Stereolithography (abbreviated STL or SLA) (composed of the words stereo, after the ancient Greek στερεός stereos - "hard", "solid", " physical " in the sense of " space " and lithography, the printing technique of the ancient Greek λίθος lithos - "Stone " and ancient Greek γραφή graphein - "writing" ) is a technical principle of rapid prototyping or rapid manufacturing, in which a workpiece is constructed by free materializing in space ( grid ) points in layers. The manufacture of a part or multiple parts at the same time is usually fully automatic computer-created from CAD data.
Principle on the example of laser stereolithography for individual components
Lichtaushärtender a plastic ( photopolymer ), for example epoxy resin, (also up to 1 micron layers standard layer thickness in the range 0.05-0.25 mm, with micro stereolithography ) hardened by a laser in thin layers. The procedure is done in a bath, which is filled with the base monomer of the light-sensitive ( photosensitive ) plastic. After each step, the workpiece will be lowered a few millimeters into the liquid and returned to a position that is lower by the amount of thickness of the previous ones. The liquid plastic over the part is then distributed evenly by a wiper. Then driving a laser that is controlled by a computer via movable mirrors on the new layer over the surfaces that are to be cured. After curing is the next step, so as to form a three-dimensional model by little.
In the micro- stereolithography no support structures are needed in many cases also eliminates the post-curing. In stereolithography method for large components this is different, since the hardened resin from the laser is still relatively soft and also certain form elements (eg, overhangs ) must be securely fixed during the construction process. This also helped to build support structures during manufacture. After the construction process, the platform with the / the part ( s) will be ejected from the container. After draining the non- cured resin, the model is removed from the platform, free from the support structures, washed with solvent and completely cured in an oven under UV light.
Another method which also uses the photopolymerisation for the preparation of physical objects, the " Solid Ground Curing " (SGC). Each layer is cured by UV light, using a light mask to be printed out in a photoplotter for each layer. This method, which was used particularly in the plants of the company cubital (Israel), but very much lost in the last few years.
- Existing 3D CAD data is converted to STL format. These data are sent to the stereolithography service providers who then add the possibly necessary support structures.
- After determining the installation position, the generation of the required geometry for the system control data, the so-called " slicing " is done.
- These data are sent to the manufacturing system, and form the basis for controlling the laser beam to the bath surface.
- Within a few hours you get a real model of virtually present in the CAD parts.
- Stereolithography allows a high precision (typically 0.1 mm in RMPD method also significantly lower up to 1 micron per layer) for fine structures and thin walls.
- Because a model is built up in a liquid which is needed for overhanging portions support structures for large components which need to be removed. In contrast to other rapid prototyping method is here, however, the support structure of the same material as the component and therefore has ( as not to prevent a connection with the element) mechanically removed
- Usually, the model created by stereolithography has to be cured in a UV cabinet after removal from the machine
In recent years, to technical developments that connect the "Multi Jet Modeling " with basic principles of stereo lithography. As support material here is a wax material is liquefied by heating. The component itself is generated similar to stereolithography of a photopolymer. Both materials are applied via a modified print head (similar to ink-jet printers ). In addition, a light source for exposure, and thus the curing of the photopolymer provides. These systems can also be used as opposed to RP- stereolithography systems in the office and are significantly cheaper with prices starting around 50,000 euros.
The stereolithography process is used in product development in the creation of prototypes ( concept, geometry, illustrative, functional models ) in engineering, especially in the automotive industry and in medicine. An increasing trend in the coming years in the direct manufacture of end products using stereolithography systems expected ( " Rapid Manufacturing "). An application example, the daily life already plays a role in this case, is the production of individual housings for hearing aids using the stereo lithography, as well as those manufactured by microTEC lab-on -chip systems.
Other application examples are cast models or architecture models.