Servosystem for electrical machining processes

#The present invention relates to a servosystem for electrical machining processes and, more particularly, to a servocontrol arrangement for spark and galvanic gaps, the latter being any dielectric filled space between a pair of electrodes adapted to sustain an electrical discharge thereacross or any electrolyte-filled space between a pair of electrodes as used for the shaping, forming, surfacing, coating or treatment of a workpiece with electrical energy.

#The invention has particular reference to electrodischarge machining (EDM) wherein an impulsive spark discharge is generated between a tool electrode and a workpiece across a machining gap which is flooded generally with a dielectric to impulsively remove particles of the workpiece material and allow the removed particles to be carried from the gap by the flowing stream of dielectric; the invention has reference as well to electrochemical machining (ECM) systems which make use of an electrolytic solubilization of workpiece materials into an electrolyte in the gap between the tool electrode and the workpiece, to electrochemical grinding (ECG) systems in which, the tool electrode is generally rotated substantially in contact with the workpiece and an electrolyte serves as the coolant, and various hybrid processes including electrochemical discharge machining (ECDM), electrochemical discharge grinding (ECDG) etc.

#The term "electrical-machining process" is intended herein to include so-called spark sintering wherein a spark discharge among a mass of particles provides both the impulsive energy and localized fusion required to sinter the particles together, high-energy-rate forming (HERF) in which a spark discharge produces a shock wave used to shape a workpiece, apply a coating or modify the surface of a workpiece and to any machining or shaping process in which control of a gap between a pair of electrodes is essential.

#These and other objects, features and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

#FIG. 1 is a circuit diagram illustrating a basic embodiment of the improved servo-signal generator constructed in accordance with the present invention;

#FIG. 1a is a graphical representation of operating characteristics of the system of FIG. 1;

#Throughout the following description, several embodiments of the invention will be illustrated in conjunction with EDM principles because of the particular adaptability of the servosystems thereto but it is to be understood that the invention is applicable also to ECM (electrochemical machining), ECDM (electrochemical-discharge machining), ECDG (electrochemical-discharge grinding), spark sintering, high-energy-rate coating and shaping and other electrical machining or shaping processes.

#In FIG. 1, there is shown a basic form of an improved servo signal generator which may be modified in various respects as will be apparent. A tool electrode E is juxtaposed with a workpiece W to form a gap or spacing g between them in the presence of a machining medium while an electrical machining current is passed through the gap from a power supply 1 to remove material from the workpiece W. Parameters of the power supply are variable in dependence on the particular type of machining operation of interest. One or both of tool electrode E and workpiece electrode W is movable (this electrode will be referred to as a movable electrode hereinafter) and is servo-controlled to maintain the gap spacing g in a manner fully described hereinbelow. Suitable power supplies with adaptively variable pulse duration or width, pulse height and/or pulse spacing are described in my application Ser. No. 838,575 copending herewith.

#The improved servo system includes a gap sensor 10 for deriving from the gap an analog-varying signal representative of variable gap spacing as well as gap state or condition. The sensor is here constituted by a resistor 10a and an integrating capacitor 10b serially connected across the gap as shown to detect the mean gap voltage. At the junction of this resistor 10a and capacitor 10b is connected the positive terminal of a voltage source 11 via a variable resistor 10c which forms part of the gap-sensing means. Thus, with the indicated polarity relationship of electrodes E and W and of the source 11, the charge on capacitor 10b is controlled by source 11 via resistor 10c and also by the gap voltage via resistor 10a. The capacitor terminal voltage achieves a higher value when the gap voltage falls, indicative of a reduced or relatively narrow gap spacing, short-circuit or arc and a lower value when the gap voltage is increased indicative of open gap or greater gap spacing.