Metal Binder Jetting (MBJ) is an emerging Additive Manufacturing technology suited for medium- to large-series production. While the process offers clear advantages in terms of productivity and design freedom, the amount of binder required and the presence of residual porosity still represent important aspects to be controlled, with implications for both sustainability and part quality. This thesis explores a geometry-driven approach to mitigate binder usage by replacing fully solid cores with lattice infill structures enclosed within a dense outer shell—shifting binder distribution control from process parameters to CAD design. Cubic specimens in 17-4PH stainless steel were printed on Desktop Metal Shop System Pro using two lattice topologies (gyroid TPMS and BCC), three relative densities (20%, 40%, 60%), and cell sizes between 1 and 3 mm, alongside fully solid and empty-core references. All samples underwent an identical processing route—printing, curing, depowdering and sintering—and were characterized in terms of green and sintered dimensions, linear shrinkage, Archimedes density, areal porosity and pore morphology, local microhardness (intra- and inter-strut regions), tensile properties and predicted binder volume. Results show that lattice-infilled cubes can reduce binder consumption, while achieving sintered densities, shrinkage, and dimensional tolerances comparable to fully solid specimens. Porosity analysis reveals distinct dense intra-strut and more porous inter-strut regions with partially densified loose powder, yet without evidence of structural collapse or integrity loss within the investigated design space; tensile tests on selected configurations confirm that mechanical performance remains compatible with the targeted application envelope. Overall, this work indicates that lattice-based infill can act as an effective design lever for lowering binder usage in MBJ while preserving part density, dimensional accuracy, microtexture, and tensile response, and it provides quantitative guidance on lattice topology and relative density to balance binder efficiency against quality requirements.
Il Metal Binder Jetting (MBJ) è una tecnologia di Additive Manufacturing emergente, adatta alla produzione in serie medio-grande. Pur offrendo vantaggi evidenti in termini di produttività e libertà geometrica, la quantità di binder impiegata e la presenza di porosità residua rimangono aspetti critici, con ricadute sia sulla sostenibilità sia sulla qualità del componente. Questa tesi propone un approccio di tipo geometrico per ridurre l’uso di binder, sostituendo i nuclei completamente “pieni” con strutture di infill reticolare, spostando così il controllo della distribuzione del binder dai parametri di processo alla progettazione CAD. Sono stati realizzati provini cubici in acciaio 17-4PH su un sistema Desktop Metal Shop System Pro, variando topologie di reticolo (gyroid e BCC), valori di densità relativa (20%, 40%, 60%) e dimensioni di cella (1-3 mm). Tutti i campioni hanno seguito lo stesso ciclo di processo (stampa, curing, depowdering e sinterizzazione) e sono stati caratterizzati in termini di dimensioni a verde e sinterizzate, shrinkage, densità mediante metodo di Archimede, morfologia e distribuzione dei pori, microdurezza locale, proprietà a trazione e volume di binder previsto. I risultati mostrano che i cubi con infill reticolare consentono di ridurre il consumo di binder, mantenendo al contempo densità, shrinkage e tolleranze dimensionali comparabili ai provini pieni. L’analisi della porosità evidenzia regioni intra-strut con pori irregolari e di dimensioni maggiori rispetto alle regioni inter-strut, costituite da micropori densamente distribuiti, senza tuttavia osservare collassi strutturali o perdita di integrità nel dominio geometrico studiato; le prove di trazione su configurazioni selezionate confermano che le prestazioni meccaniche restano compatibili con il campo applicativo di riferimento. Nel complesso, il lavoro indica che l’infill reticolare può costituire una leva progettuale efficace per ridurre l’uso di binder in MBJ, preservando densità, accuratezza dimensionale, microstruttura e risposta a trazione, e fornisce indicazioni quantitative su topologia e densità relativa del reticolo per bilanciare efficienza di binder e requisiti di qualità.
Experimental assessment of advanced printing strategies for improving metal binder jetting
Biondi, Lucia
2024/2025
Abstract
Metal Binder Jetting (MBJ) is an emerging Additive Manufacturing technology suited for medium- to large-series production. While the process offers clear advantages in terms of productivity and design freedom, the amount of binder required and the presence of residual porosity still represent important aspects to be controlled, with implications for both sustainability and part quality. This thesis explores a geometry-driven approach to mitigate binder usage by replacing fully solid cores with lattice infill structures enclosed within a dense outer shell—shifting binder distribution control from process parameters to CAD design. Cubic specimens in 17-4PH stainless steel were printed on Desktop Metal Shop System Pro using two lattice topologies (gyroid TPMS and BCC), three relative densities (20%, 40%, 60%), and cell sizes between 1 and 3 mm, alongside fully solid and empty-core references. All samples underwent an identical processing route—printing, curing, depowdering and sintering—and were characterized in terms of green and sintered dimensions, linear shrinkage, Archimedes density, areal porosity and pore morphology, local microhardness (intra- and inter-strut regions), tensile properties and predicted binder volume. Results show that lattice-infilled cubes can reduce binder consumption, while achieving sintered densities, shrinkage, and dimensional tolerances comparable to fully solid specimens. Porosity analysis reveals distinct dense intra-strut and more porous inter-strut regions with partially densified loose powder, yet without evidence of structural collapse or integrity loss within the investigated design space; tensile tests on selected configurations confirm that mechanical performance remains compatible with the targeted application envelope. Overall, this work indicates that lattice-based infill can act as an effective design lever for lowering binder usage in MBJ while preserving part density, dimensional accuracy, microtexture, and tensile response, and it provides quantitative guidance on lattice topology and relative density to balance binder efficiency against quality requirements.| File | Dimensione | Formato | |
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2026_03_Biondi.pdf
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https://hdl.handle.net/10589/252758