 The Modig Universal Holding
Fixture for Skins is used for clamping of 3D formed sheets while milling, routing, laser
scribing, etc. With its grid of posts, it offers a high degree of flexibility to clamp the
workpieces rigidly. The picture shows a fixture where the setting of
the posts are performed by a gantry setting machine, operating from above. Setting from
underneath is also available.
The Modig UHF System is designed in such a way that it is easily built
to customer specifications: the length of the stroke of the posts, the pitch between
posts, the total number of posts in the grid, etc.
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 The gantry setting machine as
shown in this example is equipped with 8 NC axes, one for each post in one row. The NC
axes move the positive stops to the required position for each post at a very high speed
with high accuracy. The setting of the posts is performed row by row.
As each post reaches position it is clamped around the periphery. The time to set 256
posts (32 rows) takes only 6 minutes.
When the gantry setting machine, as in the machine shown, uses the same
guideways as the scribing and/or milling machine, the accuracy will be very high.
With the alternative of setting posts from underneath, a row of 8 posts
are set by one elevator plate powered by one servo motor. Each row has its own elevator
plate so that the entire field is set at one time.
When the post is set in position, the locator for the workpiece will be
the reference ball in the top of each post. Around the reference ball is a vacuum cup
which tilts ± 45°.
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 The vacuum cup is designed to be
as flexible as possible to clamp workpieces with a steep contact angle to the reference
ball. It is also designed to work as a shock absorber while clamping of
a workpiece is performed: if the vacuum is applied quickly there is a risk that the
reference ball can cause a dimple in the workpiece, the rubber cup will help absorb the
shock to help prevent part damage.
The vacuum can automatically be adjusted from the CNC control during
the process.
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 While loading of a workpiece, air
is blown out of the vacuum holes. This creates an air bearing for assisting the operators
in getting the workpiece into the correct position. The peripheral
clamp of each post is designed similar to that of hydraulic chucks, providing secure
clamping for an accurate position at all times.
Each post can carry a load of 770 pounds (350 kg) so even if one post
is carrying the full load of a workpiece during any moment while loading the work it will
not deflect.
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 The posts are mounted in
cassettes; the example shows each cassette carrying 4 posts. The number
of parts in each cassette and post is very low making maintenance easy and the risk for
downtime very small.
The cassettes can easily be lifted out of the fixture for maintenance
and replaced by a spare cassette. Location of each cassette is by high precision expanding
bolts in hardened and ground reference holes.
The diameter of a post is 3.15" (80 mm) and the stroke vertically
is 29.5" (750 mm) or more as required.
The posts can be active during the machining process allowing
individual retraction of 4" from the workpiece while the cutting tool passes. The
post is repositioned as soon as the tool passes and the vacuum is re-applied.
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 The part locator is used to fix
the workpiece in its correct position during the loading operation. A plug is located in a
pre-drilled hole of the workpiece for the reference position. The part
locator can be placed on two, three, or four posts as required.
Since the posts are very rigid, it is possible to machine a custom part
locator directly on the UHF. |
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