Stereolithography Apparatus (SLA)

What is SLA?Stereolithography Apparatus (SLA) is a liquid-based process which builds parts directly from CAD software.SLA uses a low-power laser to harden photo-sensitive resin and achieve polymerization.A hopper full of the resin lies under a laser which uses its beam to harden the part in layers a Min. of 0.001 and up to 150lbs. Part weight.Parts can reach a Max. size of 20x20x23.

Click here to view a diagram of a RP Stereolithography Apparatus (SLA).

SLAClick here to view an SLA machine along with an introduction.

Companies3D Systems Corp. in Valencia, CA.

Other vendors are in the market but do not have significant market share.

The ProcessThe process begins with a 3D CAD file. The file is digitally sliced into a series of parallel horizontal cross-sections which are then provided to a StereoLithography Apparatus (SLA) one at a time. A laser traces the cross-section onto a bath of photopolymer resin which solidifies the cross-section. The part is lowered a layer thickness into the bath and additional resin is swept onto the surface. The laser then solidifies the next cross-section. This process is repeated until the part is complete. Most parts are completed in a matter of hours, thereby defined as a "Rapid Prototype".

The Process contThe process is still in use however, the software has changed dramatically.The technology first appeared on UNIX-Systems and MSDOS.Now, Windows NT, 3D Lightyear, and Buildstation are compatible.

The Process contA platform is lowered into the resin (via an elevator system), such that the surface of the platform is a layer-thickness below the surface of the resin. The laser beam then traces the boundaries and fills in a two-dimensional cross section of the model, solidifying the resin wherever it touches. Once a layer is complete, the platform descends a layer thickness, resin flows over the first layer, and the next layer is built. This process continues until the model is complete.

The Process contOnce the model is complete, the platform rises out of the vat and the excess resin is drained. The model is then removed from the platform, washed of excess resin, and then placed in a UV oven for a final curing. The model is then finished by smoothing the "stair-steps."

AdvantagesProbably the most accurate functional prototyping on the market.Smooth surface finish, high dimensional tolerance, and finely detailed features (thin-walls, sharp corners, etc)Used in: Investment Casting, Wind Tunnels, and Injection Molding as tooling Resins can be custom engineered to meet different needs: higher-temps, speed, finish

CostCost of materials: the resin costs as much as $600-$800 per gallon. (For a 20x20x23 cube thats 39.8 gallons! $27,860)Post processing Requirements: Careful practices are required to work with the resins.Frameworks must be removed from the finished part.Alcohol baths then Ultraviolet ovens are used to clean and cure the parts.

DevelopmentThe Rapid Prototyping Stereolithography (SLA) process was developed by 3D Systems of Valencia, California, USA, founded in 1986. A vat of photosensitive resin contains a vertically moving platform. The part under construction is supported by the platform that moves downward by a layer thickness (typically about 0.1 mm / 0.004 inches) for each layer. A laser beam traces out the shape of each layer and hardens the photosensitive resin.

Development cont.The SLA rapid prototyping process was the first entry into the rapid prototyping field during the 1980s and continues to be the most widely used technology.

HighlightsFirst Rapid Prototyping technique.Inexpensive compared to other techniques.Uses a light-sensitive liquid polymer.Requires post-curing.Long-term curing can lead to warping.Parts are quite brittle and have a tacky surface.No milling steps so z accuracy suffers.Support structures are typically required.Simple process: No milling or masking stepsUncured material is toxic.

Materials:The laser can be either: HeCd or Solid State and can range in power from 12 800mWThe original resin was acrylate based, then epoxy-based: ACES (Acrylic Clear Epoxy System).The resin can be modified to improve different characteristics; depending on the users needs.

Materials cont :SLA Somos 7120 - A high speed general use resin that is heat and humidty resistant. For more information on this material please read the material technical data sheet. Somos 9120 - A robust accurate resin for functional parts. For more information on this material please read the material technical data sheet. Somos 9920 - A durable resin whose properties mimic polypropylene. Offers superior chemical resistance, fatigue properties, and strong memory retention. For more information on this material please read the material technical data sheet. Somos 10120 WaterClear - A general purpose resin with mid range mechanical properties. Transparent parts are possible if finished properly. Note that finishing for transparent parts must be special ordered. For more information on this material please read the material technical data sheet.

Materials cont :Somos 11120 WaterShed - Produces strong, tough, water-resistant parts. Many of its mechanical properties mimic that of ABS plastic. For more information on this material please read the material technical data sheet. Somos 14120 White - A low viscosity liquid photopolymer that produces strong, tough, water-resistant parts. For more information on this material please read the material technical data sheet. Somos ProtoTool - ProtoTool is a high density material that transcends currently available stereolithography resins by offering superior modulus and temperature resistance. For more information on this material please read the material technical data sheet.

Models Click here to view product examples from AcuCast.com.Click on Photo 009 to view models from their StereoLithography Apparatus (SLA).

REFERENCES http://www.acucast.com/rapid_prototyping.htmhttp://www.milparts.net/sla.htmlhttp://rpdrc.ic.polyu.edu.hk/old_files/sla_introduction.htm