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Thursday, June 11, 2015

Continuous liquid interface production 3D printing Additive manufacturing processes

Additive manufacturing processes such as 3D printing use time-consuming, step wise layer-by-layer approaches to object fabrication. We demonstrate the continuous generation of monolithic polymeric parts up to tens of centimeters in size with feature resolution below 100 micrometers. Continuous liquid interface production is achieved with an oxygen-permeable window below the ultraviolet image projection plane, which creates a “dead zone” (persistent liquid interface) where photopolymerization is inhibited between the window and the polymerizing part. We delineate critical control parameters and show that complex solid parts can be drawn out of the resin at rates of hundreds of millimeters per hour. These print speeds allow parts to be produced in minutes instead of hours.

According to Carbon3D’s CMO/CSO Rob Schoeben, the fundamental difference between existing SLA printers and Carbon3D’s device is that CLIP gets rid of the layers that characterize 3D printers across all seven technologies that exist today. Yes, the computer model of the item to be printed still has to be sliced so the Carbon3D device knows where to image the resin. And, yes, as with other SLA printers such as EnvisionTEC’s, the device uses a digital light projection (DLP) chipset to project the image onto the resin.
So, what’s the difference?
Chemistry, or more to the point, the relationship between oxygen and light. Mr. Schoeben says that oxygen is the enemy of polymerization—you want to keep oxygen away from the resin as much as possible because it inhibits curing. By employing a unique oxygen permeable window at the base of the resin bath, and controlling the oxygen flux through the window, a “dead zone” of oxygen that is 20-40 microns thick is created along the window. Oxygen still exists in the resin above the dead zone, but in small amounts which don’t inhibit polymerization.
The polymerization of the resin is initiated by the DLP. As a continuous sequence of UV images are projected, the object is drawn from the resin bath. However, polymerization does not happen one discrete layer at a time, but rather happens continuously allowing cross-linking of polymer chains across layers due to a gradient of polymerization.  What that means is that the resulting part is molecularly consistent in every direction with no physical layers. According to Mr. Schoeben, CLIP-grown parts are smooth on the outside and rock solid on the inside.
So, how fast is fast?
Determining the speed or throughput of any 3D printer of any technology, much less comparing two manufacturer’s printers using the same technology, is a complicated issue because of many variables. Mr. Schoeben said that Carbon3D is capable of printing at a vertical rate of “100s of mm/hour to 1,000s of mm/hour.” The Eiffel Tower shown in the Carbon3D video online is 55 mm (2.17 inches) tall and took 6.5 minutes to print. That’s an average of approximately 500 mm/hr. In comparison, Formlabs’ Form 1+ prints at 10-30 mm per hour along the Z axis at 100 micron resolution.
Users familiar with SLA printers know that the printed piece must be cleaned and even post-cured after printing. Today, the Carbon3D parts are cleaned with isopropyl alcohol, although the company is researching additional cleaning processes. Post-curing of its parts to give them additional mechanical properties will be possible as well.
Carbon3D’s exhibit at TED included a microscope for attendee’s to see the fine detail of a 3D printed micro-needle array on a transdermal patch. While the demonstrated 3” x 4” resin bath inherently limits the build size, larger resin baths will likely be available eventually. One of the keys to further development in that area is ensuring sufficient resin flow for larger or more detailed builds. And while dealing with the thermal heat building up from the rapid chemical reaction when printing so fast is a non-trivial factor. Mr. Schoeben indicated that is not an issue at current speeds.
What does this mean?
Carbon3D will be coming to the market with its first printer within the next twelve months. The printer is being tested by beta customers in the automotive, special effects and footwear industries. Based in Redwood City CA, Carbon3D’s plans to build its printers there.
Near term, Carbon3D could have a place in marketing and engineering departments where very rapid prototyping and production of concept models is important. Of course the part can be painted afterward, offering additional uses in the movie and television industries, too. The company expects the range of resins will expand and anticipates uses in creating injection mold tooling at some point. Ultimately, Carbon3D could enable volume production of finished goods that are produced quickly and have compelling mechanical properties.
Gartner anticipated the significant expansion of SLA printers that has occurred beginning in 2014. We noted the trend and factored it into our October 2014 Forecast: 3D Printers, Worldwide, 2014. SLA printer shipments worldwide are projected to increase at a 105.6% CAGR through 2018.
SLA never generated the hype that material extrusion printers did, that is until Formlabs’ Kickstarter campaign generated $2.94 million in orders. Other providers have also come on the scene, such as Full Spectrum Laser and XYZprinting. More will arrive, too, as Autodesk’s open hardware/open software/open materials SLA printer “Ember” gets into the market.
Yes, watching a 3D printer from any of the seven technology platforms is captivating and even mesmerizing at first. Carbon3D’s rapid and fluid CLIP process goes beyond that, making its development and ultimate market introduction worth watching.

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