Additive manufacturing offers a wide range of solutions to common issues faced in industrial productions such as limitations to geometrical and material designs, waste generation, excessive production times and supply chain bottlenecks. In this scenario, binder jetting 3D printing can satisfy all these requests and provide a fundamental support to numerous industries. The research programme purpose was to define and validate an engineering framework based on the availability of liquid phase sintering for the development of binder jetting as a manufacturing method suited for different classes of materials. At each step of the framework diagram the relevant features and parameters to account for are listed and considered to predict the potential outcomes of the process. Three final scenarios are distinguished (full-, high- and low-density components), obtained following the guidelines on the powder properties and the specifics of the processing conditions. Multiple feedstocks were tested by varying the: • Material type – AISI 316L stainless steel for metals, α-alumina, and sodium potassium niobate (KNN) for ceramics and tungsten carbide in cobalt matrix for composites. • Morphology – irregular nanometric particles, spherical granules by spray drying and spherical dense particles by gas atomisation or plasma spheroidisation. The production process was analysed at each step by: • Optimising the printing parameters to obtain accurate geometries. • Defining the thermal treatments necessary for the densification of the components and the development of the desired phase compositions. • Evaluating the synergic effects of shaping parameters and post-processing conditions on the microstructural, mechanical, and functional properties of the printed parts. A comprehensive study of the process was performed to characterise the raw materials, the semifinished products, and the final components. Powders microstructure and morphology were analysed by x-ray diffractometry, elemental composition through energy dispersive x-ray analysis, scanning electron microscopy and granulometry. In addition, modelling of the feedstock powder was performed both for phases evolution by thermodynamics equilibrium simulation based on CALPHAD method and for packing density by numerical and discrete element modelling. Semifinished samples density and accuracy were measured by geometrical methods through a digital caliper and organic residue-induced phenomena were studied by thermogravimetric analysis and differential scanning calorimetry. Finally, analysis on densified components was accomplished by assessing microstructural features, mechanical performance according to proper ASTM/ISO standards and functional properties of piezoelectric materials. The results obtained allowed to validate the proposed framework and to outline the requirements for the commercialisation of the studied materials and the development of novel solutions.
La manifattura additiva offre un’ampia gamma di soluzioni a problemi comuni affrontati dalla produzione industriale, quali limitazioni al design di geometrie e materiali, generazione di scarti, prolungati tempi di produzione e colli di bottiglia nella catena di fornitura. In questo contesto, la stampa 3D a getto di legante (binder jetting) può soddisfare tutte queste richieste e fornire un supporto fondamentale a numerose industrie. L’obiettivo del programma di ricerca consisteva nella definizione di uno schema di sviluppo basato sulla possibilità di sinterizzazione allo stato liquido per lo sviluppo del binder jetting come un metodo di manifattura adatto a diverse classi di materiali. Ad ogni livello del diagramma le proprietà e i parametri rilevanti sono elencati e presi in considerazione per predire i potenziali risultati del processo. Sono definiti tre scenari finali (componenti a completa, alta e bassa densità), ottenuti seguendo le linee guida sulle proprietà della polvere e sulle specifiche delle condizioni di processamento. Numerose materie prime sono state testate, variandone: • Tipo di materiale – metallico per acciaio inossidabile AISI 316L, ceramico per α- allumina e niobato di sodio potassio (KNN) e composito per carburo di tungsteno in matrice cobalto. • Morfologia – particelle nanometriche irregolari, granuli sferici da spray drying e particelle sferiche dense da atomizzazione a gas e sferoidizzazione al plasma. Il processo di produzione è stato analizzato in tutte le fasi: • Ottimizzando i parametri di stampa per ottenere geometrie precise. • Determinando i trattamenti termici necessari per la densificazione dei componenti e lo sviluppo della composizione di fasi desiderata. • Valutando l’effetto sinergico dei parametri di formatura e delle condizioni di lavorazione successive sulle proprietà microstrutturali, meccaniche e funzionali delle parti stampate. Uno studio completo del processo è stato realizzato per caratterizzare le materie prime, i prodotti semilavorati e i componenti finali. La microstruttura e la morfologia delle polveri sono state analizzate tramite diffrattometria ai raggi x, composizione elementale con spettrometria per dispersione di energia, microscopia a scansione elettronica e granulometria. In aggiunta, una modellazione del materiale di partenza è stata effettuata sia per l’evoluzione delle fasi tramite simulazioni termodinamiche all’equilibrio basate sul metodo CALPHAD, sia per la densità di impaccamento con modellazione numerica e a elementi discreti. La densità e l’accuratezza dei campioni semilavorati è stata misurata tramite metodo geometrico con un calibro digitale e i fenomeni indotti da residui organici sono stati studiati attraverso analisi termogravimetrica e calorimetria differenziale a scansione. Infine, un’analisi sui componenti densificati è stata ottenuta determinando le caratteristiche microstrutturali, le prestazioni meccaniche secondo adeguati standard ASTM/ISO e le proprietà funzionali dei materiali piezoelettrici. I risultati ottenuti hanno consentito di convalidare il quadro proposto e di delineare i requisiti per la commercializzazione dei materiali studiati e lo sviluppo di nuove soluzioni.
Engineering framework for binder jetting of metallic, ceramic and composite materials
MARIANI, MARCO
2022/2023
Abstract
Additive manufacturing offers a wide range of solutions to common issues faced in industrial productions such as limitations to geometrical and material designs, waste generation, excessive production times and supply chain bottlenecks. In this scenario, binder jetting 3D printing can satisfy all these requests and provide a fundamental support to numerous industries. The research programme purpose was to define and validate an engineering framework based on the availability of liquid phase sintering for the development of binder jetting as a manufacturing method suited for different classes of materials. At each step of the framework diagram the relevant features and parameters to account for are listed and considered to predict the potential outcomes of the process. Three final scenarios are distinguished (full-, high- and low-density components), obtained following the guidelines on the powder properties and the specifics of the processing conditions. Multiple feedstocks were tested by varying the: • Material type – AISI 316L stainless steel for metals, α-alumina, and sodium potassium niobate (KNN) for ceramics and tungsten carbide in cobalt matrix for composites. • Morphology – irregular nanometric particles, spherical granules by spray drying and spherical dense particles by gas atomisation or plasma spheroidisation. The production process was analysed at each step by: • Optimising the printing parameters to obtain accurate geometries. • Defining the thermal treatments necessary for the densification of the components and the development of the desired phase compositions. • Evaluating the synergic effects of shaping parameters and post-processing conditions on the microstructural, mechanical, and functional properties of the printed parts. A comprehensive study of the process was performed to characterise the raw materials, the semifinished products, and the final components. Powders microstructure and morphology were analysed by x-ray diffractometry, elemental composition through energy dispersive x-ray analysis, scanning electron microscopy and granulometry. In addition, modelling of the feedstock powder was performed both for phases evolution by thermodynamics equilibrium simulation based on CALPHAD method and for packing density by numerical and discrete element modelling. Semifinished samples density and accuracy were measured by geometrical methods through a digital caliper and organic residue-induced phenomena were studied by thermogravimetric analysis and differential scanning calorimetry. Finally, analysis on densified components was accomplished by assessing microstructural features, mechanical performance according to proper ASTM/ISO standards and functional properties of piezoelectric materials. The results obtained allowed to validate the proposed framework and to outline the requirements for the commercialisation of the studied materials and the development of novel solutions.| File | Dimensione | Formato | |
|---|---|---|---|
|
Marco Mariani_Thesis Polimi.pdf
non accessibile
Descrizione: Tesi
Dimensione
57.93 MB
Formato
Adobe PDF
|
57.93 MB | Adobe PDF | Visualizza/Apri |
I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/10589/197053