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MTU Global
A thousand tons
for a good fit
By Manfred Ruopp
A dull thud behind the machine fairing announces that MTU Aero Engines’ new friction
welding machine has just joined together another pair of engine parts under up to 1,000 tons
of pressure. That’s like twelve locomotives bearing down on you all in one. After fully three
years of planning and development, Germany’s leading engine manufacturer, in partnership
with mechanical engineering company KUKA Aerospace Group, is revolutionizing the manufacture
of compressor rotors with a novel machine of theirs.
Since this spring, the machine has been
serving in the production of rotating components
like blisks and spools. Its highly precise
action makes it unique in the world: it
joins components together to tolerances of
ten hundredths of a millimeter. The technology
behind it was developed as part of research
projects, with funds provided by the
Free State of Bavaria and the Bavarian
Research Foundation. MTU assumed over
seven million euros of the cost. Partners in
the venture were Munich Technical University,
the Erlangen-Nuremberg Friedrich Alexander
University, the Bavarian Research
Foundation and the Bavarian Economics
Ministry.
For friction welding, one member of a joint is
clamped in place on a rotating spindle while
the other is attached opposite it on a tailstock.
When a given speed is reached, the
contacting surfaces heat up by friction to
welding temperature. Simultaneously, upsetting
pressure is finally applied to complete
the welding process.
What makes the new machine so unique are
its two spindles with premounted flywheels
on it, a previously unparalleled arrangement.
Unlike on conventional single-spindle machines,
variable centrifugal masses can so
be applied from 500 to 45,000 kilograms per
square meter. The upsetting pressure is infinitely
variable from 100 to 1,000 tons to suit
the component under work.
Gerhard Bähr, who heads blisk production at
MTU, views the investment in the high-end
machine as a strategic decision, one that
helps secure MTU’s technological spearhead
position. “The machine is suited for all of the
company’s current and pending engine programs.”
Highly advanced control systems help join components
with maximum precision.
A giant of that ilk: the new friction welding machine is 20 meters long and partially buried in the shop floor.
In fact, the company’s new engine projects
call for higher upsetting pressures and centrifugal
masses in friction welding than used
so far. Another consideration is that the
increasingly growing compressor temperatures
require not only titanium but also more
temperature-resistant materials to be welded,
such as the nickel-base alloys Udimet
720 or Inconel 718. In the quest for weight
and volume reduction, friction-welded joints
are often considered more desirable than
bolted connections. Likely, friction welding
will spread also to bulkier components.
Concludes Bähr: “The requirements for the
machine were dictated by the higher welding
energies needed and the size of components
it could handle.”
For the production expert, it is not only the
technical options provided by the machine
that count but moreover, and equally important,
its integrability into the production
cycle. Comparison with previous friction
The welding process proper takes only a few seconds.
It produces an extremely homogeneous joint.
welding machines makes that obvious: with
them, the machine operators need a crane to
heave the tons and tons of flywheels on to
the spindle and manually attach them there,
a process that may take as many as one-anda-half
work shifts. Whereas on the new
machine with its automated mass mechanism
the centrifugal masses are premounted
on the spindles. When the desired moment
of inertia is entered into the control unit, the
centrifugal masses are individually engaged
in the spindle. Setup times are so reduced to
two hours. This, plus the fact that the heating
cycle associated with the existing machine
is obviated, makes the new machine
suitable for multishift operation.
Toward the end of the friction cycle, care
must be taken to position the members properly
in relation to one another, and this is
where the new machine is again setting new
benchmarks. It easily cuts post-weld runout
tolerances in half, to about one tenth of a
millimeter. This is made possible by automated
laser triangulation measurement of
the spindles and components relative to
each other and automated adjustment of
their alignment. This approach opens up new
opportunities for near net shape welding
and, in production, novel approaches to the
production cycle, as for instance with complex
blisk spools.
For additional information, contact
Gerhard Bähr
+49 89 1489-8542
For interesting multimedia services
associated with this article, go to:
http://www.mtu.de/107Welding
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