Picture: Lawrence Livermore National Laboratory
Additive manufacturing with photopolymer resin usually only goes in one direction: a part is built up layer by layer and corrections are hardly possible afterwards. Researchers at the Lawrence Livermore National Laboratory (LLNL) have now presented a DLP-based system that partially reverses this process. In a study published in Advanced Materials Technologies, they describe a combination of additive and subtractive manufacturing based on a specially formulated resin.
The key component is a dual-wavelength-sensitive photoresin. Under blue light, it polymerizes as usual and forms a crosslinked, solid part. When the same material is exposed to UV light of a different wavelength, acids are generated in the resin that selectively break up the crosslinking and turn the previously cured polymer back into a flowable state.
“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.”
In the lab, the team demonstrated this on a microfluidic component with two channels that were initially separated. Using UV-induced degradation, the channels were subsequently connected.
“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 is available for licensing via LLNL’s innovation and technology transfer office and is intended for use with existing light-based 3D printing systems. Looking ahead, the researchers aim to integrate on-machine metrology and feedback loops to automatically detect errors during printing and adjust the projection images.
“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.
In the long term, the approach is also to be transferred to volumetric processes in which a part is created in a single exposure step within a rotating volume of resin.
