Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1999-03-29
2001-05-08
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069140
Reexamination Certificate
active
06229110
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a wire-cut electric discharge machine in which a workpiece is machined by intermittently applying voltage pulses across a small gap formed between the workpiece and a traveling wire electrode, known as the “machining gap.” More specifically, the present invention relates to a flushing device for a wire-cut electric discharge machine for introducing fresh dielectric fluid to the machining gap during machining.
BACKGROUND OF THE INVENTION
A pair of flushing devices for introducing machining fluid into the machining gap of a wire-cut electric discharge machine are typically placed on a generally vertical line: one above the workpiece, and one below it. The pair of the flushing devices have respective wire guides therein between which the wire electrode travels generally vertically. Fresh dielectric fluid is forced from nozzles of the upper and lower flushing devices so as to be injected into the machining gap, formed between the workpiece being machined and the traveling wire electrode. This flushing with fresh dielectric fluid cools the wire electrode and workpiece, and also flushes chips produced during machining out of the machining gap. If allowed to remain in the machining gap, chips of conductive material can cause undesirable secondary discharge, which degrades machining accuracy. In addition, flushing constantly replaces the used fluid in the machining gap with fresh dielectric, thus providing faster recovery of the insulating properties of the dielectric fluid, which increases the machining rate. The tips of the flushing device nozzles are usually placed as close as possible to the surface of the workpiece to enable more fluid to be efficiently supplied to the gap. When a first cut with a faster metal removal rate is made in a workpiece, a greater amount of electrical energy is normally supplied to the wire electrode. Under first cut conditions, flushing with a large amount of fluid under high pressure is especially important in order to prevent wire breakage. During a first cut, fluid supplied to the machining area is typically pressurized to about 15-20 kgf/cm
2
, and the gap between the tips of the nozzles and the workpiece is maintained at approximately 0.05 mm. Following the first cut, one or more “skim cuts” are normally performed. During skim cuts, a smaller amount of electrical energy is supplied to the wire electrode in order to more precisely machine the workpiece to the desired finish dimensions. A skim cut reduces surface roughness in the kerf created during the first cut. A number of skim cuts may be performed, with the machining energy reduced incrementally from one cut to the next. The dielectric fluid pressure setting used for skim cuts is quite low compared to that used for a first cut (typically on the order of 0.5-1.0 kgf/cm
2
). The reason for keeping the fluid pressure low is that greater machining precision is required during skim cuts, and maintaining the fluid pressure at a low value suppresses wire vibration, which improves accuracy. This reduction in fluid pressure is possible because, at the lower machining energy and stock removal rates used for skim cuts, the lower flow rate is sufficient to provide adequate cooling and chip removal. The flow rate and pressure of the dielectric fluid are controlled to keep them at the desired values by flow rate adjustment valves. When making skim cuts, in particular, it is important that the flow rate of the dielectric fluid being injected into the machining gap be accurately maintained at a low value. Expensive flow rate equipment is required to make accurate flow rate adjustment over the broad range of values required for both first cuts and skim cuts, and in actual practice, even with good equipment, it is very difficult to accurately control the flow rate at the low values required for skim cuts. Also, in most cases, as the wire electrode moves along the kerf, there can be wide variations in the rate at which the fluid comes at the wire from the front or back, depending on the path of the kerf that was created during the first cut. These undesirable variations, which are especially large when the wire is near a corner in the path of the kerf, can result in variances in the dimensions of the product being made from the workpiece. It can also cause the surface of the finished product to be left with machining marks in the form of lines running parallel to the direction of travel of the wire electrode between the wire guides. There is a need, then, for a simple flushing device that will enable skim cuts to be performed to precise dimensions.
SUMMARY OF THE INVENTION
The present invention is directed to a flushing device that satisfies this need.
It is an object of the present invention to provide a flushing device of simple construction that will enable skim cuts to be performed to precise dimensions.
It is a further object of the present invention to provide a flushing device through which, during skim cuts, dielectric fluid can be introduced into the machining gap at a low but constant flow rate, without using expensive flow rate adjustment equipment.
Additional objects, advantages and novel features of the invention will be set forth in the description that follows, and will become apparent to those skilled in the art upon reading this description or practicing the invention. The objects and advantages of the invention may be realized and attained by practicing the invention as recited in the appended claims.
In order to achieve the above objects, there is provided a flushing device according to the present invention having therein a chamber into which dielectric fluid is supplied, for injecting dielectric fluid into a machining gap formed between a workpiece being machined and a wire electrode in a wire-cut electric discharge machine.
A nozzle, movable between a first position and a second position that is nearer the workpiece than the first position is also provided, for directing the dielectric fluid in the chamber toward the machining gap.
A spring or other biasing means is provided for holding the nozzle in the first position.
It is a principle of the present invention that the spring constant of the spring or other bias means is such that during first cuts, when dielectric fluid is supplied to the chamber at a first pressure, the force exerted by the fluid is sufficient to overcome the force of the spring, and the nozzle is caused to move to the second position; and during skim cuts, when the dielectric fluid is supplied to the chamber at a second pressure that is lower than the first pressure, the force exerted by the fluid is insufficient to overcome the force of the spring, and the nozzle remains at the first position.
REFERENCES:
patent: 4575603 (1986-03-01), Inoue et al.
patent: 4833290 (1989-05-01), Obara
patent: 5126524 (1992-06-01), Moro et al.
patent: 5128505 (1992-07-01), Matter
patent: 1-109026 (1989-04-01), None
Ashida Shinji
Hosaka Akio
Devinsky Paul
Evans Geoffrey S.
McDermott & Will & Emery
Sodick Co. Ltd.
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