FIELD

The present disclosure relates to methods of colouring additively manufactured parts and an apparatus and system for performing the same.

BACKGROUND

In recent years, the additive manufacturing industry has seen an increased demand for coloured finishes for additively manufactured parts in order to meet the branding and aesthetic considerations of the end user.

One known method for colouring additively manufactured parts involves immersing said parts in a heated liquid, typically a mixture of dye and water, for an extended period of time.

However, additively manufactured parts tend to exhibit a rough surface finish which can make it more difficult for dyes to achieve a homogeneous dispersion across the surfaces of such parts. As such, additively manufactured parts coloured in this manner tend to exhibit sub-optimal colouring.

One known method for addressing this problem is to colour the additively manufactured parts in a pressurised environment, typically via a pressure chamber. However, such systems tend to be expensive.

In addition, both of the aforementioned methods require dyes to be pre-mixed in order to obtain a specific part colour and are therefore typically constrained to colours which are stocked by a given service provider. Consequently, such methods are poorly suited for efficiently colouring parts “to order” where a user may require a unique or bespoke colour to be applied to a part.

As such, it is an aim of the present disclosure to address at least one of the aforementioned problems with known colouring methods. SUMMARY

A first aspect of the present disclosure provides a method of colouring an additively manufactured part, the method comprising: providing an additively manufactured part having a surface to be coloured; performing a smoothing step, wherein a roughness of the surface to be coloured is reduced; and performing a colouring step, after the smoothing step, wherein the colouring step comprises: a) providing a first dyeing liquid comprising a first dye; b) heating the first dyeing liquid to a desired temperature; and c) immersing the surface of the additively manufactured part into the first dyeing liquid so as to colour said surface, and wherein the colouring step is performed at ambient pressure.

Advantageously, by smoothing the part prior to the colouring step, it has been found that a more homogeneous dispersion of dye at the surface of the part can be achieved when colouring at ambient pressures.

As a result, a better quality colour finish can be obtained without the need for expensive pressurising equipment

In exemplary embodiments, the surface to be coloured has a first surface roughness prior to the smoothing step, and a second surface roughness after the smoothing step, and wherein the second surface roughness is smoother than the first surface roughness

In exemplary embodiments, the additively manufactured part comprises an un-sintered material and the method further comprises, prior to the smoothing step, a de-powdering step, wherein at least some of the un-sintered material is removed from the surface to be coloured.

In exemplary embodiments, the additively manufactured part comprises a support material, and the method further comprises, prior to the smoothing step, a de- powdering step, wherein at least some of the support material is removed from the surface to be coloured.

In exemplary embodiments, the smoothing step comprises applying a chemical onto the surface to be coloured so as to transform at least some of the surface material from a first state, wherein said surface material is substantially rigid, to a second state, wherein said surface material is capable of movement and re-distributing the transformed surface material across at least a portion of the surface to be coloured.

In exemplary embodiments, the smoothing step comprises applying a chemical vapour onto the surface to be coloured in order to transform at least some of the surface material from the first state to the second state.

In exemplary embodiments, the smoothing step comprises condensing the chemical vapour onto at least a portion of the surface to be coloured in order to transform at least some of the surface material from the first state to the second state.

In other embodiments, the smoothing step may comprises immersing the additively manufactured part in an acid or solvent bath.

In further embodiments, the smoothing step may be performed via a mechanical- abrasive smoothing method (e.g. vibratory smoothing or media blasting).

In exemplary embodiments, the smoothing step further comprises placing the additively manufactured part into a processing chamber, introducing the chemical vapour into said processing chamber, and increasing the pressure within the processing chamber so as to assist application of the chemical onto the surface to be coloured.

In exemplary embodiments, after the chemical vapour has been introduced into the processing chamber, the absolute pressure within the processing chamber is increased into the range of 200 mBar to 1000 mBar.

In exemplary embodiments, the smoothing step further comprises cooling the additively manufactured part prior to the application of the chemical vapour. Advantageously, pre-cooling the additively manufactured part helps to create an energy difference between the part and the chemical vapour, which promotes condensation of the chemical vapour onto the surface of the part.

In exemplary embodiments, the method further comprises, between the smoothing step and the colouring step, a solvent removal step, wherein solvent is removed from the surface of the additively manufactured part.

In exemplary embodiments, the solvent removal step comprises heating the additively manufactured part to a temperature above a boiling point of the chemical.

Advantageously, heating the additively manufactured part to a temperature above a boiling point of the chemical provides an efficient method for removing the chemical from the surface of the additively manufactured part.

In exemplary embodiments, the solvent removal step comprises decreasing an absolute pressure within the processing chamber into the range of 1 mBar to 600 mBar.

In exemplary embodiments, the solvent removal step comprises decreasing an absolute pressure within the processing chamber into the range of 50 mBar to 600 mBar.

Advantageously, decreasing the pressure within the processing chamber helps to further promote evaporation of the chemical from the surface of the additively manufactured part.

In addition, at lower pressures, chemicals tend to evaporate at lower temperatures. Therefore, since chemicals can be evaporated from the surface of the additively manufactured part at lower temperatures, lowering the pressure within the processing chamber helps to reduce the likelihood of the additively manufactured parts being damaged due to excessive heat during solvent removal.

In exemplary embodiments, the colouring step further comprises: d) removing the additively manufactured part from the first dyeing liquid; e) providing a second dyeing liquid comprising a second dye, said second dye having a different colour to that of the first dye; f) heating the second dyeing liquid to a desired temperature; and g) immersing the surface coloured using the first dyeing liquid into the second dyeing liquid so as to alter the colour of the surface of the additively manufactured part.

Advantageously, by performing multiple colouring operations, it is possible to achieve a wider range of part colours without having to pre-mix dyes, thereby improving processing efficiency and flexibility.

In exemplary embodiments, the colouring step may further comprise, between steps d) and g), a step of removing excess dye from the surface of the additively manufactured part.

In exemplary embodiments, the step of removing excess dye from the surface of the additively manufactured part is performed via rinsing the surface of the additively manufactured part with a solvent (e.g. water).

Advantageously, the removal of excess dye between dyeing runs helps to prevent any cross contamination between dyeing liquids.

Advantageously, the part may be dried at elevated temperatures after step d) or after rinsing the part with water, to ensure any trace of water or previously used dye are removed.

In exemplary embodiments, the first and second dyes are CMYK dyes.

Advantageously, the use of CMYK dye colours helps to further increase the range of part colours which can be achieved using the method, without requiring pre-mixing.

In other embodiments, the first and second dyes could instead use other colour palettes, e.g. CMYKO (Cyan Magenta Yellow Black Orange), RGB or other dyes.

In exemplary embodiments, the method further comprises, between steps d) and e), a cooling step wherein the additively manufactured part is cooled. In exemplary embodiments, between steps d) and e), the additively manufactured part is cooled to a temperature of approximately 30°C.

In exemplary embodiments, the colouring step comprises adjusting one or more colouring parameters based on a desired final colour of the surface to be coloured, said colouring parameters including: a concentration of the first and/or second dye; an immersion time of the surface of the additively manufactured part in the first and/or second dyeing liquid; and/or a temperature of the first and/or second dyeing liquid.

Advantageously, adjusting such colouring parameters helps to control the final colour of the additively manufactured part based on a user’s colour requirements, therefore further increasing the range of part colours which can be achieved using the method.

In exemplary embodiments, the colouring step comprises adjusting an immersion time of the surface of the additively manufactured part in the first and/or second dyeing liquid based on a desired final colour of the surface to be coloured.

Advantageously, by controlling the colour of the part based on an immersion time, the use of excess dye and temperature can be better avoided, which helps to improve the economy of the method.

In other embodiments, the colouring step comprises adjusting a temperature of the first and/or second dyeing liquid based on a desired final colour of the surface to be coloured.

In other embodiments, the colouring step comprises adjusting a dye concentration of the first and/or second dyeing liquid based on a desired final colour of the surface to be coloured.

In exemplary embodiments, the colouring step comprises heating the first and/or second dyeing liquids to a temperature in the range of 60°C and 100°C.

Advantageously, temperatures in the range of 60°C to 100°C have been found to help efficiently colour additively manufactured parts whilst also helping to reduce the occurrence of part damage during the colouring operation. In exemplary embodiments, the colouring step comprises heating the first and/or second dyeing liquids to a temperature in the range of 70°C to 90°C.

In exemplary embodiments, the colouring step comprises heating the first and/or second dyeing liquids to a temperature of 90°C.

Advantageously, temperatures in the range of 70°C to 90°C have been found to help even more efficiently colour additively manufactured parts whilst also further helping to reduce the occurrence of part damage during the colouring operation.

In exemplary embodiments, the first and second dyeing liquids are maintained at the same temperature.

In exemplary embodiments, the first and second dyeing liquids are maintained at a temperature in the range of 60°C and 100°C.

In exemplary embodiments, the first and second dyeing liquids are maintained at a temperature in the range of 70°C to 90°C.

In exemplary embodiments, the first and second dyeing liquids are maintained at a temperature of 90°C.

In exemplary embodiments, the concentration of the second dye in the second dyeing liquid is maintained at the same concentration as the first dye in the first dyeing liquid.

In exemplary embodiments, the concentration of the first dye within the first dyeing liquid is approximately 1 g/L.

In exemplary embodiments, the concentration of the second dye within the second dyeing liquid is approximately 1 g/L.

In exemplary embodiments, the concentration of the first dye within the first dyeing liquid is approximately 2 g/L.

In exemplary embodiments, the concentration of the second dye within the second dyeing liquid is approximately 2 g/L. Advantageously, concentrations of approximately 2 g/L help to provide improved colouring when using lighter coloured dyes. In exemplary embodiments, the concentration of the first dye within the first dyeing liquid is provided in the range of 1 g/L to 5 g/L.

In exemplary embodiments, the concentration of the second dye within the second dyeing liquid is provided in the range of 1 g/L to 5 g/L.

In exemplary embodiments, the first and/or second dye is an acid-based dye.

In exemplary embodiments, the first and/or second dyeing liquid comprises an acid. In exemplary embodiments, the acid is an acetic acid, formic acid, citric acid or a carbonic acid.

In exemplary embodiments, the acid may be a mixture of acids. Advantageously, providing an acid within the dyeing liquid helps to improve the adhesion of the dye onto the part

In exemplary embodiments, the liquid of the first and/or second dyeing liquid comprises at least one of water; iso-propyl alcohol; deionised water or acetone.

In exemplary embodiments, the colouring step further comprises agitating the first and/or second dyeing liquid.

Advantageously, agitating the part within the liquid helps to achieve a more uniform coating of the dye onto the part, thereby further improving the colouring finish.

Furthermore, agitation also helps to fully dissolve the dye into the dyeing liquid if the dye was is added in a powder form. In exemplary embodiments, the first and/or second dyeing liquid are agitated via a stirrer. In other embodiments, the first and/or second dyeing liquids may be agitated via liquid jets.

A second aspect of the present disclosure provides a method of colouring an additively manufactured part, the method comprising: a) providing an additively manufactured part having a surface to be coloured; b) providing a first dyeing liquid comprising a first dye; c) heating the first dyeing liquid to a desired temperature; d) immersing said surface of the additively manufactured part into the first dyeing liquid so as to colour said surface, e) removing the additively manufactured part from the first dyeing liquid; f) providing a second dyeing liquid comprising a second dye, said second dye having a different colour to that of the first dye; g) heating the second dyeing liquid to a desired temperature; and h) immersing said surface of the additively manufactured part coloured using the first dyeing liquid into the second dyeing liquid so as to alter the colour of said surface.

Advantageously, by performing multiple, iterative colouring operations, it is possible to achieve a wider range of part colours without having to pre-mix dyes, thereby improving processing efficiency and flexibility. In exemplary embodiments, the method may further comprise, between steps e) and h), a step of removing excess dye from the surface of the additively manufactured part.

In exemplary embodiments, the step of removing excess dye from the surface of the additively manufactured part is performed via rinsing or drying the surface of the additively manufactured part with a solvent (e.g. rinsing with water or drying with hot air).

Advantageously, the removal of excess dye between dyeing runs helps to prevent any cross contamination between dyeing liquids. In exemplary embodiments, the first and second dyeing liquid are provided in the same liquid bath.

In other embodiments, the first and second dyeing liquid are provided in separate liquid baths.

In exemplary embodiments, the method further comprises, between steps e) and f), a cooling step wherein the additively manufactured part 10 is cooled.

In exemplary embodiments, between steps e) and f), the additively manufactured part is cooled to a temperature of approximately 30°C.

In exemplary embodiments, the additively manufactured part is removed from the first dyeing liquid via draining the first dyeing liquid from the liquid bath.

In exemplary embodiments, the additively manufactured part is removed from the first dyeing liquid via physically retrieving the additively manufactured part from the liquid bath.

In exemplary embodiments, the first and second dyes are CMYK dyes.

Advantageously, the use of CMYK dye colours helps to further increase the range of part colours which can be achieved using the method, without requiring pre-mixing

In other embodiments, the first and second dyes may use other colour palettes, e.g. CMYKO, RGB or other dyes.

In exemplary embodiments, the colouring step comprises adjusting one or more colouring parameters based on a desired final colour of the surface to be coloured, said colouring parameters including: a concentration of the first and/or second dye; an immersion time of the surface of the additively manufactured part in the first and/or second dyeing liquid; and/or a temperature of the first and/or second dyeing liquid.

Advantageously, adjusting such colouring parameters helps to further control the final colour of the additively manufactured part based on a user’s colour requirements, therefore further increasing the range of part colours which can be achieved using the method.

In exemplary embodiments, the colouring step comprises adjusting an immersion time of the surface of the additively manufactured part in the first and/or second dyeing liquid based on a desired final colour of the surface to be coloured.

Advantageously, by controlling the colour of the part based on an immersion time, the use of excess dye and temperature can be better avoided, which helps to improve the economy of the method.

In other embodiments, the colouring step comprises adjusting a temperature of the first and/or second dyeing liquid based on a desired final colour of the surface to be coloured.

In other embodiments, the colouring step comprises adjusting a dye concentration of the first and/or second dyeing liquid based on a desired final colour of the surface to be coloured.

In exemplary embodiments, the colouring step comprises heating the first and/or second dyeing liquids to a temperature in the range of 60°C and 100°C.

Advantageously, temperatures in the range of 60°C to 100°C have been found to help efficiently colour additively manufactured parts whilst also helping to reduce the occurrence of part damage during the colouring operation.

In exemplary embodiments, the colouring step comprises heating the first and/or second dyeing liquids to a temperature in the range of 70°C to 90°C.

Advantageously, temperatures in the range of 70°C to 90°C have been found to help even more efficiently colour additively manufactured parts whilst also further helping to reduce the occurrence of part damage during the colouring operation.

In exemplary embodiments, the colouring step comprises heating the first and/or second dyeing liquids to a temperature of 90°C. In exemplary embodiments, the first and second dyeing liquids are maintained at the same temperature.

In exemplary embodiments, the first and second dyeing liquids are maintained at a temperature in the range of 60°C and 100°C.

In exemplary embodiments, the first and second dyeing liquids are maintained at a temperature in the range of 70°C to 90°C.

In exemplary embodiments, the first and second dyeing liquids are maintained at a temperature of 90°C.

In exemplary embodiments, the concentration of the second dye in the second dyeing liquid is maintained at the same concentration as the first dye in the first dyeing liquid.

In exemplary embodiments, the concentration of the first dye within the first dyeing liquid is approximately 1 g/L.

In exemplary embodiments, the concentration of the second dye within the second dyeing liquid is approximately 1 g/L.

In exemplary embodiments, the concentration of the first dye within the first dyeing liquid is approximately 2 g/L.

In exemplary embodiments, the concentration of the second dye within the second dyeing liquid is approximately 2 g/L.

Advantageously, concentrations of approximately 2 g/L help to provide improved colouring when using lighter coloured dyes.

In exemplary embodiments, the concentration of the first dye within the first dyeing liquid is provided in the range of 1 g/L to 5 g/L.

In exemplary embodiments, the concentration of the second dye within the second dyeing liquid is provided in the range of 1 g/L to 5 g/L. In exemplary embodiments, the first and/or second dye is an acid-based dye.

In exemplary embodiments, the first and/or second dyeing liquid comprises an acid.

In exemplary embodiments, the acid is an acetic acid, or formic acid, citric acid or a carbonic acid.

In exemplary embodiments, the acid may be a mixture of acids.

Advantageously, providing an acid within the dyeing liquid helps to improve the adhesion of the dye onto the part

In exemplary embodiments, first and/or second dyeing liquid comprises at least one of water; iso-propyl alcohol; deionised water or acetone.

In exemplary embodiments, the colouring step further comprises agitating the first and/or second dyeing liquid.

Advantageously, agitating the part within the liquid helps to achieve a more uniform coating of the dye onto the part, thereby further improving the colouring finish.

In exemplary embodiments, the first and/or second dyeing liquid are agitated via a stirrer.

In other embodiments, the first and/or second dyeing liquids may be agitated via liquid jets.

In exemplary embodiments, the method further comprises, prior to step b), a smoothing step, wherein a roughness of the surface to be coloured is reduced.

In exemplary embodiments, steps b) to h) are performed at ambient pressure.

Advantageously, by smoothing the part prior to the colouring step, it has been found that a more homogeneous dispersion of dye at the surface of the part can be achieved when colouring at ambient pressures. As a result, a better quality colour finish can be obtained without the need for expensive pressurising equipment

In exemplary embodiments, the surface to be coloured has a first surface roughness prior to the smoothing step, and a second surface roughness after the smoothing step, and wherein the second surface roughness is smoother than the first surface roughness.

In exemplary embodiments, the additively manufactured part comprises an un-sintered material and the method further comprises, prior to the smoothing step, a de-powdering step, wherein at least some of the un-sintered material is removed from the surface to be coloured.

In exemplary embodiments, the additively manufactured part comprises a support material, and the method further comprises, prior to the smoothing step, a de- powdering step, wherein at least some of the support material is removed from the surface to be coloured.

In exemplary embodiments, the smoothing step comprises applying a chemical onto the surface of the to be coloured so as to transform at least some of the surface material from a first state, wherein said surface material is substantially rigid, to a second state, wherein said surface material is capable of movement and re-distributing the transformed surface material across at least a portion of the surface to be coloured.

In exemplary embodiments, the smoothing step comprises applying a chemical vapour onto the surface to be coloured in order to transform at least some of the surface material from the first state to the second state.

In exemplary embodiments, the smoothing step comprises condensing the chemical vapour onto at least a portion of the surface to be coloured in order to transform at least some of the surface material from the first state to the second state.

In exemplary embodiments, the smoothing step further comprises placing the additively manufactured part into a processing chamber, introducing the chemical vapour into said processing chamber, and increasing the pressure within the processing chamber so as to assist application of the chemical onto the surface to be coloured. In exemplary embodiments, after the chemical vapour has been introduced into the processing chamber, the absolute pressure within the processing chamber is increased into the range of 200 mBar to 1000 mBar.

In exemplary embodiments, the smoothing step further comprises cooling the additively manufactured part prior to the application of the chemical vapour.

Advantageously, pre-cooling the additively manufactured part helps to create an energy difference between the part and the chemical vapour, which promotes condensation of the chemical vapour onto the surface of the part.

In exemplary embodiments, the method further comprises, between the smoothing step and the colouring step, a solvent removal step, wherein solvent is removed from a surface of the additively manufactured part.

In exemplary embodiments, the solvent removal step comprises heating the additively manufactured part to a temperature above a boiling point of the chemical. Advantageously, heating the additively manufactured part to a temperature above a boiling point of the chemical provides an efficient method for removing the chemical from the surface of the additively manufactured part.

In exemplary embodiments, the solvent removal step comprises decreasing an absolute pressure within the processing chamber into the range of 1 mBar to 600 mBar.

In exemplary embodiments, the solvent removal step comprises decreasing an absolute pressure within the processing chamber into the range of 50 mBar to 600 mBar.

Advantageously, decreasing the pressure within the processing chamber helps to further promote evaporation of the chemical from the surface of the additively manufactured part. In addition, at lower pressures, chemicals tend to evaporate at lower temperatures. Therefore, since chemicals can be evaporated from the surface of the additively manufactured part at lower temperatures, lowering the pressure within the processing chamber helps to reduce the likelihood of the additively manufactured parts being damaged due to excessive heat during solvent removal.

A third aspect of the present disclosure provides an apparatus for colouring an additively manufactured part, the apparatus comprising: a processing chamber having a liquid bath for receiving an additively manufactured part; a heating element for heating a dyeing liquid contained within the liquid bath to a desired temperature; a plurality of dye dispensers, each being configured for dispensing a different colour of dye into the liquid bath based on a desired final colour of the additively manufactured part; and a controller configured to control the dispensing of the dyes into the liquid bath based on a desired final colour of the additively manufactured part.

In exemplary embodiments, the apparatus further comprises an acid dispenser for dispensing an acid into the liquid bath during processing.

In exemplary embodiments, the apparatus further comprises a draining mechanism for removing the dyeing liquid from the liquid bath.

In some embodiments, the draining mechanism may create a pressure differential to remove/push the liquid out of the tank to another tank using air pressure. This helps to fill and empty the chamber more quickly.

In exemplary embodiments, the apparatus further comprises a controller configured to operate the draining mechanism so as to remove the dyeing liquid from the liquid bath after a pre-determined amount of time, based upon a desired final colour of the additively manufactured part.

In exemplary embodiments, the apparatus further comprises a reservoir for storing a liquid, the reservoir being in fluid communication with the liquid bath, and a valve for controlling the flow of liquid from the reservoir into the liquid bath. In exemplary embodiments, the apparatus further comprises a controller configured to control the valve so as to re-fill the liquid bath after the dyeing liquid has been drained. In exemplary embodiments, the apparatus further comprises a stirrer for agitating the dyeing liquid located within the liquid bath.

In exemplary embodiments, the one liquid bath is an ambient pressure liquid baths.

In exemplary embodiments, the apparatus further comprises a plurality of liquid jets for agitating the dyeing liquid located within the liquid bath.

In exemplary embodiments, the liquid bath is configured to rotate around its horizontal axis to help promote mixing.

A fourth aspect of the present disclosure provides an apparatus for colouring an additively manufactured part, the apparatus comprising: a plurality of liquid baths, each bath containing a respective dyeing liquid and each dyeing liquid containing a different colour of dye; a plurality of heating elements, each being configured for heating a respective dyeing liquid contained within one of the plurality liquid baths to a desired temperature; an actuator for moving an additively manufactured part between the plurality of liquid baths; and a controller configured to control the actuator to move the additively manufactured part between the plurality of liquid baths based upon a desired final colour of the additively manufactured part.

In exemplary embodiments, the apparatus further comprises an acid dispenser for dispensing an acid into at least one of the liquid baths during processing.

In exemplary embodiments, the controller is configured to control the actuator to remove the additively manufactured part from the at least one of the liquid baths after a pre-determined amount of time, based upon a desired final colour of the additively manufactured part.

In exemplary embodiments, the plurality of liquid baths are ambient pressure liquid baths. In exemplary embodiments, the apparatus further comprises a plurality of stirrers for agitating the dyeing liquid located within each of the respective liquid baths.

In exemplary embodiments, the apparatus further comprises a plurality of liquid jets for agitating the dyeing liquid located within each of the respective liquid baths.

In exemplary embodiments, the plurality of liquid baths are configured to rotate around their horizontal axis to help promote mixing.

A fifth aspect of the present disclosure provides a system for colouring an additively manufactured part, the system comprising a smoothing apparatus for smoothing an additively manufactured part and a colouring apparatus according to the third or fourth aspects of the present disclosure.

In exemplary embodiments, the smoothing apparatus comprises a processing chamber configurable for receiving an additively manufactured part and an applicator for applying a chemical onto at least a portion of the surface of the additively manufactured part so as to transform at least some of the surface material of the additively manufactured part from a first state, wherein the surface material is substantially rigid, to a second state, wherein the surface material is capable of movement.

In exemplary embodiments, the applicator comprises a chemical inlet and a heating plate for receiving the chemical from the chemical inlet and being further configured to vaporize the chemical, received from the chemical inlet, for introduction into the processing chamber.

In exemplary embodiments, the smoothing apparatus further comprises a pumping mechanism for controlling a pressure of the processing chamber.

A sixth aspect of the present disclosure provides an apparatus for colouring an additively manufactured part, the apparatus comprising: a processing chamber having a liquid bath for receiving an additively manufactured part; and a heating element for heating a dying liquid contained within the liquid bath to a desired temperature. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure will now be described with reference to the accompanying drawings, in which:

Figure 1 is a flow diagram illustrating a method of colouring an additively manufactured part according to an embodiment of the present disclosure;

Figure 2 is a schematic front view of an apparatus suitable for smoothing an additively manufactured part, prior to the colouring operation;

Figure 3 is a schematic front view of an apparatus for colouring an additively manufactured part according to an embodiment of the present disclosure; and Figure 4 is a schematic front view of an apparatus for colouring an additively manufactured part according to an alternative embodiment of the present disclosure.

DETAILED DESCRIPTION

Figure 1 shows a method for colouring an additively manufactured part according to an embodiment of the present disclosure.

In a first step 101 of the method, an additively manufactured part 10 is provided. The additively manufactured part 10 may be of any shape or configuration and may comprise any material.

Typically, the additively manufactured part 10 is a powder-based polymer part. Examples of such materials include, but are not limited to: Nylon 12 (PA220 Duraform™ PA); Nylon 11 (Duraform™ EX Natural, Duraform™ EX Black); Thermoplastic Polyurethane (TPU); TPE-210 elastomer materials; and ABS.

Similarly, the additively manufactured part 10 is typically manufactured using a suitable powder-based process. Examples of such processes include: fused deposition modelling (FDM); laser sintering (LS); high speed sintering (HSS) and multi-jet fusion. However, it shall be appreciated that in other embodiments, other processing methods may be used. In exemplary embodiments, such as the embodiment illustrated in Figure 1 , the additively manufactured part 10 is provided in the form of a powder cake. Therefore, in the illustrated embodiment, a de-powdering step 102 is required.

During the de-powdering step 102, un-sintered material and/or support material left over from the additive manufacturing process is removed from the additively manufactured part 10.

In exemplary embodiments, the de-powdering step 102 involves applying ultrasonic vibrations to the powder cake so as to cause the un-sintered material to become detached from the additively manufactured part 10.

In other embodiments, the de-powdering step may involve detaching the support material using hand tools, applying blasts of pressurised fluid to the powder cake, inserting an expansible material between the additively manufactured part and the support structure and/or any other suitable methods.

It shall also be appreciated that in some embodiments, the additively manufactured part may be provided in a de-powdered state and hence the de-powdering step may be omitted in some embodiments.

Once a sufficiently de-powdered part has been provided, the additively manufactured part 10 is subjected to a smoothing process at step 103 so as to reduce the surface roughness of the additively manufactured part 10.

In the illustrated embodiment, during the smoothing step 103, the additively manufactured part is initially cooled, which helps to increase the amount of chemical vapour that condenses onto the surface of the part 10 during chemical smoothing processes (since chemicals typically condense more readily onto lower temperature surfaces) as will be described in greater detail below.

In exemplary embodiments, in order to cool the additively manufactured part 10, the part 10 is placed within a blast chiller (not shown) for at least 30min at a temperature of -18°C. However, it shall be appreciated that the temperature and duration of the cooling process may vary. Once the additively manufactured part 10 has been cooled, the part 10 is loaded into a smoothing apparatus 200, illustrated in Figure 2, ready for the smoothing process to be performed.

The smoothing apparatus 200 includes a vacuum-tight sealable processing chamber 202, optionally made out of stainless steel, which is sized for receiving the additively manufactured part 10.

The processing chamber 202 also includes a support in the form of a part stand 204 for supporting the additively manufactured part 10 within the processing chamber 202.

An applicator 210 is also provided for applying a chemical onto at least a portion of a surface of the additively manufactured part 10 received within the processing chamber 202.

In the embodiment illustrated in Figure 2, the applicator 210 is made up of a chemical inlet 212, a heating plate 214 and a perforated sheet 216.

In use, a chemical, suitable for transforming a surface material of the additively manufactured part 10 from a first state, wherein the surface material is substantially rigid, to a second state, wherein the surface material is capable of movement, is supplied to the heating plate 214, via the chemical inlet 212.

The heating plate 214 then heats the chemical applied thereto to a temperature above the chemical’s respective boiling point, which causes the chemical to vaporise, ready for introduction into the processing chamber 202 via the perforated sheet 216.

The provision of the perforated sheet 216 helps to ensure a uniform distribution of the vaporised chemical within the processing chamber 202 during the process. Flowever, it shall be appreciated that in other embodiments, the perforated sheet 216 may be omitted.

In addition, it shall also be appreciated that other forms of applicator may be used.

The smoothing apparatus 200 also includes a heating element 206 configured to control a temperature of the processing chamber. In the illustrated embodiment, a pair of heating elements 206a, 206b are provided which make up part of a wall of the processing chamber 202. The heating elements 206a, 206b are used to raise and lower the temperature of the processing chamber 202 so as to obtain optimal thermodynamic processing conditions during the smoothing and solvent removal steps.

Furthermore, by providing heating elements which make up part of the wall of the processing chamber 202, the apparatus 200 is able to better avoid the unwanted condensation of chemicals onto the surfaces of the processing chamber 202, which helps to reduce chemical wastage and also helps to improve the efficiency of the smoothing operation.

The apparatus also includes a pumping mechanism configured to control the pressure of the processing chamber. During operation, the pumping mechanism is used to raise and lower the pressure of the processing chamber 202 so as to obtain optimal thermodynamic processing conditions during the smoothing and solvent removal operations. In the illustrated embodiment, the pumping mechanism is made up of a vacuum pump 208 configured to control a pressure within the processing chamber 202 and an outlet 207 configured to permit egress of gas from within the processing chamber 202 to a location external to the processing chamber, such as the atmosphere, via an activated carbon filter 209. The activated carbon filter 209 helps to prevent chemical vapours from being expelled into the atmosphere.

At a first step of the smoothing process, the additively manufactured part 10 is loaded into the processing chamber 202. Once the part 10 has been loaded, a chemical solvent such as an acid, an ionic liquid or another substance suitable for transforming the surface material of the additively manufactured part 10 is introduced into the processing chamber 202.

Examples of suitable chemicals include, but are not limited to 1 ,1 ,1 ,3,3,3-hexafluoro- 2-propanol (HFIP), dichloromethane (DCM), dimethylformamide, sulphuric acid, m- cresol, formic acid, trifluoroacetic acid, benzyl alcohol, 1 ,2,4 trichlorobenzene, tetrahydrofuran, 2-methyltetrahydrofuran, Xylene and Dimethyl sulfoxide (DMSO), or the like. The amount of each chemical used during the smoothing process depends on the surface area and the number of parts to be processed.

In the illustrated embodiment, the chemical solvent is introduced into the processing chamber 202 as a solvent vapour.

As shown in Figure 2, the chemical is supplied to the heating plate 214 in a liquid state, via the chemical inlet 212. The heating plate 214 then heats the chemical to a temperature above the chemical’s respective boiling point which causes the chemical to vaporise. The chemical vapour is then introduced into the processing chamber 202, via the perforated sheet 216 ready for smoothing the surface of the additively manufactured part 10.

It shall be appreciated however that in other embodiments, the chemical may instead be stored in vapour form and so the introduction of the solvent vapour into the processing chamber may instead involve simply opening a valve, or other such mechanism, to enable to vapour to flow into the processing chamber.

Once the chemical vapour has been introduced into the processing chamber 202, the heating elements 206 and vacuum pump 208 are controlled to obtain a desired processing chamber temperature and pressure.

It has been found that when using low boiling point solvents (such as HFIP), optimal smoothing conditions can be obtained at temperatures between 10°C and 40°C and at absolute pressures between 200-1000 mBar. However, in other embodiments, it shall be appreciated that other temperatures and pressures may be used. For example, when using solvents with higher boiling points, optimal smoothing conditions can be obtained at temperatures between 120°C and 180°C and at absolute pressures between 1 -100 mBar.

Chemicals tend to condense more easily at higher pressures and at lower temperatures and therefore, by altering the thermodynamic conditions within the processing chamber 202 to lower the temperature and increase the pressure within the processing chamber 202, it is possible to cause the chemical vapour to condense onto the surface of the additively manufactured part 10, which subsequently leads to the surface material of the additively manufactured part 10 becoming dissolved by the chemical applied thereto.

Furthermore, the walls of the processing chamber 202 are also maintained above the chemical condensation temperature to help avoid chemical vapours from condensing on the chamber walls rather than onto the part 10, to help reduce wastage and to ensure that any condensation of the chemical vapour is focussed at the part 10, rather than at other parts of the processing chamber 202.

As the chemical is condensed onto the surface of the part 10, the surface of the part 10 undergoes a change of state from a first, undissolved state, in which the movement of the surface material of the part 10 is substantially prevented, to a second, dissolved state, in which the movement of the surface material of the part is permitted.

As such, once dissolved, the surface material of the part 10 is able to reflow under the influence of gravity which allows the transformed surface material to be re-distributed across at least a portion of the surface of the part 10. This material re-distribution closes the pores on the surface of the part 10, resulting in a smooth and water-tight surface.

Following the smoothing step 103, the additively manufactured part 10 is then dried at step 104 so as to remove the chemical from the surface of the additively manufactured part 10.

In the illustrated embodiment, this is done by decreasing the pressure and increasing the temperature within the processing chamber 202.

It has been found that optimal solvent removal conditions for the solvents with low boiling points (such as HFIP) can be obtained at temperatures between 30°C and 50°C and at absolute pressures between 1 mBar to 600 mBar, since chemicals typically vaporise more readily at high temperatures and low pressures. Therefore, during the solvent removal process, the heating elements 206 and vacuum pump 208 are again controlled to increase the temperature within the processing chamber 202 to a temperature between 30°C and 50°C and to reduce the pressure of the processing chamber 202 to an absolute pressure between 1 mBar to 600 mBar. In order to obtain re-vaporise the condensed chemical, the temperature of the processing chamber must be held above the respective boiling temperature of the chemical used during the process. Furthermore, by increasing the temperature of the processing chamber, a greater amount of chemical can be vaporised, which leads to faster drying times. However, as temperatures are increased, there is an increased risk of the additively manufactured part 10 becoming melted or damaged due to excessive heat. For this reason, solvents with a low boiling point tend to be preferred. It has been found that temperatures in the range of 30°C and 50°C are able to achieve optimal solvent removal for the solvents with low boiling point, without risking damage to the part.

The additively manufactured part 10 is then ready to be coloured.

Advantageously, following the aforementioned smoothing process, the surface of the additively manufactured part 10 is less undulating when compared to surface in its first, undissolved state.

The aforementioned reduction in surface roughness can be observed and validated using a standardized surface roughness test using a Mitutoyo Surftest SJ-210 with a stylus tip radius of 2pm, tip angle 60° and measuring force 0.75kN.

When dyes are applied to rough, undulating surfaces, the dye can tend to flow and gather into trough regions, which can lead to an uneven distribution of colour across the surface. This can lead to parts exhibiting an overall “duller” colour finish.

As such, by pre-smoothing the additively manufactured part 10 prior to the colouring process, the dye is able to achieve a more homogenous dispersion onto the surface of the part since the surface of the part is relatively flat and has greatly reduced undulations. As a result, it has been found that a better quality colour finish can be obtained.

It has also been found that by pre-smoothing the additively manufactured part 10, it is possible to obtain better quality colour finishes when colouring at ambient pressure, meaning that the use of expensive pressurising equipment can be better avoided. It shall be also appreciated that whilst in the illustrated embodiment the smoothing process is described as a vapour smoothing process, in other embodiments, other suitable smoothing processes may be used. For example, in some embodiments, the additively manufactured part can be smoothed via immersing the part in an acid or solvent bath, or in further embodiments, may be smoothed using mechanical-abrasive methods (such as vibratory smoothing or media blasting).

A pair of suitable colouring apparatuses for performing the method illustrated in Figure 1 are shown in Figures 3 and 4.

Figure 3 shows an apparatus 300 for colouring an additively manufactured part 10 according to one embodiment of the present disclosure.

The apparatus 300 is made up of a liquid bath 301 , a reservoir 304, a heating element 306, a plurality of dye dispensers 308, an acid dispenser 310, a drain 312 and a controller 314.

The liquid bath 301 is made up of a base and a plurality of sidewalls which together form a liquid-tight interior cavity sized for receiving an additively manufactured part 10.

In the embodiment illustrated in Figure 3, the liquid bath 301 is designed for use with a pre-smoothed part and therefore is an ambient pressure liquid bath. This helps to avoid the need for expensive pressuring equipment. Flowever, in other embodiments for use with parts that have not been pre-smoothed, the liquid bath may alternative be a pressurised bath.

The liquid bath 301 also has a part stand 302 located within the interior cavity for receiving and supporting any parts placed into the liquid bath 301 , although it shall be appreciated that in some embodiments the part stand 302 may be omitted.

The liquid bath 301 also contains a liquid agitator 301 a, in this case provided in the form of a stirrer, for agitating fluids (or other substances) located within the liquid bath 301 . This helps to achieve a more uniform dispersion of dye throughout the liquid bath 301 , which in turn helps to provide parts coloured using the apparatus 300 with a more uniform colouring, as shall be described in greater detail below. It shall also be appreciated that whilst the liquid agitator 301 a in the illustrated embodiment is provided in the form of a stirrer, in other embodiments, the liquid agitator may instead be provided in the form of a fluid jet, a propeller, an ultrasonic agitator or may be provided via any other suitable means.

Furthermore, in other embodiments, the liquid bath can be provided as a drum configured to rotate around its horizontal axis (akin to a washing machine drum) to help further promote mixing of fluids and other substances located within the liquid bath.

The reservoir 304 is similarly made up of a base and a plurality of sidewalls which provide a liquid-tight cavity for containing a liquid for use during the colouring process.

The interior cavity of the liquid bath 301 is fluidically connected to the reservoir 304 via a first channel 303 which allows the liquid contained in the reservoir, such as water, to flow into the liquid bath 301 for use during the colouring process.

The channel 303 also includes a reservoir valve (V1 ) for controlling the flow of liquid from the reservoir 304 into the liquid bath 301 .

The interior cavity of the liquid bath 301 is also fludically connected to the acid dispenser 310 via a second channel 305. The provision of an acid dispenser allows amounts of acid to be added to the liquid reservoir 301 for use in the colouring process, which helps to improve the adhesion of the dye onto the surface of the additively manufactured part 10.

The channel 305 also includes an acid valve (V2) for controlling the flow of acid from the acid dispenser 310 into the liquid bath 301 .

The interior cavity of the liquid bath 301 is also fluidically connected to the plurality of dye dispensers 308 to allow the respective dyes contained therein to be added to the liquid reservoir 301 as required during the colouring process.

In the illustrated embodiment, four dye dispensers are provided, each containing a different colour of dye. A first dye dispenser 308a contains a cyan (C) coloured dye, a second dye dispenser 308b contains a magenta (M) coloured dye, a third dye dispenser 308c contains a yellow (Y) coloured dye and a fourth dye dispenser 308d contains a black, or key (K), dye. Advantageously, the provision of a plurality of dye dispensers containing CMYK dyes helps to increase the range of part colours which can be achieved using the apparatus without requiring pre-mixing of dyes.

It shall be appreciated however that in other embodiments, a different number of dispensers and different dye colours may be used. For example, in some embodiments, the apparatus may include three dye dispensers, for containing red (R), green (G) and blue (B) coloured dyes, or five dispensers for containing Cyan (C), Magenta (M), Yellow (Y), Black or key (K) and Orange (O) coloured dyes respectively.

The plurality of dye dispensers 308 are each fluidically connected to a dye channel 307 via respective valves V3-V6.

When the respective valves V3-V6 are open, dye from the corresponding dye dispensers 306a-d is permitted to flow through the dye channel 307 and into the liquid bath 301 for use during the colouring process. However, when the valves V3-V6 are closed, dye from the corresponding dye dispensers 306a-d is not permitted to flow through the dye channel 307 and into the liquid bath 301 , which allows the colour of the dyeing liquid, contained within the liquid bath 301 , to be controlled as desired by the end user.

The heating element 306 is provided for heating the fluid (and any other substances) contained within the liquid bath 301 to a desired temperature. In the illustrated embodiment, the heating element is located at a bottom surface of the liquid bath 301 . However, it shall be appreciated that in other embodiments, the heating element may be located at other suitable locations, such as at the sidewalls of the liquid bath.

The apparatus 300 also features a draining mechanism 314 arranged to allow the egress of liquid (and other substances) from within the interior cavity of the liquid bath 301 to locations external to the liquid bath 301 , such as a waste disposal unit or a liquid recycling unit (not shown). In some embodiments, the liquid can also be redirected back into the dye dispensers 308 to be re-used (as shown in Figure 3). Furthermore, in some embodiments, the draining mechanism can create a pressure differential to remove/push the liquid out of the tank to another tank using air pressure. This helps to fill and empty the chamber more quickly.

The apparatus also features a controller 314 configured to control the opening and closing of the valves V1-V6 and draining mechanism, as well as the heating of the liquid bath 301 via the heating element 306 as shall be described in greater detail in the method below.

In the illustrated embodiment, a single wireless controller is used for controlling the valves V1 to V6, the draining mechanism and the heating element. However, it shall be appreciated that in other embodiments, the controller may be a wired controller and, in further alternatives, it shall be appreciated that each valve V1 to V6, the draining mechanism and the heating element may be controlled via a separate controller. It shall also be appreciated that the controller may be configured to activate the valves V1 -V6, draining mechanism and heating element via a manual input or automatically based on a pre-set programme.

The method of colouring the additively manufactured part 10 shall now be described with reference to Figure 1 .

At step 105 of the method, the dyeing liquid is provided.

During step 105, the controller 314 actives the reservoir valve V1 and the acid valve V2 which causes the valves V1 and V2 to open leading to the some of the liquid contained within the reservoir 304 and some of the acid contained within the acid dispenser 310 to flow through the respective channels 303 and 305 and into the liquid bath 301.

In the illustrated embodiment, the liquid contained within the reservoir is water. However, in other embodiments, the liquid may be iso-propyl alcohol, De-ionized water, acetone or any mix of the aforementioned liquids.

Optionally, the apparatus can contain water de-ioniser, or the apparatus can be fed with de-ionised water. Similarly, in the illustrated embodiment, the acid contained within the acid dispenser 310 is an acetic acid. However, in other embodiments, the acid may be a formic acid, citric acid, carbonic acid or any mix of the aforementioned acids. During step 105, the controller also activates one of the valves V3-V6 corresponding to the respective dye dispensers 308a-d to allow one of the respective dyes to flow through the channel 307 and into the liquid bath 301. The particular colour of dye added to the liquid bath 301 is chosen based on the desired final colour of the additively manufactured part 10.

In this manner, a dyeing liquid containing a liquid, an acid and at least one dye is provided for colouring the part 10. The dyeing liquid can also be stirred via the stirrer 301a at step 105 to help obtain an even dispersion of dye throughout the dyeing liquid. In the illustrated embodiment, the at least one dye is an acid-based LANASET® dye, supplied by Huntsman Textile Effects, and is added to the dyeing liquid at a concentration of 1 g/L. However, it shall be appreciated that other suitable concentrations can be used. For example, in some embodiments, the dye may be added to the dyeing liquid at a concentration of 2g/L. Details of the respective solubility’s of a variety of LANASET® dyes are provided in the table below.

Other type of dyes can be used. In another example TCN® dyes are used. Details of the respective concentrations of the TCN® dyes are provided in the table below. TCN® GTD dyes can also be used.

Once the dyeing liquid has been provided, at step 106 the controller 314 activates the heating element 306 so as to heat the dyeing liquid contained within the liquid bath 301 to a temperature in the range of 60°C and 100°C, typically in the range of 70°C to 90°C. In the illustrated embodiment, the dye is heated to a temperature of 90°C. However, it shall be appreciated that in other embodiments, other temperatures may be used.

Advantageously, heating the dyeing liquid to temperatures in this range has been found to help efficiently colour additively manufactured parts whilst also helping to reduce the occurrence of part damage during the colouring operation. However, it shall be appreciated that in other embodiments, other suitable temperatures may be used.

The liquid can also be preheated automatically before the processing shift, i.e. the controller can have timer function to start pre-heating the liquid to the desired temperature.

Once the dyeing liquid has been heated to the desired temperature, the additively manufactured part 10 is immersed into the heating dyeing liquid at step 107. However, in other embodiments, the dyeing liquid may be heated after the part has been placed into the liquid bath.

When the additively manufactured part 10 is immersed into the dyeing liquid, the acid molecules (in this case acetic acid) contained within the dyeing liquid tend to associate at the surface of the part 10. As a result, the surface of the additively manufactured part 10 exhibits an increased amount of polarity, due to the additional H ⁺ hydrogen ions located at the surface. When using an acid-based dye, these H ⁺ hydrogen ions at the surface of the additively manufactured part 10 create strong hydrogen bonds with the corresponding H ⁺ hydrogen ions of the acid-based dye, which helps to achieve better dye adhesion onto the part. However, in embodiments where a non-acid based dye is used, it shall be appreciated that the acid may instead be omitted from the dyeing liquid. The additively manufactured part 10 is then left immersed within the dyeing liquid for an amount of time, typically between 1 minute and 1 hour.

The immersion time of the additively manufactured part 10 is selected based on a desired final colour of the finished part 10. For example, longer immersion times lead to more intensely coloured parts (generally used when the dyeing liquid in which the part is immersed is the primary colour of the part) and shorter immersion times lead to a lesser degree of colouring (generally used to adjust a shade of a given colour). As such, the immersion time can be adjusted based on a desired final colour of the part.

Once the desired amount of colouring has been achieved after a given amount of time, the controller 314 activates the draining mechanism 312 so as to remove the dyeing liquid from the liquid bath 301 , thereby removing the additively manufactured part 10 from the dyeing liquid. In the illustrated embodiment, following the removal of the dyeing liquid from the liquid bath 301 , the additively manufactured part 10 is also cooled to a temperature of 30°C (approximately room temperature).

In exemplary embodiments, such as the embodiment illustrated in Figure 1 , once the part 10 has been removed from the dyeing liquid, any excess dye is removed from the surface of the part 10. In the illustrated embodiment, this step is performed by introducing a liquid (e.g. water) from the reservoir 304 into the liquid bath 301 so as to rinse the part 10 before activating the draining mechanism 312 so as to remove the liquid used to rinse the part, along with any excess dye, from the liquid bath 301. Flowever, it shall be appreciated that in other embodiments, other dye removal methods may be used. For example, in some embodiments, the part 10 may be dried at an elevated temperature in order to remove any residual dye.

Typically, the colouring process is repeated by one or more iterations using a different colour dye within the dyeing liquid to allow a wider range of coloured surfaces to be achieved, without the need for pre-mixing.

For example, if a blue coloured part is desired by an end user, the process may first be performed using a first dyeing liquid containing the cyan dye, dispensed from the first dye dispenser 308a and then may be repeated using a second dyeing liquid containing the magenta dye, dispensed from the second dye dispenser 308b. However, in other embodiments, the colouring process may only comprise a single colouring run.

In the method according to the illustrated embodiment, both the temperature of the dyeing liquid and the concentration of the dye are kept constant during each colouring run. As such, the only parameters that are changed in order to adjust the colour of the part are the dye colour used for each run and the immersion time.

For example, if an end user desires an additively manufactured part 10 having a light blue final colour, the immersion time of the part 10 in the cyan dye can be increased and the immersion time of the part 10 in the magenta dye can be decreased in order to achieve this particular desired finish.

Conversely, if the end user desires an additively manufactured part 10 having a more purple-coloured finish, the immersion time of the part 10 in the magenta dye can be increased and the immersion time of the part 10 in the cyan dye can be decreased to achieve this particular desired finish.

By adjusting the immersion time of the surface of the additively manufactured part 10 within the respective dyeing liquids, it is possible to further increase the range of colour finishes obtainable for a given part, without the need for pre-mixing dyes. Furthermore, the use of excess dye and temperature can be better avoided, which helps to improve the economy of the method.

It shall be appreciated however that in some other embodiments, parameters such as the dye concentration and dyeing liquid temperature may be adjusted during each colour run to alter the final colour of the part.

It shall also be appreciated that in some embodiments, only part of the additively manufactured part 10 may be immersed in the dyeing liquid, for example in instances where colour is only required on a single surface of the additively manufactured part 10.

Figure 4 shows an apparatus 400 for colouring an additively manufactured part 10 according to another embodiment of the present disclosure. Unlike the apparatus 300 illustrated in Figure 3, the apparatus 400 illustrated in Figure 4 is made up of a plurality of liquid baths 401 -404, each having a respective heater 406a-d, and an actuator 408 for moving the additively manufactured part 10 between the respective baths 401-404.

As with the liquid bath 301 described in Figure 3, the liquid baths 401 -404 comprise a base and a plurality of sidewalls which together form a liquid-tight interior cavity sized to receive an additively manufactured part 10.

Each of the liquid baths 401 -404 also have their own respective liquid agitators 401 a- 404a, in this case provided in the form of a stirrer, for agitating the dyeing liquids contained therein.

Flowever, unlike the liquid bath 301 illustrated in Figure 3, rather than having a drain mechanism and corresponding channels to enable the liquid bath to be re-filled with different dyeing liquids, in the apparatus 400 described in Figure 4, each liquid bath 401-404 is pre-filled with a dyeing liquid, in this case containing water, and a corresponding colour of dye.

In this case, the apparatus 400 comprises four liquid baths, a first liquid bath 401 containing a dyeing liquid having a cyan (C) coloured dye, a second liquid bath 402 containing a dyeing liquid having a magenta (M) coloured dye, a third liquid bath 403 containing a dyeing liquid having a yellow (Y) coloured dye and a fourth liquid bath 404 containing a dyeing liquid having a black, or key (K), dye. Flowever, it shall be appreciated that in other embodiments, a different number of liquid baths and different dye colours may be used.

The respective dyeing liquids may also contain an amount of acid, such as acetic acid or formic acid, to improve dye adhesion in cases where acid-based dyes are incorporated into the respective dyeing liquids.

Meanwhile, the actuator 408 is provided for moving the additively manufactured part 10 between the respective liquid baths 401 -404 depending on the desired final colour of the additively manufactured part 10. In the illustrated embodiment, the actuator 408 is provided in the form of a robotic arm. However, in other embodiments, any other suitable form of actuator may be used.

The apparatus 400 also features a controller 414 configured to control the actuator to move the additively manufactured part 10 between the liquid baths 401-404 based upon a desired final colour of the additively manufactured part, and also to control the heating of the respective liquid baths 401-404 via the heating elements 406a-d as shall be described in greater detail below. However, it shall be appreciated that in other embodiments, the actuator 408 and heating elements 406a-d may be controlled by separate controllers.

A method of colouring the additively manufactured part 10 according to an alternative embodiment of the present invention shall now be described with reference to Figure 4.

This method of colouring described below is substantially the same as that described in relation to Figure 3 and so, for the sake of conciseness, only the differences shall be described in detail herein.

As with the method described in relation to Figure 3, at step 105 of the method, the dyeing liquid is provided containing a liquid, an acid and at least one dye for colouring the part 10. In the illustrated embodiment, the at least one dye is an acid-based LANASET® dye, supplied by Huntsman Textile Effects, and is provided at a concentration of 1 g/L.

However, unlike Figure 3 wherein a single dyeing liquid is prepared for each colouring run, the apparatus 400 provides a plurality of pre-made dyeing liquids which can be used for multiple colouring runs.

Advantageously, this helps to improve processing times since there is no need to make up new dyeing liquids with each run. Furthermore, wastage is also reduced since dyeing liquids can be re-used for multiple parts and colouring runs.

Once the dyeing liquids have been provided, at step 106 the controller 414 activates one of the respective heating elements 406a-d, corresponding to the liquid bath 401- 404 in which the part 10 will be immersed, so as to heat the dyeing liquid to a temperature in the range of 60°C and 100°C, typically in the range of 70°C to 90°C.

As has been mentioned previously, heating the dyeing liquid to temperatures in this range has been found to help efficiently colour additively manufactured parts whilst also helping to reduce the occurrence of part damage during the colouring operation. However, it shall be appreciated that in other embodiments, other suitable temperatures may be used.

Once the dyeing liquid has been heated to the desired temperature, the controller 414 controls the actuator 408 to grab the additively manufactured part 10 and place the part 10 into the liquid bath 401 -404. The liquid bath 401 -404 in which the part is placed depends on the desired final colour of the part 10 as has been discussed previously.

Furthermore, in other embodiments, the dyeing liquid may be heated after the part has been placed into the liquid bath.

The additively manufactured part 10 is then left immersed within the dyeing liquid for an amount of time, typically between 1 minute and 1 hour.

Once the desired amount of colouring has been achieved after a given amount of time, the controller 414 re-activates the actuator 408 to remove the part from the dyeing liquid.

In exemplary embodiments, such as the embodiment illustrated in Figure 1 , once the part 10 has been removed from the dyeing liquid, any excess dye can be removed from the part 10 (for example via rinsing or drying).

Typically, the process is then repeated by one or more iterations and so the part may be placed into one or more of the remaining liquid baths 401-404 depending on the final colour of the part 10 desired by the user, as has been described previously. However, in other embodiments, the colouring process may only comprise a single colouring run.

In this manner, it is possible to increase the range of colour finishes obtainable for a given part, without the need for pre-mixing. Furthermore, as with the embodiment described in Figure 3, the apparatus illustrated in Figure 4 is designed for use with pre-smoothed parts and therefore each liquid bath 401-404 is an ambient pressure liquid bath. Flowever, it shall be appreciated that in other embodiments for parts which are not pre-smoothed, the liquid baths may be pressurised.

Although the disclosure 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 disclosure as defined in the appended claims.