Lithography-based Ceramic Manufacturing Research Articles

Stereolithographic Additive Manufacturing of High Precision Glass Ceramic Parts.

Lithography based additive manufacturing (AM) is one of the most established and widely used 3D-printing processes. It has enabled the processing of many different materials from thermoplast-like polymers to ceramics that have outstanding feature resolutions and surface quality, with comparable properties of traditional materials. This work focuses on the processing of glass ceramics, which have high optical demands, precision and mechanical properties specifically suitable for dental replacements, such as crowns. Lithography-based ceramic manufacturing (LCM) has been chosen as the optimal manufacturing process where a light source with a defined wavelength is used to cure and structure ceramic filled photosensitive resins. In the case of glass ceramic powders, plastic flow during thermal processing might reduce the precision, as well as the commonly observed sintering shrinkage associated with the utilized temperature program. To reduce this problem, particular sinter structures have been developed to optimize the precision of 3D-printed glass ceramic crowns. To evaluate the precision of the final part, testing using digitizing methods from optical to tactile systems were utilized with the best results were obtained from micro computed tomography (CT) scanning. These methods resulted in an optimized process allowing for possible production of high precision molar crowns with dimensional accuracy and high reproducibility.

Dense, Strong, and Precise Silicon Nitride-Based Ceramic Parts by Lithography-Based Ceramic Manufacturing

Due to the high level of light absorption and light scattering of dark colored powders connected with the high refractive indices of ceramic particles, the majority of ceramics studied via stereolithography (SLA) have been light in color, including ceramics such as alumina, zirconia and tricalcium phosphate. This article focuses on a lithography-based ceramic manufacturing (LCM) method for β-SiAlON ceramics that are derived from silicon nitride and have excellent material properties for high temperature applications. This study demonstrates the general feasibility of manufacturing of silicon nitride-based ceramic parts by LCM for the first time and combines the advantages of SLA, such as the achievable complexity and low surface roughness (Ra = 0.50 µm), with the typical properties of conventionally manufactured silicon nitride-based ceramics, such as high relative density (99.8%), biaxial strength (σf = 764 MPa), and hardness (HV10 = 1500).

Analysis of the Technological and Economic Expediency of Using Additive Technologies in Manufacturing Ceramic Parts

The experience gained in manufacturing complex ceramic parts using additive technology LCM (Lithography-based Ceramic Manufacturing) and an analysis of the economic expediency of using this technology in serial and experimental manufacturing of ceramic parts as compared with slip casting technology are presented. The results are of interest in developing and manufacturing new, complex, experimental, ceramic parts and selecting a technology and equipment for serial production.

Three-dimensional printing of zirconia: characterization of early stage material properties

Objective: The aim of this study was to evaluate the mechanical properties of 3D printed zirconia (ZrO2). Materials and Methods: The test specimens were produced with a 3D printer that uses lithography-based ceramic manufacturing (LCM) technique with two different parameters in horizontal and vertical printing orientations. Altogether four groups of nine specimens were printed and examined. Mechanical characterization was performed using 3-point bending test (ISO 10477) and surface microhardness (Vickers) test. Grain structure, porosity and printing layer morphology were examined with optical and scanning electron microscopy (SEM). Additionally fractography analysis was done to investigate and evaluate features of fracture initiation site. Numeric results were statistically analyzed with ANOVA (a = 0.05). Results: The average flexural strength reached for printed zirconia was 499 MPa (+/−75 MPa) for specimens printed in horizontal orientation and 575 MPa (+/−69 MPa) for specimens printed in vertical orientation. Optical microscopy and SEM analysis revealed that fractures initiated between the printing layers or from a local porosity. Printing layer thickness varied from under 13 μm to over 20 μm. Conclusions: The study revealed that 3D printed zirconia has challenges in regards to layer integration. Based on this study, 3D printed zirconia still suffers from low mechanical strength, which together with long carbon-debinding time, does not make 3D printed zirconia a potential material for dental appliances at this stage. Further research is needed to create more suitable zirconia precursor slurries and to optimize printing parameters and sintering conditions to be able to 3D print zirconia with higher mechanical properties.

X-ray tomography of additive-manufactured zirconia: Processing defects – Strength relations

X-ray Computed Tomography (XCT) analysis was applied to identify and quantify typical defects in dense 3Y-TZP zirconia processed by the Lithography-based Ceramic Manufacturing (LCM) technique. XCT derived strengths were anticipated from the XCT data and compared to experimental measurement. A good agreement between XCT data, bending strength measurement and fractographic analysis demonstrates the suitability of X-ray tomography for both defects detection and predictive mechanical strength estimation. It allows also to rank the different defects related to LCM in terms of their criticality versus mechanical resistance.

Lithography-Based Ceramic Manufacturing (LCM) for Dental Applications

Dental applications like crowns, veneers or bridges require high accuracy to be fitted on the patient’s stump. Stereolithography is an additive manufacturing method, which offers high precision by using light exposure as the layer generating mechanism. In the LCM process, this precision is combined with a thermal post-processing step to achieve full ceramic restorations. The overall production of such ceramic parts in a reproducible way is a highly complex procedure. The first requirement is to find a slurry formulation, which is stable against sedimentation and segregation, that is also processable in a stereolithographic system. Such a formulation has been found by us, which could be shown by rheology measurements. During experiments with this formulation, it could be observed that there is a correlation between wet film thickness and resolution. Several adjustments to the machine have been made, to fully control this parameter. Namely, changes to the vat, the doctor blade and the building platform have been made. The improvement of the process and the quality of the final parts are validated by fabricating Siemens stars and by biaxial bending tests.

Lattice Microarchitecture for Bone Tissue Engineering from Calcium Phosphate Compared to Titanium.

Additive manufacturing of bone tissue engineering scaffolds will become a key element for personalized bone tissue engineering in the near future. Several additive manufacturing processes are based on extrusion where the deposition of the filament will result in a three-dimensional lattice structure. Recently, we studied diverse lattice structures for bone tissue engineering realized by laser sintering of titanium. In this work, we used lithography-based ceramic manufacturing of lattice structures to produce scaffolds from tricalcium phosphates (TCP) and compared them in vivo to congruent titanium scaffolds manufactured with the identical computer-aided design data to look for material-based differences in bony healing. The results show that, during a 4-week period in a noncritical-size defect in a rabbit calvarium, both scaffolds with the identical microarchitecture performed equally well in terms of bony regeneration and bony bridging of the defect. A significant increase in both parameters could only be achieved when the TCP-based scaffolds were doped with bone morphogenetic protein-2. In a critical-size defect in the calvarial bone of rabbits, however, the titanium scaffold performed significantly better than the TCP-based scaffold, most likely due to its higher mechanical stability. We conclude that titanium and TCP-based scaffolds of the same microarchitecture perform equally well in terms of bone regeneration, provided the microarchitecture meets the mechanical demand at the site of implantation.

Process development for additive manufacturing of functionally graded alumina toughened zirconia components intended for medical implant application

Additive manufacturing processes become more and more important in almost all areas, also for medical implant application. Medical implants made of ceramics are known for their excellent biological compatibility. For increasing the ingrowth of cells into an implant, a function-optimized structure with a defined porosity seems to be advantageous. Additive manufacturing is suited to realize defined and filigree structures. Lithography-based ceramic manufacturing (LCM), for example, has a high resolution, but still a limited material portfolio. Alumina toughened zirconia is a very interesting material for medical applications, but not commercially available for LCM. In this study, the development of an ATZ suspension usable in the LCM process with a bulk material density higher than 99% after sintering is presented. Furthermore, printing of lattice test structures for the evaluation of accuracy in dependence of printing dimension is demonstrated.

Characterization of zirconia specimens fabricated by ceramic on-demand extrusion

The Ceramic On-Demand Extrusion (CODE) process is a novel additive manufacturing method for fabricating dense (~99% of theoretical density) ceramic components from aqueous, high solids loading pastes (>50 vol%). In this study, 3 mol% Y2O3 stabilized zirconia (3YSZ) specimens were fabricated using the CODE process. The specimens were then dried in a humidity-controlled environmental chamber and afterwards sintered under atmospheric conditions. Mechanical properties of the sintered specimens were examined using ASTM standard test techniques, including density, Young’s modulus, flexural strength, Weibull modulus, fracture toughness, and Vickers hardness. The microstructure was analyzed and grain size measured using scanning electron microscopy. The results were compared with those from Direct Inkjet Printing, Selective Laser Sintering, Lithography-based Ceramic Manufacturing (LCM), and other extrusion-based processes, and indicated that zirconia specimens produced by CODE exhibit superior mechanical properties among the additive manufacturing processes. Several sample components were produced to demonstrate CODE’s capability for fabricating geometrically complex ceramic components. The surface roughness of these components was also examined.

Fracture Toughness (KIC) of Lithography Based Manufactured Alumina Ceramic

Precision shaped ceramic components can be obtained by an emerging technique called Lithography based Ceramic Manufacturing (LCM). A green part is made from a slurry consisting of a ceramic powder in a photocurable binder with addition of dispersant and plasticizer. Components are built in a layer–by-layer way by exposing the desired cross- sections to light. The parts are subsequently sintered to their final density. It is a challenge to produce ceramic component with this method that yield the same mechanical properties in all direction. The fracture toughness (KIc) of of LCM-alumina (prepared at LITHOZ GmbH, Austria) was tested by using the Single-Edge-V-Notched Beam (SEVNB) method. Notches are made into prismatic bend-bars in all three direction X, Y and Z to recognize the value of fracture toughness of the material in all three directions. The microstructure was revealed with optical microscopy as well as Scanning Electron Microscopy (SEM). The results indicate that the fracture toughness in Y-direction has the highest value (3.10 MPam1/2) that is followed by the one in X-direction which is just a bit lower (2.90 MPam1/2). The Z-direction is found to have a similar fracture toughness (2.95 MPam1/2). This is supported by a homogeneous microstructure showing no hint of the layers used during production.

Layered Manufacturing of Dental Ceramics: Fracture Mechanics, Microstructure, and Elemental Composition of Lithography-Sintered Ceramic.

To compare the fracture mechanics, microstructure, and elemental composition of lithography-based ceramic manufacturing with pressing and CAD/CAM. Disc-shaped specimens (16 mm diameter, 1.2 mm thick) were used for mechanical testing (n = 10/group). Biaxial flexural strength of three groups (In-Ceram alumina [ICA], lithography-based alumina, ZirkonZahn) were determined using the "piston on 3-ball" technique as suggested in test Standard ISO-6872. Vickers hardness test was performed. Fracture toughness was calculated using fractography. Results were statistically analyzed using Kruskal-Wallis test followed by Dunnett T3 (α = 0.05). Weibull analysis was conducted. Polished and fracture surface characterization was made using scanning electron microscope (SEM). Energy dispersive spectroscopy (EDS) was used for elemental analysis. Biaxial flexural strength of ICA, LCM alumina (LCMA), and ZirkonZahn were 147 ± 43 MPa, 490 ± 44 MPa, and 709 ± 94 MPa, respectively, and were statistically different (P ≤ 0.05). The Vickers hardness number of ICA was 850 ± 41, whereas hardness values for LCMA and ZirkonZahn were 1581 ± 144 and 1249 ± 57, respectively, and were statistically different (P≤0.05). A statistically significant difference was found between fracture toughness of ICA (2±0.4MPa⋅m1/2 ), LCMA (6.5±1.5MPa⋅m1/2 ), and ZirkonZahn (7.7±1MPa⋅m1/2 ) (P≤0.05). Weibull modulus was highest for LCMA (m=11.43) followed by ZirkonZahn (m=8.16) and ICA (m=5.21). Unlike LCMA and ZirkonZahn groups, a homogeneous microstructure was not observed for ICA. EDS results supported the SEM images. Within the limitations of this in vitro study, it can be concluded that LCM seems to be a promising technique for final ceramic object manufacturing in dental applications. Both the manufacturing method and the material used should be improved.

Development of monoblock TM dielectric resonator filters with additive manufacturing

Transverse magnetic (TM) dielectric resonator filters are frequently affected by a poor contact in the interface between metal and ceramic walls, misalignment of the ceramic parts, and cracks due to mechanical stress. To overcome these issues, the present study proposes the development of monoblock filters fabricated by lithography-based ceramic manufacturing. To build these structures with additive manufacturing, some geometrical changes, with respect to the classical assembly, have to be applied. The effect of these changes on the electrical performance of a stand-alone resonator are studied. Then, a filter prototype is manufactured and measured to validate the feasibility of this approach.

Additive Manufacturing of Ceramic Heat Exchanger: Opportunities and Limits of the Lithography-Based Ceramic Manufacturing (LCM)

Additive manufacturing (AM) techniques allow the preparation of tailor-made structures for specific applications with a high flexibility in regard to shape and design. The lithography-based ceramic manufacturing (LCM) technology allows the AM of high-performance alumina and zirconia components. There are still some restrictions in regard to possible geometries. The opportunities and limits of the LCM technology are discussed in the following paper using the example of ceramic heat exchangers. Structures are presented which combine a large surface for heat exchange with a small component volume and low pressure drop. This paper concludes summarizing the essential remarks.

Lithography-based ceramic manufacturing (LCM) – Viscosity and cleaning as two quality influencing steps in the process chain of printing green parts

The advantages of suspension based Additive Manufacturing (AM), e.g. the lithography-based ceramic manufacturing (LCM), are high structural resolution, and compared to other available AM techniques, the manufacturing of dense (>99%) ceramic components with high performance. This novel manufacturing technique permits innovative designs, new types of ceramic components, and offers a range of new applications; like micro reactors, catalyst supporting structures or heat exchangers, as well as cutting edge biomedical devices and personalized medical products. Some examples of personalized medical products are customised ceramic knee implants or custom spinal fusion implants. Producing these implants using LCM would allow product offerings not possible before. However, the LCM process chain includes several open points, which have to be solved, in order to get high quality end results. In this paper, the development of suspensions (curable slurries) based on different binders, and the procedures for cleaning printed parts are thoroughly considered.

Fractography of zirconia-specimens made using additive manufacturing (LCM) technology

A relatively new method to manufacture complex ceramic prototypes and components is additive manufacturing (AM). With the LCM (Lithography-based Ceramic Manufacturing)-technology the green body is manufactured layer-by-layer using selective curing of light-sensitive ceramic slurry by a mask exposure process. After curing by blue light the component is removed from the building platform and the green body is sintered to a ceramic component.The aim of this work is to investigate the influence of processing and layer architecture on the mechanical properties of an Yttria-stabilized zirconia ceramic. Strength tests were performed by uniaxial bending tests and by biaxial Ball-on-three Balls (B3B) tests. To identify typical fracture initiating flaws a systematic fractographic investigation was performed on different batches of Ball-on-three Balls-test and bending test specimens, respectively.Through additional investigations it was found that hardness and fracture toughness were independent on the layer architecture. But an extensive fractographic analysis showed that the strength was limited by flaws, which were introduced by processing and handling. If these flaws can be avoided by optimisation of the process the strength should be equal to that of conventional processed ceramics.

Stabilization of tricalcium phosphate slurries against sedimentation for stereolithographic additive manufacturing and influence on the final mechanical properties

AbstractCeramic parts manufactured by lithography‐based ceramic manufacturing (LCM) excel in resolution and surface quality. The material for LCM is a photosensitive ceramic particle‐filled slurry which needs to have homogeneous properties over time and during each processing step. The goal of this study was to use “mechanical” stabilization for a tricalcium phosphate‐filled slurry done by increasing slurry viscosity, solids loading, or inducing thixotropic behavior. The modified slurries were compared with a nonstable reference slurry. While all methods lead to increased storage stability, only the stabilized slurry with 0.5 wt% fumed silica is stable during the printing process.

Lithography-based ceramic manufacture (LCM) of auxetic structures: present capabilities and challenges

Auxetic metamaterials are known for having a negative Poisson’s ratio (NPR) and for displaying the unexpected properties of lateral expansion when stretched and densification when compressed. Even though a wide set of micro-manufacturing resources have been used for the development of auxetic metamaterials and related devices, additional precision and an extension to other families of materials is needed for their industrial expansion. In addition, their manufacture using ceramic materials is still challenging. In this study we present a very promising approach for the development of auxetic metamaterials and devices based on the use of lithography-based ceramic manufacturing. The process stands out for its precision and complex three-dimensional geometries attainable, without the need of supporting structures, and for enabling the manufacture of ceramic auxetics with their geometry controlled from the design stage with micrometric precision. To our knowledge it represents the first example of application of this technology to the manufacture of auxetic geometries using ceramic materials. We have used a special three-dimensional auxetic design whose remarkable NPR has been previously highlighted.

Innovative and novel manufacturing methods of ceramics and metal-ceramic composites for biomedical applications

Recently, the so-called freeze-foaming method, for achieving open porous and mainly interconnected foam structures, was combined with the Additive Manufacturing technique Lithography-based Ceramic Manufacturing which provides personalized and complex 3D structures. After a co-sintering step, composite structures, combining the advantages of dense and porous features in one single part were achieved. These novel potential bone replacement structures might serve as possible next-generation bioceramics/-composites used for personalized implants which, additionally, allow a structural adaption according to the customer's needs. In other current projects, metal-ceramic composites were obtained by tape-casting technologies and reshaping methods like lamination and deep drawing. After final co-sintering demonstrators of a bipolar scissor and a miniature button-sized device for medical application were developed. These composites provide biocompatible and isolating properties given by zirconia and at the same time, conductive properties given by steel layers. Thus, they are applicable to prevent bleedings and initiate a localized tissue vaporization respectively.

Additive Manufacturing of Dense Alumina Ceramics

In this study, a new process for additive manufacturing (AM) of dense and strong ceramic objects is described. The lithography‐based ceramic manufacturing (LCM) technique is based on the selective curing of a photosensitive slurry by a dynamic mask exposure process. The LCM technique is able to produce strong, dense and accurate alumina ceramics without virtually any geometrical limitations. With over 99.3% of a theoretical alumina density, four‐point bending strength of 427 MPa, and very smooth surfaces, the LCM process distinguishes itself from other AM techniques for ceramics and provides parts with very similar mechanical properties as conventionally formed alumina.