Towards an Improved Ceramic Vat Photopolymerization Process Chain for Novel Complex Porous Structures : From resin formulation to post-processing
Zakeri, Setareh (2025)
Tampere University
2025
Teknisten tieteiden tohtoriohjelma - Doctoral Programme in Engineering Sciences
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Väitöspäivä
2025-09-05
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-03-4084-1
https://urn.fi/URN:ISBN:978-952-03-4084-1
Tiivistelmä
Ceramic vat photopolymerization (VPP) has become a crucial additive manufacturing technique, enabling the production of intricate, high-resolution ceramic structures. However, despite notable advancements, a comprehensive understanding of the entire ceramic VPP process chain from resin formulation to post-processing remains incomplete. This thesis adopts an integrated approach addressing several critical stages of the ceramic VPP process chain, aiming to enhance the fabrication of novel complex porous structures. It examines the interdependencies between resin formulation, curing depth and width measurements, 3D printing parameters, and cleaning protocols, highlighting their collective impact on the dimensional accuracy of printed parts.
As the binder largely governs photocuring behavior, a systematic study was conducted on difunctional and multifunctional monomers with varied chemical structures to understand the effects of linker chain length, ethoxylation, functional groups, and functionality. Curing depth measurements showed that rigid monomers with longer chains yielded higher critical energy (Ec), while flexible monomers exhibited lower Ec. Methacrylate-based formulations had significantly higher Ec than their acrylate-based counterparts. Although higher monomer functionality often correlated with increased Ec, this trend was not entirely consistent.
The influence of multiple ceramic powders on photocuring behavior was also examined. A novel resin comprising γ-alumina (γ-Al2O3) and ceria (CeO2) was developed and successfully printed into honeycomb structures. The addition of ceria, characterized by a high refractive index and fine particle size, significantly reduced the depth sensitivity (Dp) of the γ-alumina resin—from 408.06 to 75.19 μm—enhancing printing accuracy.
Photosensitive additives, such as photoinitiators (PIs) and dyes, were studied to assess their roles in photocuring kinetics and resolution. Increasing PI concentration improved width sensitivity (Sw) but reduced curing depth, indicating a trade-off between surface accuracy and vertical resolution. Conversely, increasing dye concentration reduced both (Sw and Dp), improving overall resolution.
The effects of printing parameters, particularly peel-off speed and curing depth (or exposure time), on dimensional accuracy were also evaluated. Slower peel-off speeds enhanced accuracy for delicate structures, while reduced curing depth led to improved printing precision.
Post-processing protocols were optimized for effective removal of uncured resin from intricate geometries while preserving structural fidelity. Various cleaning solutions, including a commercial solution (LithaSol 80) and a non-commercial solution (dibasic ester, DBE), were assessed alongside different cleaning methods, such as ultrasonic cleaning and soaking. LithaSol 80 produced smoother surfaces, whereas DBE led to contracted pores and a peeling effect, suggesting more aggressive interaction with cured resin. Mass loss analyses confirmed the superior cleaning efficiency of DBE, though LithaSol 80, particularly when used with soaking, was better suited for preserving structural integrity.
Through comprehensive experimental validation, this work establishes critical correlations between resin chemistry, process parameters, and final part quality. The findings contribute valuable insights into the design of advanced resin systems for ceramic VPP and support the development of more precise and reliable additive manufacturing workflows.
As the binder largely governs photocuring behavior, a systematic study was conducted on difunctional and multifunctional monomers with varied chemical structures to understand the effects of linker chain length, ethoxylation, functional groups, and functionality. Curing depth measurements showed that rigid monomers with longer chains yielded higher critical energy (Ec), while flexible monomers exhibited lower Ec. Methacrylate-based formulations had significantly higher Ec than their acrylate-based counterparts. Although higher monomer functionality often correlated with increased Ec, this trend was not entirely consistent.
The influence of multiple ceramic powders on photocuring behavior was also examined. A novel resin comprising γ-alumina (γ-Al2O3) and ceria (CeO2) was developed and successfully printed into honeycomb structures. The addition of ceria, characterized by a high refractive index and fine particle size, significantly reduced the depth sensitivity (Dp) of the γ-alumina resin—from 408.06 to 75.19 μm—enhancing printing accuracy.
Photosensitive additives, such as photoinitiators (PIs) and dyes, were studied to assess their roles in photocuring kinetics and resolution. Increasing PI concentration improved width sensitivity (Sw) but reduced curing depth, indicating a trade-off between surface accuracy and vertical resolution. Conversely, increasing dye concentration reduced both (Sw and Dp), improving overall resolution.
The effects of printing parameters, particularly peel-off speed and curing depth (or exposure time), on dimensional accuracy were also evaluated. Slower peel-off speeds enhanced accuracy for delicate structures, while reduced curing depth led to improved printing precision.
Post-processing protocols were optimized for effective removal of uncured resin from intricate geometries while preserving structural fidelity. Various cleaning solutions, including a commercial solution (LithaSol 80) and a non-commercial solution (dibasic ester, DBE), were assessed alongside different cleaning methods, such as ultrasonic cleaning and soaking. LithaSol 80 produced smoother surfaces, whereas DBE led to contracted pores and a peeling effect, suggesting more aggressive interaction with cured resin. Mass loss analyses confirmed the superior cleaning efficiency of DBE, though LithaSol 80, particularly when used with soaking, was better suited for preserving structural integrity.
Through comprehensive experimental validation, this work establishes critical correlations between resin chemistry, process parameters, and final part quality. The findings contribute valuable insights into the design of advanced resin systems for ceramic VPP and support the development of more precise and reliable additive manufacturing workflows.
Kokoelmat
- Väitöskirjat [5143]