In process monitoring of the thermal profile during solidification in laser directed energy deposition of aluminium

Abstract

• In situ infrared imaging of directed energy deposition in high spatial resolution. • Image processing to determine changes of weld pool geometry during deposition. • Experimental determination of local solidification rates during deposition. • Experimental determination of local temperature gradients during deposition. The manufacturing of parts in a layer-by-layer fashion in laser based directed energy deposition (L-DED) of wire enables a unique flexibility and freedom of part design, but some technological challenges remain unsolved. The cumulative heat input, which results from the subsequent addition of individual layers, leads to a continuous temperature change with proceeding build progress. In order to access a comprehensive investigation of this effect, the process was analysed by infrared imaging in spatial and temporal resolution. The present work describes an image based processing method, to monitor the process zone of the L -DED process. The algorithm detects the point in time, when the process zone is present in the field of view of the infrared camera, and determines the current location of the melt pool and the solidification zone. The captured isotherms determine the change of the temperature field in case of L -DED-manufacturing with different process parameters. Finally, the local solidification rates and temperature gradients were deduced from the geometry and position of the captured isotherms. The comparison of spatial distribution of these solidification conditions highlights the significant influence of the process parameters on solidification in L -DED.