Simulating the laser-material interaction in an LPBF process requires implementing relevant physics models at relevant temporal and spatial scales. Process parameters such as laser power, scanning velocity, scanning path, and powder size distribution influence melt pool dynamics, playing a key role in process stability. We will look at underlying mechanisms behind the formation of defects such as balling, porosity and spatter using computational thermal-fluid dynamics models built in FLOW-3D AM. While low energy densities can lead to lack of fusion defects, high energy densities result in strong recoil pressure and unstable keyholes that lead to the formation of porosity and spatter. Additionally, the need for temperature dependent material properties such as surface tension, viscosity, density, thermal conductivity, specific heat, etc. and their influence on melt pool dynamics shall be discussed. Lastly, such models output thermal gradient and cooling rate data that can be used to predict microstructure evolution.