Researchers from the University of Texas at Austin have developed a more cost-effective LED alternative to ultraviolet (UV) polymerization 3D printing techniques.
By replacing the UV beams found in conventional visible light systems with multicolored LEDs, the Texan team were able to produce parts at the same speed and level of detail, but in a more energy-efficient way. As part of their study, the scientists also fine-tuned four different photoredox catalysts, which accelerated the solidification of resins once exposed to specific colors of LED light.
Leveraging their novel process, the researchers managed to print parts with features smaller than 100µm, at a speed of eight seconds per layer. As a result, Zachariah Page, the study’s lead author, claimed that the team’s novel method could rival those used by more established firms. “There are some conventional UV-based printers that are faster or higher resolution,” said Page, “but the combination we have is close to state of the art.”
“There hasn’t been a ton of chemical innovation [in visible light printing] until recent years”
The limitations of existing UV printing processes
In a process that’s often dubbed ‘photocuring,’ 3D printing techniques such as stereolithography (SLA) and Digital Light Processing (DLP), use UV light to transform matter from liquid resins into solid objects. DLP machines, based on this technology, provide many benefits to the user, such as build rates of 100mm/h, and the ability to fabricate objects with feature resolutions of less than 100 μm.
Although the majority of DLP 3D printers are based on these powerful UV light systems which provide short build times, they are also more expensive and less energy-efficient than other photocuring methods. Visible Light Printing (VLP) for instance, offers several potential benefits compared to traditional DLP.
The less intensive light rays used in VLP, are more compatible with biological materials such as live cell hydrogels, as well as opaque composites, making it more conducive to creating multi-material structures. Despite these apparent benefits, the reduced power behind the beams used in VLP, has made the method slower than other photocuring techniques, and limited its adoption as a result.
The Texans’ high-speed visible light photocuring process
In order to accelerate the VLP process, the researchers developed a series of panchromatic resins which incorporated a monomer, cross-linker, and several co-initiators. The resins were custom-designed to increase the speed of photocuring, providing stronger absorption, longer wavelengths and therefore allowing faster printing speeds than ordinary materials.
To validate their approach, the team gutted a standard DLP system of its UV components, and fitted it with blue (∼460 nm), green (∼525 nm), and red (∼615 nm) LED light emitters. Utilizing their home-made printer, the researchers conducted a series of tests by irradiating 100 μm thick argon degassed resins, between glass microscope slides using a low-intensity LED light.
A subsequent RT-FTIR spectroscopy on the samples revealed that all three colors were successfully cured. In order to examine the level of fidelity possible with their machine, the team then produced a resolution print with lateral dimensions of 20 × 20 μm2 and a layer thickness of 25 μm. The optimization sample contained 12 squares that were simultaneously printed with varying exposure times, and each layer featured an array of smaller patterns that were 1–16 pixels wide.
Leveraging the breadth of data gained from their varying resolution prints, the research team were able to optimize their custom-VLP process for each type of resin. For example, the green and red light sensitive samples needed a blanket of inert gas during printing to achieve comparable speeds to those achieved during DLP. Violet and blue light-sensitive resins on the other hand, proved to be unaffected by atmospheric conditions.
Further inconsistencies were also observed in the blue and red light-sensitive resins, which didn’t reach the maximum desired level of thickness at a consistent rate, which limited the process’ reproducibility. On the flipside, adding Opaquing Agents (OAs) was found to improve the method’s level of consistency.
The integration of OAs enabled the team to reach build speeds of 33 to 45 mm/h, and create parts with features less than 100 μm size, including a complex octet truss shape. As a result, the researchers concluded that while their approach had successfully matched the speed and resolution of commercial machines, further optimization was still required.
The team hypothesized that increasing light intensity could lead to even faster print times, and oxygen-consuming molecules could be integrated into future resins to mitigate their sensitivity to atmospheric conditions. If the scientists did manage to perfect their novel VLP method, then it could be used within a range of new tissue engineering or soft robotics applications.
As it stands though, the team still have some parameters to tweak, if they’re to consistently match the speed and resolution of existing DLP machines.
DLP production in the 3D printing industry
The potential impact of the Texas scientists’ research could be far-reaching, as DLP 3D printing has been highly-commercialized, and numerous companies offer their own variations of the technology.
Austrian 3D printer manufacturer Genera for instance, have recently launched their first DLP machine, the G2. The system features adjustable 4K DLP technology, meaning that users can change the system’s pixel settings between presets of 40, 70, or 100 microns.
Elsewhere, 3D printer producer Admatec has announced that medical grade ceramic materials are now compatible with its Admaflex DLP systems. The combination of the bioresorbable ceramic with the design freedom provided by 3D printing, could enable the production of a new range of healthcare products.
Taiwanese 3D printer manufacturer XYZPrinting launched its latest DLP system known as the PartPro120 xP last year. According to the company, the printer’s Ultra-Fast FIlm technology allows it to deliver speeds up to 75 times faster than comparable machines.
The researchers’ findings are detailed in their paper titled “Rapid High-Resolution Visible Light 3D Printing,” which was published in the ACS Central Science journal, and co-authored by Dowon Ahn, Lynn M. Stevens, Kevin Zhou, and Zachariah A. Page.
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Featured image shows an octet truss that the researchers 3D printed to test their novel VLP method. Photo via ACS Central Science.
