WO2017019102A1

WO2017019102A1 - Three-dimensional object production

Info

Publication number: WO2017019102A1
Application number: PCT/US2015/042987
Authority: WO
Inventors: David RAMIREZ MUELA; Lihua Zhao; Alejandro Manuel De Pena
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2015-07-30
Filing date: 2015-07-30
Publication date: 2017-02-02
Anticipated expiration: 2018-01-30
Also published as: EP3271152A1; JP2018511502A; CN114434791A; US11958239B2; JP6495480B2; EP3271152A4; BR112017023154A2; KR20170130592A; KR102045231B1; US20180133957A1; CN107548345A; EP3271152B1; BR112017023154B1

Abstract

Apparatus to produce a three-dimensional object and methods of producing a three-dimensional object are described. In some examples, a first fluid comprising a colorant and a second fluid comprising an absorber to absorb electromagnetic radiation are applied on a layer of particulate material. Application of the second fluid to the layer of particulate material is in dependence on an ability of the first fluid to absorb the electromagnetic radiation.

Description

THREE-DIMENSIONAL OBJECT PRODUCTION

BACKGROUND

[0001] Apparatus that generate three-dimensional objects, including those commonly referred to as "3D printers", have been proposed as a potentially convenient way to produce three-dimensional objects. These apparatus typically receive a definition of the three-dimensional object in the form of an object model. This object model is processed to instruct the apparatus to produce the object using a production material or plural production materials. This may be performed on a layer-by-layer basis. The processing of the object model may vary based on the type of apparatus and/or the production technology being implemented. Generating objects in three-dimensions presents many challenges that are not present with two-dimensional print apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Various features of the present disclosure will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the present disclosure, and wherein:

[0003] Figure 1 is a schematic diagram of an apparatus to produce a three- dimensional object according to an example;

[0004] Figure 2 is a flow diagram showing a method of producing a three- dimensional object according to an example;

[0005] Figure 3 is a flow diagram showing a method of producing a three- dimensional object according to an example;

[0006] Figure 4 is a schematic diagram of a print head assembly for producing a three-dimensional object according to an example;

[0007] Figure 5 is a schematic diagram showing a strategy for dispensing fluids according to an example; [0008] Figure 6 is a schematic diagram showing a strategy for dispensing fluids according to an example;

[0009] Figure 7 is a schematic diagram showing a strategy for dispensing fluids according to an example; and

[0010] Figure 8 is a schematic diagram showing a strategy for dispensing fluids according to an example.

DETAILED DESCRIPTION

[0011] In the following description, for purposes of explanation, numerous specific details of certain examples are set forth. Reference in the specification to "an example" or similar language means that a particular feature, structure, or characteristic described in connection with the example is included in at least that one example, but not necessarily in other examples.

[0012] In the production of three-dimensional objects, e.g. in so-called "3D printing", there is a challenge to control the structure of generated objects. For example, it may be desired to produce objects with a variety of mechanical properties, which may influence, or be influenced by, material properties of a produced object. It is also desirable to control the color of produced objects. In certain cases, it may be desired to vary the color of at least one part of an object without affecting the mechanical properties of the object, or to vary the mechanical properties of part of an object without affecting a color of the object. Such considerations are not present with two-dimensional printing.

[0013] Certain examples described herein facilitate a three-dimensional object with a desired structure to be produced in a printing operation.

[0014] An example of an apparatus to produce a three-dimensional object will now be described with reference to Figure 1 . Figure 1 shows an example of an apparatus 100 to produce a three-dimensional object 1 10. The apparatus 100 may comprise a so-called "3D printer". The apparatus 100 comprises a build area 102, a dispensing apparatus 104, and a processor (referred to hereinafter as a controller) 106. [0015] The build area 102 may comprise a platen 108 upon which a three- dimensional object 1 10 may be constructed.

[0016] The dispensing apparatus 104 is to dispense, deposit, or otherwise apply a plurality of materials to generate the three-dimensional object 1 10. Examples of these materials are discussed in more detail below. The materials may comprise, for example, clear and/or colored agents (such as fusing or coalescing agents) for use on a substrate.

[0017] In Figure 1 , the dispensing apparatus 104 is communicatively coupled to the processor 106, e.g. via a wired interface and/or via a wireless interface. The processor 106 may be programmed to control the dispensing apparatus 104 based on manufacturing control data. The manufacturing control data may indicate placement instructions for the plurality of materials. For example, these instructions may comprise firing signals for at least one print head 1 12 to deposit a particular material. These firing signals may be associated with a particular location in two or three dimensional space.

[0018] The dispensing apparatus 104 may be moveable relative to the platen 108 in order to deposit a material at a particular location. The three-dimensional object 1 10 may be constructed layer-by-layer, in which case the dispensing apparatus 104 may deposit material onto each layer. In this case, placement instructions may relate to the placement of an available material or material combination at a particular print-resolution pixel for a particular layer (e.g. to deposit a material composition for a voxel associated with the layer).

[0019] The dispensing apparatus 104 may in certain examples comprise an inkjet deposit mechanism. In the example of Figure 1 , the apparatus is to print a plurality of liquid agents onto layers of a powdered substrate 1 14. The powdered substrate is a particulate material. In some examples, the dispensing apparatus 104 may comprise first and second dispensers. In this example, the dispensing apparatus 104 comprises six inkjet print heads 1 12. Each inkjet print head 1 12 may be adapted to deposit an agent onto the substrate 1 14. In particular, each inkjet print head 1 12 may be to deposit a particular agent upon defined areas of a plurality of successive layers of the substrate 1 14. An agent may act as a fusing agent or as a fusing inhibitor. The latter may cause a "blank" or "empty" material composition to be created.

[0020] In Figure 1 , the apparatus 100 comprises a substrate supply mechanism 1 16 to supply at least one substrate layer onto which the plurality of materials may be dispensed, deposited or otherwise applied by the dispensing apparatus 104. In this example, the substrate supply mechanism 1 16 comprises a powdered substrate supply mechanism to supply successive layers of powdered substrate 1 14. Two layers are shown in Figure 1 : a first layer 1 14a onto which a second layer 1 14b has been deposited by the substrate supply mechanism 1 16. In certain cases, the substrate supply mechanism 1 16 is to move relative to the platen 108 so that successive layers may be deposited on top of each other.

[0021] In the present example, the apparatus also comprises a fuser 1 18 to apply energy to form portions of the three-dimensional object from the powdered substrate 1 14. For example, Figure 1 shows a particular print head 1 14 depositing a controlled amount of a fluid agent onto an addressable area of the second layer of powdered substrate 1 14b. The fluid agent is deposited onto the powdered substrate and, as such, a drop of agent on an addressable area unit of the layer relates to a print resolution voxel. The height of the voxel is determined by the depth of each layer of substrate 1 14. The placement instructions discussed above may control the operation of the print head 1 12 to form the voxel. Following application of the agent, the fuser 1 18 is to fix or solidify the portion of the layer of substrate 1 14b. For example, the fuser 1 18 may apply electromagnetic radiation within a wavelength range to the layer of substrate 1 14b. The application of electromagnetic radiation may melt, sinter or fuse the material of the layer of substrate 1 14b, as described below with reference to Figure 2. In certain examples, the fuser 1 18 may comprise an energy source such as a ultra-violet or infra-red light source, e.g. a lamp or laser. Figure 1 shows four print resolution voxels that have been fixed in the first layer 1 14a. As such, a voxel in the second layer 1 14b may be built on voxels formed in the first layer 1 14a to build the three dimensional object. Lower layers of the substrate 1 14 may also provide support for overhanging fixed portions of a three-dimensional object, so that the substrate may be removed at the end of production to reveal the completed object.

[0022] In the example shown in Figure 1 , there may be six agents, with each agent relating to a different property. For example, four of the agents may comprise colorants to provide a full color space for producing three-dimensional objects. One of the agents may be a substantially colorless, or neutrally-colored, electromagnetic radiation absorbing agent. One of the agents may be a detailing agent to cool the substrate or otherwise prevent fusion of the particulate material of the substrate.

[0023] The processor 106 may control the dispensing, deposition or application of the different agents in accordance with the placement instructions. In certain examples, the placement instructions may specify colors to be formed in various portions of the three-dimensional object 1 10. The processor 106 may determine the relative amounts of different colorants to achieve the specified colors. The desired color and/or optical density of a voxel may be adjusted by varying the amount of colorant(s) in the voxel.

[0024] In some examples, the processor 106 may determine an amount of substantially colorless or neutrally-colored absorber to apply to a given voxel. The quantity of colorless or neutrally-colored absorber may be determined as described below. Control of the amount of colorless or neutrally-colored absorber may facilitate the formation of a multi-colored three-dimensional object 1 10 with mechanical properties that are substantially uniform throughout the object. That is, the mechanical properties may not be color dependent. Alternatively or additionally, control of the amount of colorless or neutrally-colored absorber may facilitate variation in the mechanical properties of a colored three-dimensional object 1 10. That is, different portions of the object 1 10 may have different respective mechanical properties.

[0025] More generally, the apparatus 100 is to apply a first fluid on a layer of particulate material. The first fluid comprises a colorant. The apparatus is also to apply a second fluid on the layer of particulate material. The second fluid comprises an absorber to absorb electromagnetic radiation. The apparatus is to apply the second fluid to the layer of particulate material in dependence on an ability of the first fluid to absorb the electromagnetic radiation.

[0026] The apparatus may comprise a dispensing apparatus to dispense the first fluid and the second fluid on a layer of particulate material. The apparatus may comprise a processor to control the dispensing apparatus to dispense the second fluid on the basis of an electromagnetic radiation absorption characteristic of the first fluid.

[0027] In some examples, the fluids may be applied directly on the layer of particulate material. In other examples, the fluids may be applied indirectly on the particulate matter; for example, one fluid may be applied on a previously-applied fluid without contacting the layer of particulate material.

[0028] In some examples, a quantity or volume of the second fluid to be applied may be dependent on the ability of the first fluid to absorb the electromagnetic radiation. In other examples, the second fluid may be selected from a plurality of fluids that have different respective electromagnetic absorption characteristics, dependent on the ability of the first fluid to absorb the electromagnetic radiation. In some examples, the ability of the first fluid to absorb electromagnetic radiation may be known or determined based on an absorption characteristic of the first fluid, such as an absorption spectrum.

[0029] Figure 2 shows a method 200 by which an apparatus such as the apparatus 100 shown in Figure 1 may produce a three-dimensional object 1 10.

[0030] At block 202, a layer of particulate material is provided. The layer of particulate material is a first layer of substrate 1 14a. The particulate material may be chosen so that it absorbs electromagnetic energy that is within a range of wavelengths of electromagnetic energy emitted by the fuser 1 18.

[0031] The layer of particulate material may in some examples be between 60 and 300 microns thick. In some examples, the layer of particulate material may be made uniformly, or substantially uniformly, thick using a roller. In other examples, the layer of particulate material may be made uniformly, or substantially uniformly, thick using a wiper.

[0032] At block 204, a fusing agent is applied to the substrate 1 14. The fusing agent may be selectively applied to portions of the substrate 1 14 that are to be solidified to produce the three-dimensional object 1 10. The fusing agent may comprise an absorber to absorb electromagnetic radiation in the range of wavelengths of electromagnetic radiation emitted by the fuser 1 18. A path description for the print head assembly may be contained in the placement instructions, which may be generated by a path generator system.

[0033] At block 206, the fuser 1 18 may emit electromagnetic radiation so that the substrate may be irradiated with the electromagnetic radiation emitted by the fuser 1 18.

[0034] At block 208, the fusing agent may absorb the electromagnetic radiation emitted by the fuser 1 18. In absorbing the electromagnetic radiation emitted by the fuser 1 18, the temperature of the fusing agent increases. Heat from the fusing agent is transmitted, for example by conduction, to particulate material in the substrate 1 14 in the vicinity of the fusing agent. The temperature of the particulate material of the substrate 1 14 in the vicinity of the fusing agent thereby also increases.

[0035] At block 210, the temperature of the particulate material of the substrate 1 14 in the vicinity of the fusing agent reaches a temperature sufficient for the particulate material to melt, sinter or otherwise fuse together. At this point the fuser 1 18 may cease emitting electromagnetic radiation.

[0036] At block 212, the method 200 may return to block 202 and a second layer of particulate material may be provided over the first layer of substrate 1 14a, to form the second layer of substrate 1 14b. The method may continue for plural iterations. In each iteration, the fusing agent may be applied in a pattern determined so as to define layers of the three-dimensional object 1 10.

[0037] Figure 3 shows a method 300 of producing a three-dimensional object 1 10. This method may be implemented, for example, by the processor 106 of Figure 1 . Alternatively, the method may be implemented by another processor in the apparatus 100, or may be implemented by a processor of a computing device sending instructions to the apparatus 100.

[0038] At block 302, a first fluid is applied on a layer of particulate material. The first fluid comprises a colorant.

[0039] At block 304, a second fluid is applied on the layer of particulate material, the second fluid comprising an absorber to absorb electromagnetic radiation. The application of the second fluid is dependent on an ability of the first fluid to absorb the electromagnetic radiation.

[0040] Blocks 302 and 304 may be performed in any order or may be performed simultaneously, in different examples.

[0041] In some examples, the particulate material weakly absorbs electromagnetic radiation having a wavelength in the range of wavelengths emitted by the fuser 1 18.

[0042] The colorant of the first fluid may comprise organic pigment, inorganic pigment, organic dye, thermochromic dye such as leuco dye, or the like. In some examples, the colorant has a decomposition temperature greater than 250°C. In some examples, the colorant has a decomposition temperature greater than 300°C. This may help prevent the color of the three-dimensional object being adversely effected by the increased temperature for fusion.

[0043] The colorant may be part of a full color space which may be applied to the three-dimensional object. For example, the colorant may form part of a four color model, such as the CMYK (cyan, magenta, yellow and key) model, or the like.

[0044] The absorber of the second fluid may comprise a photon-absorbing additive. Such an additive helps reduce the energy needed to increase the temperature of an exposed voxel to the melting point of the powder forming the substrate 1 14. This may increase the efficiency of the apparatus and/or reduce the carbon footprint of the fabrication method. In some examples, the absorber may be a near infrared dye (NIRD) or a near infrared pigment (NIRP). Such absorbers may, for example, absorb electromagnetic radiation having wavelengths from about 800 nm to about 1400 nm, and convert the absorbed energy to thermal energy.

[0045] In some examples, heat dissipation may be suppressed in regions of the substrate 1 14 that are not to be fused. For example a fluid, referred to herein as a detailing agent, may be applied to regions of the substrate 1 14 that are not to be fused. In some examples, the detailing agent may evaporate when irradiated with electromagnetic radiation emitted by the fuser 1 18. Such evaporation may cool regions of the substrate 1 14 that are not to be fused. This may prevent the particulate material in regions close to the edges of the three-dimensional object 1 10 from fusing to the three-dimensional object 1 10. This may reduce undesired part growth and improve accuracy and surface finish of the three-dimensional object 1 10.

[0046] In some examples, the substrate 1 14 may be preheated to a temperature slightly below the temperature to fuse the particulate material. The energy provided by the electromagnetic radiation emitted by the fuser 1 18 may bring the particulate material in regions in the vicinity of the absorber to a temperature for fusion. The particulate material in these regions may then fuse, and quickly return to a temperature below the temperature for fusion after cessation of the emission of the electromagnetic radiation. For a semi-crystalline polymer, the optimal pre-heat temperature may be slightly below the melting temperature of the polymer.

[0047] Preheating the substrate 1 14 may minimize shrinkage that may otherwise occur during cooling and re-crystallization. By controlling the rate of crystallization, parts can be produced with improved dimensional accuracy and reduced risk of distortion.

[0048] Figure 4 is a schematic diagram showing side and bottom views of an example of a print head assembly 400. In the example, the print head assembly 400 is a thermal print head assembly comprising dies for jetting CMYK colorants, the fusing agent, and the detailing agent. In particular, the print head assembly 400 of this example comprises plural colorant print heads 402 for dispensing fluid comprising a colorant, a fusing agent print head 404 for dispensing fusing agent (comprising an absorber), and a detailing print head 406 for dispensing detailing agent.

[0049] The colorant print heads 402 shown in Figure 4 may include print heads for dispensing cyan, magenta, yellow, black (key), red and green printing fluids. In some examples other printing fluids may be dispensed. For example, more or fewer colorant print heads 402 may be included in the print head assembly 400. In some examples, other printing fluids than those described above may be dispensed, such as, for example, fluorescent printing fluids, gloss enhancers, gloss modifiers, or the like.

[0050] The print head assembly 400 may comprise a translation system, comprising an x-direction translation mechanism and a y-direction translation mechanism, for causing relative movement of the print heads 402 and a build area. Each of the x- and y-direction translation mechanisms may comprise, for example, a translation motor 408x, 408y and a translation belt 41 Ox, 41 Oy. In other examples, other mechanisms for providing relative movement of the print heads 402 and the build area may be provided. In some examples, one or other of the x- and y-direction translation mechanisms may be omitted, such as in examples where the print head assembly 400 is a "page-wide array" print head assembly. A page-wide array print head may be used to increase the throughput of the apparatus 100.

[0051] In some examples, the print head assembly 400 comprises a z- direction translation mechanism (not shown). For example, the z-direction translation mechanism may provide that the print heads 402, 404, 406 can be in close proximity to the substrate 1 14 while dispensing. In some examples, the print heads 402, 404, 406 may be substantially maintained at a distance of 0.25 mm to 3 mm from an uppermost surface of the substrate 1 14. The print head assembly 400 may be driven in a raster scan motion over the substrate 1 14, so that the substrate 1 14 is passed by the print head assembly 400 at least once. Multiple passes of the print head assembly 400 may be executed. [0052] In some examples, the print head assembly 400 may not include any translation mechanisms. For example, the print head assembly 400 may be fixed and stationary and the platen 108 or build area 102 may instead be translated in relation to the print head assembly 400.

[0053] In some examples, the print head assembly may include a thermal shield (not shown) around the print heads 402, 404, 406. Such a thermal shield may help to prevent overheating of the print heads 402, 404, 406 during operation, thereby improving the reliability of the print heads 402, 404, 406. Additionally or alternatively, thermal shutters can be implemented to cap a nozzle that is not being used at a given point in the production process. In some examples, printing fluids may be circulated out of the print heads 402, 404, 406 so that the printing fluids achieve thermal equilibrium. This may facilitate stable dispersion.

[0054] In some examples, the print head assembly 400 may be cooled. In some examples, the temperature of the print head assembly 400 may be monitored by a thermal sensor (not shown) during operation, and the temperature of the print head assembly 400 may be controlled based on the temperature indicated by the thermal sensor.

[0055] In some examples, a temperature sensing system may be used to obtain a thermal map of the substrate 1 14 to provide feedback to the fuser 1 18, thus enabling the fuser 1 18 to be controlled to provide adjustment of the radiation the fuser 1 18 is emitting. This may facilitate compensation for shrinkage, and/or improve fusing uniformity. In some examples, parallel or serial segmented exposures may be implemented with feedback based on the thermal map. This may help improve fusing uniformity.

[0056] In some examples, a non-colored or neutrally-colored absorber may be included in the colorant and be dispensed directly with the colorant. The amount of non-colored absorber included may be dependent on an ability of the first fluid to absorb the electromagnetic radiation. In such examples, the fusing print head 404 may be omitted from the print head assembly 400. In such examples, variation of the mechanical properties of a three-dimensional object that would otherwise be caused by including different colorant can be compensated using the non-colored or neutrally-colored absorber.

[0057] In additive manufacturing approaches that recycle unused build material for subsequent uses, it may be desirable to minimize or prevent contamination of unfused material with colorant so that the unfused material can be recycled. Color-contamination may limit the reuse of un-molten powder for subsequent builds, increasing material waste and the cost of the final part, making the system impractical. In order to minimize contamination, various deposition strategies may be employed, as described below with reference to Figures 5 to 8.

[0058] In Figures 5 to 8, droplets or discrete volumes of printing fluid are represented by circles. Unshaded circles represent droplets or discrete volumes of non-colored or neutrally-colored printing fluid. Shaded circles represent droplets or discrete volumes of printing fluid comprising colorant.

[0059] Figure 5 shows a schematic representation of a deposition strategy according to an example. In the example of Figure 5, droplets of colorant are interspersed with droplets of non-colored or neutrally-colored printing fluid. The result is that the printed part is colored throughout its structure. However, by varying the relative amount of non-colored or neutrally-colored absorber printing fluid to colorant, the mechanical properties and color of the three-dimensional object may be varied separately.

[0060] As discussed above, additionally or alternatively, the amount or volume of non-colored or neutrally-colored absorber dispensed may be varied according to an ability of the colorant to absorb electromagnetic radiation. For example, the amount of non-colored or neutrally-colored absorber may be greater for colorants that weakly absorb the electromagnetic radiation emitted by the fuser 1 18, as compared with colorants that more strongly absorb the electromagnetic radiation emitted by the fuser 1 18.

[0061] In an example, such a deposition strategy may be implemented using a print head assembly 400 with six print heads (or "trenches"). One trench may be used for each of the CMYK colorants, one trench may be used for a non-colored or neutrally-colored absorbing fusing agent, and, one trench may be used for a detailing agent.

[0062] Figure 6 is a schematic representation of a deposition strategy according to another example. In this example, non-colored or neutrally-colored absorber is deposited on internal portions of the three-dimensional object 600 (those in the "core" of the object), and colorant is applied to the outer surface (the "shell") of the object 1 10. Since, the majority of the three-dimensional object 600 is formed by heat absorbed by the absorber, and a relatively small amount of the part is formed by the action of colorant absorbing electromagnetic radiation, the mechanical properties of the three-dimensional object 600 are less susceptible to changes in the ability of the colorant to absorb the electromagnetic radiation. The thickness of the shell may be varied according to the desired appearance of the three-dimensional object 600. For example, the thickness of the shell may be between about 100 microns and about 500 microns.

[0063] Figure 7 is a schematic representation of a deposition strategy similar to that shown in Figure 6. However, in the strategy depicted in Figure 7, just the visible external surfaces of the three-dimensional object 700 are colored.

[0064] Figure 8 is a schematic representation of a deposition strategy which may be used when the absorber is included in the printing fluid containing colorant. In this example, the printing fluid comprising the colorant and the absorber is uniformly deposited throughout the three-dimensional object 800.

[0065] In certain examples, the processor 106 may use a combination of strategies depending on the desired color properties and mechanical properties of the three-dimensional object being produced.

[0066] In some examples, printing fluids dispensed by the apparatus 100 may include other fluids, such as water, dispersants to provide a stable dispersion and improve "jetting" performance, surfactants to control the wetting behavior of droplets of printing fluid (so as to ensure that the droplets penetrate through the substrate 1 14), co-solvents (such as aliphatic alcohols, aromatic alcohols, diols, glycol ethers, polyglycol ethers, caprolactams, formamides, acetamides, and long chain alcohols) to provide good deposition of printing fluids in examples where the print head is out of a capping station, so that evaporation of printing fluid may lead to changes in printing fluid viscosity (so-called "decap" performance), and examples where debris may form on the print head, which may lead to changes in droplet weight and/or droplet velocity (so-called "decel" performance), and the like. In some examples, the printing fluid may include a UV marker which provides a means for alignment of x-y image planes, and may provide a means to authenticate a produced three-dimensional object 1 10.

[0067] The examples described above in which the amount of colorless or neutrally-colored absorber may be controlled may facilitate control of the mechanical properties and color of a three-dimensional object and may facilitate compensation for variation of the mechanical properties of a three-dimensional object that would otherwise be caused by including different colorant. For example, the examples described above may facilitate the formation of a multicolored three-dimensional object with mechanical properties that are substantially uniform throughout the object. That is, the mechanical properties may not be color dependent. Alternatively or additionally, control of the amount of colorless or neutrally-colored absorber may facilitate variation in the mechanical properties of a colored three-dimensional object 1 10. That is, different portions of the object may have different respective mechanical properties.

[0068] Any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with a feature or features of any other of the examples, or any combination of any other of the examples. Furthermore, equivalents and modifications not described above may also be employed.

Claims

CLAIMS What is claimed is:

1 . Apparatus to produce a three-dimensional object, the apparatus being to: apply a first fluid on a layer of particulate material, the first fluid comprising a colorant; and

apply a second fluid on the layer of particulate material, the second fluid comprising an absorber to absorb electromagnetic radiation;

wherein the apparatus is to apply the second fluid to the layer of particulate material in dependence on an ability of the first fluid to absorb the electromagnetic radiation.

2. Apparatus according to claim 1 , wherein the apparatus is to apply a quantity of the second fluid to the layer of particulate material, and the quantity is

determined in dependence on the ability of the first fluid to absorb the

electromagnetic radiation.

3. Apparatus according to claim 1 , wherein the apparatus is to select the second fluid from a plurality of fluids that have different respective electromagnetic absorption characteristics in dependence on the ability of the first fluid to absorb the electromagnetic radiation.

4. Apparatus to produce a three-dimensional object, the apparatus comprising: a dispensing apparatus to dispense a first fluid and a second fluid on a layer of particulate material, the first fluid comprising a colorant and the second fluid comprising an absorber to absorb electromagnetic radiation; and

a processor to control the dispensing apparatus to dispense the second fluid on the basis of an electromagnetic radiation absorption characteristic of the first fluid.

5. Apparatus according to claim 4, comprising an electromagnetic radiation source to emit electromagnetic radiation having a wavelength corresponding to a wavelength at which the absorber absorbs electromagnetic radiation and converts absorbed electromagnetic radiation into thermal energy.

6. Apparatus according to claim 4, comprising a supply mechanism to provide the layer of particulate material.

7. Apparatus according to claim 4, wherein the dispensing apparatus comprises first and second dispensers, wherein the first dispenser is to dispense the first fluid, and the second dispenser is to dispense the second fluid.

8. Apparatus according to claim 4, wherein the dispenser is to dispense one of plural colorants, and the processor is to control a dispensed amount of the second fluid on the basis of a color of the colorant.

9. A method of producing a three-dimensional object, the method comprising: applying a first fluid on a layer of particulate material, the first fluid

comprising a colorant; and

applying a second fluid on the layer of particulate material, the second fluid comprising an absorber to absorb electromagnetic radiation;

wherein the application of the second fluid is dependent on an ability of the first fluid to absorb the electromagnetic radiation.

10. A method according to claim 9, comprising:

controlling an amount of the second fluid applied on the layer of particulate material on the basis of a color of the colorant.

1 1 . A method according to claim 9, comprising irradiating the layer of particulate material with electromagnetic radiation having the first and second fluids applied thereto, thereby melting, sintering or fusing the particulate material in the vicinity of portions of the layer of particulate material on which at least one of the first and second fluids has been applied.

12. A method according to claim 1 1 , comprising providing a further layer of particulate material on the layer of particulate material.

13. A method according to claim 9, comprising applying a third fluid to a portion of the layer of particulate material onto which neither the first nor the second fluid is applied or to be applied, the third fluid being to reduce heating of the layer of particulate material by irradiation with the electromagnetic radiation.

14. A method according to claim 9, wherein an area in which the first fluid is applied on the layer of particulate material substantially overlaps an area in which the second fluid is applied on the layer of particulate material.

15. A method according to claim 9, comprising applying the first fluid to a portion of the layer of particulate material located at an external surface of the three- dimensional object, and applying the second fluid to a portion of the layer of particulate material located within a core of the three-dimensional object.