U.S. patent application number 10/506446 was filed with the patent office on 2005-05-12 for method for shaping a bent single- or multiple-chamber hollow profile internal high pressure.
Invention is credited to Gehrig, Markus, Leppin, Christian.
Application Number | 20050097935 10/506446 |
Document ID | / |
Family ID | 27675801 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050097935 |
Kind Code |
A1 |
Gehrig, Markus ; et
al. |
May 12, 2005 |
Method for shaping a bent single- or multiple-chamber hollow
profile internal high pressure
Abstract
A method for manufacturing bent hollow bodies with inner and
outer arcs forming inner arc wall regions and outer arc wall
regions. The method including bending a starting hollow body, and,
using at least one high internal pressure (HIP) forming process
step, transforming the hollow body in an HIP tool to a final
cross-sectional shape. The starting hollow body exhibits a readily
bent cross-section at least in a region to be bent, in which by
means of specific cross-sectional shaping, wall material lies
closer to a neutral stress plane with reference to bending stresses
than in the final cross-sectional shape. The HIP tool has a slide
element. The method includes moving the slide element in the inner
arc wall region of the bent starting hollow body, making contact at
least with part of a surface area of the inner arc wall region, and
withdrawing the slide element during the HIP process in the inner
arc wall region in a direction of an opening of the bend, whereby
the inner arc wall region of the bent starting hollow body is
displaced in a direction of the withdrawing slide element by action
of the high internal pressure.
Inventors: |
Gehrig, Markus;
(Schaffhausen, CH) ; Leppin, Christian;
(Schaffhausen, CH) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
|
Family ID: |
27675801 |
Appl. No.: |
10/506446 |
Filed: |
September 1, 2004 |
PCT Filed: |
February 21, 2003 |
PCT NO: |
PCT/EP03/01775 |
Current U.S.
Class: |
72/61 |
Current CPC
Class: |
B21D 7/00 20130101; B21D
26/047 20130101; B21C 37/283 20130101 |
Class at
Publication: |
072/061 |
International
Class: |
B21D 026/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 2002 |
EP |
02405154.2 |
Claims
1-15. (canceled)
16. A method for manufacturing bent hollow bodies with inner and
outer arcs forming inner arc wall regions and outer arc wall
regions, comprising the steps of: bending a starting hollow body;
and, using at least one high internal pressure (HIP) forming
process step, transforming the hollow body in an HIP tool to a
final cross-sectional shape, whereby the starting hollow body
exhibits a readily bent cross-section at least in a region to be
bent, in which by means of specific cross-sectional shaping, wall
material lies closer to a neutral stress plane with reference to
bending stresses than in the final cross-sectional shape, the HIP
tool having a slide element, the method including moving the slide
element in the inner arc wall region of the bent starting hollow
body, making contact at least with part of a surface area of the
inner arc wall region, and withdrawing the slide element during the
HIP process in the inner arc wall region in a direction of an
opening of the bend, whereby the inner arc wall region of the bent
starting hollow body is displaced in a direction of the withdrawing
slide element by action of the high internal pressure.
17. The method according to claim 16, including controlling the
withdrawal of the slide element and the high internal pressure so
that wall material flows along a surface of the slide element from
the inner arc wall region in a direction of an adjacent, bending
distal wall zone of the hollow body.
18. The method according to claim 16, including shape forming the
hollow body in the outer arc wall region into the final
cross-sectional shape and, subsequently, withdrawing the slide
element from the inner arc wall range.
19. The method according to claim 16, wherein during the
withdrawing the slide element the inner arc wall region of the bent
starting hollow body is shape-formed at least close to the final
cross-sectional shape and, by a further HIP process, the hollow
body is transformed to the shape of the final hollow body in a
further tool having the cross-sectional shape of the final hollow
body.
20. The method according to claim 16, wherein at least in the inner
arc wall region the bent starting hollow body has a recess which,
viewed from outside, is concave in form.
21. The method according to claim 16, wherein the bent starting
hollow body is a simple hollow section, and the readily bent
cross-sectional shape exhibits two recesses that are counter to
each other in shape and form a necking region.
22. The method according to claim 16, wherein the final hollow body
is a simple hollow section.
23. The method according to claim 22, wherein the final hollow body
is a tube-shaped hollow section.
24. The method according to claim 23, wherein the tube-shaped
hollow section has a circular cross-section at an end.
25. The method according to claim 23, wherein the tube-shaped
hollow section has an oval cross-section at an end.
26. The method according to claim 16, wherein the hollow body is a
metal hollow body and a ratio B of an average bending radius
R.sub.m to an outer diameter D of the bent final hollow body lies
in a range: 0.5.ltoreq.R.sub.m/D.ltoreq.2.
27. The method according to claim 26, wherein the hollow body is
made of aluminum.
28. The method according to claim 26, wherein the hollow body is
made of an aluminum alloy.
29. The method according to claim 26, wherein the ratio B is in a
range: 0.7.ltoreq.R.sub.m/D.ltoreq.1.
30. The method according to claim 16, wherein a bending angle of
the bent final hollow body lies in a range of 40.degree. to
180.degree..
31. The method according to claim 30, wherein the bending angle
lies in a range of 60.degree. to 180.degree. C.
32. The method according to claim 31, wherein the bending angle
lies in a range of 90.degree. to 180.degree..
33. A device for forming bent starting hollow bodies to a final
cross-sectional shape or a cross-sectional shape approaching that
of a final hollow section using a high internal pressure (HIP)
process, whereby a starting hollow body exhibits a readily bent
cross-section at least in a region to be bent, in which by means of
specific cross-sectional shaping, wall material lies closer to a
neutral stress plane with reference to bending stresses than in the
final cross-sectional shape, the device comprising an HIP tool
configured to accommodate the bent starting hollow body, the HIP
tool having a slide element situated in an inner arc wall region of
the bent starting hollow body, the slide element being arranged to
be movable in a direction of an opening of the bend so that the
slide element is withdrawn.
34. The device according to claim 33, wherein the shape-forming
tool is a multi-part tool with upper and lower halves and the slide
element.
35. The device according to claim 33, wherein the slide element is
arranged to lie in a supportive manner at least on part of a
surface of the inner arc wall region.
36. The device according to claim 33, wherein the bent starting
hollow body exhibits a recess at least in the inner arc wall
region, the slide element having a face that faces the inner arc
wall region of the starting hollow body, the face having a convex
shape which is counter-identical to a shape of the recess.
37. The device according to claim 33, wherein, in plan view, the
slide element is tongue-shaped.
Description
[0001] The invention relates to a method for producing bent hollow
bodies that copmprise an inner arc and an outer arc forming inner
and outer arc wall regions, whereby a starting hollow body is bent
and, by means of one or more High-Internal-Pressure (HIP)
processes, is transformed in an HIP tool to its final
cross-sectional shape, whereby the starting hollow body exhibits a
cross-section that is readily bent, at least in its region of
bending in which, by means of a specific cross-sectional shape,
wall material lies--with respect to bending stress--closer to the
neutral stress plane than in the final cross-sectional shape.
[0002] Further, the invention also relates to a device for forming
bent starting hollow bodies into a final cross-sectional shape or a
cross-section close to the final cross-sectional shape using a high
internal pressure (HIP) process, whereby the initial hollow body
exhibits a cross-section that is readily bent, at least in its
region of bending in which, by means of specific profiling, wall
material is with respect to bending stress closer to the neutral
stress plane than in the final cross-sectional shape, said device
containing an HIP tool which accommodates the bent starting hollow
body.
[0003] In addition, the invention includes the use of the product
manufactured using the process according to the invention.
[0004] The production of high quality, curved or bent hollow bodies
such as e.g. tube-shaped sections, is associated with a large
number of difficulties. On the one hand the hollow body should--in
particular in the curved region--exhibit as uniform as possible
wall thickness, in particular no zones of weakness such as cracks
or folds resulting from the forming steps. On the other hand, it
should be possible to manufacture the bent hollow body economically
and efficiently in as few cold forming steps as possible.
[0005] The production of bent hollow bodies normally involves
taking a straight starting hollow body which is bent to a given
bending radius and bending angle by means of a conventional bending
process. The difficulty in bending is to maintain the cross-section
in the region of bending. A known method of maintaining the
cross-sectional shape in the region of bending is e.g. to introduce
mandrels such as finger-shaped mandrills that are flexible in the
direction of bending. This leads, however, to pronounced elongation
in the outer lying arc-shaped wall and consequently to excessive
thinning of the section wall there, up to the point of forming
cracks, while in the inner lying arc-shaped wall region pronounced
compression occurs, resulting in a build up of material and
folding.
[0006] Using that process, therefore, it is possible to realise
only limited radii and angles of curvature as a function of the
diameter of the hollow section and the thickness of section
wall.
[0007] With the introduction of high internal pressure processes,
hereinafter HIP processes, for forming hollow sections, new
possibilities have been opened up in recent years for the
production of high quality bent sections. The HIP process is
characterised by way of applying high internal pressure via a
medium in the interior of the section in a tool cavity into which
the hollow section is placed beforehand. This way it is possible to
change e.g. the cross-sectional shape of a hollow section.
[0008] The modified process for manufacturing bent hollow bodies is
characterised by way of conducting a bending process and HIP
process in a series of steps. A straight starting hollow section
with a cross-section that is readily bent and at that stage does
not conform to the final cross-section of the hollow body, is bent
using a conventional bending process. The bent starting hollow
section is transformed to the final cross-sectional shape in a
subsequent HIP process.
[0009] The above manufacturing process exhibits the advantage in
that the cross-section of the starting hollow section that is to be
bent no longer needs to be that of the final bent hollow section.
An ideal cross-section permits the mechanical load and the
deformation of the section wall in the region of bending to be
reduced considerably during the bending process. This progress
results in bent hollow sections which exhibit excellent mechanical
properties and meet optical requirements also in the bent
region.
[0010] In spite of the progress attained by the integration of an
HIP process, it has been found that when employing the known
methods of manufacture, the production of bent hollow sections, in
particular tube-shaped hollow sections with very small bending
radii and very large bending angles of e.g. 90-180.degree. (degrees
of angle) does not meet the high level of requirements with respect
to mechanical properties and optical appearance.
[0011] Consequently, also with the present day methods of bending
and shape-forming there are great limitations with respect to
bending radii and bending angles.
[0012] The object of the present invention is therefore to provide
a process and a device for carrying out the process which permit
bent hollow bodies, in particular simple hollow sections, to be
produced with small radii of bending and large bending angles.
[0013] That objective is achieved by way of the invention in that
the HIP tool contains in the inner arc-shaped wall region a slide
element, which rests at least in part on the surface of the inner
arc-shaped wall region and, during the HIP process, the slide
element is withdrawn from the inner arc-shaped wall region in the
direction of the the bend opening, with the result that the inner
arc-shaped wall region in the starting hollow body is displaced by
the high internal pressure in the direction of the withdrawing
slide element.
[0014] The device is characterised in that the HIP tool contains a
slide element at the inner arc-shaped wall region of the bent
starting hollow body, and the slide element can be displaced in the
direction of the bend opening.
[0015] The starting hollow body i.e. the hollow body before the
start of the bending and HIP process, is preferably a single or
multi-chamber section, in particular a simple hollow section. The
starting hollow body or starting hollow section is usefully of
metal, preferably steel or aluminium or an aluminium alloy. The
starting hollow section is to advantage in the form of a straight
hollow section.
[0016] The starting hollow section exhibits a cross-section that is
readily bent, at least at its length or lengths that are to be
bent. The starting hollow section may also exhibit a cross-section
that is readily bent over its whole length, whereby the
cross-sectional shape and/or size is preferably constant over the
whole length of the hollow section.
[0017] Is readily bent means that the wall material, by specific
shape of the cross-section of the hollow section is as close as
possible to the neutral plane with respect to bending stress--also
know as neutral stress plane--so that the smallest possible
deformation forces, such as tensile and compressive forces, are
applied to the wall material. This way a low polar moment of
inertia is achieved. The neutral stress plane then runs through the
middle line of the section. Consequently, the wall material of a
cross-section that is readily bent is situated close to the middle
line of the section.
[0018] Cross-sections that are readily bent are, therefore,
characterised by flat cross-sectional shapes with relatively height
to breadth ratios. Such shapes may e.g. be in the form of upright
sections. Also, the cross-sectional shape may be elliptical or
oval. Further, the cross-section of the hollow section may exhibit
flanking walls bent inwards in the direction of the neutral stress
plane e.g. in the form of dents or recesses by means of which a
kind of tapering or necking is achieved, whereby the narrowest part
of the necking preferably lies at the level of the section middle
line. Such a cross-section which is favourable to bending may e.g.
be in a form similar to that of an hour-glass, whereby the extent
of narrowing at the middle can vary at will.
[0019] There are, however, limits to the flattening of the section
cross-section, as the said cross-section may not contain too
pronounced degrees of curvature in the wall--this because, during
the HIP process, the wall material is subjected to very high local
deformation at such curvatures, and so can result in places of
weakness.
[0020] The starting hollow section may be an extruded section
which, by means of extrusion, is preferably directly given a
cross-section that is readily bent.
[0021] The starting hollow section may also be made from a rolled
product such as sheet which is shape-formed and joined, in
particular by welding. The said starting hollow section may be made
with a cross-section that is readily bent, or be transformed into a
cross-sectional shape in a subsequent process step. The production
of a cross-section that is readily bent may also be an integral
process step of the bending process whereby, immediately prior to
bending, the starting hollow section is given the readily bent
cross-section by appropriate tools.
[0022] Suitable bending processes are e.g. draw bending such as
rotational draw bending, compression draw bending, press bending,
stretch bending or roll bending. The bending process may also be
aided by a flexible mandrel insert introduced into the section
interior. Further, alignment and fixing aids such as clamping jaws,
bending rolls, sliding rails and/or fold smoothers may assist the
bending process.
[0023] The bent starting hollow section may feature single or
multiple bends, whereby the bending axes may lie parallel to or at
an angle to each other. The bent starting hollow section may e.g.
exhibit an S-shape with parallel bending axes.
[0024] In a preferred version, the bent and HIP-formed hollow
section with its final cross-section--in the following designated
simply as the final hollow section--features, at least in the inner
arc-shaped wall region, a cross-sectional contour which--as viewed
from the outside--is curved in a convex manner. In a particularly
preferred version the final hollow section is tube-shaped with a
circular, elliptical or oval cross-section at least in the bent
length. The cross-section at the end of the final hollow section
may if desired also contain corners in the outer and/or inner
arc-shaped wall region. The uncoiled circumferential length of the
easy-to bend cross-section of the initial hollow section may be
smaller, larger and preferably of the same magnitude as the
uncoiled cross-section of the final hollow section.
[0025] In the preferred version of the invention the ratio B of the
average bending radius R.sub.m to the tube outer diameter D
(B=R.sub.m/D) for tubes of metal, in particular aluminium or an
aluminium alloy, lies in the range of: 0.5.ltoreq.B.ltoreq.2, in
particular in the range of 0.7.ltoreq.B.ltoreq.1.
[0026] The average bending radius R.sub.m extends from the bending
axis to the middle line of the section.
[0027] The bending angle may lie in the range of larger than
0.degree. to 180.degree. (degrees of angle). The bending angle
preferably lies in the range 40.degree. to 180.degree.,
advantageously from 60.degree. to 180.degree., and in particular
from 90.degree. to 180.degree..
[0028] The HIP tool according to the invention contains a basic
tool, usefully with two or more parts or tool halves, whereby
partially i.e. preferably at least in the region of the outer
curved wall, the basic tool forms a cavity to accommodate the bent
starting hollow section. The contour of the tool cavity in the
region of the outer curved wall may be the contour of the final
hollow section, the contour of the bent initial hollow section or a
contour lying between these two shapes.
[0029] The forming tool contains, in addition to the basic tool, a
moveable slide element which forms at least a part of the surface
making up the contour of the tool cavity in the inner curved wall
region. The slide element has the function here of providing
counterpressure. The contour of the slide element forming at least
part of the inner arc-shaped wall region of the tool cavity is
preferably countershaped to the contour of the bent starting hollow
section in the inner arc-shaped wall region.
[0030] If the cross-sectional shape of the starting hollow section
features a recess in the inner arc-shaped wall region, or if the
bent starting hollow section is hour-glass shaped in cross-section,
then the slide element preferably has a convex surface form which
fits into the depression.
[0031] The slide element extends preferably from the inner
arc-shaped wall region back to the opening of the bend.
Correspondingly, the slide element forms at least part of the
contour surface of the tool cavity both in the inner arc-shaped
wall region and in the adjacent wall lengths of the neighbouring
hollow section flange. The said contour is preferably
counter-shaped to the cross-sectional shape of the bent starting
hollow section at the said wall parts. As a result, the slide
element--on withdrawal in the direction x towards the opening to
the bend--is prevented from being blocked by the expansion of the
section wall in the wall length of the hollow section flange.
[0032] In plan view the slide element fits the curvature of the
inner arc and exhibits an arc-shaped end. In a preferred version,
the slide element is a tongue shaped in form.
[0033] The slide element is preferably such that it is capable of
providing resistance to the forces created by the high internal
pressures and is thus able to support the inner arc-shaped wall
region.
[0034] The slide element can usefully be displaced e.g. linearly
displaced, and preferably in the direction of the bend opening x.
Further, the slide element is preferably connected to an alignment
facility guiding the slide element. The alignment facility may if
desired contain a drive unit.
[0035] The slide element is to advantage introduced between the an
upper and a lower tool half.
[0036] On carrying out the process according to the invention the
starting hollow section, which is bent and, at least in the length
to be bent has a cross-section that is readily bent, is laid in the
cavity of a basic tool.
[0037] Subsequently, a high internal pressure is applied, whereby,
in the outer arc-shaped wall region, the starting hollow section is
pressed into the contour of the tool cavity. During the HIP
process, the slide element is withdrawn, in the direction x of the
bend opening, a specific distance out of the inner arc-shaped wall
region, whereby the inner arc-shaped wall region in contact with
the slide element is pushed by the high internal pressure. The high
internal pressures can e.g. amount to 500-2000 bar.
[0038] When the slide element has reached its predetermined final
position, the HIP process is completed and the part removed from
the tool. In the inner arc-shape wall region the resultant hollow
section exhibits a cross-sectional shape which corresponds to or is
close to that of the final hollow section.
[0039] Subsequently, the hollow section is placed in a further
forming tool, the cross-section of which corresponds to that of the
final hollow section.
[0040] By optimal design of slide element it is also possible to
achieve the final cross-section of the hollow section in the first
HIP forming step.
[0041] The process according to the invention permits the
production of bent tubes with large bending angles and extremely
small bending radii in a multi-stage cold forming process. The use
of a slide element according to the invention makes it possible to
control the flow of material caused by the cross-sectional shaping
process in the inner arc-shaped wall region. In the cross-sectional
shaping by conventional processes all flow of material was in the
direction of expansion of the section cross-section i.e. in the
radial direction. This, however, leads to thickening of the wall
and to folds. By employing a slide element which specifically
controls the radial flow of material, lateral flow of material is
achieved along the surface of the slide element in the direction of
the wall region of the section flange neighbour-ing the internal
arc-shaped wall region. The thickening of the wall in the internal
arc region is thus reduced and the formation of folds
prevented.
[0042] The process according to the invention permits hollow
sections, in particular tube-shaped hollow sections with very small
bending radii and large bending angles to be manufactured, viz.,
such as are not achievable using conventional processes. Further,
the process according to the invention allows the use of hollow
sections with comparably small wall thickness, achieving as a
result a savings in material.
[0043] Using the process according to the invention it is possible
to manufacture e.g. singly or multiply bent input manifolds e.g.
suction pipes for internal combustion engines, preferably for
internal combustion engines for vehicles. The internal combustion
engines on which the mentioned manifolds find application are
preferably internal combustion engines functioning according to the
Otto principle or that of the diesel engine, in particular suction
engines, turbo supercharged or compressor charged engines.
[0044] Singly or multiply bent tubes manufactured using the process
according to the invention can also be employed as automobile body
parts e.g. space-frame components, engine suspension, chassis
components, components for exhaust gas units e.g. bent tubes, and
as constructional or component parts e.g. for wing spars, bow-wing
skids, or roll bars. Further, singly or multiply bent tubes
manufactured using the process according to the invention can find
application in pipelines of all kinds e.g. for conveyance of
liquids and gases under pressure such as hydraulic pipelines, as
railings and for further applications in the construction of
vehicles, ships and aircraft as well as in above or below ground
level building.
[0045] The invention is described in the following in greater
detail by way of examples and with reference to the accompanying
schematic drawings. These show in:
[0046] FIG. 1: a perspective view of a bending process;
[0047] FIG. 2 a perspective view of a bent starting hollow
section;
[0048] FIG. 3: a perspective view of a first HIP process according
to the invention;
[0049] FIG. 4a-c: a perspective view of a second HIP process for
manufacturing the final hollow section;
[0050] FIG. 5a-f: a cross-section through the position A-A in FIG.
3 in various stages of the first HIP process;
[0051] FIG. 6a-b: a cross-section through the position B-B in FIG.
7 in various stages of the second HIP process;
[0052] FIG. 7: a plan view of a final hollow section;
[0053] FIG. 8: a graphic representation relating to the feasibility
of 90.degree. bending of tube-shaped sections.
[0054] FIGS. 1-7 show illustrations obtained from process
simulations, whereby the grid contour lines correspond to the
middle planes of the body being bent or the surfaces of the forming
tool. The figures show therefore only schematically simplified
illustrations for the purpose of explaining the process and device
according to the invention.
[0055] The following example illustrated in FIGS. 1-7 relates to
the manufacture of final hollow sections of circular cross-section
and a bending angle of 180.degree.. The hollow sections shown are
only extracts from hollow sections of any desired length featuring
e.g. straight or further bent lengths.
[0056] FIG. 1 shows how, using a conventional bending process, a
bent starting hollow section 10a (FIG. 2) is produced from an
originally straight starting hollow section 5 e.g. an extruded
section with a readily bent cross-section, whereby the bending
device 1 employed for that purpose contains a guide rail 2 for the
starting hollow section 5 and a bending roll 4 for bending the
starting hollow section 5. The starting hollow section 5 is held by
a clamping jaw fixed to the bending roll 4 which subsequently bends
the fixed starting hollow section 5 by means of a rotational
movement. During the bending operation the starting hollow section
5 is fed in the guide rail 2 in the direction of the bending roll
4.
[0057] The starting hollow section 5 has a readily bent
cross-section which is produced e.g. by means of a forming process
or directly by extrusion. The production of the starting hollow
section 5 with readily bent cross-section and the bending process
are independent of subsequent process steps in which the bent
starting section 10a is shape-formed into the cross-section of the
final hollow section 10g; i.e. other bending processes may be
used.
[0058] The bent starting hollow section 10a has an especially
preferred readily bent cross-sectional shape which is characterised
by way of two mirror image recesses 13a,b, whereby the recesses
13a,b form a kind of necking in the middle. The mirror image
arrangement relates to an axis 14 or plane running parallel to the
bending axis. The bent starting hollow section 10a features an
outer arc with outer arc wall region 11 and an inner arc with an
inner arc wall region 12, whereby the inner and outer arc wall
regions are usefully delimited with respect to each other by the
neutral stress line or plane 14, 65 running parallel to the bending
axis.
[0059] FIG. 3 shows the arrangement of a part of the HIP tool after
conclusion of the first HIP process. The hollow section 10e lies in
a lower half 22b of the tool. For reasons of clarity, the upper
half of the tool is not shown here. Inserted into the inner arc
wall region of the hollow section 10e is a slide element 21 which
in the course of the process has been withdrawn a specific distance
in the direction x towards the bend opening and has now reached its
end position, so that the inner arc wall region in contact with the
slide element 21 is able to expand in the direction x of the
withdrawing slide element 21 and take on a contour which is
approaching that of the final hollow section. Viewed in plan view,
the slide element 21 exhibits a tongue-shaped form corresponding to
the curvature of the inner arc wall region.
[0060] To carry out the second HIP process, the hollow section 10e
is placed in a second HIP tool (FIG. 4a-c), which defines the final
contour of both the inner and outer arc wall region. The outer arc
wall region of hollow section 10e has already been shaped to the
contour of the final hollow section which is given by the tool
cavity. Further, the inner arc wall region has already been
expanded in the region of most pronounced curvature, approximately
to the cross-sectional shape of the final hollow section (FIG. 4a).
The hollow section 10e is now transformed by the action of the high
internal pressure into the cross-sectional shape of the final
hollow section log (FIG. 4b-c). For reasons of clarity only the
lower half 32b of the HIP tool is shown schematically here.
[0061] FIGS. 5a-f show in a series of steps the first HIP process
according to the invention as seen along the line A-A in FIG. 3. A
bent hollow section 10a (see also FIG. 2) with a readily bent
cross-section according to FIG. 2 is placed in a forming tool 22 in
the form of a cavity and having an upper half 22a and a lower half
22b and the tool closed. A slide element 21 which forms the cavity
wall over at least one wall area of the inner arc wall is moved
before, after or along with the closing of the two tool halves
22a,b, up to the inner arc wall region of the bent starting hollow
section 10a. The contour of the slide element 21 in contact with
the inner arc wall region of the starting hollow section 10a is
identical to the contour of the concave inner arc wall region. In
the present example the said contour of the slide element 21
corresponds to that of a torus.
[0062] After preparation for forming, a high internal pressure is
applied to the section interior 43, whereby in a first step the
outer arc wall region of the hollow section 10b is pressed into the
contour of the tool cavity, whereby the tool cavity exhibits in the
outer arc wall region the contour of the final hollow section.
[0063] The slide element 21 is subsequently drawn back in direction
x towards the bend opening, whereby the inner arc wall region
follows it under the action of the high internal pressure and
increasingly approaches or takes on the contour of the final hollow
section (FIGS. 5b-f).
[0064] When the slide element 21 reaches its end position, the high
internal pressure is reduced, the hollow section 10e the contour of
which is now closer to that of the final hollow section in the
inner arc wall region is removed (see also FIGS. 3, 4a) and
introduced into a second HIP tool 32 with upper and lower tool
halves 32a, 32b. The second HIP tool 32 has the contour of the
final hollow section 10g, i.e. both in the inner arc wall region
and in the outer arc wall region. The hollow section 10e, 10f is
then shaped into the contour of the final hollow section 10g in a
second HIP process step.
[0065] Of course it is possible to carry out the shape-forming of
the outer arc wall region 11, 61 to the cross-sectional shape of
the final hollow section 10g in a second HIP process step. That is,
the HIP tool 22 operating with the slide element 21 features in the
outer arc wall region 11 the contour of the bent starting hollow
section 10a or a contour which lies between that of the starting
hollow section 10a and the final hollow section 10g.
[0066] FIG. 7 shows in plan view the final hollow section 10g (see
also FIG. 4c) which has been bent to a circular cross-sectional
shape. The bending plane or line 65 also forms the middle line of
the section and is also the reference plane for the bending radius
R.sub.m. The grid lines 63 illustrate the flow of material within
the section walls, whereby grid lines that are pressed close
together indicate an accumulation of wall material and widely
spaced grid lines indicate a reduction in the wall material. As can
be readily seen from FIG. 7 the final hollow section 10g exhibits
remarkable flow of material 66 (arrows) from the inner arc wall
region 62 in direction x towards the bend opening, i.e. in the
direction of both adjacent section flanges 67a, 67b. The said flow
of material is effected by the above mentioned slide element 21, in
that the wall material is forced under the action of the high
internal pressure and the resistance of the slide element 21 to
flow along the adjacent face of the slide element 21 from the inner
arc wall region 62 outwards in the direction of the walls of the
section flanges 67a, 67b. By drawing back the slide element 21 the
wall material of the inner arc wall region 62 is led outwards in a
controlled manner radially, while approaching the cross-sectional
shape of the final hollow section 10g, whereby as a result of the
simultaneous flow of material towards the section flanges 67a, 67b
folding in the inner arc wall region is prevented. Further, using
the process according to the invention it is possible to reduce the
reduction in wall thickness.
[0067] FIG. 8 shows a graph 50 relating to applications for
90.degree. bending of tube-shaped sections of a typical aluminium
alloy, here as a function of tube diameter, bending radius and wall
thickness.
[0068] Plotted on the horizontal axis is the ratio of average
bending radius Rm to the outer diameter D of the tube and on the
vertical axis the ratio of tube outer diameter D to wall thickness
t. The shaded area 51 shows the ranges within which 90.degree.
bending is possible, whereby the feasibility refers to a
conventional bending process. The region outside the shaded area
delineated by a straight line represents that range in which
successful bending is no longer guaranteed.
[0069] If e.g. a tube which has to be bent has a diameter D of 20
and a wall thickness of 1, then FIG. 8 shows that the said tube can
be bent to 90.degree. with a bending radius of 40 as the ratio
R.sub.m/D=2 and the ratio D/t=20, and the intersection lies in the
shaded area. If, however, a bending radius Rm of 30 is chosen for a
tube of the same dimensions, the intersection lies in the range in
which bending cannot be successfully carried out, i.e. it can be
assumed that the tube will fail.
[0070] Using computer simulations it was possible to show that
using the process according to the invention it seems possible to
produce bent tubes of an aluminium alloy, which have bends lying in
the non-feasible range in FIG. 8. Further, using computer
simulations it seems possible using the said process to achieve
bends with a bending radius that is equal to or smaller than the
diameter of the tube. It was therefore possible in a computer
simulation successfully to bend a 56 mm diameter tube of 2.5 mm
wall thickness to a bending radius of 40 mm using the process
according to the invention. Point 52 in FIG. 8 shows the relevant
ratios, whereby it is evident that tubes with the said dimensions
and bending radius could not be bent satisfactorily using
conventional bending processes.
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