Thermal process monitoring for additive manufacturing
Additive-manufactured functional parts allow highly complex geometries, but in return require individually adapted process parameters and stable process control. The process window for optimized material processing, in which the complete melting and joining of the individual layers is guaranteed as well as gas voids and deep welding pores are prevented, is very small and can vary across the component. Therefore, the process temperature during the heating and cooling phase is of particular interest, as it allows conclusions about component quality and microstructure.
So far, component properties can mostly be verified and validated by invasive, destructive measuring methods. In addition, in many cases the already implemented optical sensor technology does not provide sufficient information density, accuracy and traceability, so that in-line process optimization can yet be realized.
The University of Applied Sciences Würzburg – Schweinfurt (FHWS) and the Bavarian Centre for Applied Energy Research (ZAE Bayern) cooperate in various projects and develop innovative optical sensor systems, which are tested in a laboratory setup.
The present paper introduces a first approach based on a preliminary test setup for temperature monitoring and analysis of the melt pool and the heat affected zone during the heating/cooling process and discusses the resulting possibilities for in-situ material analysis in real applications. Knowledge from the well-known laser flash method is applied and the determined material parameters are used to make a statement about the thermal conductivity of the layers. These in turn provide information about the material properties. In this way, errors in the melting process and resulting material defects can be detected early.
Acknowledgement: The work is funded by the Federal Ministry of Education and Research (FKZ 03FH007IN6), by the Federal Ministry of Economics and Energy (FKZ 03ET7082) and by the Bavarian State Ministry of Economics, Energy and Technology (FKZ 6665e/366/