A method for increasing thermal stability of a build bed surface in an apparatus for layer-by-layer manufacture of a 3D object from particulate material;
- the apparatus comprising a controller, at least one heat source and a thermal sensor;
- the method comprising:
- performing a calibration layer cycle in which a single layer of the particulate material is provided as a calibration layer, the calibration layer cycle sequentially including the steps of:
- (a) distributing the calibration layer of the particulate material over a build bed along a first direction, the calibration layer providing a build bed surface of the build bed;
- (b) after initiating step (a), operating a first heat source along the first direction at a first input power profile to heat the calibration layer;
- (c) after step (b), measuring a first set of temperatures using the thermal sensor, the first set of temperatures comprising respective first temperature measurements of each of a plurality of regions within the build bed surface;
- (d) after step (c), depositing a radiation absorber over each region of the plurality of regions;
- and/or depositing an absorption inhibitor over a surrounding area surrounding the plurality of regions;
- (e) after initiating step (d), operating a second heat source along the first direction at a second input power profile to heat each region;
- and
- (f) after step (e), measuring a second set of temperatures using the thermal sensor, the second set of temperatures comprising respective second temperature measurements of each region of the plurality of regions;
- repeating the calibration layer cycle of steps (a) through (f) for a number of calibration layers, each subsequent calibration layer cycle using a respective pair of first and second input power profiles, wherein each of the respective pair of first and second input power profiles is different to a preceding pair or pairs of first and second input power profiles;
- and
- after repeating the calibration layer cycle of steps (a) through (f) for the number of calibration layers,
- the controller comparing each of the measured first sets of temperatures to a first target temperature and determining a first range in which each of the measured first sets of temperatures falls, and
- the controller comparing each of the measured second sets of temperatures to a second target temperature and determining a second range in which each of the measured second sets of temperatures falls;
- and
- the controller comparing the determined first range and second range of previous pairs of input power profiles and determining therefrom an adjusted first input power profile and/or an adjusted second input power profile,
- performing a further layer cycle including at least the steps of (a), (b), (d) and (e) using the adjusted first and/or second input power profiles in the heating steps (b) and (e) thereby increasing the thermal stability of the build bed surface such that each of a further measured first set of temperatures are within a reduced first range of the first target temperature and each of a further measured second set of temperatures are within a reduced second range of the second target temperature, the reduced first and second ranges of subsequent layers being reduced relative to the first and second ranges of previous calibration layers.