System and method for wire cut discharge machining

Electric heating – Metal heating – Cutting or disintegrating

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Details

B23H 710

Patent

active

060282827

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a wire cut electric discharge machine which machines a workpiece by generating an electric discharge between a wire electrode and the workpiece while conveying the wire electrode along a wire transport path with a fixed tension applied thereto. In particular, the invention relates to a wire cut electric discharge machine provided with a device which controls the tension applied to the wire electrode as it travels along the wire transport path.


BACKGROUND OF THE INVENTION

Generally in a wire cut electric discharge machine, the wire electrode travels in a direction which is essentially perpendicular to an X-Y plane between a pair of wire guides, while either the wire electrode or the workpiece moves relative to the other within the X-Y plane. During machining, a voltage pulse is applied to the gap formed between the wire electrode and the workpiece, and the workpiece is machined by the electric discharge generated in that gap as though the workpiece were being cut by a thread. This type of wire cut electric discharge machine has a high machining accuracy and is appropriate for precision machining.
Wire electrodes having a diameter of 0.01-0.3 mm are normally guided from a wire bobbin through multiple pulleys and a wire tensioning device to a pair of wire guides arrayed respectively above and below the workpiece. Furthermore, the wire electrode is conveyed through multiple pulleys and a wire pulling device to an appropriate recovery device. The wire pulling device is controlled such that the wire electrode travel speed is maintained at a set value. The tensioning device is controlled such that the tension imparted to the wire electrode reaches a set value. Wire electrode tension is set in accordance with, for example, the wire electrode diameter and material, and the type of machining performed. If that tension is set at a large value, good wire electrode straightness between the pair of wire guides is obtained. However, if excessive tension is applied, undesirable breakage of the wire electrode may be induced.


SUMMARY OF THE INVENTION

An object of the present invention is to provide a wire cut electric discharge machine which reliably maintains a set wire electrode tension value.
Another object of the present invention is to provide a wire cut electric discharge machine which reduces variations in wire electrode tension.
Other objects of the present invention are partially described in the explanation below, or will be apparent to practitioners of the art through implementation of the invention.
In order to achieve the above-described and other objectives, the wire cut electric discharge machine of the present invention includes a device which conveys a wire electrode such that the wire electrode travels along a specified transport path, a servo motor which imparts tension to the traveling wire electrode, an NC device which generates a signal indicating the tension setting value signal, a tension detector which detects the tension applied to the wire electrode and generates a signal indicating the detected value, and a tension control device which corrects the speed command signal which commands the rotational speed of the servo motor; the tension control device includes a non-essential frequencies setting device, which sets a non-essential frequencies signal and generates a signal indicating the setting value, and an electric filter device, which blocks non-essential frequencies based on the output signal from the non-essential frequencies setting device.
Preferably, the non-essential frequencies setting device sets non-essential frequencies based on the output signal from the tension detector.
The wire cut electric discharge machine of the present invention further includes a memory which records data indicating the relationship between the wire electrode diameter, material, etc. and the non-essential frequencies. The non-essential frequencies setting device may also set the non-essential frequencies based on the data stored in that memory.
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REFERENCES:
patent: 4298781 (1981-11-01), Inoue
patent: 4301349 (1981-11-01), Inoue
patent: 5023420 (1991-06-01), Aso et al.
patent: 5166490 (1992-11-01), Morishita et al.
patent: 5216217 (1993-06-01), Morishita et al.
patent: 5324909 (1994-06-01), Derighetti

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