Cold plastic extrusion in 3D printing for technical ceramics
Ceramic components with a high thermal shock resistance
In cold plastic extrusion, a ceramic paste is fed from a tank into a screw extruder by means of air pressure. This plasticizes and conveys the mass further to a nozzle, which produces a strand, selectively deposits it on a building platform and thus builds up a component layer by layer using the usual 3D printing process.
Our product range extends from extrudable pastes to various porcelain mixtures and oxide ceramics such as Al2O¬2, ZrO2 or MgO. In addition, we have recently gained experience in the field of refractory ceramic pastes and developed components with high thermal shock resistance. We will be pleased to advise you on the choice of the material suitable for your application. Due to our many years of experience in the field of paste development, we can also offer you more individual solutions within the framework of feasibility studies, which can be tailored even more precisely to your needs.
How is a ceramic paste produced?
The paste is a mixture of ceramic material and various additives. Traditionally, clay is homogeneously mixed with water in a mixing unit and thus processed into an extrudable mass. However, since most ceramic powders, unlike clay, do not have plastic properties, much more sensitivity is required when selecting the additives. It is important to strike a successful balance between solvent(s), dispersant and plasticizer in order to be able to produce a paste with the optimum properties. On the one hand, the paste must have the optimum viscosity so that it can be extruded through the die at relatively low pressure, but on the other hand, it must have the necessary adhesion between the individual particles to ensure its plasticity. Last but not least, the paste must also have a certain adhesive force so that it can adhere to the building platform for the first layer and to the previous layer for all subsequent layers.
How does cold plastic extrusion work in detail?
First of all, a CAD model must be created, which is then sliced into individual horizontal slices with the help of software. Furthermore, these individual slices must in turn be translated into the individual travel paths of the nozzle during printing. The resulting G-Code file can then be read by the 3D extruder and translated into movements. It controls things like the individual travel paths of the nozzle, the speed of the nozzle and the material flow at different points.
In order to be able to extrude the ceramic paste produced, it is conveyed with compressed air from a tank to a screw extruder, which then conveys the paste to the nozzle. In this way, the screw extruder ensures a continuous material flow during printing, while the printer itself controls the movements and positions of the print head. During printing, the screw extruder also helps to mix the ceramic paste and ensure its homogeneity. The paste is then applied layer by layer through the nozzle. After a layer is completed, depending on the model, the building platform moves downwards or the extrusion head moves upwards accordingly, so that a new layer of material can be applied, which adheres to the previous layer. The process is repeated until a complete object is created. The layer thickness is always slightly less than the die inside diameter to ensure optimum adhesion between the layers. The nozzle used is interchangeable and can have different diameters, which affects the accuracy of the printed object, although the precision decreases as the nozzle inner diameter increases.
What happens to the part after ceramic 3D printing?
After the component has been printed, it is dried for several hours at moderate temperatures to remove any residual solvent that could otherwise cause unwanted cracks during the sintering process. After drying, it can already be moved by hand and fired in an oven at the appropriate sintering temperature, with debinding taking place immediately during firing. After firing, the ceramic component then has its final mechanical and physical properties.
What are the possibilities of cold plastic extrusion?
With cold plastic extrusion, complex geometries can be produced relatively inexpensively at high design speeds (up to approx. 300 cm³/h). The degree of precision of the component can be adjusted by the choice of the die, whereby die diameters of 0.5 mm to 8 mm are possible.
Components produced by cold plastic extrusion can have very low porosity and relatively high strength compared to other 3D printing processes. On the other hand, parts with defined high porosity can also be produced if required by the specific application. Since, in contrast to FFD and FFF, comparatively low additive contents can be used, the components do not have to undergo a separate debinding step. In addition, the range of ceramic powders that can be processed is significantly increased and there is no need to resort exclusively to commercial products. With our in-house developed 3D-extruder even multi-material printing is possible due to the two separately controllable nozzles.
Where are the limits of cold plastic extrusion?
With this procedure, the general wall thickness should not fall below 1 mm and should not exceed 10 mm. In addition, it should also always be remembered that the desired wall thickness cannot naturally be smaller than the nozzle diameter used. The maximum component geometry to be produced by us is 600 mm in X and Y direction and 300 mm in Z direction. Components with overhanging geometries (from 45°) require additional support structures during printing.
Because the individual layers of a part are assembled from individual strands, this process cannot compete with other 3D printing processes, such as Binder Jetting, in terms of resolution and surface finish.