Additive Manufacturing (or 3D printing) is a technique to produce unique products with complex geometries. Due to new innovations in printing concepts and material systems, the list of materials that can be printed is growing constantly. In our group, we study the mechanical properties of these materials as a function of the printing process conditions. By understanding this relation, we aim at improving material properties and printed product quality. We develop multi-scale and multi physics numerical tools to simulate the microstructural evolution of the material and the actual printing process. These models are used in combination with advanced in-situ measurements closed loop control algorithms to improve the quality of 3D printed products.