Note: Descriptions are shown in the official language in which they were submitted.
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Pao422s/wo/1
DaimlerChrysler AG
Method and device for producing a peripherally
closed hollow profile
The invention relates to a method of producing a
peripherally closed hollow profile according to the
preamble of patent claim 1 and to a device for this
according to the preamble of patent claim 3.
A method of the generic type or a device of the generic
type has been disclosed by DE 195 30 056 A1. In the
method described there, a branch is shaped from a hollow
profile blank by means of internal high pressure, this
branch being supported at its cap by a yielding
counterhold~r during the shaping process. In the marginal
region of the cap, the branch in each case has a large
radius, so that it bears only with its center region
against the end face of the counterholder. The supporting
surface formed by the end face of the counterholder is
enclosed by a collar-like, concave cutting edge. The
center region of the cap of the branch is thus located,
as it were, in a hollow of the counterholder, After the
desired height of the branch is reached, the forming
pressure is considerably increased, as a result of which
the radius in the marginal region of the cap of the
branch decreases and the latter is pressed against the
vertically projecting cutting edge. As a result, the
cutting edge cuts an encircling groove in the cap. The
counterholder is now displaced toward the branch against
the shaping direction of the branch, as a result of which
the cutting edge of the counterholder cuts completely
through the cap. In the process, the counterholder
plunges into the opening, thus produced, of the branch,
In this case, a calibrating bead axially adjoining the
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cutting edge smooths the inner wall of the branch.
Considerable outlay is required in order to produce this
cutting edge of special design. Furthermore, this cutting
edge of special design is subjected to extremely
pronounced loading by the increased internal pressure
above the forming pressure, a factor which relatively
quickly leads during operation to chipping at the cutting
edge and thus results in a short service life of the
counterholder. On account of the described high
susceptibility of the cutting edge to the high, fluidic
and mechanical loads, severing of the cap in series
production in a reliable manner in terms of the process
is not possible, since, after damage to the cutting edge,
the stamping of the openings at the branch is effected
only incompletely and as a result the component thus
produced has to be scrapped. The costs arising here are
considerable, which, in addition to the increased use of
material, also include the downtimes for re-setting or
repairing the counterholder.
The object of the invention is to develop a method of the
generic type to the effect that the production of a
hollow profile having secondary features and/or branches
is made possible, during which reliable severing of the
cap of the secondary feature or of the branch is achieved
in a simple manner. Furthermore, a device for carrying
out the method is to be shown.
The object is achieved according to the invention by the
features of patent claim 1 with regard to the method and
by the features of patent claim 3 with regard to the
device.
The invention is based on the surprising knowledge that
the cap of the secondary feature and/or of the branch can
be neatly severed even at an internal high pressure which
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corresponds at most to the forming pressure for forming
the hollow profile from the blank. Unlike in the prior
art, the severing of the caps is effected solely by a
stroke of the counterholding punch in the opposite
direction to the expansion direction of the hollow
profile. In the process, the end face of the
counterholding punch runs in a continuously even manner
and thus has no cutting or severing contours of special
design. As a result, not only is the counterholding punch
of markedly simpler configuration, which considerably
reduces the outlay in terms of equipment, but the end
face and the severing contour of the counterholding punch
also become less susceptible to mechanical loads, which
ensures especially long durability of the severing
contour of the counterholding punch. There is also the
fact that the internal high pressure still does not have
to exceed the forming pressure in order to sever the cap
of the secondary feature and/or of the branch, but rather
the forming pressure normally applied or also pressures
which do not exceed said forming pressure are sufficient
in order to neatly sever the cap, a factor which
additionally relieves the severing contour. Excessive
outlay in terms of equipment is not necessary far this
purpose, this outlay being necessary at pressures which
exceed the forming pressure, since the closure force for
the hydroforming tool can only be applied by
extraordinarily powerful hydraulic cylinders and an
extremely robust press frame. However, the width of the
annular gap between the wall of the passage, which is
formed in the forming tool and in which the punch is
guided in a displaceable manner, and the punch
circumference should correspond approximately to the wall
thickness of the secondary feature or of the branch,
since otherwise hollow profile material can be displaced
into the annular gap by means of the internal high
pressure during the shaping of the branch or of the
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secondary feature, a factor which may lead to an
undesirable shape of the branch or of the secondary
feature and also to premature severing of the cap on
account of the hollow profile material bearing against
the severing contour. Therefore reliable severing of the
cap of the secondary feature or of the branch is achieved
overall in a simple manner by the solution according to
the invention.
In an especially preferred development of the invention
as claimed in claim 2 or in a corresponding preferred
development of the device according to the invention as
claimed in claim 5, the secondary feature and/or the
branch, after the severing operation, by a plunging
movement of the counterholding punch into the opened
secondary feature and/or the branch, is calibrated by
means of a calibrating contour corresponding to the shape
of the secondary feature or of the branch. Said
calibrating contour adjoins the punch end on the side
facing away from the hollow profile. A number of
practical tests have shown that the known encircling bead
is not necessary in order to calibrate the secondary
feature or the branch. On the contrary, it may be
dispensed with in a simple manner, which substantially
simplifies the configuration of the counterholding punch.
The configuration of the counterholding punch is merely
to be adapted to the desired shape of the branch or of
the secondary feature.
In a further, especially preferred development of the
device according to the invention as claimed in claim 6,
an encircling collar is formed on the counterholding
punch and directly adjoins the calibrating contour on the
side facing away from the hollow profile. This ensures
that the inhomogeneous material distribution of the
secondary feature or of the branch which occasionally
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occurs due to the calibration and which leads to an
unevenly drawn-in margin of the branch or of the
secondary feature is made more uniform by the collar
being pressed axially onto the end edge, obtained by the
trimming, of the secondary feature or of the branch. The
end edge, which is of high quality on account of its
evenness and as a result of the almost tolerance-free
design, has a favorable effect for subsequent processes
for connecting the hollow profile to further components
l0 which have to be fastened to the branch or the secondary
feature in the sense that the joining gap between the end
edge and the component is of uniform size and therefore a
homogeneous joint which thus provides an especially good
long-term hold is achieved. In this case, joining
techniques such as welding, adhesive bonding or the like
can be used in a reliable manner.
In a further, especially preferred configuration of the
device according to the invention as claimed in claim 4,
the punch end which contains the severing contour is of
frustoconical design and has bevel surfaces facing the
secondary feature or the branch. Due to the conical shape
of the counterholding punch, a radially encircling
sealing seat is produced on the branch or secondary
feature, as a result of which a pressure drop inside the
hollow profile is prevented in a most advantageous
manner. Thus, by means of a plurality of stamping
counterholding punches arranged at the hollow profile, a
plurality of branches can be opened simultaneously or one
after the other, that is to say the cap can be severed
from the branch, without the internal high pressure in
the hollow profile dropping and thereby resulting in
inadequate process reliability.
In a further preferred development of the device
according to the invention as claimed in claim 7, the end
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edge of the counterholding punch is rounded. The rounding
of the end edge, which forms the severing contour,
additionally prevents a severing operation from already
being effected during the shaping of the branch or of the
secondary feature. In this way, during the subsequent
deliberate severing of the cap, the same is not stamped
out sharply but rather is torn out by the counterholding
punch, as a result of which an undefined opening margin
is produced, which, however, is smoothed by the
subsequent calibration and therefore leads to the desired
production result.
The invention is explained in more detail below with
reference to two exemplary embodiments shown in the
drawings, in which:
fig. 1 shows a lateral longitudinal section of a device
according to the invention in the expansion phase
of the hollow profile, with yielding counterholding
punch,
fig. 2 shows a lateral longitudinal section of the device
from figure 1 after completion of the hollow
profile expansion, with a counterholding punch
severing the cap of the shaped secondary feature,
fig. 3 shows a cutaway side view of a counterholding
punch of a device according to the invention, with
a calibrating contour adjoining the punch end at
the rear,
fig. 4 shows a cutaway side view of a counterholding
punch of a device according to the invention, with
an encircling collar.
Shown in figure 1 is a device 1 which comprises a
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hydroforming tool 2 and with which a peripherally closed
hollow profile 3, which is inserted into the hydroforming
tool 2, serves with a secondary feature and/or a branch
4. Furthermore, the device 1 contains a counterholding
punch 5 which is integrated in the forming tool 2 in such
a way as to be displaceable with little clearance.
To form said hollow profile 3, a hollow profile blank 23
inside the hydroforming tool 2 is put under such a
fluidic internal high pressure Pr that said hollow profile
blank 23 expands and comes into contact with the cavity 6
of the forming tool 2, in which the blank 23 is inserted,
in such a way as to conform to the contour. In the region
of a passage 7 which is formed in the forming tool 2 and
1S in which the counterholding punch 5 is accommodated in a
displaceable manner, the hollow profile material is
displaced into said passage 7 as a result of the internal
high pressure P1 and forms a secondary feature or the
branch 4 in the process. To shape the branch 4 in a
reliable manner in terms of the process, it is supported
by the end face 8 of the counterholding punch 5 while it
is being produced, the punch 5 yielding in the arrow
direction with increasing shaped length of the branch 4.
In order to deliver sufficient hollow profile material
into the expansion region of the branch 4, two axial
punches 9 of the device 1 are provided, which act upon
the hollow profile 3 on both ends in a sealing manner and
advance both ends 10 in the arrow direction in the
direction of the expansion region during the expansion.
As shown in figure 2, after the desired branch length has
been achieved, the drive of the counterholding punch 5 is
reversed, so that the latter plunges into the secondary
feature or the branch 4 and in the process severs its cap
11, with a hole slug being formed, by means of a severing
contour which is formed by the end edge 12 of the punch
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5. This takes place according to the arrow direction with
a force F. In the meantime, a pressure which corresponds
to or is lower than the forming pressure prevails in the
hollow profile 3. The end face 8 enclosed by the end edge
12 of the punch 5 runs in a continuously even manner. In
order to permit problem-free plunging into the branch 4,
the width of the annular gap 22 between the circumference
13 of the punch 5 and the passage wall 1~! is dimensioned
in such a way that it corresponds approximately to the
wall thickness of the secondary feature or of the branch
4. The cap 11 of the branch 4 is therefore severed solely
by a stroke of the counterholding punch 5 in the opposite
direction to the expansion direction of the hollow
profile 5. After the pressure is released, the
hydroforming tool 2 is opened and the finish-formed and
processed hollow profile 3 is removed.
As can be seen from f figures 1 and 2 , the counterholding
punch 5 can be of continuously cylindrical design. In
deviation therefrom, the punch end 15 which faces the
branch 4 and contains the severing contour may be of
frustoconical design according to fig. 3, in which case
it has bevel surfaces 16 facing the secondary feature or
the branch 4. The opened branch 4 is sealed off in a
completely pressure-tight manner via these bevel surfaces
16. As a result, a pressure drop inside the hollow
profile 3 is avoided, so that branches 4 formed at other
points of the hollow profile 3 can be effected
sequentially in a reliable manner in terms of the process
by severing the cap by means of a counterholding punch 5
arranged there in each case.
In deviation from the preceding exemplary embodiment of
the configuration of the counterholding punch 5, as can
be seen from figure 3, a counterholding punch 17,
according to figure 4, in another exemplary embodiment,
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additionally has a calibrating contour 18, which, on that
side of the punch 17 which faces away from the hollow
profile, adjoins the punch end 19 arid is designed in
accordance with the contour of the secondary feature or
of the branch. In this way, when the counterholding punch
17 plunges deeper into the branch 4, the region of the
opening on the branch, this region being formed by the
cap trimming, is readily smoothed to a sufficient extent
in accordance with the desired shape. This provides for
optimum connection to further components which have to be
put into or onto the branch of the hollow profile 3.
Furthermore, an encircling collar 20 of the
counterholding punch 17 directly adjoins the calibrating
contour 18 on the side facing away from the hollow
profile. This collar 20 acts upon the end face of the
opening margin of the branch, thereby ensuring uniform
evenness of this end face. If need be, the end edge 21 of
the counterholding punch 17 may also be rounded in order
completely to prevent an encircling predetermined
breaking point from being produced during the supporting
function of the counterholding punch 17, which
predetermined breaking point may burst open at least
locally on account of the prevailing internal high
pressure, whereupon the further formation of the branch 4
can no longer be effected in a reliable manner in terms
of the process. Nonetheless, after the supporting
function of the counterholding punch 17 has been
dispensed with, the cap 11 can still be severed from the
branch 4 by the rounded end edge 21 of the punch end 19.
