Abstract: An EDM apparatus provided with an adaptive self-correcting system for achieving optimum maximum efficiency of machining operations. As the machining performance factor or index of an EDM apparatus continuously varies as a function of one of the machining parameters as, for example, the cut-off time interval between consecutive electrical discharges, such that the maximum performance index, achieved for a given optimum cut-off time interval, deteriorates rapidly when the cut-off time interval is shortened, thus resulting in poor and unstable machining conditions, the invention contemplates varying the cut-off time interval in successive steps, the steps being larger when operating along the negative slope portion of the representative curve of the performance index as a function of the cut-off time interval duration, and the steps being much smaller when operating within the portion of the representative curve having a positive slope.

Abstract: In a travelling wire EDM apparatus, the electrode tool in the form of a wire used for cutting an electrode workpiece is passed through a first zone in which the wire is straightened, preferably by exerting a pull on the wire while the wire is heated. The wire is subsequently cut-off at the bottom of the first zone, and the straightened portion of the wire is then threaded by a carriage through a hole pre-drilled in the workpiece, or through a cut in the workpiece in the event that the wire ruptures during machining, until the end of the wire is engaged in the wire conveyor mechanism.

Abstract: A device for applying electrical current and voltage pulses between an electrode workpiece and an electrode tool, in the form of a wire or ribbon, in a travelling wire EDM apparatus, wherein a pulse generator providing such current and voltage pulses is connected across the electrodes. The travelling wire electrode is supported and guided by a pair of support and guide members and the pulse generator is connected across one of the support and guide members of the travelling wire electrode and the workpiece. A capacitor is connected across two contact members one engaged with the travelling wire electrode and the other with the workpiece, and is supported by one of the travelling wire support and guide members. The effect of the capacitor connected directly across the machining gap is to reduce considerably to a negligible value the inductance of the electrical circuit applying the current and voltage pulses across the electrodes.

Abstract: A correction system for a travelling wire EDM machine cutting a workpiece by means of a travelling electrode wire stretched between two guide members and comprising a pair of servo motors for effecting displacement of the guide members relative to their respective support arms, such as to incline the electrode wire relative to the workpiece for providing the cut in the workpiece with an appropriate predetermined conicity or draft. One of the servo motors providing such displacement is, in addition, controlled such as to compensate for thermally-induced expansions or contractions of one of the support arm guide members relative to the other.

Abstract: A process and apparatus for monitoring the concentration of electrically conductive solid particles in suspension in a fluid by circulating the fluid between a pair of electrodes opposed surfaces disposed at a fixed distance from each other, the electrodes being connected across a DC power supply. Electrical discharges occur across the gap between the electrodes, and the concentration of solid particles is determined as an inverse function of the average delay time interval required for triggering the electrical discharges, which is in turn measured by counting the number of electrical discharges occurring within a predetermined time interval.

Abstract: An automatic wire rethreading mechanism for traveling wire EDM apparatus wherein the workpiece is cut by electrical discharges by an electrode in the form of a wire, comprising a mechanism for automatically threading the electrode wire through a pre-drilled hole in the workpiece, the automatic wire threading mechanism being adapted to thread the wire at the beginning of a cutting operation and any time the electrode wire is ruptured in the course of a cutting operation. The position of the pre-drilled hole is memorized, as well as the relative position of the wire and workpiece at the instant of wire rupture.

Abstract: A method and apparatus for compensating for the wear of an electrode tool during machining by EDM of an electrode workpiece by the electrode tool. During penetration of the electrode tool into the electrode workpiece, relative displacement of the electrodes is stopped as soon as it reaches a predetermined reference position corresponding for example to a machining depth limit data entered in a control buffer memory. The reference position data is corrected as a function of the actual wear of the electrode tool which is measured by comparing the positions taken by the electrode tool when one of its active surfaces reaches the same reference position before and after a machining pass. The correction of the reference position data may be obtained either by successive approximations, or by a single calculation step effected after the first machining pass.

Abstract: A metallic wire, for cutting a workpiece by electrical discharge machining, coated with at least one layer of a metal having a low temperature of vaporization and a film of a metal oxide on the metal layer. The metallic coating is preferably made of zinc and is subjected to an oxidizing thermal or electrolytic treatment such as to form on the surface of the metallic layer a thin film of zinc oxide.

Abstract: A hydraulic system for feeding an action turbine comprising a rectilinear gate and an injector mounted in series on a conduit through which water is supplied to the turbine wherein the gate has a shut-off which is mounted in an outer body member for the injector, said shut-off having a seat member associated therewith, the injector including a needle valve which has a seat member associated therewith, said seats being located adjacent one another. The needle valve may have a support associated therewith and the shut-off for the gate may be located upstream thereof. The needle valve seat may be displaceable downstream to permit closing of the gate. In such position, the needle vale and its seat may be disassembled without emptying the water supply conduit.

Abstract: An arrangement for detecting abnormal concentration of electrical discharges between a travelling wire electrode and a workpiece in a travelling wire EDM apparatus. The abnormal electrical discharge detector of the invention comprises a circuit measuring the voltage across a pair of contacts supplying machining current to the electrode wire. The length of the electrode wire between the two contacts forms a pair of variable resistors connected in a branch of a Wheatstone bridge circuit. The voltage measuring circuit, connected across a diagonal of the bridge, in turn controls some of the machining parameters such as to prevent damages, as for example rupture of the wire electrode, when an abnormal concentration of electrical discharges is detected at a given point of the machining zone between the wire electrode and the workpiece.

Abstract: The present invention is a process and apparatus for machining an electrode workpiece by electrical discharges, wherein the electrode workpiece and an electrode tool are displaced relative to each other at least in one slant direction disposed at a predetermined angle with the principal axis of feed of one electrode relative to the other, the machining gap between the electrodes is set at a finite value such as to maintain predetermined machining conditions, consecutive machining passes are effected and, at the end of each machining pass, the slant direction of feed is displaced as soon as the amplitude of relative displacement between the electrodes reaches a predetermined limit value, and such limit value is changed from one pass to the next.

Abstract: An EDM apparatus for machining by electrical discharges an electrode workpiece by one of a plurality of electrode tools individually and selectively mounted by an automatic tool changer on the apparatus electrode tool holder. The tool changer comprises a tool transfer carriage provided with a grasping mechanism adapted to take hold of electrode tool supports of diverse shapes provided with cut-out portions enabling connection with the carriage for carrying the electrode tools from a storage magazine to the electrode tool holder and back from the electrode tool holder to the magazine.

Abstract: A method and apparatus for cutting a workpiece by electrical discharges by means of a travelling wire electrode according to a path determined by a numerical control program without reducing the machining speed or the current flowing into the wire electrode. At least one of the support and guiding members of the wire electrode is displaced relative to the workpiece along a path resulting from shifting each point of the desired cutting path a predetermined distance in the direction of machining along a tangent to each point of such path. The angle between the tangent at each point of the path relative to the coordinate axes is determined, and each point of the path is shifted relative to the programmed path along coordinates having values proportional respectively to the sine and cosine of the angle.

Abstract: Process and apparatus for cutting by electrical discharge machining cavities and slots in an electrode workpiece by means of an electrode tool, the electrodes being displaced one relative to the other in translation along a predetermined path. The translation motion is controlled such as to maintain predetermined machining conditions in the machining zone between the electrodes, and for additionally displacing the electrodes relative to each other in a direction different from the direction of the cutting path. The additional relative displacement of the electrode may be linear, non-linear, slanted or curvilinear.

Abstract: A process and apparatus for increasing the frequency of the effective machining electrical discharges between the electrode workpiece and the electrode tool of an EDM apparatus. The process of the invention consists in monitoring the electrical parameters in the machining zone between the electrodes such as to detect short circuits, and, when a short circuit is detected, in continuing monitoring the electrical parameters until monitoring indicates the disappearance of the short circuit, in cutting off the ongoing electrical discharge after a predetermined time interval following the moment at which said short circuit disappears and in re-establishing normal electrical voltage pulses after another time interval following the end of the discharge. The invention also provides appropriate apparatus for practicing the process.

Abstract: An EDM method and apparatus for cutting a workpiece by a wire electrode in the form of a metallic tape or wire, in which the traction exerted on the wire electrode by the mechanism feeding the wire electrode in the machining zone between the wire electrode and the workpiece is modified momentarily, and the variation of machining rate caused by the momentary modification of the force of traction exerted on the wire electrode is detected. The direction in which the machining rate is changed provides an indication of the effect, on the wire electrode, of the transverse forces which deflect the wire in the machining zone, relative to its longitudinal axis. The direction in which the machining rate varies is used to select the direction in which a predetermined machining parameter affecting the transverse forces applied on the wire electrode is changed, such as to maintain the wire electrode properly aligned along its longitudinal axis.

Abstract: An electrode for machining a workpiece by electrical discharges, the electrode having an active surface comprising at least 50% by weight of a metal or alloy selected from the group consisting of zinc, cadmium, tin, lead, antimony and bismuth. Preferably, the active surface is in the form of a coating electrolytically plated on the surface of a conventional metallic wire having good mechanical characteristics. The invention contemplates continuously plating a metallic filament electrode such as an electrode wire with the active surface coating after the electrode wire has been used for machining a workpiece by EDM.

Abstract: In an EDM apparatus in which the relative displacement between an electrode tool and an electrode workpiece is effected by a servo motor, a control system for the servo motor to effectuate the relative displacement of the electrodes at a speed depending from the machining conditions at the gap between the electrodes and from the difference between a reference position signal and a signal representing the actual relative position of the electrodes, such as to limit the relative displacement of the electrodes until a predetermined final relative position has been reached.

Abstract: An EDM process and apparatus for effecting a cut in an electrode workpiece by means of an electrode tool wire, wherein consecutive current pulses are caused to flow through a machining gap between the electrode wire and the workpiece, and the electrode wire is maintained under traction in the machining zone and is displaced longitudinally and fed laterally through the machining zone. The electrical resistance of the wire is measured through the portion of the wire disposed in the machining zone, and the machining current or the force stretching the wire by exerting a traction thereon, or both, is adjusted such as to maintain the electrical resistance within a predetermined range. This adjustment insures a continuous control of the mechanical and thermal constraints exerted on the electrode wire as well as preventing rupture of the wire.

Abstract: A method for machining materials difficult to cut by EDM conventional processes and consisting in providing contamination of the machining or dielectric fluid used in the course of electrical discharge machining with particles of a metal or metallic alloy of low vaporization temperature selected, for example, from the group consisting of zinc, cadmium, tin, lead, antimony and bismuth. The contamination particles are obtained directly from a surface coating placed directly on the electrode tool or from an additional piece of metal or metallic alloy which is electro-eroded at the same time as a cut is effected by the electrode tool in an electrode workpiece, and the contaminated fluid is circulated in the machining zone between the electrodes, the contaminated fluid facilitating the triggering of the electrical discharges in the machining zone and providing an increase of the machining rate, or material removal rate.