3D printing is an Additive Manufacturing (AM) process that enables physical realization of a CAD (Computer-Aided Design) model. 3D printing can be classified into several variants; Material Extrusion Additive Manufacturing (MEAM) is the most versatile and widely used. MEAM is a continuous extrusion and selective deposition process commonly used for thermoplastics. Screw Extrusion Additive Manufacturing (SEAM), a sub-domain of MEAM, uses an extruder screw to push the polymer-melt out of the nozzle. Computational Fluid Dynamics (CFD) analysis of a single screw extrusion of thermoplastics is presented in this paper. The effect of various control parameters like screw rotation, wall heat flux/temperature profile, screw geometry, etc., has been studied on the required output parameters like productivity, torque capacity, power requirement, metering efficiency, etc. It is found that the incrementally-variable-pitch screw geometry provides the best metering characteristics. However, every screw design is a compromise between melt temperature, productivity, and power requirements.