AMS Spring 2023

LLNL’s Diode-Based Additive Manufacturing Technology 3D Prints Metal Parts Faster Than Ever

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Lawrence Livermore National Laboratory delivers amazing research, often related to 3D printing, on a regular basis, so it’s never surprising when they announce something big. This week, however, LLNL researchers have made an announcement that could change the 3D printing industry – they’ve developed a new metal 3D printing technology that can print objects faster than ever before.

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.”

In DiAM 3D printing, the light source is four diode laser arrays and a pulsed laser. The light passes through the OALV, which creates an image of a two-dimensional slice of the part. The images are transferred from a digital file to the laser in a two-stage liquid crystal modulation process. In the first stage, the images from a CAD model are imprinted on a low-power blue LED source with a regular pixelated liquid crystal projector. In the second stage, the blue images activate the OALV’s photoconductive layer, creating conductive patches where the blue light is present. Those conductive patches transfer voltage to the liquid crystal layer, enabling the low power blue images to modulate the high power laser beam. The beam is then directed at the build, where it 3D prints an entire layer at once.

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]

 

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