Electric heating – Metal heating – Cutting or disintegrating
Patent
1988-05-24
1990-01-02
Pellinen, A. D.
Electric heating
Metal heating
Cutting or disintegrating
2041295, B23H 718
Patent
active
048914860
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
1. Background of the Invention
This invention relates to electric discharge machining of electrically conducting materials and, in particular, to devices for feed control of electrode-tools in electro-erosion machines.
2. Description of the Prior Art
The basic problem in controlling the feed of tool during electro-erosion machining is to control the feed rate so that it corresponds to the rate of erosion in the gap between the tool and workpiece. It is also important to achieve high quality electric discharge machining in terms of the surface finish, precise shape of the hole, etc. The process of electro-erosion machining is subject to many accidental disturbances due to the presence of electrically conducting particles in the spark gap and instability of the power supply voltage. It is, therefore, advisable that the desired operating conditions and the desired feed rate of the electrode-tool are maintained by a device for feed control of the electrode-tool in electro-erosion machines.
Known in the art is a tool feed control device for spark erosion machines (SU,A, No. 1202767), comprising a pulse generator having its input connected to one of the outputs of a timer, and a servo drive. The device also comprises, connected in series, a resistance transducer, an electronic switch controlled by the timer, a reservoir capacitor, and an amplification and comparison device having its output connected to the servo drive and its input connected to a standard voltage source.
This device can be used to measure the resistance of the spark gap in the intervals between current pulses supplied from the pulse generator.
But this device is deficient in that it cannot take into account the resistance of the electrode-tool during the spark erosion process. When deep and super-deep holes are made with a small diameter, the electrode-tool wears out quickly and its resistance changes very fast. This may be the cause of many serious errors.
Some aspects of this problem are dealt with in the known device for feed control of an electrode-tool (B. A. Artamonov et al., Elektricheskie i elektrokhimicheskie metody obrabotki materialov, Vysshaya shkola Publ., 1983, vol. 1, p. 53, FIG. 1.41), which comprises, connected in series, a measuring transducer, a comparison unit, and an amplifier having its output connected to an actuating device for shifting the electrode-tool, while a power source is connected to the spark gap, a signal therefrom being fed to the measuring transducer.
Here the control parameter, that is the signal carrying information on the size of the spark gap and picked up from the operational circuit of the power supply, may be instantaneous or mean voltages across the electrodes in the spark gap, or the mean strength of current in the electrode circuit, or the sparkgap breakdown delay time, etc. In this case the tool characteristics, e.g. its material or electric resistance, have no effect on the accuracy and stability of the metal working process. When the mean erosion voltage is measured in the spark gap, it can be used to assess the size of the spark gap, given the current of the power source. Information is continuously fed to the comparison unit and, further on, via the amplifier, in accordance with the sign, to an actuator, e.g. control winding of a bidirectional electric motor.
However, this device is deficient in that it cannot be used to produce deep and super-deep small-diameter high-quality holes. When the signal from the spark gap and the reference signal are equal, no instructions are produced by the comparison unit to the actuator. The electrode-tool stops. Zero feed of the tool or its slow retraction followed by forward feed result in longer erosion voltage effect in some portions of the workpiece surface. This negatively affects the quality of the surface due to lateral erosion and holes become barrel-shaped or oval. Faster tool feed rate also results in more frequent stops of the electrode-tool and, consequently, in deterioration of the treatment quality. When deep holes are pie
REFERENCES:
E. V. Armensky, G. B. Falk, "Elektricheskie Mikromashiny", third edition, 1985.
Ju. Kh. Lukes, "Skhemy na Poluprovodnikovykh Diodakh", 1972, Energia Publ., Moscow, see pp. 170-171, FIGS. 6.29-6.34.
B. G. Gutkin, "Avtomatizatsia Elektroerozionnykh Stankov", 1971.
B. A. Artamonov et al., "Elektrofizicheskie Elektrokhimicheskie Metody Obrabotki Materialov", 1983.
Abdukarimov Erkin T.
Khainov Vladimir I.
Rasulev Vadim A.
Evans Geoffrey S.
Pellinen A. D.
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