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Materials • Processes


satellites and microsatellites. Hall thrusters are propulsion devices that keep satellites in the correct orbit. Small amounts of xenon gas are fired out of the thrusters, but this can erode the chamber walls. The research aims to identify ceramics that have better erosion resistance than the existing boron nitride materials used in Hall thrusters and manufacture them more cheaply and efficiently by using rapid prototyping techniques


the micro-architecture - or internal inter-connectivity of the pores - and the macro-architecture, or profile shape.” The porous nature of the scaffold helps to promote bone growth, and the implant can be combined with bio-additives, including bone marrow, blood and drugs. At the same time, German research - published in the


Journal of Dental Research – offers an alternative to CAD/ CAM milling for making dental prostheses. Researchers at the Dental Materials and Biomaterials Research unit at the University Hospital Aachen in Germany - together with four partners – prepared a zirconia-based ceramic suspension with 27 percent solid content by volume. A modified drop-on- demand inkjet printer was used in a 3D printing process to produce a crown, which was then sintered. UK materials consultancy CERAM uses a similar process,


Fig. 3. Consultants from CERAM have worked with DEKEMA Dental-Keramiköfen GmbH to optimise the design of a new furnace heating element.


Javelin used its CerLAM method to prepare prototype ceramic insulators for testing. If successful, the technique could be used to manufacture the parts in order to avoid large tooling costs. So far two ceramics with improved erosion resistance have been identified, although erosion patterns were seen – possibly due to impurities and imperfections caused by traces of the organic material used to bind the ceramic particles together. Many short-run metal and plastic production parts are


now being made using prototyping techniques and it is inevitable that the same will happen in ceramics. Phil Reeves, managing director of prototyping consultancy Econolyst, comments: “The production of ceramic layer-manufactured parts for end-use applications is in its infancy. However, processes and materials are being developed that will see rapid manufacturing used in the consumer goods and toy industries, biomedical industry and the aerospace and automotive sectors.”


3D printing


One USA company, Therics, which is part of medical device manufacturer Integra Lifesciences, has developed a 3D printing process called Theriform to make synthetic bone products using its own line of beta tri calcium phosphate (beta- TCP) materials. Originally developed at the Massachusetts Institute of Technology (MIT), Theriform is a process in which a print heads travel across a fine layer of beta- TCP, adding tiny droplets of binder solution to build a 3D component. The company states: “Using this method, we can control both essential elements of true scaffolding materials:


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which it calls Direct Ceramic Jet Printing (DCJP), to build ceramic prototypes and short-run production parts. Giuliano Tari, the director of operations, explains: “We use an ink with a fine ceramic powder inside.” The company routinely uses this process to print patterns directly onto ceramic tiles (Ferro’s Kerajet is an example of a commercial product). But Tari says the technique could also be used to make more sophisticated products such as sensors. A good example of the consultants’ work is a project undertaken with German ceramic furnace manufacturer DEKEMA Dental-Keramiköfen GmbH , relating to a heating element. The company needed to ensure that its new design would meet the requirements for a low-wear, highly dynamic furnace operation while improving on long-term temperature stability. Consultants worked with the client to develop a recipe formulation that matched the product performance requirements. At the same time, computer modelling was used to simulate the heating element, enabling a new element support to be developed that can operate at high temperature gradients thanks to the enhanced material properties and optimised geometry. The new part was manufactured using a visco-plastic


processing (VPP) technique in which a material impregnated with ceramics can be extruded thanks to the material’s clay- like consistency. In this case, no physical prototype was needed; instead, the consultants produced a virtual prototype, which was then approved prior to production commencing. Tari says: “There was no aesthetic aspect to the design, so we did not need to build a physical prototype.” Better design of ceramic components can also improve the


performance of metal parts. For example, Morgan Technical Ceramics has developed a flow modelling technique for the design of ceramic cores that are used in the manufacture of metal castings. The software optimises the injection moulding of the cores, enabling designers to create cast parts with more complex geometries. Flow simulation software is commonly used in plastics manufacturing, but has not previously been used by the ceramics industry before, according to Morgan, whose specialists use the software to predict how the ceramic core cavity will fill. Areas of stress and potential breakage are highlighted early on, so the design of the core can be refined to ensure the mould is filled in a controlled, uniform way. Morgan claims the process is more efficient than traditional methods because simulation is carried out before any metal is cast. l


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