Using their new 3D powder printing technique, scientists of the Bundesanstalt für Materialforschung und -prüfung (BAM) can produce fine ceramic structures without sharp edges and pores. The ceramic structures produced in this way have a higher stability than structures produced by comparable additive methods: missing edges reduce fracture tendency and nonexistent pores increase the density of the component. The method is very suitable for industrial application: it is simple, fast, inexpensive and uses non-hazardous raw materials from the cosmetics industry.
Additive manufacturing procedures using plastics and metals as materials are now state of the art. But only a few methods are available for additive ceramics processing. This is due to the nature of the ceramic materials. The process requires high temperatures to blend the ceramic powder into a uniform component – i.e. into a component of one piece. Also, ceramics cannot be cross-linked like resins or deformed plastically like most polymers and metals under heat.
Professor Dr. Jens Günster, Head of Division 5.4 Ceramic Processing and Biomaterials at BAM and his team therefore rely on pre-ceramic polymers in 3D powder printing. Pre-ceramic polymers are special polymers that can be converted into ceramics. They can be cross-linked, plastically deformed, melted or dissolved in a variety of solvents. Thus, the shaping problems of ceramics can be cleverly avoided.
"We use a commercial, very inexpensive powder which is used in industrial processes and in the production of cosmetics. We apply it layer by layer and glue it locally with a solvent when the desired structure is completed," explains Günster. In this 3D printing process, the solvent is printed in layers using a print head as in ink-jet printing. The polymer formed is then fired under the exclusion of oxygen at temperatures above 1200 degrees Celsius: The result is a ceramic of vitreous silicon oxycarbide (SiOC).
The trick with the cross-linking agent
The process does not work however, without a ploy that was needed to help the research team develop the procedure. The problem was that the printed polymer starts to melt at 60 degrees Celsius and firing is then not possible. In order to obtain a ceramic component the researchers added a "cross-linking agent" to the dissolved powder. This cross-linking agent is introduced with the solvent into the polymer during printing with the result that the printed structure maintains its shape during firing
"Inspired by the properties of the cross-linking agent, we have further developed the method. We now use two print heads, as in colour printing on paper. A solvent and a cross-linking agent are emitted from one of the print heads and a pure solvent without a cross-linking agent from the other print head of the 3D print head. We use these two liquids to print the structure’s skeleton and the covering in one process. The skeleton retains its structure during firing since it contains the cross-linking agent. The covering applied without the cross-linking agent melts. It merges with the skeleton and even enters its lattice structure due to an interaction of viscosity, surface tension and gravity. As a result, we obtain a ceramic whose surface is smooth and has no pores or sharp edges. The structure has been optimised through self-assembly and withstands pressure," explains Günster.
Technology transfer: ceramic-friendly design by additive manufacturing
This process has been developed by the BAM research group together with Voxeljet AG, a market leader in Germany for the production of platforms for powder-based 3D printing. In 3D printing, an additive manufacturing process, the material for the production of a component is added in layers. This layer building principle enables the production of complex geometrical structures that are difficult or expensive to produce using conventional manufacturing methods. However, the limits and the associated need to maintain technical reliability of these materials must be considered. This is a task for BAM with its proven expertise in the field of materials research and testing over decades. Within its focus area ‘Materials’, BAM combines the issues of characterisation, service life, reliability and sustainability of materials and substances.
BAM promotes safety in technology and chemistry.
As a BMWi departmental research institute, BAM performs research and testing and advisory activity to protect people, the Environment and material goods. Its activity in the fields of materials science, materials engineering and chemistry is focussed on the technical safety of products and processes. BAM’s research is directed towards substances, materials, building elements, components and facilities as well as natural and technical systems important for the national economy and relevant to society and tests and assesses their safe handling and operation. BAM develops and validates analysis procedures and assessment methods, models and necessary standards and provides science-based service for the German industry in a European and international framework.
Safety creates markets
BAM sets and represents high standards for safety in technology and chemistry for Germany and its global markets to further develop the successful German quality culture „Made in Germany“.