FIELD OF INVENTION
[0001] The invention relates to the forming of tubular work-pieces by internal pressure
created by a fluid, i e hydroforming, and in particular to a segmented tool used for
said forming operation.
BACKGROUND
[0002] The hydroforming process is described in "Hydroforming - Umformen mit Wirkmedien
im Automobilbau, Verlag Moderne Industrie, Landsberg, 2002". In this process tubes
formed to final shape by insertion in a tool where the tubes are expanded by applying
an internal pressure to the inside of the tube using a fluid. The tubes may be straight
or pre-bent depending on the final requirements.
Hydroforming of large work-pieces, such as side-members for car body structures presents
significant problems due to the difficulty of handling the very heavy tools that are
required as moulds during forming. For this reason segmented tool inserts, i e tools
that consists of two or more parts, are sometimes used, which considerably facilitates
the handling and makes it possible to exchange parts of the inserts if the insert
has been damaged or worn, without replacing the whole tool. To keep the segments in
place the tool insert is surrounded by a base block, with tight tolerances to the
segmented inserts. The base block may be manufactured in one part or may comprise
a base and vertical supports fixed to it. The disadvantage of this arrangement is
the high cost for the base blocks and the fact that these base blocks are even heavier
and more difficult to handle than single piece inserts.
[0003] The problems connected with the use of large toolings become particularly pronounced
when small series or prototypes are manufactured, which means that the tool has to
be replaced frequently. The problem is discussed in "Innenhochdruck-Umformen für Karosseriekomponenten,
3. Chemnitzer Karosseriekolloquium, CBC 2002, Verlag Wissenschaftliche Scripten, Zwickau",
page 62, where it is suggested that tools for prototypes are manufactured by forming
a cavity directly in a single piece of metal and simplified in the sense that no inserts
are used. This does not make handling of the tool easier and no possibility to exchange
a part of the tool is possible.
[0004] In "Hydroforming-Umformen mit Wirkmedien im Automobilbau" segmented inserts are mentioned,
but always in combination with base blocks that keep the segments from separating
during forming.
SUMMARY OF THE INVENTION
[0005] An object of the present invention is to provide a simplified tool for hydroforming
of tubular work-pieces, where the use of very large tooling blocks can be prevented.
The invention is particularly useful when small series or prototypes are manufactured.
[0006] According to a first aspect of the present invention a tool comprising a pair of
upper and lower tool inserts having open axial ends and defining an elongated cavity
there between when said tool inserts are forced together. The upper and/or lower tool
inserts are composed of segments that are attached to the upper and a lower base plates
by bolts. Retaining elements, such as pins, are introduced into holes in the base
plates from where they extend thorough the base plate and continue into cavities formed
in the segmented insert (or extend from the insert into holes in the baseplate). This
prevents the insert segments from moving during the forming operation. The retaining
elements normally have a round or a conical shape for easier guidance into the cavities
and a tight tolerance to the cavities to minimise movement of the segments. In this
way the use of base blocks may be omitted.
[0007] To guide the tool inserts to the desired position on the base plate guide columns
are used. The guide columns are attached to the upper base plate and extend through
the base plate and the insert. By lowering the upper tool punch vertically towards
the lower base plate the guide columns from the upper tool half are introduced into
spaces in the lower half of the insert. The guide columns and the retaining elements
may also be attached or form part of the inserts and extend through the base plate
into the
[0008] The retaining elements may act as guide columns, or separate guide columns may be
used. The tolerances, however, has to be tight between pin and the hole in the base
plate to assure the non-movement of the insert segments.
[0009] According to a second aspect of the invention the friction force between the base
plate and the insert may be high enough to prevent axial movement of the segments,
and in this case the retaining elements may be omitted.
[0010] A pair of mandrels adjacent the axial open ends of the elongated cavity retain the
tubular work-piece in the cavity and forms a sealed closure of the ends of the tubular
work-piece. Work-piece material is forced axially inwardly during forming of the work-piece
and hydroforming liquid is entered through the mandrel into the work-piece for hydroforming
the work-piece into the final shape. The pressurising of the work-piece may be done
either before of after the closure of the tool.
[0011] The method of the present invention allows the elimination of the very large and
heavy base blocks that has been a prerequisite in previously used methods. In this
way production times may be shortened and the costs reduced.
DESCRIPTION OF THE DRAWINGS
[0012]
Figure 1 is a plan view of a hydroforming tool according to the prior art.
Figure 2 is a plan view of a hydroforming tool according to the invention.
DETAILED DESCRIPTION
[0013] In figure 1 a segmented tool according to the state of the art is shown. Vertical
supports (V) fixed to the base block, prevents movement of the segments.
[0014] Referring to figure 2, a hydroforming tool comprising a base plate (A) and a segmented
insert (B), having through holes for guide columns (C) and smaller diameter holes
(D) for the retaining elements (pins not shown in figure). The retaining elements
are snugly fitted into the base plate, which makes attachment of the elements superfluous.
As can be seen the tool is free from vertical supports acting on the outer surface
of the insert.
[0015] When the upper tool half is lowered, the guide columns assure the guiding of the
tool parts to their exact position. When pressure is applied to the hydroforming liquid,
high forces act on the tool parts, some of these in directions that would cause separation
of the segments of the inserts if no opposed forces counteract them. The retaining
elements or sometimes, depending on the dimension and shape of the workpiece, only
the friction force acting between the base plate and segmented inserts caused by the
high pressure applied to the tool surfaces, will prevent the separation of the segments.
There is thereby no need for vertical supports acting on the outer surfaces of the
insert.
[0016] The number of segments may be varied freely, it is however common for the number
of segments to exceed two.
[0017] In particular, the invention provides a method of hydroforming hollow work-pieces
by providing a pair of upper and lower tool inserts (B) having open axial ends and
defining an elongated cavity (E) there between when said tool inserts are forced together,
said upper and/or lower tool inserts being composed of at least two segments that
are in a locked position in all directions (X, Y, Z) during the forming of the work-piece
and in contact with a base plate (A) on the side opposite to the cavity and
- a) providing a hollow work-piece in said cavity;
- b) sealing the ends of the hollow work-piece;
- c) filling said work-piece with liquid;
- d) applying an internal pressure to the inside of the work-piece by increasing the
pressure on said liquid;
- e) moving said upper and lower tool inserts together to deform portions of the work-piece
at any time after step a),
where the movement of said segments in the X- and the Y-direction is prevented by
other means than by using vertical supports acting on the outer surfaces of the inserts.
Example 1
[0018] A hydroforming tool comprising an upper punch, base plates with a pair of upper and
lower tool inserts attached to them is used for forming of a tubular work-piece made
from extruded aluminium. The inserts have open axial ends and define an elongated
cavity between them when the tool is closed. The inserts are each composed of at least
two segments that are screwed onto the base plates. Retaining elements are introduced
into holes in the base plate and partially through the segments of the inserts. Guide
columns extending through and from the base plates are introduced into cavities formed
in the segmented inserts when the upper punch is lowered.
[0019] A tubular work-piece was put in said cavity and the upper and lower tool inserts
moved together to deform portions of the work-piece. The ends of the tubular work-piece
were sealed and the work-piece filled with liquid through an inlet in the mandrels
while supplying work-piece material axially inwardly.
[0020] Pressure was then applied to the inside of the work-piece by increasing the pressure
on said liquid. The cavities in the base plates have a tight tolerance to the retaining
elements, so that the movement of the segment during forming is as low as possible.
The tool was opened and the formed pieces removed. No marks could be found on the
work-piece to indicate that a movement of the segments had taken place. When a number
of tubes have been formed the tool insert was replaced by removing each segment separately.
Example 2
[0021] A hydroforming tool as in example 1, but without retaining elements, is used for
forming a tubular work-piece made from extruded aluminium. The tubular work-piece
is put in said cavity and the upper and lower tool inserts are moved together to deform
portions of the work-piece while supplying work-piece material axially inwardly. Pressure
of 1500 tonnes is applied to the tool parts by the tool punch. Pressure is then applied
to the inside of the work-piece by increasing the pressure on said liquid to 1000
bar. The tool is opened and the formed pieces are removed. No movement of the segments
could be observed
1. A method of hydroforming hollow work-pieces by providing a pair of upper and lower
tool inserts (B) having open axial ends and defining an elongated cavity (E) there
between when said tool inserts are forced together, said upper and/or lower tool inserts
being composed of at least two segments that are in a locked position in all directions
(X, Y, Z) during the forming of the work-piece and in contact with a base plate (A)
on the side opposite to the cavity and
a) providing a hollow work-piece in said cavity
b) sealing the ends of the hollow work-piece
c) filling said work-piece with liquid
d) applying an internal pressure to the inside of the work-piece by increasing the
pressure on said liquid
e) moving said upper and lower tool inserts together to deform portions of the work-piece
at any time after step a
characterized in that movement of said segments in the X- and the Y-direction is prevented by other means
than by using vertical supports acting on the outer surfaces of the inserts.
2. Method according to claim 1, characterized in that movement of the segments are prevented by retaining elements extending from said
base plate into cavities (D) formed in said segments, said cavities being adapted
to receive said retaining elements.
3. Method according to claim 1, characterized in that movement of the segments are prevented by retaining elements extending from said
segments into cavities formed in said base plate, said cavities being adapted to receive
said retaining elements.
4. Method according to any of claims 1-2, characterized in that the segments are guided onto the upper and the lower base plates by guide columns
(C).
5. Method according to claim 3, characterized in that the retaining elements act as said guide columns.
6. Method according to claim 1, characterized in that the segments are kept in a fixed position mainly by friction forces acting between
the base plate and the insert.
7. A tool for hydroforming a hollow work-piece comprising a pair of upper and lower tool
inserts (B) having open axial ends and defining an elongated cavity (E) there between
when said tool inserts are forced together, said upper and/or lower tool inserts each
being composed of segments that are in a locked position in all directions (X, Y,
Z) and in contact with an upper and a lower base plate (A) characterized in that said tool is free from vertical supports acting on the outer surfaces of the insert
to prevent movement thereof in the X- and the Y-direction.
8. A tool for hydroforming a hollow work-piece, comprising a pair of upper and lower
tool inserts (B) having open axial ends and defining an elongated cavity (E) there
between when said tool inserts are forced together, said upper and/or lower tool inserts
each being composed of segments that are in a locked position in all directions (X,
Y, Z) and in contact with an upper and a lower base plate (A), characterized in that retaining elements preventing movement of the segments extend from said base plates
into cavities (D) formed in said segments, said cavities being adapted to receive
said retaining elements.
9. A tool for hydroforming a hollow work-piece according to claim 7, characterized in that retaining elements preventing movement of the segments extend from said segments
into cavities formed in said base plates, said cavities being adapted to receive said
retaining elements.
10. A tool for hydroforming a hollow work-piece according to any of claims or 7-9, characterized in that the segments are guided onto the upper and the lower base plates by guide columns
(C) extending from said base plates.
11. A tool for hydroforming a hollow work-piece according to any of claims or 7-10, characterized in that the upper and the lower base plates are guided onto the segments by guide columns
(C) extending from said segments.
12. A tool for hydroforming a hollow work-piece according to claim 8-11, characterized in that the retaining elements also act as said guide columns.
13. A tool for hydroforming a hollow work-piece according to any of claims 8-12, characterized in that the retaining elements are in the shape of pins.