3D screen printing - brings the advantages of technical ceramics to the smallest dimensions
Large series production using additive processes - with 3D screen printing possible
Technical high-performance ceramics, which follow the trend to miniaturization and lightweight construction, can be primarily produced with 3D screen printing method. The 3D screen printing method enables filigree structures – e.g. thin-walled channels or narrow webs – with a contour sharpness that cannot be achieved by any other additive manufacturing method. Further advantages of this process are:
- The required screens – the tools of this process – are technically advanced and affordable.
- The systems technology is well-developed and offers continuous processes allowing high throughput rates – large-scale production is already possible today in ceramic 3D screen printing.
- This process produces no raw material waste, because excess material remains in one place (on the screen) and can be easily returned to the production cycle. This process is therefore well suited for expensive or environmentally critical raw materials.
What is 3D screen printing?
Screen printing – “two-dimensional” – is a thick-film process that has been established for decades and is used in a variety of ways, e.g. to print coloured motifs or conductor paths on substrates. The basic technical know-how is highly developed and ready for use. The craft of screen construction is widespread, in every region inexpensive screens on a high quality level are available. These screens are the tools that are also used in 3D screen printing. They bear the motif pattern, i.e. the areas in the filigree steel mesh of the screen that are not closed with a polymer layer and are therefore permeable to the image.
For the additive manufacturing of ceramic bodies by screen printing, the automated procedure has to be modified by installing a z-direction, which releases the third dimension for the construction of a solid body structure. Using a modified device, the 3D solid body is built up layer by layer in an iterative procedure by always printing one layer on top of the solidified previous layer.
The material application – thus the printing step – is done with a rubber lip (squeegee) that passes over the screen by through-printing the motif onto the building platform.
The main focus of the development work and key step for the success of the whole method is to find a matrix for the ceramic raw material suitable for passing homogeneously through the screen mashes and to show the motif sharply contoured. Nevertheless, the final 3D solid body not only needs to show sharp contours but also has to lead to a monolithic, low-porosity microstructure after firing. For this purpose, so-called screen printing pastes need to be developed individually for each application. Carrier solvent, amount of ceramic particle filling and additive supplements are the key adjustments in paste composition – thixotropy, drying and debinding dynamics, sinter compaction are the parameters to be optimized.
Finally, the fired components meet all criteria known from traditionally produced ceramics.
How does 3D screen printing work in detail?
The screen printing paste – filled with ceramic particles and optimized with additives – is placed onto the screen.
The device operates periodically: the squeegee lowers onto the screen in a programmable frequency and pushes the paste along over the motif patterns of the screen. A paste image results inside the uncovered mashes of the screen and the motive is deposit on the previously printed structure while touching it. During the return movement, a recovery slide is activated, which brings the residual screen printing paste back to its initial position. Then the process starts again.
The squeegees flexural onset-stress stretches the filigree steel mesh of the screen (screen lift-off) while moving over it and the bottom side of the screen touches the previously printed structure in such a way that the screen polymer layer forms a flush connection with it. This ensures that the resulting walls are smooth, steep and with a high aspect ratio.
The shear-thinning behaviour of the paste promotes homogeneous application of the new layer on the previously printed solid body fragment. In order to build up height, two more actions must be performed between the printing cycles:
- As the component grows, the building platform must be continuously lowered step by step from the screen lift-off level – frequently in the extent corresponding to one layer thickness.
- The freshly printed solid body fragment must be able to withstand the contact during the short-time recovery stress, i.e. it must have a certain stability (also to give a structural basis for deposition of the newly applied layer). To achieve this, the solid body fragment must be dried between cycles. A binder additive attracts during drying and ensures a stable (not too brittle) bonding of the ceramic particles.
Layer by layer the hole part is built up successively. The layer thicknesses per cycle varies between 10 and 30 µm depending on the individual conditions, which corresponds to a construction progress of about 3 mm/h.
What is 3D screen printing particularly suitable for?
3D screen printing is comparable to the classic extrusion process, in which mass is pressed through a mask and the structured semi-finished product is then cut out off. 3D screen printing is therefore particularly suitable for comparable geometries for which the conventional extrusion process is too coarse.
In general, the 3D screen printing process is limited to components that do not have a large number of geometry changes in the z-direction. Although change of screen can also support a change of geometry, constant changes of shape – such as with spherical bodies, where each layer would require a different screen – are examples of unsuitable geometries (in this case, the Vat photopolymerization methode (VPP) showing a similar resolution is recommended).
Component examples from our development history: microreactors, miniature mechanical parts, catalyst carriers with large macroscopic (and microscopic, adjustable via porosity) surface.
The component options for the 3D screen printing methode can be summarized in three keywords: filigree, flat, many.