Electric heating – Metal heating – Cutting or disintegrating
Patent
1995-08-04
1998-05-12
Evans, Geoffrey S.
Electric heating
Metal heating
Cutting or disintegrating
219 6912, B23H 102, B23H 704
Patent
active
057509514
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a power supply system for use in an electric discharge machine (EDM). More specifically, it relates to a power supply system for use in a wire cut EDM which uses a traveling wire as a tool electrode and generates an electric discharge in the space between the wire electrode and a workpiece so as to machine a desired profile into the workpiece.
BACKGROUND
Electric discharge machines are conventionally equipped with a power supply which supplies a series of controlled power pulses to the machining space--the "gap"--formed between the tool electrode and a conductive workpiece. The workpiece is positioned in a work tank, and the gap is filled with a dielectric fluid such as kerosene or de-ionized water having a high relative resistance. Application of a power pulse to the gap causes the dielectric fluid to ionize and an electric discharge to be generated when the voltage across the gap reaches a certain value. As a result, an electric discharge flows through the gap, and a small portion of the workpiece material vaporizes or fuses, after which it is washed away from the gap by the flow of dielectric fluid. In this way, small crater-like holes are formed in the surface of the workpiece. Insulation across the gap is restored at the cessation of each power pulse application. Electric discharge machining is a process for the precision manufacturing of parts, dies, etc. by generating many electric discharges across a gap while moving the tool electrode relative to the workpiece. It is appropriate for the machining of hard metals.
Typically, a power pulse is produced by a power supply unit which is unavoidably positioned at a certain physical distance from the machine section parts which support the workpiece, and which include the mechanical parts for moving the tool electrode relative to the workpiece. The power supply unit is housed in a cabinet and includes an electrical part which produces the power pulses, as well as a control device which controls the amount of energy in a pulse, the pulse polarity, the pulse ON and OFF times, and the relative movement between the tool electrode and the workpiece. The power supply unit is connected to the machine section by appropriate conductors.
In a wire cutting electric discharge machine, a wire which travels between a pair of wire guides so as to be perpendicularly opposed to the workpiece is normally used as the tool electrode. During machining, as power pulses are applied across the gap and machining progresses, the traveling wire is moved relative to the workpiece in such a way that the axis of the traveling wire approaches the workpiece. When machining a desired profile into the workpiece, wire cut EDM machining is similar to conventional machining performed using a band saw blade.
It is known that during machining, when a wire under tension is traveling at a certain speed between the pair of wire guides, there is a slight vibration of the wire between wire guides. Because of this undesirable wire vibration, the portion of the workpiece which faces the wire is eroded unequally, more in the center than at the top and bottom surfaces, resulting in an adverse effect on product shape accuracy. Increasing the wire travel speed tends to improve wire straightness. Further, increasing the amount of energy supplied to the gap per unit time tends to reduce the amplitude of wire vibration caused by the pressure of the electric discharges on the wire. However, when power pulses having a small energy per pulse are required at the gap, reducing the amplitude of wire vibration may not be sufficient. For example, after a given profile is roughly machined into the workpiece by moving the wire along a prescribed path, machining pulses having a small energy per power pulse are usually used for the so-called "second cut" to improve the roughness of the machined workpiece surface, during which the wire is moved over a path which is offset from the prescribed path. In order to restore sufficient insulation across the gap after each elec
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Journal of the Japan Society of Electrical Machining Engineers, vol. 24/No. 27 (English Abstract).
Kiyonori Masui, (Jul. 1993) Study On Characteristics of A Wire-Cut Electro-erosion Machined Surface Of A Mold Steel And Improvement Of Of Surface (pp. 65-105).
Kaneko Yuji
Toyonaga Tatsuo
Ueda Tadao
Watanabe Yoshihiro
Evans Geoffrey S.
Sodick Co. Ltd.
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