Form 4 Series: Why MSLA over DLP

First, apologies if this is the wrong place for this… hoping for someone from Formlabs with knowledge of this subject to weigh in, but if you’ve heard Formlabs answer this question before or have your own ideas, feel free to contribute.

I’m wondering why Formlabs decided to go with MSLA instead of DLP technology for the Form 4 Series. From my understanding, DLP can be superior in almost every way, other than super high pixel densities (higher than 8K screens). And DLP lasts much longer too, something I would think would be important for a printer in this price range. Is it only cost and availability that drive the decision, DLP being more expensive and (I believe) less available? Or is there some technical reason MSLA is better for the Form 4?

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Well, size I believe is one of them because most projectors need a further distance for focusing and I think you can also get an issue around the edges if I’m not mistaken. Essentially any flaws a normal projector would have a DLP machine could have as well.

EDIT: Found a link that might help

Thanks for the reply, and that link was a great read! It sounds like Formlabs believe their MSLA technology has caught up with DLP in terms of overall quality, and yes it seems DLP will usually suffer from some distortion or lack of uniformity near the edges of the projection area. I guess columnation suffers, or at least changes near the edges too, which isn’t good. And apparently DLP chips with enough pixels to have decent density at large build sizes (even the base model Form 4 size) are hard to come by or don’t exist, so they aren’t usually used for large format printers, especially the more modern inverted-platform types that don’t require a vat filled with liters of costly resin at all times. So with some well designed and calibrated optics, I suppose DLP could have been as good as Formlab’s MSLA on the Form 4, but DLP would fall short of MSLA for the Form 4L and uniformity of tech across the Form 4 line is clearly important. So it makes sense… and Formlabs says their LCDs last a long time and can be easily replaced for cheap (how cheap though? I’m worried Formlabs’ idea of “cheap” is a bit different from that of most non-commercial 3D printer enthusiasts lol).

Still curious if someone from Formlabs would be able to weigh in here. I still think DLP is cool and has more potential… just need to embrace taller printers and someone needs to develop a cheap and available super high res (16K+) chip that can power up to medium format printers, and for small format printers, some portion of the display near the edges can be sacrificed (i.e. refracted outside of the build platform area) to improve uniformity at the cost of pixel size (less of a concern for small format if the chip is already super high res). Anyone want to group-buy some super high res DLP chips (joking!)?

Hello everyone, Andrew Goldman here from formlabs. I’m the head of hardware engineering and occasional optical system architect. This is a great question, so I thought I would jump in and give you all a look behind the curtains. As you can see from the attached image, it was a very scientific process!

When we started Form 4, the print data told us that the world had changed from the days of Form 1 and Form 2, where most prints were a small portion of the print area to most prints filling up the print area with either larger parts or multiple parts. This was a clear signal that we had to move on from our beloved lasers and galvos to an area projection system, but we had to decide which technology is best for now and in the future, LCD or DLP.

Like we do with all decisions, big and small, we started with determining how this decision would affect our customers. The optical system drives or contributes to many things that our customers care about, including cost, print speed, dimensional accuracy, surface finish, and print area to name a few. We knew that we wanted to use whatever technology we chose for multiple printer generations, so we did not treat this decision lightly.

We took the approach of trying to develop the best possible LCD and DLP implementation for a 3D printer in a parallel effort. This is where the dial indicator came in; as we gathered more data for each system, we tweaked the dial back and forth between LCD and DLP. This was a great (and fun) way for the full printer team to get a quick snapshot of where we were with this decision at any point in time.

I agree that you can make a great 3D printer optical system with either technology. In the end, we made a trade matrix with LCD and DLP on the horizontal axis, and the optical system affected customer value parameters on the vertical axis. The differentiators that tipped the scale towards LCD were cost/print area, print speed/print area, and dimensional accuracy.

Cost/print area
LCD is a lower cost technology today, and cost continues to trend downwards. As each new generation of LCD technology is introduced, it creates excess capacity in older generation fabs which LCD companies are happy to use for tangential applications like 3D printing. Additionally, LCD screen cost scales linearly with size. DLP chips are made up of tiny rotating mirrors. They are fabricated as larger wafers and then cut into smaller chips. The issue is that the yield for the tiny rotating mirrors is far from perfect. This means that it’s hard to find large contiguous areas with perfect yield on a wafer. So the cost for a larger DLP chip is exponentially higher than that of a smaller DLP chip. Additionally, the larger the DLP chip, the larger and more expensive the projection optics become. One of the most requested improvements for our printers is always larger print area, so choosing a technology that scales well was important.

Print speed/print area
LCD print speed/print area can scale perfectly. We used an LED array the same size as the LCD in Form 4 and Form 4L, and we have exactly the same optical intensity in each system. The optical power output from a DLP chip is thermally limited by how much light can impinge on the chip. As the print area gets larger, the optical intensity at the resin is reduced (along with the pixel resolution, FWIW). If we wanted to build a 3D printer a very small print area, like for a single dental arch as an example, I would strongly consider DLP. For larger print areas, LCD is the clear winner for print speed.

Dimensional accuracy
Simply put, with LCD, the pixels are always in exactly the right place. This is HUGE for dimensional accuracy. It also makes LCDs easily swappable. As was mentioned, DLP projection systems come along with optical distortion, and sensitivity to mounting. While this can be overcome with elaborate calibration routines, we felt it best to focus our engineering resources on improving customer value in a thousand other places on the printer.

In terms of LCD vs DLP reliability, we think about this in terms of total cost of ownership (TCO). We were able to engineer an LCD system that the majority of users will never have to replace. It prints millions of layers on most materials before replacement is needed, and for less than half the cost of a similarly performing DLP system. This make the average TCO across our customer base skewed heavily in favor of LCD. For those power users that print so much that they wear out their LCD occasionally, we made the LCD module super easy to swap, and affordable as a replacement part.

Well there you have it, I hope that satisfies your curiosity. Thanks for the question!

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Thanks for the detailed feedback; it’s always nice to hear about behind the scenes so that we can be better informed.

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Hi Andrew, thank you so much for weighing in! I love this about Formlabs - you are active in your own community. That’s a great explanation, and I understand and agree with the decision to go with MSLA. I wasn’t aware DLP was power limited, at least at larger areas.

Obviously it wouldn’t make much commercial sense, but I’d still love to see you guys build a small DLP machine for super detailed prints (or use an array of DLPs to extend the size? probably a nightmare), or maybe a hybrid machine that uses DLP for small prints and MSLA for larger prints (since so much of the architecture is shared). I have an Elegoo DLP printer with a build area not much smaller than my Form 4 (though I haven’t tested how it looks near the edges). I wish it were as nice to use and reliable as the Form 4. I have to manually input suggested parameters for each resin and hope that they’re close, since there are rarely validated parameters available for my machine (I guess it’s not popular enough), and who knows how they were validated or even optimized. So far I can’t tell a difference in print quality between the Form 4 and the Elegoo - it also has 50um size pixels but people generally agree that it produces nicer prints than even MSLA printers with smaller pixels, another reminder that pixel size isn’t everything when it comes to print quality and details.

Anyway, thank you again for the detailed explanation!

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Amazing explanation, love hearing these product design and engineering decisions!

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I can say from an empirical point of view, FormLab’s adoption of MSLA is much better than other’s DLP tech. We have an EnvisionOne and a Form4, and aside from threaded parts, the Form4 always does better. The EnvisionOne will produce better details at times, but almost always I’ve seen planar slip discontinuities on geometric transitions, debris getting tossed around the inside of the projector hood, and lots of failed features due to printer overall reliability. Let’s just say I’ve had to dismantle the EnvisionOne down to its core multiple times (construction is very janky, we’re talking hot glue gunned’ USB hubs to the base) and a very very painful manual bed levelling that goes out after a few prints, versus none of that with the Form4 after 100’s of prints.

Now, the Form4 will have issues with holes and o-ring groves ~1mm in size, especially if they’re planar to the bed, but these are easy to work around. I’ve gone with Mitutoyo digital calipers that were certified calibrated to our Form4 parts and they are within 1 thou repeatedly after many uses of the printer. Could never get that with the Envision.

Safe to say, you can verify that the MSLA vs DLP is more than just resolution. I would make the comparison of FPS and HDR are more important on a gaming monitor than resolution at the 1440p level.

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I will never remember this, but it’s awesome :slight_smile:

We have printed threads and o-ring grooves in clear without any issues (down to 2.5mm) on Form 4. You do have the ability to adjust z-axis resolution (down to 0.25mm in clear). But perhaps your application requires better tolerances than we’ve used for somewhat generic applications.

Kudos to Formlabs for the great explanation. I am now armed with the correct information when me and the other nerds are talking about this technology.