3D Systems: SLA®
SLA is a process invented by Charles Hull and developed by 3D Systems of Valencia, CA. The acronym SLA (stereolithography apparatus) comes from the name of the company's first machine, the SLA-1, introduced in 1988 and a registered trademark of 3D Systems (www.3Dsystems.com). SLA is the most common rapid prototyping system in use today. Numerous service bureaus offer SLA part production, competing on price, speed of delivery, and ease of ordering. Other companies, such as Sony, now also offer similar UV laser and photopolymer-based RP in their Solid Creation System (SCS®) line of RP machines (www.sonypt.com).
In stereolithography, a UV laser is used to trace the surface of a photoreactive polymer that hardens to produce a solid object based on a three-dimensional computer file, usually.STL (stereolithography) format. The stereolithography process builds the object in layers, as if you were building an object of stacked pieces of paper. A base on an elevator starts at the top of a tank of plastic and drops a small amount every time a new layer is laid down, and this "grows" the part. Support structures are required to support cantilevered areas of the part. These vertical supports are removed during finishing. When completed, the part is ready to remove from the tank. The part is then placed in a postcuring oven, where it is cured under a UV lamp to harden any uncured polymer. The part will have a characteristic stair-step finish equal to the per-slice resolution of the stereolithography machine. This stair-step finish is usually removed by sandblasting the parts, giving the parts a translucent frosted finish. Stereolithography machines require a controlled and vented shop environment.
Stereolithography machines are limited in the size of parts produced by the width and depth of the liquid material vat. Larger parts may be produced by making a large part (such as large instrument housings) in smaller sections, bonding the sections together with stereolithography resin.
Stereolithography machines are expensive pieces of capital equipment and require special setup and venting, as well as trained operators. Some larger corporations with specialized or high-volume prototype requirements have chosen to bring stereolithography in-house. Most start-ups, small companies, and consulting offices find using a service bureau vendor to get stereolithography parts to be quite convenient and cost-effective.
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