Stereolithography (SLA) 3D Printing Design Guidelines

Stereolithography, otherwise known as SLA, is a 3D printing method which uses a laser to cure photopolymer resin layer by layer. SLA is famously known for producing smooth parts with extreme fine detail and high accuracy levels. Stereolithography uses a vat of liquid UV-curable photopolymer resin and also includes a UV laser to build 3D parts layer by layer. As each layer progresses, the laser beam carefully traces a part of the cross-section pattern on the surface of the liquid resin. UV laser light cures and solidifies patterns once it’s been exposed. Once a pattern has been traced, the elevator platform descends a single layer thickness. The thickness is usually 0.05 mm-0.15 mm (0.002 in.-0.006i= in.). After, a fresh material is re-coated as the resin-filled blade sweeps across the part section.

Through following these Stereolithography (SLA) 3D printing design guidelines your parts should come out as intended, but for additional questions and complex problems be sure to reach out to a member of our engineering team.

Feature	Description
Supported Walls	Walls attached to structures on a minimum of two sides  Smaller chance of the product warping  Suggested design = 0.4 mm  thick
Unsupported Walls	Walls attached to the print on fewer than two side  Walls have higher chance of warping/detaching from the print  0.6 mm thickness required
Overhangs	Overhangs only occur when your model is printed without substantial internal/external support structures
Engraved Details (Including text)	Details must be 0.4 mm wide and 0.4 mm thick
Embossed Details (Including text)	Required height of 0.1 mm above surface  This ensures details become visible
Horizontal Bridges	Wider bridges must be kept shorter (21 mm) than thin bridges
Holes	X, Y, Z axis can close off during printing  To prevent this, have hole diameter less than 0.5 mm
Connections/Moving Parts	0.5 space separating moving parts  0.2 mm space for assembly connections  0.1 mm space provides close knitted fit
Minimum Features	Recommended minimum = 0.8 mm

Compared to FDM, SLA can reach a higher resolution as it uses a laser to solidify the material. When printing SLA in the horizontal/XY-direction, the laser spot and size can range from 30-140 microns. Note that the smallest feature size can’t be less than what the laser spot size is.

 

 

 

SLA machines have the capability to print a solid and dense 3D printed model. Hollowing the model can reduce the  required amount of material and it can also reduce the print time significantly. When printing, ensure the walls located on the hollowed print are a minimum of 2 mm thick. Failure becomes less likely during printing this way. Drainage holes are necessary when printing a hollow part to prevent uncured resin from getting trapped inside the final part.  Pressure within the unsecured resin creates imbalances within the hollow chamber and will cause ‘cupping’ Cracks and holes spread throughout the part and will cause ultimate failure. Part explosion is also a possibility if not corrected/ The minimum requirement of drain holes are 3.5 mm in diameter, and a minimum of one hole must be involved per hollow section.

Accura Xtreme

 

 

 

 

Accura ClearVue

 

 

 

Accura Bluestone

 

 

 

 

  Accura 25

 

 

 

 

 

Accura 55

 

 

 

 

 

Somos Watershed 11122

 

 

Print Volume
Take into consideration that SLA printers have a significantly smaller build volume compared to FDM printers (besides commercial machines). The build volume when using  The traditional SLA desktop printer, Formlabs Form 2, have a build volume of 145 mm x 145 mm x 175 mm. Meanwhile, the common FDM desktop printer, the Ultimaker 2+, offers a build volume of 223 mm x 223 mm x 205 mm. Another thing to keep in mind when printing with SLA is that if the print geometries exceed the printer capacity, they can be printed in smaller sections and then be assembled. Best practices when bonding SLA printed parts together is a 5-30 minute epoxy.

Material Properties
If you’re looking to produce functional parts that are subjected to loads, it’s best to stray away from SLA parts. SLA resins tend to be brittle and not as reliable compared to other 3D materials. Over a certain amount of time, these SLA parts tend to experience creep. Curing in a UV chamber is needed for most SLA printed parts.

SLA vs. FDM cost
Using SLA resin is higher in cost when comparing it to FDM filament. However, SLA holds the potential to print details with more complex details, while other 3D printing options, don’t hold that title.

Resin Type	Description	Application
Standard Resin	Used for generic printing  High detailed finish  Resolution less than 25 microns	Used to achieve high   detail prototyping  Works with models that     are not functional
Engineering Resins	Resin manufacturers have been simulating engineering plastics  ABS/polypropylene-like/flexible/high temperature resins  Resins have stronger engineering properties	Durable  Flexible  Used in high temperature applications
Dental Resins	Often used for general orthodontics  Class 1/2 bio-compatible resin released to allow SLA technology to create surgical guides  Highly precise and durable	Dental applications
Castable	Specialized in fine detail  Delicate feature printing  Designed for direct investment casting  Minimum feature size is 0.2 mm	Jewllery  Fine detail models  Investment casting applications

 

SLA has a wide range of surfaces finished which are determined by cost and application. Details with features as small as 0.3 mm are possible when using SLA printers. However one of the biggest issues faced when using an SLA printer is that prints are made extremely small, therefore most prints should be put on an angle. Support structures are necessary when SLA printing

Process	Description	Pros	Cons
Basic Support Removal	Support structure cut from the model  Results in bumpy surface	100% control of finish  Drilling achieves vertical hole diameter accuracy  Suitable for all SLA resins  High speed  Moderate tolerance	Not appealing  Required amount of skills needed to get a clean finish
Sanded Support Nibs	Made for flat surfaces	Surface accuracy  Matte finishes hide imperfections  Suitable for all SLA resins  High speed	Uneven surfaces  Not aesthetically  pleasing
Wet Sanded	Smoothest finishes  Build lines require sanding  Finish is cheap using high grade sandpaper	Smooth finish  Useful for complex geometries  Ideal surface preparation for   painting	Accuracy is low on supported side  Mixing sand and water could lead to spots on your print
Mineral Oil Finish	Process relates to wet sanded finish, except oil layer is added after sanding process  Mineral oil hides white spots on finsih  Finish is made best for mechanical parts	Semi transparent finish for clear resins  Suitable for all SLA resins	Paint doesn’t adapt to  finish surface properly
Spray Paint (clear UV protective acrylic)	Spray painting makes layer lines invisible  Varnish protects the model from   yellowing and post curing by   limiting UV exposure	Clear finish  Offers UV protection  Suitable for all SLA   resins	‘Orange peel effect’   on surfaces  Increases dimensions  Not made for moving   parts
Polished-Clear Transparent Finish	Grit levels of sandpaper are used to sand the surface  Polishing compound is then sued to polish the surface  This leaves the most clear surface   possible, but can be time   consuming  Finish is made for simple shapes	Finish is as clear as glass  Smooth surface	Intense labour involved  Not attainable without complex geometries  Only suitable for clear resin