What’s the Difference between SLA and DLP 3D-Printers?

The basic principles are the same, but the main difference is the light source. Read about what it means for the 3D-printing process and how to choose the best DLP projector for your application.

DLP and SLA 3D-printing are both Vat photopolymerization processes where a photopolymer bed is exposed to UV light to shape a 3D-printed object.DLP and SLA 3D-printing are both Vat photopolymerization processes where a photopolymer bed is exposed to UV light to shape a 3D-printed object.

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The past few years have created incredible advances in today’s modern 3D printing technology, with much of the excitement happening in photopolymerization and resin applications. This technology offers the benefits of high resolution, excellent surface finish, and incredible accuracy. From creating finely-detailed prototypes to making works of art, those working within this niche have several options to choose from when determining the best way to product accurate results.

Two such printing tech options, SLA and DLP, are often touted as the go-to technology for resin applications and have changed the landscape for healthcare, medical device industries, and consumer goods.

What is the difference between SLA and DLP 3D printers? First, it’s helpful to know the needs that those working with resin have. Since they work with very fine printed parts and prototypes, they require a printer that can print in high accuracy without accidental gaps that water or air can get into. Part size will range, as well, with some of the creations of a minute scale that would be hard for us to fully realize with the naked eye.

Resin 3D printing looks similar between SLA and DLP methods; they both use a vat setup and a light source to stabilize the liquid resin layers to build up and eventually form the product. This entire category of resin printing is known as “vat photopolymerization.” That’s where their similarities end, however.

While they use the same basic principle to create a product, the main distinction is the light source used. Here is a breakdown to help you decide between the two.

How do SLA printers work?

Stereolithography (SLA) printing is one type of vat photopolymerization, which forms the object upside down in a tank of liquid resin. Light from a laser is bounced off of two mirror galvanometers. The laser, often a solid-state laser, may have a wavelength of around 405 nm and can offer the possibility of incredible accuracy.

As this laser light hits the correct spot on a layer of liquid resin, this resin is cured and hardens, while it is still submerged under the resin bed. The layer then breaks free from the bottom of the tank, moves up a little, and makes room for another layer of liquid resin to be cured by the reflected laser light.

On and on it goes until the full 3D object has been cured from the liquid. The object is then usually rinsed and may also be set into a curing station before being cut away from the supports that were printed along with the final object.

Basic principle of SLA 3D-printing. A laser scans the build area and cures each layer point by point.
SLA 3D printing

This process differs from other substantive 3D printing solutions that extrude the printed material into layers upon a flat platform.

While a laser is a very precise tool, the accuracy and precision of an SLA printer depends on a variety of other factors, incl. the material’s properties, the software and the overall design of the printer. It requires a high degree of calibration to pinpoint the perfect placement of the laser, and since the laser is constantly moving, it has to be calibrated regularly to ensure the repeatability of the prints.

Finer details can be achieved with the laser point. Again, this is dependent on the know-how of the designers and calibration of the equipment to achieve excellent results.

Each pinpoint detail comes at the cost of time, making even simplified print jobs a time-consuming endeavor. For those who want a rough prototype within minutes or hours, the SLA option may not be a good fit.

How do DLP printers work?

The digital light processing 3D printer, or DLP 3D printer, also uses the same vat photopolymerization materials of liquid resin, and can create the final product through a top-down or bottom-up approach. It achieves stabilization of the printed parts through the flashing of UV light from a digital projector or light engine. This light shines simultaneously on every part of the printed object at once. Every point on the resin model is cured at the same time.

The most apparent advantage is speed. With every part of the model being cured at once, it takes much less time to complete a build than with the SLA method. The most cumbersome part of the 3D process may, in fact, be the design and refinement steps, not the actual print.

DLP can offer high resolution, depending on the pixel size of your light engine. Since high resolution means smaller image size, you may be limited to only small build areas. What happens if you want to create a large product? It’s possible to combine (or “stitch) several DLP projectors together to create the area you need without sacrificing resolution.

Basic principle of DLP 3D-printing. A UV projector projects an image onto the photopolymer bed and cures each layer of the object image after image.
DLP 3D printing

As for SLA, the accuracy and precision of a DLP 3D-printer will depend on a variety of factors including the materials. However, calibration will be a much easier process with DLP, since the UV projector is stationary, and there won’t be any additional moving parts in the optical path. This also means that there will be less maintenance required.

While speed and lower maintenance costs are the clear advantages of DLP, picking the right UV projector is important for ensuring a consistent outcome. Not all DLP projectors have the same quality; uniformity in size and shape of pixels will ultimately determine how satisfied you are with your final product. Investing in a quality DLP is imperative for good results.

Choosing the right DLP projector for 3D printing

For anyone looking to build a high-quality resin printer, reviewing different DLP projectors should be one of the first things you discuss with your decision-makers. Determining the resolution, the image size and the speed you’ll want to achieve with your printer are the first steps towards identifying the right DLP solution for your application.

What else should you look for? Beyond the right wavelength and resolution, consider the contrast values and a high level of uniformity. Each pixel needs to have the same size and shape, something you’ll only find in a high-end DLP light engine. Irradiance, (sometimes called the “output power” or “light intensity”) also matters. This determines the speed of your print process, since a brighter light cures faster. An example of this high-powered light is the Helios, which emits up to 12W of power and offers a simple switch-out of the LED for maximum accessibility and flexibility.

Also, the type of DLP chipset (the micromirror array used to modulate the light in a DLP projector) will play a role in the quality and lifetime you can expect from your UV light engine. For example, teams hoping to make a move to a 4K resin printer need to understand the difference the types of chipsets used to achieve a 4K image and how it might affect the detail and quality they want from every print. The Phoenix projector, a new addition to the 4K UV lineup, will provide 3D manufacturers with a reliable and powerful light source capable of the fine details needed for accurate 4K printing.

With any new technology, expect a learning curve. One way to get up to speed quickly is with a thorough understanding of the light sources available and how they affect the quality of any resin print. As more resin materials become common, including the more photosensitive resins, a higher-powered light engine may be required. By investing in this technology early, you will be set up for new advances in the photopolymerization trend.