A Guide To Resin Printer Technologies: SLA vs DLP

There are countless ways to 3D print your parts. When most people picture 3D Printing they imagine a nozzle melting filament layer by layer. This is called FDM or FFF. This is not the only way though!

There is a resin type printing too, a technology that has become more accessible for desktop usage over the last few years. We’ll be comparing the two main resin printing technologies: SLA and DLP. We hope this works as a helpful guide for choosing which one is for you.

So What Are Resin Printers?

The resin printing process that has been with us since the invention of 3D printing, but only in recent years has it become accessible for anyone with tighter budgets. The process consists of curing photosensitive liquid resin to get a solid geometry.

Their main components are a vat or tank, a moving platform, the cover and, the most important one, the curing light system. Here is where an SLA and a DLP differentiate from each other: An SLA uses single moving laser light and a DLP a projector uses a digitally selected pattern. The process consists essentially of the following:

1. Pouring resin on the vat.

2. Adjusting the printing platform position.

3. Setting slicing data and start the process.

4. Light reaches the platform surface to selectively adhere the resin.

5. The same process repeats, stacking layer by layer until the object is finished.

6. Rinsing the object with alcohol to remove resin excess.

7. Exposing it to the sun or a UV lamp to completely cure.

Resin Printing Capabilities

Before comparing SLA and DLP technologies, it’s good to know resin’s printing place in the additive manufacturing market as a whole. Here are key traits to point out:

1. The best choice when precision and smoothness is what you need. It can get as thin as 0.025 mm in layer height and manages a range of 25 to 100 microns of XY resolution.

2. It requires fewer moving parts than other technologies. Basically, it needs just a mechanism for the printing plate to move along one axis only. For this simple movement, one step motor is enough.

3. Easy and direct slicing process.

4. It has many budget-friendly options compared to most technologies.

5. Weak to bridges and overhangs, being highly reliant on support use.

6. Not the best when you want to try different kinds of materials and colours. Furthermore, resins are not the choice for high levels of mechanical performance.

7. The best choice for mould building, jewellery, dental and medical applications and highly detailed figurines.

SLA vs DLP: Comparison

The difference between both is the light source used for the curing process. SLA (Stereolithography) uses a single point laser reflection that changes coordinates through a set of mirrors moved by galvos.

On the other hand, DLP (Digital Light Processing) consists of a light projected through a DMD (Digital Micromirror Device) that contains thousands of microscopic mirrors. Each mirror represents an “on or off” pixel on the final shape of a layer.

We’ll use the following criteria to make a comparison between both technologies:  

1. Printing speed

2. Resolution

3. Accuracy

4. Pricing

Printing Speed

The obvious difference. While an SLA laser must travel point by point, the DLP projector projects the entire image from the get-go. Anything that could take hours to complete on an SLA could take minutes on a DLP. It all comes to the XY dimensions, the wider and denser the layer (build volume), the broader the difference between printing times.

If time is of the essence, and you need high quantity production or to get big and dense objects fast, DLP seems to be the choice. On the other side, it is important to consider the possibility of downgrading resolution in order to get faster printing times on an SLA.  

Resolution

When comparing both technologies, you may think the obvious choice is an DLP. You might be right, but the answer is not as intuitive as it may seem. DLP projectors can reproduce pixels roughly equal in size to the laser spot produced on an SLA.

The answer to this is the fact that a DLP resolution is limited to a static grid of squares (pixels), while an SLA laser moves freely and depends on how precise the galvos move the laser. If we reevaluate the DLP process, the main issue here is curved shapes build from rectangular steps. It could require an extra sanding process to achieve smoothness.

Furthermore, each pixel needs to adapt in scale to the printing area. Meaning that printing wider build volumes would need a higher resolution screen to adapt to the requirements. This would mean much higher costs.

Accuracy

In reality, what affects printing quality, more than resolution, is accuracy. Accuracy refers to how much the result deviates from the intended position and it could be affected by many factors. Material qualities and post-processing are important, but what matters most is performance and calibration.

How do SLA and DLP differ on this? Both have a high performance compared to other technologies, but in the end, it is a matter of comparison between different models, not technologies. When it comes to calibration for DLP, you must make sure that the projected pixels are uniform in size. For SLA, you don’t get the uniformity issue but still needs calibration regularly.

Pricing

There are so many printers and brands on the market, made for many target audiences. If we are talking about DIY printers, there are countless options between £200 – £500.

But, if you are looking for a professional printer, it could get up to a few thousand pounds. For example, a Formlabs Form 3 SLA printer costs around £2,900. Now, if you are looking for something on an industrial level, prices can rise from £20,000.

Final Thoughts On SLA And DLP

Resin printing is growing each year as a technology, closing the gap between high quality and affordability. Even with LCD as a newer, strong, and budget-friendly technology (We’ll write about this in a future post), Both SLA and DLP definitely have their place as relevant options on today’s market.

If you would like to discuss High Resolution 3D Printing please call us on 01926 333 777 or email on info@solidprint3d.co.uk

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