Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1999-09-22
2001-12-04
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069170, C219S069150
Reexamination Certificate
active
06326576
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to electrical discharge machining and more particularly to electrical discharge machining workpieces, such as aircraft engine parts, which have several features machined therein.
Electrical discharge machining (EDM) is a well known process for forming features, such as holes, slots and notches of various shapes and configurations, in an electrically conductive workpiece. Conventional EDM apparatuses typically employ an electrode having the desired shape that is advanced toward the workpiece. A suitable power supply is applied to create an electrical potential between the workpiece and electrode for forming a controlled spark which melts and vaporizes the workpiece material to form the desired feature. The cutting pattern of the electrode is usually computer numerically controlled (CNC) whereby servomotors control the relative positions of the electrode and workpiece. During machining, the electrode and workpiece are immersed in a dielectric fluid, which provides insulation against premature spark discharge, cools the machined area, and flushes away the removed material.
One drawback to electrical discharge machining is that it is a relatively slow process, especially when several distinct features need to be machined into a workpiece. This is particularly so in the aircraft engine industry where electrical discharge machining is widely used for machining various features into aircraft engine parts. To increase the manufacturing output of such parts, it is common to use an EDM apparatus that machines a number of parts at one time. Such an apparatus has a plurality of work stations, each of which has a workpiece fixture located in a single dielectric tank. The work stations are all typically connected to a common power supply. Thus, machining takes place in series one part at a time. That is, a spark will be created in the first work station and then the next work station and so on until each station has a spark supplied. This sequence is repeated until the machining operation is completed for each workpiece.
A problem with this type of apparatus is that is whenever one station gets hung up (i.e., fails to discharge for some reason such as electrode misalignment or a EDM particle remaining in the electrode-workpiece gap) all of the stations will become hung up. And since all stations are stopped, it is not evident which station is causing the stoppage. Furthermore, each station must use the same electrode material and polarity because of the series power connection. Thus, each station machines the same feature into the parts. Parts requiring additional features must then be moved to another machine. This means that multiple machines, fixtures and part handling are required before a part is completed. Another inefficiency with these conventional EDM apparatuses is that the dielectric tank must be drained and refilled between each cycle to load and unload the parts because the workpiece fixtures are all located and submerged in the tank.
Accordingly, there is a need for an EDM apparatus that more efficiently machines workpieces having multiple features to be machined therein.
SUMMARY OF THE INVENTION
The above-mentioned need is met by the present invention which provides an electrical discharge machining apparatus including at least one work station having an electrode fixedly mounted to a base and a workpiece fixture slidingly mounted to the base above the electrode. A servomotor is mounted to the base and arranged to drive the workpiece fixture toward and away from the workpiece. Preferably, the EDM apparatus will include a number of such work stations, and each work station will be connected to a separate control system for independently controlling and energizing the work station.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.
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de Graaff Willem T.
Krenz Rudi O.
Mascarenas Kenneth E.
Cooke Colleen
Elve M. Alexandra
General Electric Company
Hess Andrew C.
Ramaswamy V.
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