Coated sheets for improved additive manufacturing parts
A coated sheet 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. At least the coating polymer material is susceptible to dielectric heating in response to electromagnetic radiation, thereby promoting fusion between adjacent coated sheets during the additive manufacturing process. Specifically, when electromagnetic radiation is applied to at least an interface area between adjacent coated sheets, the polymer coating layer of each coated sheet melts to diffuse across an interface area, thereby preventing formation of voids. The base polymer material and the coating polymer material also may have similar melting points and compatible solubility parameters to further promote fusion between sheets.
1. A method of fabricating a coated sheet for use in an additive manufacturing (AM) process, the method comprising:
positioning a sheet on a substrate, the sheet being formed of a base polymer material having a first dielectric loss factor with a first tan value in a predefined microwave frequency range;
applying a liquid coating to at least a portion of an exterior of the sheet, the liquid coating being formed of a coating polymer material distinct from the base polymer material and having a second dielectric loss factor with a second tan value in the predefined microwave frequency range, the second tan value being substantially larger than the first tan value of the base polymer material and thereby more susceptible to heating in response to electromagnetic energy than the base polymer material during the AM process;
drying the liquid coating on the sheet to form the coated sheet; and
forming an object using the coated sheet in the AM process,
wherein the coated sheet includes a base polymer layer formed by the sheet, and a coating polymer layer formed by the liquid coating after drying the liquid coating.
2. The method of claim 1 , in which applying the liquid coating to at least the portion of the exterior of the sheet comprises spraying the liquid coating from a nozzle positioned adjacent the substrate.
3. The method claim 1 , in which the second tan value of the second dielectric loss factor of the coating polymer material is at least about 50 times greater than the first tan value of the first dielectric loss factor of the base polymer material in the predefined microwave frequency range.
4. The method of claim 1 , in which:
the base polymer material has a first melting point;
the coating polymer material has a second melting point; and
the first melting point is within about 20 degrees Celsius of the second melting point.
5. The method of claim 1 , in which:
the base polymer material has a first solubility parameter;
the coating polymer material has a second solubility parameter; and
the second solubility parameter is within about 10 (J/cc) 0.5 of the first solubility parameter.
6. The method of claim 1 , in which the base polymer material comprises polyetherimide and the coating polymer material comprises polyvinyl alcohol.
7. The method of claim 1 , in which the base polymer layer has a thickness of from about 0.1 to about 5 millimeters, and the coating polymer layer has a thickness of from about 1 to about 1,000 microns.
8. The method of claim 1 , wherein the first tan value of the first dielectric loss factor of the base polymer material is less than 0.05, and wherein the second tan value of the second dielectric loss factor of the coating polymer material is greater than 0.05.
9. The method of claim 4 , wherein the first and second melting points permit formation of a solid and liquid morphology.
10. The method of claim 1 , wherein the coating polymer material is immiscible with the base polymer material thereby preventing phase separation and promoting fusion of the base polymer layer with adjacent beads of the liquid coating.
11. The method of claim 1 , wherein the coating polymer material includes a material or solvent containing at least one of —OH, —NH, C═O, or —N═O functional groups.
12. A method of fabricating an object by additive manufacturing, the method comprising:
forming a first coated sheet by:
providing a first sheet formed of a base polymer material having a first dielectric loss factor with a first tan value in a predefined microwave frequency range;
applying a liquid coating to at least a portion of an exterior of the first sheet, the liquid coating being formed of a coating polymer material distinct from the base polymer material and having a second dielectric loss factor with a second tan value in a predefined microwave frequency range, the second tan value being substantially larger than the first tan value of the base polymer material and thereby more susceptible to heating in response to electromagnetic energy than the base polymer material during the AM process; and
drying the liquid coating on the first sheet to form the first coated sheet, the first coated sheet including a base polymer layer formed by the first sheet and a coating polymer layer formed by the liquid coating after drying the liquid coating;
forming a second coated sheet by:
providing a second sheet formed of the base polymer material;
applying the liquid coating to at least a portion of an exterior of the second sheet; and
drying the liquid coating on the second sheet to form the second coated sheet, the second coated sheet including a base polymer layer formed by the second sheet and a coating polymer layer formed by the liquid coating after drying the liquid coating;
positioning the first coated sheet relative to the second coated sheet so that the coating polymer layer of the first coated sheet overlies the coating polymer layer of the second coated sheet at an interface area;
compressing the first and second coated sheets; and
forming an object using the first and second coated sheets in the AM process, including dielectrically heating at least the coating polymer layer of the first coated sheet and the coating polymer layer of the second coated sheet using electromagnetic radiation, thereby to fuse the first coated sheet to the second coated sheet across the interface area.
13. The method of claim 12 , in which the second tan value of the second dielectric loss factor of the coating polymer material is at least about 50 times greater than the first tan value of the first dielectric loss factor of the base polymer material in a predefined microwave frequency range.
14. The method of claim 12 , in which:
the base polymer material has a first melting point;
the coating polymer material has a second melting point; and
the first melting point is within about 20 degrees Celsius of the second melting point.
15. The method of claim 12 , in which:
the base polymer material has a first solubility parameter;
the coating polymer material has a second solubility parameter; and
the second solubility parameter is within about 10 (J/cc) 0.5 of the first solubility parameter.
16. The method of claim 12 , in which the base polymer material comprises polyetherimide and the coating polymer material comprises polyvinyl alcohol.
17. The method of claim 12 , further comprising, after dielectrically heating at least the coating polymer layer of the first coated sheet and the coating polymer layer of the second coated sheet, cutting the first coated sheet and the second coated sheet to shape the object.
18. The method of claim 12 , in which dielectrically heating at least the coating polymer layer of the first coated sheet and the coating polymer layer of the second coated sheet comprises applying electromagnetic radiation in a microwave range of frequencies.
19. The method of claim 12 , wherein the first dielectric loss factor of the base polymer material has a first tan value less than 0.05 and the second dielectric loss factor of the coating polymer material has a second tan value greater than 0.05.
20. The method of claim 14 , wherein the first and second melting points permit formation of a solid and liquid morphology.