Stereolithography (SLA) is the oldest additive technology and has been used for over 30 years. This does not make the technology outdated, but the most mature and reliable technology in rapid prototyping. Stereolithography generates superior surfaces and high-accuracy models. The main application of the technology are precise, high-quality plastic prototypes.
The basic principle of Stereolithography is the selective curing of a photopolymer (a resin) using a UV laser. A thin layer of liquid resin (generally 50-100 microns deep) is prepared in the machine’s building space. The Laser draws a pattern on that layer curing only the shape desired in the first layer of the model. When a layer is completed, a new layer of liquid resin is created will follow (by moving the part up or the bottom of the building space down) and the process continues.
There are two types of SLA technology machines, one prints the model upwards (‘bottom-up’), and the other prints the model downwards (‘top-down’). Furthermore, the UV light source can be either a laser or projector (i.e. DLP). With a DLP (Digital Light Processing) system the whole model layer pattern can be projected simultaneously instead of drawing the pattern with the single point of a laser. This means DLP 3D printers are both faster and often cheaper in cost, but have resolution limitations so are usually limited to smaller build spaces.
Since the part is surrounded by liquid resin in both technologies, both require support structures for overhanging geometry to prevent those sections from moving out of position from the rest of the model..
Illustration of the Stereolithography process. Source: YouTube/3D-Systems
No additive technology has been in the market as long as Stereolithography. Still, when it comes to high quality, high accuracy prototyping parts, Stereolithography sets the standard. The surfaces are smooth and can be polished or coated. Unlike Polyjet or MJM, which rivals Stereolithography in surface quality and accuracy, SLA is a cost-efficient technology even for larger parts.
Stereolithography is the major technology to create prototypes for molding processes like vacuum casting or investment casting. The large choice of materials allows to use dimensionally stable, high-resolution materials (e.g. our SLA Detail Resin) for vacuum casting or high-resolution castable resin in investment casting.
Stereolithography is used to create high-quality visual prototypes. This includes technical (e.g. cases, mechanic parts) parts, as well as design studies (e.g. elements in architectural models, design models for new car models).
- High accuracy
- Smooth, high-quality surfaces
- High-resolution of small details
- Short turn-around times
- Limited mechanical and thermal strength
- Support structures required – some designs cannot be printed
- Surface quality of area with support structures rough with scars from support (dots)
In general, SLA uses UV curable resins. Those are normally on epoxy- or acrylic-base, more rarely on a vinyl-base. All resins are liquid, and solidify when exposed to UV. While there were only a few, mostly low-performance resins in the beginning, there are plenty of high-performance materials available today, with a wide range of characteristics.
SLA High Detail Resin
Our SLA Detail Resin with ABS like properties is a translucent high-quality material. It allows smooth surfaces, high-resolution and excellent accuracy models.
SLA Detail Resin can be well post-processed after printing. Our finishing options include
- Removal of support structures (standard)
- Sanding support structure scars (standard)
- Clear coat coating (standard, UV protection)
- Glas bead blasting (on request, free of charge)
- Spray painting (on request with additional fee, translucent or opaque colors available)
- Coating (on request with additional fee)
Stereolithography had to be developed several times before it actually hit the market. The first attempts date back to 1971, when Wyn Kelly Swainson registered a patent. He described the creation of 3D objects out of photopolymers. However, his work was interrupted in the 1980s, as his method proved to be impractical.
In the 1970s, Dr. Hideo Kodama made a new attempt. He was the first to describe the layer-by-layer construction we recognize in modern SLA 3D printing. The breakthrough finally happened almost simultaneously by a group of french engineers – Alan Le Mehaute, Jean Claude André and Olivier de Witte – and the American Chuck Hull. The work of the French team was unfortunately abandoned due to lack of business perspective so ultimately Chuck Hull was able to successfully commercialize the technology, coining the word “stereolithography” along the way.
With his development Hull then founded today’s industry giant 3D-Systems. His great work also includes many fundamental technologies, such as the STL file format and slicing software. Those inventions were instrumental in making the present 3D printing world possible.
Part of the original draft created by Chuck Hull from the patent register. Picture: Google Patents.
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