Lori - The Working Curve Device
Updated: Jan 3, 2019
During my time at polySpectra, my main project was creating Lori. In February of 2018, I was tasked with creating a device which could measure the intrinsic light absorption properties of resins easily and reliably and by August, a version of the project was complete.
What does polySpectra do?
polySpectra is a Berkeley, CA based 3D printing materials start-up. They make high performing engineering resins which are manufactured using Vat Photopolymerization 3D printing processes - those in which a resin is cured layer by layer to make a 3D part.
What does Lori do?
Simply put, Lori precisely exposes resin using high-power UV LEDs, thus making several samples which are measured in order to map exposure to thickness. Let's break that down.
The process of making an Exposure vs. Thickness relationship is incredibly valuable in Vat Photopolymerization. Without knowing how the resin will respond to certain doses of light, developing print settings (i.e. layer exposure times) becomes a guessing game, rather than knowing that, for example, a 10 second exposure of 15 mW/cm^2, 405 nm wavelength light will cure a 100 micron thick layer of material. A working curve is the name given to this relationship.
There is a great Instructables project which details the process of making a working curve using a typical DLP projector, but there are several problems with using this method for resin development:
It requires too much resin
The printer used has a lot to do with results
Printers aren't made to do this
This keeps the tests from being easy, modular, and quick.
2. Mechanically concentrate light into small disc-shaped samples
3. Vary intensity within the typical ranges of 3D printers
4. Calibration method for LEDs
5. Intuitive UI