Temperature control in additive manufacturing systems

1. An additive manufacturing system comprising:

a dispensing device to deposit a layer of build material over a build surface;

an applicator to apply a fusing agent and to apply a detailing agent on the layer of build material,

a thermal energy source;

a thermal imaging device; and

a controller:

to cause the dispensing device to deposit the layer of build material over the build surface;

to cause the applicator to selectively apply:

the fusing agent to form an object portion in the layer of build material; and

the detailing agent to form a reference portion in the layer of build material, wherein the reference portion is outside a boundary of the object portion;

to cause the thermal energy source to:

heat the reference portion; and

heat and fuse the object portion;

to cause the thermal imaging device to measure a temperature of the reference portion, and

to regulate a power level of the thermal energy source based on a comparison between the temperature of the reference portion and a temperature set-point for the reference portion,

wherein the temperature set-point for the reference portion is based on a target temperature for the object portion.

2. The system of claim 1 wherein the controller is to define the build surface to comprise a buildable region having a perimeter and a thermal boundary region disposed outside the perimeter of the buildable region, and

wherein the controller is to control the applicator to dispose the object portion in the buildable region and to dispose the reference portion in the thermal boundary region.

3. The system of claim 1 wherein the thermal imaging device is to measure the temperature of the reference portion using the portion of the reference portion that is to lack the fusing agent.

4. The system of claim 3 wherein the entirety of the reference portion is to lack the fusing agent, and

wherein the detailing agent includes a coolant.

5. The system of claim 1 wherein the temperature set-point is less than the target temperature for the object portion, differing by a temperature offset.

6. The system of claim 1 , wherein the controller is to:

determine the temperature set-point for the reference portion based on a target temperature for the object portion and a temperature offset between the reference portion and the object portion; and

perform the comparison between the temperature of the reference portion and the temperature set-point for the reference portion.

7. The system of claim 1 , wherein the controller is to:

measure a first temperature at the reference portion before a pass by the thermal energy source;

measure a second temperature of the reference portion after the pass by the thermal energy source; and

verify a location of the reference portion based on a difference of the first temperature and the second temperature being less than a threshold amount.

8. The system of claim 1 , wherein the controller is to regulate the power level of the thermal energy source based on a comparison between a temperature of a first reference portion and a first temperature set-point for the reference portion, wherein the first reference portion has a detailing agent applied thereon and the first temperature set-point corresponds to a target temperature for fused build material within a buildable region.

9. The system of claim 8 , wherein the controller is to regulate the power level of the thermal energy source based on a comparison between a temperature of a second reference portion and a second temperature set-point for the reference portion, wherein the second reference portion comprises uncoated build material and the second temperature set-point corresponds to a target temperature for uncoated build material within the buildable region.

10. The system of claim 1 , wherein:

the applicator is to apply the detailing agent in a selected two-dimensional (2D) pattern across a layer of build material; and

the controller is to establish 2D coordinates for the build surface based on thermal image data of the 2D pattern of detailing agent.