Performance analysis of triple-zone extruder screw pitch for 3D concrete printing using CFD simulation

Abstract

In 3D concrete printing (3DCP) systems, the use of a screw-type extrusion mechanism is crucial for maintaining a stable and uniform material flow. However, designing a reliable extrusion system is challenging due to the non-Newtonian nature of fresh mortar. This material often causes blockages and fluctuations in output velocity, which can ultimately compromise the strength of the printed structure. This study evaluated the mechanical performance of a variable-pitch screw design. The screw has a total length of 51 cm and an effective thread length of 33.8 cm. Through analytical modeling and Computational Fluid Dynamics (CFD) simulations, the screw geometry was divided into three main zones: a feed zone with a pitch of 45 cm, a transition zone that gradually narrows from 45 cm to 36 cm, and a metering zone with a fixed pitch of 36 cm. The simulations were conducted at a constant rotational speed of 40 rpm with a mortar plastic viscosity of 60.75 Pa·s. Computational results showed that the proposed variable-pitch screw generated a stable mass flow and thrust pressure distribution under the investigated operating conditions. Meanwhile, the use of a denser pitch at the end demonstrated helps stabilize the pressure profile and reduce flow pulsations. Overall, the proposed variable-pitch mechanism demonstrated stable extrusion characteristics throughout the CFD simulation. From both an academic and practical perspective, these results confirm that intentionally the present results suggest that adjusting pitch geometry may be a promising strategy for provided the reliability of large-scale concrete construction automation systems.