U.S. patent application number 16/612232 was filed with the patent office on 2020-07-02 for a method for forming curved lengths of extruded profiles/sections in metal alloys.
The applicant listed for this patent is IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY AND MEDICINE. Invention is credited to Trevor Dean, Jianguo Lin, Liliang Wang, Wenbin Zhou.
Application Number | 20200206794 16/612232 |
Document ID | / |
Family ID | 59065707 |
Filed Date | 2020-07-02 |
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United States Patent
Application |
20200206794 |
Kind Code |
A1 |
Zhou; Wenbin ; et
al. |
July 2, 2020 |
A METHOD FOR FORMING CURVED LENGTHS OF EXTRUDED PROFILES/SECTIONS
IN METAL ALLOYS
Abstract
A method of extruding a material, comprising providing the
material into an extrusion chamber of an extrusion apparatus,
wherein the extrusion chamber comprises an extrusion orifice and
the extrusion apparatus comprises a first compression element and a
second compression element in communication with the interior of
the extrusion chamber, the first and second compression elements
being independently movable relative to the extrusion chamber,
moving at least one of the first and second compression elements to
compress the material within the extrusion chamber and cause a
velocity gradient in the extrusion material across the extrusion
orifice and extruding the material through the extrusion orifice
such that the velocity gradient forms an extrudate with a curved
profile.
Inventors: |
Zhou; Wenbin; (London,
GB) ; Lin; Jianguo; (London, GB) ; Dean;
Trevor; (London, GB) ; Wang; Liliang; (London,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY AND MEDICINE |
London |
|
GB |
|
|
Family ID: |
59065707 |
Appl. No.: |
16/612232 |
Filed: |
May 10, 2018 |
PCT Filed: |
May 10, 2018 |
PCT NO: |
PCT/GB2018/051260 |
371 Date: |
November 8, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B21C 23/12 20130101;
B29C 48/48 20190201; B29C 48/131 20190201; B21C 23/002
20130101 |
International
Class: |
B21C 23/00 20060101
B21C023/00; B21C 23/12 20060101 B21C023/12 |
Foreign Application Data
Date |
Code |
Application Number |
May 10, 2017 |
GB |
1707519.3 |
Claims
1. A method of extruding a material, comprising: providing the
material into an extrusion chamber of an extrusion apparatus,
wherein the extrusion chamber comprises an extrusion orifice and
the extrusion apparatus comprises a first compression element and a
second compression element in communication with the interior of
the extrusion chamber, the first and second compression elements
being independently movable relative to the extrusion chamber;
moving at least one of the first and second compression elements to
compress the material within the extrusion chamber and cause a
velocity gradient in the extrusion material across the extrusion
orifice; and extruding the material through the extrusion orifice
such that the velocity gradient forms an extrudate with a curved
profile.
2. A method according to claim 1, comprising moving both of the
first and second compression elements to compress the material
within the extrusion chamber.
3. A method according to claim 2, comprising moving the first
compression element and second compression element at different
speeds.
4. A method according to claim 2 or 3, wherein the first
compression element and second compression element have different
cross-sectional areas perpendicular to their direction of
movement.
5. A method according to any of claims 1 to 4, wherein moving the
first and second compression elements comprises moving the first
and second compression elements along a common axis.
6. A method according to claim 5, wherein moving the first and
second compression elements along a common axis comprises moving
the first and second compression elements towards each other in
opposite directions along the common axis.
7. A method according to claim 5 or 6, wherein the plane of the
cross-section of the extrusion orifice is parallel to the common
axis such that extruding the material through the extrusion orifice
comprises extruding the material through the extrusion orifice
substantially perpendicular to the common axis.
8. A method according to any of claims 1 to 4, wherein moving the
first and second compression elements comprises moving the first
compression element along a first axis and moving the second
compression element along a second axis different to the first
axis.
9. A method according to claim 8, wherein the first axis and the
second axis are parallel to each other.
10. A method according to claim 9, wherein the plane of the
cross-section of the extrusion orifice is perpendicular to the
first and second axes such that extruding the material through the
extrusion orifice comprises extruding the material through the
extrusion orifice substantially parallel to the first and second
axes.
11. A method according to claim 8, wherein the first axis and the
second axis are at an angle to one another.
12. A method according to claim 11, wherein the plane of the
cross-section of the extrusion orifice is perpendicular to a line
that bisects the first and second axes such that extruding the
material through the extrusion orifice comprises extruding the
material through the extrusion orifice substantially parallel to
the line.
13. A method according to any one of the preceding claims, wherein
the material is a metal alloy.
14. A method according to claim 13, wherein the metal alloy is
aluminium alloy or magnesium alloy.
15. A method according to any one of the preceding claims, wherein
the extrusion orifice is provided by an extrusion die that defines
the geometry of the orifice.
16. A method according to any one of the preceding claims, further
comprising providing a guide means adjacent to the extrusion
orifice to control curvature of the extruded material.
17. A method according to any one of the preceding claims, further
comprising providing a mandrel in the extrusion chamber opposite to
the extrusion orifice.
18. A method according to claim 17, wherein extruding the material
through the extrusion orifice comprises extruding the material with
a hollow cross-section defined by the mandrel and orifice.
19. A method according to any one of the preceding claims, further
comprising preheating the material before providing it into the
extrusion chamber.
20. A method according to any one of the preceding claims, wherein
the extrusion chamber is cylindrical.
21. A method according to claim 20, wherein the cross-sectional
area of the extrusion chamber is larger than the cross-sectional
area of the extrusion orifice.
22. An apparatus for extrusion of a material, the apparatus
comprising: an extrusion chamber for receipt of an extrusion
material, the extrusion chamber comprising an extrusion orifice; a
first compression element and a second compression element, the
first and second compression elements being in communication with
the interior of the extrusion chamber and being independently
movable relative to the extrusion chamber.
23. An apparatus according to claim 22, wherein the first
compression element and second compression element are configured
to be moved simultaneously.
24. An apparatus according to claim 23, wherein the first
compression element and second compression element are configured
to be moved at different speeds.
25. An apparatus according to claim 23 or 24, wherein the first
compression element and second compression element have different
cross-sectional areas perpendicular to their direction of
movement.
26. An apparatus according to any of claims 22 to 25, wherein the
first compression element and second compression element are
configured to be moved along a common axis.
27. An apparatus according to claim 26, wherein the first
compression element and second compression element are configured
to be moved towards each other in opposite directions along the
common axis.
28. An apparatus according to claim 26 or 27, wherein the plane of
the cross-section of the extrusion orifice is parallel to the
common axis.
29. An apparatus according to any of claims 22 to 25, wherein the
first compression element is configured to be moved along a first
axis and the second compression element is configured to be moved
along a second axis different to the first axis.
30. An apparatus according to claim 29, wherein the first axis and
the second axis are parallel to each other.
31. An apparatus according to claim 30, wherein the plane of the
cross-section of the extrusion orifice is perpendicular to the
first and second axes.
32. An apparatus according to claim 29, wherein the first axis and
the second axis are at an angle to one another.
33. An apparatus according to claim 32, wherein the plane of the
cross-section of the extrusion orifice is perpendicular to a line
that bisects the first and second axes.
34. An apparatus according to any one of claims 22 to 32, wherein
the extrusion material is a metal alloy.
35. An apparatus according to claim 24, wherein the metal alloy is
aluminium alloy or magnesium alloy.
36. An apparatus according to any one of claims 22 to 35, wherein
the extrusion orifice is provided by an extrusion die that defines
the geometry of the orifice.
37. An apparatus according to any one of claims 22 to 36, further
comprising a guide means adjacent to the extrusion orifice to
control curvature of the extruded material.
38. An apparatus according to any one of claims 22 to 37, further
comprising a mandrel in the extrusion chamber opposite to the
extrusion orifice.
39. An apparatus according to any one of claims 22 to 38, wherein
the extrusion material is preheated.
40. An apparatus according to any one of claims 22 to 39, wherein
the extrusion chamber is cylindrical.
41. An apparatus according to claim 40, wherein the cross-sectional
area of the extrusion chamber is larger than the cross-sectional
area of the extrusion orifice.
42. A method according to any one of claims 1 to 21, further
comprising varying the speed of movement of the first compression
element and/or the second compression element to vary the velocity
ratio as the material is extruded.
43. An apparatus according to any one of claims 22 to 41, wherein
the first compression element and/or the second compression element
are configured to be moved at a varying speed.
Description
FIELD
[0001] This disclosure relates to a method and equipment for
forming curved metal alloy profiles and more particularly aluminium
alloy profiles with predesigned curvature in one extrusion-bending
process.
BACKGROUND
[0002] Reducing the weight of metal components used in land, sea
and air conveyances leads to a reduction of fuel consumption and
therefore a decrease of CO.sub.2 emissions. Aluminium alloy
profiles are extensively used as construction elements in
industrial manufacturing for the production of ultra-light
component structures with a high contour complexity, including seat
rails, stringers, and frames in the aircraft industry as well as
window frames and roof rails in the automotive industry. This is
mainly because they facilitate construction of lightweight, strong,
and stiff structures. Taking into account the demand for reduced
aerodynamic resistance as well as improved aesthetics, the
manufacture and application of highly precise curved aluminium
alloy profiles with well adapted properties are quite
necessary.
[0003] There are several widely acknowledged methods for curving
aluminium alloy profiles. Normally they start with manufacturing
straight profiles by shape rolling or extrusion, followed by the
subsequent secondary bending process such as stretch bending,
rotary draw bending, press bending, or roll bending (three-, four-,
and six-roll-bending). However, these procedures have disadvantages
since: (i) more than one process is needed to achieve the profiles
with desired curvature, which greatly decreases manufacturing
productivity; (ii) spring-back and cross-sectional deformations
usually occur due to the high external bending strain applied in
the second bending process; (iii) for hollow sections various
fillers and mandrels are used in the secondary bending process to
avoid the potential cross-sectional deformation and buckling; (iv)
due to the high forces needed for bending profiles, heavy machines
are required; and (v) many hollow profiles cannot be bent if the
shell is too thin or the curvature is too high.
[0004] The challenge to improved production is to manufacture
curved profiles with precise curvature, non-distorted
cross-sections and well-defined properties at increased
productivity.
SUMMARY
[0005] In accordance with an aspect of the disclosure there is
provided a method of extruding a material, comprising providing the
material into an extrusion chamber of an extrusion apparatus,
wherein the extrusion chamber comprises an extrusion orifice and
the extrusion apparatus comprises a first compression element and a
second compression element in communication with the interior of
the extrusion chamber, the first and second compression elements
being independently movable relative to the extrusion chamber,
moving at least one of the first and second compression elements to
compress the material within the extrusion chamber and cause a
velocity gradient in the extrusion material across the extrusion
orifice, and extruding the material through the extrusion orifice
such that the velocity gradient forms an extrudate with a curved
profile.
[0006] In accordance with an aspect of the disclosure there is
provided an apparatus for extrusion of a material, the apparatus
comprising an extrusion chamber for receipt of an extrusion
material, the extrusion chamber comprising an extrusion orifice, a
first compression element and a second compression element, the
first and second compression elements being in communication with
the interior of the extrusion chamber and being independently
movable relative to the extrusion chamber.
[0007] The method may comprise moving both of the first and second
compression elements to compress the material within the extrusion
chamber. The method may comprise moving the first compression
element and second compression element at different speeds.
[0008] Moving the first and second compression elements may
comprise moving the first and second compression elements along a
common axis. Moving the first and second compression elements along
a common axis may comprise moving the first and second compression
elements towards each other in opposite directions along the common
axis. The plane of the cross-section of the extrusion orifice may
be parallel to the common axis such that extruding the material
through the extrusion orifice comprises extruding the material
through the extrusion orifice substantially perpendicular to the
common axis.
[0009] Moving the first and second compression elements may
comprise moving the first compression element along a first axis
and moving the second compression element along a second axis
different to the first axis. The first axis and the second axis may
be parallel to each other. The plane of the cross-section of the
extrusion orifice may be perpendicular to the first and second axes
such that extruding the material through the extrusion orifice
comprises extruding the material through the extrusion orifice
substantially parallel to the first and second axes.
[0010] The first axis and the second axis may be at an angle to one
another. The plane of the cross-section of the extrusion orifice
may be perpendicular to a line that bisects the first and second
axes such that extruding the material through the extrusion orifice
comprises extruding the material through the extrusion orifice
substantially parallel to the line.
[0011] The method may further comprise providing a guide means
adjacent to the extrusion orifice to control curvature of the
extruded material. The method may further comprise providing a
mandrel in the extrusion chamber opposite to the extrusion orifice.
Extruding the material through the extrusion orifice may comprise
extruding the material with a hollow cross-section defined by the
mandrel and orifice. The plane of the cross-section of the mandrel
that defines the hollow cross-section of the extruded material may
be parallel to the plane of the cross-section of the extrusion
orifice.
[0012] The method may further comprise preheating the material
before providing it into the extrusion chamber.
[0013] The first compression element and second compression element
may be configured to be moved simultaneously. The first compression
element and second compression element may be configured to be
moved at different speeds. The first compression element and second
compression element may have different cross-sectional areas
perpendicular to their direction of movement.
[0014] The first compression element and second compression element
may be configured to be moved along a common axis. The first
compression element and second compression element may be
configured to be moved towards each other in opposite directions
along the common axis. The plane of the cross-section of the
extrusion orifice may be parallel to the common axis.
[0015] The first compression element may be configured to be moved
along a first axis and the second compression element may be
configured to be moved along a second axis different to the first
axis. The first axis and the second axis may be parallel to each
other. The plane of the cross-section of the extrusion orifice may
be perpendicular to the first and second axes.
[0016] The first axis and the second axis may be at an angle to one
another. The plane of the cross-section of the extrusion orifice
may be perpendicular to a line that bisects the first and second
axes.
[0017] The extrusion material may be a metal alloy. The metal alloy
may be aluminium alloy or magnesium alloy. The extrusion orifice
may be provided by an extrusion die that defines the geometry of
the orifice.
[0018] The apparatus may further comprise a guide means adjacent to
the extrusion orifice to control curvature of the extruded
material. The apparatus may further comprise a mandrel in the
extrusion chamber opposite to the extrusion orifice.
[0019] The extrusion material may be preheated. The extrusion
chamber may be cylindrical. The cross-sectional area of the
extrusion chamber may be larger than the cross-sectional area of
the extrusion orifice.
[0020] According to the present disclosure, there is provided a
method of forming curved metal alloy profiles comprising: [0021]
(i) providing the sideways extrusion setup, forward extrusion setup
or angled extrusion setup; [0022] (ii) pre-heating a metal alloy
billet before transferring it to an extrusion container for hot
extrusion; or directly transferring the unheated metal alloy billet
to the extrusion container for cold extrusion; [0023] (iii)
applying pressure to the two dummy blocks through the corresponding
two punches simultaneously, the metal alloy billet is pressed
against the extrusion die and squeezed through the die opening; and
[0024] (iv) adjusting the velocities of the two punches so as to
form a velocity gradient across the die orifice and produce a
curved profile of the long extruded section.
[0025] This has the following advantages: [0026] (i) forming curved
profiles without defects such as distortion or thinning of the
cross-section, spring-back, wrinkling and folding. Bending is
intrinsic to the process, based on internal differential material
flow, rather than external bending force; [0027] (ii) forming
profiles with ultra-fine grain size for cold extrusion and
therefore improved mechanical properties due to severe plastic
deformation (SPD) caused by shear stresses in the intersecting
deformation zone of the container; [0028] (iii) forming profiles
with adjustable arbitrary curvatures in one extrusion-bending
procedure, which greatly increases the manufacturing efficiency;
and [0029] (iv) no fillers or extra heavy machines are needed for
the bending process, which greatly reduces the production cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Exemplary embodiments of the disclosure shall now be
described with reference to the drawings in which:
[0031] FIG. 1a is a schematic illustration of an extrusion
apparatus known in the art;
[0032] FIG. 1b is a schematic illustration of another extrusion
apparatus known in the art;
[0033] FIG. 2 is a schematic illustration of an extrusion apparatus
according to an embodiment;
[0034] FIG. 3a is a schematic illustration of another extrusion
apparatus according to an embodiment;
[0035] FIG. 3b is a cross-section through the line m-m in FIG.
3a;
[0036] FIG. 4 is a schematic illustration of yet another extrusion
apparatus according to an embodiment;
[0037] FIG. 5 is a schematic illustration of the orientation of a
first, second and third axis of an extrusion apparatus according to
an embodiment.
[0038] Throughout the description and the drawings, like reference
numerals refer to like parts.
SPECIFIC DESCRIPTION
[0039] FIG. 1a shows an extrusion apparatus known in the art. A
cylindrical extrusion chamber 102 has two open ends 104 and 106. An
extrusion die 108 with a designed orifice 110 is installed at the
first open end 104. The geometry of the orifice 110 is designed to
form the extruded material into a chosen shape. A hot or cold
billet 112 is placed into the extrusion chamber 102 from the second
open end 106.
[0040] A punch 114 is positioned at the second open end 106. Its
working face 116 would usually be protected by a dummy block 118.
The punch 114, together with dummy block 116, acts as a compression
element and moves along the extrusion chamber 102 at a velocity
v.sub.1, forcing the billet 112 through the die orifice 110,
producing a straight extrudate 120.
[0041] Another extrusion apparatus known in the art is shown in
FIG. 1b. In this case, an extrusion chamber 130 has an L-shape in
transverse section, rather than being a straight cylinder. In this
manner, the billet 132 is forced along a straight section 134 to
form the straight extrudate 136. The straight section 134 is of
sufficient length to ensure that the extrudate 136 is formed in a
straight manner.
[0042] Once the straight extrudate 120 or 136 is produced, bending
processes such as stretch bending, rotary draw bending, press
bending, or roll bending are used to form a curved piece. However,
forming curved sections of extrudate in this way has disadvantages
such as reduced manufacturing productivity, spring-back,
cross-sectional deformation and a requirement for various fillers,
mandrels and heavy machinery, as discussed above.
[0043] FIG. 2 shows an extrusion apparatus 200 according to the
present disclosure. A cylindrical extrusion chamber 202 has two
open ends 204 and 206. A hot or cold billet 208 is placed into the
extrusion chamber 202 from the first open end 204 and/or the second
open end 206. For example, an aluminium alloy billet may be
pre-heated to 350-550.degree. C. for warm or hot extrusion or
remain unheated for cold extrusion. A first punch 210 is positioned
at the first open end 204. A second punch 212 is positioned at the
second open end 206. The respective working faces 214 and 216 of
the first and second punches 210 and 212 are protected by
respective dummy blocks 218 and 220. An extrusion die 222 with a
designed orifice 224 is installed in the side wall of the extrusion
chamber 202.
[0044] The first punch 210 together with dummy block 218 act as a
first compression element and the second punch 212 together with
dummy clock 220 act as a second compression element. The skilled
person with recognise that these compression elements could be
replaced by any other suitable compression means. The first and
second compression elements are independently movable relative to
the extrusion chamber 202. As described below, this allows the
profile of an extrudate to be controlled, particularly with respect
to its curvature.
[0045] In operation, pressure is applied to the two dummy blocks
218 and 220 via the corresponding two punches 210 and 212
simultaneously. The velocity of the first punch 210 is v.sub.1, and
the velocity of the second punch 212 is v.sub.2. As the punches
move towards each other, the billet 208 is forced sideways out of
the extrusion chamber 202 through the die orifice 224. Its exiting
direction is perpendicular to the punch motion direction.
[0046] To produce a curved extrudate, the rate of mass flow
provided by each of the compression elements can be adjusted. In
one embodiment, the velocities of the punches 210 and 212 can be
adjusted to provide a curved extrudate. When one punch is moved
faster than the other, a flow velocity gradient is produced across
the die orifice 224. Therefore, the extruded profile bends towards
the side of the extrusion chamber 202 which has the lower extrusion
velocity. In FIG. 2, the velocity v.sub.1 of the first punch 210 is
larger than the velocity v.sub.2 of the second punch 212.
Therefore, the extrudate 226 bends towards the second open end 206.
In another embodiment, the area of the first dummy block 218 is
greater than that of the second dummy block 220. In this instance,
the extruded profile will bend downwards as shown in FIG. 2 even
when v.sub.1=v.sub.2.
[0047] The essence is to control the volume of material flowing
into the die exit 222 per unit time, which can be expressed as
Q=Sv. Here S is the cross-sectional area and v is the velocity.
Therefore, increasing the velocity v.sub.1 and/or the area of the
first dummy block 218 can lead to more material flowing into the
upper side of the die exit 222 compared with the lower side.
[0048] By creating a controlled gradient of flow velocity across
the exit of an extrusion die orifice utilizing two extrusion
punches, the extrusion and bending operations are performed
simultaneously. This removes the need for post-processing of
straight extruded pieces to provide curvature, and overcomes the
issues mentioned above.
[0049] By adjusting the ratio of the velocities of the two punches
(or more generally the rate of material flow Q), the curvature of
the extrudate 226 can be adjusted. If the velocity ratio is defined
as v.sub.2/v.sub.1, a lower velocity ratio tends to increase the
material flow velocity gradient at the die exit and lead to greater
curvature. When this velocity ratio is less than 1/3, bending
curvature increases significantly with reducing velocity ratio.
Maximum curvature results at zero velocity of the lower punch 212.
The velocity ratio could be changed during extrusion. This will
enable the curvature of the extrudate 226 to be changed as
extrusion proceeds, which allows more complex extrusions.
[0050] Additionally, the relative cross-sectional areas of the
extrusion chamber 202 and the orifice 224 can be adjusted to change
the curvature. An extrusion ratio is defined as the ratio of the
cross-sectional area of the billet to the cross-sectional area of
the extruded profile. These areas are controlled by adjusting the
cross-sectional area of the extrusion chamber 202 and the extrusion
orifice 224 respectively. For solid circular bar extrusion, the
extrusion ratio can be defined as the square of the diameter ratio
of the extrusion chamber 202 to the orifice 224. For a tubular
circular extrusion (a hollow bar), it can be defined as
D.sub.1.sup.2/(D.sub.2.sup.2-D.sub.3.sup.2), where D.sub.1,
D.sub.2, D.sub.3 are the respective diameters of the extrusion
chamber 202, the orifice 224 and a mandrel fixed to the inner wall
of the extrusion chamber opposite to the exit die to define the
wall thickness of the tube.
[0051] A larger extrusion ratio tends to increase the material flow
velocity gradient at the die exit and lead to greater curvature.
For a constant diameter of the extrusion chamber 202, the curvature
of the extrudate 226 is increased as the diameter of the orifice
224 is decreased. Conversely, the curvature of the extrudate 226 is
reduced as the diameter orifice 224 is increased. The effect of
changing the extrusion ratio is less than that of changing the
velocity ratio, especially when velocity ratio is greater than 0.5.
Below this value, the effect of extrusion ratio increases as
velocity ratio v.sub.2/v.sub.1 decreases.
[0052] FIG. 3a shows an alternative extrusion apparatus 300
according to the present disclosure. The apparatus 300 is similar
to the apparatus 100 of FIG. 1a, except that two adjacent punches
are used instead of a single punch. A cylindrical extrusion chamber
302 has two open ends 304 and 306. A hot or cold billet 308 is
placed into the extrusion chamber 302 from the second open end 306.
First and second punches 310 and 312 are positioned adjacent to one
another at the second open end 306. The respective working faces
314 and 316 of the first and second punches 310 and 312 are
protected by a respective dummy blocks 318 and 320. An extrusion
die 322 with a designed orifice 324 is installed at the first open
end 304.
[0053] The length of the first dummy block 318 is shown as longer
than that of the second dummy block 320. In the case that the
second dummy block 320 moves faster than the first dummy block 318,
then the second dummy block 320 may entirely pass the first dummy
block 318. In this case, the billet 308 may flow out of the chamber
302 from the gap between the first dummy block 318 and the second
dummy block 320. By implementing a longer profile of the first
dummy block, this situation is mitigated.
[0054] In operation, pressure is applied to the two dummy blocks
318 and 320 via the corresponding two punches 310 and 312
simultaneously. The velocity of the first punch 310 is v.sub.1, and
the velocity of the second punch 312 is v.sub.2. As the punches
move alongside each other, the billet 308 is forced out of the
extrusion chamber 302 through the die orifice 324.
[0055] As in the above embodiment, when one punch is moved faster
than the other, a flow velocity gradient is produced across the die
orifice 324. Therefore, the extruded profile bends towards the side
of the extrusion chamber 302 which has the lower extrusion
velocity. In FIG. 3a, the velocity v.sub.1 of the first punch 310
is larger than the velocity v.sub.2 of the second punch 312.
Therefore, the extrudate 326 bends towards the side of the
cylindrical extrusion chamber 302 with the second punch 312.
Additionally or alternatively, the areas of the dummy blocks 318
and 320 may be adjusted to provide this effect. FIG. 3b shows the
dummy blocks 318 and 320 with different cross-sectional areas
perpendicular to their direction of movement.
[0056] FIG. 4 shows yet another alternative extrusion apparatus 400
according to the present disclosure. The apparatus comprises a
Y-shaped extrusion chamber 402, having a first bore 404, a second
bore 405 and a central container 406. The first bore 404 and the
second bore 405 are positioned at an angle to each other and
converge to meet the central container 406, forming the Y-shape.
Each of the first bore 404, the second bore 405 and the central
container 406 has an open end opposite to the point of
convergence.
[0057] A first hot or cold billet 407 is placed into the open end
of the first bore 404. A second hot or cold billet 408 is placed
into the open end of the second bore 405. A first punch 410 is
positioned at the open end of the first bore 404. A second punch
412 is positioned at the open end of the second bore 405. The
respective working faces 414 and 416 of the first and second
punches 410 and 412 are protected by a respective dummy block 418
and 420. An extrusion die 422 with a designed orifice 424 is
installed at the open end of the central container 406.
[0058] In operation, pressure is applied to the two dummy blocks
418 and 420 via the corresponding two punches 410 and 412
simultaneously. The velocity of the first punch 410 is v.sub.1, and
the velocity of the second punch 412 is v.sub.2. As the punches
move towards each other, the billet 408 is forced sideways out of
the extrusion chamber 402 through the die orifice 424.
[0059] As in the above embodiments, when one punch is moved faster
than the other, a flow velocity gradient is produced across the die
orifice 424. Therefore, the extruded profile bends towards the side
of the extrusion chamber 402 which has the lower extrusion
velocity. In FIG. 4, the velocity v.sub.1 of the first punch 410 is
larger than the velocity v.sub.2 of the second punch 412.
Therefore, the extrudate 426 bends towards the second bore 405.
Additionally or alternatively, the areas of the dummy blocks 418
and 420 may be adjusted to provide this effect.
[0060] In the embodiments described above with reference to FIGS. 2
to 4, the first and second compression elements can be positioned
at an angle .alpha., shown in FIG. 5. In FIG. 5, the first and
second axes correspond to the first and second compression
elements, with the third axis bisecting the first and second axes
and corresponding to the direction of extrusion from the die
orifice. Hence, the plane of the cross-section of the extrusion
orifice is perpendicular to a line bisecting the first and second
axes, with the third axis being parallel to this line.
[0061] The first axis is at an angle of
.beta.=180.degree.-.alpha./2 to the direction of flow of the
extrudate from the extrusion apparatus (i.e. the third axis).
Likewise, the second axis is at an angle of
.beta.=180.degree.-.alpha./2 to the third axis.
[0062] By having an angle of .beta.<180.degree., a shear stress
can be exerted while the billet passes from the entrance to the
extrusion chamber to the exit from the extrusion chamber. The shear
stress exerted at the intersection between the first axis and the
third axis (and likewise at the intersection between the second
axis and the third axis) causes severe plastic deformation (SPD) of
the billet at the point of intersection of the axes. SPD of the
billet results in an extruded profile with an ultra-fine grain
size, thereby improving the mechanical properties of the extruded
profile. SPD of the billet increases as the angle .beta. decreases
(i.e. as angle .alpha. increases), thereby giving rise to improved
mechanical properties arising from SPD with reduced angle A.
[0063] The first and second axes may be orientated at an angle
0.degree..ltoreq..alpha..ltoreq.360.degree.. The extrusion
apparatus schematically illustrated in FIG. 2 corresponds to an
angle of .alpha.=180.degree.. The extrusion apparatus schematically
illustrated in FIG. 3 corresponds to an angle of .alpha.=0.degree..
The extrusion apparatus schematically illustrated in FIG. 4 may
have any arbitrary angle between 0.degree. and 360.degree..
[0064] By using any of the above embodiments, curved sections with
undistorted cross-sections can be achieved by utilising asymmetric
flow in the extrusion die. Since it is a natural bending process
based on internal differential material flow rather than external
bending force, defects such as distortion and thinning of the
cross-section are avoided. The combination of the extrusion and
bending processes into a single process, thus eschews the
complication of an extra external bending apparatus.
[0065] This effect is achieved by variations in velocities v.sub.1
and v.sub.2 of the compression elements (formed of punches and
dummy blocks). However, in some embodiments, the compression
elements may move at the same velocity, with the velocity gradient
across the extrusion orifice being a function of geometric features
(such as a greater surface area for one dummy block/compression
element in comparison with the other). In other examples, a
combination of geometric features and the velocities of the
compression elements may result in a desired velocity gradient at
the extrusion orifice.
[0066] In any of the above embodiments, a guide external to the die
orifice 224 may be employed to ensure precise curve accuracy. Any
of the above embodiments may be used for extrusion of solid bars or
tubes. For hollow extrusion, a mandrel may be fixed to the inner
wall of the extrusion chamber opposite to the exit die. The size of
the mandrel relative to the size of the die orifice will define the
wall thickness of the extruded tube. The curvature of the tube is
reduced with increase of wall thickness of the tube. However, the
effect of the wall thickness on curvature is small, compared with
that of the velocity ratio. Otherwise, a similar tendency in the
extrusion of round bars described before also occurs in extrusion
of round tubes.
[0067] Any of the above embodiments may be used to produce curved
profiles in any material that can be manufactured by the
conventional extrusion procedure. The principal application is
extrusion of metal alloys. These include aluminium, magnesium,
copper, steel, titanium and nickel. The system has been described
with reference to aluminium since this is where the most
commercially feasible applications are likely to be, but the
implementation is not exclusively related to aluminium.
[0068] Any of the above embodiments may be used for hot or cold
extrusion. In the case of hot extrusion, the hot metal billet used
can be virtually any metal alloy billet which is heated to the
temperature generally used in the hot extrusion process. A True
Temperature Technology (3T) facility is utilized to record exit
temperature of the extruded part. By adjusting the extrusion
velocities of the two punches while keeping the extrusion velocity
ratio constant, exit temperature is maintained at a reasonable
temperature where solution heat treatment (SHT) takes place. The
target exit temperature for an extruded part is dependent on the
metal alloy. For the 6xxx series aluminium alloys, temperatures
within a range of 500-530.degree. C. for solution heat treatment
should be realised at the die exit to achieve optimal mechanical
properties. The extruded part can be quenched after SHT using
water, mist spray or air cooling, depending on the alloy and the
final mechanical property requirements.
[0069] Although the embodiments described in FIGS. 2 to 4 above
comprise two compression elements, it will be understood that
further compression elements could be incorporated to control
curvature in other planes.
[0070] Further embodiments of the present disclosure are set out in
the following clauses: [0071] 1. A method of extruding a material,
comprising: [0072] providing the material into an extrusion chamber
of an extrusion apparatus, wherein the extrusion chamber comprises
an extrusion orifice and the extrusion apparatus comprises a first
compression element and a second compression element in
communication with the interior of the extrusion chamber, the first
and second compression elements being independently movable
relative to the extrusion chamber; [0073] moving at least one of
the first and second compression elements to compress the material
within the extrusion chamber and cause a velocity gradient in the
extrusion material across the extrusion orifice; and extruding the
material through the extrusion orifice such that the velocity
gradient forms an extrudate with a curved profile. [0074] 2. A
method according to clause 1, comprising moving both of the first
and second compression elements to compress the material within the
extrusion chamber. [0075] 3. A method according to clause 2,
comprising moving the first compression element and second
compression element at different speeds. [0076] 4. A method
according to clause 2 or 3, wherein the first compression element
and second compression element have different cross-sectional areas
perpendicular to their direction of movement. [0077] 5. A method
according to any of clauses 1 to 4, wherein moving the first and
second compression elements comprises moving the first and second
compression elements along a common axis. [0078] 6. A method
according to clause 5, wherein moving the first and second
compression elements along a common axis comprises moving the first
and second compression elements towards each other in opposite
directions along the common axis. [0079] 7. A method according to
clause 5 or 6, wherein the plane of the cross-section of the
extrusion orifice is parallel to the common axis such that
extruding the material through the extrusion orifice comprises
extruding the material through the extrusion orifice substantially
perpendicular to the common axis. [0080] 8. A method according to
any of clauses 1 to 4, wherein moving the first and second
compression elements comprises moving the first compression element
along a first axis and moving the second compression element along
a second axis different to the first axis. [0081] 9. A method
according to clause 8, wherein the first axis and the second axis
are parallel to each other. [0082] 10. A method according to clause
9, wherein the plane of the cross-section of the extrusion orifice
is perpendicular to the first and second axes such that extruding
the material through the extrusion orifice comprises extruding the
material through the extrusion orifice substantially parallel to
the first and second axes. [0083] 11. A method according to clause
8, wherein the first axis and the second axis are at an angle to
one another. [0084] 12. A method according to clause 11, wherein
the plane of the cross-section of the extrusion orifice is
perpendicular to a line that bisects the first and second axes such
that extruding the material through the extrusion orifice comprises
extruding the material through the extrusion orifice substantially
parallel to the line. [0085] 13. A method according to any one of
the preceding clauses, wherein the material is a metal alloy.
[0086] 14. A method according to clause 13, wherein the metal alloy
is aluminium alloy or magnesium alloy. [0087] 15. A method
according to any one of the preceding clauses, wherein the
extrusion orifice is provided by an extrusion die that defines the
geometry of the orifice. [0088] 16. A method according to any one
of the preceding clauses, further comprising providing a guide
means adjacent to the extrusion orifice to control curvature of the
extruded material. [0089] 17. A method according to any one of the
preceding clauses, further comprising providing a mandrel in the
extrusion chamber opposite to the extrusion orifice. [0090] 18. A
method according to clause 17, wherein extruding the material
through the extrusion orifice comprises extruding the material with
a hollow cross-section defined by the mandrel and orifice. [0091]
19. A method according to any one of the preceding clauses, further
comprising preheating the material before providing it into the
extrusion chamber. [0092] 20. A method according to any one of the
preceding clauses, wherein the extrusion chamber is cylindrical.
[0093] 21. A method according to clause 20, wherein the
cross-sectional area of the extrusion chamber is larger than the
cross-sectional area of the extrusion orifice. [0094] 22. An
apparatus for extrusion of a material, the apparatus comprising:
[0095] an extrusion chamber for receipt of an extrusion material,
the extrusion chamber comprising an extrusion orifice; [0096] a
first compression element and a second compression element, the
first and second compression elements being in communication with
the interior of the extrusion chamber and being independently
movable relative to the extrusion chamber. [0097] 23. An apparatus
according to clause 22, wherein the first compression element and
second compression element are configured to be moved
simultaneously. [0098] 24. An apparatus according to clause 23,
wherein the first compression element and second compression
element are configured to be moved at different speeds. [0099] 25.
An apparatus according to clause 23 or 24, wherein the first
compression element and second compression element have different
cross-sectional areas perpendicular to their direction of movement.
[0100] 26. An apparatus according to any of clauses 22 to 25,
wherein the first compression element and second compression
element are configured to be moved along a common axis. [0101] 27.
An apparatus according to clause 26, wherein the first compression
element and second compression element are configured to be moved
towards each other in opposite directions along the common axis.
[0102] 28. An apparatus according to clause 26 or 27, wherein the
plane of the cross-section of the extrusion orifice is parallel to
the common axis. [0103] 29. An apparatus according to any of
clauses 22 to 25, wherein the first compression element is
configured to be moved along a first axis and the second
compression element is configured to be moved along a second axis
different to the first axis. [0104] 30. An apparatus according to
clause 29, wherein the first axis and the second axis are parallel
to each other. [0105] 31. An apparatus according to clause 30,
wherein the plane of the cross-section of the extrusion orifice is
perpendicular to the first and second axes. [0106] 32. An apparatus
according to clause 29, wherein the first axis and the second axis
are at an angle to one another. [0107] 33. An apparatus according
to clause 32, wherein the plane of the cross-section of the
extrusion orifice is perpendicular to a line that bisects the first
and second axes. [0108] 34. An apparatus according to any one of
clauses 22 to 32, wherein the extrusion material is a metal alloy.
[0109] 35. An apparatus according to clause 24, wherein the metal
alloy is aluminium alloy or magnesium alloy. [0110] 36. An
apparatus according to any one of clauses 22 to 35, wherein the
extrusion orifice is provided by an extrusion die that defines the
geometry of the orifice. [0111] 37. An apparatus according to any
one of clauses 22 to 36, further comprising a guide means adjacent
to the extrusion orifice to control curvature of the extruded
material. [0112] 38. An apparatus according to any one of clauses
22 to 37, further comprising a mandrel in the extrusion chamber
opposite to the extrusion orifice. [0113] 39. An apparatus
according to any one of clauses 22 to 38, wherein the extrusion
material is preheated. [0114] 40. An apparatus according to any one
of clauses 22 to 39, wherein the extrusion chamber is cylindrical.
[0115] 41. An apparatus according to clause 40, wherein the
cross-sectional area of the extrusion chamber is larger than the
cross-sectional area of the extrusion orifice. [0116] 42. A method
according to any one of clauses 1 to 21, further comprising varying
the speed of movement of the first compression element and/or the
second compression element to vary the velocity ratio as the
material is extruded. [0117] 43. An apparatus according to any one
of clauses 22 to 41, wherein the first compression element and/or
the second compression element are configured to be moved at a
varying speed.
* * * * *