Abstract: A method of operating an apparatus for the layerwise manufacture of 3D objects. The method includes two or more operational cycles of a warm up phase, starting from ambient, followed by a build phase and a cooling phase. The warm up phase and the build phase each include a layer cycle of: (a) dosing build material to the work surface; (b) distributing a portion of the dosed amount over a build area; (c) heating the dosed amount; and (d) monitoring a temperature of the build material to determine a thermal state. The build phase includes melting layer-specific regions. These steps are repeated until the warm up and build phases are completed. A property of the subsequent warm up phases is determined such that the duration of a subsequent warm up phase is shorter than the duration of a preceding warm up phase.