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Manufacturing Technology Insights | Tuesday, January 31, 2023
With continued research and advancements, ceramic AM holds immense potential for transforming industries by enabling the production of complex ceramic components with improved strength, reliability, and surface quality.
FREMONT, CA: Additive Manufacturing (AM) has revolutionized various industrial sectors with its disruptive capabilities. While metal and polymer AM have witnessed significant progress in the past decade, ceramic AM has faced unique material forming, shaping, and post-processing challenges. Despite these hurdles, ceramic AM is actively being explored for aerospace, defense, energy, and healthcare applications and has already succeeded in tooling for investment casting. Among the different approaches to ceramic AM, slurry-based 3D printing can produce high-strength, fully dense ceramics. Due to pores, agglomerates, cracks, and inhomogeneities, dry powder-based methods often result in low strength and poor reliability.
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Ceramic components' Selective Laser Sintering (SLS) can be categorized into direct and indirect approaches. A laser beam is used in direct SLS to heat and sinter the deposited ceramic powder layers locally. On the other hand, indirect SLS involves laser melting of a sacrificial organic binder phase in a polymer-ceramic composite powder to create green parts. These green parts undergo debonding and furnace sintering to achieve the final ceramic structure.
Direct SLS without a sacrificial binder phase is being explored for SiSiC ceramics. In this process, a free-flowing powder mixture of silicon and silicon carbide powders is SLSed to form a porous structure where molten silicon is the glue for SiC grains. Subsequently, the porous structure is infiltrated with a phenolic resin, followed by pyrolysis of the resin. Finally, the component is infiltrated with molten Si, resulting in a fully dense Si-SiC component containing up to 85% SiC.
Indirect SLS utilizes local laser melting of a sacrificial organic binder phase in a polymer-ceramic composite powder to create green parts. One method to achieve this is through thermally induced phase separation (TIPS), which involves the production of polypropylene-zirconia or polyamide-alumina free-flowing microspheres. Although the sintered density of the parts obtained through SLS alone may be low, it can be increased through pressure infiltration with a ceramic powder suspension.
Slurry-based Indirect SLS (S-SLS) offers the advantage of starting from highly homogeneous and densely packed powder layers. The deposition of slurry layers is commonly done through doctor blading and subsequent drying. Slurry deposition systems have been developed for the AM of ZrO2 and Al2O3 components. The process involves local low-power SLS of the binder in the slurry, followed by the removal of non-SLS material with water and subsequent drying, debinding, and sintering of the components.
Ceramic stereolithography (CSL) is an extension of stereolithography (SLA) that relies on the selective photo-polymerization of a photosensitive slurry containing ceramic particles to create green parts. These green parts then undergo debinding and sintering. The precision and surface quality achieved through CSL makes it a promising technique for ceramic AM.
Robocasting, also known as Direct Ink Writing (DIW), is a filament-based direct-writing approach to fabricating complex shapes. It involves continuously extruding highly concentrated colloidal ink through a nozzle layer-by-layer manner. DIW utilizes a 3D CAD model to deposit a controlled material filament, resulting in a geometrically complex ceramic green body. After drying, organic additives are removed through thermal debinding, and conventional pressureless sintering finally consolidates the green body.
Ceramic additive manufacturing has made significant strides in recent years, although it still faces challenges unique to ceramic materials. Direct and indirect selective laser sintering, slurry-based indirect SLS, ceramic stereolithography, and robocasting are some prominent techniques explored to overcome these challenges. Each technique offers its advantages and is suited to specific applications.
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