Three-dimensional (3D) printing

1. A method of three-dimensional (3D) printing comprising:

applying a sinterable material;

selectively applying a fusing agent on a portion of the sinterable material;

applying a first amount of radiation energy to the portion of the sinterable material to pre-heat the portion of the sinterable material to a temperature at least as high as a temperature of surrounding sinterable material but below a melting point; and

applying a second amount of radiation energy to the portion of the sinterable material to further heat the portion of the sinterable material to a temperature that fuses the portion of the sinterable material, the second amount of radiation energy being higher than the first amount of radiation energy.

2. A method as in claim 1 , wherein:

applying a first amount of radiation energy comprises sweeping a heating lamp across the portion of the sinterable material at a first speed; and

applying a second amount of radiation energy comprises sweeping the heating lamp across the portion of the sinterable material at a second speed different than the first speed.

3. A method as in claim 2 , wherein sweeping the heating lamp across the portion of the sinterable material at a second speed comprises sweeping the heating lamp across the portion of the sinterable material at a slower speed than the first speed.

4. A method as in claim 2 , wherein sweeping the heating lamp across the portion of the sinterable material at a first speed comprises sweeping the heating lamp across the portion of the sinterable material at a speed between 15 inches per second and 20 inches per second.

5. A method as in claim 2 , wherein sweeping the heating lamp across the portion of the sinterable material at a second speed comprises sweeping the heating lamp across the portion of the sinterable material at a speed between 5 inches per second and 15 inches per second.

6. A method as in claim 1 , further comprising selectively applying a detailing agent on the portion, on an other portion, or on both the portion and the other portion of the sinterable material.

7. A method as in claim 1 , further comprising heating the sinterable material before applying the fusing agent.

8. A method as in claim 7 , wherein heating the sinterable material comprises heating the sinterable material to a temperature ranging from about 50° C. to about 400° C.

9. A system for three-dimensional (3D) printing comprising:

a support for sinterable material;

a sinterable material distributor to provide a layer of sinterable material on the support;

a fusing agent distributor to selectively deliver a fusing agent onto a portion of the layer of sinterable material; and

a pre-fusing/fusing module to control a radiation source to apply a first amount of radiation energy to pre-heat the layer of sinterable material to a temperature that is below a melting point of the sinterable material during a first pre-fusing operation and to apply a second amount of radiation energy to further heat the layer of sinterable material to a temperature that fuses a portion of the layer of sinterable material during a fusing stage, the second amount of radiation energy being higher than the first amount of radiation energy.

10. A system as in claim 9 , further comprising:

a detailing agent distributor to selectively deliver a detailing agent onto the portion of the layer of the sinterable material; and

an imaging module to control the fusing agent distributor to deposit the fusing agent according to an image pattern of a cross-section of a 3D object for the layer of sinterable material and to control the detailing agent distributor to deposit the detailing agent according to a detail pattern for the layer of sinterable material.

11. A system as in claim 10 , wherein the fusing agent distributor comprises a first array of nozzles of a printhead, and wherein the detailing agent distributor comprises a second array of nozzles of the printhead.

12. A non-transitory machine-readable storage medium storing instructions that when executed by a processor of a three-dimensional (3D) printing device, cause the 3D printing device to:

deposit a sinterable material onto a fabrication bed to form a 3D object layer;

heat the sinterable material to a temperature ranging from about 50° C. to about 400° C.;

deposit a fusing agent onto a portion of the sinterable material according to an image pattern of a cross-section of the 3D object layer;

expose the sinterable material to radiation for a first duration in a pre-fusing stage to pre-heat the sinterable material to a temperature below a melting point of the sinterable material; and

expose the sinterable material to radiation for a second duration in a fusing stage, wherein the second duration is longer than the first duration and the radiation from exposure for the second duration is greater than the radiation from exposure for the first duration.

13. A medium as in claim 12 , wherein depositing a fusing agent comprises depositing a colored fusing agent whose color is selected from the group consisting of cyan, magenta, yellow, or combinations thereof.

14. A medium as in claim 12 , wherein the instructions further cause the 3D printing device to deposit a detailing agent on the portion, on another portion, or on both the portion and the another portion of the sinterable material.

15. A medium as in claim 12 , wherein the instructions further cause the 3D printing device to repeat the spreading a sinterable material into a fabrication bed, the heating the sinterable material, the depositing a fusing agent, the exposing the sinterable material to radiation for a first duration, and the exposing the sinterable material to radiation for a second duration, to form subsequent object layers of a 3D object.