Within the last decade, Additive Manufacturing (AM) technologies have been established as key manufacturing processes in the space propulsion panorama. When applied to space components, they provide advantages associated to both technical and economic constraints. Complex parts with small resolution features can be designed involving challenging metal alloys: new optimizations of engine components are achieved, reducing assembly complexities and providing rapid design iterations. The expansion and consolidation of additive processes, in particular Selective Laser Melting (SLM), applied to small thrust chambers for satellite applications still face open challenges which span the overall end-to-end manufacturing chain: from part design to feedstock material supply chain, process parameters, postprocess operations, verification and standardization efforts. Among the criticalities, the inclusion of convoluted internal channels and cavities within final components provides major concerns. Inner channels shall be properly designed in order to be consistently printed during the manufacturing process: diameters, overhanging angles and channel shapes have to be tuned according to process limitations. The characteristics of the powder implemented in the AM process shall be monitored as they affect the properties of final components: feedstock shall be controlled along the entire supply chain, from raw material to powder recycling steps. Postprocess operations have to be implemented and complex cleaning and depowdering operations are defined to identify potential issues within inner cavities and remove possible powder remnants. Within this work, an analysis of the AM end-to-end process for a space bipropellant thruster involving green and self-pressurized propellants is proposed. The overall workflow is detailed starting from thruster requirements and needs as provided by the company D-Orbit. From constraints evaluation, SLM and Inconel® 718 (IN718) are selected as thruster manufacturing technology and material respectively. The engine assembly structural design, based on additive manufacturing regulations, is highlighted. Challenges associated to inner thruster channel cleanliness are evidenced from part design: therefore, the research is focused on the characterization of these issues along the overall manufacturing chain. Starting from the feedstock supply chain definition, powder modification criticalities due to recycling steps and postprocesses application are considered. Powder characteristics are studied through a series of dedicated experiments: the effects of recycled powders properties on surface texture and geometrical characteristics of inclined inner channels are explored during a dedicated AM process analysis. To evaluate the thruster inner channels cleanliness at postprocessing level, a specimen, reproducing the inner thruster geometry is designed: depowdering techniques are selected, and each one is applied to a separate sample during a dedicated experimental campaign. Results from both non-destructive and destructive inspections are retrieved with the aim to compare the efficacy of each technique. Furthermore, a cleanliness predictive model is developed for inner surface roughness variation prediction before and after the application of each depowdering technique. A final comparison between cleaning methodologies allows to select the best alternative for the specific thruster design. Within the conclusions, the outcomes provided from the supply chain, process and postprocess evaluations are retrieved and combined to provide design feedbacks on the overall manufacturing process for inner channel cleanliness improvement.
Nell’ultimo decennio, le tecnologie di fabbricazione additiva (AM) si sono stabilite come processi chiave nella panoramica della propulsione spaziale. Quando applicate a componenti spaziali, forniscono vantaggi sia in termini tecnici che economici. Attraverso tali tecnologie, parti complesse dotate di piccole caratteristiche possono essere costruite utilizzando leghe metalliche impegnative: ottimizzazioni di componenti complessi possono essere raggiunte, riducendo le difficoltà associate all’assemblaggio e fornendo rapide iterazioni di progettazione. L’espansione e la consolidazione dei processi additivi, in particolare la fusione selettiva laser (SLM) applicata a piccole camere di spinta per applicazioni satellitari, si confronta ancora con sfide aperte che riguardano l’intera catena di produzione: dalla progettazione del pezzo alla fornitura dei materiali, i parametri di processo, le operazioni di post-processo, la verifica dei componenti finali e le criticità di standardizzazione. Tra le criticità, l’inclusione di canali complessi e cavità direttamente all’interno di componenti finali presenta sfide impegnative. I canali interni devono essere progettati in modo da essere stampati correttamente durante il processo di produzione: diametri, angoli di sbalzo e forma dei canali devono essere regolati in base alle limitazioni del processo. Le caratteristiche della polvere implementata nel processo AM devono essere monitorate in quanto influenzano le proprietà dei componenti finali: la polvere deve essere controllata lungo l’intera catena di approvvigionamento, dalla materia prima alle sue fasi di riciclo. Successivamente, operazioni di postprocesso sono richieste incluse complesse operazioni di pulizia e rimozione della polvere, che devono essere definite per identificare potenziali problemi all’interno delle cavità e rimuovere eventuali residui di polvere interna. In questo lavoro, viene proposta un’analisi del processo end-to-end della manifattura additiva di un propulsore bipropellente spaziale, che coinvolge propellenti "green" e auto-pressurizzanti. Il flusso di lavoro complessivo viene dettagliato a partire dai requisiti e dalle esigenze del propulsore, forniti dall’azienda D-Orbit. Dalla valutazione dei vincoli, la tecnologia a fusione laser selettiva e l’Inconel® 718 (IN718) vengono selezionati rispettivamente come processo e materiale di fabbricazione. Il design strutturale del motore, basato sulle normative della fabbricazione additiva, viene successivamente sviluppato. A partire dalla progettazione del pezzo, si evidenziano difficoltà associate alla pulizia dei canali interni del propulsore: pertanto, la ricerca di dottorato è incentrata sulla caratterizzazione di questi problemi lungo l’intera catena di produzione. A partire dalla definizione della catena di approvvigionamento del materiale, il lavoro analizza le criticità associate alle modifiche dei parametri della polvere dovute alle fasi di riciclaggio e all’applicazione di post-processi. Vengono dunque studiate le caratteristiche della polvere attraverso una serie di esperimenti dedicati: partendo da un’analisi del processo AM, si studiano gli effetti delle proprietà del materiale riciclato sulla texture superficiale e sulle caratteristiche geometriche dei canali interni. Per valutare la pulizia delle cavità del propulsore a livello di post-processo, viene progettato un campione che riproduce la geometria interna del propulsore: successivamente, vengono selezionate tecniche di rimozione del materiale interno ai canali, e ciascuna viene applicata a un campione separato durante una campagna sperimentale dedicata. I risultati delle ispezioni non distruttive e distruttive sono analizzati con l’obiettivo di confrontare l’efficacia di ciascuna tecnica. Viene infine sviluppato un modello predittivo di pulizia per la variazione della rugosità superficiale interna prima e dopo l’applicazione di ciascuna tecnica di rimozione della polvere. Un confronto finale tra metodologie di pulizia permette di selezionare la migliore alternativa per il design specifico del propulsore. Nelle conclusioni, i risultati forniti dall’analisi della catena di approvvigionamento, del processo e del post-processo vengono confrontati per fornire feedback di progettazione sull’intero processo di produzione del motore, col fine di migliorarne la pulizia interna.
AM end-to-end process and cleanliness challenges for a space propulsion thruster
Davide, Zuin
2024
Abstract
Within the last decade, Additive Manufacturing (AM) technologies have been established as key manufacturing processes in the space propulsion panorama. When applied to space components, they provide advantages associated to both technical and economic constraints. Complex parts with small resolution features can be designed involving challenging metal alloys: new optimizations of engine components are achieved, reducing assembly complexities and providing rapid design iterations. The expansion and consolidation of additive processes, in particular Selective Laser Melting (SLM), applied to small thrust chambers for satellite applications still face open challenges which span the overall end-to-end manufacturing chain: from part design to feedstock material supply chain, process parameters, postprocess operations, verification and standardization efforts. Among the criticalities, the inclusion of convoluted internal channels and cavities within final components provides major concerns. Inner channels shall be properly designed in order to be consistently printed during the manufacturing process: diameters, overhanging angles and channel shapes have to be tuned according to process limitations. The characteristics of the powder implemented in the AM process shall be monitored as they affect the properties of final components: feedstock shall be controlled along the entire supply chain, from raw material to powder recycling steps. Postprocess operations have to be implemented and complex cleaning and depowdering operations are defined to identify potential issues within inner cavities and remove possible powder remnants. Within this work, an analysis of the AM end-to-end process for a space bipropellant thruster involving green and self-pressurized propellants is proposed. The overall workflow is detailed starting from thruster requirements and needs as provided by the company D-Orbit. From constraints evaluation, SLM and Inconel® 718 (IN718) are selected as thruster manufacturing technology and material respectively. The engine assembly structural design, based on additive manufacturing regulations, is highlighted. Challenges associated to inner thruster channel cleanliness are evidenced from part design: therefore, the research is focused on the characterization of these issues along the overall manufacturing chain. Starting from the feedstock supply chain definition, powder modification criticalities due to recycling steps and postprocesses application are considered. Powder characteristics are studied through a series of dedicated experiments: the effects of recycled powders properties on surface texture and geometrical characteristics of inclined inner channels are explored during a dedicated AM process analysis. To evaluate the thruster inner channels cleanliness at postprocessing level, a specimen, reproducing the inner thruster geometry is designed: depowdering techniques are selected, and each one is applied to a separate sample during a dedicated experimental campaign. Results from both non-destructive and destructive inspections are retrieved with the aim to compare the efficacy of each technique. Furthermore, a cleanliness predictive model is developed for inner surface roughness variation prediction before and after the application of each depowdering technique. A final comparison between cleaning methodologies allows to select the best alternative for the specific thruster design. Within the conclusions, the outcomes provided from the supply chain, process and postprocess evaluations are retrieved and combined to provide design feedbacks on the overall manufacturing process for inner channel cleanliness improvement.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.14242/205621
URN:NBN:IT:POLIMI-205621