Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR MANUFACTURING A PART OF
A METAL MATRIX COMPOSITE MATERIAL
BACKGROUND OF THE INVENTION
1. Field of the Invention:
This invention relates to a process for manufacturing a
part of a metal matrix composite material.
2. Description of the Related Art:
A process for manufacturing a cylinder as disclosed in
Japanese Patent Laid-Open Publication No. SHO-59-206154, for
example, is known as a process for manufacturing a desired shape
by plastic working from an aluminum-based composite material.
It comprises:
(a) Dispersing SiC chips in a molten bath of aluminum under
stirring and causing it to solidify;
(b) HeatS.ng a solidified product to a temperature of about
250 deg. C and drawing it into a pipe; and
(c) Cutting a sleeve from the pipe, fitting it in a die
casting mold and casting an aluminum,alloy (JIS-ADC12) about it
to make a cylinder.
The sleeve is a composite material obtained by putting SiC
chips in a molten bath of aluminum and has a high resistance to
plastic deformation, and its aluminum and SiC are mechanically
joined to each other. Therefore, it is low in elongation and
is as poor in workability as any other common composite material.
As a consequence, it is difficult to employ for plastic working,
such as drawing, to make a molded product of high quality at a
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reduced cost.
A part of a composite material can also be made by press
forming, but a high resistance to plastic deformation brings about
a high cost of production and makes it difficult to obtain a product
of improved quality.
FIG. 17 hereof shows a disk brake device for an automobile.
The disk brake device 202 has a brake disk 203 mounted by a hub
201 attached to the end of a drive shaft 200, and a caliper 206
in which an edge portion of the disk 203 is engaged. A hydraulic
pressure is transmitted through a passage 208 to a cylinder not
shown in the caliper 206 to press two brake pads 207 against the
edge portion 205 of the brake disk 203 to thereby brake a wheel
209. Therefore, the brake disk 203 has to be formed f romamaterial
of high strength, while it is also desirable to use a light material
to reduce the weight of the automobile_
A metal matrix composite material is known as a material
of high strength and light weight. For example, a composite
material containing an aluminum alloy can be used to achieve a
weight reduction and a material containing SiC (silicon carbide)
particles in an aluminum alloy makes it possible to achieve a
high strength_
A brake disk 203 can be made by casting from such an
aluminum-based composite material. A large amount of heat energy
is, however, required for melting such a material and brings about
an increase of production cost. study has, therefore, been madeof the
possibility of relying upon press forming formanufacturing
brake disks 203 in a large quantity without having to melt the
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material.
FIGS. 18A and 18B show a known method of manufacturing a
brake disk from a composite material containing an aluminum alloy
as a metal matrix. An aluminum-based composite material 210 is
prepared in the form of a flat sheet, as shown in FIG_ 18A, and
is press formed into a brake disk 211, as shown in FIG. 18B. The
brake disk 211 has a hub 213 having a recessed central portion
and a flat disk portion 212 extending from the edge of the hub
213. The material 210, however, contains SiC particles which
produce a relatively high frictional resistance in that portion
of the material 210 which is contacted by a press whereby the
disk 211 is formed, and the disk 211 is very likely to crack in
its bent portions 214 and 215. Under these circumstances, it
is difficult to manufacture a brake disk 211 by press forming
from such a composite material.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a process for
manufacturing a part of high quality from a metal matrix composite
material at a low cost.
According to a first aspect of this invention, there is
provided a process comprising the steps of preparing an
aluminum-based composite material containing an aluminum alloy
and having an appropriate diameter, cutting the material into
a plurality of blanks each having an appropriate thickness,
heating the blanks to an appropriate temperature ranging from.
the solidus temperature, Ta, of the aluminum alloy minus 50 (Ta
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- 50) deg. C to Ta deg. C, and press forming each blank, while
holding it at the appropriate temperature.
When the temperature of the material is lower than (Ta -
50) deg. c, it has a high resistance to plastic deformation, is
difficult to work on and requires a high working load. When its
temperature exceeds Ta, a liquid phase may be formed and cause
the material to crack during its plastic deformation because of
its low compressibility. According to this invention,therefore,
the temperature to which the blank is heated is at least equal
to (Ta - 50) deg. c to ensure its good workability, and does not
exceed Ta deg. C to ensure its good compressibility.
The aluminum-based composite material is prepared by
reducing a porous reinforcing material composed of a metal oxide
in a furnace containing a magnesium nitride atmosphere to expose
a metal on at least a part of the reinforcing material, and
impregnating the porous material with a molten aluminum alloy.
The reduction of the metal oxide forms a metallized surface on
the porous.material and thereby produces an improved wetting
property between the metal oxide and the molten aluminum alloy.
The composite material is of high workability, since the aluminum
and reinforcing material are strongly joined to each other by
chemical contact. It is easy of plastic working and enables a
reduction of production cost.
The die may have a heater for holding the blank at the
temperature between (Ta - 50) deg. C and Ta deg. C, so that the
blank may be high in workability and easy to press form into a
desired shape. The blank temperature is preferably in the range
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of (Ta - 20) to Ta, or for example, from 563 to 583 deg. C to
ensure that it be easy to work on to thereby enable a reduction
of production cost. Moreover, it is preferably in the range of
(Ta - 40) to (Ta - 33), or for example, from 543 to 550 deg. C
to ensure that the blank be of high compressibility to thereby
attain a high working accuracy.
According to a second aspect of this invention, there is
provided a process comprising the steps of preparing a die and
a dual punch having a solid cylindrical inner punch portion and
a hollow cylindrical outer punch portion surrounding the inner
punch portion, setting a blank of an aluminum-based composite
material on the die, lowering the inner punch portion to press
against the central portion of the blank and holding it
thereagainst to give a nearly final shape to the central portion
of the blank and lowering the outer punch portion to press against
the remaining portion of the blank to give a nearly final shape
thereto.
The process includes two press forming steps in which a
dual punch is used to form a blank of an aluminum-based composite
material into a disk-shaped part. Firstly, the inner punch
portion is pressed down against the central portion of the blank
to form it into a desired shape, while drawing out the composite
material uniformly from the center of the blank to give a high
working accuracy to its central portion. Then, the inner punch
portion is held against the central portion of the blank and the
die is closed. Secondly, the outer punch portion is pressed down
against the remaining portion of the blank to draw it out or cause
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it to flow in the die to form the composite material into a nearly
final shape. As a result, there is obtained a product which
requires only a small amount of machining work thereafter and
thereby contributes to a reduction of production cost.
The outer punch portion forced into the closed die
compresses the composite material therein by applying a uniform
compressive force to the outer surface of the material at right
angles thereto, so that it may be possible to reduce any tensile
stress on the surface of the blank, prevent its surface from
cracking, remove any internal defects from it and give it a tight
structure to thereby make a part of improved quality.
The first press-forming step employing the inner punch
port.ion may be used to form, for example, the boss portion of
a crank damper pulley. The boss portion is easy to form by press
forming from an aluminum-based composite material if the inner
punch portion has an appropriately shaped surface.
According to a third aspect of this invention, there is
provided a process comprising the steps of forming a sheet of
an aluminum alloy covering the whole surface of a sheet of a metal
matrix composite material to preparea sandwiched structure having
an aluminum alloy layer on both sides of the composite material,
pressing the central portion of the sandwiched structure to form
a recess therein, and removing the aluminum alloy layer from the
remaining portion of the structure surrounding the recess.
A sheet of an aluminum alloy is formed to cover both sides
of a sheet of a metal matrix composite material to prepare a
sandwiched structure and the sandwiched structure is pressed in
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its central portion to have a recess formed therein. The aluminum
alloy is high in workability and can,'therefore, be shaped to
cover both sides of the compos ite material to reduce any frictional
resistance shown by the composite material during press forming,
so that it may be possible to reduce any stress produced in the
material and prevent it from cracking. The aluminum alloy layers
are removed from the remaining portion of the material surrounding
thEa recess to expose the metal matrix composite material to thereby
enable the manufacture of a part of high strength. Thus, the
process may most advantageously be employed for making a disk
of a metal matrix composite material for a disk brake for an
aut:omobile.
The metal matrix composite material may be prepared by
incorporating ceramic particles into an aluminum alloy. The
aluminum alloy used as the matrix contributes to a reduction in
weight of the composite material and the ceramic particles
contribute to improving its strength. Thus, it is the most
suitable material for brake disks.
BRIEF DESCRIPTION OF THE DRAWINGS
Certain preferred embodiments of this invention will be
described in detail below, by way of example only, with reference
to the accompanying drawings, in which:
FIG. 1 is a diagram showing the layout of an apparatus for
preparing an aluminum-based composite material according to this
invention;
FIGS. 2A to 2D are a set of views illustrating a process
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for preparing a billet of an aluminum-based composite material
by the apparatus shown in FxG. 1;
FIG. 3A is a perspective view showing the preparation of
blanks from the billet according to a first embodiment of this
invention;
FIG. 3B is a diagram showing the heating of blanks;
FIG. 4A is a view showing a blank mounted in a die for press
forming;
FIG. 4B is a sectional view taken along the line b-b of
FIG. 4A;
FIG. 5A is a view showing the blank pressed by a lowered
punch;
FIG. 5B is a fragmentary perspective view of a part obtained
from the blank pressed as shown in FIG. 5A;
FIG_ 6 is a graph showing the compressibility of blanks
in relation to their temperature;
FIG. 7 is a flowchart showing a process for press forming
a disk-shaped part from an aluminum-based composite material
according to a second embodiraent of this invention;
FIGS. 8A to 8D are a series of views showing the step of
preparing a pressing die and the first and second press-forming
steps according to the second embodiment of this invention;
FIGS. 9A and 9B are a set of views showing a disk-shaped
part made by the process shown in FzGS. 8A to 8D and its machining;
FIG. 10 is a fragmentary perspective view of a crank damper
pulley made by using the part as shown in FIGS. 9A and 9B;
FIG. 11 is a perspective view of a brake disk formed from
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a metal matrix composite material;
FIG. 12 is a sectional view taken along the line 12-12 of
FIG. 11;
FIGS. 13Ato 13C area series of views showing the preparation
of a flat clad material by extrusion from a billet of an
aluminum-based composite material;
FIG. 14 is a graph showing the tensile strength and yield
strength of clad materials in relation to their reduction ratio;
FIG. 15 is a view showing the formation of a disk-shaped
sandwiched structure from a clad material;
FIGS. 16A to 16F are a series of views showing themanufacture
of a brake disk by pressing from a disk-shaped sandwiched
structure;
FIG. 17 is a side elevational view, partly in section, of
a typical automobile disk brake known in the art; and
FIGS_ 18A and 18B are a set of views explaining a known
process for manufacturing a brake disk from a metal matrix
composite material.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following description is merely exemplary in nature
and is in no way intended to limit the invention, its application
or used.
Referring first to FIG. 1, an apparatus 1 for preparing
a metal matrix composite material,for example,an aluminum-based
material has an atmosphere-controlled furnace 2, a heater 3
associated with the furnace 2, a device 6 for supplying an inert
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gas into the furnace 2 and a vacuum pump 7 for evacuating the
furnace 2. The furnace 2 contains a first crucible 8 and a second
crucible 9. The heater 3 has a control unit 11, a temperature
sensor 12 and a heating coil 13. The gas supplying device 6
includes a bottle 15 holding argon gas (Ar) 14, a bottle 17 holding
nitrogen gas (N2) 16, a pipeline 18 for supplying those gases
from the bottles 15 and 17 to the furnace 2 and a pair of pressure
gauges 19 connected to the pipeline 18. The first crucible 8
is a container for a porous reinforcing material consisting of
a metal oxide, or more specifically porous alumina (A1203) 21
and an aluminum alloy 31. The second crucible 9 is a container
for magnesium (Mg) 32. The aluminum alloy 31 may, for example,
be an Al-Mg-Si alloy known as JIS-A6061 (hereinafter referred
to siunply as A6061). A magnesium alloy may be used instead of
magnesium 32.
Description will now be made of the preparation of an
aluminum-based composite material with reference to FIGS. 2A to
2D. The first crucible 8 in the furnace 2 is charged with alumina
21 and then an aluminum alloy 31, and the second crucible 9 with
magnesium 32, as shown in FIG. 2A. The vacuum pump 7 is driven
to evacuate the furnace 2 and is stopped when an appropriate vacuum
degree has been obtained therein. Argon gas 14 is supplied from
its bottle 15 into the furnace 2 as shown by arrows (1) to create
an argon gas atmosphere which protects the aluminum alloy 31 and
magnesium 32 from oxidation. Then, the furnace 2 is heated by
the heating coil 13, so that the alumina 21, aluminum alloy 31
and magnesium 32 may be heated to a temperature of, say, about
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750 to 900 deg. C. As a result, the aluminum alloy 31 is melted
and the m.agnesium. 32 is vaporized, as shown by an arrow (2). The
temperature of the furnace 2 is detected by the temperature sensor
12 and is controlled to a set level by the control unit 11 in
accordance with a signal received from the sensor 12.
Then, nitrogen gas 16 is supplied from its bottle 17 into
the furnace 2 as shown by arrows (3) in FIG_ 2B. The furnace
2 has an elevated pressure (of , say, 0. 5 kg/cm2 over the atmospheric
pressure) and is purged with nitrogen gas 16, while the argon
gas 14 is discharged through the vacuum pump 7, so that the furnace
2 may have a nitrogen gas atmosphere. The nitrogen gas 16 reacts
with magnesium 32 to produce magnesium nitride ( Mg3Nz ) 34. The
magnesium nitride 34 has a reducing action and converts at least
a part of alumina 21 to metallic aluminum. The aluminum exposed
on at least a part of alumina 21 gives it an improved wetting
property. The molten aluminum alloy 31 is diffused through the
aluminum converted from alumina 21, and is solidified to make
an aluminum-based composite material 35 in the form of a billet
as shown in FIG. 2C. The improved wetting property of alumina
21 as mentioned above gives a high elongation to the composite
material 35, so that it is high in workability and easy of plastic
deformation.
An elevation in the pressure of the nitrogen gas atmosphere
in the furnace 2 accelerates the diffusion of the molten aluminum
alloy 31 and thereby the formation of the composite material 35,
while a reduction of the pressure is equally effective for
promoting the diffusion. It is alternatively possible to employ
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a porous molded body of alumina2 containing an aluminum alloy
containing magnesium as a starting material. It is also possible
to employ a porous molded body of alumina particles containing
a magnesium powder and an aluminum alloy placed on it.
The composite material 35 is finished by a numerically
controlled lathe 36 into a billet having a specific diameter D,
as shown in FIG. 2D.
Description will now be made with reference to FIGS. 3A
to 5B of a process for preparing a part from the billet 35 as
obtained. The billet 35 is cut by a cutter 41 into a plurality
of blanks 42 each having a specific thickness t, as shown in FIG.
3A. The volume VO of each blank 42 can be expressed as v0 =(n/4 )
x D2 x t. The blanks 42 are heated in a heating furnace 45, as
shown in FIG. 3B. The blanks 42 are placed in the main body 46
of the furnace 45 and after heating conditions including the target
temperature, heating rate and holding time are set on a control
panel 47, the furnace 45 is switched on. The furnace 45 also
has a heating coil 48 and a temperature sensor 49.
The target temperature is based on the solidus temperature
Ta of the aluminum alloy and should not be over 50 deg. C lower
than Ta, or should be at least (Ta - 50) deg. C, while it should
not be higher than Ta. If the aluminum alloy is A6061, the target
temperature may, for example,be 580 deg. C, since its solidus
temperature Ta is 583 deg_ C and (Ta - 50) is 533 deg. C. The
solidus temperature is the temperature at which a substance which
is composed of two or more components and undergoes a change from
solid (phase) to (solid and liquid phases) and to liquid (phase)
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when heated with a rise in temperature starts melting and changing
from solid to liquid (phase) . It is alternatively the temperature
at which a substance which undergoes changing from liquid ( phase )
to (liquid and solid phases) and to solid (phase) when cooled
with a drop in temperature completes solidification.
The blanks 42 which have been properly heated are removed
from the furnace 45 and are transferred to a press. Each blank
42 is set in a press mold 50, as shown in FIG. 4A. The mold 50
comprises a punch 51 and a die 52. The punch 51 has a working
surface 53 and the die 52 has a central rod-shaped inner die 54,
an outer die 55 surrounding it, the inner and outer dies 54 and
55 defining a working surface 55a at their top, and a heater 56
embedded in the outer die 55 below its working surface for holding
the blank 42 at an appropriate temperature. The blank 42 is placed
on the working surface 55a of the die 52 held at an appropriate
temperature by the heater 56. The heater 56 comprises a plurality
of solid cylindrical cartridge heaters 58 shown by phantom lines
in FIG. 4B to be fitted in one of a plurality of holes 57 made
in the outer die 55 below its working surface 55a. Each cartridge
heater 58 has lead wires 59 connected to a mold temperature
controller not shown, and the die 52 has a temperature sensor
connected to the mold temperature controller, whereby its
temperature is automatically controlled to a selected level. The
.selec:ted level is a temperature between (Ta - 50) and Ta, and
may, for example, be 580 deg. C if the aluminum alloy is A6061,
as mentioned before. In any event, each blank 42 is so heated
by the heater 56 that its temperature may not drop below (Ta -
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50). The heater 56 may alternatively be of any other type and
the punch 51 may be equipped with an appropriate heater, too,
if required.
Then, each blank 42 is pressed in the mold 50 to make a
part A of the aluminum-based composite material, as shown in FIG.
5A. More specifically, the punch 51 is operated under appropriate
conditions including stroke, speed and pressure, and fitted in
the die 52 to close the mold 50 and press its working surface
53 against the blank 42 to draw out its composite material 35
or cause it to flow, so that the material 35 may be compressed
in the closed mold 50 to foxm the part A.
The composite material 35 is easy to work on owing to its
low resistance to plastic deformation, since its temperature is
mairitained between (Ta - 50) and Ta. Thus, the part can be produced
at a reduced cost. Its low resistance to plastic deformation
does not require any high working load, either, but permits the
use of any existing facilities for production at a reduced cost.
owing to its temperature maintained as mentioned above, the
composite material 35 is very easy to move in the closed mold
by a single application of pressure by the punch 51 and compress
into a nearly final shape, so that it is possible to reduce the
amount of any machining work including cutting and grinding and
thereby realize a great reduction in any allowance for machining
work with an improved yield of the material and thereby a reduced
cost of production. It is also possible to remove any internal
defects of the composite material 35 and make a product of high
quality having a txght structure to thereby reduce the amount
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of any inspection work and therefore the cost of production.
Then, the punch 51 is raised and the inner die 54 is ejected
upward, so that the part Amay be separated from the working surface
55a of the die and removed from the mold 50. The part A is better
shown in FIG. 5B, though partially, and has a cylindrically formed
central portion Al.
FIG. 6 shows the results of a test conducted on a plurality
of blanks for determining their compressibility c under heat in
relation to their temperature T. The blanks were of an
alumninum-based composite material containing alumina in a matrix
of an aluminum alloy A6061. The compressibility C represents
a change made in volume by compression, and is calculated as c
(%) = ((VO - V1)/v0) x 100, where VO is the volume of a blank
and Vi is that of a part formed therefrom by compression. In
the graph, each black circle indicates a blank compressed without
cracking, while each x indicates a cracked blank.
As is obvious from FIG. 6, a higher compressibility C with
a less possibility of cracking can be obtained with a rise in
blank temperature T until it reaches about 540 deg. C. A higher
blank temperature T over about 550 deg. C, however, brings about
a lower compressibility c with a more possibility of cracking.
A higher blank temperature T brings about anamproved workability,
but if it exceeds a solidus temperature of 583 deg. C, the formation
of a liquid phase brings about a drastic lowering in
compressibility C with a higher possibility of cracking. A high
compressibility C is desirable for making an aluminum-based
composite material of improved quality having a tight structure
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in a nearly final shape. Thus, a blank of an aluminum-based
composite material containing a matrix of A6061 is heated to a
temperature T which should not be lower than 533 deg. C (Ta -
50) in view of workability, but should not be higher than 583
deg. C (Ta, or solidus temperature of A6061) in view of
coxnpressiblity C.
A further temperature limitation can be introduced to
achieve a higher working accuracy and a lower cost of production.
For, example, a reduction in the cost of temperature control can
be obtained if the blank temperature is set at 535 deg. C, so
that its control may be easier within the range of 523 deg. C
(Ta - 60) to 548 deg. C (Ta - 35), while a high compressibility
C is maintained. The blank temperature is preferably in a higher
range of from 563 deg. C (Ta - 20) to 583 deg. C (ta) to ensure
tha-t it be easier to work on to thereby enable a further reduction
of production cost. Moreover, it is preferably in the range of
from 543 deg. C (Ta - 40) to 550 deg. C (Ta - 33) to ensure that
the blank be of higher compressibility to thereby attain a higher
working accuracy.
Description will now be made of a process for making a part
according to a second embodiment of this invention with reference
to F]_GS. 7 to 8D. Referring first to FIG. 7, the process comprises
Steps 1 to 4:
STO1 - Preparing a die and a dual punch having an inner
and an outer punch portion;
ST02 - Setting a blank of an aluminum-based composite
material in the die;
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ST03 - Shaping the central portion of the blank by the inner
punch portion; and
ST04 - Shaping the remaining portion thereof by the outer
punch portion.
Referring now to FIGS. 8A to 8D, a press mold 60 comprises
a punch 61, a cylindrical stripper 62 surrounding the punch 61
and a die 63 facing the punch 61. The punch 61 is of the dual
type having a solid cylindrical inner punch portion 64 and a hollow
cylindrical outer punch portion 65 surrounding it. The inner
punch portion 64 has a.working surface 66 at its lower end and
the outer punch portion 65 also has a working surface 67 at its
lower end, while the stripper 62 likewise has a working surface
68. The die 63 has a working surface 69 and an ejector rod 71.
A blank 42 is set in the die 63 and positioned in the center of
its working surface 69, as shown in FIG. BA. Then, the stripper
62 is lowered to start closing the mold, while its working surface
68 is held against the blank 42 along its edge to prevent its
movement, as shown in FIG. 8B.
Then, the inner punch portion 64 is lowered under
appropriately controlled conditions includingi.ts stroke, speed
and pressure so that its working surface 66 may be pressed down
against the blank 42 to shape its central portion, as shown in
FIG. 8C (first press-forming step) - The inner punch portion 64
is left at a standstill to hold the blank 42 in position. As
the inner punch portion 64 is pressed down into the central portion
of the blank 42, the blank 42 has its volume distributed uniformly
from its center and can be worked on with an improved accuracy.
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As the inner punch portion 64 compresses only the central portion
of the blank 42, its composite material 35 (FIG. 3A) is easily
drawn out-or caused to flow into a particular shape. As theworking
surface 66 of the inner punch portion 64 has a limited area, it
exerts a high pressure on the blank 42 to facilitate its plastic
working.
Then, the outer punch portion 65 is lowered under
appropriately controlled conditions including its stroke, speed
and pressure to shape the remaining portion of theblank 42 , whereby
a disk-shaped part 72 is obtained, as shown in FIG. 8D (second
press-forming step). The outer punch portion 65 is lowered to
have its working surface 67 pressed against the blank 42 in the
mold closed by the working surfaces 66, 68 and 69 of the inner
punch portion 64 , stripper 62 and die 63, respectively, and exerts
a uriiform compressive force on the surface of the composite
material 35 at right angles thereto, while allowing it to be drawn
out or flow into every corner of the mold, so that no undesirably
high tensile stress may be produced in the surface of the material
and cause it to crack, but a part of high quality may be obtained.
The part 72 has a nearly final shape and does not require any
undesirably large amount of machining work, such as cutting or
grinding. Its nearly final shape makes it poss_ible to realize
a drastic reduction in the amount of the material as an allowance
for machining work, an improved yield of material and thereby
a corresponding reduction in the cost of production. It is also
possible to remove any internal defects from the composite
material 35 and obtain a product of high quality having a tight
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structure to thereby eliminate any complicated step of inspection
and achieve a corresponding reduction in the cost of production.
Then, the punch 61 is raised, then the stripper 62 is raised,
and finally the ejector rod 71 is raised to release the part 72
from the die surface 69, wbereafter the part 72 is removed from
the mold 60.
The disk-shaped part 72 is used to make a part for a pulley
and has a boss portion 73 for attaching the pulley to a shaft
and a disk portion 74 extending radially outwardly from the outer
periphery of the boss portion 73, as shown in FIG. 9A. The boss
portion 73 is not yet in its final shape, but a shaft bore 75
and a key groove 76 are formed through the boss portion 73, as
shown in FIG. 9B, whereby a pulley part 77 is obtained. The part
77 is conveyed to a pulley assembly station. The formation of
the shaft bore 75 not during the press-forming operation, but
thereafter makes it possible to use a single press mold for making
several kinds of parts having different diameters (nominal)
fal:ling within a certain range and thereby cut down the cost of
preparing press molds.
The part 77 is used to make a crank damper pulley 80 as
shown in FIG. 10. The pulley 80 has a damping member 81 attached
to the rim 78 of the disk-shaped part 77 and a grooved member
82 fitted about the damping member 81. The boss portion 73 of
the pulley 80 is easy to form from an aluminum-based composite
material at a low cost by the inner punch portion 64 as shown
in FIG. 8C.
Although the punch 61 shown in FIGS. 8A to 8D is of the
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dual structure, it is alternatively possible to use a punch having
three or even more portions. Moreover, the punch 61, stripper
62 and die 63 may each have a different working surface other
than what has been shown, as required.
Attention is now directed to FIGS. 11 and 12 showing a brake
disk made from an aluminum-based composite material by a process
according to a third embodiment of this invention. The brake
disk 110 has a substantially cylindrical hub portion 111 and a
sliding flange or disk portion 118 extending radially outwardly
from it. The hub portion 111 has a side wall 114 and a cover
115 formed at the top of the side wall 114 as an integral part
thereof. The cover 115 has a central opening 116 and a plurality
of bold holes 117a and a plurality of stud holes 117b around the
opening 116. Each bolt hole 117a is used to receive a bolt not
shown for securing the brake disk 110 to a drive shaft not shown,
while each stud hole 117b is used to fit a stud not shown for
attaching awheel not shownto the brake disk 110. The disk portion
118 is gripped between two brake pads not shown and is, therefore,
required to be of high strength and wear resistance.
The hub portion 111 is a sandwiched structure formed from
an aluminum-based composite material 112 sandwiched between two
aluminum alloy layers 113, as shown in FIG. 12. The aluminum
alloy layers 113 do not present any problem, since the hub portion
111 is attached to a drive shaft by bolts, and to a wheel by studs,
as stated above. On the other hand, the disk portion 118 does
not have any aluminum alloy layer 113, but has the composite
material 112 exposed on both sides, since it is required to be
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of high strength and wear resistance on both sides to withstand
its contact with the brake pads. The composite material 112 may
contain ceramic particles, such as S iC, in an aluminum alloy matrix,
though it may contain any other reinforcing material. The brake
disk 110 is light in weight owing to the aluminum alloy used as
the metal matrix, and high in strength owing to the ceramic
particles which it may contain. Thus, it may contribute to a
reduction in vehicle weight.
Description will now be made of a process for making a brake
disk of the kind as described above. The process described before
with reference to FIGS. 2A to 2D is employed for preparing a billet
of an aluminum-based composite material and forming it into a
shape suitable for extrusion molding. The aluminum-based
composite material is suitable for extrusion molding owing to
its high moldability and plastic deformability as stated before.
FIGS. 13A.to 13C show a process for making a sandwiched
structure having an aluminum-based composite material sandwiched
between two aluminum alloy layers as shown in FIG. 12. FIG.
13A shows an extrusion press 140 having a container 141 closed
at one end by a die 143. A billet 142 of an aluminum alloy is
first placed in the container 141 in close proximity to the die
143 and a billet 135 of an aluminum-based composite material as
prepared by the process shown in FIGS. 2A to 2D is placed behind
the billet 142 . The billet 142 is preferably of an aluminum alloy
having a high corrosion resistance, such as A3000 or A5000
according to the Japanese Industrial Standard. A rain 144 is driven
in the direction as shown by an arrow in FxG. 13B to push the
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composite material 135 and thereby force the aluminum alloy 142
out through a slot in the die 143 to form a thick sheet 145 thereof .
The composite material 135 starts to flow into the aluminum alloy
142. As the composite material 135 is further pushed by the ram
5-144, it is forced out through the die 143 to form a sheet 146
in the sheet 145 of the aluminum alloy 142, while converting the
sheet 145 into a thin sheet 147 covering the sheet 146, whereby
a sheet of a clad material 148 is formed, as shown in F7rG- 13C.
The thin sheet 147 of the aluminum alloy is so formed as
to have a thickness t over 0.2 mm, since a sheet having a thickness
t of 0.2 mm or less is very likely to peel off the sheet 146 of
the composite material. A high extrusion speed can be obtained
with a low extrusion force, since the sheet 147 of the aluminum
alloy contacts the die 143 and is so high in workability that
no undesirable frictional resistance may occur to the sheet 146
of the composite material- Moreover, the aluminum alloy sheet
147 is so low in hardness that the die 143 may not easily be worn,
but may have a prolonged life.
The clad material 148 is easy to form by extrusion, since
the composite material 135 is high in workability owing to a strong
bond made by chemical contact between its aluminum alloy and
reinforcing material. The sheet 146 of the composite material
is still easier to formowing to the high workability of the aluminum
alloy sheet 147 forming the surface portion contacting the die
143.
The deformation of the composite material 135 in a high
reduction ratio makes it possible to remove any internal defects
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from it and obtain an extruded product of high quality having
a tight structure. The reduction ratio R can be calculated by
equation, R = SO/S1, where SO is the cross sectional area of the
composite material 135 to be extruded and sl is that of the clad
material 148 as extruded.
FIG. 14 shows the tensile and yield strength (o:a and ao.2)
of clad materials made as described above in relation to the
reduction ratio (R) employed. The symbol aa,Z stands for 0.2%
yield strength. As is obvious from the graph, tensile strength
(ca) increases with reduction ratio (R) as long as R is less than
10 - Therefore, it is possible to obtain a higher tens ile strength
by employing a higher reduction ratio in that range. It is
likewise possible to obtain a higher yield strength. If R is
10 or higher, however, the tensile strength does not show any
appreciable increase with the reduction ratio, but remains nearly
the same. The yield strength also remains nearly the same. A
high reduction ratio is desirable for productivity. A reduction
ratio over 100, however, requires a large extrusion force which
may only be produced by new facilities having a large capacity.
Thus, the reduction ratio for the aluminum-based composite
material may range from 10 in view of its mechanical properties
to 100 in view of the capacity of the extruder which is available.
The clad material 148 is set in a press not shown and a
disk-shaped sandwiched structure 150 is cut from it with a punch
and a die, as shown in FIG. 15. The sandwiched structure 150
has a disk 151 of aluminum-based composite material sandwiched
betwEaen two disks 152 of aluminum alloy.
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Attention is now directed to FIGS. 16A to 16F showing a
process for press forming the sandwiched structure 150 into a
desired shape. The sandwiched structure 150 is placed between
an upper punch assembly 156 and a lower die assembly 157 in a
press 155, as shown in FIG. 16A, after the upper punch assembly
156 has been raised to its top dead center, and the upper punch
assembly 156 is lowered as shown by arrows (1). The upper punch
assembly 156 includes a punch 158 for holding the sandwiched
structure 150 in position to prevent its displacement and
wrinkling. The sandwiched structure 150 has its edge portion
150a held against a fixed die 159 in the lower die assembly 157
by the punch 158, as shown in FIG. 16B. The upper punch assembly
156 also includes a central punch 160 and an outer punch 161 which
are lowered as shown by arrows (2).
The central and outer punches 160 and 161 are further lowered
as shown by arrows (2) in FIG. 16C, while a movable die 162 in
the lower die assembly 157 is lowered as shown by an arrow (3),
so that the sandwiched structure 150 may have its central portion
150b pressed down by the punches 160 and 161. The movable die
162 stops its lowering upon reaching a specific position P1, as
shown in FIG. 16D, so that the sandwiched structure 150 may have
a recess formed in its central portion 150b. Then, the punches
158, 160 and 161 are raised as shown by arrows (4), while the
die 162 is raised as shown by an arrow (5) to lift the press-formed
product of the sandwiched structure 150 from the fixed die 159.
The press-formed product 154 has a hub portion 111 (see
FIGS. 11 and 12) formed by its central recess, as shown in FIG.
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16E. The aluminum siloy sheets 152 covering both sides of the
composite material 151 as shown in FIG. 15 reduce any frictional
resistance to reduce any stress occurring to the composite
material 151 and causing it to crack. The aluminum alloy sheets
152 now exist as aluminum alloy layers 153 on the product 154.
The product 154 has the edge portion 150a not worked on
by the press. The aluminum alloy layers 153 are removed from
the edgeportion 150a by a cutter 163 as shown inFIG. 16F, whereupon
the product has a disk (or sliding) portion 118 adapted to face
brake pads not shown. Then, the product has bolt and stud holes
formed in its disk portion 118 to provide a brake disk of a metal
matrix composite material as shown at 110 in FIG. 11. This brake
disk is less expensive than any product made by casting. The
disk portion 118 made by exposing the composite material 151 is
very high in strength.
Although the sandwiched structure 150 has been shown and
described as being disk-shaped, it is alternatively possible to
employ a rectangular sandwiched structure for press forming and
cut the disk portion of its press-formed product into a circular
shape.
obviously, various minor changes and modifications of the
present invention are possible in the light of the above teaching.
it is therefore to be understood that within the scope of the
appended claims, the invention may be practiced otherwise than
as specifically described.
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