Tech Briefs Magazine - February 2024 - 10

Q & A
Robotic Additive Manufacturing of
Large Steam Turbine Blades
Michael Kirka and a
team of researchers at
the Department of Energy's
Oak Ridge National
Laboratory are
the first to 3D-print
large rotating steam
turbine blades. They
achieved it with robot-controlled
wire arc additive manufacturing.
Tech
Briefs: What got you started
on this project?
Michael Kirka: The project was originally
birthed out of our industrial partner,
Siemens Corporation (Now Siemens
Technology), because of a need to repair
large-scale steam turbine blades and other
components that even pre-COVID
had long lead times.
Tech Briefs: Could you describe
your process?
Kirka: It's large-scale manufacturing
via arc welding. We use a standard
electric arc welder on a robotic arm
that can move in three-dimensional
space. The welder feeds a wire, melts
it, and the robot moves it around to
deposit the molten metal in a controlled
manner.
Tech Briefs: It seems that this is very
different from standard 3D printing.
It must be challenging to precisely
control the robotic arm.
Kirka: Yes, with the most common
printing techniques, you are looking
at printing parts that are 20 pounds up
to several thousand pounds. Standard
metal-printing does five to maybe 50
or 100-pound parts, using powder bed
techniques. We've been looking at how
to scale up to large objects - the steam
turbine blade we printed, for example,
is about 3-feet tall. Generally, you can't
print something like that in a powder
bed system.
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Tech Briefs: Do you use scanning to
check the piece?
Kirka: We've used different types of
scanning: blue light scanning to get an
idea of the geometry as it was growing,
and after the print is completed, we use
computed tomography to look internally
into the structure for defects. But
also on the robot, when we start a new
layer, there's a sensor that will touch the
very top of the part to locate it, because
when you print, you're at very high temperatures,
close to the melting point,
as you're depositing material. But then
it cools down and shrinks. So, for every
layer you have to find the top of the part
because it's not where it was when you
stopped the process, and then relocate
the robot accordingly.
Tech Briefs: What about the problem
of having contoured surfaces so
there are no perpendicular edges to
use as locating features?
Kirka: In general, that's a challenge
with any part that has something like a
turbine blade type geometry - they all
have a taper or curvature. So, we call
what we print, the preform. We then
have to identify where the part is within
that preform to be able to machine it.
Even if a turbine blade is made by casting
or forging, every surface has to be
machined because it's a precision object.
Tech Briefs: What are the next steps?
Kirka: This project was originally looking
at ways to repair blades. Although
we're looking for funding for new projects
in that area, we're also looking at
printing larger components of steam turbines.
We'd like to apply our technology
to other areas of industrial needs in the
energy sector that have long lead times
associated with them - six months to
two-years.
To read the full interview, visit www.
techbriefs.com.
Tech Briefs, February 2024
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Tech Briefs Magazine - February 2024

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