Face shield donations are coming fast and furious these days. Ford, Apple, Prusa Research and Foster + Partners are just a few of the organizations pitching in with different designs, which have by necessity evolved rather quickly. Let's look at the design changes.
First off, what's needed with a face shield is a curved, transparent sheet that stands off of the face. All designs accomplish this by incorporating a forehead band that serves as both a spacer and, in concert with an elastic band, the thing that holds it onto the user's head.
The designs diverge depending on the production method and materials used. The classic face shield design (from just a few weeks ago, when these could be produced at a leisurely pace) uses a thick strip of foam as the forehead band:
Now that we need many of these in a hurry, the design has quickly been evolved depending on what volunteer producers have on hand. 3D-printed designs like this one by Prusa Research, replace the foam with this two-arch design for the forehead band:
Prusa's initial design, RC1 in the photo below, was printed in the compressed shape you see in the photo. That allows you to fit more units onto the bed, but a trade-off revealed in testing was that the built-in springiness produced a lot of pressure on the user's temples. Updated design RC2 takes up more space on the bed, but it removes the temple pressure, and the design update also moves the facemask out further to accommodate goggles.
Adding holes to the forehead band confers a materials savings.
Printable plastic is what they have, so that's what they use. One downside is that 3D printing takes a long time; deep-pocketed Ford reportedly started out 3D printing the forehead bands, then switched to expensive-but-faster injection molding.
Apple's laser-cut design, which I struggled to make out in Tim Cook's Twitter video, is comprehensible now that Foster + Partners has released clear photos of their design, which appears to be similar.
The innovation here is production speed. Both the face shield and the forehead band can be laser-cut "in under 30 seconds and the elements can be assembled in under a minute," F+P writes. "With a single cutting machine, we were able to cut and assemble components for 1,000 visor masks in a day, representing a reduction of days in the time taken to produce 3D-printed alternatives."
The band is silicone rubber. Initially I'd thought the face shield and forehead band were the same material, which would save on sourcing, but F+P is using 0.5mm PET-G for the shields and polypropylene for the forehead band. They describe the latter material as "soft," though I'm not sure how comfortable it would be to wear for long stretches; unfortunately some sacrifices have to be made, as this is an emergency. Perhaps people could donate those self-adhering window insulation foam strips from a hardware store? If the foam were notched to accommodate the bend, perhaps they could quickly be added to the forehead bands on-site by a volunteer.
Then again, adding foam might obviate a key benefit of the F+P design: "An important advantage is that the visor can be easily disassembled, cleaned, sanitised and reused, addressing the growing shortage of raw materials for visor production," F+P explains.
As dismal as these times are, it's pretty exciting to see so many people pitching in and using what they've got to help out. I'm looking forward to seeing more of this improvisational innovation.
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The face shield design I just released myself just uses a single material (PETG) and folds together. I've found the plastic headband to be quite comfortable because it uses a ratcheting action to finely adjust to the user's head diameter. Here's the project page: http://www.designconcentric.com/origami
There's a new version of the PRUSA that was redesigned by Design that Matters and is approved by NIH. It incorporates a brim on top to protect the wearer when they're looking down.
As I've said in other postings online, being fast to production shouldn't necessarily be the goal. Most of the Apple face shields will have to be disposed of quickly, where other designs will be able to last multiple shifts after cleaning. Smaller clinics are preferring designs that can last a week or more, being sterilized each night.