Processing and characterisation of process parameters on pellet extrusion 3D printed alumina
Additive manufacturing, also known as 3D printing, has been widely used to fabricate complex polymeric components in the recent decades. Along with the advancements in 3D printing technology, there has been a considerable amount of efforts to enable the fabrication of non-polymer materials such as c...
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| Format: | Final Year Project |
| Language: | English |
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Nanyang Technological University
2024
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| Online Access: | https://hdl.handle.net/10356/181850 |
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| Institution: | Nanyang Technological University |
| Language: | English |
| Summary: | Additive manufacturing, also known as 3D printing, has been widely used to fabricate complex polymeric components in the recent decades. Along with the advancements in 3D printing technology, there has been a considerable amount of efforts to enable the fabrication of non-polymer materials such as ceramics. One such 3D ceramic printing strategy the fused deposition modelling (FDM) technique which utilizes feedstocks such as polymer-ceramic composites filaments. However, due to rheological issues related to the ceramic powder, loading within filaments tend to be limited to 60 vol%, and additional powder loadings would lead to a highly viscous filament that would cause extruder issues such as filament buckling. While an alternative to overcome this fabrication shortfall is to rely on powder-based slurries, the potential health hazards and lack of commercial availability of the slurries makes them unattractive for small volume production, which is common in 3D printing. However, the development of commercially available screw-extrusion 3D printing technologies, such as Pollen’s pam o2 MC 3D printer, has made 3D printing ceramic materials inexpensive and safe, by creating a new feedstock format for 3D printing, which are traditionally used in injection moulding.
This study investigates the application of screw-extrusion 3D printing using injection moulding grade alumina, with the aim of developing a robust 3D printing profile and post-processing parameters that yields defect-free components. The increasing demand for advanced technical ceramics in various industries necessitates innovative manufacturing methods that improves the manufacturability at reduced costs of these materials. This research addresses the challenges associated with the 3D printing of alumina, and focuses on obtaining a robust 3D print profile, and to optimise the post-processing parameters to enhance its physical and mechanical properties.
The study starts off with a systematic testing and development of various print profiles to minimize printing defects such as poor inter-layer adhesion. Key parameters such as temperature, material flow rate and feedstock conditions were evaluated. Results showed that the alumina was hygroscopic in nature, leading to absorption of moisture from the atmosphere. The presence of a moist feedstock led to the formation of bubbles, which disrupted material flow through the nozzle. Thus, feedstocks had to be dried prior to printing operations. In addition, a higher extruder temperature of 145°C was required to ensure a homogeneous melt to prevent sudden fluctuations in material flow rate.
Post-processing parameters were also explored to identify the optimal parameters to enhance the physical and mechanical properties of the printed specimens without inducing any defects. A solvent debinding study was conducted to determine the suitable immersion temperature and duration. Through this study, it was determined that the ideal immersion temperature and duration was 65°C and 24 hours, respectively. These parameters allowed for the maximum debinding rates without inducing defects, whilst also removing a significant portion of the soluble PEG binders within the specimen.
For thermal debinding, it was noted that the removal of thermoplastic binder components was greater in an oxidising atmosphere as compared to a protective atmosphere such as argon. This is mainly due to the carbon-based thermoplastic binders being able to decompose more readily in oxygen as compared to argon.
Sintering was carried out at temperatures ranging from 1550°C to 1620°C to understand the influence of temperature on the grain boundary morphology and mechanical properties of the specimens. This study revealed that there was significant grain growth on specimens that were sintered above 1550°C. This led to the phenomenon of grain boundary strengthening, whereby specimens sintered at 1550°C resulted in the finest grains and had the highest average microhardness value of 14.902 GPa. In comparison, specimens sintered at 1600°C and 1620°C had a lower average microhardness of only 13.514 GPa and 12.977 GPa, respectively. Flexural strength studies also indicated that the rough surface along the specimen resulted in a localised stress concentration, which resulted in the reduction in the load carrying capacity of alumina specimens, which led to the underperformance in terms of flexural strength, with readings between 165-187 MPa.
Finally, the potential effects of infill patterns including (a) zig zag, (b) triangle, (c) line, (d) cubic, (e) concentric, and (f) gyroid on the physical and mechanical properties of 3D printed alumina were also investigated. The density and hardness measurement results indicated that the effects of infill patterns were negligible. However, flexural test results indicated that the line infill pattern were not suitable for the fabrication of thin materials (~4 mm) as specimens printed with this pattern underperformed significantly, with an average flexural strength of 152.492 MPa, which is significantly lower than the other infill patterns which had an average flexural strength in the range of 170 – 187 MPa. |
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