Patent Description:
Inkjet printing has also been used to print liquid functional materials in three-dimensional (3D) printing. 3D printing may be an additive printing process used to make three-dimensional solid parts from a digital model. 3D printing is often used in rapid product prototyping, mold generation, mold master generation, and short run manufacturing. Some 3D printing techniques are considered additive processes because they involve the application of successive layers of material. This is unlike traditional machining processes, which often rely upon the removal of material to create the final part. 3D printing often requires curing or fusing of the building material, which for some materials may be accomplished using heat-assisted extrusion, melting, or sintering, and for other materials may be accomplished using digital light projection technology.

<CIT> discloses a process for making a component by (A) depositing a first layer of a powder material in a confined region and then (B) depositing a binder material to selected regions of the layer of powder material to produce a layer of bonded powder material at the selected regions.

Examples of the three-dimensional (3D) printing method and the 3D printing system disclosed herein utilize Selective Laser Melting (SLM), Selective Laser Sintering (SLS), or Multi Jet Fusion (MJF). During selective laser melting and selective laser sintering, a laser beam is aimed at a selected region (in some instances less than the entire layer) of a layer of a build material (also referred to as build material particles). Heat from the laser beam causes the build material under the laser beam to melt (in selective laser melting) or sinter (in selective laser sintering). This causes the build material to fuse, bind, cure, etc. to form the layer of the 3D part. During multi jet fusion, an entire layer of a build material is exposed to radiation, but a selected region (in some instances less than the entire layer) of the build material is fused and hardened to become a layer of a 3D part.

Examples of the 3D printing method and 3D printing system disclosed herein utilize a liquid functional agent that contains an energy source material dispersed in an aqueous or non-aqueous vehicle. The energy source material of the liquid functional agent is capable of undergoing a reaction, namely an exothermic reaction that supplies additional heat to the build material.

The liquid functional agent allows for control over the heating and cooling rates of the build material and therefore the kinetics and thermodynamics of phase transformations during the formation of a 3D printed part. Because the liquid functional agent may be jetted (using inkjet technology) onto the build material in discrete amounts (e.g., <NUM> ng to several hundred ng), control over phase nucleation and growth, morphology, microstructure, and grain size may be localized throughout the 3D printed part. Thus, physical properties of the 3D printed part, such as hardness, ultimate tensile strength, elastic modulus, electrical conductivity, and surface finish, may be customized on the voxel scale.

As used herein, the terms "3D printed part," "3D part," or "part" may be a completed 3D printed part or a layer of a 3D printed part.

The 3D printing method shown in <FIG> utilizes the liquid functional agent <NUM> disclosed herein. In some examples, the liquid functional agent <NUM>, which includes an energy source material, does not include an energy absorber. In some of the examples disclosed herein, the energy source material may absorb a sufficient amount of energy in order to initiate an
exothermic reaction. In other examples, the energy source material may absorb little or none of the energy, as the exothermic reaction may be initiated upon exposure to an oxidizer without any outside energy. When energy is absorbed to initiate the exothermic reaction, the energy may be directly applied by an energy source, or it may be energy transferred from a build material which absorbs the energy applied by the energy source. As such, the energy source material does not function as a typical energy absorber, which absorbs a significant amount of the applied energy and converts the applied energy to heat, which is then transferred to the surrounding build material. Rather, some examples of the energy source material absorb little to none of the applied energy, other examples of the energy source material absorb enough energy to initiate an exothermic reaction that produces additional energy.

The liquid functional agent <NUM> is a liquid, and may be included in a single cartridge set or a multiple-cartridge set. In the multiple-cartridge set, any number of the multiple dispersions may have an energy source material incorporated therein.

In one example, the liquid functional agent <NUM> disclosed herein includes a liquid vehicle, and the energy source material. In some examples the liquid functional agent <NUM> consists of these components, with no other components. In still other examples, the liquid functional agent <NUM> may include the energy source material, with no other components.

As used herein, "liquid vehicle," and "vehicle" may refer to the liquid fluid in which the energy source material is placed to form the liquid functional agent(s) <NUM>. A wide variety of vehicles may be used in the liquid functional agent <NUM> and methods of the present disclosure. The vehicle may include water alone, a master solvent alone, or water or a master solvent in combination with a mixture of a variety of additional components. Examples of these additional components may include organic co-solvent(s), surfactant(s), antimicrobial agent(s), anti-kogation agent(s) (for thermal inkjet formulations), and/or chelating agent(s). One example vehicle includes water, co-solvent(s), and surfactant(s). In any of the examples disclosed herein, the co-solvent(s) may be used to improve reliability, nozzle health, and decap performance (i.e., the ability of the fluid to readily eject from a printhead, upon prolonged exposure to air), and the surfactant(s) may be used to quickly wet the build material <NUM>.

The water-based or master solvent-based vehicle may include an organic co-solvent present, in total in the liquid functional agent(s) <NUM>, in an amount ranging from about <NUM> wt% to about <NUM> wt% (based on the total wt% of the liquid functional agent <NUM>), depending, at least in part, on the jetting architecture. In an example, the co-solvent is present in the liquid functional agent <NUM> in an amount of about <NUM> wt% based on the total wt% of the liquid functional agent <NUM>. It is to be understood that other amounts outside of this example and range may also be used. Examples of suitable co-solvents include high-boiling point solvents (some of them may also have a humectant functionality), which have a boiling point of at least <NUM>. Classes of organic co-solvents that may be used include aliphatic alcohols, aromatic alcohols, diols, glycol ethers, polyglycol ethers, <NUM>-pyrrolidinones, caprolactams, formamides, acetamides, glycols, and long chain alcohols. Examples of these co-solvents include primary aliphatic alcohols, secondary aliphatic alcohols, <NUM>,<NUM>-alcohols, <NUM>,<NUM>-alcohols, <NUM>,<NUM>-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs (C<NUM>-C<NUM>) of polyethylene glycol alkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams, both substituted and unsubstituted formamides, both substituted and unsubstituted acetamides, and the like. In some examples, the vehicle may include <NUM>-(<NUM>-hydroxyethyl)-<NUM>-pyrrolidone.

It is to be understood that some of the high-boiling point solvents capable of oxidation may also function as energy source materials (e.g., when an oxidizer is present in the surrounding environment or introduced by jetting) or energy sink materials (e.g., in the absence of oxidizer). For example, in the presence of O<NUM> or O<NUM> precursors, many organic solvents suitable for inkjet formulations (and for the liquid functional agent <NUM> disclosed herein) can be oxidized to CO<NUM>, H<NUM>O and, in some cases, N<NUM>, with a significant amount of heat released. Some specific examples include <NUM>-butanol (ΔHc = -2670kJ/mol), <NUM>,<NUM>-pentanediol (ΔHc = -<NUM>. 8kJ/mol), <NUM>,<NUM>-Hexanediol.

(ΔHc = -<NUM>. 8kJ/mol); <NUM>-pyrrolidone (ΔHc = -<NUM>. 40kJ/mol); glycerol (ΔHc = - <NUM>. 3kJ/mol); diethylene glycol (ΔHc = -<NUM>. 7kJ/mol); tetraethylene glycol (ΔHc = - <NUM>. 8kJ/mol); <NUM>-hexanol (ΔHc = -<NUM> kJ/mol); sorbitol (ΔHc = -<NUM>. 4kJ/mol), etc..

As mentioned above, the vehicle may also include surfactant(s). As an example, the liquid functional agent <NUM> may include non-ionic, cationic, and/or anionic surfactants, which may be present in an amount ranging from about <NUM> wt% to about <NUM> wt% based on the total wt% of the liquid functional agent <NUM>. In at least some examples, the vehicle may include a silicone-free alkoxylated alcohol surfactant such as, for example, TEGO® Wet <NUM> (EvonikTegoChemie GmbH) and/or a self-emulsifiable wetting agent based on acetylenic diol chemistry, such as, for example, SURFYNOL® SE-F (Air Products and Chemicals, Inc. Other suitable commercially available surfactants include SURFYNOL® <NUM> (ethoxylatedacetylenic diol), SURFYNOL® CT-<NUM> (now CARBOWET® GA-<NUM>, non-ionic, alkylphenylethoxylate and solvent free), and SURFYNOL® <NUM> (non-ionic wetting agent based on acetylenic diol chemistry), (all of which are from Air Products and Chemicals, Inc. ); ZONYL® FSO (a. CAPSTONE®, which is a water-soluble, ethoxylated non-ionic fluorosurfactant from Dupont); TERGITOL® TMN-<NUM> and TERGITOL® TMN-<NUM> (both of which are branched secondary alcohol ethoxylate, non-ionic surfactants), and TERGITOL® <NUM>-S-<NUM>, TERGITOL® <NUM>-S-<NUM>, and TERGITOL® <NUM>-S-<NUM> (each of which is a secondary alcohol ethoxylate, non-ionic surfactant) (all of the TERGITOL® surfactants are available from The Dow Chemical Co.

The vehicle may also include antimicrobial agent(s). Suitable antimicrobial agents include biocides and fungicides. Example antimicrobial agents may include the NUOSEPT® (Ashland Inc. ), UCARCIDE™ or KORDEK™ (Dow Chemical Co. ), and PROXEL® (Arch Chemicals) series, ACTICIDEO M20 (Thor), and combinations thereof. In an example, the liquid functional agent <NUM> may include a total amount of antimicrobial agents that ranges from about <NUM> wt% to about <NUM> wt%.

When the liquid functional agent <NUM> is to be applied via thermal inkjet applications, an anti-kogation agent may also be included in the vehicle. Kogation refers to the deposit of dried ink on a heating element of a thermal inkjet printhead. Anti-kogation agent(s) is/are included to assist in preventing the buildup of kogation. Examples of suitable anti-kogation agents include oleth-<NUM>-phosphate (commercially available as CRODAFOS™ O3A or CRODAFOS™ N-<NUM> acid) or dextran <NUM>. Other suitable examples of the anti-kogation agents include CRODAFOS™ HCE (phosphate-ester from Croda Int. ), CRODAFOS® N10 (oleth-<NUM>-phosphate from Croda Int. ), or DISPERSOGEN® LFH (polymeric dispersing agent with aromatic anchoring groups, acid form, anionic, from Clariant), etc. The anti-kogation agent may be present in the liquid functional agent <NUM> in an amount ranging from about <NUM> wt% to about <NUM> wt% of the total wt% of the liquid functional agent <NUM>.

The vehicle may also include a chelating agent. Examples of suitable chelating agents include disodium ethylenediaminetetraacetic acid (EDTA-Na) and methylglycinediacetic acid (e.g., TRILON® M from BASF Corp. Whether a single chelating agent is used or a combination of chelating agents is used, the total amount of chelating agent(s) in the liquid functional agent <NUM> may range from <NUM> wt% to about <NUM> wt% based on the total wt% of the liquid functional agent <NUM>.

The balance of the vehicle is water or a master solvent. As such, the amount of water or master solvent may vary depending upon the weight percent of the other liquid functional agent components.

In an example, the water is deionized water.

Examples of the master solvent may be water-soluble solvents or non-aqueous solvents, such as lower polarity solvents or non-polar solvents. Examples of water-soluble solvents with polar groups include primary aliphatic alcohols, secondary aliphatic alcohols, <NUM>,<NUM>-alcohols, <NUM>,<NUM>-alcohols, <NUM>,<NUM>-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs (C<NUM>-C<NUM>) of polyethylene glycol alkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams, both substituted and unsubstituted formamides, both substituted and unsubstituted acetamides, and the like. In some examples, the master solvent may be <NUM>-(<NUM>-hydroxyethyl)-<NUM>-pyrrolidone. In other cases, the master solvent may be based on lower polarity or non-polar solvents, both of which have poor water solubility. Examples of lower polarity or non-polar solvents include aliphatic, cyclic aliphatic or aromatic hydrocarbons. Water insoluble fatty alcohols, esters, ketones, ethers and other liquid (at ambient temperatures) oxidizable organic species are suitable candidates for non-aqueous formulations, especially for piezo applications. It is desirable that any of the master solvents disclosed herein have a boiling temperature that is higher than water.

The liquid functional agent <NUM> (shown in <FIG>) also includes the energy source material. The energy source material are each capable of undergoing a reaction. When an energy source material is included in the liquid functional agent <NUM>, the reaction is an exothermic reaction that supplies additional heat/energy to a composite layer <NUM> (i.e., a portion of the build material <NUM> patterned with the liquid functional agent <NUM>). Also described herein is an energy sink material that may be included in the liquid functional agent <NUM>. In this case, the reaction is an endothermic reaction that consumes heat/energy from the composite layer <NUM>.

An energy sink material may consume heat not through chemical reaction but through phase change. Examples of these energy sink materials include polar organic solvents and other species (usually organic) with high boiling temperatures and considerable heat of vaporization, for example, glycerol (Tboil=<NUM>°K; ΔvapH = <NUM>. <NUM> kJ/mol); <NUM> ,<NUM>-pentanediol (Tboil=<NUM>°K; ΔvapH = <NUM> kJ/mol); sorbitol (Tboil=<NUM>°K; ΔvapH = <NUM> kJ/mol); and urea (Tevaporation=<NUM>°K; ΔvapH = <NUM> kJ/mol). Many of the organic species with significant negative oxidation enthalpy may act both as an energy source material in the presence of an oxidizer and also as an energy sink material in an absence of an oxidizing species. An example of a species with such behavior would be a majority of combustible high boiling organic solvents (fatty alcohols, diols, triols, etc.). On the other hand, some of the species with relatively low negative oxidation enthalpy can be confined to an energy sink role alone (such as urea, which is not combustible at ambient conditions).

By selectively applying the liquid functional agent <NUM> and selectively initiating exothermic reactions, the heating and cooling rates of the build material <NUM> may be controlled. The cooling rate directly defines the phase and morphology of the resulting 3D printed part, which in turn defines the physical properties of the 3D part. For example, when steel <NUM> heated to <NUM> or higher has a cooling rate of greater than <NUM>/s, martensite is formed. When the cooling rate is less than <NUM>/s and greater than <NUM>/s, a combination of martensite and bainite is formed. At a cooling rate of less than <NUM>/s and greater than <NUM>/s, a combination of martensite, bainite, and ferrite is formed. At a cooling rate of less than <NUM>/s and greater than <NUM>/s, a combination of martensite, bainite, ferrite, and pearlite is formed, and at a cooling rate of less than <NUM>/s, a combination of pearlite and ferrite is formed. Ferrite is soft and tough. Pearlite has a lamellar structure and is stronger and harder than ferrite. Bainite is generally harder and stronger than pearlite but still retains good toughness. Martensite is very hard and brittle. Thus, by controlling the cooling rates at different areas of the 3D part, different physical properties can be achieved at those different areas of the part. For example, the 3D part may have different levels of structural integrity at different areas based on the cooling rates of those areas, which may be controlled using examples of the liquid functional agent <NUM> disclosed herein.

The exothermic reaction involving the energy source material that supplies additional heat/energy to a composite layer <NUM> (i.e., a portion of the build material <NUM> patterned with the liquid functional agent <NUM>) generates a gaseous byproduct. If the byproduct of the exothermic reaction is not a gas, the byproduct may contaminate the build material <NUM> and the resulting 3D printed part may be contaminated with a solid residue. The energy source material may be a reactant including a fuel and an oxidizer, or a reactant fuel.

When the energy source material is the reactant including both the fuel and oxidizer, some oxidizable parts of the reactant molecule structure act as a fuel while other parts of the reactant molecule structure act as oxidizer. In these examples, the exothermic reaction may be initiated by exposing the composite layer <NUM> to energy. Examples of this type of reactant (including the fuel and oxidizer) include organic molecules with nitro (NO<NUM>) groups such as picric acid and its esters, dinitrotoluene, trinitrotoluene, cyclotrimethylenetrinitroamine, nitroguanidine, triaminodinitrobenzene, triaminotrinitrobenzene, ethylenediamine dinitrate, ethylene dinitramine, etc. Further examples include organic esters of nitric acid, such as nitrocellulose, dinitroglycerol, and ethyleneglycol dinitrate; nitrates of mannitol of variable degrees of esterification; and nitrates of pentaerythritol. Still further examples include organic salts of nitric, chloric and perchloric acids, such as methylammonium nitrate.

When the energy source material is a reactant fuel, the exothermic reaction may be initiated by exposing the composite layer <NUM> to both an oxidizer and energy, or the exothermic reaction may be initiated by exposing the composite layer <NUM> to an oxidizer (i.e., no outside energy or ignition source is utilized). Examples of the reactant fuel, whose exothermic reaction may be initiated by exposure to both the oxidizer and energy, include oxidizable species with low vapor pressure at ambient conditions (e.g., vapor pressure less than that of water at ambient conditions). As used herein, ambient conditions refer to the air temperature of any environment where a human can function comfortably without means of protection, e.g., from about <NUM> to about <NUM>. In an example, the reactant fuel produces oxidation products in the gas phase (e.g., water, carbon monoxide and dioxide, nitrogen, etc.) with very little or no oxidation products formed in the state of solid residue. Some examples include sugars and sugar alcohols such as sucrose, sorbitol, mannitol, glucose, fructose, etc. Still further examples include high boiling hydrocarbons (e.g., having a boiling point greater than the boiling point of water) of aliphatic and aromatic nature, such as diesel fuel, decalin, decalene, naphthalene, tetralin, and hydrocarbon waxes. Still further examples include high boiling alcohols (e.g., having a boiling point greater than the boiling point of water), such as glycerol, ethylene glycol, and diethylene glycol; organic amines of low volatility (e.g., slow evaporation at ambient conditions), such as hexamethylenetetramine; and dispersions of carbon particles, such as carbon black and graphite. Examples of the reactant fuel, whose exothermic reaction may be initiated by exposures to the oxidizer alone, include hydrazine, monomethylhydrazine, dimethylhydrazine, aniline, furfuryl alcohol, turpentine, tetramethylethylenediamine, and other easy to oxidize chemical species capable of spontaneous combustion (i.e., without external ignition) when in direct contact with aggressive oxidizing agents.

Examples of the oxidizer that may be used to initiate the reaction involving sugars, sugar alcohols, high boiling aliphatic hydrocarbons, high boiling aromatic hydrocarbons, high boiling alcohols, organic amines of low volatility, or dispersions of carbon particles may be introduced through the environment or by jetting. Examples of the oxidizer which may be introduced through the environment include oxygen gas and nitrous oxide (N<NUM>O) gas. Examples of the oxidizer which may be introduced by jetting onto the composite layer <NUM> include soluble chemical species capable of generating sufficient amounts of oxygen during their thermal decomposition, such as ammonium nitrate, ammonium perchlorate, potassium permanganate, potassium perchlorate, and aggressive oxidizing agents, such as red fuming nitric acid, high concentration hydrogen peroxide (e.g., greater than <NUM> wt% solution in water), and perchloric acid.

Examples of the oxidizer that may be used to initiate the reaction involving hydrazine, monomethylhydrazine, dimethylhydrazine, aniline, furfuryl alcohol, turpentine, or tetramethylethylenediamine, include ammonium nitrate, ammonium perchlorate, potassium permanganate, potassium perchlorate, red fuming nitric acid, high concentration hydrogen peroxide (e.g. greater than <NUM> wt% solution in water), perchloric acid, nitrogen tetroxide (NTO), and nitric acid. Any of the liquids or solid state oxidizers that can be incorporated into a liquid, including ammonium nitrate, ammonium perchlorate, potassium permanganate, potassium perchlorate, red fuming nitric acid, high concentration hydrogen peroxide, nitrogen tetroxide (NTO), nitric acid, and perchloric acid, may be applied by jetting onto the composite layer <NUM>.

The additional heat supplied by the exothermic reaction of the energy source material may super heat areas of the build material <NUM> to a temperature far above its melting temperature. This will cause the super heated portions of the build material <NUM> to cool at a different rate than the build material <NUM> that was not super heated. Thus, the super heated areas will have a different microstructure, and therefore, different physical properties, than the areas that were not super heated. Additionally, the additional heat supplied by the exothermic reaction may contribute to the fusing of the build material <NUM> during the 3D printing process. This additional heat may allow for the use of an energy source (during the 3D printing process) with reduced power (as compared to the power that would be needed to fuse the build material <NUM> without the aid of the reaction involving the energy source material). This additional heat may also allow the temperature supplied by the energy source to be reduced (as compared to the temperature that would be supplied by the energy source when the reaction involving the energy source material is not utilized). In this example, the energy source may heat the build material <NUM> to a temperature that is below the melting point of the build material <NUM>, and the additional heat supplied by the exothermic reaction may bring the build material <NUM> to its melting point. This additional heat may further allow the build material <NUM> to fuse or melt in a shorter amount of time (as compared to the amount of time that would be required to fuse the build material <NUM> without the aid of the reaction involving the energy source material).

The energy source material may be present in the liquid functional agent <NUM> in an amount ranging from greater than <NUM> wt% to about <NUM> wt% of a total weight percent of the liquid functional agent <NUM>. For example, a piezoelectric printhead may jet a liquid functional material <NUM> including <NUM> wt. % of a hydrocarbon fluid that is used the reactant fuel. It is believed that the energy source material loadings may be selected to provide a balance between the liquid functional agent <NUM> having jetting reliability and heat supply efficiency. Additionally, the energy source material selected and the amount of the energy source material to be incorporated into the liquid functional agent <NUM> may be based on the amount of additional heat desired and the build material <NUM> to which the heat is to be supplied.

Any of the heat source materials that are soluble in the selected vehicle (when a vehicle is used) do not require a dispersing agent.

Any of the heat source materials that are present in the liquid functional agent <NUM> as solid particles (e.g., carbon black) may include a dispersing species/agent. Examples of suitable dispersing species may be polymer or small molecule dispersants, charged groups attached to the particle surface, or other suitable dispersants. The dispersing agent helps to uniformly distribute the heat source material throughout the liquid functional agent <NUM>. Some examples of suitable dispersing agents include a water soluble acrylic acid polymer (e.g., CARBOSPERSE® K7028 available from Lubrizol), water-soluble styrene-acrylic acid copolymers/resins (e.g., JONCRYL@ <NUM>, JONCRYL@ <NUM> , JONCRYL® <NUM>, JONCRYL@ <NUM>, JONCRYL@ <NUM>, JONCRYL® <NUM>, etc. available from BASF Corp. ) or water-soluble styrene-maleic anhydride copolymers/resins. When utilized, the dispersing agent may be present in an amount ranging from about <NUM> wt% to about <NUM> wt% of the total wt% of the heat source material.

In examples of the 3D printing method disclosed herein, it is to be understood that one liquid functional agent <NUM> may be used to alter a thermal condition of the composite layer <NUM>. It is also to be understood that multiple liquid functional agents <NUM> may be mixed at the same area of build material <NUM> to alter a thermal condition of the composite layer <NUM>, or multiple liquid functional agents <NUM> may be applied to different areas of build material <NUM> (thus forming different composite layers <NUM>) in order to alter a combination of thermal conditions of the composite layers <NUM>.

An example of the 3D printing method <NUM> is depicted in <FIG>. As an example, the method <NUM> may be used to control the physical properties of a 3D part on the voxel level.

Several variations of the method may take place. Generally, the liquid functional material <NUM> and the build material <NUM> are applied, where the liquid functional material <NUM> may be applied before the application of the build material <NUM>, after the application of the build material <NUM>, or both before and after the application of the build material <NUM>. Each of these scenarios is depicted in the method <NUM>.

In one example of the method <NUM>, the liquid functional agent <NUM> is applied below and on the build material <NUM> before the composite layer <NUM> is exposed to energy (e.g., reference numerals <NUM>-<NUM> and either <NUM> or <NUM><NUM>). In another example, the liquid functional agent <NUM> is only applied below the build material <NUM> before the composite layer <NUM> is exposed to energy (e.g., reference numerals <NUM>, <NUM> and either <NUM> or <NUM><NUM>). In still another example, the liquid functional agent <NUM> is only applied on the build material <NUM> before the composite layer <NUM> is exposed to energy (e.g., reference numerals <NUM> - without the liquid functional material <NUM> - and <NUM> and either <NUM> or <NUM><NUM>).

While not shown, some examples of the method <NUM> include the application of a second liquid functional agent including an oxidizer to the composite layer <NUM>. Additionally, in some examples of the method <NUM>, the composite layer <NUM> is exposed to energy by using a spatially broad source <NUM> of energy (e.g., reference numeral <NUM>), and in other examples of the method <NUM>, the composite layer <NUM> is exposed to energy by using a tightly focused source <NUM> of energy. Each of these examples of the method <NUM> will be described in more detail below.

As shown in <FIG> at reference numeral <NUM>, one example of the method <NUM> includes selective applying the liquid functional agent <NUM>, which includes the energy source material, before the build material <NUM> is applied. In the example illustrated at reference numeral <NUM>, the liquid functional agent <NUM> is selectively applied to a build surface <NUM> before any build material <NUM> is applied thereto. In other examples (not shown), the liquid functional agent <NUM> is selectively applied below the build material <NUM> by selectively applying liquid functional agent <NUM> to a previously formed layer (e.g., a previously solidified layer of the 3D object). When the liquid functional agent <NUM> is applied, it forms a patterned area on the build surface <NUM> or on the previously formed layer. As shown at reference numeral <NUM>, the build surface <NUM> may be the contact surface of a fabrication bed <NUM>.

When the liquid functional agent <NUM> is applied before the build material <NUM>, it is to be understood that the liquid functional agent <NUM> may penetrate into the subsequently applied layer of build material <NUM>. The liquid functional agent <NUM> may completely saturate the subsequently applied layer of build material <NUM> or may partially penetrate the subsequently applied layer of build material <NUM>. The level of saturation/penetration may depend, at least in part, on the layer thickness, the particle size of the build material <NUM> particles, and the volume of the liquid functional agent <NUM> that is applied.

In the example shown at reference numeral <NUM>, applying the liquid functional agent <NUM> includes the use of the 3D printing system <NUM>. The 3D printing system <NUM> may include an inkjet applicator <NUM>, a supply bed <NUM> (including a supply of the build material <NUM>), a delivery piston <NUM>, a spreader <NUM> (an example of which is the roller shown in <FIG>), a fabrication bed <NUM> (having the build surface <NUM>), and a fabrication piston <NUM>. Each of these physical elements may be operatively connected to a central processing unit (i.e., controller, not shown) of the printing system <NUM>. The central processing unit (e.g., running computer readable instructions stored on a non-transitory, tangible computer readable storage medium) manipulates and transforms data represented as physical (electronic) quantities within the printer's registers and memories in order to control the physical elements to create the 3D part (not shown). The data for the selective delivery of the liquid functional agent <NUM>, the build material <NUM>, etc. may be derived from a model of the 3D part to be formed. For example, the instructions may cause the controller to utilize an applicator (e.g., an inkjet applicator <NUM>) to selectively dispense the liquid functional agent <NUM>, and to utilize a build material distributor to dispense the build material <NUM>. Each of the components of the 3D printing system <NUM> will be described in more detail throughout the description of the method <NUM>.

The liquid functional agent <NUM> may be dispensed from any suitable applicator. As illustrated in <FIG> at reference number <NUM>, the liquid functional agent <NUM> may be dispensed from an inkjet printhead <NUM>, such as a thermal inkjet printhead or a piezoelectric inkjet printhead. The printhead <NUM> may be a drop-on-demand printhead or a continuous drop printhead. The inkjet printhead(s) <NUM> selectively applies the liquid functional agent <NUM> on those portions <NUM> of the build surface <NUM> or the previously formed layer upon which the composite layer <NUM> is to be formed. The liquid functional agent <NUM> is not applied on the portions <NUM>. As such, build material <NUM> that is applied on those portions <NUM> of the build surface <NUM> or the previously formed layer will not be patterned by the applied liquid functional agent <NUM>.

In the example shown at reference numeral <NUM> in <FIG>, the liquid functional agent <NUM> is deposited on less than all of the build surface <NUM>. In other examples (not shown), the liquid functional agent <NUM> is deposited in different patterns than the one shown in <FIG> on less than all of the build surface <NUM> or on less than all of the previously formed layer. In still other examples (not shown), the liquid functional agent <NUM> is deposited on all of the build surface <NUM> or on all of the previously formed layer.

The printhead <NUM> may be selected to deliver drops of the liquid functional agent <NUM> at a resolution ranging from about <NUM> dots per inch (DPI) to about <NUM> DPI. In other examples, the printhead <NUM> may be selected to be able to deliver drops of the liquid functional agent <NUM> at a higher or lower resolution. The drop velocity may range from about <NUM>/s to about <NUM>/s and the firing frequency may range from about <NUM> to about <NUM>. The printhead <NUM> may include an array of nozzles through which it is able to selectively eject drops of fluid. In one example, each drop may be in the order of about <NUM> ng per drop, although it is contemplated that a higher (e.g., <NUM> ng) or lower (e.g., <NUM> ng) drop size may be used. In some examples, printhead <NUM> is able to deliver variable size drops of the liquid functional agent <NUM>.

The inkjet printhead(s) <NUM> may be attached to a moving XY stage or a translational carriage (neither of which is shown) that moves the inkjet printhead(s) <NUM> adjacent to the build surface <NUM> in order to deposit the liquid functional agent <NUM> in desirable area(s) <NUM>. In other examples, the printhead(s) <NUM> may be fixed while a support member (supporting the build surface <NUM>) is configured to move relative thereto.

In an example, the printhead(s) <NUM> may have a length that enables it to span the whole width of the build surface <NUM> in a page-wide array configuration. As used herein, the term 'width' generally denotes the shortest dimension in the plane parallel to the X and Y axes of the build surface <NUM>, and the term 'length' denotes the longest dimension in this plane. However, it is to be understood that in other examples the term 'width' may be interchangeable with the term 'length'. In an example, the page-wide array configuration is achieved through a suitable arrangement of multiple printheads <NUM>. In another example, the page-wide array configuration is achieved through a single printhead <NUM>. In this other example, the single printhead <NUM> may include an array of nozzles having a length to enable them to span the width of the build surface <NUM>. This configuration may be desirable for single pass printing. In still other examples, the printhead(s) <NUM> may have a shorter length that does not enable them to span the whole width of the build surface <NUM>. In these other examples, the printhead(s) <NUM> may be movable bi-directionally across the width of the build surface <NUM>. This configuration enables selective delivery of the liquid functional agent <NUM> across the whole width and length of the build surface <NUM> using multiple passes.

The inkjet printhead(s) <NUM> may be programmed to receive commands from a central processing unit and to deposit the liquid functional agent <NUM> according to a pattern of thermal condition(s) of the composite layer <NUM> to be achieved. In an example, a computer model of the part to be printed is generated using a computer aided design (CAD) program. The computer model of the 3D part is sliced into N layers, which are then divided into voxels. The printing parameters for each voxel are computed based on the desired physical properties of the part to be printed. The printing parameters for each voxel may include the X, Y, and Z coordinates that define its location and the amounts of which liquid functional agents <NUM> (if any) that are to be received. The central processing unit may then use this information to instruct the inkjet printhead(s) <NUM> as to how much (if any) of each liquid functional agent <NUM> should be jetted into each voxel.

After the liquid functional agent <NUM> is selectively applied in a pattern on the desired portion(s) <NUM> of the build surface <NUM> or the previously formed layer, a build material <NUM> is applied to the build surface <NUM> or the previously formed layer. When the liquid functional agent <NUM> is applied to the build surface <NUM> or the previously formed layer prior to the build material <NUM> being applied to the build surface <NUM> or the previously formed layer, the build material <NUM> and the liquid functional agent <NUM> combine to form the composite layer <NUM>, as shown at reference numeral <NUM>.

In another example of the 3D printing method <NUM>, the build material <NUM> may be applied to the build surface <NUM> or the previously formed layer without the liquid functional agent <NUM> having been applied to the build surface <NUM> or the previously formed layer first. In this example, the method <NUM> begins at step <NUM>, and while the liquid functional agent <NUM> is shown at the bottom of the build material <NUM> at reference numerals <NUM>-<NUM>, it would not be present. Additionally, in this example of the method <NUM>, the build material <NUM> does not form the composite layer <NUM> with the liquid functional agent <NUM> until the liquid functional agent <NUM> is applied at reference numeral <NUM>.

The build material <NUM> may be a metallic material or a ceramic material. In an example, the build material <NUM> may be a powder.

Some examples of metallic build material <NUM> include steels, stainless steel, titanium (Ti) and alloys thereof, nickel cobalt (NiCo) alloys, gold (Au) and alloys thereof, silver (Ag) and alloys thereof, and copper (Cu) and alloys thereof. Some specific examples include A!Si10Mg, CoCr MP1, CoCr SP2, MaragingSteel MS1, NickelAlloy HX, Inconel IN625, Inconel IN718, SS GP1, SS PH1, SS <NUM>, Ti6Al4V, and Ti-6Al-4V ELI7.

Examples of the ceramic build material <NUM> include metal oxides, inorganic glasses, carbides, nitrides, borides, or combinations thereof. Some specific examples include alumina (Al<NUM>O<NUM>), Na<NUM>O/CaO/SiO<NUM> glass (soda-lime glass), silicon carbide (SiC), silicon nitride (Si<NUM>N<NUM>), silicon dioxide (SiO<NUM>), zirconia (ZrO<NUM>), titanium dioxide (TiO<NUM>), iron oxide (Fe<NUM>O<NUM>), hafnia (HfO<NUM>), barium titanate (BaTiO<NUM>), tungsten carbide (WC), lead zirconate titanate (PZT), Hydroxyapatite, or combinations thereof. As an example of one suitable combination, <NUM> wt% glass may be mixed with <NUM> wt% alumina.

The build material <NUM> may have a melting point ranging from about <NUM> to about <NUM>. As examples, the build material <NUM> may be metal having a melting point ranging from about <NUM> to about <NUM>, or a metal oxide having a melting point ranging from about <NUM> to about <NUM>.

The build material <NUM> may be made up of similarly sized particles or differently sized particles. In the examples shown herein, the build material <NUM> includes similarly sized particles. The term "size", as used herein with regard to the build material <NUM>, refers to the diameter of a substantially spherical particle (i.e., a spherical or near-spherical particle having a sphericity of ><NUM>), or the average diameter of a non-spherical particle (i.e., the average of multiple diameters across the particle). The average particle size of the particles of the build material <NUM> may be greater than <NUM> and may be up to about <NUM>. Substantially spherical particles of this particle size have good flowability and can be spread relatively easily. As another example, the average size of the particles of the build material <NUM> ranges from about <NUM> to about <NUM>. As still another example, the average size of the particles of the build material <NUM> ranges from <NUM> to about <NUM>. In an example, the particle size of the ceramic build material particles <NUM> is greater than or equal to <NUM> for materials with a bulk density of greater than or equal to <NUM>. For lower density ceramic build material particles, the particle size can be much larger.

As mentioned above, the 3D printing system <NUM> may include the supply bed <NUM>, the delivery piston <NUM>, the spreader <NUM>, the fabrication bed <NUM>, and the fabrication piston <NUM>. The delivery piston <NUM> and the fabrication piston <NUM> may be the same type of piston, but are programmed to move in opposite directions. In an example, when a layer of the 3D part is to be formed, the delivery piston <NUM> may be programmed to push a predetermined amount of the build material <NUM> out of the opening in the supply bed <NUM> and the fabrication piston <NUM> may be programmed to move in the opposite direction of the delivery piston <NUM> in order to increase the depth of the fabrication bed <NUM>. The delivery piston <NUM> will advance enough so that when the spreader <NUM> pushes the build material <NUM> into the fabrication bed <NUM> and onto the build surface <NUM> or the previously formed layer, the depth of the fabrication bed <NUM> is sufficient so that a composite layer <NUM> of the build material <NUM> and the liquid functional agent <NUM> may be formed in the fabrication bed <NUM>. The spreader <NUM> is capable of spreading the build material <NUM> into the fabrication bed <NUM> to form a build material layer, which is relatively uniform in thickness. In an example, the thickness of the build material layer ranges from about <NUM> to about <NUM>, although thinner or thicker layers may also be used. For example, the thickness of the layer <NUM> may range from about <NUM> to about <NUM>. Depending upon the desired thickness for the layer <NUM> and the particle size of the build material <NUM>, the layer <NUM> that is formed in a single build material application may be made up of a single row of build material particles or several rows of build material particles (as shown at reference numeral <NUM>).

It is to be understood that the spreader <NUM> may be replaced by other tools, such as a blade that may be useful for spreading different types of powders, or a combination of a roller and a blade.

The supply bed <NUM> that is shown is one example, and could be replaced with another suitable delivery system to supply the build material <NUM> to the fabrication bed <NUM>. Examples of other suitable delivery systems include a hopper, an auger conveyer, or the like.

The fabrication bed <NUM> that is shown is also one example, and could be replaced with another support member, such as a platen, a print bed, a glass plate, or another build surface.

In one example of the method, after the build material <NUM> is applied, as shown in <FIG> at reference numeral <NUM>, the liquid functional agent <NUM> may be selectively applied to the build material <NUM>, as shown at reference number <NUM>. As illustrated at reference numeral <NUM>, the liquid functional agent <NUM> may be selectively applied to the build material <NUM> by the inkjet printhead <NUM>.

When the liquid functional agent <NUM> is applied on the build material <NUM>, it is to be understood that the liquid functional agent <NUM> may reside at the top of the layer <NUM>, may completely saturate the layer <NUM>, or may partially penetrate the layer <NUM>. The level of saturation/penetration may depend, at least in part, on the layer thickness, the particle size of the build material <NUM> particles, and the volume of the liquid functional agent <NUM> that is applied.

It is to be understood that when the same liquid functional agent <NUM> is applied both below and on the build material <NUM>, it may be applied in the same pattern or in a different pattern. When multiple liquid functional agents <NUM> are used, they may be applied in the same pattern or different patterns, which may be above and/or below the build material <NUM>.

It is also to be understood that in some examples of the method <NUM>, the liquid functional agent <NUM> is applied before the build material <NUM> is applied (and thus penetrates a lower portion of the applied build material <NUM>) and is not applied after the build material <NUM> is applied (i.e., is not applied on the build material <NUM>). In these examples, the method <NUM> proceeds from reference numeral <NUM> to either reference numeral <NUM> or reference numeral <NUM>.

In some examples of the 3D printing method, the composite layer <NUM> is exposed to an oxidizer (not shown). As previously described, the oxidizer may be used when particular reactants are used which participate in an exothermic reaction. Exposing the composite layer <NUM> to the oxidizer may initiate the reaction involving the energy source material when the energy source material is the reactant fuel. The reaction may be initiated by exposing the composite layer <NUM> (which includes the energy source material) to the oxidizer alone or exposing the composite layer <NUM> (which includes the energy source material) to both the oxidizer and energy.

The composite layer <NUM> may be exposed to the oxidizer by introducing the oxidizer through an environment in which the reaction takes place. For example, the oxidizer may be oxygen gas or nitrogen oxide (N<NUM>O, NO, NO<NUM>) gases in the environment around the fabrication bed <NUM>.

Alternatively, the composite layer <NUM> may be exposed to the oxidizer by selectively applying a second liquid functional agent (not shown), including an oxidizer, to the composite layer <NUM>. The second liquid functional agent may be applied on all or less than all of the same portion(s) <NUM> of the build material <NUM> in contact the liquid functional agent <NUM> having the energy source material therein. In this example, the second liquid functional agent may be applied on the portion(s) of the composite layer <NUM> where it is desirable for the exothermic reaction to take place.

In an example, the second liquid functional agent may be an oxidizer that is jettable without a liquid vehicle. Examples of oxidizers that are jettable without a liquid vehicle include HNO<NUM>, H<NUM>O<NUM>, HClO<NUM> and other liquid oxidizers that may be jetted without a vehicle in concentrated state. In another example, the oxidizer may be a liquid dissolved in a vehicle. Examples of solid state oxidizers dissolved in liquid vehicle include ammonium nitrate, ammonium perchlorate, potassium permanganate, potassium perchlorate. Examples of liquid oxidizers which can be delivered with or w/o another liquid vehicle include red fuming nitric acid, high concentration hydrogen peroxide (e.g. greater than <NUM> wt% solution in water), perchloric acid, nitrogen tetroxide (NTO), and nitric acid. In still another example, the oxidizer may be suspended in the liquid vehicle (e.g., a non-polar liquid).

The liquid oxidizer may be present in the second liquid functional agent in an amount ranging from greater than <NUM> wt% to about <NUM> wt% of a total weight percent of the second liquid functional agent. The solid state oxidizer may be present in the second liquid functional agent in an amount ranging from greater than <NUM> wt% to about <NUM> wt% of a total weight percent of the second liquid functional agent. In one example, the amount of the solid state oxidizer is present in an amount ranging from greater than <NUM> wt% to about <NUM> wt%. When the second liquid functional agent includes a liquid vehicle in addition to the oxidizer, the liquid vehicle may include similar components to the liquid vehicle of the liquid functional agent <NUM> (e.g., co-solvent(s), surfactant(s), dispersing agent(s), water or master solvent, etc.).

The second liquid functional agent may be dispensed from an inkjet applicator, such as an inkjet printhead. The printhead may be any of the printheads described above in relation to the printhead(s) <NUM> (which is used to apply the liquid functional agent <NUM> at reference numerals <NUM> and/or <NUM> in <FIG>). The printhead used to dispense the second liquid functional agent may also function (e.g., move, receive commands from the central processing unit, etc.) and have the same dimensions (e.g., length and width) as the printhead(s) <NUM> described above. The liquid functional agent <NUM> and the second liquid functional agent may be applied in a single pass or sequentially.

After the liquid functional agent <NUM> is selectively applied below, on, or below and on the build material <NUM>, and, in some instances, after the composite layer <NUM> is exposed to an oxidizer, the composite layer <NUM> is exposed to energy. Energy exposure is shown at reference numerals <NUM> and <NUM>.

As shown in <FIG> at reference numeral <NUM>, the entire layer of the build material <NUM> (which includes the composite layer <NUM> as well as unpatterned build material <NUM>) may be exposed to a spatially broad energy source <NUM>. The spatially broad energy source <NUM> may be a thermal heat source or an electromagnetic radiation source. Examples of suitable spatially broad energy sources <NUM> include ovens, conventional furnaces, IR lamps, UV lamps, or planar microwave emitters.

Some examples of the spatially broad energy source <NUM> may be attached, for example, to a carriage that also holds the inkjet printhead(s) <NUM>. The carriage may move the spatially broad source <NUM> into a position that is adjacent to the fabrication bed <NUM>. The spatially broad energy source <NUM> may also be fixed above the fabrication bed <NUM>. Other examples of the spatially broad energy source <NUM> may require that the entire layer of the build material <NUM> (which includes the composite layer <NUM> as well as unpatterned build material <NUM>) be removed from the fabrication bed <NUM> and positioned within the source <NUM>.

As shown in <FIG> at reference numeral <NUM>, the energy source may be a tightly focused energy source <NUM> such as a laser, electron beam or microwave tip emitter. As illustrated at reference numeral <NUM>, an energy beam <NUM> may be applied using a tightly focused energy source <NUM> and scanner system <NUM>. The scanning system <NUM> allows the energy beam <NUM> to be selectively applied to the composite layer <NUM> and/or unpatterned portions <NUM> of the build material <NUM>. While a single tightly focused energy source <NUM> is shown at reference numeral <NUM>, it is to be understood that multiple tightly focused energy sources <NUM> may be used.

The tightly focused energy source <NUM> and the scanning system <NUM> may be attached to a moving XY stage or a translational carriage (neither of which is shown) that moves them adjacent to the fabrication bed <NUM> in order to direct the energy beam <NUM> in desirable area(s). In other examples, the tightly focused energy source <NUM> and the scanning system <NUM> may be fixed while a support member (similar to the fabrication bed <NUM>) is configured to move relative thereto.

The spatially broad energy source <NUM> or the tightly focused energy source <NUM> and the scanning system <NUM> may be programmed to receive commands from the central processing unit and to expose the composite layer <NUM> (including the liquid functional agent(s) <NUM> and the build material <NUM>) and/or unpatterned portions <NUM> of the build material <NUM> to energy.

The energy exposure time may be dependent on the characteristics of the energy source chosen, the characteristics of the liquid functional agent(s) <NUM> used and/or the characteristics of the build material <NUM>.

Exposing the composite layer <NUM> and/or unpatterned portions <NUM> of the build material <NUM> to energy may cause curing (e.g., melting, sintering, binding, fusing, etc.) of the build material particles <NUM> to take place. The build material <NUM> may absorb thermal energy or may convert radiation to thermal energy. In some instances, the energy from the source <NUM>, <NUM> may be sufficient to elevate the temperature of the build material <NUM> to a temperature below its melting point but suitable to cause softening and bonding. In other instances, the energy from the source <NUM>, <NUM> may be sufficient to elevate the temperature of the build material <NUM> above the melting point of the build material <NUM>. In an example, the temperature may be elevated up to or even beyond <NUM> above the build material melting temperature.

The cured 3D part is not shown in <FIG> because the portions of the build material <NUM> that fuse/melts may depend on whether the liquid functional agent <NUM> includes an energy source material or an energy sink material, whether the spatially broad energy source <NUM> or the tightly focused energy source <NUM> is used, and whether the liquid functional agent <NUM> is deposited below and/or on all or less than all of the build material <NUM>. In some instances, the portions of the build material <NUM> that fuse/melts may also depend on whether the oxidizer is present to participate in the reaction with the energy source material of the liquid functional agent <NUM>. It is to understood that the oxidizer is considered to be present when it is part of the liquid functional agent <NUM>, when it is applied in the form of a second liquid functional agent, or when it is supplied from the environment.

When an energy source material is included in the liquid functional agent <NUM>, the reaction involving the energy source material is an exothermic reaction that supplies additional heat to the build material <NUM> that is in contact with the energy source material (i.e., the build material <NUM> in the composite layer <NUM>). When the liquid functional agent <NUM> (including the energy source material) is deposited below and/or on all of the build material <NUM>, the oxidizer is present, and the spatially broad energy source <NUM> is used, all of the build material <NUM> fuses/melts. In these examples, the exothermic reaction involving the energy source material may provide additional thermal energy needed to allow the build material <NUM> to fuse/melt. The exothermic reaction may provide additional thermal energy needed to heat (e.g., super heat) the build material <NUM> to a temperature necessary to achieve the desired cooling rate, microstructure, and physical properties (e.g., structural integrity).

Some examples of the composite layer <NUM> include all of the build material <NUM> that is applied in the fabrication bed <NUM>. In some of these examples, the thermal energy provided by the exothermic reaction involving the energy source material is insufficient to fuse/melt the build material <NUM>. In these examples, when the oxidizer is present, and the tightly focused energy source <NUM> is used, only the build material <NUM> where the energy is applied fuses/melts. In some other of these examples, the thermal energy provided by the exothermic reaction involving the energy source material is sufficient to fuse/melt the build material <NUM>. In these examples, when the oxidizer is present, and the tightly focused energy source <NUM> is used, all of the build material <NUM> may fuse/melt, and those areas where the energy from the source <NUM> has been applied will be super heated, and thus will have a different cooling rate, microstructure, and physical properties than the fused/melted build material <NUM> to which energy from the source <NUM> has not been applied.

Some examples of the composite layer <NUM> include less than all of the build material <NUM> that is applied in the fabrication bed <NUM>. In some of these examples, when the liquid functional agent <NUM> (including the energy source material) is applied on the composite layer <NUM> and the oxidizer is present, the energy from the source <NUM>, <NUM> and the additional thermal energy provided by the exothermic reaction allows the composite layer <NUM> to fuse/melt. In these instances, the unpatterned build material <NUM> (in portions <NUM>) will not fuse/melt, and the build material <NUM> that is not exposed to energy from the source <NUM>, <NUM> will not fuse/melt. As an example of this, when the spatially broad energy source <NUM> is used, the build material <NUM> may fuse/melt only where the liquid functional agent <NUM> (including the energy source material) has been applied (i.e., the composite layer <NUM>) and the oxidizer is present. As another example of this, when the tightly focused energy source <NUM> is used, the build material <NUM> may fuse/melt only where both energy and the liquid functional agent <NUM> (including the energy source material) have been applied and the oxidizer is present.

As mentioned above, some examples of the composite layer <NUM> include less than all of the build material <NUM> that is applied in the fabrication bed <NUM>. In some other of these examples, the energy from the source <NUM>, <NUM> is sufficient to fuse/melt the build material <NUM>, and the thermal energy provided by the exothermic reaction involving the energy source material is insufficient to cause the build material <NUM> to fuse/melt. The additional thermal energy provided by the exothermic reaction allows the composite layer <NUM> to reach a higher temperature than the build material <NUM> that is not in contact with the energy source material so that the composite layer <NUM> has a different cooling rate, microstructure, and physical properties (e.g., structural integrity) than the unpatterned build material <NUM> (in portions <NUM>). In these instances, the unpatterned build material <NUM> (in portions <NUM>) will fuse/melt, the build material <NUM> that is not exposed to energy from the source <NUM>, <NUM> will not fuse/melt. As an example of this, when the spatially broad energy source <NUM> is used, all of the build material <NUM> may fuse/melt, and those areas where the liquid functional agent <NUM> (including the energy source material) has been applied (i.e., the composite layer <NUM>) will super heat and thus have a different cooling rate, microstructure, and physical properties than the fused/melted build material <NUM> that was not in contact with the energy source material. As another example of this, when the tightly focused energy source <NUM> is used, the build material <NUM> fuses/melts wherever energy has been applied and will not fuse/melt where energy is not applied, and those areas where both energy and the liquid functional agent <NUM> (including the energy source material) have been applied (i.e., the composite layer <NUM>) will super heat and thus have a different cooling rate, microstructure, and physical properties than the fused/melted build material <NUM> that was not in contact with the energy source material.

As mentioned above, some examples of the composite layer <NUM> include less than all of the build material <NUM> that is applied in the fabrication bed <NUM>. In some of these examples, the energy from the source <NUM>, <NUM> alone is sufficient to fuse/melt the build material <NUM>, and the thermal energy provided by the exothermic reaction alone is also sufficient to allow the build material <NUM> to fuse/melt. In these examples, all of the build material <NUM> that is exposed to energy from the source <NUM>, <NUM> will fuse/melt, and all of the patterned build material <NUM> (in portions <NUM>) will fuse/melt when the oxidizer is present and the reaction is initiated. The unpatterned build material <NUM> to which energy is not applied will not fuse/melt. The unpatterned build material <NUM> that is exposed to energy from the source <NUM>, <NUM>, the patterned build material <NUM> that is not exposed to energy from the source <NUM>, <NUM> but is exposed to the exothermic reaction, and the patterned build material <NUM> that is exposed to energy from the source <NUM>, <NUM> may each reach a different temperature, and therefore, have a different cooling rate, microstructure, and physical properties (e.g., structural integrity). The patterned build material <NUM> that is exposed to energy from the source <NUM>, <NUM> will reach a higher temperature than the build material <NUM> to which energy is not applied as well as the unpatterned build material <NUM>.

In examples where the exothermic reaction supplies a sufficient amount of energy to fuse/melt the build material <NUM> patterned with the liquid functional agent <NUM> (including the energy source material), it is to be understood that the exposure to energy (for fusing/melting) comes from the exothermic reaction and not the source <NUM>, <NUM>. When the exothermic reaction does not require an outside energy source to initiate the reaction, the source <NUM>, <NUM> is not utilized at all in the method.

In the examples of the method <NUM> disclosed herein, exposing the composite layer <NUM> to energy may initiate the reaction involving the energy source material. Alternatively, the reaction may be initiated by exposing the composite layer <NUM> to an oxidizer or by exposing the composite layer <NUM> to both an oxidizer and energy.

The exothermic reaction involving the energy source material may be an oxidation reaction that generates a gaseous byproduct. For example, when the energy source material is fully nitrated nitrocellulose, a reactant including the fuel and the oxidizer, exposure to energy may initiate the following reaction (I):.

2C<NUM>H<NUM>N<NUM>O11 + <NUM>/2O<NUM> → 12CO<NUM> ( g) + 3N<NUM> ( g) + <NUM><NUM>O(g)     (I).

to produce gaseous carbon dioxide and nitrogen and water vapor. The enthalpy of reaction for reaction (I) is -<NUM> kJ/g.

In another example, if the energy source material is sucrose, as the reactant fuel, exposure to oxygen and energy will initiate the following reaction (II):.

C<NUM>H<NUM>O<NUM> + 12O<NUM> (g) <NUM><NUM>O (g) + 12CO<NUM> (g)     (II).

to produce gaseous carbon dioxide and water vaper. The enthalpy of reaction for reaction (II) is -<NUM> kJ/g.

In still another example, if the energy source material is hydrazine, as the reactant fuel, exposure to nitric acid will initiate the following reaction (III):.

5N<NUM>H<NUM> + 4HNO<NUM> <NUM><NUM>O (g) + 7N<NUM> (g)     (III).

to produce gaseous nitrogen and water vaper.

The liquid functional agent(s) <NUM> and the amounts of those liquid functional agent(s) <NUM> jetted into each voxel determine the reactions that will occur in each voxel. The chemical reactions that occur in each voxel determine the heating and cooling rates of each voxel, which in turn determines the physical properties of the 3D part.

In the example of the 3D printing method shown in <FIG> , additional layers of the 3D part may be formed by repeating reference numerals <NUM>-<NUM> and <NUM> or <NUM>; <NUM>, <NUM> and <NUM> or <NUM><NUM>; or <NUM>, <NUM> and <NUM> or <NUM><NUM>. For example, to form an additional layer of the 3D part, the liquid functional agent <NUM> may be selectively applied to the previously formed layer, an additional layer of the build material <NUM> may be applied to the previously formed layer to form an additional composite layer, the liquid functional agent <NUM> may be selectively applied to the additional composite layer, and the additional composite layer may be exposed to energy to form that additional layer. In other examples, additional layers may be formed by depositing the liquid functional agent <NUM> only below or only on the additional layer of the build material <NUM> to form the additional composite layer. Any number of additional layers may be formed.

Referring now to <FIG>, another example of the printing system <NUM>' is depicted. The system <NUM>' includes a central processing unit <NUM> that controls the general operation of the additive printing system <NUM>'. As an example, the central processing unit <NUM> may be a microprocessor-based controller that is coupled to a memory <NUM>, for example via a communications bus (not shown). The memory <NUM> stores the computer readable instructions <NUM>. The central processing unit <NUM> may execute the instructions <NUM>, and thus may control operation of the system <NUM>' in accordance with the instructions <NUM>. For example, the instructions <NUM> may cause the controller to utilize a liquid functional agent distributor <NUM> (e.g., an inkjet applicator <NUM>) to selectively dispense the liquid functional agent <NUM>, and to utilize a build material distributor <NUM> to dispense the build material <NUM> to form a three-dimensional part.

In this example, the printing system <NUM>' includes a liquid functional agent distributor <NUM> to selectively deliver the liquid functional agent <NUM> to portion(s) <NUM> below and/or on the layer (not shown in this figure) of build material <NUM> provided on a support member <NUM>.

The central processing unit <NUM> controls the selective delivery of the liquid functional agent <NUM> to the layer of the build material <NUM> in accordance with delivery control data <NUM>.

In the example shown in <FIG>, it is to be understood that the distributor <NUM> is a printhead(s), such as a thermal inkjet printhead(s) or a piezoelectric inkjet printhead(s). The printhead(s) <NUM> may be a drop-on-demand printhead(s) or a continuous drop printhead(s).

The printhead(s) <NUM> may be used to selectively deliver the liquid functional agent <NUM>, when in the form of a suitable fluid. As described above, the liquid functional agent <NUM> includes a non-aqueous vehicle or an aqueous vehicle, such as water, co-solvent(s), surfactant(s), etc., to enable it to be delivered via the printhead(s) <NUM>. The liquid functional agent <NUM> may be selectively dispensed before, after, or both before and after the build material <NUM> to pattern the build material <NUM> and form a composite layer <NUM>.

In one example, the printhead(s) <NUM> may be selected to deliver drops of the liquid functional agent <NUM> at a resolution ranging from about <NUM> dots per inch (DPI) to about <NUM> DPI. In other examples, the printhead(s) <NUM> may be selected to be able to deliver drops of the liquid functional agent <NUM> at a higher or lower resolution. The drop velocity may range from about <NUM>/s to about <NUM>/s and the firing frequency may range from about <NUM> to about <NUM>.

The printhead(s) <NUM> may include an array of nozzles through which the printhead(s) <NUM> is able to selectively eject drops of fluid. In one example, each drop may be in the order of about <NUM> ng per drop, although it is contemplated that a higher (e.g., <NUM> ng) or lower (e.g., <NUM> ng) drop size may be used. In some examples, printhead(s) <NUM> is able to deliver variable size drops.

The printhead(s) <NUM> may be an integral part of the printing system <NUM>', or it may be user replaceable. When the printhead(s) <NUM> is user replaceable, they may be removably insertable into a suitable distributor receiver or interface module (not shown).

As shown in <FIG>, the distributor <NUM> may have a length that enables it to span the whole width of the support member <NUM> in a page-wide array configuration. In an example, the page-wide array configuration is achieved through a suitable arrangement of multiple printheads. In another example, the page-wide array configuration is achieved through a single printhead with an array of nozzles having a length to enable them to span the width of the support member <NUM>. In other examples of the printing system <NUM>', the distributor <NUM> may have a shorter length that does not enable it to span the whole width of the support member <NUM>.

While not shown in <FIG>, it is to be understood that the distributor <NUM> may be mounted on a moveable carriage to enable it to move bi-directionally across the length of the support member <NUM> along the illustrated y-axis. This enables selective delivery of the liquid functional agent <NUM> across the whole width and length of the support member <NUM> in a single pass. In other examples, the distributor <NUM> may be fixed while the support member <NUM> is configured to move relative thereto.

As used herein, the term 'width' generally denotes the shortest dimension in the plane parallel to the X and Y axes shown in <FIG>, and the term 'length' denotes the longest dimension in this plane. However, it is to be understood that in other examples the term 'width' may be interchangeable with the term 'length'. As an example, the distributor <NUM> may have a length that enables it to span the whole length of the support member <NUM> while the moveable carriage may move bi-directionally across the width of the support member <NUM>.

In examples in which the distributor <NUM> has a shorter length that does not enable it to span the whole width of the support member <NUM>, the distributor <NUM> may also be movable bi-directionally across the width of the support member <NUM> in the illustrated X axis. This configuration enables selective delivery of the liquid functional agent <NUM> across the whole width and length of the support member <NUM> using multiple passes.

The distributor <NUM> may include therein a supply of the liquid functional agent <NUM> or may be operatively connected to a separate supply of the liquid functional agent <NUM>.

As shown in <FIG>, the printing system <NUM>' also includes a build material distributor <NUM>. This distributor <NUM> is used to provide the layer of the build material <NUM> on the support member <NUM>. Suitable build material distributors <NUM> may include, for example, any spreader, such as a wiper blade, a roller, or combinations thereof.

The build material <NUM> may be supplied to the build material distributor <NUM> from a hopper or other suitable delivery system. In the example shown, the build material distributor <NUM> moves across the length (Y axis) of the support member <NUM> to deposit a layer of the build material <NUM>. As previously described, a first layer of build material <NUM> will be deposited on the support member <NUM>, whereas subsequent layers of the build material <NUM> will be deposited on a previously deposited (and solidified) layer.

It is to be further understood that the support member <NUM> may also be moveable along the Z axis. In an example, the support member <NUM> is moved in the Z direction such that as new layers of build material <NUM> are deposited, a predetermined gap is maintained between the surface of the most recently formed layer and the lower surface of the distributor <NUM>. In other examples, however, the support member <NUM> may be fixed along the Z axis and the distributor <NUM> may be movable along the Z axis.

Similar to the system <NUM> (shown in <FIG>), the system <NUM>' also includes the spatially broad energy source <NUM> and/or the tightly focused energy source <NUM> to apply energy to the deposited layer of build material <NUM> and the liquid functional agent <NUM> to cause the solidification of portion(s) of the build material <NUM>. Any of the previously described spatially broad energy sources <NUM> or tightly focused energy sources <NUM> may be used.

While not shown, it is to be understood that the spatially broad energy source <NUM> and/or the tightly focused energy source <NUM> may be mounted on the moveable carriage or may be in a fixed position.

The central processing unit <NUM> may control the spatially broad energy source <NUM> and/or the tightly focused energy source <NUM>. The amount of energy applied may be in accordance with delivery control data <NUM>.

The system <NUM>' also includes an initiator to initiate the reaction involving i) the energy source material or ii) the energy sink material to alter a thermal condition of the composite layer <NUM>. The initiator may be the oxidizer, energy from the source <NUM>, <NUM>, or both the oxidizer and energy from the source <NUM>, <NUM>. The oxidizer may be in the ambient environment around the system <NUM>' or the oxidizer may be contained in a second liquid functional agent applied by a second liquid functional agent distributor (not shown). The energy may be from the spatially broad energy source <NUM> or the tightly focused energy source <NUM>.

To further illustrate the present disclosure, an example is given herein. It is to be understood that this example is provided for illustrative purposes and is not to be construed as limiting the scope of the present disclosure.

An example of the liquid functional agent was prepared. The energy source material used in the example of the liquid functional agent was sucrose. The formulation of the liquid functional material is provided in the following table:.

The liquid functional agent was dispensed using a pipette into a tungsten crucible containing approximately <NUM> of -<NUM> mesh Fe<NUM>O<NUM> powder sourced from Alfa Aesar (Ward Hill, MA).

The liquid vehicle of the liquid functional agent was removed by baking the crucible containing the Fe<NUM>O<NUM> powder and the liquid functional agent on a hotplate for <NUM> hours at <NUM> in an argon environment. About <NUM> of sucrose remained in the powder bed after the liquid vehicle was removed. A black and white photographic image of the crucible containing the Fe<NUM>O<NUM> powder and the sucrose thereon after baking on the hotplate is shown <FIG>.

The crucible containing the Fe<NUM>O<NUM> powder and the sucrose thereon was then placed in a furnace box at <NUM> for <NUM> minutes. The environment in the furnace box contained oxygen. The crucible was removed from the furnace box and allowed to air cool. The portions of the Fe<NUM>O<NUM> powder with liquid functional agent thereon reacted to the heat treatment in the furnace box differently and have a different visual appearance than the Fe<NUM>O<NUM> powder without liquid functional agent thereon. A black and white photographic image of the crucible after it was removed from the furnace box is shown in <FIG>.

A SEM image was taken of part of the region that was not treated with the liquid functional agent. This is shown in <FIG>. The SEM image in <FIG> shows that the Fe<NUM>O<NUM> powder particles have been sintered together, but not fully melted.

A SEM image was also taken of part of the region that was treated with the liquid functional agent. This is shown in <FIG>. The SEM image in <FIG> shows that the Fe<NUM>O<NUM> powder particles have melted and solidified. The melting temperature Fe<NUM>O<NUM> is approximately <NUM>. Therefore, this example illustrates that the exothermic reaction of the sucrose in the liquid functional agent provided additional energy to allow the Fe<NUM>O<NUM> to melt in the treated zone.

Reference throughout the specification to "one example", "another example", "an example", and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the example is included in at least one example described herein, and may or may not be present in other examples. In addition, it is to be understood that the described elements for any example may be combined in any suitable manner in the various examples unless the context clearly dictates otherwise.

It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range. For example, a range from greater than <NUM> and up to about <NUM> should be interpreted to include the explicitly recited limits of greater than <NUM> to <NUM>, as well as individual values, such as <NUM>, <NUM>, <NUM>, <NUM>, etc., and sub-ranges, such as from about <NUM> to about <NUM>, from about <NUM> to about <NUM>, etc. Furthermore, when "about" is utilized to describe a value, this is meant to encompass minor variations (up to +/- <NUM>%) from the stated value.

In describing and claiming the examples disclosed herein, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

Claim 1:
. A three-dimensional (3D) printing method, comprising:
selectively applying a liquid functional agent including an energy source material;
applying a metallic or ceramic build material;
wherein the liquid functional agent is selectively applied any of before the metallic or ceramic build material, after the metallic or ceramic build material, or both before and after the metallic or ceramic build material, and wherein the liquid functional agent patterns the metallic or ceramic build material to form a composite layer;
exposing at least some of the metallic or ceramic build material to energy; and initiating a reaction involving the energy source material to alter a thermal condition of the composite layer;
wherein the reaction involving the energy source material is an exothermic reaction that supplies additional energy to the composite layer and generates a gaseous byproduct;
wherein the energy source material is a reactant including a fuel and an oxidizer, and wherein the initiating of the reaction is accomplished by the exposing of the composite layer to the energy;
or wherein the energy source material is a reactant fuel, and wherein the initiating of the reaction is accomplished by exposing the composite layer to an oxidizer and by the exposing of the composite layer to the energy;
or wherein the energy source material is a reactant fuel, and wherein the initiating of the reaction is accomplished by exposing the composite layer to an oxidizer.