Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
APPARATUS AND METHOD OF MACHINING BRAKE COMPONENTS
BACKGROUND OF THE INVENTION
The present invention relates to rotors for caliper
disc brakes and the like, and in particular to an electric
discharge machine for producing brake components and a
method for making same.
Rotors are generally well known in the art, and are
used extensively in vehicle braking systems, power
transmission devices, clutches, and other similar machinery
and mechanisms. Vehicle caliper disc braking systems slow
the vehicle by inhibiting the rotation of the vehicle
wheels. Rotors used in typical vehicle braking systems
include a central hat section for attaching the rotor to a
vehicle wheel and drive member for rotation therewith, and
an outer friction section having opposite friction
surfaces.
A caliper assembly is secured to a non-rotating
component of the vehicle, such as the vehicle frame. The
caliper assembly includes a pair of brake pads disposed
adjacent the rotor friction surfaces, and a moveable piston
operatively connected to one or more of the brake pads.
When the driver brakes the vehicle, hydraulic or pneumatic
forces move the piston which clamps the pads against the
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friction surfaces of the rotating rotor. As the brake pads
press against the moving rotor friction surfaces,
frictional forces are created which oppose the rotation of
the wheels and slow the vehicle. The friction converts the
vehicle's kinetic energy into large quantities of heat,
much of which is absorbed by the friction surfaces and
conducted to the rest of the rotor and to other components
to which the rotor is connected
Brake rotors are typically cast from a ferrous
material, such as cast or grey iron, and are then machined
in multiple operations to shape the rotor, to form the
inner hub portion and friction surfaces. However, ferrous
material rotors are relatively heavy and they corrode
during normal use. Brake rotors are also cast from
aluminum based metal matrix composite (MMC) containing
silicon carbide particulate reinforcement. Aluminum MMC
rotors have sufficient mechanical and thermal properties at
a significantly reduced weight compared to ferrous metal
rotors. Typically, the rotor is cast from aluminum MMC and
then machined in a conventional manner to form the finished
rotor.
During conventional machining, a tool is pressed
against the part to remove a portion of the surface of the
part. However, conventional machining offers a
disadvantage in that the physical contact between the tool
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and the part partially deforms the part during machining
producing imprecision in the finished parts. For example,
it is desirable to produce rotors having flat friction
sections. Variations in the surface of the friction
section produces undesirable brake noise, pedal pulsations,
and non-uniform wear.
Additionally, the particulate reinforcement in
aluminum MMC parts is very hard which makes the aluminum
MMC castings difficult to machine. Special cutting tools
made from expensive materials such as polycrystalline
diamond are needed to machine aluminum MMC, yet the tools
still tend to wear quickly which increases production
costs. It is desirable to produce brake components, such
as metal rotors, made from materials such as cast iron or
aluminum MMC using an apparatus and technique which will
reduce production costs while improving the tolerances of
the parts.
Electric discharge machining (EDM) is a known method
of machining metal parts using electric sparks. The
electric sparks are directed against the surface to be
machined. A high temperature is reached where the spark
contacts the metal surface. The high temperature vaporizes
the metal at that location. A series of sparks are
directed at the surface to burn away a portion of the metal
resulting in a finish machined part.
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EDM offers advantages over conventional machining in
that the EDM apparatus does not physically contact the part
thereby improving the tolerances of the finished part.
However, known EDM apparatus and machining techniques are
slow, typically producing only about 5,000 sparks per
second. The number of sparks produced per unit time in
part determines how quickly the part can be machined.
Conventional EDM apparatus are too slow to be cost
effective for use in mass production. It is desirable to
provide an apparatus and a method for machining metal brake
components such as cast iron or aluminum MMC rotors using
electrically discharged sparks which is quick and cost
effective.
SUMMARY OF THE INVENTION
This invention relates to an improved apparatus and
method for finish machining brake components. The
apparatus includes an electrode ring adapted to be secured
to a rotatable shaft. The electrode ring includes a
plurality of circumferentially spaced apart first
electrodes adapted to be electrically connected to a first
power supply, and a plurality of circumferentially spaced
apart second electrodes adapted to be electrically
connected to a second power supply. The first and second
electrodes are arranged adjacent each other in an
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alternating fashion around the circumference of the
electrode ring so that the electrodes from the first group
are not adjacent electrodes from the same group. The
apparatus further includes a positioning mechanism for
positioning a rotating, electrically grounded brake rotor
or other brake component adjacent the electrode ring until
sparks are formed between the electrode ring and the rotor.
The sparks vaporize a portion of the rotor surface thereby
creating a finished surface on the rotor having the desired
dimensions.
In an alternative embodiment, the apparatus includes
only one plurality of circumferentially spaced apart
electrodes adapted to be electrically connected to a power
supply. In this embodiment, the apparatus includes just
one power supply. The power supply is connected to the
plurality of circumferentially spaced apart electrodes. In
all other respects, the apparatus is the same as earlier
described.
The invention also includes a method of finish
machining a brake rotor with the EDG apparatus. First, the
brake rotor is cast to produce a brake rotor casting having
a radially inner hub portion with generally axially
extending hat wall, a radially outer annular friction
section having a radially inner edge, and an annular groove
disposed adjacent the hat wall at the radially inner edge
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of the friction section. The rotor casting is then mounted
on the component mount thereby electrically connecting it
to ground and rotated. The electrode ring is also rotated
while submerged in the dielectric oil.
The first electrodes are electrically connected to a
first power supply and the second electrodes are
electrically connected to a second power supply. The
rotating rotor is then at least partially submerged in the
dielectric oil and moved close to the electrode ring such
that sparks form between the discharge surfaces of said
first and second electrodes and said rotor which vaporize a
portion of the surface of said rotor. The rotor and
electrode ring are rotated while the sparks are generated
between them until a sufficient amount of material is
removed to achieve a rotor with a finished friction section
having the desired dimensions. The opposite friction
surface may be finish machined in a variety of different
ways, including using a second electrode ring adjacent that
side and simultaneously finishing both sides, moving the
electrode ring to the opposite side and finishing it in a
similar manner as the first side described above, or by
turning the rotor over on the component mount and repeating
the previously described steps.
The previously cited alternate embodiment operates
similarly to the embodiment cited above. The main
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difference is that the alternate embodiment does not
require that the second electrodes are electrically
connected to the second power supply. This for the reason,
that these two elements are not required to practice the
alternate embodiment. Therefore the steps to manipulate
these elements are not required.
These and other advantages of the invention will be
further understood and appreciated by those skilled in the
art by reference to the following written specification,
claims and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an elevational section view of a rotor
casting to be machined in accordance with the present;
Fig. 2 is an elevational view of a portion of an
electrical discharge machining apparatus in accordance with
the present invention;
Fig. 3 is a elevational sectional view of a portion of
the electrical discharge machining apparatus in accordance
with the present invention;
Fig. 4 is an elevational view of a portion of the
electrical discharge machining apparatus in accordance with
the present invention;
Fig. 5 is a perspective view of a portion of the
electrode disks for use in the electrical discharge
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machining apparatus in accordance with the present
invention;
Fig. 6 is an elevational view of the electrode ring
for use in the electrical discharge machining apparatus in
accordance with the present invention;
Fig. 7 is a side elevational view of the electrode
ring for use in the electrical discharge machining
apparatus in accordance with the present invention;
Fig. 8 is a elevational sectional view of a portion of
the electrode ring disposed adjacent the rotor during
operation of electrical discharge machining apparatus in
accordance with the present invention; and
Fig. 9 is an elevational view of an alternate
embodiment of the electrode ring for use in the electrical
discharge machining apparatus in accordance with the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
For purposes of description herein, the terms "upper,"
"lower," "right," "left," "rear," "front," "vertical,"
"horizontal," and derivatives thereof shall relate to the
invention oriented in Figs. 1 and 2. However, it is to be
understood that the invention may assume various
alternative orientations and step sequences, except where
expressly specified to the contrary. It is also to be
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understood that the specific devices and processes
illustrated in the attached drawings, and described in the
following specification are simply exemplary embodiments of
the inventive concepts defined in the appended claims.
Hence, specific dimensions and other physical
characteristics relating to the embodiments disclosed
herein are not to be considered as limiting, unless the
claims expressly state otherwise.
Referring to Fig. 1, a rotor casting 10 is
illustrated. The rotor casting 10 is preferably formed by
casting aluminum MMC in a conventional manner to produce
the casting having physical dimensions which are close to
the desired final dimensions. However, the rotor casting
may be formed from other suitable materials such as iron,
including grey iron or cast iron. The rotor casting 10 is
then finished machined using an Electric Discharge
Machining (EDM) apparatus, also referred to as an Electric
Discharge Grinding (EDG) apparatus described below in a
machining method described below to achieve the finished
part having the desired dimensions.
The rotor casting 10 includes a radially inner hub
portion 12 having a central, generally circular mounting
section 14 which mounts the same on an associated drive
member (not shown), such as a spindle or vehicle axle. The
rotor axis of rotation X typically extends through the
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middle of the mounting section 14. A hat wall 16 extends
generally axially from the periphery of the mounting
section 14. The hat wall 16 is preferably straight and
cylindrical extending at a right angle from the mounting
section 14, however, the hat wall may be inclined, forming
a portion of a cone, or portions of it may be curved. The
central mounting section 14 has a central pilot aperture 18
cast therein, in which the drive member is closely
received. Fastener apertures 20 may be cast into the
central mounting section 14 for receiving fasteners to
secure the rotor to the drive member. Alternatively, the
fastener apertures 20 may be machined into the rotor
casting 10 using conventional machining techniques.
The rotor 10 also includes a radially outer annular
friction section 22 having opposite friction surfaces 24
which interface with associated friction members (not
shown), such as brake pads or the like. The friction
surfaces 24 are coaxially disposed about the rotor axis of
rotation X. The annular friction section 22 of the rotor
10 has a radially inner edge 26 and a radially outer edge
28. An annular groove 30 is disposed adjacent the hat wall
16 at the radially inner edge 26 of the friction section
22. Optional vents (not shown) may extend radially or
axially through the friction section 22 for cooling.
Referring now to Fig. 2, a portion of an EDG apparatus
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is illustrated generally at 36. The EDG apparatus 36
includes an electrode assembly 38 submerged in a tank 40
containing a dielectric oil 42 which is known in the art.
The EDG apparatus 36 further includes a positioning
mechanism 44 for positioning the rotor 10 a predetermined
distance from the electrode assembly 38 and providing a
path to ground for the spark (not shown).
The positioning mechanism 44 includes a component
mount 46 having shaft 48 for receiving the rotor 10. The
component mount 46 is electrically connected to ground, the
same ground to which the power supplies are also connected.
When the rotor 10 is mounted to the component mount 46 it
is also connected to ground. A motor 53 is drivingly
coupled to a pulley 50 mounted to the shaft 48 for rotating
the shaft and the rotor 10. The motor 53 and shaft 48
rotate the rotor about the rotor axis X. The positioning
mechanism 44 also includes a dual axis positioning guide 51
having a vertical guide 52 and horizontal guide 54. A
positioning driver 56 moves the component mount 46 along
the vertical and horizontal guides 52, 54 into the desired
position adjacent the electrode assembly 38. A spark
sensor 58 senses for sparks between the electrode assembly
38 and the rotor 10, and communicates with the positioning
driver. When the spark sensor 58 indicates to the
positioning driver 56 that sufficient sparks exist, the
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rotor has obtained the proper position relative to the
electrode assembly for machining and the positioning driver
56 stops the positioning movement of the rotor. Throughout
the machining process, the spark sensor 58 continually
communicates with the positioning driver 56. The
positioning driver 56 uses the spark sensor information for
making adjustments in the position of the rotor 10 to
achieve the most sparks possible thus maximizing the
machining efficiency of the EDG apparatus.
Referring now to Fig. 3, the electrode assembly 38 is
illustrated in detail. The electrode assembly 38 includes
a shaft 60 mounted for rotation in bearings 62 which are
supported by the body 64 of the electrode assembly. The
shaft 60 is preferably constructed of steel or some other
electrically conductive material. An electric motor 68 is
drivingly coupled to the shaft 60 for rotating the shaft
and the rotor 10. The shaft 60 preferably includes two
similar halves 60a and 60b. Each halve of the shaft is
similar in construction and function, and to avoid
duplication, only one of the shaft halves 60a shall be
described in detail. A pair of electrode disk assemblies
70, which shall be described in detail below, are mounted
to the opposite ends of each half of the shaft 60a and 60b.
An electrically conductive first ring 72 is mounted to
the shaft 60a for rotation therewith. The first ring 72
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encircles the shaft and is electrically connected thereto.
The first ring 72 is preferably constructed of copper, but
may be made of any suitable electrically conductive
material. A first brush 74 abuts the first ring 72. The
first brush 74 is electrically conductive and known in the
art. The first brush 74 is connected to a voltage terminal
of a first power supply 75.
A second ring 76 encircles the shaft 60a, but is
electrically insulated from the shaft by an annular
insulator 78 disposed between the shaft and the second
ring. The second ring 76 is preferably constructed of
copper, but may be made of any suitable electrically
conductive material. A second brush 80 abuts the second
ring 76. The second brush 80 is electrically conductive
and known in the art. The second brush 80 is connected to
a voltage terminal of a second power supply 81. A wire 82
is electrically connected to the second ring 76. The wire
82 extends through a bore 84 formed through the middle of
the shaft 60a extending from the second ring 76 to the
opposite end of the shaft. The wire 82 exits the bore 84
and is electrically connected to a portion of the electrode
assembly 70 as described in detail below.
Referring now to Figs. 4, 5 and 6, the electrode disk
assembly 70 is illustrated in detail. The electrode disk
assembly 70 includes a first electrode disk 86 and a second
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electrode disk 88. The first electrode disk 86 includes a
central mounting hub 90 for mounting the disk to the shaft
60a. The first electrode disk 86 further includes a
plurality of circumferentially spaced apart electrode pads
92 extending from the radially outer periphery of the disk.
The electrode pads 92 are regularly spaced around the
entire circumference of the first electrode disk 86. The
electrode pads 92 are preferably rectangular, extending
along the axis of the first disk 86.
The second electrode disk 88 also includes a plurality
of circumferentially spaced apart electrode pads 94
extending from the radially outer periphery of the second
disk. The second electrode pads 94 are regularly spaced
around the entire circumference of the second electrode
disk 88. The first and second electrode disks 86 and 88,
and the first and second electrode pads 92, and 94 are
preferably constructed from steel, although any suitable
electrically conductive material may be used. The
electrode pads 92, 94 may be formed integrally with the
respective electrode disk 86, 88, or they may be secured
thereto.
As shown in Fig. 5, the first and second electrode
disks 86 and 88 are mechanically secured together in a
coaxial relationship such that the first and second
electrode pads 92 and 94 are disposed adjacent each other
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in an alternating configuration forming an electrode pad
ring 95. The disks 86 and 88 are electrically insulated
from each other by insulators (not shown) disposed between
the disks. The first electrode pads 92 are
circumferentially spaced apart from the adjacent second
electrode pads 94. The shaft 60a is received in the
central mounting hub 90 of the first disk 86 to secure the
first and second disks 86, 88 to the shaft for rotation
therewith.
Individual first electrodes 96 are mounted to each
first electrode pad 92 by screws 98 extending through
apertures 100 in the pads 92. Approximately 18 first
electrodes are mounted to the first electrode disk 86,
although any suitable number may be used. Individual
second electrodes 102 are mounted to each second electrode
pad 94 by similar screws 98 extending through apertures 100
in the pads 94. Approximately 18 second electrodes are
mounted to the second electrode disk 86, although any
suitable number may be used. The first and second
electrodes 96 and 102 are preferably constructed from
graphite or copper, although any known suitable electrode
material may be used. The electrodes 96 and 102 are
disposed along the ring of electrode pads 95 to form an
electrode ring 103 consisting of alternating first and
second electrodes 96 and 102. The first and second
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electrodes 96 and 102 have respective flat discharge
surfaces 96a and 102a. The discharge surfaces 96a and 102a
are circumferentially spaced apart around the electrode
ring 103 such that each discharge surface forms a separate
sector of the electrode ring. That is, each of these
separate sectors is occupied by only a single electrode
discharge surface.
The first electrodes 96 are electrically connected
together. A first electrical connection is formed from the
voltage terminal of the first power supply 75, through the
first brush 74, through the first ring 72, through the
shaft 60a, through the first electrode disk 86, through the
first electrode pads 92 to the first electrodes 96. The
first electrodes 96 are electrically insulated from the
second electrodes 102. Similarly, the second electrodes
102 are also electrically connected together. The wire 82
is electrically connected to the second electrode disk 88
via a terminal 104 disposed on the disk. A second
electrical connection is formed from the voltage terminal
of the second power supply 81, through the second brush 80,
through the second ring 76, through the wire 82, through
the second electrode disk 88, through the second electrode
pads 94 to the second electrodes 102.
Referring now to Fig. 7, the first and second
electrodes 96 and 102 are arranged in the electrode ring
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103 such that the discharge surfaces 96a and 102a define a
plane 105. The electrode ring 103 has a radially outer
cylindrical surface 103a and a radially outer edge 103b
formed by the intersection of the cylindrical surface 103a
with the discharge surfaces 96a, 102a of the first and
second electrodes 96, 102. As described above, the
electrode assembly 38 includes a second half 60b of the
shaft 60, which includes a second electrode disk assembly
similar to the one described above, having a second
electrode ring similar to the one described above. Also,
the EDG apparatus includes a second positioning mechanism
similar to the one described above. The EDG apparatus can
therefore, finish machine two rotors or other brake
components simultaneously.
Referring now to Figs. 2 and 7, the operation of the
EDG apparatus 10 shall now be described. The electrode
assembly 38 is submerged in the dielectric oil 42 as
described above. The voltage terminals of the first and
second power supplies 75, and 81 are connected to the first
and second brushes 74 and 80 respectively. The shaft 60a
and electrode disk assembly 70 are then rotated by the
motor 68. The rotor 10 is mounted on the component mount
shaft 48 of the positioning mechanism 44, and rotated about
the axis of rotation X by the motor 53. The rotor and
electrode assembly preferably rotate in opposite directions
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as shown at 110. The positioning driver 56 moves the rotor
along the vertical and horizontal guides until a portion
of the rotor including part of the friction surfaces is
partially submerged. The positioning driver 56 continues
5 to move the rotor 10 until it is adjacent the electrode
disk assembly 70 so that only a small gap exists between
the first and second electrode discharge surfaces 96a, 102a
and the rotor friction surface 24. When the gap shrinks to
a predetermined distance, preferably 1/1000 to 3/1000 of an
10 inch, the dielectric 42 no longer provides sufficient
resistance, and a first spark 107 is created between one of
the first electrode discharge surfaces 96a and the nearest
point on the rotor friction surface 24. A second spark 109
is created between one of the second electrode discharge
surfaces 102a and the nearest point on the rotor friction
surface 24.
As the electrode disk assembly 70 rotates, the next
pair of first and second electrode discharge surfaces 96a,
102a pass near the rotor friction surface 24 creating two
more sparks, while the previous pair of first and second
electrode discharge surfaces begin to move away from the
rotor friction surface thereby preventing sparks from these
electrodes. As both the rotor and the elctrode disk
assembly continue to rotate, a different set of first and
second electrode discharge surfaces pass near the friction
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surface creating sparks, while the discharge surfaces just
previously emitting the sparks are moved away from the
friction surface. By rotating the electrode disk assembly
70, the sparks are discharged from the first and second
groups of discharge surfaces as one electrode from each
group is sequentially moved near enough to the friction
surface, while other electrodes from the groups are moved
away from the friction surface.
Each spark creates a very high temperature of
approximately 10,000 to 12,000 degrees Celsius at the
friction surface 24 of the rotor 10. The high temperatures
vaporize a portion of the metal of the friction surface 24.
The rotor is rotated about the axis of rotation so that the
sparks strike different portions of the friction surface
15 until the entire surface is finished to the desired
dimensions. The opposite friction surface may be finish
machined in a variety of different ways, including using a
second electrode ring adjacent that side and simultaneously
finishing both sides, moving the electrode ring to the
20 opposite side and finishing it in a similar manner as the
first side described above, or by turning the rotor 10 over
on the component mount 46 and repeating the previously
described steps. Although the EDG apparatus is described
finish machining the friction surfaces of a rotor, other
25 surfaces of the rotor may finish machined in a similar
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manner. Also, other brake components may be finish
machined in a similar manner by the EDG apparatus.
By using two groups of electrodes 96 and 102,
connected to two different power supplies 75 and 81, the
EDG apparatus produces two sparks at a time between the
electrode ring 103 and the rotor 10, resulting in twice as
many sparks per unit of time as known EDM apparatus using
only one group of electrodes. The EDG apparatus can thus
finish machine a part more quickly than previously known
1U EDM apparatus. Alternatively, the EDG apparatus may use 3
or more groups of electrodes connected to 3 or more
respective power supplies to achieve even more sparks per
unit time. The electrodes within each group are
electrically connected together, and each group is
electrically insulated from the other groups. The
electrodes of any single group are preferably disposed so
as not to be adjacent each other, but rather adjacent
electrodes from the other groups.
Referring now to Fig. 8, the friction section 24 of
the rotor 10 is illustrated adjacent a portion of the
electrode ring 103 comprising electrode 96 as described
above. During operation of the machining apparatus, the
rotor 10 is preferably aligned with respect to the
electrode ring 103 such that the radially outer edge 103b
of the ring 103 is positioned adjacent the groove 30
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thereby increasing the distance between the electrodes 96,
102 and the rotor 10 at the outer edge 103b. The increased
distance prevents arcing between the radially outer edge
103a and the rotor friction surface 24 which causes
premature wear at the edges of the electrodes 96, 102.
When the opposite friction surface 24 is machined, the
radially outer edge 103b of the ring 103 is positioned
radially inwardly from the radially inner edge 26 of the
friction section 26 for similar reasons.
The method of finish machining a brake rotor with the
EDG apparatus shall now be described. First, the brake
rotor is cast to produce a brake rotor casting having a
radially inner hub portion with generally axially extending
hat wall, a radially outer annular friction section having
a radially inner edge, and an annular groove disposed
adjacent the hat wall at the radially inner edge of the
friction section. The rotor casting is then mounted on the
component mount 46 thereby electrically connecting it to
ground and rotated. The electrode ring 103 is also rotated
while submerged in the dielectric oil 42.
The first electrodes are electrically connected to a
first power supply and the second electrodes are
electrically connected to a second power supply. The
rotating rotor is then at least partially submerged in the
dielectric oil and moved close to the electrode ring such
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that sparks form between the discharge surfaces of said
first and second electrodes and said rotor which vaporize a
portion of the surface of said rotor. The rotor 10 and
electrode ring 103 are continued being rotated while
separated by the predetermined distance until a sufficient
amount of material is removed to achieve a rotor with a
finished friction section having the desired dimensions.
The opposite friction surface may be finish machined in a
variety of different ways, including using a second
electrode ring adjacent that side and simultaneously
finishing both sides, moving the electrode ring to the
opposite side and finishing it in a similar manner as the
first side described above, or by turning the rotor 10 over
on the component mount 46 and repeating the previously
described steps. Although the method described is for
finish machining the friction surfaces of a rotor, other
surfaces of the rotor may finish machined in a similar
manner. Also, other brake components may be finish
machined in a similar manner.
The method described above may also include aligning
the rotor with respect to the electrode ring 103 such that
the radially outer edge 103b of the ring 103 is positioned
adjacent the groove 30 thereby increasing the distance
between the electrodes 96, 102 and the rotor 10 at the
outer edge 103b. The increased distance prevents arcing
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between the radially outer edge 103a and the rotor friction
surface 24 which causes premature wear at the edges of the
electrodes 96, 102. When the opposite friction surface 24
is machined, the radially outer edge 103b of the ring 103
is positioned radially inwardly from the radially inner
edge 26 of the friction section 26 for similar reasons.
An alternative embodiment of the EDG apparatus 36 is
shown in Fig. 9, illustrated generally at 136. The EDG
apparatus 136 finishes a rotor in a similar manner as the
EDG apparatus 36 described above. The EDG apparatus 136
includes mostly the same elements as previously described
regarding the EDG apparatus 36. The main difference is
that the electrode disk assembly 70 includes only one
electrode disk 186 (as shown in Fig. 9). The alternate
embodiment electrode disk 186 is attached to the apparatus
38 in the same manner as the first electrode disk 86. The
alternate embodiment electrode disk 186 also includes a
plurality of circumferentially spaced apart electrode pads
192, regularly spaced around the entire circumference of
the electrode disk 186. The electrode pads 192 are similar
to the electrode pads 92. This embodiment does not include
a second electrode disk.
In the alternate embodiment, the apparatus includes a
plurality of individual electrodes 196. Each electrode 196
is attached to an electrode pad 192 in the same manner as
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the each first electrode 96 is attached to each first
electrode pad 92. Each individual electrode 196 is
constructed from the same material as each individual
electrode 96. The alternate embodiment does not include a
plurality of individual second electrodes.
The EDG apparatus 136 also includes an electrode ring
203. The electrode ring 203 is similar to the electrode
ring 103, except the electrode ring 203 consists of
electrodes 196 that are all connected to the same power
supply. In comparison, the electrode ring 103 consisted of
first and second electrodes 96, 102 which were connected to
the first and second power supplies 75, 81 respectively.
Due to the fact that all of the electrodes 196 that make up
electrode ring 203 are electrically connected to the same
power supply, the EDG apparatus 136 will produce only one
spark at a time to machine rotor 10. In all other
respects, electrode ring 203 is analogous to electrode ring
103.
In the alternate embodiment, the invention is
practiced with only the first power supply as the sole
power supply. The alternate embodiment does not include a
second power supply and its associated components. This
power supply, in the alternate embodiment, is electrically
attached to each electrode 196 in the same manner as each
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electrode 96 is attached to the first power supply 75. The
power supply of the alternate embodiment operates in the
same manner as the first power supply 75.
The EDG apparatus 136, of the alternate embodiment,
operates in a alike manner as the EDG apparatus 36,
previously discussed. The changes in the operation of the
alternate embodiment mostly result from the lack of the
second power supply 81. Like before, the electrode
assembly 38 is submerged in the dielectric oil 42 as
previously stated. The operation of the EDG apparatus 136
proceeds in a similar manner except that there is no
connection of the voltage terminals of the second power
supply 81 to the brush 80.
Just as stated before, when the gap between the
electrode discharge surface, for electrode 196, shrinks to a
predetermined distance, preferably 1/1000 to 3/1000 of an
inch, the dielectric 42 no longer provides sufficient
resistance and a spark is created. The spark is similar to
spark 107 previously cited. As stated before, the alternate
embodiment does not include a second spark 109. In the
alternate embodiment, the spark only occurs between the
electrode 196 and the point on the friction surface 24 of
the rotor 10 nearest the electrode 196. Thus, this
embodiment uses only one spark at a time to finish the
rotor.
CA 02401314 2002-08-26
WO 01/66294 PCTNS00/06083
The method associated with this alternate embodiment is
analogous to the method of the apparatus as previously
described. The significant differences are the lack of the
steps regarding the second power supply 81 and the finishing
of the rotor 10 with the second spark 109. In all other
respects, the method of the invention is the same.
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