Method of operation for an apparatus for layer-by-layer manufacture of 3D objects

1 . A method of operation for an apparatus for a layer-by-layer manufacture of a 3D object from particulate material, the apparatus comprising a preheat source, a fusing heat source, and a stationary overhead heat source arranged above a build bed surface, and a thermal sensor; the method comprising:

carrying out a thermal calibration process comprising a thermal calibration routine for a thermal control component of the layer, wherein the thermal control component comprises the thermal sensor and the thermal calibration routine is for the measurement scale of the thermal sensor, and subsequently carrying out a build process to manufacture a 3D object;

wherein the thermal calibration routine includes a calibration layer cycle having the steps of:

(i) distributing a layer of particulate material over a build area, the layer providing the build bed surface of the build area;

(ia) after the distributing step, heating the build bed surface by the preheat source;

(ii) after the step of heating by the preheat source, depositing a radiation absorber over a layer-specific region within the build bed surface; and

(iii) after the depositing step, heating the layer-specific region by passing, while operating, the fusing heat source across the build bed surface;

wherein the calibration layer cycle also includes measuring a temperature of the build bed surface using the thermal sensor at least once after one or more of steps (i) to (iii);

wherein the calibration layer cycle also includes heating the build bed surface of each layer by continuously operating the stationary overhead heat source operated in response to the one or more measured temperatures with respect to a target layer temperature between the solidification temperature and the melting temperature of the particulate material;

wherein the calibration layer cycle is repeated a number of times until the thermal calibration routine complete;

wherein an outcome of the completed thermal calibration routine is based on the measured temperature in step (iv) of the build bed surface and is applied to the measurement scale of the thermal sensor for the subsequent build process;

wherein the build process is performed after the calibration process and includes a build layer cycle having the steps of:

(i-2) distributing a layer of particulate material over a build area, the layer providing the build bed surface of the build area;

(ia-2) after the distributing step (i-2), heating the build bed surface by the preheat source to preheat the layer to a preheat temperature between the solidification temperature and the melting temperature of the particulate material;

(ii-2) after the step (ia-2) of heating by the preheat source, depositing radiation absorber over at least one of a layer-specific region within the build bed surface; and

(iii-2) after the depositing step (ii-2), heating the layer-specific region by passing, while operating, the fusing heat source across the build bed surface and causing the particulate material within the layer-specific region to melt;

wherein the build layer cycle also includes measuring a temperature of the build bed surface using the thermal sensor at least once after one or more of steps (i-2) to (iii-2);

wherein the build layer cycle also includes heating the build bed surface of each layer by continuously operating the stationary overhead heat source operated in response to the one or more measured temperatures with respect to the target layer temperature between the solidification temperature and the melting temperature of the particulate material;

wherein the build layer cycle is repeated a number of times until the build process is complete.

2 . The method of claim 1 , wherein the calibration layer cycle steps (i) and (i-2) of distributing each layer and (iii) and (iii-2) of passing the fusing heat source over each layer are carried out in a first direction.

3 . The method of claim 2 , wherein the measuring of the build layer cycle includes measuring a temperature of the surrounding area surrounding the layer specific region, and operating the stationary overhead heat source and/or the preheat source over a subsequent layer cycle in response to the measured temperature of the surrounding area.

4 . The method of claim 2 , wherein the thermal control component further comprises one or both of the fusing heat source and the preheat source, and wherein the calibration process comprises at least one further calibration routine selected from:

an alignment correction routine for the measurement position of the thermal sensor, wherein the thermal sensor comprises an array of a plurality of individually controllable pixels;

a distortion correction routine for the measurement position and/or scale of the thermal sensor, wherein the thermal sensor comprises an array of a plurality of individually controllable pixels; and

a calibration routine for the input power profiles of the fusing heat source and the preheat source with respect to one another and/or with respect to the measurement scale of the thermal sensor;

wherein the layer cycle of the further calibration routine is the same as the calibration layer cycle.

5 . The method of claim 2 , wherein the steps (i), (ia), (iii), (i-2), (ia-2) and (iii-2) are all carried out in the same direction and at the same speed profile.

6 . The method of claim 2 , wherein for each layer of the thermal calibration routine, the calibration layer cycle further comprises:

initiating the step (iii) of heating the build bed surface with the fusing heat source after a predefined first time interval after initiating the step (i) of distributing the layer;

initiating the step (i) of distributing each layer after a predefined second time interval after the step (iii) of heating the previous build bed surface with the fusing heat source; and

initiating the step (ia) of heating the build bed surface with the preheat source after a predefined third time interval after initiating the step (i) of distributing the layer;

wherein for each layer of the build process, the build layer cycle further comprises:

initiating the step (iii-2) of heating the build bed surface with the fusing heat source after the predefined first time interval after initiating the step (i-2) of distributing the layer;

initiating the step (i-2) of distributing each layer after the predefined second time interval after the step (iii-2) of heating the previous build bed surface with the fusing heat source; and

initiating the step (ia-2) of heating the build bed surface with the preheat source after the predefined third time interval after initiating the step (i-2) of distributing the layer;

wherein the predefined first, second and third time intervals are constant and the duration of the build layer cycle is the same for each layer of the build process.

7 . The method of claim 6 , wherein the predefined first, second and third time intervals are constant and the period of time of the calibration layer cycle is the same for each layer of the thermal calibration routine.

8 . The method of claim 1 , wherein the steps (ia) and (ia-2) of heating are carried out by passing the preheat source over each layer while operating the preheat source to heat the layer; and wherein the steps (i) and (i-2) of distributing each layer, (ia) and (ia-2) of passing the preheat source over the build bed surface, and (iii) and (iii-2) of passing the fusing heat source over each layer are carried out in a first direction.

9 . The method of claim 1 , wherein the measuring of the build layer cycle includes measuring a post-fuse temperature of the layer-specific region after the step (iii-2) of heating with the fusing heat source; and heating a subsequent layer-specific region by operating the fusing heat source at a subsequent step (iii-2) in response to the measured post-fuse temperature.

10 . The method of claim 1 , wherein the stationary overhead heat source comprises an array of individually operable heating elements positioned above the build bed surface, and wherein the thermal sensor comprises an array of individual sensor pixels, wherein the measuring of the calibration layer cycles and of the build layer cycles includes:

determining a zonal temperature for each of a plurality of zones of the build bed surface as measured by a subset of the sensor pixels; and

determining a zonal temperature difference between each zonal temperature and the target layer temperature;

wherein the steps of heating the build bed surface by the stationary overhead heat source includes heating each zone by operating one or more corresponding heating elements in response to the determined zonal temperature difference.

11 . The method of claim 1 , wherein the stationary overhead heat source comprises an array of individually operable heating elements positioned above the build bed surface, and wherein the thermal sensor comprises an array of individual sensor pixels, wherein the measuring of the calibration layer cycles and the build layer cycles includes:

measuring a temperature of the surrounding area using the array of individual sensor pixels;

determining a zonal temperature for each of a plurality of zones of the build bed surface as measured by a subset of the array of sensor pixels; and

determining a zonal temperature difference between each zonal temperature and the target layer temperature;

wherein the steps of heating the build bed surface by the stationary overhead heat source includes heating each zone continuously throughout each step of the layer cycle by operating one or more corresponding heating elements in response to the determined zonal temperature difference.

12 . The method of claim 1 , wherein the thermal control component further comprises the stationary overhead heat source; and wherein the calibration process comprises at least one further calibration routine selected from:

an alignment correction routine for the measurement position of the thermal sensor, wherein the thermal sensor comprises an array of a plurality of individually controllable pixels to be aligned with the build bed surface;

a distortion correction routine for the measurement position and/or scale of the thermal sensor, wherein the thermal sensor comprises an array of a plurality of individually controllable pixels to be aligned with the build bed surface; and

a calibration routine for the input power profile of the stationary overhead heat source;

wherein the layer cycle of the further calibration routine is the same as the calibration layer cycle.

13 . The method of claim 1 , wherein step (iii), when carried out during at least one of the calibration layer cycles of the thermal calibration routine for the thermal sensor, comprises: operating the fusing heat source at a fusing power input so as to cause the particulate material of the layer-specific region to melt; and wherein the one or more measured temperatures of step (iv) of the calibration layer cycles are used to determine a set point for the temperature scale of the thermal sensor based on a thermal characteristic of the particulate material, and to calibrate the measurement scale of the thermal sensor to the set point, and wherein the measurements by the thermal sensor in step (iv-2) of the build layer cycle are calibrated temperature measurements.

14 . The method of claim 13 , wherein the calibration process comprises a pre-calibration routine for the fusing heat source carried out before the calibration routine for the thermal sensor, wherein the layer cycle of the pre-calibration routine is the same as the calibration layer cycle, and wherein successive layer cycles of the pre-calibration routine comprise:

operating the fusing heat source during step (iii) at a power input different to a preceding power input of a preceding layer so as to heat the layer-specific region to a temperature different to that of the layer-specific region of the preceding layer;

wherein the measuring includes measuring the temperature of the layer-specific region following the step of heating with the fusing heat source at step (iii);

wherein the outcome of the pre-calibration routine is a corrected power input for the fusing heat source based on the measured temperatures of the layer-specific region of each layer; and

wherein the calibration routine for the thermal sensor comprises, during step (iii) of heating with the fusing heat source, applying the corrected the power input of the fusing heat source.

15 . The method of claim 1 , wherein the thermal control component further comprises the preheat source and the fusing heat source, and wherein the calibration process comprises a calibration routine for the preheat source and the fusing heat source applied before and/or after the calibration routine for the thermal sensor; wherein the outcome of the calibration routine for the preheat source and the fusing heat source is a corrected first and/or second input power profile, and wherein the layer cycle of the calibration routine for the preheat source and the fusing heat source is the same as the calibration layer cycle and also comprises:

operating the fusing heat source at a first input power profile during the step (iii);

operating the preheat source at a second input power profile during step (ia);

wherein, for each layer of the calibration routine for the preheat source and the fusing heat source, each pair of first and second input power profiles is different to a preceding pair of a preceding layer by at least one of the first and second input power profiles;

wherein the measuring of the calibration routine for the preheat source and the fusing source further includes measuring a first set of temperatures of each layer-specific region after step (iii) of heating with the fusing heat source and measuring a second set of temperatures of each layer-specific region after the step of heating with the preheat source; and

receiving a first target temperature for the layer-specific region after heating with the fusing heat source and a second target temperature of the layer-specific region after heating with the preheat source;

determining, from the measured first and second set of temperatures, and based on the first target temperature and the second target temperature, a corrected first input power profile along the first direction for the fusing heat source and/or a corrected second input power profile along the first direction for the preheat source; and

wherein, when the calibration routine for the preheat source and the fusing heat source is applied before that of the thermal sensor, the calibration layer cycle of the thermal calibration routine comprises applying the corrected first input power profile to the fusing heat source during the step (iii) and/or applying the corrected second power input profile to the preheat source during the step of heating the build bed surface; and when the calibration routine for the preheat source and the fusing heat source is applied after that of the thermal sensor, the build layer cycle of the build process comprises applying the corrected first input power profile to the fusing heat source during the step (iii-2) and/or applying the corrected second power input profile to the preheat source during the step (ia-2) of heating the build bed surface.

16 . The method of claim 1 , wherein the layer-specific region for the thermal calibration routine comprises a plurality of layer-specific regions.

17 . The method of claim 1 , wherein respective time periods between the initiation of each step and the initiation of the previous step in the calibration layer cycle and the build layer cycle are constant for each corresponding step in each successive layer cycle.

18 . The method of claim 1 , wherein for each layer, the calibration layer cycle and the build layer cycle further comprises:

initiating the steps (iii) and (iii-2) of heating the build bed surface with the fusing heat source after a predefined first time interval after initiating the steps (i) and (i-2) of distributing the layer; and

initiating the steps (i) and (i-2) of distributing each layer after a predefined second time interval after the steps (iii) and (iii-2) of heating the previous build bed surface with the fusing heat source; and

wherein a duration of the calibration layer cycle and of the build layer cycle is the same for each layer.