Electric heating – Metal heating – Cutting or disintegrating
Patent
1993-04-15
1994-04-26
Evans, Geoffrey S.
Electric heating
Metal heating
Cutting or disintegrating
B23H 704
Patent
active
053068882
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a technique for detecting the position along the axial direction of a wire electrode of an electrical-discharge wire cutting machine ("WC-EDM") where spark discharges are generated. The invention further relates to a wire breakage detection apparatus and apparatus for detection of the wear of upper and lower electrical feed members.
BACKGROUND ART
A typical wire cut electrical-discharge machining apparatus uses a thin wire of about 0.05 to 0.35 mm in diameter as an electrode tool. The wire is disposed under a predetermined tension between a pair of guide members in such a manner that the portion of the wire in the working zone can be renewed by axial displacement while maintaining the wire under tension.
A contour may be cut in the workpiece to be machined by moving the workpiece with respect to the wire electrode and in a direction which is generally orthogonal to the axis of the wire electrode, while maintaining a minute gap between the wire and the workpiece and under conditions wherein a working fluid is introduced into the gap between the wire and work piece. Contour machining is carried out by impressing voltage pulses across the gap between the wire and the workpiece and moving the workpiece with respect to the wire electrode in order to establish a work feed in the desired machining direction.
However, unless suitable operating conditions are maintained during machining, wire breakage is apt to interrupt production.
Recently, WC-EDM's have been available which have included a self-recovery means for dealing with wire electrode breakage. More specifically, WC-EDM's have been provided with functions for automatically inserting and joining the wire electrode ends. However, these arrangements do not necessarily assure 100% effective or reliable automatic wire electrode insertion and joining. Further, even if a repair is appropriately achieved, the rethreading function not only wastes time but also generally impairs machining accuracy, finish, and the like. Hence it is preferable in the first instance to avoid the causes of wire breakage.
When wire cut electrical-discharge machining, a number of problems which tend to cause wire breakage may be encountered. It is usually impossible to carry out high speed machining with accuracy and high efficiency unless high-load working conditions, and in particular electrical conditions such as voltage pulse width, off time duration and amplitude of the discharge current, and machining feed control, are established and controlled. However, when machining under high load conditions, there is a higher risk of wire breakage. In addition, for precision machining, other conditions, such as high wire tension and the like, are required which exacerbate the danger of wire breakage.
Therefore, some recent WC-EDM's have included devices to carry out various detection and control strategies in order to prevent wire electrode breakage. Further in the event of wire electrode breakage, some recent WC-EDM's have included devices to quickly detect the break and, thereafter, execute a control function which at least temporary arrests the supply of machining voltage pulses or power, or arrests the travelling (renewal) of the wire electrode, or temporally arrests the machining action including cutting off the work fluid supply, machining feed and the like. This is done to prevent malfunctions and the consequences of such abnormal failures on the workpiece, the working fluid nozzle, the supply and travel systems for the wire electrode and the like in the event of wire electrode breakage.
However, the foregoing broken-wire detection systems are not necessarily as quick as desired. Accordingly, it has been difficult to avoid obstacles to machining progress and accuracy due to excessive detection and control, and problems involving different failures which result from delays in adaptive control.
There are various type of wire electrode broken-wire detectors or broken-wire detecting control devices already available for conventional wire
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patent: 4575605 (1986-03-01), Martin
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patent: 4675491 (1987-06-01), Marendaz
patent: 4691089 (1987-09-01), Balleys
patent: 4963711 (1990-10-01), Obara
Kaneko Yuji
Nishimura Hideo
Evans Geoffrey S.
Sodick Co. Ltd.
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