Design Guide: SLA 3D Printing

Stereolithography (SLA) is a mature and versatile additive manufacturing (AM) process that is capable of producing highly accurate isotropic parts with superior finish and excellent design feature resolution. These qualities make it ideal for creating intricate prototypes, cosmetic parts, concept model and master patterns.

SLA 3d printing design guide

To help achieve better part quality and a successful print, it is important that your 3D model meets a number of recommendations. This article offers a comprehensive guide to the best practices for SLA 3D printing. Discover the characteristics and capabilities of SLA, design guidelines, summary of best design practices and cost reduction tips.

SLA 3D Printing Process

SLA is one of the most widely used vat photopolymerization technologies. It uses an ultraviolet (UV) laser beam light source to selectively cure photosensitive liquid resins layer by layer into solid shapes.

Disadvantages of the SLA Process

Shrinkage and Curling: During the curing process, the SLA resin shrinks slightly due to exposure to the printer’s light source. When the shrinkage is considerable, large internal stresses develop between the new layer and the previously solidified material, which results in the part curling.
Support Structures: Support structures are always required, which can limit design freedom. Support structures are printed in the same material as the part and must be manually removed after printing.

Characteristics of SLA 3D Printing

Maximum Build Size	800 x 800 x 550 mm
Resolution	±0.2mm
Dimensional Accuracy	±0.2% (with a lower limit of ±0.127 mm)
Layer Height	50-100 um
Materials	Generic, transparent, high performance, rigid and high temp resins
Surface Structure	Smooth structure
Support	Required

SLA Design Guidelines

Unsupported Walls

With SLA, unsupported walls (walls connected to the rest of the print on less than two sides) are at a high risk of warping or breaking off. To avoid this, such walls should be at least 0.8m-1.0mm thick and be designed with filleted bases to reduce stress concentrations along the joint.

Designing unsupported walls for 3D printing

Supported Walls

Supported walls (walls connected to the print on at least two sides) are at much lower risk of warping. To ensure successful print, they should be at least 0.5mm thick.

Designing thickness for supported walls

Overhangs

Overhanging features — extended or at an angle — in SLA designs always require support. Supports are the cornerstone of a successful SLA print. If it is necessary to print without supports, overhangs must be kept less than 1.0mm in length and at least 19° from level, but even then, there is a risk of warpage. It is, therefore, not recommended.

Designing overhang angles for 3D printing

Holes

In SLA printing, holes that are too small may seal before the polymer is fully cured. To avoid this, holes should be at least 0.8mm in diameter.

Designing hole diameters in 3D printing

Hollow Parts

For hollow designs, add drainage holes to the lowest area of your model to prevent uncured resin from accumulating and becoming trapped inside the finished part. This can lead to pressure imbalances within the hollow chamber and cause cracks, holes and even explosions. Drainage holes should be at least 3.5mm in diameter. To reduce the risk of print failure, keep the walls of hollow prints at least 2mm thick.

Slots

What size to design a slot is determined by the depth or thickness of the wall. We recommend a minimum slot size of 0.5mm, but the larger, the better — especially as wall thickness or depth increases.

Designing slots in 3D printing designs

Pins

Pins are tall thin features with a circular cross-sectional area. The diameter of a pin can be designed to 0.8mm, but even then, risk breaking. The minimum reliable pin diameter is 1mm.

Designing pin diameter and height in 3D printing designs

Mating Parts

For SLA parts, adequate clearances must be designed between mating parts to prevent the assembly from turning into a single solid unit. To avoid this, models must be designed with a minimum clearance of 0.5mm.

How to design mating parts in 3D printing

Embossed Details

Embossed features must be designed using a minimum height, otherwise, it will not appear visible. It should be designed with a height of at least 0.3mm. To ensure embossed details come out nicely, make them larger than the indicated.

Engraved Details

If too small, such features, which are recessed into the model, are at risk closing up if not designed. Engraved details should be at least 0.5mm wide and 0.5mm deep.

How to design engraved text and details

Summary of SLA Best Design Practices

Unsupported Walls	At least 0.8-1.0mm thick
Supported Walls	At least 0.5mm thick
Overhangs	Less than 1.0mm in length and at least 19° from level
Holes	Greater than of 0.8mm in diameter
Hollow Parts	Add drainage holes with minimum diameter of 3.5mm
Slots	At least 0.5mm (depends on wall thickness and depth)
Pins	At least 1mm (depends on pin height)
Mating Parts	At least 0.5mm apart
Embossed Details	Minimum embossed height of 0.3mm
Engraved Details	Minimum engraved height of 0.5mm and width of 0.5mm

SLA Cost Reduction Tips

In this section, we outline some simple tips and tricks to help reduce the overall cost of your SLA part. In 3D printing, there are three main drivers of cost to bear in mind: material, printing time, and post processing time.

Reduce Support Demand — With SLA, removing support structures can be tricky and time-consuming, which increases the amount of post-processing involved. Minimising the number of support needed for your design can help save time and money.
Hollow Out Your Parts — By default, SLA will print completely solid components. Hollowing the model significantly reduces the amount of resin required and print time, which reduces overall manufacturing costs.
Use Scaling to Your Advantage — Bigger parts require more material and more print time. If you are manufacturing an SLA part for proof of concept, scale down your model. This will allow you to get through the prototyping phase faster and cheaper than a full-scale design.