New for 2022 Ultimate Guide to Digital Light Processing 3D Printing

October 20, 2022 by Team Desktop Metal 3D Printing Materials Sponsored

History of DLP

Over its 20-plus years of existence the DLP process has largely been executed in the same way: a video projector is stationed below a vat of photosensitive resin, and print jobs are built as a job advances vertically out of the vat attached to a build plate. While the field has enjoyed many advancements, most have been incremental in nature and focused on limiting the detrimental separation forces inherent to building parts bottom-up.

As global manufacturers begin to utilize 3D printing for the production of functional end parts, there is a requirement to print larger batch sizes, bigger parts and engineered polymers. These requirements shine the spotlight on the limitations of bottom-up DLP.

For one, there’s a limit to how many parts and how much weight can be suspended vertically from a build plate when printing with a bottom-up projector. More importantly, this printing approach forces serious constraints on the types of resins that can be used. Because the resin in the bottom-up DLP printing approach must flow back under the build plate easily and quickly during recoating, it must be a relatively low viscosity. This ultimately limits the final material properties the resin can deliver, or requires two-part resins that must be mixed together then quickly printed before they spoil.

Top-Down Developments

The SLA market, the precursor process to DLP, has long offered a healthy commercial market for both bottom-up and top-down designs, with bottom-up styles often featured in more affordable desktop units while industrial models often deploy the top-down approach.

Now, ETEC is embarking on this more industrial approach to DLP with the Xtreme 8K. This cutting-edge DLP machine features a top-down design with two industrial overhead projectors stationed above the resin vat. This allows the Xtreme 8K to offer the largest DLP build area — 166,950 mm2 (450 x 371 mm) — among commercially-available, production-grade DLP printers. Additionally, two intense and direct light sources that don’t have to penetrate through a vat film or tray enable new materials with higher energy requirements for curing.

This innovative machine design has unlocked the ability to produce large parts and manufacture in high-volumes with DLP 3D printing as well as process new materials that directly compete with thermosets used in traditional plastic injection molding.

Breakthrough New Category of Photopolymers

Many of the initial low-viscosity photopolymer resins used in vat photopolymerization – whether DLP or SLA – were derived from the protective coatings industry, where they were applied in ultra-thin layers and then cured with UV lights.

During curing, the materials are crosslinked, or chemically bonded to form a polymer. While these early photopolymer resins rapidly cure and offer good surface finish, they tend to be brittle and prone to cracking and shattering, offering poor impact resistance and little of the toughness and resilience needed to compete with today’s traditionally manufactured plastics. Their performance also tends to degrade over time or as parts are exposed to light and hot or cold temperatures.

For decades, the field of polymer AM has been working to enhance the material properties to overcome these hurdles and deliver more resilient, elastomeric properties.

DuraChain is a new category of materials invented by Adaptive3D, a subsidiary of Desktop Metal, to solve these problems. Adaptive3D developed a proprietary and unique blend of materials that takes advantage of a specific chemical reaction process, called Photo Polymerization-Induced Phase Separation, or Photo PIPS, to deliver all-new material properties in DLP.

When exposed to light during DLP printing, DuraChain photopolymer resins phase separate at the nano level and then cure into a resilient, high-performance network much like legacy two-part material systems that have a shorter pot life. One of the challenges in printing these materials is that they contain high-viscosity base oligomers — similar to honey or molasses — and miscible monomers that would not be easy to process on bottom-up DLP systems, which require more free-flowing resins.

Ultimately, this groundbreaking portfolio of photo-elastomers is delivering the tough and resilient properties that the market requires — with high tear strength, elongation, and toughness. What’s more, this unique approach is delivered in a one-part, pot-stable chemistry. Because these materials are so viscous and produce durable parts they currently require a top-down DLP printer for processing.