Printing a multi-structured 3D object

1. A method of printing a multi-structured three-dimensional (3D) object comprising:

from layers of sinterable material to be thermally fused by applying energy absorbing fusing agent and radiation thereto, forming an internal core structure surrounded by an external shell structure;

applying a carbon black-based energy absorbing fusing agent and radiation to internal core structure layers to form the internal core structure; and,

applying a non-carbon black-based, colored, energy absorbing fusing agent and radiation to external shell structure layers to form the external shell structure.

2. A method as in claim 1 , wherein forming an internal core structure surrounded by an external shell structure comprises:

forming a first layer of sinterable material;

applying to the first layer, non-carbon black-based, colored, energy absorbing fusing agent, and radiation to form part of the external shell structure;

forming a second layer of sinterable material; and,

applying to the second layer, carbon black-based, energy absorbing fusing agent, and radiation to form part of the internal core structure;

wherein radiation applied to the first layer comprises radiation applied with at least one of, a lower intensity and shorter duration, than radiation applied to the second layer.

3. A method as in claim 2 , further comprising:

forming a third layer of sinterable material; and,

applying to the third layer, non-carbon black-based, colored, energy absorbing fusing agent, and radiation to form part of the external shell structure.

4. A method as in claim 1 , wherein:

the carbon black-based energy-absorbing fusing agent comprises a fusing agent having a first ink density; and,

the non-carbon black-based, colored, energy-absorbing fusing agent comprises a fusing agent having a second ink density.

5. A method as in claim 1 , wherein applying radiation to the internal core structure layers comprises applying radiation with at least one of, a higher intensity and longer duration, relative to the external shell structure layers, and applying radiation to the external shell structure layers comprises applying radiation with at least one of, a lower intensity and shorter duration, relative to the internal core structure layers.

6. A system for printing a multi-structured three-dimensional (3D) object comprising:

a support member receiver to receive a support for sinterable material;

a distributor receiver to receive a sinterable material distributor to provide layers of sinterable material that is to be thermally fused on the support; and

a multi-structure processing module to apply energy absorbing fusing agent and radiation to layers of the sinterable material to form a 3D object with an internal core structure surrounded by an external shell structure;

wherein applying fusing agent and radiation comprises, to form part of the internal core structure, applying a carbon black-based energy absorbing fusing agent and radiation to internal core structure layers of sinterable material, and to form part of the external shell structure, applying a non-carbon black-based, colored, energy absorbing fusing agent and radiation to external shell structure layers of sinterable material.

7. A system as in claim 6 , wherein applying radiation to the internal core structure layers comprises applying radiation with at least one of, a higher intensity and longer duration, relative to the external shell structure layers, and applying radiation to the external shell structure layers comprises applying radiation with at least one of, a lower intensity and shorter duration, relative to the internal core structure layers.

8. A system as in claim 6 , wherein the carbon black-based energy absorbing fusing agent comprises a fusing agent having a first ink density, and the non-carbon black-based, colored, energy absorbing fusing agent comprises a fusing agent having a second ink density.

9. A system as in claim 6 , further comprising a fusing agent distributor to selectively deliver fusing agent onto a portion of a layer of sinterable material, the multi-structure processing module to control the fusing agent distributor to deposit fusing agent according to an image pattern of a cross-section of the 3D object for the layer of sinterable material.

10. A system as in claim 9 , further comprising a detailing agent distributor to selectively deliver a detailing agent onto a portion of the layer of the sinterable material, the multi-structure processing module 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.