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.