JOSH: In order to get Astronauts beyond the
International Space Station, NASA needs the most advanced
materials, and innovative ways to tie it all together.
Take a closer look at the leading edge of the
technology that will launch us towards the lunar surface...
It’s lessons in heavy metal... and it’s next on Real World.
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To create a very special spacecraft... one that could
one day take astronauts back to the moon...
NASA is using some very special parts.
The Ares I rocket is made up of advanced materials and amazing engineering.
Take for instance the spacecraft’s skin.
Ares 1’s shell will be made from Aluminum-lithium 2195,
which is very strong and very light.
But when you weld pieces of this material together...
using traditional fusion methods that melt the metal...
you get big problems in the form of tiny holes.
These small pores weaken the metal and make it useless
in an application like Ares 1.
So NASA needed to find a better way to do it.
ROBERT CARTER: Here at the Marshal Space Flight Center, we do friction-stir welding.
JOSH: Robert Carter is shop floor lead in the Weld
Process Development Facility at the Marshal Space Flight
Center in Huntsville, Alabama.
ROBERT: Friction-stir welding is a solid state welding process.
Solid state means that there is no melting involved in this process.
JOSH: In conventional fusion welding, pieces of metal are
melted at their common area and joined together.
But this is different. In friction-stir welding the
heat and force cause the two pieces to become one.
Yeah... I weld.
ROBERT: The way it works is we have what we call a pin-tool,
this is a pin-tool, and this tool is rotated at several hundred rpms.
It’s plunged into the surface of a work piece with
tens of thousands of pounds of force.
It’s then traversed along this weld joint while it’s rotating,
til it gets to the end of a weld and then we retract,
and that’s the end of the weld.
JOSH: So the friction causes the heat. The faster the pin
tool rotates and the faster the traverse, the more friction,
and thus, more heat. The heat softens the metal,
but it doesn’t melt it. This state where the metal is soft,
but not liquefied, is known as plasticity.
This happens at about 800 degrees Fahrenheit for most metals.
To find the Celsius equivalent, Subtract 32
from the Fahrenheit temperature, 800 and
multiply by five-ninths. That’s nearly 427 degrees Celsius.
The force applied to the soften metal by the rotating
pin-tool, turns the two pieces of metal into one seamless solid sheet.
ROBERT: If you look at the very beginning of this plate
here you can see that this was originally two pieces of
metal that have been welded together using friction-stir welding.
And then just to look at the back, when we perform
friction-stir welds, we’re pushing up against a solid backing anvil.
And so this is what the root side of the weld joint looks like.
It’s completely smooth.
JOSH: For welding two very large pieces together,
Robert uses a slightly different process.
ROBERT: There is another version of friction-stir
welding that we developed here at Marshal called self-
reacting friction-stir welding, which is done with a
tool that looks like this. And what we do in self
reacting is rather than having this type of pintail,
which would push against a solid backing anvil,
we actually install the tool in the plate, like so,
and we pinch the part between two shoulders, while this
assembly is rotating and traveling.
So in this process what we do is we eliminated the need for a backing anvil.
The benefit there is it makes our tooling somewhat simpler
and easier to fabricate when we’re building large scale.
JOSH: Without stir friction welding, Ares I might never
be able to get off the ground.
ROBERT: We get improved mechanic properties over
conventional fusion welding. We also tend to produce fewer
defects and those two things together mean we can build a
vehicle that’s lighter because the improved
strengths allows us to reduce our weld and thicknesses.
So we have better tensile strength, and also we have
improved fracture properties.
Basically that means that there is less of a propensity for cracks to grow.
In general, friction-stir welds have strengths that are
roughly 20 percent better. That means a 20 percent
improvement in mechanical properties relative to fusion welds.
JOSH: They do all the work in this huge building at Marshal.
ROBERT: This facility is called the Weld Process
Development Facility. Everything you see in here
right now today is being designed, developed,
installed specifically to build Ares I upper stage full
scale developmental hardware.
So we’re going to be building manufacturing demonstration article.
We’re also going to be building potentially at least,
some of the structural development test articles
that will be used for the Ares 1 upper stage.
We’re developing all the manufacturing techniques so
that we can find the problems and work out the bugs,
even develop our tooling designs, develop our fixture
designs, develop the software for the weld tools.
We do all that up here at Marshal, offline, so that we
don’t end up having to solve these problems on the shop floor.
JOSH: All this hard work and amazing engineering has this
next generation spacecraft pointed in the right
direction as NASA looks beyond the space station,
to take astronauts to new worlds.
Follow the journey at www.nasa.gov.
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