Abrading – Abrading process
Reexamination Certificate
1998-11-16
2001-07-17
Scherbel, David A. (Department: 3723)
Abrading
Abrading process
C451S177000, C451S559000, C451S902000, C451S908000
Reexamination Certificate
active
06261153
ABSTRACT:
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 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 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. 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 alternating fashion around the circumference of the electrode ring. 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 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 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.
REFERENCES:
patent: 1620519 (1927-03-01), Claws
Dickerson Weston E.
Jakovljevic Petar
Hayes Lemmerz International Inc.
Marshall & Melhorn
McDonald Shontese
Scherbel David A.
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