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New in SLA

20 October 2019 - 3D printing

Unusual to see the three authors of a Science article also listed as the CEO, CTO and chairman of a commercial business. The article is about 3D printing (DOI) and the company is 3D printing company Azul3D. Okay, Walker, Hedrick and Mirkin also work at Northwestern University.

Stereolithography (SLA) is around since the eighties: a laser illuminates a 2D pattern at the bottom of a tank of photopolymerizable liquid through a window and as the resulting solid object is step-wise dragged out of the tank, 3D printing takes place. The inventor filed a patent and founded 3D Systems (600 million dollar in annual revenues).

In 2014 , also as an article in Science (DOI) a variation was introduced called continuous liquid interface printing (CLIP), the associated patents are now commercialized by company carbon3d.com (raised 260 million dollar in funding this year link) CLIP, according to the inventors is truly continuous which allows for faster production and industrial-scale production. To prevent clogging up the window at the bottom with polymer, a oxygen-permeable membrane creates a dead-zone just above the window with oxygen acting as a polymerization inhibitor.

The new Northwestern work promises even higher throughput as we go from SLA and CLIP to HARP ((high-area rapid printing). The dead zone at the bottom of the tank is replaced by a flow of fluorinated oil with the key additional advantage that it can remove the generated heat. Heat generation from the polymerization process is now a bottleneck. The oil is recycled with the heat removed in a heat exchanger and filtered to get rid of interfering debris. The new system does not require a oxygen-depleted zone and therefore tolerates more photopolymerizable resins. A polyurethane resin is reported with a vertical speed of 12 cm per second. Funding was provided by a bunch of non-profits and inevitably the military.