Liquid purification or separation – Flow – fluid pressure or material level – responsive
Reexamination Certificate
2001-07-17
2003-03-18
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Flow, fluid pressure or material level, responsive
C210S167050, C210S195100, C219S069140
Reexamination Certificate
active
06533927
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a dielectric fluid system of an electric discharge machining apparatus for collecting dielectric fluid from a work tank of the electric discharge machining apparatus cleaning the fluid and re-supplying the fluid to the work tank.
DESCRIPTION OF THE RELATED ART
Electric discharge machining is a process for machining a workpiece into a desired shape by periodically applying an appropriate electric discharge machining voltage between the workpiece and a tool electrode (hereafter referred to simply as an electrode) arranged opposite to each other across a specified electric discharge machining gap (hereafter referred to simply as the machining gap) to continuously generate electric discharges, and moving the workpiece and the tool electrode relative to each other. In order to be better able to carry out this electric discharge machining process, electric discharge machining fluid (hereafter referred to simply as dielectric fluid) is supplied to the machining gap.
The dielectric fluid plays several important roles as a machining medium for electric discharge machining. A first role is to remove chips and debris generated as a result of electric discharges from the machining gap, as well as tar-like products which may become entrained in some dielectric fluids as a result of the heat due to the electric discharges. A second role is to cool the machining gap so as to create favorable conditions for the electric discharge machining process, and to suppress the tendency for deformation of the workpiece due to thermal expansion. A third role is to maintain isolation of the machining gap in order to maintain favorable electric discharge machining conditions. As will be described below, when an aqueous dielectric fluid is used, the specific resistance of water is usually adjusted.
Therefore, the dielectric fluid used for electric discharge machining in the work tank is filtered, cooled and subjected to specific resistance adjustment as required, and then re-supplied to the work tank after being collected in a dielectric fluid reservoir. Where an electric discharge machine uses a flushing device such as a flushing nozzle, dielectric fluid is similarly supplied to a machining gap after being filtered. A typical electric discharge machining apparatus is therefore provided with a dielectric fluid system for supplying and controlling dielectric fluid.
A typical dielectric fluid system includes a dielectric fluid reservoir having a dirty dielectric fluid tank and a clean dielectric fluid tank. Dirty dielectric fluid that has been discharged from the work tank is temporarily collected in the dirty dielectric fluid tank, and chips and debris having a comparatively heavy specific gravity precipitate here. The dielectric fluid in the dirty fluid tank is pumped through a filter apparatus by a pump, and chips and debris in the fluid are removed from the fluid which is then stored in the clean dielectric fluid tank. Decontaminated dielectric fluid in the clean fluid tank is re-supplied to the work tank by a pump, and supplied to the machining gap for flushing, as required.
This type of dielectric fluid system may also include a dielectric fluid cooling apparatus, for keeping the dielectric fluid in the work tank at a specified temperature. Also, a dielectric fluid system of an electric discharge machining apparatus which uses water based dielectric fluid may be provided with, for example, a specific resistance control apparatus including a deionizer using mixed-bed resin, which regulates the specific resistance of the dielectric fluid so as to maintain it at a value within a specified range.
The above-described conventional dielectric fluid system has several short commings which the present invention is intended to overcome.
A first object of the present invention is to reduce the time for supplying dielectric fluid to an empty work tank (hereafter referred to as rapid feed), and more specifically to shorten the rapid feed time. Conventionally, when submerging a workpiece in dielectric fluid to perform electric discharge machining, the amount of dielectric fluid to be supplied to the work tank is comparatively large, and the waiting time until the work tank is filled is too long. Accordingly, an apparatus has been proposed to supply dielectric fluid to the clean dielectric fluid tank having a large capacity matching the work tank, arranged at a position higher up than the work tank, thus supplying the dielectric fluid to the empty work tank in a reduced amount of time. This is disclosed, for example, in Japanese laid open Patent No. Hei. 5-004117 and Japanese laid open Patent No. Hei. 5-042424.
A second object of the present invention is to reduce the installation space occupied by an electric discharge machining apparatus. Conventionally, in those electric discharge machining apparatus in which the workpiece is submerged in a dielectric fluid for machining, in order to replace the workpiece after machining it is necessary to temporarily store the dielectric fluid which is in the work tank in a dirty dielectric fluid tank having a capacity matching the volume of the work tank. Also, in order to supply cleaned dielectric fluid to the empty work tank in a reduced time, it is also necessary to store, in the clean dielectric fluid tank, a volume of clean dielectric fluid which matches the volume of the work tank. As a result, the capacity of the dielectric fluid reservoirs for both the dirty dielectric fluid tank and the clean dielectric fluid tank is from 2.5 to 3.0 times the capacity of the work tank. This gives rise to a problem in that the installation space required by the dielectric fluid system is quite large compared to the overall installation space of the electric discharge machining apparatus. As a countermeasure in order to reduce the installation space of the storage tank, the height of the storage tank is increased or the dirty dielectric fluid tank and the clean dielectric fluid tank are arranged so as to have a two-stage overlapping structure. This is disclosed, for example, in Japanese laid open Patent No. Hei. 4-171123.
A third object of the present invention is to efficiently perform collection and filtration of some of the dielectric fluid in the work tank, and return it to the work tank during electric discharge machining (hereafter referred to as circulation). Conventionally, when the dielectric fluid reservoir is provided with a dirty dielectric fluid tank and a clean dielectric fluid tank, some of the dielectric fluid in the work tank is collected in the dirty dielectric fluid tank, is filtered by being passed through a filter, and is temporarily stored in the clean dielectric fluid tank. Then, dielectric fluid in the clean dielectric fluid tank is circulated by being re-supplied to the work tank. In this case, as preparation for feeding clean dielectric fluid to the empty work tank at the time of commencing the subsequent electric discharge machining operation, it is necessary to store a large volume of dielectric fluid, significantly more than the amount of dielectric fluid required for circulation, in the clean dielectric fluid tank during the preceding electric discharge machining operation. For this reason, a pump having a large discharge capacity and a filtration device for filtering a large volume are required, thus increasing costs. Also, particularly when water based dielectric fluid is used, the dielectric fluid comes into contact with more air while being stored in the large fluid tank, and there is a problem that the specific resistance value is reduced due to carbon dioxide penetration, etc. As a countermeasure, it has been considered to directly collect dielectric fluid overflowing while performing electric discharge machining using a pump, filtering using a filter, and to return the fluid directly to the work tank. This is disclosed, for example, in publications such as Japanese laid open Patent No. Hei. 5-037422, Japanese laid open Patent No. 8-215940 and Japanese Utility Model No. 2557992.
As described above, there
Cecil Terry K.
Devinsky Paul
Drodge Joseph W.
McDermott & Will & Emery
Sodick Co. Ltd.
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