Design Guide: Stereolithography (SLA)

Last updated: November 8th, 2018


Overview

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Stereolithography (also known as SLA or SL for short) is an additive manufacturing process that creates models through photopolymerization, in which an ultraviolet light causes chains of molecules to link together, solidifying them into hardened resin layer by layer. Structural supports will be created during the pre-build setup process, and manually removed after the print is completed. The parts are then washed in a solvent solution to remove uncured resin. Then the parts will receive a final post cure in a UV light oven.

SLA generally has a smoother surface finish than other 3D processes, such as FDM, because the liquid resin is solidified by a laser rather than melting and then cooling a plastic filament. This gives the parts a relatively smooth, almost glassy finish.

This guide covers specific details on how to avoid unintended failures when designing for SLA. To avoid these failures, be sure to meet the minimum tolerances discussed, or design features as described to eliminate the possibility of certain failures from occurring.


General Tolerances

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If a drawing or specification sheet has not been provided by the customer, Xometry will manufacture the product from the model to the specifications listed below:

Tolerances for standard resolution:

  • X/Y planes: +/- .005” for the first inch, plus +/- .002” for every inch thereafter
  • Z plane: +/- .010” for the first inch, plus +/- .002” for every inch thereafter
  • Minimum linear feature size: under .030” are at risk and under .020” will not build
  • Minimum radial feature size: .035"

Tolerances for high resolution:

  • X/Y planes: +/- .005” for the first inch, plus +/- .002” for every inch thereafter
  • Z plane: +/- .010” for the first inch, plus +/- .002” for every inch thereafter
  • Minimum linear feature size: under .020” are at risk and under .010” will not build
  • Minimum radial feature size: .030"

Please see our Manufacturing Standards for more information.


Build Orientation

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Build orientation is determined by Xometry with the primary goal of optimizing prominent features or details while minimizing build height. Adding additional supports can often be justified if it helps to effectively reduces the chance of failures during the build. Support structure is made of the same material as the part, and is generated to be easily removed by hand with minimal post processing after the build is complete.


Supports

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Wall Thickness

While SLA can image walls less than 0.02” (0.5mm), we recommend a minimum wall thickness of 0.039” (1mm) for the most repeatable results. This will minimize chances of damaging the parts during post processing or shipping.

 

Holes & Gaps

Xometry recommends holes & gaps for SLA parts be designed with a diameter greater than 0.03” (0.75mm) to retain shape & ensure they do not close off during printing. The minimum diameter may increase with channels or gaps greater than 0.472” (12mm) long.

 

Embossing Details

Text and other embossed details are easy to achieve with SLA due to the precision and finish of the process. We recommend that any protruding text must maintain at least 0.012” (0.3mm) in height and 0.016” (0.4mm) width. For very fine text details Xometry recommends using the high resolution option if available.

 

Engraving Details

These features must be large enough to avoid fusing together during printing, so Xometry recommends a thickness for engraved texts of 0.02” (0.5mm) wide and 0.016” (0.4mm) deep.


Features

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Fillets

Fillets are a design feature that you can implement in order to reinforce fragile features and should be utilized generously. Fillets greatly increase structural rigidity, and should be used in the bases of any unsupported walls.

 

Overhangs

Overhangs are an area of concern for many 3D printing processes, these are of relatively little concern when it comes to SLA due to the presence of support structures.

 

Drafts

Drafting extrusions outwards is another way to drastically increase their strength due to the resulting increase in area at the base. This can also be useful for embossed text and tab features.

 

Long, Broad Parts

Parts that are overly long and broad are subject to uneven curing, which can lead to warping. They are also more susceptible to distortion caused by heat and moisture which can happen during post processing or shipping. This can be prevented by creating cut-outs wherever possible to reduce heat generated, and by applying ribs to hold and prevent warping.


Finishes

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Xometry offers the following types of finishes for SLA:

  • Standard: Parts are cleaned, stripped of supports, and may be lightly sanded around the supported area. Supported areas may show small grid-like dots where structure was required.
  • Matte: Parts are cleaned, stripped of supports, and then either wet or dry grit blasted to give a consistent matte finish across the part. Supported areas may show small grid-like dots where structure was required.
  • Additional Finishes: Xometry provides a variety of additional SLA finishing options, including but not limited to: sanding, painting, post thermal processing, and plating to meet your needs.

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