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!
