T
he radioscopy process is run-
ning at full tilt. At intervals
lasting just a few seconds,
the heavy rectangular parti-
tion opens and closes. One after the
other, gleaming silver test specimens
disappear inside to be X-rayed. The
“
patients” in this case are unmachined
cast alloy wheels. “Rapid acceleration
and dynamic cornering may be excit-
ing for drivers of sports cars, but they
subject the alloy wheels to extreme
loads. This means that manufacturers
are obliged to conduct thorough tests.
Even the smallest air bubbles, pinholes
or foreign bodies in the aluminium
cast can cause the wheels to break,”
explains Felix Richter, engineer with
Bavarian automation specialists Erhardt
+ Abt, who developed “HeiDetect
Wheel”, a fully automatic in-line testing
system that offers significant benefits
in mass production. At the heart of the
system is an X-ray test system with
detector developed by the Fraunhofer
Institute for Integrated Circuits (IIS).
Its powerful vision system detects even
the tiniest of casting defects quickly
and reliably.
Rapid handling
A handling gantry from Festo is responsi-
ble for delivering the high process speed.
It transports up to 140 wheels per hour
through the system. It was implemented
according to the exact specifications
of Erhardt + Abt. “The system has an
extremely compact design. At some
points the distance to the housing is just
two to three millimetres. This demanded
maximum precision from Festo,” says
Richter approvingly. Festo delivered
the gantry as a ready-to-install unit.
Richter’s team simply had to connect up
the interfaces and base plate of the sys-
tem and then mount the radiation-safe
steel-lead-steel chamber on top of it.
Before the wheel enters the system,
an upstream station reads its technical
data, including diameter and height,
using a bar code. The gripper unit in the
X-ray cabinet gets ready for action in
accordance with the registered values
and moves into the optimal position. As
soon as the partition opens and the alloy
wheel enters, the gripper grasps it using
its support wheels. A multi-position
cylinder ADNM ensures a perfect grip
by adapting the movable front pair of
rollers precisely to the wheel size. To
ensure that even the smallest detail
is recorded, two servo motors of type
EMMS turn the wheel clockwise around
the hub during the X-ray process.
A tough nut
Including the fixed alloy wheel, the
gripper supports up to 168 kg. “Ensur-
ing that the gantry construction had
the necessary rigidity and dynamic
response, that was a tough nut to crack.
Particularly as the operating tempera-
tures can fluctuate between 15 and 60
degrees Celsius depending on the time of
year and throughput,” explains Wolfram
Turnaus, sales engineer at Festo. It’s his
job to work with customers in search of
new solutions. In this case he needed to
find high-performance cushioning for
the partition. As soon as an alloy wheel
enters the X-ray cabin, the 90 kg parti-
tion drops like a trap door. “It closes in
just 0.6 seconds,” says Turnaus. A con-
ventional oil-pressure shock absorber
or servo-controlled drive were ruled
out for the partition due to cost and
maintenance reasons.
Ready-to-use precision:
Erhardt + Abt
only had to connect the handling
gantry with the gripper unit using
defined interfaces.
“
The handling gantry was supplied
ready-to-install. This allowed us to
concentrate fully on the engineering
and design of the testing system.”
Felix Richter, design engineer with Erhardt + Abt