GB2611314A

GB2611314A - Additive manufacturing method and apparatus

Info

Publication number: GB2611314A
Application number: GB2113932.4A
Authority: GB
Inventors: Crabtree Joseph; Rybalcenko Konstantin; Pap-Kovács Viktor
Original assignee: Additive Manufacturing Technologies Ltd
Current assignee: Additive Manufacturing Technologies Ltd
Priority date: 2021-09-29
Filing date: 2021-09-29
Publication date: 2023-04-05
Also published as: GB202113932D0

Abstract

Method and apparatus 100 for additively manufacturing a part comprises providing a first layer of powder-based build material, applying a solvent or binder to a selected area of the first layer based on a desired geometry of the part, providing a second layer of powder material on top of the first build layer, and repeating the process in a layer-by-layer fashion until a part is formed. The method may include extracting excess solvent or binder, by heating the additively manufactured part to a temperature above a boiling temperature of the solvent or binder and/or reducing the pressure within the sealed chamber to cause the solvent or binder to evaporate. A pH control agent, viscosity enhancer and or colouring agent may be used. The binder may be a polymerising agent and the apparatus further comprises a condenser, to condense evaporated solvent or binder from within the sealed chamber to facilitate its recovery. The apparatus may include a liquid reservoir 110 for containing a solvent or binder, a powder supply bed 120 for containing a powder-based build material, a print bed 130, a powder distributor 140 and a printing nozzle 150 for applying the solvent or binder.

Description

ADDITIVE MANUFACTURING METHOD AND APPARATUS

FIELD

The present invention relates to a method of additively manufacturing a part, a part obtainable via the aforementioned method and an apparatus for performing the same.

BACKGROUND

Additive manufacturing is becoming rapidly adopted across many industries due to its capabilities for manufacturing one-off and/or complexly shaped parts cheaply and efficiently (when compared to more traditional manufacturing and machining methods).

Additive manufacturing methods can typically be grouped into two main groups or methodologies, those being liquid-based methods and powder-based methods. One of the most common powder-based additive manufacturing methods is a method known as Selective Laser Sintering (or SLS).

Selective Laser Sintering is performed by firstly laying down a layer of powder-based build material. The layer of build material is then selectively heated via a laser to cause the powder build material to bind together, thereby forming a first "layer" of the additively manufactured part. The area at which the laser is applied is controlled based on the desired geometry of the part being created. The process is then repeated in a layer-by-layer fashion until a part having the desired geometry is formed.

However, such methods require expensive heating equipment (such as lasers) and also require a large amount of energy during operation in order to obtain the necessary amount of heat to cause the powder build materials to bind together. This makes Selective Laser Sintering processes expensive to run. Furthermore, since heat tends to dissipate into neighbouring regions of powder during processing, it is difficult to achieve high levels of resolution using such methods. Therefore, significant amounts of post-processing is usually required after the build has been completed.

It is an aim of the present invention to address at least one of the aforementioned issues.

SUMMARY

A first aspect of the present disclosure provides a method of additively manufacturing a part comprising: a) providing a first layer of powder-based build material; b) providing a solvent or binder, said solvent or binder being provided in liquid form and being capable of joining constituent particles of the powder-based build material upon application to form a processed build layer; c) applying the solvent or binder to a selected area of the first layer of powder-based build material to create a first build layer, said selected area being chosen based on a desired geometry of the additively manufactured part; d) providing a second layer of powder-based build material on top of the first build layer; and e) applying the solvent or binder to a selected area of the second layer of powder-based build material so create a second build layer on top of the first build layer, said selected area also being chosen based on a desired geometry of the additively manufactured part.

Advantageously, the aforementioned method enables additively manufactured parts to be created without the need for expensive laser heating equipment.

Furthermore, when additively manufactured parts are manufactured using known techniques, when heat is selectively applied to an area of the AM part in order to sinter the build material, said heat is often dissipated to neighbouring regions of the part. This residual heating can cause build material outside of the selected area to also become sintered together which is detrimental to the resolution of the final part.

However, since the claimed method does not rely on heating in order to join the build material together, and hence does not suffer from the same issues of residual heating, the aforementioned method is able to achieve an improved part resolution when compared to know methods.

In some exemplary embodiments, the method further comprises, between steps c) and d), extracting excess solvent or binder, applied during step c), from the first build layer.

In some exemplary embodiments, the method further comprises, between steps d) and e), extracting excess solvent or binder, applied during step c), from the first build layer.

Advantageously, by extracting the solvent or binder from the first build layer between steps c) and d) or between steps d) and e), the solvent or binder can be more easily extracted since there are fewer build layers through which the solvent or binder must pass in order to be extracted.

This helps to prevent solvent or binder from becoming trapped deep within the matrix of the part which can adversely impact the homogeneity and structural integrity of the part.

In some exemplary embodiments, the method further comprises, after step e), extracting excess solvent or binder, applied during step e), from the second build layer.

In some exemplary embodiments, the method further comprises, after step e), extracting excess solvent or binder, applied during steps c) and e), from the first and second build layers.

In some exemplary embodiments, the method further comprises, after step e), providing a third layer of powder-based build material on top of the second build layer.

In some exemplary embodiments, the method further comprises, after steps e) but before the extraction of excess solvent or binder from the second build layer, providing a third layer of powder-based build material on top of the second build layer.

In some exemplary embodiments, the method further comprises applying the solvent or binder to a selected area of the third layer of powder-based build material so create a third build layer on top of the second build later, said selected area also being chosen based on a desired geometry of the additively manufactured part.

In some exemplary embodiments, the method further comprises extracting solvent or binder from the third build layer.

In some exemplary embodiments, the method further comprises, providing a fourth layer of powder-based build material on top of the second build layer.

In some exemplary embodiments, the method further comprises applying the solvent or binder to a selected area of the fourth layer of powder-based build material so create a fourth build layer on top of the third build later, said selected area also being chosen based on a desired geometry of the additively manufactured part.

In some exemplary embodiments, the method further comprises extracting solvent or binder from the fourth build layer.

In some exemplary embodiments, steps a) to e) are performed sequentially.

In some exemplary embodiments, the method further comprises heating the solvent or binder prior to application.

In some exemplary embodiments, the solvent or binder is heated to a temperature above ambient temperature and below a boiling temperature of the solvent or binder.

In some exemplary embodiments, the solvent or binder is heated to a temperature in the range of 10°C and 250°C.

In some exemplary embodiments, the solvent or binder is heated to a temperature in the range of 30°C and 140°C.

Advantageously, applying heated solvents / binders helps to achieve improve the dissolution of the built material.

In some exemplary embodiments, the selected area of the first layer of powder-based build material to which the solvent or binder is applied during step c) has a first geometry, and the selected area of the second layer of powder-based build material to which the solvent or binder is applied during step e) has a second geometry, said second geometry being different to the first geometry.

In some exemplary embodiments, the solvent is selected such that, upon application of the solvent to the powder-based build material, adjacent particles of the powder-based build material within the selected area become dissolved and fuse together to create the first and second build layers.

In some exemplary embodiments, steps c) and e) are performed within a sealed chamber.

In some exemplary embodiments, the method further comprises, during steps c) and e), controlling the atmospheric conditions within the sealed chamber such that the solvent or binder is maintained in a liquid state.

In some exemplary embodiments, the temperature within the sealed chamber is maintained between -10°c and 100°c.

In some exemplary embodiments, the pressure within the sealed chamber is maintained between 1 mbar and 1000 mbar (or 1 atm).

Advantageously, controlling the atmospheric conditions within the sealed chamber can help to maintain the solvent or binder in a liquid state which subsequently improves the resolution of the part since unprinted areas (where the binder liquid has evaporated before the material layer has been formed) can be better avoided.

In some exemplary embodiments, the extraction of excess solvent or binder comprises heating the additively manufactured part to a temperature above a boiling temperature of the solvent or binder to cause the solvent or binder to evaporate.

In some exemplary embodiments, the extraction of excess solvent or binder comprises reducing the pressure within the sealed chamber to cause the solvent or binder to 30 evaporate.

Advantageously, by reducing the pressure within the sealed chamber, it is possible to cause the solvent or binder at lower temperatures than would otherwise be required under atmospheric conditions. This helps to prevent heat damage being caused to the part upon extraction of the solvent or binder.

In some exemplary embodiments, the solvent or binder is applied as a series of liquid droplets, optionally having a size of approximately 100 microns.

In some exemplary embodiments, the droplet size may vary between the range of 0.1 to 500 microns.

In some exemplary embodiments, the size of said droplets is selected based on at least one property of the powder-based build material.

In some exemplary embodiments, the size of said droplets is selected based on one or more of: a chemical composition of the powder-based build material; a particle size of the powder-based build material; a melting point of the powder-based build material; a glass transition temperature of the powder-based build material; and/or a density of the powder-based build material.

In some exemplary embodiments, the speed at which the series of liquid droplets are ejected from the printing nozzle is in the range of 0.1 m/s to 100 m/s, and optionally in the range of 1m/s to 10m/s.

In some exemplary embodiments, the rate at which the series of liquid droplets are ejected from the printing nozzle is in the range of 1 kHz to 1000 kHz, and optionally in the range of 10 kHz to 50 kHz The droplet ejection rate is selected based on the printing method being used (e.g. Droplet on Demand or Continuous Inkjet printing).

In some exemplary embodiments, the method further comprises, prior to steps c) and e), applying a colouring agent to the solvent or binder.

In some exemplary embodiments, the colouring agent may be a dye.

Advantageously, applying a colouring agent to the solvent or binder enables parts manufactured using to the aforementioned method to be better tailored to the aesthetic needs of the end user without requiring a separate colouring operation to be performed post-process.

In some exemplary embodiments, the method further comprises, prior to steps c) and e), adding a pH control agent to the solvent or binder to bring the pH of the solvent or binder into the range of 1 to 9, and optionally to a value of approximately 7.

In some exemplary embodiments, the pH control agent may comprise one or more of: an organic acid: a mineral acids; a base; a neutralising agent; a buffering agent; a solid powder; a salt; water and/or an oil.

Advantageously, keeping the pH of the solvent or binder around 7 helps to improve the longevity of the printing apparatus used for performing the aforementioned method.

Advantageously, the solvent or binder are formulated to be Newtonian liquids to be appropriately jetted or dispensed.

In some exemplary embodiments, the method further comprises, prior to steps c) and e), adding a viscosity enhancer to the solvent or binder to bring the kinematic viscosity of the solvent or binder into the range of 0.1 to 10,000 mm2/s.

In some exemplary embodiments, the method further comprises, prior to steps c) and e), adding a viscosity enhancer to the solvent or binder to bring the dynamic viscosity of the solvent or binder into the range of 0.1 to 10,000 mPa.s, and optionally into the range of 1 to 100 mPa s.

In some exemplary embodiments, the viscosity enhancer may comprise one or more of: an oil; an alcohol; water; gelatin; an acid; a base; guar gum; starch; cellulose; a silicate; pectin; a polymer; a co-polymers; acrylates, Polyvinylpyrrolidone, and/or glycol.

In some exemplary embodiments, the viscosity enhancer may comprise castor oil and/or olive oil In some exemplary embodiment, the viscosity enhancer may comprise ethyl alcohol.

Advantageously, tailoring the viscosity of the solvent or binder so that it is within the aforementioned range helps to achieve optimal droplet ejection whilst also better avoiding solvent or binder splatter, causing droplet satellites or leakage during use.

In some exemplary embodiment, the method further comprises, prior to steps c) and e), adding an additive to the solvent or binder to bring the density of the solvent or binder into the range 0.1 to 10 g/cm3; and, optionally, into the range of 0.7 to 2 g/crna.

In some exemplary embodiments, the additive may comprise one or more of: water; an alcohol; an acid; a base; an oil; a polymer; a co-polymer; a salt; a solvent; and/or a silicone.

Advantageously, tailoring the density of the solvent or binder so that it is within the aforementioned range helps to achieve optimal droplet ejection and wettability during use in the aforementioned method.

In some exemplary embodiments, the method further comprises, prior to steps c) and e), adding an additive to the solvent or binder to bring the surface tension of the solvent or binder into the range of 10 to 100 N; and, optional, into the range of 20 to 50N.

In some exemplary embodiments, the additive may comprise one or more of: water; an alcohol; an acid; a base; an oil; a mineral oil; a polymer; a co-polymer; a salt; a silicone; an acrylate; and/or ionic liquid.

Advantageously, tailoring the surface tension of the solvent or binder so that it is within the aforementioned range helps to promote rapid meniscus recovery at high ejection frequencies whilst also helping to prevent the solvent or binder from spreading following application thereby improving the resolution of parts obtained via the aforementioned method.

In some exemplary embodiments, the method further comprises, prior to steps c) and e), adding an additive to the solvent or binder to bring the conductivity of the solvent or binder into the range of 1 x 1010 to 1 x103 0.m In some exemplary embodiments, the method further comprises, prior to steps c) and e), adding an additive to the solvent or binder to bring the conductivity of the solvent or binder into the range of 1 x 10-8 to 1 x 10-6 0.m.

Advantageously, when using a Droplet-on-Demand (DOD) method of printing, where each droplet is selectively ejected from the nozzle, a low electric conductivity helps to prolong the lifetime of such printheads as they cannot tolerate a high conductivity of fluid However, it should be noted that if a Continuous Inkjet (CU) method is being utilised, where droplets are being continuously ejected, a degree of control is required which is achieved by charging and deflecting the ejected droplets. In such circumstances, some degree of conductivity is desirable.

In some exemplary embodiments, the additive comprises carbon particles.

In some exemplary embodiments, the additive comprises silver particles.

In some exemplary embodiments, the solvent comprises at least one of 1,1,1,3,3,3-Hexafluoroisopropanol, Acetone, Isopropyl alcohol, Dichloromethane, Cyclohexanol, Ethylene glycol, Hexylene glycol, Dioxane, Anisole, Pentan-1-ol, 2-Phenoxy ethanol, N-anyl alcohol, Sulphuric acid, M-cresol, Formic acid, Butylal, an acetal, Trifluoroacetic acid, Benzyl alcohol, glycol ether, DMSO, 1,2,4 Trichlorobenzene, Tetrahydrofuran, 2-methyltetrahydrofuran, Xylene, 1-methoxy-2-propanol, Triethyleneglycol, 2,2,2-Trifluoro ethanol, Acetophenone, Dibutoxymethane, Propionaldehyde diethyl Acetal, Acrolein Diethyl Acetal, Aminoacetaldehyde Dimethyl acetal, Anisaldehyde Dimethyl Acetal, Ethyl Diethoxy acetate, Citral Diethyl Acetal, 2,2 -Diethoxyacetophenone.

In some exemplary embodiments, the solvent comprises at least one acetal.

In some exemplary embodiments, the solvent comprises Propionaldehyde diethyl acetal.

In some exemplary embodiments, the powder-based build material is a saturated polymeric material.

In some exemplary embodiments, the binder is a polymerising agent selected such that, upon application of the polymerising agent to the powder-based build material, adjacent particles of the powder-based material within the selected area become polymerised to create the first and second build layers.

In some exemplary embodiments, the powder-based build material is a polymeric build material.

In some exemplary embodiments, the powder-based build material comprises at least one of Acrylonitrile butadiene styrene, Polyethylene, terephthalate glycol, Perfluoroalkoxy Polymer, polylactic acid, Polypropylene Polyether ether ketone, Polyether ketone ketone, Polycarbonate, Polyethylene, Nylon 6, Nylon 66, Nylon 11, Nylon 12, Nylon 46, Nylon 6/12, Polyphthalamide, Thermoplastic polyurethane, Thermoplastic polyamide Thermoplastic copolyester.

In exemplary embodiments, the method further comprises recovering the solvent or binder extracted from the material layer.

In exemplary embodiments, the step of recovering the solvent or binder extracted from the material layer comprises condensing the extracted solvent or binder.

In exemplary embodiments, the step of recovering the solvent or binder extracted from the material layer comprises passing the evaporated solver or binder through a water column.

In exemplary embodiments, the method further comprises passing the evaporated solvent or binder through a filter (such as a carbon filter).

According to a second aspect of the present disclosure, there is provided an additively manufactured part obtainable according to the first aspect of the present disclosure.

According to a third aspect of the present disclosure, there is provided an additive manufacturing apparatus for performing the method of the first aspect of the present disclosure, the apparatus comprising: a print bed for receiving a layer of powder-based build material; a powder supply bed for containing a powder-based build material; a liquid reservoir for containing a solvent or binder; a powder distributor for applying a layer of powder-based build material from the powder supply bed onto the print bed; a printing nozzle for applying the solvent or binder onto the layer of powder-based build material applied onto the print bed; a controller configured to control the powder distributor to sequentially apply layers of powder-based build material onto the print bed and further configured to control the printing nozzle to sequentially apply solvent or binder to selected areas of the powder-based build material to cause constituent particles of the powder-based build material to join together to create an additively manufactured part formed from sequential build layers.

In some exemplary embodiments, the printing nozzle comprises a chemical resistant material.

The term "chemical resistant' is hereby used to define a material which is resistant to attack from the solvent or binder.

In some exemplary embodiments, the printing nozzle comprises a stainless steel.

In some exemplary embodiments, the printing nozzle comprises parylene.

Advantageously, the feature of a chemical resistant nozzle helps to improve the longevity of the apparatus.

In some embodiments, the apparatus further comprises a heating element for heating the solvent or binder prior to application.

In some embodiments, the liquid reservoir comprises a heating element for heating the solvent or binder prior to application.

Advantageously, pre-heating the solvents / binders helps to achieve improve the dissolution of the built material.

In some exemplary embodiments, the printing nozzle is configured for ejecting the solvent or binder as a series of liquid droplets.

In some exemplary embodiments, the printing nozzle is configured to achieve a droplet size of approximately 100 microns.

In some exemplary embodiments, the apparatus is arranged such that a distance between the printing nozzle and the build material is between 0.1mm to 10mm, and ideally between 0.5mm to 2mm.

In some exemplary embodiments, the printing nozzle is configured to eject the series of liquid droplets at a speed in the range of 0.1 m/s to 100 m/s, and optionally in the range of 1m/s to 10m/s.

In some exemplary embodiments, the printing nozzle is configured to eject the series of liquid droplets at a rate in the range of 1 kHz to 1000 kHz, and optionally in the range of 10 kHz to 50 kHz.

Advantageously, the application of the solvent or binder as a series of liquid droplets helps to improve the part resolution achieved by the apparatus.

In some exemplary embodiments, the apparatus comprises a sealed chamber containing the print bed, powder distributor and printing nozzle.

In some exemplary embodiments, the apparatus further comprises a temperature control element and/or a vacuum device in operable communication with the sealed chamber, and the controller is configured to control the temperature control element and/or vacuum device such that, when the solvent or binder is applied to the powder-based build material, the solvent or binder are maintained in a liquid state.

In some exemplary embodiments, the apparatus further comprises an extractor configured to extract the solvent or binder from said build layers.

In some exemplary embodiments, the extractor comprises a heating element configured to heat the additively manufactured part to a temperature above a boiling temperature of the solvent or binder to cause the solvent or binder contained therein to evaporate.

In some exemplary embodiments, the heating element is located within the print bed.

In some exemplary embodiments, the extractor comprises a vacuum device configured lower a pressure within the sealed chamber to cause the solvent or binder contained therein to evaporate.

In some exemplary embodiments, the apparatus further comprises a condenser, and the condenser is configured to condense evaporated solvent or binder from within the sealed chamber to facilitate its recovery.

In some exemplary embodiments, the apparatus further comprises a water column and a conveying mechanism, and the conveying mechanism is configured to convey the evaporated solvent or binder through the water column to facilitate its recovery.

In some exemplary embodiments, the apparatus further comprises a filter, optionally a carbon filter, for recovering evaporated solvent or binder within the sealed chamber.

In some exemplary embodiments, the apparatus further comprises a powder collection bed for recovering powder-based build material which does not form part of the respective build layer created after each run.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 illustrates a schematic view clan additive manufacturing apparatus according to an aspect of the present disclosure; Figure 2 illustrates a schematic representation of a method of additively manufacturing a part according to an aspect of the present disclosure; Figure 3 illustrates a schematic representation of a solvent which can be used in the method illustrated in Figure 2; and Figure 4 illustrates a schematic representative of the part manufactured using the method illustrated in Figure 2.

DETAILED DESCRIPTION

Figure 1 shows an apparatus 100 for additively manufacturing AM parts (hereinafter the "additive manufacturing apparatus" or "apparatus").

The apparatus 100 is made up of a liquid reservoir 110 for containing a solvent or binder, a powder supply bed 120 for containing a powder-based build material, a print bed 130 having a substantially parallel top surface for receiving one or more layers of powder-based build material, a powder distributor 140 for applying one or more layers of powder-based build material from the powder supply bed 120 onto the print bed 130 and a printing nozzle 150 for applying the solvent or binder onto the one or more layers of powder-based build material.

The print bed 130, powder distributor 140 and printing nozzle 150 are all moveable relative to one another to enable build material and solvent to be applied across the top surface of the print bed 130 and also to allow the respective heights of the print bed 130, powder distributor 140 and printing nozzle 150 to be adjusted after each run in order to account for the incrementally increasing height of the AM part manufactured using the apparatus 100.

In the illustrated embodiment, the print bed 130 is moveable linearly in the vertical direction, for example via a ball-screw actuator 130a, so that the top surface of the print bed 130 can be lowered after each printing run to allow a new layer of build material to be applied on top of the previous layer (as is typical in layer-by-layer manufacture).

Similarly, the powder supply bed 120 and powder distributor 140 are also moveable in the vertical direction, for example via a further ball-screw actuator 120a, to allow the height of the distributor 140 to be adjusted based on the height of the print bed 130. The powder distributor 140 is also laterally moveable across the print bed 130 to enable layers of build material to be spread across the top surface of the print bed 130.

In the illustrated embodiment, the powder distributor 140 is provided in the form of a roller having a length approximately equal to that of the print bed 130. As such, the powder roller is moveable in two axial directions, those being along the lateral X-axis (i.e. across the print bed) and along the vertical Z-axis. However, it shall be appreciated that other variants of this design may also be used. For example, in embodiments wherein the length of the powder distributor 140 is less than the length of the print bed 130, the powder distributor 140 may be moveable in three axial directions, those being along the lateral X-axis (i.e. across the print bed), along the lengthwise Y-axis (i.e. along the length of the print bed perpendicular to the X-axis) and along the vertical Z-axis to ensure that the powder distributor 140 is able to distribute build material effectively across the top surface of the print bed 130. Similarly, in embodiments where the powder roller has a width which is approximately equal to that of the print bed 130, the powder roller may instead be moveable along the lengthwise Y-axis and along the vertical Z-axis.

It shall also be appreciated that in some embodiments, where the powder distributor 140 is of a type that does not require direct contact with the print bed 130, the powder distributor 140b may be fixed at a vertical position. In such embodiments, the powder distributor may only be permitted to move in one or two axial directions, such as along the lateral X-axis or lengthwise Y-axis, or along the lateral X-axis and along the lengthwise Y-axis. It shall also be appreciated that in some embodiments, the powder supply bed 120 may also be fixed in a pre-set position, and so in some embodiments the powder supply bed 120 may not be moveable in the vertical direction.

Returning back to the illustrated embodiment, the powder distributor 140 is configured to transport the powder-based build material from the powder supply bed 120 and to deposit a layer of said build material onto the top surface of the print bed 130. The powder roller may be supported via a robotic arm actuator, a series of guide rails, one or more ball-screw actuators or any other suitable method.

At the start of each run, the powder distributor 140 takes up build material from the powder supply bed 120 and moves to a location proximal to the print bed 130. Once the powder distributor 140 is located proximal to the print bed 130, the powder roller is brought into contact with the print bed 130 and the powder roller is moved along the print bed 130 so that a layer of powder-based build material is applied thereon (either directly onto the print bed or onto one or more layers of build material already deposited thereon from previous runs) ready for application with a solvent or binder. The powder roller may then be returned back to its initial position, proximal to the powder supply bed 120, ready for the next run.

The printing nozzle 150 is configured to eject the solvent or binder onto the layer of powder-based build material applied via the powder distributor 140 onto the print bed 130. In the illustrated embodiment, the printing nozzle 150 is configured to eject the solvent or binder as a series of liquid droplets, with each droplet having a droplet size of approximately 100 microns. This feature enables the aforementioned apparatus to achieve an optimal part resolution. However, it shall be appreciated that in other embodiments, other suitable nozzle types may be used. For example, in some embodiments, standard 720 DPI or 300x600 DPI resolution nozzles may be used.

The printing nozzle 150 typically incorporates a chemical resistant material which is resistant to the solvent being used for a given application. In some embodiments, the printing nozzle may be formed from a stainless steel material or may be coated with a chemical-resistant coating such as Parylene. This helps to improve the longevity of the apparatus.

In the illustrated embodiment, the printing nozzle 150 is provided at a fixed vertical position and is supported via a series of guide rails 150a. The printing nozzle 150 is also linearly moveable relative to the print bed 130 along said guide rails, via a ball-screw actuator or the like, to allow the printing nozzle 150 to apply solvent or binder across the entire top surface of the print bed 130.

In the illustrated embodiment, a single printing nozzle 150 is provided which spans a distance which is less than a length and width of the print bed 130. As such, the printing nozzle is moveable relative to the print bed in two axial directions, those being along the lateral X-axis and along the lengthwise Y-axis. This enables the printing nozzle 150 to effectively apply solvent across the entirety of the print bed 130.

In other embodiments apparatuses featuring multiple printing nozzles (such as an array of printing nozzles) may be envisaged. In such embodiments where the one or more printing nozzles span across the full width or length of the print bed 130, the printing nozzles may be moveable in a single axial direction, either along the lateral X-axis or along the lateral Y-axis since in these circumstances, freedom of movement along a single axis would be sufficient to enable the one or more printing nozzles to effectively apply solvent to the entirety of the print bed 130. Furthermore, in embodiments wherein an array of printing nozzles is utilised which span across the full width and length of the print bed 130, the printing nozzles 150 may be fixed in the lateral X-axis and lengthwise Y-axis directions relative to the print bed 130.

Furthermore, in embodiments where the printing bed 130 is provided at a fixed vertical position, it shall be appreciated that the printing nozzle 150 may also be moveable along the vertical Z-axis, for example via a guide rail and ball-screw actuator system, so that the height of the printing nozzle 150 can be adjusted after each run to account for the incrementally increasing height of the AM part manufactured via the apparatus 100.

A controller 170 is also provided for controlling the powder distributor 140 to sequentially apply layers of powder-based build material onto the print bed 130 and for controlling the printing nozzle 150 to sequentially apply solvent or binder to the layers of powder-based build material to cause the constituent particles of the powder-based build material to join together to create an additively manufactured part, as will be described in greater detail in the associated method section below.

The controller 170 may be provided in the form of a control panel to allow for manual control via an operator, or may be provided in the form of a computer for running an associated computer programme for commanding the apparatus to perform the aforementioned method.

In the illustrated embodiment, an extractor 132 is also provided for extracting the solvent or binder from the layers of build material formed during the manufacturing process. In the illustrated embodiment, the extractor 132 is provided in the form of a heating element located within the print bed 130. Once activated, the heating element is configured to heat the print bed 130. The heat from the print bed 130 then in turn becomes conducted by the part causing its temperature to rise. Once the temperature of the part reaches a boiling temperature of the solvent or binder, the solvent or binder located within the part will being to evaporate thereby facilitating its extraction from the part. In this manner, the removal of solvent or binder from the AM part can be easily initiated.

In other embodiments, it shall be appreciated that other forms of extractor may be used.

It shall also be appreciated that in some embodiments, the heating element may be provided as a separate component external to the print bed, rather than being embedded within it.

Optionally, a powder collection bed 160 may also be provided to allow for any powder-based build material which does not end up forming part the AM part to be collected after each processing run. The excess powder is accumulated in the powder collection bed 160 where it is delivered by the powder distributor 140. Once collected, the unprocessed powder may be recycled back into the powder supply bed 120 (either manually or via a suitable return mechanism) for re-use or may be discarded.

In the illustrated embodiment, the powder collection bed 160 is moveable linearly in the vertical direction, for example via a ball-screw actuator 160a, so that the height of the powder collection bed 160 can be adjusted based on a height of the print bed 130. In other embodiments however, the powder collection bed 160 may be instead be fixed.

In the illustrated embodiment, the print bed 130, powder distributor 140 and printing nozzle 150 are provided within a sealed chamber 102. In the illustrated embodiment, the powder supply bed 120 and powder collection bed 160 are also located within the sealed chamber 102, although it shall be appreciated that in other embodiments the powder supply bed 120 and/or powder collection bed 160 may be located external from the sealed chamber 102 with a suitable communication means being provided to allow the powder-based build material to be passed to the powder distributor 140 and to allow for unprocessed powder to be passed from the sealed chamber 102 to the powder collection bed 160.

The sealed chamber 102 further comprises a temperature control element, which in the illustrated embodiment is provided in the form of a heater 104, and a vacuum device 106 to allow for better control of the atmospheric conditions within the sealed chamber 102. For example, the heater 104 and vacuum device may be controlled to ensure that the atmospheric conditions within the sealed chamber remain below a boiling temperature of the solvent or binder (at a given pressure) to prevent evaporation of the solvent during the application process which can be detrimental to the resolution of a given build layer. It shall also be appreciated that in some embodiments, the temperature control element may comprise a cooling device alongside, or in place of, the heater 104.

The temperature control device may also be movable within the sealed chamber 102 as shown in Figure 1. In this case, the heater 104 is supported by respective guide rails 104a which extend across a width and length of the sealed chamber 102 such that the heater 104 is linearly moveable in the axial X and Y axis directions. By moving the heater 104 across the sealed chamber 102, the heater 104 can target heating power onto required area where the printing nozzle 150 has dispensed the solvent ink. This helps to evaporate the dispensed solvent ink faster once it has dissolved the material and avoids further dissolution of the material by the solvent. This control may be performed manually by a user or, in other embodiments, may be performed via a controller (such as the controller 170 described below) based on temperature or pressure data obtained from within the sealed chamber 102 (collected from one or more sensors or the like).

However, it shall be appreciated that in other embodiments, the temperature control element may instead be moveable in only one axial direction, in all three axial directions or may be completely fixed within the sealed chamber.

The provision of a sealed chamber 102 also helps to prevent the vaporised solvent or binder from being lost following extraction. To this end, in the illustrated embodiment the apparatus 100 further comprises a recovery system 180 for facilitating recovery of the evaporated solvent or binder following its extraction from the respective build layers which make up the AM part.

The recovery system 180 may take a number of suitable forms. In some embodiments, the recovery system may comprise a condenser for condensing the evaporated solvent back into a liquid state. In other embodiments, the recovery system 180 may comprise a water column and a suitable conveying mechanism for conveying the evaporated solvent through the water column as so the cause the evaporated solvent to condense.

In the illustrated embodiment, the recovery system 180 comprises conduit for returning the condensed solvent back into the liquid reservoir. However, in other embodiments, the condensed solvent may be collected in a separate reservoir ready for disposal. In further embodiments, the evaporated solvent may not be condensed and may instead be passed through a filter (such as a carbon filter) to capture the solvent and any harmful chemicals, with the remaining gases being allowed to exit the sealed chamber and be returned into the external atmosphere.

A method of manufacturing an AM part using the apparatus according to an aspect of the present disclosure shall now be described with reference to Figures 2 to 4.

In a first step 201 of the aforementioned method, a first layer of powder-based build material is applied onto the print bed 130 via the powder distributor 140.

For solvent-based methods, the powder-based build material can be provided in any form, provided that the material chosen is capable of being dissolved by a given solvent. Typically, the powder-based build material will be a polymeric material such as TPU or PA12.

Similarly, for binder-based methods wherein the binder is a polymerising agent, any suitable saturated polymeric material may be used, provided that said material is capable of becoming polymerised upon application of the polymerising agent during the build process.

Some embodiments of suitable materials for use as a build material for the aforementioned method include Acrylonitrile butadiene styrene (ABS); Polyethylene terephthalate glycol; Perfluoroalkoxy Polymer; polylactic acid; Polypropylene; Polyether ether ketone (PEEK); Polyether ketone ketone (PEKK); Polycarbonate: Polyethylene; Nylon 6; Nylon 66; Nylon 11; Nylon 12; Nylon 46; Nylon 6/12; Polyphthalamide; Thermoplastic polyurethane (TPU); Thermoplastic polyamide; and Thermoplastic copolyester.

In a second step 202, a solvent or binder is applied.to a selected area of the first layer of powder-based build material based on a desired geometry of the part to be manufactured. The area to which the solvent or binder is applied is typically controlled via the controller 107 based on the geometry of the CAD model of the part.

The solvent or binder is provided in liquid form and is chosen so at to be capable of joining constituent particles of the build material upon application, as will be described in greater detail below, in order to form a processed build layer.

Some embodiments of suitable solvent and binder types include 1,1,1,3,3,3-Hexafluoroisopropanol, Acetone, one or more acetals (such as Propionaldehyde diethyl acteal), isopropyl alcohol, Dichloromethane, Cyclohexanol, Ethylene glycol, Hexylene glycol, Dioxane, Anisole, Pentan-1-ol, 2-Phenoxy ethanol, N-anyl alcohol, Sulphuric acid, M-cresol, Formic acid, Butylal, Trifluoroacetic acid, Benzyl alcohol, glycol ether, DMSO, 1,2,4 Trichlorobenzene, Tetrahydrofuran, 2-methyltetrahydrofuran, Xylene, 1-methoxy-2-propanol, Triethyleneglycol, and 2,2,2-Trifluoro ethanol, Acetophenone, Dibutoxymethane, Propionaldehyde diethyl Acetal, Acrolein Diethyl Acetal, Aminoacetaldehyde Dimethyl acetal, Anisaldehyde Dimethyl Acetal, Ethyl Diethoxy acetate, Citral Diethyl Acetal, 2,2 -Diethoxyacetophenone, although it shall be appreciated that other solvents or binders may be used.

As specified previously, the solvent or binder as typically applied as a series of liquid droplets (generally having a size of approximately 100 microns) although the size of each droplet may vary depending on the respective properties of the chosen build materials. Typically, the size of the liquid droplets will be chosen based on one or more of a chemical composition of the powder-based build material; a particle size of the powder-based build material; a melting point of the powder-based build material; a glass transition temperature of the powder-based build material; and/or a density of the powder-based build material.

During the application step 202, the atmospheric conditions within the sealed chamber 202 are controlled by the controller 107 such that the solvent and/or binder are maintained in a liquid state. Typically, the atmospheric conditions within the sealed chamber are maintained between -10°c and 100°c in temperature, and between 1 mbar and 1000 mbar (1 atm) pressure. This helps to prevent unwanted evaporation of the solvent and/or binder and thereby helps the method to achieve an improved part resolution. However, it shall be appreciated that the precise atmospheric conditions maintained within the sealed chamber may vary depending on the particular boiling and freezing points of the solvent or binder used for a particular application.

Control or adjustment of some of the properties of the solvent or binder may also be required prior to application to help ensure the solvent or binder features the required rheological properties so that the solvent or binder is able to sufficiently "wet" the build material following application without spreading too much, which can be detrimental to the resolution of the part.

Although the optimal rheological properties of the solvent or binder will differ somewhat based upon which material is being used as the build material, typically it is desirable for the solvent or binder to exhibit the following properties in order to obtain an optimal printing resolution: * Dynamic viscosity (mPa.$) -0.1 to 10,000, preferable from 1 to 100 * Kinematic viscosity (mm2/s) -0.1 to 10,000, preferable from 1 to 100 * Density (g/cm3) -0.1 to 10, and preferably 0.7 to 2 * Surface Tension (N) -10 to 100, and preferably 20 to 50 The main constituents of the solvent are solvent, pigments and additives/agents. This is to help maintain solvent properties for the efficient printability, solubility and adding of function or colour onto the build material. The concentration of these additives may be from 1% to 99%, preferably from 5% to 35%.

In some instances, one or more additives 300a may be added to the solvent or binder material 300 prior to application as is shown in Figure 3.

In some embodiments, a viscosity enhancer may be added to the solvent or binder prior to application to help achieve optimal droplet ejection and reduce splatter or leakage during application.

Suitable viscosity enhancers include one or more of an oil; an alcohol; water; gelatin; an acid; a base; guar gum; starch; cellulose; a silicate; pectin; a polymer; a copolymers; and/or glycol.

Similarly, one or more additives may be added to the solvent or binder. As with the kinematic and dynamic viscosity mentioned above, achieving a density between 0.1 and 10 g/cm3 (and preferably between 0.8 to 2 g/cm3) helps to achieve optimal droplet ejection and reduce splatter or leakage during application. Meanwhile, tailoring the surface tension of the solvent or binder so that it is within the aforementioned range helps to promote rapid meniscus recovery at high ejection frequencies whilst also helping to prevent the solvent or binder from spreading following application thereby improving the resolution of parts obtained via the method.

Suitable additives for this purpose can include one or more of water; an alcohol; an acid; a base; an oil; a polymer; a co-polymer; a salt; a solvent; an acrylate; an ionic liquid and/or a silicone.

It is also preferable for the pH level of the solvent or binder to be as close to 7 (or neutral) as possible to help deterioration of the printing nozzle 150 and other components of the apparatus during use. As such, one or more chemical agents may also be added to the solvent or binder to bring the pH of the solvent or binder to help reduce such effects. Depending on the application, the pH of the solvent or binder will typically range from 1 to 9, although values close to 7 are generally preferable when looking to maintain the longevity of the apparatus.

Suitable pH control agents may include one or more of an organic acid; a mineral acids; a base; a neutralising agent; a buffering agent; a solid powder; a salt; water and/or an oil.

It shall also be appreciated that other additives such as colourants, carbon, metal or ceramic particles as well as various other solvents, co-solvents, surfactants, functionalising agents, oils, water, resin, plasticisers and/or binding agents may also be added to the solvent or binder in order to tailor the physical and/or rheological properties of the solvent or binder prior to a particular printing application.

Conductive particles such as carbon or silver particles, or other suitable additives, may also be added to the solvent or binder to bring the conductivity of the solvent or binder into the range of 1 x 10-10 to 1 x103 0.m, and more typically into the range of 1 x 10-8 to 1 x 10-6 Q.m.

Meanwhile, colourants such as dyes, pigment particles and/or UV inks to apply a colouring effect to the part manufacturing via the aforementioned method may also be applied to the solvent or binder based on the aesthetic considerations of the end user. 20 The temperature of the applied solvent depends on the type of solvent but is between 10°C and 250°C. Preferably between 30°C and 140°C. In some embodiments, the solvent may be heated (for example via a heating element provided within the liquid reservoir of the apparatus) prior to application. This helps to achieve better dissolution of the build material during printing. The temperature of the applied solvent is kept below its boiling point temperature to avoid vaporising it during the application.

In the cases where superheated solvent temperatures may be applied, the sealed chamber 102 may be applied with overpressure to increase the boiling point of the solvent.

The solvent may be applied in the form of steam or vapor onto the built material. This would make the dissolution of the built material faster and increase the accuracy of the printing.

Once a solvent or binder having the desired properties has been obtained and applied to the first layer of powder-based build material, the solvent or binder acts on the build material to form a first build layer as shown in Figure 4.

In the case where a solvent is used, as solvent droplets 300 are applied onto the layer of build material 400, adjacent particles of build material (which become "wetted" by the solvent) begin to dissolve and fuse together thereby creating a first build layer 500, see Figure 4c).

Conversely, in cases where a binder in the form of a polymerising agent is used, as the binder droplets are applied onto the layer of saturated polymeric build material, adjacent build material particles become polymerised thereby creating the first build layer much in the same way as is illustrated in Figure 4c).

Once the first build layer 500 has been obtained, the solvent or binder is extracted during step 204 to stop any further unwanted dissolution or polymerisation which could be detrimental to the resolution of the final part. In the illustrated embodiment, the solvent or binder is extracted via heating the print bed 130 to a temperature above a boiling point of the solvent or binder in order to cause the solvent or binder to evaporate the solvent or binder which is then recovered via the recovery system 180. The heating of the print bed 130 is controlled via the controller 170 (although in some embodiments a separate controller may be used) to ensure that the temperature of the print bed 130 does not exceed a melting point of the build material, which could cause damage to the part.

In some embodiments, the un-processed build material 600 may also be removed from the print bed 130 for collection in the powder collection bed 160 prior to the next run.

A second layer of powder-based build material 700 is then applied on top of the first build layer 500 during step 205. It shall be appreciated that whilst the illustrated embodiment depicts a method wherein the solvent or binder is extracted prior to the second layer of build material being applied, in some embodiments, the extraction step may be performed after the second layer of build material has been applied. Furthermore, in other embodiments, the solvent or binder may be extracted even later, for example after third or even fourth layers of build material have been applied.

When determining the frequency at which solvent or binder is extracted, the user must weigh up the relative importance of solvent/binder extraction compared with the throughput (or speed) of the manufacturing process. For example, extracting the solvent or binder during each run allows the solvent or binder to be be more easily extracted since there are fewer build layers through which the solvent or binder must pass in order to be extracted. This helps to prevent solvent or binder from becoming trapped deep within the matrix of the part which can adversely impact the homogeneity and structural integrity of the part. Conversely, performing the extraction step after a number of runs helps to improve processing times and throughput, but can risk more solvent or binder becoming trapped within the matrix.

After step 205, the solvent or binder is then applied to the second layer of powder-based build material 700 to form a second build layer 800 on top of the first build layer 500, as is shown in Figures 4d) to 4f). The process is then repeated sequentially (to create third, fourth, fifth layers and so on) until an AM part having the desired geometry has been achieved. In some instances, the first and second build layers may have substantially the same geometry or, in other instances, may have different geometries depending on the shape of the part being created via the method. It shall also be appreciated that the extraction step may be performed before or after the application of a further layer of powder-based build material for each sequential run, or may be performed less frequency (for example every 2, 3rd or 41" run).

In this manner, the inventors of the present disclosure have realised an apparatus and method which enables additively manufactured parts to be created without the need for expensive laser heating equipment. Furthermore, since the present disclosure does not rely on heating in order to join the build material together, and hence does not suffer from the same issues of residual heating, the apparatus and method of the present disclosure is able to achieve an improved part resolution when compared to know methods.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMS1. A method of additively manufacturing a part comprising: a) providing a first layer of powder-based build material; b) providing a solvent or binder, said solvent or binder being provided in liquid form and being capable of joining constituent particles of the powder-based build material upon application to form a processed build layer; c) applying the solvent or binder to a selected area of the first layer of powder-based build material to create a first build layer, said selected area being chosen based on a desired geometry of the addifively manufactured part; d) providing a second layer of powder-based build material on top of the first build layer; and e) applying the solvent or binder to a selected area of the second layer of powder-based build material so create a second build layer on top of the first build layer, said selected area also being chosen based on a desired geometry of the addifively manufactured part.
2. The method according to claim 1, wherein the method further comprises, between steps c) and d), extracting excess solvent or binder, applied during step c), from the first build layer, or wherein the method further comprises, between steps d) and e), extracting excess solvent or binder, applied during step c), from the first build layer.
3. The method according to claim 1 or 2, wherein the method further comprises, after step e), extracting excess solvent or binder, applied during step e), from the second build layer, or wherein the method further comprises, after step e), extracting excess solvent or binder, applied during steps c) and e), from the first and second build layers.
4. The method according to any preceding claim, wherein the method further comprises, after step e), providing a third layer of powder-based build material on top of the second build layer.
5. The method according to any preceding claim, wherein the selected area of the first layer of powder-based build material to which the solvent or binder is applied during step c) has a first geometry, and wherein the selected area of the second layer of powder-based build material to which the solvent or binder is applied during step e) has a second geometry, said second geometry being different to the first geometry.
6. The method according to any preceding claim, wherein the solvent is selected such that, upon application of the solvent to the powder-based build material, adjacent particles of the powder-based build material within the selected area become dissolved and fuse together to create the first and second build layers.
7. The method according to any preceding claim, wherein steps c) and e) are performed within a sealed chamber, and wherein the method further comprises, during steps c) and e), controlling the atmospheric conditions within the sealed chamber such that the solvent or binder is maintained in a liquid state.
8. The method according to any preceding claim, wherein the extraction of excess solvent or binder comprises heating the additively manufactured part to a temperature above a boiling temperature of the solvent or binder and/or reducing the pressure within the sealed chamber to cause the solvent or binder to evaporate.
9. The method according to any preceding claim, wherein the solvent or binder is applied as a series of liquid droplets, optionally having a size of approximately 100 microns, and wherein the size of said droplets is selected based on at least one property of the powder-based build material.
10. The method according to any preceding claim, wherein the method further comprises, prior to steps c) and e), adding a pH control agent to the solvent or binder to bring the pH of the solvent or binder into the range of 1 to 9, and optionally to a valve of approximately 7.
11. The method according to any preceding claim, wherein the method further comprises, prior to steps c) and e), adding a viscosity enhancer to the solvent or binder to bring the kinematic viscosity of the solvent or binder into the range of 0.1 to 10,000 mm2/s and/or to bring the dynamic viscosity of the solvent or binder into the range of 1 to 10,000 mPa.s.
12. The method according to any preceding claim, wherein the method further comprises, prior to steps c) and e), adding an additive to the solvent or binder to bring the density of the solvent or binder into the range 0.1 to 10 g/crna; and, optionally, into the range of 0.8 to 2 g/crna.
13. The method according to any preceding claim, wherein the method further comprises, prior to steps c) and e), adding an additive to the solvent or binder to bring the surface tension of the solvent or binder into the range of 10 to 100 N; and, optional, into the range of 20 to 50N.
14. The method according to any preceding claim, wherein the method further comprises, prior to steps c) and e), applying a colouring agent to the solvent or binder.
15. The method according to any preceding claim, wherein the method further comprises heating the solvent or binder prior to application, optionally to a temperature in the range of 10°C to 250°C, and further optionally to a temperature in the range of 30°C and 140°C.
16. The method according to any preceding claim, wherein the powder-based build material is a saturated polymeric material, and wherein the binder is a polymerising agent selected such that, upon application of the polymerising agent to the powder-based build material, adjacent particles of the powder-based material within the selected area become polymerised to create the first and second build layers.
17. The method according to any preceding claim, wherein the powder-based build material comprises at least one of Acrylonitrile butadiene styrene, Polyethylene, terephthalate glycol, Perfluoroalkoxy Polymer, polylactic acid, Polypropylene Polyether ether ketone, Polyether ketone ketone, Polycarbonate, Polyethylene, Nylon 6, Nylon 66, Nylon 11, Nylon 12, Nylon 46, Nylon 6/12, Polyphthalamide, Thermoplastic polyurethane, Thermoplastic polyamide Thermoplastic copolyester.
18. An additively manufactured part obtainable according to the method of any of claims 1 to 17.
19. An additive manufacturing apparatus for performing the method of claims 1 to 17, the apparatus comprising: a print bed for receiving a layer of powder-based build material; a powder supply bed for containing a powder-based build material; a liquid reservoir for containing a solvent or binder; a powder distributor for applying a layer of powder-based build material from the powder supply bed onto the print bed; a printing nozzle for applying the solvent or binder onto the layer of powder-based build material applied onto the print bed; a controller configured to control the powder distributor to sequentially apply layers of powder-based build material onto the print bed and further configured to control the printing nozzle to sequentially apply solvent or binder to selected areas of the powder-based build material to cause constituent particles of the powder-based build material to join together to create an additively manufactured part formed from sequential build layers.
20. The apparatus according to claim 19, further comprising an extractor configured to extract the solvent or binder from said build layers. 15
21. The apparatus according to claim 20, wherein the extractor comprises a heating element configured to heat the additively manufactured part to a temperature above a boiling temperature of the solvent or binder to cause the solvent or binder contained therein to evaporate, and optionally wherein the heating element is located within the print bed.
22. The apparatus according to any of claims 19 to 21, wherein the printing nozzle comprises a chemical resistant material (such as stainless steel or parylene).
23. The apparatus according to any of claims 19 to 22, wherein the printing nozzle is configured for ejecting the solvent or binder as a series of liquid droplets, and optionally wherein the liquid nozzle is configured to achieve a droplet size of approximately 100 microns.
24. The apparatus according to any of claims 19 to 23, wherein the apparatus comprises a sealed chamber containing the print bed, powder distributor and printing nozzle, wherein the apparatus further comprises a temperature control element and/or a vacuum device in operable communication with the sealed chamber, and wherein the controller is configured to control the temperature control element and/or vacuum device such that, when the solvent or binder is applied to the powder-based build material, the solvent or binder are maintained in a liquid state.
25. The apparatus according to claim 24, wherein the apparatus further comprises a condenser, and wherein the condenser is configured to condense evaporated solvent or binder from within the sealed chamber to facilitate its recovery.