Material Extrusion Additive Manufacturing (MEAM) is inherently constrained by a fundamental trade-off between print speed, resolution, and strength when using fixed-diameter nozzles. This limitation prohibits the spatial variation of these critical properties within a single printed object, thus hindering the full realization of functionally graded manufacturing. This paper presents a novel coaxial dual-orifice nozzle system designed to overcome this trilemma. The core of our design is a tandem nesting architecture, featuring an inner brass nozzle and an outer steel nozzle joined by a fine-pitched thread. A key innovation is the implementation of a thermal latching mechanism, which exploits the differential thermal expansion between the two materials to achieve a reliable seal at operating temperatures, eliminating the need for complex additional sealing components. The system enables in-process switching between a small orifice for high-detail outer walls and a large orifice for high-speed infill and strong internal structures. We detail the comprehensive design process, including computational fluid dynamics (CFD) and conjugate heat transfer (CHT) simulations that validated the flow characteristics and thermal management. A functional prototype was implemented on a modified Prusa Mini+ printer, and a customized slicing strategy was developed to orchestrate the layer-by-layer nozzle switching. Experimental results demonstrate that, compared to a standard single-diameter nozzle, our system significantly reduces print time while maintaining high surface quality and enhancing inter-layer strength. This work establishes a practical and mechanically elegant pathway towards spatially graded additive manufacturing, bridging the gap between high-speed production and high-fidelity fabrication.
La Produzione Additiva a Estrazione di Materiale (MEAM) è limitata da un compromesso fondamentale tra velocità di stampa, risoluzione e robustezza quando si utilizzano ugelli a diametro fisso. Questa limitazione impedisce la variazione spaziale di queste proprietà critiche all'interno di un singolo oggetto. Questo articolo presenta un innovativo sistema di ugelli coassiali a doppio orifizio, progettato per superare questo trilemma. L'innovazione principale risiede in un'architettura ad annidamento tandem che incorpora un meccanismo di blocco termico, sfruttando la differente espansione termica per ottenere una tenuta affidabile tra l'ugello interno (ottone) e quello esterno (acciaio) alle temperature di esercizio. Questa soluzione meccanicamente elegante permette la commutazione in-process tra un orifizio piccolo per contorni ad alto dettaglio e uno grande per strutture interne ad alta velocità e robustezza. Il processo di progettazione, convalidato attraverso simulazioni di fluidodinamica computazionale e di trasferimento termico coniugato, è dettagliato insieme alla realizzazione di un prototipo funzionale su una piattaforma Prusa Mini+ modificata. I risultati sperimentali dimostrano che il sistema riduce significativamente i tempi di stampa mantenendo un'alta qualità superficiale e migliorando la robustezza meccanica rispetto agli ugelli standard a diametro singolo. Questo lavoro stabilisce una via pratica verso la produzione additiva spazialmente graduata.
Design and implementation of a coaxial dual-orifice nozzle system for material-extrusion 3D printing
YU, HUANGLIANG
2024/2025
Abstract
Material Extrusion Additive Manufacturing (MEAM) is inherently constrained by a fundamental trade-off between print speed, resolution, and strength when using fixed-diameter nozzles. This limitation prohibits the spatial variation of these critical properties within a single printed object, thus hindering the full realization of functionally graded manufacturing. This paper presents a novel coaxial dual-orifice nozzle system designed to overcome this trilemma. The core of our design is a tandem nesting architecture, featuring an inner brass nozzle and an outer steel nozzle joined by a fine-pitched thread. A key innovation is the implementation of a thermal latching mechanism, which exploits the differential thermal expansion between the two materials to achieve a reliable seal at operating temperatures, eliminating the need for complex additional sealing components. The system enables in-process switching between a small orifice for high-detail outer walls and a large orifice for high-speed infill and strong internal structures. We detail the comprehensive design process, including computational fluid dynamics (CFD) and conjugate heat transfer (CHT) simulations that validated the flow characteristics and thermal management. A functional prototype was implemented on a modified Prusa Mini+ printer, and a customized slicing strategy was developed to orchestrate the layer-by-layer nozzle switching. Experimental results demonstrate that, compared to a standard single-diameter nozzle, our system significantly reduces print time while maintaining high surface quality and enhancing inter-layer strength. This work establishes a practical and mechanically elegant pathway towards spatially graded additive manufacturing, bridging the gap between high-speed production and high-fidelity fabrication.| File | Dimensione | Formato | |
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2025_12_Yu.pdf
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Descrizione: Huangliang Yu thesis file
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https://hdl.handle.net/10589/246096