SLA 3D printing is one of the earliest and most widely used rapid prototyping technologies. In this article, we will explore what SLA 3D printing is and how it works. We will also compare SLA to two other popular 3D printing processes, FDM and DLP, to help you choose the best technology for your project.

What is SLA 3D printing?

SLA 3D printing is a technique that uses ultraviolet light to cure layers of resin and create 3D objects. The full name of SLA is Stereolithography. The process involves using an ultraviolet laser to draw the cross-sections of the object along a specific path in the resin pool, causing it to solidify. Then the platform moves along the Z-axis to start printing the next layer. This process is repeated until the final 3D object is completed.

What is the workflow of SLA 3D printing?

1. Pre-printing

Using CAD, a three-dimensional solid model is designed and subjected to data conversion, orientation determination, support application, and slicing using a discrete program. The scanning path is designed, and the resulting data accurately controls the motion of the laser scanner and the lifting platform.

2. Printing

  • Fill the printing tank with liquid photosensitive resin material.
  • The printing platform rises until it stops at a position one layer thickness away from the liquid surface.
  • The horizontal scraper moves in a fixed direction to scrape the liquid surface into a horizontal plane.
  • By focusing a laser beam through a lens and irradiating it onto a polarizing mirror, the laser generator generates a laser beam. The polarizing mirror automatically shifts according to the slicing path of the cross-section, allowing the laser beam to selectively scan the liquid surface according to the model data. Due to the photosensitive properties of the resin, the irradiated liquid resin gradually solidifies.
  • After solidification is complete, the printing platform automatically lowers by a fixed height (one layer thickness), and the horizontal scraper again scrapes the liquid surface flat. The laser irradiation then solidifies the resin. The process is repeated until the entire model is printed.

SLA vs FDM in 3D printing?

FDM (Fused Deposition Modeling) is a 3D printing technology that uses a heating device to melt ABS, PLA, and other filament materials, which are then extruded through a nozzle like toothpaste, layer by layer, to form the final product. 

Printing size

FDM can print small or large parts, but when printing large parts, stability, and speed can be an issue due to the mechanical structure of larger FDM models. It makes it challenging to meet long-term printing needs.

SLA printers require the depth of the forward-facing resin tank to be the same as the height of the workpiece, and the working space must be filled with resin material. It means that the equipment volume must be very large. When printing large-sized products, SLA is faster compared to FDM.

Printing accuracy

FDM prints parts by layering melted material through a nozzle, resulting in a noticeable step effect (surface texture), making it unsuitable for building large parts.

SLA can achieve a layer thickness precision of up to 0.05mm, and universal photosensitive resin materials have smooth surface quality and are easy to post-process. So it can produce various complex precision parts and assemblies.


FDM machines are now more common, with relatively inexpensive consumables such as PLA, ABS, TPE, and TPU. PLA is a biodegradable thermoplastic material. ABS is a high-strength, resilient, and easy-to-process thermoplastic polymer material. Its melting point temperature is higher than PLA, so when printing, the platform must be heated to avoid warping and shrinkage. TPE/TPU are flexible materials that can produce objects with excellent stretchability. However, printing with flexible materials can be challenging, especially for 3D printers that feed from a distance.

SLA uses liquid photosensitive resin as consumables. They have fast curing times, high molding accuracy, good surface roughnesses, and are easy to post-process. They are suitable for making hand samples of automobiles, medical devices, electronic products, architectural models, and more. It is important to keep in mind that photosensitive resin has an odor and toxicity and needs to be sealed. It must also be protected from light to prevent premature polymerization reactions.

SLA vs DLP in 3D printing?

Digital Light Processing (DLP) is a rapid prototyping technology that uses a DLP projector to project sliced models onto resin layer by layer. Each layer of the projected image is solidified into a thin layer in the resin layer, and the forming platform moves one layer to continue solidifying the next layer, repeating this process until the entire print is completed.

Both SLA and DLP use light-curing resin as consumables, and the two molding technologies have similar principles, but there are still differences in many aspects.

Printing size

In contrast to SLA, DLP is limited by the resolution of digital mirrors and can only print smaller products.

Working speed

The working efficiency of SLA is much lower than that of DLP. DLP works by using a digital micromirror device to project the sectional shape of the product onto the surface of the liquid photosensitive resin, so the printing speed is very fast. SLA uses a laser beam to draw the object on the liquid resin surface, from point to line, then from line to surface to form a solid model.

Printing accuracy

DLP has higher printing accuracy than SLA. In theory, both can achieve a printing accuracy of microns. DLP can reach a minimum spot size of ±50 microns, while SLA can realize a minimum spot size of ±100 microns. Due to the high power of SLA lasers, it is easy to cause molding spot errors. In addition, the requirement for laser and mirror components in SLA is very high, and it is hard to meet these requirements domestically without increasing costs significantly. Compared to SLA, DLP is easier to achieve micron-level accuracy. 

What are the material options for SLA?

General acrylic resin

These materials offer varying levels of toughness and transparency.

Flexible polyurethane elastomer

It is used to create flexible parts.

Hard polyurethane

These materials have good aesthetic value and are more durable than general materials, making them ideal for product testing and prototyping.

Rigid resin

They offer chemical and thermal stability, making them suitable for engineering test components.

Dental and medical resin

These resins are safe for medical use and can be employed to create high-quality finishes and transparent items like mouthguards and splints.

Antistatic resin

They are used to manufacture antistatic fixtures for manufacturing processes.

What are the surface treatment options for SLA?

Untreated SLA 3D-printed products may have visible layer lines on their surface, which can detract from the overall appearance and quality of the final product. Polishing is a simple and effective way to remove these lines and prepare the surface for various finishing processes.

Polishing can be done manually or with a polishing machine, using a series of abrasive materials to remove the layer lines and smooth out the surface. Once polished, the surface can be finished with various techniques such as sandblasting for a matte finish, spraying or dyeing for color, silk screening for printing logos or patterns, or electroplating for a metal coating.

By polishing and finishing SLA 3D-printed products, you can achieve a high-quality, professional-looking final product that meets your specifications and requirements.

When do you need SLA 3D printing?

In addition to high precision, intricate details, and smooth surface finishes, SLA 3D printing is also known for its speed and cost-effectiveness. Compared to CNC machining, typically used for one-off prototype production, SLA 3D printing is faster and more cost-effective, especially for complex geometries.

SLA 3D printing is ideal for creating high-quality prototypes that accurately represent the final product's shape, size, and texture. It can also be used to create small-scale manufacturing parts with high precision and accuracy. Compared to other 3D printing technologies such as FDM and DLP, SLA can produce parts with the highest level of detail and accuracy.

When you have a tight lead time and tolerance requirement for a complicated part, SLA 3D printing may be preferred. With SLA 3D printing, you can quickly produce high-quality prototypes and parts with intricate details and smooth surface finishes, all while keeping costs low.

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