offers quality assurance for riveted joints
FMW
Nietcontrol
offers quality assurance for riveted joints
FMW Nietcontrol, the control system for radial point riveters with patented
measuring axes.
This is the formula for success offered by the FMW
Nietcontrol:
Minimum operator work = maximum safety of operation = optimum quality assurance
meters are monitored by measuring the path length, the force of pressure and the
riveting time.
All relevant data is shown on the display and saved under a programme number.
Errors are localised
and their point of origin is shown. Path measurement is the most important
parameter for assuring the
quality of a riveted joint. The path, i.e., the rivet length, the projection and
the rivet head height can be
verified at the riveting workplace at any time, in a reproducible way and
accurately to a hundreth.
The compliance with tolerances specified on drawings can be checked and
documented by the machine.
With the FMW riveting process visualisation system the
measured values emitted by the control system
are collected on a continuous basis and used to determine machine capability and
process capability.
FMW
Riveter with Length Measurement
The lengths are measured at the unriveted rivet bolt (length Z1) and at the
finish riveted rivet bolt (length
Z2). The length measuring device arranged directly at the riveting spindle
transmits the measured values to
the FMW Nietcontrol at millisecond intervals.
Measurements are permanently taken during the riveting oper-
ation. At the same time, programmable time frames enable the operator to check
whether the material
properties meet the specifications.
The riveting operation when a length measurement is taken
At
start pressure and with the riveting die aligned in the longitudinal axis, the
FMW Nietcontrol directs the
riveting spindle to the rivet. The pressure is reduced to avoid a deformation of
the rivet bolt during measuring.
If the length of the unriveted rivet (Z1) is outside the tolerance, a NIO (not
in order) message is given. As the
rivet bolt was not deformed during the measurement it can be replaced by a new
one to finish the riveting
operation. If the length (Z1) is within the specified tolerance the riveting
motor is started at the programmed
riveting pressure and riveting takes place until the finished dimension (Z2) is
reached. If the finished dimension
(Z2) entered in the control unit is within the tolerance and if the riveting
operation takes place within the specified
time frame, the riveted joint is ok. The riveting spindle travels back and the
riveting die is again aligned in the
longitudinal axis. If the finished dimension measured is outside the specified
tolerance or if the riveting operation
does not take place within the time frame set, a NIO message will be given.
FMW
Riveter with Projection Measurement
What is measured on this machine is the projection of the rivet bolt (H1) on the
unriveted rivet and the rivet head
height (H2) on the finish riveted rivet. The projection measuring device is
arranged directly at the spring-loaded
downholder. For adjusting purposes the downholder measuring system is compressed
on a plane surface.
The measuring system is zeroized when the downholder and the riveting die are at
one level. The compression of
the downholder is released while the riveting spindle moves back, and the
riveting die will come to stand behind the
downholder by the dimension of the downholder movement. The projection value is
shown on the display.
The riveting operation when a projection measurement is taken
At
start pressure and with the riveting die aligned in the longitudinal axis, the
FMW Nietcontrol directs the riveting
spindle to the rivet. When the riveting spindle is advanced, the downholder
measuring system is first pre-loaded
until the riveting die meets the rivet. The measuring (H1) takes place at low
pressure so that no deformation
is caused to the rivet bolt. At the same time the projection measurement makes
it possible to check whether all parts
of the joint to be riveted are available. If a part is missing, a NIO message is
sent. The part can be inserted sub-
sequently and finish riveted. The projection measurement thus helps to avoid
unwanted faulty rivetings. If the pro-
jection dimension of the unriveted rivet is within the specified tolerance the
riveting motor is started at the programmed
riveting pressure and riveting takes place until the finished dimension is
reached. If the finished dimension (rivet head
height H2) entered is within the tolerance and if the riveting operation takes
place within the specified time frame,
the riveted joint is ok. The riveting spindle travels back and the riveting die
is again aligned in the longitudinal axis.
If the finished dimension measured (H2) is outside the specified tolerance or if
the riveting operation does not
take place within the time frame set, a NIO message will be given.
FMW
Nietcontrol with Projection and Length Measurements
The riveter is equipped with two measuring axes. The operator is thus enabled to
set the priorities considered most
important for his quality assurance goals. He can for example select Priority 1
for measuring the overall length of the
unriveted rivet bolt with the length measuring system and Priority 2 for
measuring the finish riveted rivet head height
with the projection measuring system. The operator can, at his option, select
priorities and associate them to differ-
ent riveting points.
Identifying the correct rivet material is of paramount importance for quality
assurance. If aluminium rivets are used
instead of steel rivets to rivet components subject to maximum strain, this
error can entail disastrous consequences.
This is why it is so important for the machine to identify a wrong material
unequivocally.
To identify and check material properties, the following processes are known:
2. Measuring the force-time curve of a riveted joint
3. Measuring the path-time curve of a riveted joint
Owing to the intricacy of a force measurement during the riveting operation,
methods 1 and 2 are not suited for
quality assurance purposes. In highly dynamic riveting processes an exact
determination of the force is almost
impossible. Checking the material properties is only possible by making use of
the „hard“ parameters. The
“hard“, reproducible parameters such as the path and the time can be measured
very exactly and, accordingly,
be well documented. Such parameters are suited for quality assurance. By means
of measurement transducers
the path of the riveting spindle is precisely measured in the hundredth mm
region and recorded. With the FMW
Nietcontrol software the space of time is divided into millisecond
intervals. In theory it would be possible to record
a permanent curve with any number of time frames. In practise, however, one or
two time frames will do.
Representation of a riveting sequence as a function of path and time
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