Additive manufacturing (AM) is a non-conventional manufacturing process that enables the solid physical realization of a given model. Various AM processes and techniques are available that provide flexibility over the material, quality, and cost. Screw extrusion-based additive manufacturing (SEAM) is a novel AM technique that uses a single-screw extruder for continuous extrusion and selective deposition of thermoplastic materials. The process depends heavily on the extruder screw and its geometry in terms of pitch, helix angle, and length; defines the process parameters such as mass flow rate, extrudate size, and metering capacity. In this paper, geometric design optimization of an indigenously fabricated single-screw extruder set-up is performed, for AM applications. The objective is to optimize the helix angle of the extruder screw for maximum output flow rate. It is found that, for the given set of conditions (melt viscosity, extruder screw size, screw speed, nozzle dimensions, flight height, and flow rate), the optimum helix angle is 20.184°. The corresponding flow rate, in terms of extrusion velocity, showed an improvement of almost 1.5 times. The overall size of the set-up is also reduced to almost 50% of the original. The optimized screw geometry showed escalated results at all temperature and rotation conditions. Similar heuristics can be applied to any given screw-extruder set-up.