoided and a single powder type recovered by the modules.

The weight detector(s) may be arranged to determine the weight of the recovered metallic powder in each of the module and to output an indication of the determined weight either independently or collectively. Thus a total powder recover weight can be determined and additionally the location at which the powder was recovered can be determined. This may then provide additional information regarding the particle sizes that make up the recovered powder since each module may be arranged to recover powder of a different size. For example the modules may be arranged to recover particles in excess of 15 microns in diameter to less than 150 microns. For laser beam melting processes the power size may be 25 - 63pm. For Electron Beam Melting the power size may be 45 - 105 pm.

One module may be a mechanical sieve arranged to output recovered powder from a build into a blend container and to prevent metallic powder having a size greater than a predetermined size from entering a blend container. The blend container may serve as a vessel which can collect suitable powder which may be re-used.

For example, recovered powder may be designated as:

(a) re-usable powder having a size within a predetermined range which may be blended and recycled for reuse; or

(b) un-usable powder that cannot be recycled owing to the powder sizes being outside of an acceptable predetermined range.

A blend container or vessel may advantageously be arranged to receive recovered powder from the first group (a) from one or more of the modules. Additionally the blend container may be arranged to receive multiple batches of recovered powder from multiple build jobs i.e. recovered powder from more than 1 component built. The resulting powder (provided it is the same powder) can then be collected from multiple AM builds and blended and re-used as described herein.

The blend container or vessel may be provided with a weight module arranged to determine the weight of the recovered metallic powder for each of a series of builds. Thus, the recovered powder can be determined on a per-build basis which can then be used for further process auditing.

The apparatus may be provided with a data processing/recording apparatus which may log where in the apparatus powder is recovered and the amount (weight) of powder recovered. Advantageously using the total weight of powder used in the manufacturing process and subtracting the weight of the part and the sum of the weight of recovered powder provides an indication of the residual powder remaining in the system. Advantageously the data processing/recording apparatus may then be used to establish contamination levels within the system and to assess the quality of the powder recovered and intended for re-use.

Viewed from another aspect there is provided a modular powder recovery system for metallic powder recovery from an additive manufacturing process, the system comprising a plurality of metallic powder recovery modules, each module arranged to remove metallic powder entrained within a gas flow passing through the modules and to determine the weight of metallic powdered removed by the respective modules.

A total recovered mass of powder may additionally be determined based on the sum of the values determined at each module.

The data processor/logging apparatus may advantageously be configured to compare:

- the weight of the build cake received from the additive manufacturing process;

- a cumulative weight of the metallic powder removed at each module;

- the weight of the component formed by the additive manufacturing process;

- the weight of the material recovered at the final step of the modules;

and to determine the weight/volume of metallic powder remaining in the system.

The data processor/logging apparatus may be provided with a visual display or other means to alert a system controller or operative of the results of the analysis, such as the levels in the blending vessel, contamination build up or any other anomalies in the process.

Viewed from another aspect there is provided a method of recovering metallic powder from an additive manufactured component comprising the steps of:

- removing un-sintered and/or semi-sintered metallic powder from an additive manufacturing build cake surrounding a manufactured component;

- causing a gas flow to communicate removed powder from the build cake through one or more powder recovery modules; and

- recovering metallic powder at each module, each module recovering powder with a different average particle/agglomerate size.

Advantageously, as described herein, the (or each) module may comprise a weight detector arranged in use to determine the weight of powder recovered by the module and to output the weight of recovered powder by the respective module. A cyclonic separator, dust filter and/or mechanical sieve may be arranged to remove metallic powder from the gas flow having predetermined average particle/agglomerate sizes.

The powder recovered by the modules may be selected to have a particle size less than a predetermined threshold and may be collected and supplied to an additive manufacturing machine for a subsequent additive manufacture build.

The recovered powder may additionally be assessed for suitability for re-use and may optionally be blended with previously un-used metallic powder to provide a blended powder containing recovered metallic powder and new powder.

Viewed from yet another aspect there is provided an additive manufacturing powder recovery apparatus, comprising a plurality of powder recovery modules arranged in series, wherein each module is configured to recover metallic powder with a predetermined size threshold, and wherein metallic powder that is permitted to pass through the series of powder recovery modules is supplied to a vessel for re-use in a subsequent additive manufacturing process.

Drawings

Aspects of the invention will now be described, by way of example only, with reference to the accompanying figures in which:

Figure 1A shows a build tank used in accordance with an invention described herein with a movable base plate;

Figure 1 B shows a cross-section through the build tank of figure 1 A after an EBM build;

Figure 1 C shows a cross-section through the build tank and build cake after the build cake has been released from the build tank;

Figure 1 D shows a final EBM formed component after excess metallic powder has been removed;

Figure 2 shows a schematic flow chart of the stages of EBM additive manufacturing and powder recovery according to an invention described herein; and

Figure 3 shows a flow diagram of a process described herein identifying material weighing points throughout the process.

While the present teachings are susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that drawings and detailed description thereto are not intended to limit the scope to the particular form disclosed, but on the contrary, the scope is to cover all modifications, equivalents and alternatives falling within the spirit and scope defined by the appended claims.

As used in this specification, the words "comprises”,“comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean“including, but not limited to”.

It will be recognised that the features of the aspects of the invention(s) described herein can conveniently and interchangeably be used in any suitable combination. It will also be recognised that the invention covers not only individual embodiments but also combinations of the embodiments that have been discussed herein. Detailed Description

Figure 1A shows a build tank used in accordance with an invention described herein with a movable base plate. Specifically the figure shows a build tank 1 of the type used with an electron beam melting (EBM) process.

The build tank 1 comprises an outer body 2 and a movable plate 3 located within the body 2. During the EBM process an electron beam scans or rasters across a layer of metallic powder which is deposited on the build plate. The build plate is then successively lowered, a new layer of powder deposited and a new layer melted using the electron beam. Each layer is melted in a predetermined pattern to create a desired component in three dimensions as illustrated with reference to figure 1 B.

Figure 1 B shows a cross-section through a build tank. The multiple layers 4 are shown in cross-section together with a component 5 which has been formed by melting regions of each layer 4. The component 5 is formed in a series of steps until the desired shape is complete. The material 6 within the build tank 1 which surrounds the component 5 is un melted metallic powder or semi-sintered powder which is still in powder form.

An example of the powder material that may be used in an EBM machine, such as a machine manufacturer by Arcam of Sweden, includes but is not limited to Ti 64, manufactured for example by GKN Floeganaes.

The build tank may be made from any suitable material such as, for example, stainless steel. Build tanks for EBM machines are well understood by a person skilled in the art of EBM and will not therefore be described in detail herein.

Once the build is complete the component must be removed. The combination of melted material (forming the component 5) and the surrounding powder is termed a‘cake’ within the art. To release the component 5 the base plate is elevated forcing the cake from the top of the build tank 1 as shown in Figure 1 C. The next process is to remove or blast the excess powder from the component 5 to fully release the component 5.

The elevation of the base plate may take place in a blast chamber which is a sealed vessel in which the powder and semi-sintered powder can be blasted away from the component 5 and safely collected. Specifically, the build tank or chamber is loaded into a blast chamber and raised up slowly whilst an automated programme causes a metal, such as titanium media, 7 (such as a metallic powder) to be directed at high velocity onto the cake from an ejection nozzle 8. As the nozzle is moved relative to the build cake the excess material surrounding the component is abraded away by the hard metallic (e.g. titanium) media and collected within the blast chamber.

Figure 1 D shows the resultant component 5 after the excess material has been abraded by the titanium media and nozzle arrangement.

Aspects of an invention described herein are concerned with recovery of the metallic powder which has been blasted from the build cake. It is desirable to collect the removed metallic material for a number of reasons, including but not limited to:

- Collection of the powder reduces the environmental impact of additive manufacturing processes by reducing material wastage which would otherwise require land-fill disposal;

- Collection of powder allows for control inventory of the amount of material that has been used in the additive manufacturing process, in this example an EBM process; Collection of removed powder allows for the re-use of the un-sintered powder which reduces the manufacturing costs of the additive manufacturing process.

Component integrity can also be assessed through the establishment of the amount and type of powder that has been used in the component build.

The final point listed above is of particular relevance within the aerospace industry and most specifically for primary components which are essential to the flight of an aircraft. Such components must be carefully certified by the relevant regulatory bodies to ensure the integrity of the component (for example component 5 described herein). The integrity of a component is related, amongst other things, to how homogenous or uniform the material making up the manufactured component is.

If, for example, pockets of dissimilar material are contained with the built component 5 the structural integrity of the component may be significantly and even catastrophically compromised. Such pockets may be caused by, for example, contamination of the raw powder materials or, in cases where recycled powder is used, cross-contamination between manufacturing jobs on the manufacturing line. Specifically, when material is recovered using a blast chamber as described herein powder may be entrapped within the powder recovery system. Conventionally recycling of powder may simply take waste powder from the blast chamber and re-use it in combination with new or virgin powder and re-supply this‘blend’ back to the EBM machines. The inventors have established that this is not sufficient for aerospace requirements and extremely tight tolerances cannot be achieved without a method of understanding or assessing the re-used or recycled powder. This is particularly important when consecutive manufacturing processes use different or dissimilar powders. In such a situation different powders may inadvertently become mixed from residual material in the powder recovery system. Thus, the blended powder that is then re-used or recycled may include dissimilar and potentially unwanted cross-contamination of powders.

It follows that during EBM (or other AM) processes the resulting component may contain within the structure pockets of not only porosity but also different material combinations. This could be catastrophic for component structure integrity.

Figure 3 shows a flow diagram of a modified powder recovery system (PRS) according to an invention described herein.

The start and end of the PRS loop is the EBM (or other additive manufacturing machine) 9. The supply of powder through path 10 is described below.

Once the component 5 has been formed in the EBM machine the build tank (described above) is loaded into a blast chamber 1 1 shown schematically in figure 2. The excess powder and semi-sintered powder is removed as described above with reference to figures 1 A to 1 D and the resulting component 5 is removed and taken for final finishing (not shown).

The invention described herein is concerned with the recovery of powder from the EBM process using the following steps.

The waste from the blast chamber 1 1 contains large particles that have broken away from the build cake, powder and fine dust. This mixture of waste is passed to the cyclone 12 where a cyclonic circulating airflow is used to centrifugally force the larger waste and powder towards the outside of the cyclone for collection whilst leaving unwanted dust in the middle of the cyclonic airflow which may then be drawn and evacuated using a filter/dust extractor which captures/removes the dust from the air. The next stage of the PRS process is the sieve 13. The sieve acts as a further process to remove contaminants from the powder including, by means of a magnet, any ferritic material that may have become entrained in the powder flow/powder. This may for example originate from abrasion of a nozzle in the blast chamber or abrasion of other metallic components in the PRS system. A magnet may thereby optionally capture any ferritic material and prevent this from passing into the recovered powder.

The sieve works in a conventional way to capture particles above a predetermined size and entrap them for removal. The remaining powder can then be communicated to the next stage which is collection in a blend container 14 located adjacent to the sieve 13 and arranged to receive a plurality of sieve loads. Such sieve loads correspond to multiple builds from the EMB machine and form a series of layers of captured powder being collected in the blend container 14. The sieve also works to improve the flowability of the powder by removing‘lumps’ or agglomerations within the powder.

Once the blend container is filled to a predetermined level the blend container is transferred to a blend station 15 where the contents of the blend container can be blended i.e. mixed/agitated to form a homogeneous mix of powder from the multiple builds from the EBM. This may be achieved in a range of ways but may advantageously be achieved by rotating the blend container in the blend station to pour the powder over on itself repeatedly. Importantly the blending step mixes the different layers from the multiple EBM builds. Each build may have a different level of oxidation of the powder (through the melting process) and the blending allows an average or aggregate oxidation level to be achieved. The blend station may therefore incorporate an optional oxygen indicator which can identify the oxidation level of the powder blend at the blend station stage. Blending may also be performed in an inert atmosphere, for example using Argon gas.

A final determination is made at step 16 where an assessment of whether the blend is suitable for re-use is made. A number of tests may be performed.

This assessment of suitability of the powder may be made on a number of parameters including but not limited to:

Oxidisation (primary check) of expected mechanical strength of the component;

Hall flow rate; Particle size distribution; and

Apparent density and again the oxygen content for full characterisation and subsequent certification of powder.

If the powder characteristics comply with the predetermined requirements for the next build the recovered or recycled powder can be loaded via stage 17 into the EBM powder holding canisters 18 and then re-used via path 10 in the next EBM (or alternative build).

If the powder characteristics do not comply with the predetermined requirements for the next build for whatever reason (for example excess oxidation levels) then the powder can be returned, via path 19, to the sieve where it can be recombined with new material from subsequent EBM jobs and/or with virgin i.e. new metallic powder from supply 20. Steps 13 to 16 can then be repeated until the desired powder characteristics are achieved.

The modular arrangement described with reference to figure 2 provides a process, in the form of a series of discrete steps that not only allow for the recovery of metallic powder but allow for the grading or characterisation of the powder for re-use in subsequent EBM jobs.

An invention described herein extends beyond the module arrangement described with reference to figure 2 to include a more comprehensive apparatus and method for powder characterisation. Specifically according to an invention described herein the amount of metallic powder that is used or retained at various stages is determined through the process steps. This provides a number of technical advantages as described below.

As discussed herein the incorporation of dissimilar metallic powders or different concentrations of metallic powders can have a detrimental effect on the mechanical performance of components manufactured through an additive manufacturing process such as EBM.

If repeated cycles of components are formed with the same metallic powder then the issues of dissimilar powder being accidentally or erroneously used in an AM build are not problematic i.e. if only 1 metallic powder is used no such problems arise. However, the diversity and complexity of manufacturing facilities as well as the cost of commissioning and operating AM machines mean that the machines are sequenced to make as many and diverse components as possible. Such components often necessitate different metallic powders being used.

A further problem is where residual metallic powder in the modular system shown in figure 2 builds up during one or more cycles of manufacture using a first metallic powder. Switching to a second powder for a new component may initially appear to provide adequate characterisation of the blend at the blend stage but a sudden release or movement of a build up of powder within the process may create a pocket of material which is not identified.

Accordingly an invention described herein incorporates one or more weighing steps within the modular powder recover system.

The inventors have established that for such a modular system, a known volume of residual powder will remain in the system (within the conduits/pipes and channels that connect each module together) and may be expelled within the next build cakes cycle run. According to an invention this information can be captured for traceability/future containment/if necessary the determination of contamination risks.

This is described with reference to figure 3.

Figure 3 corresponds to the modular arrangement shown in figure 2 but illustrates the additional component and metallic powder weight measuring points through the modular system.

There are 4 weighing steps illustrated in the modular arrangement shown in figure 3 (although additional steps may be included if additional modules are added). These weighing steps are:

- Wi the weight of the formed component 5 (and semi-sintered powder);

- W ₂ the weight of powder recovered from the build and collected by the cyclone.;

- W the weight of the contents of the blending container; and

- W ₄ the weight of the contents of the AM machine canisters. This weight data may be obtained using a variety of commercially available weighing devices such as load cells, industrial scales or the like.

The output of each determined weighing step may be recorded manually by an operative or may advantageously be communicated to a data logging device 21 and user interface/data processor 22.

Using the known metallic powder weight being supplied and consumed by the EBM machine and then subtracting each of the weights to W ₃ above it is possible to determine how much metallic powder is remaining within the module system. This information can be used for a number of purposes including:

- Assessing when a system clean is needed owing to build ups of metallic powder;

- The expected location of the metallic powder; and

- The possible cross-contamination levels which could be seen in a consecutive powder recovery cycle

In respect of the final point the data logger and data processor may be configured to store data from previous builds and to develop a historical model to predict when metallic powder levels may reach unacceptable levels. For example it may be possible to determine if certain metallic powders are more prone to build up in the modules and when predetermined levels of metallic powder have been reached in the system which would cause potentially flawed EBM components.

The final weight measurement W ₄ may advantageously be used as the input metallic material weight for the next consecutive build. It will be recognised that metallic powder remaining in the canisters will also be used in the weighing model since this identified how much powder has been consumed in the build of component 5.

It will be recognised that whilst 4 weighing points are shown in the embodiments any number of weighing points may be used to improve the accuracy of the model formed by the data logger/processor.

Although the embodiments described above refer to an electron beam melting additive manufacturing process the method and apparatus may equally be applied to other forms of additive manufacturing where the characterisation of the metallic powder used must be determined.

The term additive manufacture is intended to refer to a technique where the components are created layer by layer until the complete component or part is formed. It will be recognised that although the main example described herein relates to EBM other forms of additive manufacturing may also benefit from the apparatus and method described herein.

Examples of additive manufacturing techniques which could conveniently be used include powder bed techniques such as electron beam welding, selective laser melting, selective laser sintering or direct metal laser sintering.

A method and apparatus described herein may be used with different AM techniques including EBM and Laser Powder Bed technologies. The materials may be selected according to the manufacturing technique used.

In an electron beam melting process parts may be manufactured from any powder where the base material displays metallic bonding.

Examples of electron bam melting materials include but are not limited to:

Titanium Ti64

Titanium Ti64 ELI

Nickel Alloy IN718

Nickel Alloy IN625

Stainless Steel 316L

Stainless Steel GP1

Stainless Steel PH1

Stainless Steel CX

Aluminium AISM OMg

ALSi13Mg

Copper Alloys

Tungsten Alloys; and

Rare Earth Alloys

Examples of Laser Powder Bed materials include but are not limited to: Titanium Ti64

Titanium Ti64 ELI NickelAlloy IN718 Direct Metal 20 Cobalt Chrome MP1

Cobalt Chrome SP2 Maraging Steel MS1 Nickel Alloy HX Nickel Alloy IN625 Stainless Steel 316L

Stainless Steel GP1 Stainless Steel PH1 Stainless Steel CX; and Aluminium AISM OMg