Additive manufacturing is a powerful technique capable of producing fully dense metallic components. However, process instabilities can introduce defects that may compromise the structural integrity and performance of the fabricated parts. Among the most critical defects are lack of fusion and gas porosities, which significantly affect mechanical properties. Joule Heating Thermography (JHT) represents a promising non-destructive testing method to detect manufacturing defects in metal components. Nevertheless, its application to additive manufactured parts remains limited and requires proper calibration to ensure accurate and reliable measurements. To support calibration and interpretation of experimental data, numerical simulations are an effective tool. The objective of this thesis is to develop a numerical model capable of simulating the JHT process on components manufactured using additive manufacturing techniques for metals and to use the developed model to evaluate the influence of part geometry and defects characteristics on defect detectability.