What is SLA 3D Printing?

SLA 3D printing is a type of resin 3D printing, which you may have come across in your search for 3D printers. If you have ever seen a video of something solid being created out of the liquid (like magic), you’ve already seen an SLA 3D printer in action.

What is SLA?

SLA was actually the first 3D printing process to ever exist. It was invented by Charles W. Hull in 1984 as a way to create 3D parts “rapidly, reliably, accurately, and economically”. If you’re interested in the advantages of 3D printing over traditional manufacturing, check out the article on how 3D printing is revolutionizing manufacturing.

In a nutshell, SLA is a 3D printing process that uses high-frequency light to solidify/cure a liquid photopolymer (resin) in layers to create a solid object.

Video from the Cracow University of Technology

SLA is an abbreviation for stereolithography. To most of us, stereolithography sounds like a jumble of meaningless words, so let’s break it down.

What is the Definition of Stereolightography?

From a google search on the definition of ‘stereo’, I found that it comes from the Greek word ‘stereos’, meaning solid. We now use stereo as a prefix (stereo-something) to anything that relates to solid 3D forms.

Lithography is an old method of mass 2D printing invented in the late 18th century. ‘Litho’ in Greek means stone, and ‘graphy’ means writing. These two words describe lithography pretty well.

Basically, a limestone slab combined with oil is used to create multiple copies of drawings. The key here is using oil or some other liquid material making a 2D impression.

How does this all come together? Let’s put ‘stereo-‘ before lithography, and now we have a word that describes using a liquid material to make a 3D shape.

What’s a Photopolymer?

A photopolymer is a plastic that hardens when it’s exposed to light. ‘Photo’ is the Greek word for light (we’ll be speaking with the locals in Greece in no time), and polymer usually refers to plastics in 3D printing, since all plastics are polymers.

Therefore, the word photopolymer literally translates to ‘light-plastic’. When using SLA, we just call these resins.

Some types of resins include:

• Standard resin
• Clear resin
• Castable resin (for creating molds)
• Tough resin

How Does SLA Work?

How can a light harden a liquid plastic? And how can we direct that light properly? These are the questions I had when I first learned about SLA.

There are three essential parts of an SLA 3D printer. These are the build platform, a transparent resin tank, and an ultraviolet light system. Most SLA 3D printers have the build platform above the resin tank and the light system below.

The build platform is lowered into a pool of liquid resin (photopolymer), leaving a tiny space between the platform and the bottom of the tank. This space is where the first layer of the 3D model will be made.

To begin fabricating the 3D model, the light system uses a combination of mirrors to produce a UV laser aims at selective locations of the bottom of the resin tank to harden the resin. The hardened resin sticks to the build platform as it is raised slightly to create space for another layer.

Some SLA 3D printers use an LED UV light screen instead, which is much more effective and provides shorter curing times, by doing a whole layer at a time. One of these is the Longer3D Orange 30.

The next layer hardens and combines with the previous, creating a smooth structure where layers are indiscernible, unlike results from most FDM 3D printers.

After completing the print, the model should be washed with a solvent to clean any wet resin off of its surface.

Pros

• High-quality 3D models
• Strong pattern-like structures
• Fast process; print time depends on the height of the model with LED SLA 3D printers
• Many applications
• Unused resin can be saved
• Looks really cool

Cons

• Dealing with resin, which is
  • overwhelmingly smelly,
  • prone to spilling,
  • cures in sunlight, and
  • requires gloves when being handled.
• Removing the model and draining excess resin is time-consuming
• Completed models need to be washed, cured, and dried
• Not easy to use
• Costly resin and machines

Applications of SLA 3D Printing

The high quality of SLA 3D printing makes it very effective at creating figurines and jewelry. Castable resins, also work great for making detailed metal jewelry.

SLA 3D printing is also used in rapid prototyping and product design because it can create high-quality 3D models of irregular shapes. Functional prototypes or tools can also be made with SLA because of its accuracy.

Injection-molded parts can also be made quickly and inexpensively for early prototypes, lowering the barrier to entry of new products for inventors/manufacturers.

SLA is used in medical applications as well, to create models of patients’ anatomical areas. This can aid in designing and preparing for medical implants.

If you’re a designer, engineer, jeweler, or in the medical field, SLA could be a great investment to improve your efficiency. SLA aids in presenting detailed ideas for others to understand, which can help in persuading clients or educating.

If you’re a hobbyist who wants a higher quality 3D printer than what FDM provides, and you’re willing to spend more money and deal with resin, then SLA could also be for you.