stereolithography

A stereolithography machine

A SLA produced part

Stereolithography (SL) is an additive manufacturing technology for producing models, prototypes, patterns, and in some cases, production parts.

Technology description

Stereolithography is an additive manufacturing process using a vat of liquid UV-curable photopolymer "resin" and a UV laser to build parts a layer at a time. On each layer, the laser beam traces a part cross-section pattern on the surface of the liquid resin. Exposure to the UV laser light cures, or, solidifies the pattern traced on the resin and adheres it to the layer below.

After a pattern has been traced, the SL's elevator platform descends by a single layer thickness, typically 0.05 mm to 0.15 mm (0.002" to 0.006"). Then, a resin-filled blade sweeps across the part cross section, re-coating it with fresh material. On this new liquid surface, the subsequent layer pattern is traced, adhering to the previous layer. A complete 3-D part is formed by this process. After building, parts are cleaned of excess resin by immersion in a chemical bath and then cured in a UV oven.

Stereolithography requires the use of support structures to attach the part to the elevator platform and to prevent certain geometry from not only deflecting due to gravity, but to also accurately hold the 2-D cross sections in place such that they resist lateral pressure from the re-coater blade. Supports are generated automatically during the preparation of 3-D CAD models for use on the stereolithography machine, although they may be manipulated manually. Supports must be removed from the finished product manually; this is not true for all rapid prototyping technologies.

Advantages and disadvantages

Stereolithography has many common names such as: 3D printing, optical fabrication, photo-solidification, solid free-form fabrication, and solid imaging. One of the appealing aspects about SL is that a functional part can be created within one day which becomes useful when working in a “time is money” environment. However the amount of time to produce any one part depends on the size and complexity of it and can take anywhere from a few hours to more than a day. Most SL machines can produce parts with a maximum size of 20” x 20” x 24”. Prototypes made by SL can be very beneficial as they are strong enough to be machined and can be used as master patterns for injection molding, thermoforming, blow molding, and also in various metal casting processes. Although there are almost no limitations when it comes to the shapes of the parts that can be created the process is not by any means inexpensive. The photo-curable resin can cost anywhere from $300 to $800 per gallon. An SL machine can cost from about $100,000 to more than $500,000.

History

The first working stereolithography system, invented by Chuck Hull. Photo circa 1986.

The term “stereolithography” was coined in 1986 by Charles (Chuck) W. Hull^[1]. Stereolithography was defined as a method and apparatus for making solid objects by successively “printing” thin layers of the ultraviolet curable material one on top of the other. Hull described a concentrated beam of ultraviolet light focused onto the surface of a vat filled with liquid photopolymer. The light beam draws the object onto the surface of the liquid layer by layer, causing polymerization or crosslinking to give a solid. Because of the complexity of the process, it must be computer-controlled.^[2] The first company aiming to generalize and commercialize the procedure was founded immediately alongside the invention.

See also

• Rapid prototyping
• 3D printing
• Solid freeform fabrication
• Stereolithography in medicine
• Fused deposition modeling
• Selective laser sintering
• Polyjet matrix
• Objet geometries
• Lithography

References

Notes

Bibliography

• Kalpakjian, Serope and Steven R. Schmid. Manufacturing Engineering and Technology 5th edition. Ch. 20 (pg 586-587 Pearson Prentice Hall. Upper Saddle River NJ, 2006.

External links

• Graphical Display of the Stereolithography Process: A resource page maintained by Laser Prototypes (Europe) Ltd,
• Castle Island's Worldwide Guide to Rapid Prototyping, with comprehensive information on rapid prototyping, rapid tooling, stereolithography and solid freeform fabrication technology products and services. Complete rapid prototyping service bureau listings.
• How Stereolithography (3-D Layering) Works from HowStuffWorks.com
• Manufacturing Engineering Centre (MEC), Cardiff University, UK
• Rapid Prototyping and Stereolithography animation - Animation demonstrates stereolithography and the actions of an SL machine.