Coating Powders for Improved Additively Manufactured Parts

Abstract

To provide a coated powder that prevents, in powder-based additive manufacturing such as selective laser sintering (SLS) and selective laser melting (SLM), formation of voids between powder particles within a build layer and between adjacent build layers formed during the process.SOLUTION: A coated powder 6 for use in additive manufacturing includes a base polymer layer formed of a base polymer material, and a coating polymer layer formed of a coating polymer material 24. At least the coating polymer material 24 is susceptible to dielectric heating in response to electromagnetic radiation, thereby promoting fusion between adjacent particles 4 of the coated powder 6 that are deposited during the additive manufacturing process. Specifically, when electromagnetic radiation is applied to at least an interface area between adjacent particles 4 of the coated powder 6, the polymer coating layer melts to diffuse across the interface area, thereby preventing formation of voids.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to additive manufacturing apparatus and methods, and more particularly to powder-based additive manufacturing. The additive manufacturing processes disclosed herein are useful in manufacturing parts, such as environmental control ducts, door panels, tools, jigs, fixtures, etc. Additionally, embodiments of the present disclosure may be used in a wide variety of applications, particularly in the aerospace, marine, automotive, and other transportation industries, such as casings for auxiliary power units (APUs). [Background technology]

[0002] Parts and other components are produced using a variety of manufacturing techniques depending on the part's performance requirements and the availability of manufacturing equipment. Selective laser sintering (SLS) and selective laser melting (SLM) are powder-based additive manufacturing methods that can be used to build components, in which a layer of powder is maintained at an elevated temperature and selectively sintered or melted using a laser. After the first build layer is built, subsequent build layers are built on top of the first build layer by a similar process until the desired three-dimensional article is completed. The powders used in these processes are typically made of thermoplastics, polycarbonates, or other materials of similar composition. Powder-based additive manufacturing, such as SLS and SLM, can result in voids between the powder particles within the build layer and between adjacent build layers during the process, which can result in a weaker structural strength of the article. Summary of the Invention

[0003] According to one aspect of the present disclosure, there is provided a coating powder for use in an additive manufacturing process, the coating powder comprising a base polymer layer formed by a base polymer material having a first dielectric loss factor and a coating polymer layer overlying the base polymer layer and formed by a coating polymer material having a second dielectric loss factor, the second dielectric loss factor of the coating polymer material being greater than the first dielectric loss factor of the base polymer material.

[0004] According to another aspect of the present disclosure, there is provided a method of manufacturing a coated powder for use in an additive manufacturing process, comprising: delivering a plurality of powder particles into a chamber, each of the plurality of powder particles being formed of a base polymer material; applying a liquid paint to an exterior surface of each of the plurality of powder particles, the liquid paint being formed of a coated polymer material; and drying the liquid paint on the plurality of powder particles to form a plurality of coated powder particles, each of the plurality of coated powder particles including a base polymer layer formed by the powder particles and a coated polymer layer formed by the liquid paint after drying.

[0005] According to a further aspect of the present disclosure, there is provided a method of manufacturing an article by fused powder manufacturing, comprising forming a coating powder by feeding a plurality of powder particles into a chamber, each of the plurality of powder particles being formed of a base polymer material, applying a liquid coating to an exterior surface of each of the plurality of powder particles, the liquid coating being formed of a coating polymer material, and drying the liquid coating on the plurality of powder particles to form a plurality of coated powder particles, each of the plurality of coated powder particles including a base polymer layer formed by the powder particles and a coating polymer layer formed by the liquid coating after drying, the method further comprising depositing the coating powder onto a substrate to form a first build layer and heating selected portions of the first build layer, depositing the coating powder onto the substrate to form a second build layer and heating selected portions of the second build layer, and dielectrically heating at least the coating polymer layer of the coating powder in the selected portions of the first and second build layers using electromagnetic radiation, thereby fusing adjacent particles of the coating powder at an interface region.

[0006] The described features, functions, and advantages may be realized individually in various embodiments, but may also be combined with each other in other embodiments, further details of which will become apparent by reference to the following description and drawings. [Brief description of the drawings]

[0007] The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims. The illustrative embodiments, however, as well as the preferred mode of use, together with their objects and advantages, will be best understood by reference to the following detailed description of illustrative examples of the present disclosure taken in conjunction with the accompanying drawings.

[0008]

Figure 1

Figure 2

Figure 3

Figures 4 - 8

[0009] The following detailed description relates to powder-based additive manufacturing techniques such as selective laser sintering (SLS) and selective laser melting (SLM). Examples disclosed herein include coating powders for use in such processes, methods of forming the coating powders, and methods of building articles using the coating powders in additive manufacturing processes. The coating powders include particles having a base polymer layer formed by a base polymer material covered by a coating polymer layer formed by a coating polymer material. The coating powders are susceptible to selective heating, such as dielectric heating using electromagnetic radiation, thereby enhancing the strength of the built article. <Definition>

[0010] "Fused Filament Fabrication" (FFF) is an additive manufacturing technique used to build up layers to form products, such as three-dimensional products, prototypes, or models. The process is a rapid prototyping and manufacturing process in which successive layers of molten material are built up to rapidly create models, products, or articles.

[0011] As used herein, "filament" refers to a thin, thread-like feed material used in additive manufacturing processes.

[0012] As used herein, "powder coating," "coating powder," or similar terms refer to a type of coating that is applied, typically electrostatically, as a dry powder and then cured by heat, electromagnetic radiation such as microwaves, or other curing source, such as a thermoplastic material, a thermosetting polymer, or other similar polymer or material.

[0013] As used herein, "selective laser sintering" or "selective laser melting" and similar terms refer to an additive manufacturing process in which a laser is used to sinter powdered material, firing the laser into space and using a 3D model as a pattern to bond the material together to form a solid structure. Typically, the powdered material is nylon, polyamide, or similar material. Description of the embodiment

[0014] Reference is made to the accompanying drawings which form a part hereof, and in which specific embodiments or examples are shown by way of illustration. Like numerals in the several drawings refer to like elements.

[0015] 1 shows an apparatus 2 for converting a powder 4 into a coating powder 6 that can be used in an additive manufacturing process to build articles with greater structural integrity. Specifically, the apparatus 2 includes a coating chamber 8 having a sidewall 10 and a base 12. The base 12 defines an aperture 14 for allowing air from a pressurized air source 16 to enter the coating chamber 8. A nozzle 18 is disposed within the coating chamber 8 and is fluidly connected to a paint source 20.

[0016] In operation, powder particles 4 are placed at the bottom of the coating chamber 8. The pressurized air source 16 is activated to generate an air stream 22 that blows the powder particles 4 up into the coating chamber 8. At the same time, the paint source 20 is activated to spray paint 24 from the nozzle 18 throughout the coating chamber 8, thereby coating the powder particles 4 with the paint 24. In some instances, positively or negatively charged ions may also be dispensed from the nozzle 18 to aid in coating the powder particles 4 with the paint 24. The paint 24 may be dispensed, for example, in a liquid phase and subsequently dried and solidified on the powder 4. Ultimately, as best seen in FIG. 2, the apparatus 2 forms a coating powder 6 having a base polymer layer 26 and a coating polymer layer 28.

[0017] The materials used to form the base polymer layer 26 and the coating polymer layer 28 in the coating powder 6 can be selectively heated during a powder-based additive manufacturing process to promote chain diffusion and bonding between the layers, resulting in a shaped article with improved structural integrity. As described in more detail below, the materials used for the base polymer layer 26 and the coating polymer layer 28 can be selected based on their relative reactivity to dielectric heating, as well as the closeness of their melting points and solubility parameters.

[0018] With regard to responsiveness to dielectric heating, for example, the material used for the coating powder 6 is selected so that the coating polymer layer 28 is more susceptible to heating in response to electromagnetic radiation than the base polymer layer 26. The ability of a material to dissipate irradiated electromagnetic energy in the form of heat is quantified by a property known as the dielectric loss factor (also known as the loss factor and represented by the symbol tan δ). A material with a higher dielectric loss factor will heat up more in response to an applied electromagnetic field than a material with a lower dielectric loss factor. To concentrate the heating on the outer surface of the coating powder 6, the coating polymer layer 28 is formed from a coating polymer material with a higher dielectric loss factor than the base polymer material used for the base polymer layer 26. In some examples, the coating polymer material has a tan δ value that is at least about 50 times the tan δ value of the base polymer material. Additionally or alternatively, the base polymer material may have a tan δ value less than 0.05 and the coating polymer material may have a tan δ value greater than 0.05.

[0019] The coating powder 6 may also be made of materials with similar melting points for the base polymer layer 26 and the coating polymer layer 28, which may improve the strength of the built article formed by the build layers of the coating powder 6 deposited during the additive manufacturing process. As described above, the coating polymer material has a higher dielectric loss factor and therefore generates heat in direct response to the application of electromagnetic energy. The base polymer material may be selected to have a melting point close to that of the coating polymer material, such that heating the coating polymer layer 28 by electromagnetic energy may also heat at least the outer portion of the base polymer layer 26. Indirect heating of the base polymer layer 26 in this manner may maintain the base polymer layer 26 in a softened and / or molten state for a longer period of time, which may further promote diffusion and bonding between adjacent particles of the coating powder 6 after being deposited on a substrate. The melting points of the base polymer material and the coating polymer material respectively preferably allow the formation of a solid and liquid morphology. In some examples, the base polymer material has a first melting point and the coating polymer material has a second melting point, the first melting point of the base polymer material being within 20 degrees Celsius of the second melting point of the coating polymer material. It has been found that such materials having melting points within about 20 degrees Celsius, or about 18 degrees Celsius, or about 15 degrees Celsius, can generate sufficient heat to prolong the molten state of the base polymer layer 26 to promote diffusion and bonding between particles of the coating powder 6 that are deposited and heated during additive manufacturing.

[0020] Additionally, the materials selected for the base polymer layer 26 and the coating polymer layer 28 may have compatible solubility parameters to further promote bonding between adjacent particles of the coating powder 6 when used in an additive manufacturing process. For example, the coating polymer material may be immiscible with the base polymer material to prevent phase separation and promote fusion of the base polymer layer between adjacent particles during additive manufacturing. In some examples, the base polymer material has a first solubility parameter and the coating polymer material has a second solubility parameter that differs from the first solubility parameter by about 10. (J / cc) 0.5 The difference in solubility parameters is about 10 (J / cc) 0.5 , or about 8 (J / cc) 0.5 , or about 5 (J / cc) 0.5 Materials within the above range have been found to be advantageous in promoting mixing when heated during additive manufacturing processes.

[0021] With the above in mind, suitable base polymer materials include polyethylene, polyethylene terephthalate, polypropylene, polyamide, polyetheretherketone, polyphenylene sulfide, polyetherimide, polystyrene, acrylonitrile-butadiene-styrene, polyacrylate, polyacrylonitrile, polycarbonate, or any mixture thereof.

[0022] Suitable coating polymeric materials include polyvinyl alcohol, polyvinylidene fluoride, polyurethane, polyamideimide, polyamide, polyvinyl chloride, acrylic, cellulose ester, or mixtures thereof. Other examples of suitable coating polymeric materials include high dielectric loss factor materials and solvents containing -OH, -NH, C=O, -N=O functional groups. Further examples of suitable coating polymeric materials include polyacrylonitrile (tan δ=0.1 at 60 Hz), polyethylene glycol, or mixtures thereof. In some examples, the coating polymeric material is particularly responsive to electromagnetic energy in a particular frequency range, such as microwave energy in the gigahertz range.

[0023] Table 1 compares the dielectric loss factor, melting point, and solubility parameters for examples in which the coating polymer material is polyvinyl alcohol and the base polymer material is Ultem® 1010 (a polyetherimide). [Table 1]

[0024] In this example, using Ultem® 1010 (a polyetherimide) as the base polymer material and polyvinyl alcohol as the coating polymer material is advantageous because polyvinyl alcohol has a high dielectric loss factor (tan δ=0.185 in the MHz-GHz frequency range) compared to Ultem® 1010 (tan δ=0.001 in the MHz-GHz frequency range), the melting points of these two materials differ by 14 degrees Celsius, and their solubility parameters are close to each other, i.e., compatible.

[0025] In addition to chemical properties, base polymer layer 26 and coating polymer layer 28 may also have suitable physical properties to facilitate fusing, bonding, and intermixing. For example, base polymer layer 26 may have a diameter in the range of about 0.01 to about 0.5 millimeters, or about 0.05 to about 0.4 millimeters, or about 0.1 to about 0.3 millimeters. Coating polymer layer 28 may have a thickness in the range of about 1 micron to about 50 microns, or about 5 microns to about 25 microns, or about 10 microns to about 20 microns.

[0026] FIG. 3 shows an example of an article 50 formed using conventional powder-based additive manufacturing techniques. The article 50 is formed by depositing a first build layer 52 of particles of uncoated powder 54 on a substrate 56. Selected particles of the uncoated powder 54 in the first build layer 52 are melted or sintered using a laser. A second build layer 60 of particles of uncoated powder 54 is then deposited on the first build layer 52 and selectively melted or sintered. In the illustrated embodiment, a third build layer 70 of particles of uncoated powder 54 is deposited on the first and second build layers 52, 60 and selectively melted or sintered. Due to the nature of conventional uncoated powders, each build layer 52, 60, 70 at least partially solidifies before the next build layer is deposited, which creates voids 80 between adjacent particles of uncoated powder 54. These voids 80 weaken the article 50.

[0027] 4-8 show an example of a method of forming an article 90 using particles of a coating powder 6 according to the present disclosure. As best seen in FIG. 4, the method begins by depositing a first build layer 102 of particles of the coating powder 6 on a substrate 104. Each particle of the coating powder 6 includes a core formed by a base polymer layer 26 and covered by a coating polymer layer 28. The particles of the coating powder 6 may be formed using the apparatus 2 of FIG. 1 or may be formed using a different apparatus and / or method. As shown in FIG. 5, selected particles of the coating powder 6 of the first build layer 102 are melted or sintered using a laser 106. FIG. 6 shows selected particles 108 of the coating powder 6 of the first build layer 102 after melting or sintering. The method then proceeds to deposit a second build layer 110 of particles of the coating powder 6 on the first build layer 102 and melt or sinter the selected particles of the coating powder 6 to form a three-dimensional article 90 as shown in FIG. 7.

[0028] As further shown in FIG. 7, the method includes directing electromagnetic radiation 120 toward the article 90 to promote diffusion and bonding between adjacent particles of the coating powder 6. At least the coating polymer material is responsive to dielectric heating and therefore melts and fills any voids between adjacent particles of the coating powder 6. The electromagnetic radiation 120 is applied by a controlled heating source 122 that directs the electromagnetic radiation 120 at selected areas of the article 90 or over the entire article 90. The duration of the application of the electromagnetic radiation 120 can also be controlled to strengthen one or more localized areas of the article 90 or to strengthen the entire article 90. In one example, the electromagnetic radiation 120 can be microwave with a frequency in the range between 300 MHz and 300 GHz. In this case, the coating polymer material has a high dielectric loss factor and is susceptible to microwave radiation, i.e., dielectric heating.

[0029] Since the coating polymer material has a higher dielectric loss factor and the base polymer material has a lower dielectric loss factor, the frequency of the electromagnetic radiation can be selected such that only the coating polymer layer 28 directly melts in response to the electromagnetic radiation. Alternatively, the base polymer material may have a melting point close to that of the coating polymer material, in which case the base polymer layer 26 at least partially melts in response to heating of the coating polymer layer 28. Thus, in response to the electromagnetic radiation 120, the coating polymer layer 28 directly melts and the base polymer layer 26 indirectly melts. In other examples, the electromagnetic radiation 120 may directly heat both the coating polymer layer 28 and the base polymer layer 26. In either case, the melted portions of the base polymer layer 26 of adjacent particles fuse together, thereby preventing the formation of voids between adjacent particles and improving the structural integrity of the shaped article.

[0030] If the coat polymer material and the base polymer material have compatible solubility parameters (see Table 1 for a non-limiting example), then melting both the coat polymer layer 28 and the base polymer layer 26 will form a homogenous mixture, and therefore will not undergo phase separation when the molten layers subsequently cool and solidify.

[0031] 8 shows the final article 90 after all unmelted or unsintered particles of coating powder 6 have been removed from the substrate 104. The resulting article 90 has no voids between particles or between the built layers. <Additional Notes>

[0032] The present disclosure also includes embodiments or examples according to the following appendices.

[0033] Appendix 1. A coating powder (6) for use in additive manufacturing processes, comprising: a base polymer layer (26) formed from a base polymer material having a first dielectric loss factor; a coating polymer layer (28) covering the base polymer layer (26) and formed by a coating polymer material having a second dielectric loss factor, the second dielectric loss factor of the coating polymer material being greater than the first dielectric loss factor of the base polymer material.

[0034] Appendix 2. The coating powder (6) of Appendix 1, wherein the base polymer material has a first melting point and the coating polymer material has a second melting point, the first melting point being within about 20 degrees Celsius of the second melting point.

[0035] Addendum 3. The base polymer material has a first solubility parameter, and the coating polymer material has a second solubility parameter, and the second solubility parameter has a difference of about 10 from the first solubility parameter. (J / cc) 0.5 The coating powder (6) according to Appendix 2, wherein the coating powder (6) is within the range of 0.1 to 1.0 μm.

[0036] Addendum 4. The base polymer material has a first solubility parameter, and the coating polymer material has a second solubility parameter, and the second solubility parameter has a difference of about 10 from the first solubility parameter. (J / cc) 0.5 The covering sheet (6) according to any one of appendices 1 to 3, wherein the thickness is within the range of 0.1 to 0.5 mm.

[0037] Appendix 5. The coating powder (6) according to any one of Appendixes 1 to 4, wherein the base polymer material contains polyetherimide and the coating polymer material contains polyvinyl alcohol.

[0038] Appendix 6. The coated powder (6) according to any one of Appendixes 1 to 5, wherein the base polymer layer (26) has a diameter of about 0.1 to about 5 millimeters, and the coating polymer layer (28) has a thickness of about 1 to about 1,000 microns.

[0039] Appendix 7. A method for producing a coating powder (6) for use in an additive manufacturing process, comprising: feeding a plurality of powder particles (4) into the chamber (8), each of the plurality of powder particles (4) being formed from a base polymer material; A liquid paint (24) is applied to an outer surface of each of the plurality of powder particles (4), the liquid paint (24) being formed by a coating polymer material; drying the liquid paint (24) on the plurality of powder particles (4) to form a plurality of coated powder particles (6); Each of the plurality of coated powder particles (6) includes a base polymer layer (26) formed by the powder particles (4) and a coating polymer layer (28) formed by the liquid paint (24) after drying.

[0040] Addendum 8. The method according to Addendum 7, wherein when feeding the plurality of powder particles (4) into the chamber (8), a hole (14) is provided in the chamber (8) and pressurized air is sent through the hole (14) to form an air flow (22) in the chamber (8).

[0041] Addendum 9. The method according to Addendum 8, wherein the liquid paint (24) is sprayed from a nozzle (18) disposed within the chamber (8) when the liquid paint (24) is applied to the outer surface of each of the plurality of powder particles (4).

[0042] Addendum 10. The base polymer material has a first dielectric loss factor; the coating polymeric material has a second dielectric loss factor; 10. The method according to any one of claims 7 to 9, wherein the second dielectric loss factor of the coating polymer material is greater than the first dielectric loss factor of the base polymer material.

[0043] Clause 11. The base polymer material has a first melting point; the coating polymeric material has a second melting point; 11. The method of any one of Appendices 7 to 10, wherein the first melting point is within about 20 degrees Celsius of the second melting point.

[0044] Addendum 12. The base polymer material has a first solubility parameter; the coating polymeric material has a second solubility parameter; The second solubility parameter has a difference of about 10 from the first solubility parameter. (J / cc) 0.5 12. The method according to any one of claims 7 to 11, wherein the

[0045] Addendum 13. The method of any one of Addendums 7 to 12, wherein the base polymer material comprises polyetherimide and the coating polymer material comprises polyvinyl alcohol.

[0046] Addendum 14. The method according to any one of Addendums 7 to 13, wherein the base polymer layer (26) has a diameter of about 0.1 to about 5 millimeters, and the coating polymer layer (28) has a thickness of about 1 to about 1,000 microns.

[0047] Appendix 15. A method for producing an article (50) by fused powder manufacturing, comprising: forming a coating powder (6), feeding a plurality of powder particles (4) into the chamber (8), each of the plurality of powder particles (4) being formed from a base polymer material; A liquid paint (24) is applied to an outer surface of each of the plurality of powder particles (4), the liquid paint (24) being formed by a coating polymer material; drying the liquid paint (24) on the plurality of powder particles (4) to form a plurality of coated powder particles (6); Each of the plurality of coated powder particles (6) includes a base polymer layer (26) formed by the powder particles (4) and a coated polymer layer (289) formed by the liquid paint (24) after drying, the method further comprising: The coating powder (6) is deposited on a substrate (104) to form a first build layer (52); heating selected portions of the first build layer (52); depositing the coating powder onto the first build layer (52) on the substrate (104) to form a second build layer (60); heating selected portions of the second build layer (60); The method includes dielectrically heating at least the coating polymer layer of the coating powder (6) in the selected portions of the first and second build layers (52, 60) using electromagnetic radiation (120), thereby fusing adjacent particles of the coating powder (6) at interface regions.

[0048] Addendum 16. The base polymer material has a first dielectric loss factor; the coating polymeric material has a second dielectric loss factor; 16. The method of claim 15, wherein the second dielectric loss factor of the coating polymeric material is greater than the first dielectric loss factor of the base polymeric material.

[0049] Clause 17. The base polymer material has a first melting point; the coating polymeric material has a second melting point; 17. The method of claim 15 or 16, wherein the first melting point is within about 20 degrees Celsius of the second melting point.

[0050] Addendum 18. The base polymer material has a first solubility parameter; the coating polymeric material has a second solubility parameter; The second solubility parameter has a difference of about 10 from the first solubility parameter. (J / cc) 0.5 18. The method according to any one of claims 15 to 17, wherein the range is within 1 to 20 minutes.

[0051] Addendum 19. The method of any one of Addendums 15 to 18, wherein the base polymer material comprises polyetherimide and the coating polymer material comprises polyvinyl alcohol.

[0052] Addendum 20. The method of any of Addendums 15 to 19, wherein the dielectric heating of at least the coated polymer layer of the coating powder in the selected portions of the first and second build layers comprises irradiating with electromagnetic radiation (120) in the microwave frequency range.

[0053] It should be noted that the drawings are not necessarily drawn to scale, and that the examples of the present disclosure may be shown in schematic form. Furthermore, the detailed description is merely exemplary in nature and is not intended to limit the present disclosure or its application or uses. Thus, for convenience of explanation, the present disclosure is shown and described in terms of several exemplary embodiments, but the present disclosure may be implemented in a variety of other types of embodiments and in various other systems and environments.

Claims

1. 1. A coating powder for use in an additive manufacturing process, comprising: a base polymer layer formed from a base polymer material having a first dielectric loss factor; a coating polymer layer covering the base polymer layer and formed by a coating polymer material having a second dielectric loss factor, the second dielectric loss factor of the coating polymer material being greater than the first dielectric loss factor of the base polymer material; the base polymer material is selected from the group consisting of polyethylene, polyethylene terephthalate, polypropylene, polyamide, polyetheretherketone, polyphenylene sulfide, polyetherimide, polystyrene, acrylonitrile-butadiene-styrene, polyacrylate, polyacrylonitrile, polycarbonate, and mixtures thereof; the coating polymeric material is selected from the group consisting of polyvinyl alcohol, polyvinylidene fluoride, polyurethane, polyamideimide, polyamide, polyvinyl chloride, acrylic, cellulose ester, polyacrylonitrile, polyethylene glycol, and mixtures thereof; The coating powder, wherein the base polymeric material has a first melting point and the coating polymeric material has a second melting point, the first melting point being within 20 degrees Celsius of the second melting point.

2. The base polymer material has a first solubility parameter, and the coating polymer material has a second solubility parameter, and the second solubility parameter has a difference of 10 (J / cc) from the first solubility parameter. 0.5 The coating powder according to claim 1 , wherein

3. A coating powder for use in an additive manufacturing process, comprising: a base polymer layer formed from a base polymer material having a first dielectric loss factor; a coating polymer layer covering the base polymer layer and formed by a coating polymer material having a second dielectric loss factor, the second dielectric loss factor of the coating polymer material being greater than the first dielectric loss factor of the base polymer material; A coating powder, wherein the base polymeric material comprises polyetherimide and the coating polymeric material comprises polyvinyl alcohol.

4. 1. A method for producing a coating powder for use in an additive manufacturing process, comprising: delivering a plurality of powder particles into the chamber, each of the plurality of powder particles being formed from a base polymer material; applying a liquid coating to an exterior surface of each of the plurality of powder particles, the liquid coating being formed by a coating polymer material; drying the liquid paint on the plurality of powder particles to form a plurality of coated powder particles; each of the plurality of coated powder particles includes a base polymer layer formed by the powder particles and a coated polymer layer formed by the liquid paint after drying; The method, wherein the base polymeric material has a first melting point and the coating polymeric material has a second melting point, the first melting point being within 20 degrees Celsius of the second melting point.

5. 5. The method of claim 4, further comprising the step of forming an air flow in the chamber by providing holes in the chamber and passing pressurized air through the holes while feeding the plurality of powder particles into the chamber.

6. 6. The method according to claim 4 or 5, wherein the liquid paint is applied to the outer surface of each of the plurality of powder particles by spraying the liquid paint from a nozzle disposed within the chamber.

7. The method of any of claims 4 to 6, wherein the base polymer layer has a diameter of 0.1 to 5 millimeters and the coating polymer layer has a thickness of 1 to 1,000 microns.

8. 1. A method of producing an article by fused powder manufacturing, comprising the steps of: forming a coating powder, delivering a plurality of powder particles into the chamber, each of the plurality of powder particles being formed from a base polymer material; applying a liquid coating to an exterior surface of each of the plurality of powder particles, the liquid coating being formed by a coating polymer material; drying the liquid paint on the plurality of powder particles to form a plurality of coated powder particles; Each of the plurality of coated powder particles includes a base polymer layer formed by the powder particles and a coated polymer layer formed by the liquid paint after drying, the method further comprising: depositing the coating powder onto a substrate to form a first build layer; heating selected portions of the first build layer; depositing the coating powder onto the first build layer on the substrate to form a second build layer; heating selected portions of the second build layer; The method of claim 1, further comprising: dielectrically heating at least the coated polymer layer of the coating powder in the selected portions of the first and second build layers using electromagnetic radiation, thereby fusing adjacent particles of the coating powder at interface regions.

9. 10. The method of claim 8, further comprising: applying electromagnetic radiation in the microwave frequency range to dielectrically heat at least the coated polymer layer of the coating powder in the selected portions of the first and second build layers.

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