Digital Light Processing, also known as DLP, is a popular method for manufacturing polymer parts in the complex world of 3D printing technologies.
DLP harnesses the power of light from an area-wide projector to cure photosensitive liquid resins into parts layer by layer, one quick flash at a time — delivering smooth, accurate parts in a fraction of the time of laser-based stereolithography, or SLA, which must draw out part designs individually.
The DLP process has been around for over 20 years. It is essentially the same. A video projector is placed below a vat photosensitive resin. Print jobs are constructed vertically from the vat attached by a plate. Although the field has seen many improvements, the majority have been incremental and focused on limiting harmful separation forces inherent in building parts from the bottom up.
Global manufacturers are increasingly using 3D printing to produce functional end-use parts. This means that there is an increasing demand to print larger batches, larger parts, and engineered polymers. These requirements highlight the limitations in 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. This printing method places serious restrictions on the types and uses of resins. It is important that the resin used in bottom-up DLP printers must flow quickly under the build plates during recoating. This reduces the final material properties.
Resin can be delivered, or require two-part resins which must be mixed together and printed quickly before they spoil.
Interesting that there is no robust market approach for top-down DLP Printers is because SLA 3D Printers, which are the precursor to DLP, have always offered a viable commercial market for both top-down and bottom-up designs. The bottom-up style is often found in desktop units, while industrial models typically use the top down approach.
Now, ETEC With the Xtreme 8K, is taking a more industrial approach in DLP. Aside from holding the distinction as the world’s largest production-grade DLP printer, the Xtreme 8K is also one of the industry’s only top-down DLP printers — two features that are, as it turns out, highly interconnected. Users will find it has an enormous build area, superior material properties, and a high degree of part accuracy.
The DLP machine’s cutting-edge design was first shown in 2021. It features two overhead projectors that are placed above the resin vat. This allows the Xtreme 8K to offer the largest DLP build area — 166,950 mm2 (450 x 371 x 399 mm) — among commerciallyavailable, 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 machine design is innovative and allows for large-part production, high-volume manufacturing with DLP 3D printing, as well as the processing of new materials that compete directly with traditional thermoplastic injection moulding.
A BREAKTHROUGH NEW CATEGORY OF PHOTOPOLYMERS
Many of the initial low-viscosity photopolymer resins used in vat photopolymerisation – 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.
The materials are chemically bonded or crosslinked during curing to create 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. As parts are exposed to heat and light, their performance can also decrease.
Polymer AM has worked for many decades to improve material properties in order to overcome these obstacles and deliver stronger, more elastic properties.
Adaptive3D, a subsidiary to Desktop Metal, has created DuraChain, a new class of materials that solves 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.
DuraChain photopolymer resins can be exposed to light during DLP printer printing. They phase separate at the nano-level and cure into a resilient network that is high performance, much like two-part legacy material systems with 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 finally 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 have a viscous nature, they require a top down DLP printer to be processed.
DuraChain resins today, which include all of the materials below, can only be printed on the ETEC Extreme 8K:
Elastic ToughRubber 90 – ETR 90
– The toughest AM elastomer on the market. ETR 90 can be found in many parts and products already on shelves. It can be used to make shoe midsoles and heel cups, seals or door boots, and bellows.
Elastic ToughRubber70 (ETR70)
– A softer, stretchier ToughRubber useful when printing resolution limits of individual struts and minimum feature sizes do not allow ETR 90 to achieve the requisite soft feel via microarchitecture alone.
Soft ToughRubber STR
– Designed for functional prototypes of audio earbuds, wearable electronics, and anatomical medical models, Soft ToughRubber (STR) delivers a silicone feel and mechanical properties with the resolution and surface finish that DLP printing provides.
FreeFoam
– A new family of photopolymer resins containing a heat-activated foaming agent. After printing a design with FreeFoam the part is expanded in an oven during foaming. This results in a closed-cell foam which can be customized for different Shore A hardnesses.
This story comes from:
TCT Europe Magazine 30.5
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