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Design Guide

Due to the nature of the process, SLA is a very easy process to design for. The primary difficulty lies in avoiding large, thin sections which tend to warp while curing. The main concern for designers making parts for SLA is to consider the eventual process. If so, the part will eventually be mass produced, hence the part should follow the design guide for the eventual high production volume process.

From Accelerated Technologies:

Trapped volumes or "traps" is a term coined for the SLA process. A trapped volume is created by geometry that cups or holds the liquid resin. Consider a coffee mug sitting on your desk full of coffee, this mug creates a trapped volume. If inverted, this same mug no longer has a "trap". Due to material properties of the SLA resins, a trapped volume creates variances in the resin height. This deviation is likely to result in an aborted build or a poor quality prototype.

To overcome a trapped volume, there are techniques available, but these can impact build times and quality.

• Allow for significant dwell time between layers. This can result in build times of 200% to 300% of the normal build style. Additionally, this technique is dependent on both the size of the trap and the type of resin. The epoxy resins are very sensitive to trapped volumes and will not allow them to be built if the trap is greater than 2.0 in³.

• Invert the part to eliminate the trapped volume. This is the most beneficial way to deal with a "trap". However, support structure removal must be considered. If a typical injection molded housing is considered, the internal area of the part will contain a significant amount of detail (ribs, bosses, etc.). When the supports are removed from this complex geometry, there is the potential to affect quality.

• Change the geometry. The part can be built in sections or it can be fabricated with a hole in the bottom. This procedure will eliminate the trap, but once again, it can affect quality due to the bonding of parts.