Abstract: A generator for machining by means of electrical discharges between a tool electrode and a workpiece electrode. The generator consists of a main voltage source connected between the tool electrode and the workpiece electrode through an improved switching circuit which is activated by an adjustable oscillator. The switching circuit delivers short pulses of high pulse current and consists of a plurality of identical impulse amplification stages. A first one of these impulse amplification stages drives all the additional ones. Power transistors are used. With a base current regulating system, the turn-off delay of these power transistors is eliminated by keeping them far away from saturation. Resistance-capacitance and resistance-inductance elements and a special cabling are used to eliminate certain impulse transmission problems.

Abstract: In a spark erosion machine in which the tool electrode comprises a tensioned flexible wire or tape, machining induced force due, for example, to the magnetic and electric fields induced by the sparks, act on the tool electrode and may cause it to vibrate. To reduce the tendency for such vibration, a compensating signal is passed through the tool electrode or applied between the tool electrode and workpiece so as to produce a magnetic or electric field which compensates for the machining induced forces. The compensating signal is preferably adjustable in magnitude and/or frequency (the latter assuming it is an alternating signal) and the output of the generator which produces it is decoupled from the output of the spark pulse generator. The spark pulse generator and the compensating signal generator may be interdependently synchronized by a synchronizing signal lead connected between them.

Abstract: An assembly such as a tool head for a spark erosion profiling machine tool comprises an elongate tool holding member having first and second opposed lengthwise bearing surfaces and third and fourth opposed lengthwise bearing surfaces. By way of example the member can be square, the bearing surfaces then being the four long sides of the member. The member is partly housed in a housing wherein there are mounted bearings which support the member for movement in the direction of its length with respect to the housing. The bearings can comprise discrete circulating roller bearing shoes and they are in abutting contact with the member at five positions in the region of each of two planes spaced apart along the length of the member by a calculated optimum distance.

Abstract: Casting apparatus for use in making intermediate molds for the preparation of tool electrodes comprises a pallette for holding the casting and adjusting devices for ensuring parallelity and correct alignment for the mouldingfaces. There is also vibrator to ensure improved consolidation of the casting material and to provide for degassing.

Abstract: A pulse generator for use in forming the erosion pulses of an electro-erosion machine tool comprises means for forming two envelope curve signals representing upper and lower limit levels for the instant level of the output pulse, a comparing device for comparing the actual current level of the output pulse with the envelope curve signals, and a current supply for forming the pulse under the control of a switch which is turned on and off by the comparing means in such a way as to maintain the output pulse current level in the region represented by the space between the envelope curves.

Abstract: An over or undersize abrasive master mould is used to form tool electrodes by abrading a workpiece using a circular reciprocatory motion. The master mould is made by a casting process which starts with a preformed model, positive or negative, of the exact shape to be machined by the tool electrodes to be made. Positive and negative castings of the model, one of which castings is abrasive, are subjected to a relative circular reciprocatory motion in an abrading operation to provide the correct under or oversize of the master mould, which is then made directly or indirectly from the abraded casting. Casting apparatus for use in the method comprises a pallette for holding the casting and adjusting devices for ensuring parallelity and correct alignment for the moulding faces and there is also disclosed apparatus for the abrading operation in which an error detection system regulates the amplitude of the reciprocatory abrading movement.

Abstract: A control system, for a machine tool of the kind in which electrical energy passes across a gap between a tool electrode and a workpiece to erode the workpiece, comprises means for forming signals representative of the rate of erosion of the workpiece and the rate of undesirable erosion or "wear" of the tool electrode, and a computer means which receives the signals and combines them with a signal received from a data input device, which signal represents a desired optimum relationship between the two rates of erosion, and forms an appropriate output signal for controlling the machine tool. The data input device is usable, in rough machining operations where the tool electrode may be relatively cheaper than machine time, to ensure that machining is done in the shortest time by allowing a relatively high rate of tool wear and, in fine machining where the tool electrode is expensive, to ensure minimal tool wear at the cost of machine time.

Abstract: In order to machine a multidimensionally curved surface on a workpiece using an electro-erosion, i.e. spark erosion or electro-chemical erosion, machine tool, the machine tool is provided with a tool electrode which has an effective machining face inclined to the direction in which the advance feed drive of the machine tool advances the tool electrode towards the workpiece. By using transverse feeding mechanisms for the tool electrode or the workpiece acting under the control of a computer, or by using a cam and guide arrangement coupled to the tool electrode, the tool electrode and workpiece are so relatively moved that the effective machining face of the electrode always moves in the direction of the momentary largest radius curvature of the curve to be machined. When a cam and guide arrangement is used, the tool electrode can be coupled to the advance feed drive by way of a coupling device which incorporates a universal joint, or a domed surface sliding joint.

Abstract: Electroerosion machining (EDM or ECM) is carried out with a minimum of manual intervention. Under control of recorded data an electronic control system utilizing control logic directs the set-up operations as well as the actual machining process. The operations automatically (i.e., without the necessity of manual intervention) include loading and removal of workpieces and electrode material, trueing up of the workpiece (which may be by providing a transformation of the data rather than by adjusting the position of the workpiece), making starting bores, threading the electrode through a starting bore, applying a low melting alloy or other conducting adhesive to cement a core in the process of being cut out by machining, cutting the electrode after completing a starting bore and joining electrode ends after rethreading in a new starting bore. In threading the electrode it may be pushed simply or with the support of a surrounding jet of pressure medium, or it may be pulled by a grapple member.

Abstract: Two condition index variables are used for controlling operation in such a manner that one of the variables is kept as close as possible to a minimum value, while the other is held within an assigned range. Both condition index variables depend on the rate of flow of the flushing liquid through the working gap, on the interval between discharges in the gap or on the duty cycle or repetition frequency and amplitude of the discharge pulses. The condition index variable held to a minimum may be the integral of the square of the error signal from the regulating circuit of the electrode advancing drive, the integral of the square of the acceleration of electrode movement or the quotient obtained by dividing the square of the error signal by the square of the gap current. The regulating value to be held within an assigned range is a calculated breakdown potential defined by the relation of the variation of the error signal to the variation of the electrode spacing.

Abstract: A workpiece-supporting table of an electro erosion machining equipment is provided with a mechanism for subjecting the workpiece to a circling motion of continuously variable radius during operation from zero to a maximum value. The same tool electrode can be used, without withdrawal from the work, for coarse machining at first and fine machining under circling movement immediately thereafter.

Abstract: The peak voltage of each discharge pulse is measured and, if the voltage of the pulse exceeds a high threshold value, there is also measured the time between the passing of that value and the moment the pulse voltage thereafter drops below a second lower threshold value. The two measurements are expressed in pulses that are combined, preferably by addition, to provide a regulating value, whose deviation ("error") from a standard value is predicted for a coming period, taking account of recent electrode position change as well as regulating value trend. The sign of the predicted error determines in which direction the electrode drive motor will be energized, but if the predicted error is less than a threshold value no motor energization occurs until the next error prediction.

Abstract: In order to provide respective series of control signals for controlling separate items of apparatus, some of which may be redunant, there are provided a plurality of independently operable signal generators and a plurality of gating circuits connected to the generators and each operable to produce a respective control signal when it receives at least a predetermined number, dependent upon a chosen degree of redundancy of the generators, of correctly timed signals from the generators. Each generator is provided with a phase comparator type timing control device which adjusts the generator if its signals go out of synchronism with those of the other generators. The apparatus to be controlled can be a computer, a multiple-rectifier power supply or the like, and in connecting lines between various parts of the control apparatus and the controlled apparatus isolating devices can be provided.