The technology is called diode-based additive manufacturing, or DiAM, and it was originally developed to smooth and pattern laser beams at the National Ignition Facility (NIF). It uses high-powered arrays of laser diodes and a specialized laser modulator to flash print an entire layer of metal powder at a time, instead of raster scanning with a single laser after each layer as SLM and SLS 3D printers do. This means that large metal objects could potentially be 3D printed significantly faster than with current processes, and with much more design flexibility.
The research was published in a paper entitled “Diode-based additive manufacturing of metals using an optically-addressable light valve,” which you can access here.
“By cutting the print time and having the ability to upscale, this process could revolutionize metal additive manufacturing,” said lead author Ibo Matthews, an LLNL scientist heading the research. “The speed, we estimate, is a one cubic meter build that would normally take 10 years to make could be done in a matter of weeks, because you can image the whole thing at once. Printing layer-by-layer also allows you to reduce residual stress because you can have the laser light coming through only where it’s needed.”
The key is the customized laser modulator, called an Optically Addressable Light Valve or OALV. It contains a liquid crystal cell and photoconductive crystal in series and works like a liquid crystal-based projector, sculpting the laser according to preprogrammed images. Unlike a conventional liquid crystal projector, however, the OALV is unpixelated and can handle high-powered lasers.
The technology was originally developed for NIF as part of the Laser Energy Optimization by Precision Adjustments to the Radiant Distribution (LEOPARD) system, which was implemented in 2010 and won an R&D 100 award in 2012. At NIF, the OALV optimizes the profile of the laser beams and locally shadows and protects optics subject to higher intensities and energy density. NIF uses the LEOPARD system to electronically protect regions of its beams containing potentially threatening flaws on its final optics, identified by the Final Optics Damage Inspection system. This allows NIF to continue firing until the flawed optics can be removed, repaired and replaced.
“The DiAM project marries two technologies that we’ve pioneered at the Lab — high-power laser diode arrays and the OALV,” said John Heebner, who led the development of the OALV. “Given that we put all this time and development into this light valve, it became a natural extension to apply it to this project. We went through some calculations and it was clear from the outset that it would work (with 3D printing). The ability to change a serial process to a parallel process is critical to ensuring that as parts increase in complexity or size that the patterning process speed can be increased to catch up.”
The process has benefits beyond just greater speed and the ability to produce larger parts. The OALV allows for image quality that is much sharper than that of metal 3D printers on the market today, and users can have better control over residual stress thanks to the ability to fine-tune gradients in the projected image. Laser diodes are also inexpensive, making the whole system more cost-effective.
Authors of the paper include Manyalibo J. Matthews, Gabe Guss, Derrek R. Drachenberg, James A. Demuth, John E. Heebner, Eric B. Duoss, Joshua D. Kuntz, and Christopher M. Spadaccini. Discuss in the LLNL forum at 3DPB.com.
[Source: LLNL / Images: Kate Hunts]