Abstract: The electrode wear rate is determined by using two detectors and a clock to measure the time taken for the voltage across the gap to drop between two preset values which are chosen to measure the speed in which the voltage drops from the no load voltage to the cutting voltage. This value of time is used by an arithmetic circuit which uses an exponential equation to determine the amount of material removed in a single discharge. A second arithmetic circuit is used to sum up the amount of electrode wear taking place and to supply the pulse generator with a control signal for adjusting the pulse generator as a function of the electrode wear rate.

Abstract: The rethreading mechanism of a travelling wire EDM apparatus has a scrap wire disposal mechanism for disposing of the unusable length of electrode wire, or scrap, remaining in the machining zone after accidental rupture of the wire. The wire scrap disposal mechanism takes the form of a shaft having a bifurcated end defining tines between which the wire passes. Upon accidental rupture of the wire, the bifurcated shaft is automatically set in rotation such as to wind the length of wire between the shaft bifurcated end and the point of rupture of the wire in a bundle around the bifurcated end, and simultaneously exert a pull on a length of unused wire, which is also caused to wind around the shaft bifurcated end, such as to straighten the wire upstream of the bifurcated shaft. After cutting off the wire, the bundle of scrap wire around the bifurcated shaft is pushed off such as to fall in a disposal chute.

Abstract: In a travelling wire EDM apparatus, the electrode wire is divided into a plurality of sectors disposed along the active length of the electrode wire, and the numbers of electrical discharges occurring in each of the sectors from a predetermined starting time is detected. Those numbers are compared to reference values to determine the difference between the numbers of detected electrical discharges and corresponding reference values. In its simplest form, all the reference values are equal to the average value of the number of electrical discharges per sector. If one or more of the differences is higher than a predetermined threshold, an adequate modification of the machining parameters is effected as a function of the difference.

Abstract: In a travelling wire EDM apparatus in which a workpiece is cut by an electrode wire by electrical discharges between the wire and the workpiece, a detector circuit detecting each electrical discharge occuring in each sector along the length of the wire in the machining zone. The information detected by the detector circuit is supplied to a circuit simulating the increase of heat of the wire, and the convection of heat into the ambient and into adjoining wire sectors. A control signal for modifying a machining parameter is supplied when the simulator circuit provides an indication of abnormal heating of the wire in one of the wire sectors. Accidental rupture of the wire is thus avoided while assuring that machining is effected at maximum efficiency.

Abstract: In a travelling wire EDM apparatus for effecting a cut by electrical discharges on a workpiece blank by an electrode wire, the workpiece blank is supported by two support members mounted on a rotary table, one support member being disposed in the interior of the perimeter of the cutting path and the other support member being disposed exteriorly to the perimeter of the cutting path such as to support the two portions of the workpiece blank severed from each other during the cutting operation. A partial cut is first effected through the workpiece blank and the workpiece blank is subsequently angularly oriented to a different position by rotating the rotary table such that collision between any one of the electrode wire support arms and the workpiece blank support member disposed within the perimeter of the cutting path is prevented.

Abstract: An arrangement for applying an electromagnetic force on the electrode wire of a travelling wire EDM apparatus by passing through the workpiece an auxiliary current parallel to the current flowing through the electrode wire, in one direction or the other. The points of application of the auxiliary current on the surface of the workpiece are disposed opposite to the front of a cut relative to the electrode wire in order to obtain a resultant force which either pulls the electrode wire away from the front of the cut or draws it closer to the front of the cut.

Abstract: A method and apparatus for threading the electrode wire of a travelling wire EDM apparatus through an aperture in a workpiece. Prior to automatically threading the wire through the aperture in the workpiece, the wire is continuously straightened by pulling longitudinally on the wire, and the wire is passed through a guide tube and through a nozzle to which fluid under pressure is supplied for forming a jet stream at the outlet of the nozzle. Prior to a threading or rethreading operation the wire is cut off proximate to the outlet of the nozzle. The nozzle outlet is brought in close proximity to the aperture in the workpiece and the jet stream is aimed at the aperture in the workpiece for guiding the wire through the aperture, while being maintained coaxially by the jet stream.

Abstract: In a travelling wire EDM apparatus the thermal stresses of the electrode wire are substantially reduced by detecting the position of the triggering electrical discharges preceding the machining electrical discharges, and by controlling the supply of the machining electrical discharge current at one end of the machining zone, at the other end of the machining zone or at both ends of the machining zone. When a machining electrical discharge is located between one end of the machining zone and a first reference position, the machining current is applied at that end. When the electrical discharge is located between the other end of the machining zone and a second reference position, machining current is supplied at that second end. When the electrical discharge is located between the two reference positions, the machining current is applied simultaneously at both ends of the machining zone.

Abstract: An EDM electrode wire changer has a plurality of conduits, one for each available electrode wire, all conduits converging towards the threading axis of a selected electrode wire through the workpiece or, alternatively, disposed substantially parallel on a slide that is indexable such as to dispose the outlet of a selected one of the conduits in alignment with the threading axis. A common motor-driven threading roller is disposed proximate the inlet of the conduits in a stationary position relative to the conduits, and a pinch roller for each wire co-operates with the threading roller for feeding the selected one of the wires through its corresponding conduit by forcing the selected wire against the peripheral surface of the common threading roller, while the other pinch rollers are remaining in a position away from the threading roller.

Abstract: A method and apparatus for polishing a workpiece by electrical discharges by way of an electrode tool, machining pulses of relatively low power being obtained from a machining pulse generator. A cross-slide table provides the workpiece with a translation cyclical motion during polishing. Input control circuits enable the machine operator to program a chosen speed of translation for the cyclical motion, the radius of circular translation and the time of duration of machining. A counter counts the number of cycles being effected and a discriminator stops the pulse generator as soon as the chosen number of desirable cycles is obtained, such number being inversely proportional to the amplitude chosen for the translation motion.

Abstract: An apparatus and method for improving the surface finish of a workpiece machined by an EDM apparatus having an electrode tool mounted in a tool holder insulated from the rest of the apparatus structure, the EDM apparatus comprising a pulse generator applying electrical discharges across the electrode tool and the workpiece, and wherein a parasitical capacitor is formed by the tool holder insulated from the rest of the apparatus. The parasitical capacitor, connected across the pulse generator output, is charged and discharged during operation of the pulse generator, and the discharge energy of the parasitical capacitor is added to the energy of the electrical discharge supplied by the pulse generator. For the purpose of obtaining a smooth surface finish on the workpiece with decreased energy of the machining electrical pulses, a compensating inductance is placed in series in the discharge circuit.

Abstract: A travelling wire EDM apparatus wherein a workpiece is cut by electrical discharges by a travelling wire electrode, relative motion of the workpiece and the wire electrode being controlled by a numerical control unit which, in addition, controls transverse oscillations of the electrode wire relative to the workpiece along the cutting path. The energy of the electrical discharges is varied as a function of the amplitude of the transverse oscillations of the electrode wire relative to the workpiece such as to obtain maximum electrical discharge energy when the amplitude of vibration of the electrode wire is at a minimum and minimum energy when the amplitude of vibration of the electrode wire is at a maximum.

Abstract: In a travelling wire EDM apparatus, the location of an electric discharge along the portion of the electrode wire in the machining zone between the electrode wire and the workpiece, in the course of a cut being effected on the electrode workpiece by electrical discharges, is measured by measuring the currents flowing through each of the two lines connecting one output of the pulse generator associated with the EDM apparatus to the electrode wire on one side and the other of the machining zone. The measured currents are added and subtracted and the position, or location, of an electrical discharge is determined by a signal proportional to the quotient of the difference by the sum of the currents.

Abstract: A travelling wire EDM apparatus having a pair of support and guide arms for an electrode wire effecting a cut on an electrode workpiece mounted in a tank filled with machining liquid fluid and capable of being displaced along two directions, relative to the support and guide arms, by a cross-slide table. At least the lower arm passes through an opening in one of the walls of the tank, such wall being formed by two parallel panels, a plate being slidably mounted between the two panels and having a tubular member through which the arm is disposed. Flexible joints are mounted between the plate and the two panels and at least one annular seal provides a sliding leakproof connection between the interior of the tubular member and the arm.