Tony Rollett: Additive Manufacturing with Metals

Tony Rollett: Additive Manufacturing with Metals


So, my research these days is focused on additive
manufacturing, and in particular the 3-D printing of metals. Although the basic machines for 3-D printing
that work with polymers have been around for quite a while, we now have these machines
that can print with metals. And so, it’s now possible to print parts
like this, which are complex metallic parts that really work. Something that’s particularly satisfying
about the 3-D metal printing research and activity is the opportunity to use advanced
characterization techniques, such as the high-energy x-rays from the synchrotron, to solve problems
and challenges that are of immediate interest to industry, as well as addressing basic research
questions that train students. The reason that we are so interested in this
advanced characterization technique, which, by the way, very few places know how to do,
is that one of the things you have to be concerned about when you print a metal part and then
you use it is that many parts get subjected to cyclic loading. So they’re subjected to loads that vary,
that fluctuate. And these fluctuating loads seek out the weakest
points in the material. So one of the things that we’re finding
is that these 3-D pictures allow a much more complete understanding. And what it does for us is it shows us the
bubbles inside the metal powder particles, and it’s turning out that those bubbles
inside the particles survive or they carry through to the 3-D printed metals. So another
thing that happens when you print metals is that what you’re doing is you’re coming
along with your laser beam or your electron beam, and you’re rastering back and forth
on the top of the material that you’re building, the powders, and you’re causing the metal
to melt, and everywhere that it melts and then re-freezes, then it’s pulling in. And that gives rise to something that we call
residual stress. Now, another huge advantage of having access
to this machine called a synchrotron is that you can do diffraction experiments. With the diffraction experiments, what you’re
doing is you’re bouncing the x-rays off the atomic planes in the material, and so
you are measuring the spacing between those planes. And if that spacing varies or is different
from the spacing that’s recorded in the books, then you know that you have some residual
stress. However, one of the most fascinating aspects
of this process, this technology, is that you get different microstructures and you
get different opportunities to control those microstructures and therefore the properties. So what we are doing in various different
projects is varying the microstructure by varying the composition, and exploiting, taking
advantage of, this novel process. And an important part of that variation in
composition is to understand things like residual stress, as well as the porosity, as well as
the material’s strength, as well as its fatigue resistance. So all of these things come together in a
very satisfying way to apply these basic research tools to very technological and near-term
needs that exist in the industry.

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