All commercially available ceramic AM technologies in the 3dpbm map of ceramic AM (from 3dpbm’s just-released report on Ceramic AM Opportunities and Trends) are based on processes that bind ceramic particles to shape three-dimensional objects before sintering them in a furnace as a post-processing step. Unlike in metal AM, where bound metal is a relatively new and standalone family of technologies, all-ceramic AM hardware technologies come from the bound material family. For this reason, the segment is more limited in its evolution, but it has simultaneously opened opportunities for emerging metal AM technologies (bound filament, metal binder jetting) that work in a similar way. Furthermore, although they require sintering in a furnace, most bound material technologies are considered production-ready processes. As such, ceramic was born and continues to evolve as a production method that can also be used for prototyping rather than a prototyping method that is evolving into production (as is the case for many polymer and metal AM technologies).
Another fact that may seem surprising (and perhaps discouraging) is that no commercially available powder bed fusion process exists today for ceramics. Attempts have been made in the past, and dozens of published studies have tried and continue to try to demonstrate the viability of direct laser sintering of ceramics as a production method. However, the challenges associated with direct laser sintering of ceramic, due primarily to the extremely high temperatures required to sinter or melt ceramic powders, have kept these processes from becoming a viable commercial opportunity. Hybrid processes, in which lasers operate on materials that bind ceramic powders in a single process, have been trialed but with limited commercial success to date.
Source: 3dpbm Research
Nevertheless, as the metal AM industry comes to the realization that binder jetting may ultimately provide the fastest production rates, ceramic AM technologies—as shown in the 3dpbm map of ceramic AM—have already made significant strides in this area. Likewise, as metal AM comes to accept that bound metal filament technologies can offer the most cost-effective and office-friendly solutions, the same technologies can easily be (and are being) applied to ceramics. Finally, as the metal AM industry discovers the high-resolution capabilities of bound metal slurry stereolithography, this technology is already well established in ceramic AM.
While the stereolithography (SLA) process is mostly associated with polymer 3D printing materials, the process is also suitable to produce ceramic parts. As shown in the map of ceramic AM technologies, stereolithography is the most recognized and reliable technique for 3D printing technical ceramic materials. In the ceramic stereolithography process, layers of a ceramic slurry, made from monomer resins with high ceramic content, are cured using a light source. This light source varies depend- ing on the technology. For instance, an SLA system will use a laser to cure the slurry, while a DLP printer relies on a digital micromirror projector. The monomer resin hardens when exposed to the light source (the process of photopolymerization) which in turn binds the ceramic particles inside the polymer matrix. Because the ceramic stereolithography process results in a green printed part, it is typically accompanied by post-processing, including heat treatments to remove the binder and sintering to create a fully dense ceramic part.
Binder jetting uses the selective application of binding fluids to bond powdered materials in layers. It is similar to inkjet printing, but instead of applying ink to a sheet of paper to create a two-dimensional product, binder jetting printers bond individual layers of powder to create a three-dimensional object. In ceramic AM technologies, binder jetting avoids the common sintering pitfall of shrinkage and allows for the creation of complex shapes. Other advantages include part support from surrounding powder, relatively easy debinding and suitability for large and medical-grade parts. Common materials include sand and cement, technical ceramics like silicon carbide and boron carbide, and, to a lesser extent, oxide ceramics such as alumina and zirconia. Binder jetting is arguably the most efficient process for ceramic tools, molds and foundry cores. Key variables include ceramic materials, binding methods and mechanisms and post-processing steps like depowdering and densification.
Bound Filament Material Extrusion
Fused filament fabrication (FFF) is the most common 3D printing technology due to its inexpensive printers and the wide range of materials available. To print ceramic components via FFF, several companies have developed very highly filled ceramic materials (ceramic within a thermoplastic matrix) and introduced a complete process chain. In general, materials with a ceramic content of 50% are printable with nozzle sizes down to 150 microns. Layer thicknesses of 80 microns and bar widths of 160 microns can be achieved with open demonstrator structures. However, parts printed by this method cannot yet achieve post-sintering densities comparable to stereolithography or ceramic injection molding, thus limiting the range of possible applications in the advanced ceramic parts segment. During the extrusion and deposition printing process, pores and cavities are introduced, though these can be gradually eliminated via increasingly intelligent path management tools. Offered by the companies shown in the map of ceramic AM technologies, at present, FFF offers a promising way to produce ceramic prototypes or small series of non-technical ceramic objects.
Pneumatic extrusion processes use air pressure to extrude material in layers, with printhead mechanisms otherwise like those used in thermoplastic extrusion processes. Compatible materials include traditional ceramics like clay and earthenware (as well as thermosets and bioprinting materials like bioinks and hydrogels). In ceramic AM, pneumatic extrusion may be favored for arts and design applications. The process uses pressure, often supplied by a compressed air system or a syringe, to extrude and selectively deposit ceramic paste. Such pastes, similar to those used in handcrafted ceramics, are a mix of ceramic powders and water in a ratio that is liquid enough to be extruded but thick enough to be built up in layers without collapsing. Pneumatic extrusion systems can be independent printers built specifically for ceramics (either cartesian or, more often, delta-style) or take the form of add-on kits for standard thermoplastic extrusion 3D printers.
Material jetting can be considered the most technologically advanced type of 3D printing and the technology that can best achieve voxel-level control. Material jetting systems use inkjet heads that jet material through thousands and even millions of digitally controlled nozzles. In some cases, material jetting processes are combined with extrusion or binder jetting. As shown in the 3dpbm map of ceramic AM technologies, the sole representative of binder jetting technology in ceramics is Israeli company XJet. The XJet NanoParticle Jetting process leverages metal nanoparticles mixed with water, resulting in a solution that behaves both as a solid and a liquid. This solution is jetted onto a heated platform where it solidifies as the water evaporates, forming green parts. The technology is also able to use a different water-soluble material for supports, thus enabling the production of complex geometries. The green parts are then sintered in a furnace during post-processing, resulting in highly dense parts.