Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02359792 2001-10-23
HEMMING MACHINE
Background of the Invention
I. Field of the Invention
The present invention relates generally to sheet metal hemming
machines.
II. Description of Related Art
There are many previously known hemming machines. Many
industries, such as the automotive industry, utilize sheet metal hemming
machines to secure two metal parts together. These sheet metal hemming
machines typically comprise a base having a nest vertically slidably mounted
relative to the base. The nest, in turn, supports the part to be hemmed.
At least one, and typically three to five hemming die sets are laterally
slidably mounted to the base and movable between an extended position and a
retracted position. In the extended position, the die overlaps the nest so
that
vertical displacement of the nest toward the hemming die causes the part to be
hemmed to be compressed upon the die thus forming the hem. Typically, a
prehem is first formed by a prehem die to bend the sheet metal at an angle of
approximately 45° while a final hem die retrorsely flattens the sheet
metal hem
together.
In order to form the hem, the part to be hemmed is first positioned on
the nest and, with the hemming dies retracted, the nest is moved to a position
just below the prehem die and clearing the part flange to be hemmed. The
prehem die set is then moved to an extended position after wlucb the nest is
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displaced vertically upwardly against the prehem die and retracted after
having
reached the nominal hemming pressure. The hemming dies are then moved to
a retracted position and the nest is moved to a position just below the final
hem
die. The final hem die is then moved to an extended position and the nest is
vertically displaced against the final hem die to complete the hem and also
retracted after having reached the final hem pressure. The dies are then moved
to their retracted position and the finished part is removed from the nest.
These previously known hemming machines have all suffered from a
number of disadvantages. One disadvantage is that the previously known
hemming machines have required the use of multiple hydraulic actuators to
vertically displace the nest due to the massive weight of the nest. Such
actuating means are expensive, hard to maintain and polluting.
Derivated from the previously already known maclunes, . a first
generation of electric hemmer has been developed by simply replacing the
hydraulic cylinders by one or more linear ball screws powered by
electronically
synchronized drives.
But to face the double constraint of high production rate and high
hemming pressure force, these drive configurations are generally oversized to
be able to move quickly for a prehem to a final hem position in lugh speed,
and
then to deliver a lugh torque in static. Such oversizing (x4; x6) is not only
expensive, but presents a real risk for the tooling in case of jamming or
other
incidental event, by introducing a tremendous reverse inertia to the system.
CA 02359792 2001-10-23
Summary of the Present Invention
The present invention provides a hemming machine which overcomes
all of the above-mentioned disadvantages of the previously known devices.
In brief, the hemming machine of the present invention comprises a
S base which is fixed to a ground support surface. Both a nest and nest earner
are vertically slidably mounted to the base with the nest earner positioned
beneath the nest. In the conventional fashion, the nest is adapted to support
the
part to be hemmed.
Similarly, in the conventional fashion, at least one, and more typically
three to five sets of dies, are laterally slidably mounted to the base between
an
extended and a retracted position. In their extended position, the dies
overlie
the nest and thus the part to be hemmed. Conversely, in their retracted
position, the dies are laterally spaced from the nest to permit free. vertical
movement of the nest past the dies as well as the part loading/unloading. One
die set typically performs the prehem while the other die forms the final hem.
The nest carrier and nest are vertically movably mounted not only
relative to the base, but also relative to each other. In order to displace
the nest
relative to the nest carrier, at least one hydraulic driven bladder is
sandwiched
in between the nest and the nest carrier while a lock unit selectively locks
the
nest carrier against downward movement. Thus, with the nest carrier locked
against vertical movement, inflation of the driven bladder vertically
displaces
the nest upwardly relative to the nest carrier.
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In order to selectively inflate and deflate the driven bladder, at least one
drive bladder is sandwiched in between a piston and the nest. This drive
bladder is fluidly connected to the driven bladders by fluid conduits. Thus,
with the nest carrier locked against downward vertical movement, movement
of the piston toward the nest compresses the drive bladders thus pumping
hydraulic fluid contained within the drive bladders from the drive bladders
and
to the driven bladders. This in turn vertically displaces the nest upwardly
relative to the nest carrier so that, with the hemming dies in their extended
position, the part to be hemmed is compressed against the hemming dies in the
desired fashion.
In the preferred embodiment of the invention, a plurality of pressurized
pneumatic spring (or air) bladders are sandwiched between the base and nest
earner and urge the nest and nest earner upwardly. Additionally, .a. single
rotary shaft is rotatably mounted to the base and extends through an opening
in
the nest earner and threadably engages the piston. The piston in turn abuts
against an upper surface of the nest carrier thus holding the nest carrier
against
upward movement due to the force developed by the pneumatic spring
bladders.
With the lock unit in its retracted position so that both the nest earner
and nest can move vertically relative to the base, rotation of the shaft
vertically
moves the piston upwardly so that the inflation of the air spring bladders
likewise moves both the nest and nest carrier upwardly in unison with each
other in order to position the upper surface of the nest beneath either the
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prehem or final die. When the nest is so positioned, one or more lock units
engage the nest Garner to preclude downward movement of the nest carrier.
Thereafter, continued rotation of the shaft in the same direction
continues to move the nest together with the part to be hemmed upwardly until
the part engages the hemming die. When this occurs, the upward movement of
the piston encounters an increasing downward force due to the compression of
the part against the hemming die. When this occurs, the continued upward
movement of the piston causes the piston to separate from the nest carrier
and,
in doing so, compress the drive bladders. This in turn inflates the driven
bladders with amplified force thus displacing the nest upwardly from the nest
carrier and performing either the hem or prehem operation.
The surface ratio between the drive and driven bladders is such that the
force developed by the drive bladder is amplified by a factor of four to
eight.
Brief Description of the Drawing
A better understanding of the present invention will be had upon
reference to the following detailed description, when read in conjunction with
the accompanying drawing, wherein like reference characters refer to like
parts
throughout the several views, and in which:
FIG. 1 is a sectional view illustrating the preferred embodiment of the
hemming machine of the present invention being moved to a prehem operation
position, ready to engage the upper die set, and pre-engage locks;
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FIG. 2 is a view similar to FIG. l, but illustrating the hemming machine
just after the pretending at 45°, and prior to developing the prehem
force to
sharpen the 45°edge;
FIG. 3 is a view similar to FIG. 2, but illustrating the end of the
prehemming operation;
FIG. 4 is a view similar to FIG. 1, but illustrating the hemming machine
being moved to a position ready to engage the final hemming die set and pre-
engage lock units for a final hem operation;
FIG. 5 is a view similar to FIG. 4, but illustrating the hemming machine
moved to a position in preparation for the final hemming operation;
FIG. 6 is a view similar to FIG. 5, but illustrating the hemming machine
just prior to applying the final hemming force to fully flatten the hem flange
at
the final hem operation;
FIG. 7 is a view similar to FIG. 6, but illustrating a final hem operation;
and
FIG. 8 is a view similar to FIG. 2, but illustrating the hemming machine
following completion of the final hemming operation and on its way to reach
the part unload/reload position:
Detailed Description of a Preferred
?0 Embodiment of the Present Invention
With reference first to FIG. 1, a preferred embodiment of the hemming
machine 10 of the present invention is there shown and comprises a stationary
base 12 supported by a ground surface 14. A nest carrier 18 is vertically
slidably mounted to the base 12 by vertical slides 20 and a nest 16 is
laterally
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guided by slides 21 against the base frame, both of which may be of any
conventional construction. In the initial stage of the hemming operation
illustrated in FIG. l, i.e. part loading and unloading, the nest 16 is
positioned
above and supported by the nest carrier 18 in a fashion which will be
S subsequently described in greater detail. Furthermore, the part to be hemmed
is supported by the upper surface 22 of the nest 16.
Still referring to FIG. l, at least one, and more typically three to five
sets of hemming dies 24 and 26 are laterally slidably mounted to the base 12
between an extended position, illustrated in FIG. 2, and a retracted position,
illustrated in FIG. 1. Any conventional means, such as an electric or
pneumatic
cylinder 28, is utilized to move the die sets 24 and 26 between their extended
and retracted position.
With the die sets 24 and 26 in their extended position as illustrated in
FIG. 2, the dies 24 and 26 overlie the upper surface 22 of the nest 16 and
thus
overlie the part to be hemmed. Conversely, with the dies 24 and 26 in their
retracted position as shown in FIG. 1, the nest may be vertically displaced
without interference with either the dies 24 or 26. Typically, one die 24 is
utilized to produce the prehem typically at a 45° angle on the part,
while the
other die 26 performs the final hem.
Still refernng to FIGS. 1 and 2, a lock units) 30 is laterally slidably
mounted to the base 12 and movable between an extended position, illustrated
in FIG. 2, and a retracted position, illustrated in FIG. 1. Any conventional
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means, such as a pneumatic or electric cylinder 32, may be used to selectively
move the lock units) 30 between its extended and retracted position.
The lock unit includes an upper abutment surface 34 as well as a lower
abutment surface 36. These abutment surfaces 34 and 36, furthermore, are
spaced apart from each other by substantially the same distance as the
vertical
spacing between the dies 24 and 26. Thus, with the nest earner in the upper
position illustrated in FIG. 2 such that the nest surface 22 is positioned 2"
to 3"
below the prehem die 24, and after a preliminary stroke of the next earner
(1 7/8" to 2 7/8"), the lock unit is finally engaged to its extended position
(FIG.
2), a lower surface 40 of the nest carrier abuts against the upper abutment
surface 34 of the lock unit 30. Consequently, in this position, the lock unit
30
prevents downward movement of the nest carrier 18 relative to the base.
Similarly, as shown in FIG. 5, with the nest carrier 18 in its lower
position such that the nest surface 22 is positioned 2" to 3" below the final
hem
die 26, and after a preliminary stroke of the nest (1 7/8" to 2 7/8"), the
lock unit
30 will reach its extended position causing the lower surface 40 of the nest
carrier 18 to abut against the lower abutment surface 36 of the lock unit 30.
The lock unit 30 thus locks the nest carrier 18 against further downward
movement relative to the base 12.
As best shown in FIG. 1, both abutment surfaces 34 and 36 on the lock
unit 30 are tapered downwardly and correspond with a like upwardly tapered
surface 40 on the nest carrier 18. The cooperating tapered surfaces 34 and 40
or surfaces 36 and 40 thus allow the cooperating surfaces to slide against
each
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other as the nest earner 18 is moved to either its upper position (FIG. 2) or
its
lower position (FIG. 6).
With reference now to FIGS. 2 and 6, in order to vertically displace the
nest 16 together with the nest carrier 18 from its lower position (FIG. 6) to
its
upper position (FIG. 2), a plurality of pressurized pneumatic spring bladders
100 are sandwiched in between the base and a lower surface 102 of the nest
carrier 18. The spring bladders 100, furthermore, are pressurized by a
pneumatic circuit with a pressure sufficient to move and accelerate both the
nest carrier 18 and nest 16 from their lower position (FIG. 6) and to their
upper
position (FIG. 2) unless restrained. One or more air reservoirs or surge tanks
104 form a part of the pneumatic circuit.
Still referring to FIGS. 2 and 6, in order to provide controlled vertical
movement of both the nest carrier 18 and nest 16 between their upper position
(FIG. 2) and lower position (FIG. 6), an externally threaded shaft 106 is
rotatably mounted by a bearing assembly 108 to the base 12 so that the shaft
106 extends through an opening 110 formed in the nest carrier 18. Any
conventional means, such as an electric motor or hydraulic motor 112, is
utilized to rotatably drive the shaft 106 via a timing belt mechanism 114.
The shaft 106 threadably engages an internally threaded piston 116
which is positioned between the nest 16 and nest carrier 18. A lower surface
120 of the piston 116 abuts against an upper surface 122 of the nest carrier
18
in order to limit the upward movement of the nest carrier 18 and thus the
upward movement of the nest 16.
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For example, assuming that the nest Garner 18 is in the position
illustrated in FIG. 6 and also assuming that the dies 24 and 26 are in their
retracted position, rotation of the shaft 106 in the direction of arrow 126
causes
the piston 116 to move upwardly. Simultaneously, the spring bladders 100,
due to their pressurization, upwardly displace both the nest Garner 18 and
nest
16 in unison with the piston 116. The expansion of the spring bladders 100
together with the rotation of the shaft 106 are utilized to move the nest 16
and
nest carrier 18 between the position shown in FIG. 6, i.e. just prior to a
final
hem operation, and the position shown in FIG. 2, i.e. just prior to a prehem
operation. With the nest carrier 18 in either the position shown in FIG. 2 or
FIG. 6, the lock unit 30 is moved to its extended position thus locking the
nest
Garner 18 against downward movement.
With reference now to FIGS. 2 and 3, in order to move the nest 16 from
a position just prior to the prehern position (FIG. 2) and to the final prehem
position (FIG. 3), at least one, and preferably several drive bladders 130 are
sandwiched in between an upper surface 132 of the piston 116 and a lower
surface 134 on the nest 16. These drive bladders 130, furthermore, are fluidly
connected by a conventional fluid circuit 136 to driven bladders 138 which are
sandwiched in between the lower surface 134 of the nest 16 and an upper
surface 140 of the nest carrier 18. Consequently, deflation of the drive
bladders 130 causes a resultant inflation of the driven bladders 138 thus
separating the nest 16 from the nest carrier 18. Preferably, the drive
bladders
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130 and driven bladders 138 are dimensioned to provide an amplification of
four to eight.
With the hemming machine 10 positioned as shown in FIG. 2, the nest
16 is positioned in preparation for a final prehem operation. At this time,
the
nest 16 is in abutment with the nest carrier 18 while the lock unit 30
prevents
downward movement of the nest carrier 18.
Continued rotation of the shaft 106 in the direction of arrow 142 causes
the nest 16 to move upwardly so that the part to be hemmed engages the
prehem die 24. When this occurs, the increased resistance caused by the
compression of the part against the prehem die 24 overcomes the pressure in
the air spring bladders 100 and causes the piston 116 to separate from the
nest
carrier 18 as shown in FIG. 3 thus compressing the drive bladders 130 and
inflating the driven bladders 138. This in turn causes the nest 16 to separate
from the nest earner 18 from the position shown in FIG. 2 and to the position
shown in FIG. 3 thus performing the prehemming operation. FIGS. 6 and 7
illustrate the identical sequence of operation for the final hem operation.
A primary advantage of Applicant's invention is that the shaft 106
together with the air springs are utilized to move the nest 16 from its lower
position as well as perform both the prehem and hem operations without
reversing the direction of rotation of the shaft 106. Reversal of the
direction of
rotation of the shaft 106 is only necessary to move the nest 16 and nest
carrier
18 from their upper position following the prehemming operation and to the
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lower position just prior to the final hem operation. Consequently, cycle time
is minimized.
The operation of the hemming machine will now be described. In FIG.
l, the nest 16 is illustrated in a part load/unload position in which the dies
24
S and 26 are in their retracted position and the lock unit 30 is likewise in a
retracted position. The nest support surface 22 is positioned in between the
dies 24 and 26.
As best shown in FIG. 2, rotation of the shaft 106 in the direction of
arrow 142 moves the piston 116 upwardly thus allowing expansion of the air
spring bladders 100. The expansion of the air spring bladders 100 moves the
nest carrier 18 as well as the nest 16 supported by the nest carrier 18 to the
position shown in FIG. 2, performing by there the prebending of the flange at
45°, and in which the nest surface 122 is in a position thus prior to
the final
prehemming operation. At tlus time, the dies 24 and 26 are moved to their
extended position while, likewise, the lock unit 30 is moved to its extended
position thus preventing downward movement of the nest carrier 18 relative to
the base 12.
With reference now to FIG. 3, continued rotation of the shaft 106 in the
salve direction as shown by arrow 142 causes the part to be hemmed to
compress against the prehem die 24. When this occurs, the increased
resistance caused by the compression of the part against the hemming die 24
overcomes the pressure of the air spring bladders 100. Consequently,
continued rotation of the shaft 106 causes the piston 132 to lift upwardly
from
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the nest carrier 18 and compress the drive bladders 130 against the nest 16.
This in turn inflates the driven bladders 138 with an amplification factor
thus
causing the nest 16 to separate upwardly from the nest carrier and compress
the
part against the prehem die 24. Furthermore, during the prehem operation, the
lock unit 30 is in its extended position thus preventing the nest carrier 18
from
shifting downwardly upon the expansion of the driven bladders 138.
Following the prehem operation, the hemming dies 24 and 26 are
moved to their retracted position by the cylinder 28 as shown in FIG. 4 and,
likewise, the lock unit 30 is moved to its retracted position by the cylinder
32.
The direction of rotation of the shaft 106 is reversed as illustrated by arrow
150
thus moving the piston 116 downwardly. The downward movement of the
piston 116 likewise moves the nest earner 18 together with the nest 16
downwardly against the force of the spring bladders 100 until the nest 16 and
nest carrier 18 reach the position illustrated in FIG. 5. At this time, the
nest
surface 22 is positioned 2" to 3" below the final hem die 26. At this time,
the
cylinder 28 moves the hemming dies 24 and 26 to their extended position and,
likewise, the cylinder 32 attends to move the lock unit 30 to its extended
position.
With reference now to FIG. 6, the rotation of the shaft 116 is reversed
as shown by arrow 126 thus moving the piston 116 upwardly. Simultaneously,
the spring bladders 100 move both the nest carrier 18 and nest 16 upwardly to
the position shown in FIG. 6 in which the nest surface 22 is positioned just
below its final hem position. At this time, under the action of cylinder 32,
the
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lock unit will fully engage, thus precluding downward movement of the nest
carrier 18.
With reference now to FIG. 7, the continued rotation of the shaft 106 in
the direction of arrow 126 causes the nest 16 to move upwardly so that the
part
is compressed against the final hem die 26. The force exerted between the
final
hem die 26 and the part, together with the weight of the nest 16, nest Garner
18,
and their associated components, overcomes the pressure of the air spring
bladders 100. When this occurs, the piston 116 again separates upwardly from
the nest carrier 18 thus compressing the drive bladders 130 and inflating the
driven bladders 138. As with the prehem operation, the inflation of the driven
bladders 138 causes the nest 16 to separate upwardly from the nest carrier 18
thus moving the nest from the position shown in FIG. 6 to the final hem
position shown in FIG. 7. '
With reference now to FIG. 8, following the final hem operation, the
hemming dies 24 and 26 are moved to their retracted position thus allowing
vertical displacement of the nest 16 without interference from the hemming
dies 24 and 26. Likewise, the lock unit 30 is moved to its retracted position
thus allowing the spring bladders 100 to urge the nest Garner 18 and nest 16
upwardly. Thus, continued rotation of the shaft 106 in the same direction as
during the final hem operation as illustrated by arrow 126 moves the nest 16
to
the load/unload position illustrated in FIG. 1 whereupon the above process is
repeated.
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From the foregoing, it can be seen that a primary advantage of the
present invention is that the entire hemming operation can be performed from
part load and through the final hem operation by only changing the direction
of
rotation of the shaft a single time. This decreases the cycle time for the
hemming machine over the previously known devices.
Having described my invention, however, many modifications thereto
will become apparent to those skilled in the art to which it pertains without
deviation from the spirit of the invention as defined by the scope of the
appended claims.
I claim:
