Additive manufacturing, or 3D printing, is normally a one-way street. In a digital light processing (DLP) printer, a structured pattern is projected onto a layer of liquid resin, which cures and solidifies. This builds an object up, layer-by-layer. But if the print isn't exactly right, there's no easy way to fix it after the fact: it usually ends up in the trash.
In a new study, published in Advanced Materials Technologies, researchers at Lawrence Livermore National Laboratory (LLNL) developed a hybrid additive and subtractive manufacturing system with a unique resin that enhances traditional 3D printing by introducing dual-wavelength behavior. Under blue light, the resin cures and hardens. Under ultraviolet light, it degrades back into a liquid. The hybrid printing system enables corrective manufacturing, provides improved print resolution and allows for upcycling and recycling of parts.
"Imagine if a company needed a part to fit a certain machine but it's a prototype and they're not quite sure what they want," said LLNL scientist and author Benjamin Alameda. "They could theoretically print with our resin. And if there were defects or something they wanted to change about it, they don't have to print a whole new part. They could just shine another wavelength on it and modify the existing part. That's useful and less wasteful."
As an example, the researchers printed a fluidic device with two separated channels. Using the degradation response of their resin, they were able to connect the channels post-printing.
"We made it like this intentionally. But if this was actually a true failure to connect the channels, you would have to redo the entire print," said LLNL scientist and author Johanna Schwartz. "Now after the fact, it's just a very simple correction. Now it's usable again."
The patented resin technology is available for commercialization through LLNL's Innovation and Partnerships Office (IPO). It allows all light-based printing systems to create more intricate, detailed parts with higher resolution, to smooth surfaces and correct errors, as well as to add and remove temporary support structures. The technology - produced using unique LLNL facilities, capabilities and expertise - can be licensed by advanced manufacturing companies and used in existing 3D printers to save time and materials cost by enabling editable, recyclable 3D prints.
The resin is the key to the success of this dual-function printing: the authors optimized each component of its chemistry. Blue light causes the molecules in the resin to combine into a cross-linked network, a standard technique in 3D printing. In a new twist, ultraviolet light generates acid in the resin. The molecules are specifically tailored to respond to acid, breaking back down into a liquid.
Balancing the stability and degradability was a challenge. The team designed the resin to harden and degrade quickly, but not so quickly that it would degrade on its own. They noted that standard coatings can prevent parts from breaking down in the sun's natural ultraviolet radiation.
Going forward, the scientists are further expanding the capability of this hybrid manufacturing by integrating on-machine metrology and feedback control to automatically and autonomously correct the print errors on-the-fly.
"Once we see there are printing errors, we can adaptively modify the projection images to correct those errors on-the-fly, which enables a true adaptive manufacturing. Besides DLP printing, we are also planning to transfer this method to volumetric additive and subtractive manufacturing, which shines light to a rotating vial of resin and fabricates a 3D part all at once," said author and LLNL scientist Liliana Dongping Terrel-Perez.
The project was funded by LDRD office and led by Liliana Dongping Terrel-Perez. In addition to Alameda and Schwartz, team members include Holden Howard, Martin De Beer and Magi Yassa.
LLNL's IPO is the Laboratory's focal point for industry engagement and facilitates partnerships to deliver mission-driven solutions that support national security and grow the U.S. economy. LLNL Business Development Executive (BDE) Austin Smith is responsible for the Laboratory's Advanced Manufacturing intellectual property (IP) portfolio and BDE Jared Lynch is responsible for the Chemicals & Materials IP portfolio.
