Characterization and investigation of process parameters in extrusion additive manufacturing of alumina ceramic parts

The unique properties of ceramics have led to their widespread use in various industries. One such material is alumina, which is known for its engineering properties and abundance. Another reason for the importance of alumina is its low sintering temperature compared to other engineering ceramics. In addition, the chemical stability and non-reactivity of alumina led to its use as medical implants. Different methods are used for manufacturing ceramics. The emergence of 3D-printing or additive manufacturing (AM) has revolutionized the production of engineering parts. AM has the potential to directly produce designed parts from computer models without molding or machining processes. It also enables customization of products for specific application. Additionally, the inherent advantages of the AM result in significant savings in process time and cost. However, ceramic materials have been less explored in the field of AM compared to metals and polymers. Ceramic extrusion additive manufacturing (CEAM) has gained popularity as a cost-effective and fast alternative to other AM methods. While this process can create relatively complex geometries, it faces challenges related to microstructural quality control in ceramic parts. Factors such as porosity, purity, and fine defects can affect the structure of extruded ceramic parts. Moreover, dimensional accuracy and surface quality compromised due to the step effect inherent in all AM methods. Therefore, achieving defect-free ceramic parts with superior mechanical properties remains a challenge. The CEAM process involves several steps:(a) preparation of raw materials, (b) mixing and preparation of paste, (c) 3D printing, (d) debinding, and(e) sintering. Proper drying of raw samples before sintering is crucial to avoid cracks or severe warping. Improving the properties of ceramic parts made by CEAM is one of the goals of ongoing study. This research field combines materials science with mechatronics. Initially, various methods for injecting alumina paste were investigated, leading to the design and assembly of ceramic 3D printer. The device was then programmed accordingly. Alumina parts were printed using this setup and analyzed for microstructure, physical and mechanical properties, dimensional accuracy, sintering, and printing parameters. Rheological properties of raw materials were also studied. For this investigation, a mixture comprising 56% α-alumina powder, 14% ball clay, 20% ionized water, and 10% polyethylene glycol was used. After weighing these compounds, they were mixed using mechanical stirrer for 5 minutes. Rheology tests showed that the mixture had a viscosity of approximately 1710 Pa.s at a shear rate of 1/s indicating good printing characterization using a 1mm diameter nozzle. After testing different syringes and extruders as reservoirs for raw materials during printing, a 10cc syringe was found to be most suitable. It was also determined that the optimal working time for paste before hardening is 30 minutes. To assess mechanical strength after sintering, samples were produced with 50 x 4 x 3 〖mm〗^3 dimensions using a printing speed of 1 mm/s; bending strength measurements were conducted according to ASTM-C1161 standards. Solid-state sintering can be challenging due to thermodynamic limitations, temperature constraints, and the possibility of decomposition. However, liquid phase sintering provides a suitable alternative by creating a liquid phase at a lower temperature. In this method, solid particles can dissolve in the liquid phase. When using the CEAM, the outer surfaces of printed parts may appear irregular both in their green and sintered states since there are no frames present. Additionally, there may be extra material in each reverse direction of the print paths. However, the SEM micrographs show that the surface irregularities in the sintered parts are smaller due to shrinkage compared to the green state. It is also noteworthy that microcracks can be seen in the green bodies which remain in the sintered parts.