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1. (WO2019027405) FORMING THREE-DIMENSIONAL (3D) PARTS
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CLAIMS

What is claimed is:

1 . A method of forming a three-dimensional (3D) part comprising: spreading a layer of build material over a print bed;

heating the layer of build material during each of consecutive passes of a scanning heating lamp on a carriage over the print bed to maintain printed portions of the build material above a melting temperature for the duration of the consecutive passes.

2. A method as in claim 1 , wherein spreading a layer of build material comprises bi-directionally spreading the layer of build material over the print bed during two of the consecutive carriage passes.

3. A method as in claim 1 , further comprising:

during two of the consecutive carriage passes, bi-directionally printing a liquid fusing agent onto the build material to form the printed portions of build material.

4. A method as in claim 3, wherein:

spreading a layer of build material and heating the layer of build material comprises passing a first carriage comprising a spreader bi-directionally over the print bed; and,

printing a liquid fusing agent onto the build material comprises passing a second carriage comprising a liquid dispenser bi-directionally over the print bed.

5. A method as in claim 4, wherein passing the first and second carriages comprises passing the carriages in-line with one another along a common support.

6. A method as in claim 1 , wherein spreading a layer of build material and heating the layer of build material comprises transporting a material spreader and multiple heating sources on a single carriage back and forth over the print bed.

7. A method as in claim 1 , wherein heating the layer of build material during each of multiple consecutive carriage passes comprises maintaining unprinted portions of the build material at a neutral temperature below a melting temperature.

8. A method as in claim 1 , wherein the build material comprises PA12 build material, and wherein maintaining printed portions of the build material above a melting temperature comprises maintaining printed portions of the build material above about 180°C.

9. A method as in claim 8, wherein maintaining printed portions of the build material above a melting temperature for the duration of the consecutive carriage passes comprises maintaining printed portions of the build material above a melting temperature for a duration of about 3.6 seconds to about 4.0 seconds.

10. A method of forming a three-dimensional (3D) part comprising: passing a first carriage comprising a spreader over a print bed multiple times to spread a new layer of build material over the print bed;

passing a second carriage comprising a liquid dispenser over the print bed multiple times to selectively print a liquid fusing agent onto the build material; and, while passing the first carriage over the print bed multiple times, applying fusing energy and warming energy from scanning lamps on the first carriage to maintain the printed build material above a melting temperature while maintaining unprinted build material in a neutral temperature zone, below a caking onset temperature and above a crystallization onset temperature.

1 1 . A method as in claim 10, wherein passing the first carriage over the print bed multiple times comprises:

in a first pass, fusing and warming a previous layer of build material, and spreading a pile of build material to form a new layer of build material;

in a second pass, spreading a remainder of the pile over the new layer of build material, and warming the new layer of build powder;

in a third pass, fusing printed areas of the new layer of build powder, and warming the new layer of build powder; and,

in a fourth pass, warming the new layer of build powder, and fusing printed areas of the new layer of build powder.

12. A method as in claim 1 1 , wherein passing the second carriage over the print bed multiple times comprises:

during second and third carriage passes, selectively printing a liquid agent onto the new layer of build material.

13. A method as in claim 1 1 , wherein spreading a remainder of the pile of build material comprises lifting a spreader from one side of the pile of build material to another side of the pile of build material to spread the build material in an opposite direction over the print bed.

14. A method as in claim 10, wherein the build material comprises PA12, and wherein:

maintaining the printed build material above a melting temperature comprises maintaining the printed build material in a temperature range from about 180°C to about 220°C; and,

maintaining the unprinted build material in a neutral temperature zone comprises maintaining the unprinted build material in a temperature range from about 153°C to about 180°C.

15. A method of forming a three-dimensional (3D) part comprising: in a first pass, passing a first carriage comprising fusing and warming lamps and a spreader over a print bed to fuse and warm a previous layer of build material and to spread a pile of build material to form a new layer of build material over the previous layer of build material;

in a second pass, passing the first carriage and a second carriage comprising a liquid dispenser over the print bed in-line with one another to spread a remainder of the pile of build material over the new layer, warm the new layer, and print a liquid fusing agent onto the new layer;

in a third pass, passing the first and second carriages over the print bed inline with one another to print a liquid agent onto the new layer, fuse the printed areas of the new layer, and warm the new layer; and,

in a fourth pass, passing the first carriage over the print bed to warm the new layer and to fuse the printed areas of the new layer.