The smaller, the more complex and the more refined certain functional ceramic devices are, the more difficult they are to manufacture using traditional processing. In the wide range of manufacturing techniques that exist, multi-material 3D printing happens to be one technique that provides the ability to incorporate multiple material constituents without an intricate process or expensive tools. The question is, with the wide manufacturing landscape of ceramic 3D printing, what AM processes are ready to deliver commercial-ready applications?
One appealing argument of multi-material 3D printing is the ability to use multiple materials at the same time to fabricate an object. As explained in this dossier, this means that from product development, prototyping, and internal tooling, to low-volume production parts, this manufacturing method can bring a significant return on investment – if well performed. While both industry and academics still fail to find common ground in the way multi-material 3D printing should be defined, let’s recall that to avoid any confusion, at 3D ADEPT, we consider multi-material 3D printing as a “specific procedure/technique” that defines the type of AM process one leverages; a procedure that can be applied to several types of AM processes.
With a key focus on technical ceramics, the present dossier aims to help AM users understand:
- The ceramic 3D printing processes that could be leveraged to deliver viable multi-material 3D printing applications
- The types of technical ceramics that could be combined in multi-material 3D printing
- The key applications that one can see thrive in the market
- The limitations that AM solutions providers should address to foster the adoption of multi-material 3D printing
What ceramic 3D printing process for multi-material 3D printing?
A research on multi-material 3D printing of functional ceramic devices reveals that most functional ceramic devices, such as multilayer ceramic capacitors, multilayer ceramic substrates, filters, chip antennas, power dividers, and duplexers, can be manufactured by a high-temperature cofired ceramic (HTCC) process or low-temperature cofired ceramic (LTCC) process. The problem is that not only do these processes require multiple steps – up to 9 different manufacturing stages from material preparation for ceramic tapes and functional pastes to post-processing, but they are not ideal for rapid prototyping and low-cost manufacturing of miniaturized, thin, refined, and highly integrated functional ceramic devices.
Additive Manufacturing (AM) can address these challenges through multi-material 3D printing. While taking into account that AM technologies are made up of direct and indirect solutions, Dr.-Ing. Uwe Scheithauer, Group Manager, Additive and Hybrid Manufacturing at Fraunhofer-Institut für Keramische Technologien und Systeme IKTS, explains:
“With indirect technologies, the starting material is deposited over the entire installation space and then selectively consolidated (e.g. Binder Jetting, Powder Bed Fusion, Vat Photopolymerization), whereas with direct AM technologies (e.g. Material Jetting, Material Extrusion), the material is deposited and consolidated only where it is needed.
For the realization of multi-material components using AM, direct technologies have the advantage that there is space for the deposition of a second material directly next to the deposited material without having to remove unconsolidated first material first.”
The examples of AM processes mentioned by Scheithauer are in the list of the dozen AM processes identified in a recent dossier on the current manufacturing landscape of ceramic 3D printing.
This implies that “multi-material printing can be carried out with all known 3D printing processes for technical ceramics”, Stefan Waldner from D3-AM GmbH notes.
“However, unlike metals and plastics, ceramics currently need to be processed using indirect methods, meaning that the green parts still need to be thermally processed/sintered after printing.
In MEX [material extrusion], different extruder heads can be used for different materials, while in DLP, there are approaches that involve working with different material vats, where the part is dipped from one vat to another and exposed, allowing for the production of highly precise parts. In SLA, there are approaches where the base material is cured by laser, and various materials are combined using dispenser systems. Even in the binder jetting area, there are R&D-level approaches to selectively apply different powders and bond them with a binder applied by inkjet printheads.
These are all ways to create multi-material green parts, though they often involve compromises in terms of material waste, cleanability, productivity, etc.
The most suitable process for multi-material 3D printing may be material jetting (or a hybrid version of it), where droplets of the object material are applied voxel by voxel via inkjet printheads, theoretically allowing for an unlimited number of different materials to be applied. However, it is important to emphasize—and this is likely the main reason why multi-material applications are still rare today—that while printing two different materials with different properties is technically feasible with manageable effort, co-sintering (i.e., sintering two or more different materials together) is a significant challenge in materials science. Currently, it is primarily mastered by various R&D institutes,” he adds.
If we only look at material jetting, one can understand that multi-material 3D printing of certain components can easily be utilized by following the same approach of conventional 2D ink jetting – the main difference being the fact that functional inks are deposited with multiple jetting heads in multi-material 3D printing.
With FDM 3D printing, the main parameters to consider include the filament (mainly its thermal, mechanical, and rheological properties and diameter), the process (temperature and speed), and specifications related to the 3D printer (the number of extrusion heads, the nozzle diameter, and the gear force). However, some of the limitations encountered with FDM are seen during the fabrication of complex structures. They include low resolution and poor surface finish, weak bonding between adjacent sections, and slow build speed.
Interestingly, in the list of VAT photopolymerization (VP) processes that exist, SLA – one of the oldest processes – is one of the processes that has been enhanced to enable multi-material 3D printing.
This year, 3DCeram for instance, the developer of ceramic 3D printing systems based on SLA, introduced Hybrid Printing on the M.A.T. (Manufacturing Additive Technology) through 3DCeram Sinto Tiwari in Berlin. The system includes a dual pellet extrusion head and addresses demands from universities and research centers. It enables multi-material 3D printing by allowing the simultaneous use of different materials in the printing process.
The M.A.T. can achieve multi-material 3D printing with Fused Filament Fabrication (FFF). “The materials involved are silicon nitride (Si3N4) blended with electrically conductive molybdenum disilicide (MoSi2) for the conductive components, and a similar material with lower MoSi2 content for electrical insulation. This process allows the production of complex heating elements with a combination of electrically conductive and insulating ceramic materials, achieving high-temperature performance and corrosion resistance,” the team explains.
While 3DCeram’s Hybrid Printing system has only been mentioned as an example, it should be noted that each AM process comes with a series of specifications (developed by the manufacturer) that can enable multi-material 3D printing.What is pivotal to achieving multi-material 3D printing is the different materials that can be combined during the manufacturing process.
Technical ceramics that can enable multi-material 3D printing
The term “technical ceramics” is often used interchangeably with the terms “engineered ceramics, advanced ceramics, precision ceramics, and high-performance ceramics”. This prevents any confusion with “traditional ceramics” that are made from naturally occurring materials such as clays.
Despite their exceptional strength-to-weight ratio and resistance to high temperatures, chemicals, and corrosion, technical ceramics have remained largely underutilized due to the difficulties in manufacturing them with conventional methods.
Ceramics can be classified in various ways, one common method being the division into three categories: oxides, non-oxides, and ceramic composites.
Oxide ceramics encompass a variety of ceramic families, including alumina (aluminum oxide or Al2O3), zirconia (zirconium oxide or ZrO2), silica (silicon oxide or SiO2), yttria (yttrium oxide, Y2O3), and other metal oxide-based materials like silicates and magnesia. These materials are non-metallic, inorganic compounds that contain oxygen in their chemical composition.
Oxide ceramics can also be combined to form mixed dispersions, such as zirconia toughened alumina (ZTA) or alumina toughened zirconia (ATZ).
Non-oxide ceramics consist of families like aluminum nitrides (AlN), silicon nitrides (Si3N4), and various carbides such as silicon carbide (SiC). These are non-metallic, inorganic compounds that incorporate either nitrogen or carbon into their structures.
Ceramic composites, on the other hand, include materials where the matrix is ceramic (ceramic-matrix composites or CMC), metallic (metal-matrix composites or MMC), or polymeric (polymer-matrix composites or PMC).
According to Waldner, among the technical ceramics that are gaining momentum in the market right now, one counts: “very pure oxide ceramics, mostly for highly complex chemical/thermal processes; as well as nitrides and carbides, especially silicon carbide, due to their excellent properties, with applications in aerospace, defense, and the semiconductor industry.”
Speaking of materials that can be combined in multi-material 3D printing, he adds: “combined materials can be used across various combinations, depending on the required properties of the final application such as temperature resistance, mechanical properties, insulation capability, conductivity, but also aesthetics, as seen in dental market where color gradients could be printed on dental crowns.”
The 3DCeram team shares a similar view on technical ceramics that are gaining momentum in the market:
“Among technical ceramics, oxides and nitrides are gaining momentum in the market. For oxides, alumina is the most common, but zirconia is increasingly in demand, particularly for aerospace applications. The choice of ceramic materials often depends on the specific application.”
For Dr. Scheithauer on the other hand, “aluminum oxide will continue to be the workhorse – it has very good properties and relatively low costs. Zirconium oxide is particularly interesting for the medical sector, as are mixtures of Al2O3 and ZrO2. HAp and TCP are also highly interesting for the medical sector. AlN, B4C, SiC and Si3N4 have extremely interesting combinations of properties but require expensive, specialized infrastructure and know-how for thermal processing.
For multi-material applications, the property combinations of electrically conductive and insulating (e.g. based on Si3N4 or LTCC), dense and porous (Al2O3, ZrO2) and multi-colored (ZrO2) are particularly relevant. We have already realized all these combinations with CerAM MMJ (a special MJT technology), in some cases also with CerAM FFF (MEX).”
Applications enabled by multi-material 3D printing
We’ve said it several times: applications are what gives a specific technology its credibility. Whether we explore it with polymers, metals or technical ceramics, multi-material 3D printing remains appealing for its ability to use multiple materials at the same time to fabricate a part with different properties or functionalities.
Many OEMs and AM users are still exploring the range of applications that could be achieved using a multi-material (MM) 3D printing technique. With VAT photopolymerization-based 3D printing technologies for instance, MM 3D printing has great potential in sensors, actuators, robots, microfluidic devices, and scaffolds. Indeed, VAT photopolymerization processes can manufacture parts with high resolution, high accuracy, high throughput, and a good surface finish, which is not always the case for MJ, DIW, and FDM.
This is something the 3DCeram team confirms as they explain – speaking of their hybrid process:
“For example, the hybrid process is particularly useful in the electronics and sensors industries. Its flexibility allows for increased electrification density in electronic devices. Additionally, the hybrid process is a suitable method for rapid prototyping of ceramic PCBs, LTCC (Low-Temperature Cofired Ceramics), and HTCC (High-Temperature Cofired Ceramics). This approach can significantly reduce both the time and cost of developing innovative applications. For instance, the hybrid process has been used to create electrical paths on alumina, as shown in benchmarking results.
“With the M.A.T. printer, we have worked on several project involving multi-material 3D Printing, like combining different kinds of zirconia – black and white ones, which is used in the luxury industry.
A conformal embedded coil in an alumina hybrid process is particularly innovative for electromagnetism applications like an embedded coil in an alumina part. The picture below shows a benchmark adapted to this application. The small metallic solenoid is embedded into the alumina part by additive manufacturing. The current resolution is close to Ø0.5mm but it can be improved by a more precise dispensing system.
The hybrid process opens new applications like the bitter coil. The technology is well adapted to the future challenge of transport electrification (magnet wheel motor). Indeed, the bitter coil is complex even impossible to manufacture by conventional manufacturing process. The 3D printing process can manufacture some devices with perfect customization to optimize performance,” the team adds.
In the long run, the expert from D3-AM GmbH also sees the greatest applications of multi-material 3D printing in the combination of insulating, conductive, and functional materials, enabling complex heaters, drives/actuators, sensors, and other applications that are, in some cases, not yet imaginable today. However, in the medium term, the medical field can also benefit from this technique – the dental industry especially, “where color gradients can be digitally applied,” he adds.
Limitations and future outlooks
Despite its obvious advantages, multi-material 3D printing with technical ceramics is slowing down due to several limitations. These limitations may be related to the process used or the materials themselves.
In FDM 3D printing, for instance, thermoplastic polymer filaments with high solid content are required to manufacture metal and ceramic parts given the low shrinkage after sintering. However, the dramatic increase in stiffness and brittleness adversely affects the production and printing process making it difficult to achieve repeatable 3D printed parts.
While he sees inkjet 3D printing as the most suitable approach for ceramic multi-material printing – given the technology’s ability to build a part with different materials drop by drop, Waldner also recognizes the technology’s limitations: The “need to have access to inkjet printheads and ink supply systems capable of reliably handling and depositing abrasive ceramic materials drop by drop.”
“D3 currently demonstrates this reliability in single-material ceramic printing, but as of today, there are still few reliable systems available for multi-material material jetting. Regardless of the type of technology used to manufacture multi-material components, it requires the right mindset from engineers to fully exploit these possibilities and to conceive and develop corresponding applications. I am convinced that machine learning will significantly enhance this capability in the future and help shape new, currently unimaginable applications,” he adds.
For the expert from Fraunhofer IKTS, the main challenge of multi-material 3D printing with technical ceramics is “the sintering route and the necessary co-sintering of the different materials. (Complex material development and adaptation (shrinkage) as well as limited material combinations that can be combined in terms of shrinkage technology).” “[Not to mention that] the identification of suitable material pairings and the adaptation of shrinkage behavior through the pre-treatment of powders is extremely complex”, he adds.
The team of 3DCeram on the other hand explains that “co-sintering presents a significant challenge. During the post-processing phase, materials with different thermal expansion rates (CTE) or sintering conditions may lead to internal stresses, and cracking of the 3D printed part. Achieving a cohesive final structure requires that the materials have compatible sintering behaviors. This makes the process highly complex and often limits the range of materials that can be used together.
Another limitation is the risk of material contamination during the printing process. When different materials are deposited in successive layers or sections of the part, cross-contamination can occur, affecting the integrity and properties of each material. To address this, 3DCeram has introduced a nozzle that blows air to clean the groove before depositing the next material. This prevents cross-contamination between materials and helps maintain the purity of each layer.”
So, what future do we foresee for multi-material 3D printing of technical ceramics?
Despite the aforementioned limitations that still need to be addressed, experts remain somewhat optimistic about the future of multi-material 3D printing with technical ceramics.
Dr. Uwe Scheithauer foresees a future where the proportion of ceramic parts will increase. This increase will come along with the rise of shaping processes and the reduction of post-processing costs; new material properties as well as the reduction in the total number of process steps required to produce complex, multifunctional components thanks to MM(J) printers.
That being said, we can’t help but agree with Waldner when he said that multi-material 3D printing will remain a niche compared to the overall AM ceramics market. “In the long term, this could change substantially, with improved printing systems, additional material systems, and AI-supported engineering significantly accelerating growth,” he concludes.
Editor’s notes
To discuss this topic, we invited three key contributors to share key insights into this dossier.
Dr. Uwe Scheithauer, Group Manager, Additive and Hybrid Manufacturing at Fraunhofer-Institut für Keramische Technologien und Systeme IKTS. The Fraunhofer Institute for Ceramic Technologies and Systems IKTS conducts applied research on high-performance ceramics. As a research and technology service provider, the Fraunhofer IKTS develops advanced high-performance ceramic materials, industrial manufacturing processes as well as prototype components and systems in complete production lines up to the pilot-plant scale. In addition, the research portfolio also includes materials diagnostics and testing. Dr. Scheithauer has been a speaker at various ceramic-dedicated conferences and has been involved in several publications – one of the most recent ones being “Additive manufacturing of ceramic single and multi-material components–A groundbreaking innovation for space applications too?”. The expert believes that ceramic materials will be used in applications where there is no other alternative such as aerospace and energy. He makes use of CerAM MMJ (MJT) – Al2O3, ZrO2, stainless steel, Si3N4; CerAM FFF (MEX) – Si3N4, as well as CerAM VPP (Lithoz LCM) – Al2O3 (dense/porous) as part of its multi-material 3D printing projects.
Stefan Waldner from D3-AM GmbH. D3-AM GmbH is a spin-off of the Durst Group, a world-leading manufacturer of digital printing and production technologies. The company has developed LABII, a hardware system for technical ceramics based on Micro-Particle Jetting process (MPJ). This development has allowed D3 to address the limitations of conventional inkjet systems, enabling the direct printing of water-based, highly concentrated suspensions with almost any particle size and distribution. D3 already uses a second inkjet-printed material for support structures in its LABII printing system. However, in the medium term, the focus remains on single-material 3D printing of high-performance ceramics using a proprietary inkjet technology. With regards to this topic, the D3 engineering team has gained significant experience in inkjet multi-material printing for graphic applications, with up to 12 different colors per machine, due to their background in 2D printing within the parent company, Durst Group. This multi-material expertise could become also relevant for D3 at some point with its Micro Particle Jetting technology.
The team at 3DCeram. If you’re a regular reader of 3D ADEPT, you may know this French manufacturer who specializes in ceramic 3D printing based on SLA technology. The company is currently helping its clients move from experimental phases to fully industrialized solutions. This approach mirrors what they have already achieved with SLA technology, where they successfully transitioned to large-scale production, notably the printing of very large parts. “As the technology continues to evolve, we expect to see more widespread applications of technical ceramics in industries such as aerospace, electronics, and energy, driven by the need for high-performance, durable materials. The focus will likely shift from research to practical, scalable solutions, making multi-material and high-precision ceramic 3D printing a standard in advanced manufacturing,” the company said.
Last but not least, the current focus of their developments is geared towards the industrialization of the process. Rather than concentrating solely on multi-material capabilities, we are directing our efforts towards multi-plateau systems, which allow for increased productivity and efficiency in large-scale production. The use of large build platforms, combined with advancements in AI, is driving significant progress in optimizing workflows and expanding the industrial application of ceramic 3D printing. This shift towards multi-plateau setups will be key to meeting the growing demand for higher volume and larger parts in various industries.
This dossier has first been published in the 2024 September/October edition of 3D ADEPT Mag.
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