Curtiss Wright Nuclear
Wire Inspection: As Fast as a World-Class Sprinter
Posted:
The wire blank shoots from the drawing die which molds it into the desired
shape. Up to ten meters per second, the workpiece is fast – and thus can keep
pace with world-class runners like Usain Bolt. At these speeds, an in-line
inspection – inspecting the workpiece during the production process – would
have been inconceivable, until now. Researchers at the Fraunhofer Institute for
Physical Measurement Techniques IPM in Freiburg have now closed this
technological gap. Their optical inspection system, WIRE-AOI, can detect defects
in strip products in real time. Strip products are long workpieces – like pipes,
rails, wires, or boards – that are manufactured at high flow velocities. The
inspection system detects micro-defects that zoom past it at ten meters per
second, and are no thicker than a human hair. Workers then see the processed
defects depicted graphically on a monitor, and can remove the corresponding
pieces. The system marks the location of the defect, and stores the associated
camera image in a database. This way, the makers of strip products can identify,
classify, and document defects during production. For instance, by determining
surface defects at the threshold levels for depth, width, and length adapted for
their own production. If the workpiece exceeds these parameters, then the
software sounds the alarm optically and acoustically.

10,000 images per second

Four high-speed cameras deliver the images of the defects. Each one is capable
of shooting 10,000 images per second, and processing them in real time. "Only a
handful of models for industrial camera inspection are able to record this
number of images in the first place, much less analyze them in real time," says
Dr. Daniel Carl, group manager for Inline Measurement Techniques at IPM.
Prerequisite for this peak performance are cellular neuronal networks. "That
means each pixel is itself a computer in its own right. In order to program these,
you need specialized knowledge about parallel architectures that the team at IPM
has at its disposal." The corresponding software must first enable the system to
analyze the images shot by the camera.

An LED light developed by Carl's research team puts sharpness into the camera
images. Its light shines at a 5 millionth of a second, as bright as 100 suns, and
flashes 10,000 times per second. "That is just like normal photographs. The
brighter the light and shorter the illumination period, the sharper the images of
moving objects. The image does not blur since, in such short periods of time, in
principle nothing moves - even at speeds of up to 10 meters per second," Carl
added. The human eye can hardly perceive these very short light times.
Therefore, the system is safe for the retina despite the extreme brightness.

Another important element: sturdy housing. Because things can get rough when
producing strip products. For example, in the production of wire: The blanks are
either rolled or drawn through dies. This can get messy, or the system vibrates.
The inspection system, with its sensitive electronic and optical components, is in
the middle of the production line. "The workpieces literally go directly through
it," describes Carl.

Minor defect, major impact

The drive to develop the sturdy, very fast and precise inspection system came
from colleagues at the neighboring Fraunhofer Institute for Mechanics of
Materials IWM. "Their job is materials inspection, including that of wires. We
noticed that these could have many and very diverse defects if they were
produced industrially, but that an inline inspection system would have missed
until now," says Carl, in whose group the first prototype was developed. Even the
smallest surface defect – not larger than a few micrometers – could have
undesired consequences: Either right in production, when the defective wires are
processed further – and bring the machinery to a stop. Or as part of the end
product, if they disrupt its function. One example is defective wire springs were
installed in motorized valves, which could lead to damage to the motor.

The inspection process has matured to the point that the scientists are now
offering it to wirepullers. The technology has already been successfully in use for
some time now; several additional projects are planned. Anyone who would like
to make an image themselves: The IPM researchers are exhibiting their superfast
wire inspection at the wire trade show from April 7 to 11, 2014 in Düsseldorf
(Hall EN/08), at Control from May 6 to 9, 2014 in Stuttgart (Hall 1, Booth 1502),
and at the Wire Industry Convention May 8, 2014 in Iserlohn.
Mistras Group