Two-Color Thermography of GMAW to Enable Real-Time Hardness Prediction

Advanced process monitoring and model validation are essential for improving weld quality in both welding and welding-based additive manufacturing processes. Specifically, temperature is a key quantity of interest for understanding defect formation and microstructural evolution, which significantly impact mechanical properties. However, achieving accurate in-situ temperature imaging is challenging due to emissivity variations across the dynamic melt pool. To address this, we implemented a two-color imaging technique using a single commercial color camera to reduce temperature readings’ sensitivity to emissivity variations. High dynamic range images during melting were captured at various exposure times, and spatial and temporal filters were applied to minimize interference from the plasma arc emissions. The resulting temperature fields within the melt pool were then utilized to estimate cooling rates, which were further correlated to ex-situ hardness measurements. The strong correlation observed between cooling rates ranging from 20 to 600 K/s and hardness ranging between 250 to 400 HV demonstrated the potential of our easy-to-use two-color thermal imaging setup for preliminary evaluation of mechanical properties in a non-destructive manner. Beyond its significance for predicting mechanical properties, this technique provides a validated temperature measurement approach that can enhance the accuracy of physics-based models, such as those used to predict defect formation mechanisms, like porosity.