The aim of this thesis is to evaluate the manufacturability of thin-walled specimens with internal cooling channels, designed for aerospace applications and made of Inconel 625 alloy using Directed Energy Deposition - Laser Powder (DED-Lp) additive manufacturing technology. In particular, the study focuses on the optimization of the geometric parameter of overlap between the internal ribs (ribs) and the side walls of the component, in order to identify the best compromise between geometric characteristics and process parameters, preventing structural defects such as necking or crack formation. For this purpose, numerical simulations were conducted using the "AM DED Process" module of the Ansys Workbench software, to predict the extent of distortions and residual stresses developed at the end of printing, once the component was removed from the build platform. The simulations showed an asymmetric distribution of the deformations, with tensile or compressive concentrations localized at the junction points between the rib and the walls, and stresses in some cases close to or higher than the tensile strength of the material (UTS), especially with the reverse printing strategy. The virtual results were compared with physical specimens printed using LASERDYNE equipment provided by Prima Additive. The geometric deviations between the CAD model and the real sample, analyzed with the CloudCompare software, highlighted surface undulations ("waviness") and edge defects consistent with the FEM predictions. The sections with maximum overlap showed a better integration between the rib and the wall, while those with minimum overlap highlighted necking phenomena. Finally, through optical and digital microscope observations and ImageJ analysis, the metallographic characterization and the quantification of the porosity were performed. The images confirmed the presence of elongated grains and spherical porosity (gas porosity), with a relative density of 99.81%, indicative of a high metallurgical quality of the component, which can be further improved with post-process heat treatments.
L’obiettivo di questa tesi è valutare la fabbricabilità di provini a pareti sottili con canali interni di raffreddamento, progettati per applicazioni aerospaziali e realizzati in lega Inconel 625 mediante tecnologia di produzione additiva Directed Energy Deposition - Laser Powder (DED-Lp). In particolare, lo studio si concentra sull’ottimizzazione del parametro geometrico di overlap tra le nervature interne (rib) e le pareti laterali del componente, al fine di individuare il miglior compromesso tra caratteristiche geometriche e parametri di processo, prevenendo difetti strutturali come il necking o la formazione di cricche. A tale scopo, sono state condotte simulazioni numeriche mediante il modulo "AM DED Process" del software Ansys Workbench, per prevedere l’entità delle distorsioni e delle tensioni residue sviluppate al termine della stampa, una volta rimosso il componente dalla piattaforma di costruzione. Le simulazioni hanno mostrato una distribuzione asimmetrica delle deformazioni, con concentrazione di trazione o compressione localizzate nei punti di giunzione tra rib e pareti, e tensioni in alcuni casi vicine o superiori alla resistenza a trazione del materiale (UTS), specialmente con strategia di stampa reverse. I risultati virtuali sono stati confrontati con provini fisici stampati tramite apparecchiatura LASERDYNE fornita da Prima Additive. Le deviazioni geometriche tra modello CAD e campione reale, analizzate con il software CloudCompare, hanno evidenziato ondulazioni superficiali ("waviness") e difetti di bordo coerenti con le previsioni FEM. Le sezioni con massimo overlap hanno mostrato una migliore integrazione tra rib e parete, mentre quelle con minimo overlap hanno evidenziato fenomeni di necking. Infine, tramite osservazioni al microscopio ottico e digitale e analisi ImageJ, è stata eseguita la caratterizzazione metallografica e la quantificazione della porosità. Le immagini hanno confermato la presenza di grani allungati e porosità di tipo sferico (gas porosity), con una densità relativa del 99,81%, indicativa di un’elevata qualità metallurgica del componente, ulteriormente migliorabile con trattamenti termici post-processo.
STUDIO DI FATTIBILITÀ DEL PROCESSO DI DIRECTED ENERGY DEPOSITION (DED): ANALISI NUMERICA, CONTROLLO DIMENSIONALE E CARATTERIZZAZIONE MICROSTRUTTURALE
BOMPADRE, STEFANO
2024/2025
Abstract
The aim of this thesis is to evaluate the manufacturability of thin-walled specimens with internal cooling channels, designed for aerospace applications and made of Inconel 625 alloy using Directed Energy Deposition - Laser Powder (DED-Lp) additive manufacturing technology. In particular, the study focuses on the optimization of the geometric parameter of overlap between the internal ribs (ribs) and the side walls of the component, in order to identify the best compromise between geometric characteristics and process parameters, preventing structural defects such as necking or crack formation. For this purpose, numerical simulations were conducted using the "AM DED Process" module of the Ansys Workbench software, to predict the extent of distortions and residual stresses developed at the end of printing, once the component was removed from the build platform. The simulations showed an asymmetric distribution of the deformations, with tensile or compressive concentrations localized at the junction points between the rib and the walls, and stresses in some cases close to or higher than the tensile strength of the material (UTS), especially with the reverse printing strategy. The virtual results were compared with physical specimens printed using LASERDYNE equipment provided by Prima Additive. The geometric deviations between the CAD model and the real sample, analyzed with the CloudCompare software, highlighted surface undulations ("waviness") and edge defects consistent with the FEM predictions. The sections with maximum overlap showed a better integration between the rib and the wall, while those with minimum overlap highlighted necking phenomena. Finally, through optical and digital microscope observations and ImageJ analysis, the metallographic characterization and the quantification of the porosity were performed. The images confirmed the presence of elongated grains and spherical porosity (gas porosity), with a relative density of 99.81%, indicative of a high metallurgical quality of the component, which can be further improved with post-process heat treatments.| File | Dimensione | Formato | |
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TESI_LM_2025_Stefano_Bompadre_FINALE.pdf
embargo fino al 16/01/2027
Descrizione: Lavoro di tesi atto a valutare la fabbricabilità di provini a pareti sottili con canali interni di raffreddamento, progettati per applicazioni aerospaziali e realizzati in lega Inconel 625 mediante tecnologia di produzione additiva DED-Lp.
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20.91 MB
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20.91 MB | Adobe PDF |
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https://hdl.handle.net/20.500.12075/22763