How Stereolithography Works: A 3d Printing Process

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Stereolithography, often called SLA, is one of the original 3D printing technologies and is still one of the most accurate methods used today. Even though it was developed decades ago, it remains a top choice for engineers, designers, and manufacturers because of its precision, smooth surface quality, and ability to create detailed shapes that are hard to produce using other methods.
If you want to understand how one of the most reliable forms of 3D Printing For Product Design works, this guide explains everything in a simple and easy-to-follow way. We’ll cover what stereolithography is, how it works step by step, what materials it uses, and why many industries depend on it.

What Is Stereolithography?
Stereolithography is an additive manufacturing process — this means it builds objects layer by layer using liquid resin. Instead of cutting away material like machining or filling a mold like injection molding, SLA forms solid shapes by shining UV light onto a special liquid called photopolymer resin, which reacts to light and becomes solid.
The word “stereo” means solid, and “lithos” ...
... means stone, which is a simple way of explaining the idea: turning liquid into a solid using light.
This precise curing process is why SLA is extremely popular in fields like medical, dental, jewelry, engineering, and product development.

The Science Behind It: Photopolymerization
The key to understanding SLA is knowing how photopolymerization works. This is a chemical reaction that happens when certain resins come in contact with UV light.
Inside the liquid resin are ingredients known as photoinitiators. When UV light hits them, they activate and quickly change the resin from liquid to solid. This reaction is fast and controlled, allowing the printer to create very thin layers with fine detail.
Because each layer can be as thin as 25 microns, SLA prints look cleaner and smoother than many other 3D printing methods.

Main Components of an SLA 3D Printer
Even though different brands and models look different from the outside, most SLA printers share the same set of essential parts:
1. Resin Tank
A clear container filled with liquid photopolymer resin. Its bottom surface allows UV light to pass through.
2. Build Platform
This is where your print grows layer by layer. The platform moves up or down depending on the printer type.
3. UV Light Source
The printer uses one of these light systems:

a UV laser

a digital projector

a UV LED light with an LCD mask

This light cures the resin to form solid layers.
4. Galvo Mirrors (in Laser SLA)
Tiny mirrors that move very fast to guide the laser beam across the resin surface.
5. Resin Mixer or Wiper
Some printers have a mechanism to keep the resin evenly spread and bubble-free.
6. Control Software
The software slices the 3D model into layers and guides the entire printing process.

How Stereolithography Works (Step-by-Step)
Now let’s walk through the entire SLA process in an easy-to-understand way.

Step 1: Preparing the 3D Model
Everything begins with a 3D model created using CAD software. Before printing:

the model is checked for errors

support structures are added

the model is sliced into thin layers

The slicing software tells the printer exactly where to shine the light for each layer.

Step 2: Filling the Resin Tank
The resin tank is filled with liquid photopolymer resin. There are many types of resin available depending on the project needs, such as:

standard resin for general use

tough resin for stronger parts

flexible resin

clear resin

heat-resistant resin

medical and dental resins

The wide choice of materials is one reason SLA plays a big role in 3D Printing For Product Design.

Step 3: Printing the First Layer
The build platform lowers into the resin tank, leaving just enough space for the first thin layer.
The UV light shines on the resin in the exact shape of the first layer, curing and solidifying it.
This first layer gets extra curing time to ensure it sticks properly to the platform.

Step 4: Curing Layer by Layer
Once the first layer is done:

the platform moves

fresh resin flows beneath or above the printed area

the light cures the next layer

This process repeats over and over, building the object from the bottom up. The printer continues this pattern until the full 3D shape is complete. Smaller prints take less time, while larger or more complex models may take several hours.

Step 5: Removing the Print
After printing finishes, the platform lifts the object out of the resin tank. The part will still be wet with uncured resin, so it must be handled carefully.

Step 6: Cleaning the Part
The printed part is washed in isopropyl alcohol (IPA) or a resin cleaner solution.
This step removes any remaining uncured resin on the surface.
There are automated cleaning stations available for consistent results.

Step 7: Post-Curing
After cleaning, the part goes through post-curing, which involves shining UV light at it in a controlled chamber. This step:

strengthens the part

improves accuracy

enhances heat resistance

gives the part its final mechanical properties

Skipping post-curing can lead to weaker or slightly flexible parts.

Step 8: Removing Supports & Finishing
Once cured, the support structures are removed. Depending on the project, finishing steps may follow:

sanding rough spots

painting

polishing

coating

assembling multiple printed pieces

Because SLA parts already have a smooth surface, these steps are usually quick and easy.

Types of SLA 3D Printers
There are three major types of stereolithography systems:
1. Laser SLA
Uses a laser beam to draw each layer.
Good for: extremely detailed and precise prints
Downside: slower for large models
2. DLP (Digital Light Processing)
Uses a projector to cure an entire layer at once.
Good for: fast printing and batch production
Downside: resolution depends on projector pixel size
3. MSLA (Masked Stereolithography)
Uses an LCD screen to control UV light exposure.
Good for: speed and affordability
Downside: LCD screens wear out over time
Despite their differences, all three types produce high-quality prints used in professional projects.

Why Stereolithography Is So Popular
SLA continues to be widely used because of several strong advantages:
1. Excellent Detail and Accuracy
Great for small, complex shapes and parts that require tight tolerances.
2. Smooth Surface Finish
Prints look professional and clean without heavy sanding.
3. Wide Range of Materials
Resins can match the properties of injected plastics, rubber-like materials, or even clear acrylic.
4. Ideal for Complex Designs
Since the resin supports the model during curing, SLA can print shapes that would be impossible with other manufacturing methods.
5. Consistent and Reliable Results
Perfect for both prototypes and small production runs.

Limitations of Stereolithography
Even though SLA is powerful, it does have a few limitations:
1. Resin Costs More
Compared to standard FDM filament, resin is pricier.
2. Supports Are Required
Most parts need supports during printing.
3. Some Resins Are Brittle
Unless you use tough or flexible resin, standard SLA parts can be less durable.
4. Post-Processing Adds Time
Cleaning and curing steps are necessary.
5. UV Exposure
SLA prints may weaken if exposed to sunlight for long periods unless coated.

Industries That Use SLA 3D Printing
SLA is used across many sectors because of its accuracy and material versatility:
1. Product Design
Perfect for early-stage prototypes, functional test models, and visual mockups.
2. Medical & Dental
Ideal for dental models, surgical tools, orthodontic devices, and other custom medical parts.
3. Engineering & Manufacturing
Used for jigs, fixtures, functional components, and end-use parts.
4. Jewelry
Creates finely detailed casting patterns for metal jewelry.
5. Film, Art & Entertainment
Used for props, miniatures, costumes, and sculptures.

Comparing SLA with Other 3D Printing Methods
SLA vs FDM

SLA offers smoother surfaces and finer details

FDM is cheaper and better for larger functional parts

SLA vs SLS

SLS doesn’t need supports but has a rougher finish

SLA is better for small, detailed models

SLA vs DLP/MSLA

All are resin-based

DLP/MSLA are faster

Traditional SLA offers slightly better accuracy

Future of Stereolithography
As the technology continues to evolve, we can expect:

faster printers

larger print volumes

stronger and more advanced resins

improved automated cleaning and curing

more uses in aerospace, dental, electronics, and medicine

SLA is set to remain a major part of modern manufacturing and 3D Printing For Product Design for many years.

Final Thoughts
Stereolithography is one of the most dependable and high-quality 3D printing processes available today. Its ability to create smooth, detailed, and accurate parts makes it a favorite for designers, engineers, and manufacturers. Although it requires cleaning, curing, and support removal, its results consistently stand out.
Whether you're building a prototype, testing a concept, or developing a final product, SLA gives you the precision and confidence needed to create high-quality parts with ease.

My name is Michel Marsin and i work full time as a freelance writer, editor former social worker. I am passionate about writing articles on different topics.