Potential of thermography for the monitoring of DED-Arc processes

Abstract

Thermography is a technique that uses, e.g., an infrared camera to visualize and measure the temperature of an object. It is often used in industrial and scientific applications to identify areas of heat loss, overheating, and other thermal anomalies. In the context of the DED-Arc (Direct Energy Deposition) process, thermography can be used to monitor the process and evaluate the temperature profile of the produced part. This can help to ensure the quality and reliability of the product, as well as to predict the resulting mechanical properties of the produced part. However, for other AM processes like LPBF (laser powder bed fusion), thermography is already used in industrial applications while for DED-Arc it is still a challenge to reliably determine the dynamically changing emission coefficient, as the emissivity strongly depends on the surface conditions. This means the emission coefficient differs for changes in surface conditions like impurities from soot and annealing colors. This work focuses on the potential of thermography for monitoring the DED-Arc process. A workflow for generating a calibration function for the emission coefficient ε is presented. In the context to the focus of this work, the resulting ε(T) function differentiates between the first three deposited layers and shows the change of emissivity for higher temperatures. This function is then used to correct the measured temperature profile with regard to different surface conditions and thus emission coefficients of a DED-Arc part.Highlights1. Temperature-dependent function for correcting the emissivity for DED-Arc with steel was defined.2. Emissivity is also influenced by the purity of the surface, leading to higher emissivity coefficients in layers that are previously deposited.3. t8/5 times are also affected by a wrongly set emission coefficient; deviations from the corrected t8/5 time depend on the cooling speed.