Dr. Matthews and his team have developed a new laser-based method for 3D printing of large metal objects called Diode-Based Additive Manufacturing (DiAM). It uses high-powered lasers to flash-print an entire layer of metal powder. The process will enable large metal objects to be printed in a fraction of the time typically needed for metal 3D printers.
Tech Briefs: How did you come to consider 3D metal printing?
Dr. Manyalibo Matthews: While 3D printing of metals was not explicitly considered within R&D activities supporting the National Ignition Facility [used for testing materials at extreme pressures, temperatures, and densities], an overlap was recognized in the optics that are used in both areas. NIF has a device called an Optically Addressable Lite Valve (OALV) that works such that shining blue light on it enables it to rotate the polarization of incoming laser light; light passing through will have its polarization rotated if the valve is not addressed, and the polarization not rotated if it is addressed. A mixed-polarizationstate beam is then sent through a polarization filter that will block the rotated polarization beam and allow the unrotated one through.
Tech Briefs: How is the OALV used for 3D printing?
Dr. Matthews: The same spatial light blocker that we’ve used to take out parts of the high-energy laser beam for an NIF experiment can be used with light suitable for 3D printing. It can pattern that light to print an entire layer at once by allowing light to irradiate and melt layers of powdered metal. In the standard process, you have a build plate of metal and a device that spreads a thin layer of metal powder on the order of 30 microns thick. A 50- to 100-micron laser beam writes a desired pattern in one layer. Where you’ve written with the laser, the powder is melted, and is surrounded by powder that didn’t melt. You lower the part down, spread another layer, and repeat. It takes a long time for the laser beam to go around, spread the powder, and move the part down. We use the OALV so that instead of having to write each trace, we can produce an entire image at once.
Tech Briefs: What sorts of parts are made using this process?
Dr. Matthews: What it does well is complex designs — things that you can’t easily or cheaply machine or assemble; for example, removing material to manufacture a high-strength, low-weight metal lattice. 3D printing can remove enough solid material to make the part light but strong, which can lead to a new generation of parts.
Tech Briefs: What are some commercial applications?
Dr. Matthews: At this moment, it depends on the industry. For medical, there are titanium-based alloys for implants and magnesium-based alloys for dissolvable implants. There are also aerospace and automotive applications. A number of alloys are used, depending on the application, such as nickel superalloys for turbines, and titanium and aluminum alloys for structure. The most common, but probably not as useful in the long term, are stainless and tool steel.
Tech Briefs: Is there still more work to do on this project?
Dr. Matthews: We just demonstrated the printing, but there’s a whole world of material science that needs to be studied to understand how different thermal gradients and thermal histories affect the microstructure and ultimate mechanical properties. There’s a new project we are starting soon that will do just that.