To build large objects quickly, researchers from Lawrence Livermore National Laboratory (LLNL) are improving upon a powdered metal printing method known as selective laser sintering.
Also referred to as “powder bed fusion additive manufacturing (PBFAM),” selective laser sintering is relatively simple: You begin with a build-plate of metal for your part. Next, you use a wiper-blade-like tool to spread a thin (30-micron or so) layer of powdered metal. Then, you focus a selective laser sintering beam down to almost that same size — 50 to 100 microns — and write a desired pattern with it. You can direct the beam to write out a pattern to create an entire layer. You then lower the part down, spread more powdered metal, and repeat, building up a layer-by-layer 3D print.
However, the selective laser sintering process takes a long time; you have to wait for the laser beam to go around, and you have to continuously spread the powdered metal.
Dr. Manyalibo “Ibo” Matthews his LLNL team from developed a faster laser-based method for 3D-printing large metal objects: Diode-Based Additive Manufacturing (DiAM). The process uses high-powered lasers to “flash-print” an entire layer of powdered metal, enabling large objects to be built in a fraction of the time typically needed for metal 3D printers. (Read our 2017 Q&A with Dr. Matthews.)
The DiAM setup has two main components: a high-power diode array and a pulsed laser. Why the combination? The diodes deliver the majority of the heat to melt the layers. To prevent melting the entire build, however, the laser sends in a 7-nanosecond pulse.
The OALV, or Optically Addressable Lite Valve, is used as a spatial light blocker. The OALV rotates polarization of incoming laser light so that instead of having to write each trace layer, the entire image is produced at once, saving a tremendous amount of time, say Matthews. The setup can pattern that light to print an entire layer at once, by allowing light to irradiate and melt layers of powdered metal.
Blue light passing through the valve will either have its polarization rotated if the valve is not addressed, and not rotated if it is. Then the “mixed-polarization-state beam” is sent through a polarization filter that will block the rotated polarization beam and allow the unrotated one through. This system of restricting the light allows the build to be made all at once, and not layer by layer.
“What we’re putting through the filter is not a focusing beam but a sheet of light — high power laser light,” Dr. Matthews told Tech Briefs in the 2017 Q&A. “Wherever the filter is blocking the beam is where we have unmelted powder; where it’s allowing the beam through, we melt the powder.”
We ask Dr. Manyalibo Matthews:
- What inspired you to advance the selective laser sintering process?
- How is the OALV used for 3D printing?
- What parts can be made from the powdered metal?
- What are some commercial applications?
- What’s next?