SLA 3D Printing Service

What is SLA 3D printing?

Stereolithography (SLA) 3D printing is a process involving VAT photopolymerisation - which is where a liquid resin (photopolymer) turns solid when hit with UV light from a laser. It is the second most common type of additive manufacturing after FDM 3D printing, and is sometimes known more generally as 'resin printing'.

To create parts, a metal build platform (build plate) is lowered into a resin tank with a transparent bottom, and covered with any one of a number of SLA resins. A low powered laser is then shone onto the material, in a precisely controlled pattern that matches the cross-section of the part being printed. The build platform then moves up a little, allowing more liquid to flow onto the (now solid) layer above, and the process repeats, so that a fully solid part builds up in layers. SLA 3D printing is known for its exceptional quality prints, high resolution, smooth surfaces, and ability to capture very fine details.

Although similar, SLA should be not confused with Digital Light Processing (DLP). DLP printing uses an LCD screen as its light source, and sometimes even hardens parts using light in the visible part of the electromagnetic spectrum. Digital Light Processing has its advantages, but parts often have lower detail, due to the fixed pixels on the screen translating to fixed voxel sizes in 3D. Both types of 3D printing excel at producing complex geometries and high resolution functional parts, however.

Advantages of SLA 3D printing

As SLA machines are able to produce printed parts with a smooth surface finish and complex features, resin 3D printing is one of the few additive manufacturing techniques with print quality that can match traditional manufacturing processes such as injection moulding. This makes it perfect for when high quality parts and prototypes are needed for client presentations, and to demonstrate how a product will look when ready for mass production.

Complex geometries are also achievable, including custom parts with small or intricate features that would be impossible to manufacture using any other methods. In particular, resin 3D printing excels at producing complex internal channels for fluid flow, which can be very difficult to make using traditional tools.

SLA printing works with a wide variety of different materials - each with different mechanical properties. Using durable and tough photopolymers, we can produce functional parts with better accuracy and detail than on a selective laser sintering (SLS) or Fused Deposition Modelling (FDM) 3D printer. It is also the only technology that can produce high transparency clear parts.

Disadvantages of SLA 3D printing

The SLA printing process is inherently more complex than some other additive manufacturing techniques. Once the SLA printer has finished, each printed part must be washed thoroughly in Isopropyl Alcohol by a Printpool engineer, and then 'post-cured' using a UV oven, to fully solidify the material ready for use. In addition, the materials used by a resin 3D printer are irritants before they have been cured by the laser beam during the additive process. This can increase the lead time, and makes SLA parts more expensive than they otherwise would be, due to the extra steps and precautions we must take to stay safe.

Parts printed from SLA materials generally have lower temperature resistance, and poorer thermal properties than other 3D printer materials. The print speed is also slower in some case, meaning they can be less useful for rapid prototyping than other options. This does depend on the layer height chosen, and how full the build volume is however.

Designing for the resin 3D printing process

Designing for the stereolithography process is complicated. Unlike with some other types of 3D printing, the support structures underneath an SLA printed part are not just designed to resist gravity, but also other forces generated during the print process. At Printpool we use low-force stereolithography, which reduces the effect, but without some expert knowledge its hard to know exactly which parts of your design will need a support structure underneath, making designing for SLA difficult.

We advise trying to remove sharp edges from your parts, as these can encourage stress concentrations to form, which will weaker your final 3D print. Also, no area of the design should be thinner than 0.5mm, as this may not build properly. We have further, more detailed advice in our resources pages.

The history of SLA 3D printing

Many people don't realise that SLA 3D printing was actually the first type of additive manufacturing technology to be developed. On March 11, 1986, Chuck Hull first patented the 3D printing technology, with his “Apparatus for Production of Three-Dimensional Objects by Stereolithography”. He had the idea after using UV light to harden tabletop coatings three years earlier. 3D systems, a very well known 3D printing company, developed SLA 3D printing for many years under Hull's leadership, before a number of other players entered the market. Most notably, Formlabs launched a series of excellent high resolution desktop SLA printers, that offered huge cost savings over the more expensive industrial SLA offerings from 3D systems. This led to a surge in new resin desktop printers from other manufacturers.

The rise of good quality cad software has also made SLA 3D printing more useful, as before this point the 3D printing wasn't used in rapid prototyping workflows, as there was no data available from which to print! Advances in chemical engineering have increased the number of materials available, and now there are flexible, durable, stiff, glass-filled and castable resins on the market, that can be used for high resolution 3D printing of just about anything.
Other types of VAT photopolymerisation 3D printers have appeared over the years, mostly differentiated from SLA by a different resin vat, light source, printing volume, and/or chemistry. All offer high resolution, require support structures, and require significant post-processing, contrasting against other technologies like selective laser sintering.