THE INFLUENCE OF NOZZLE GEOMETRY ON EXTRUSION QUALITY IN 3D PRINTING

Abstract

3D construction printer, extrusion, nozzle, extrusion quality, splitting tensile strength design of experiments.

This study investigates the influence of nozzle travel speed and nozzle geometry on extrusion quality and interlayer bond strength of cement-based mixtures in extrusion-based 3D concrete printing. The geometry of the nozzle is considered a critical parameter affecting the flow behavior of fresh mixtures, pressure distribution, and the quality of layer deposition.

Three nozzle geometries were examined: circular, rectangular, and an intermediate oval-rectangular shape with rounded edges. The latter was designed to combine the advantages of both conventional geometries by ensuring smoother flow conditions and reducing stress concentration near sharp corners. Experimental investigations were carried out using a laboratory-scale 3D printer developed at the Department of Building Materials and Products Technology.

A two-factor, three-level experimental design based on the method of design of experiments was applied. The main factors included nozzle travel speed and nozzle perimeter (as a coded representation of nozzle geometry). The responses analyzed were extrusion quality (evaluated using a qualitative scoring system) and interlayer bond strength, determined through splitting tensile strength tests.

Second-order regression models were developed to quantify the effects of the studied parameters and their interactions. The analysis revealed that both factors exhibit nonlinear effects, with clearly defined optimal regions. Increasing nozzle speed was found to improve extrusion continuity and geometric stability of the deposited layer, but simultaneously reduce interlayer adhesion due to shorter contact time between successive layers.

The results also indicate that nozzle geometry significantly affects material flow, contact area between layers, and compaction efficiency. In particular, the intermediate nozzle geometry demonstrated improved performance by balancing flow uniformity and interlayer bonding. However, increasing the complexity of the nozzle geometry may negatively affect extrusion quality due to uneven stress distribution within the material flow.

Response surface analysis confirmed that the optimal conditions for extrusion quality do not coincide with those for maximum interlayer strength, highlighting the need for a compromise in process parameter selection.

The findings of this study provide a basis for optimizing process parameters in extrusion-based 3D concrete printing and can be used to improve both the printability and mechanical performance of printed structures.

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