Electric heating – Metal heating – Cutting or disintegrating
Patent
1987-03-12
1988-07-26
Leung, Philip H.
Electric heating
Metal heating
Cutting or disintegrating
219 69M, B23H 102, B23H 914
Patent
active
047602333
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric discharge machining system.
2. Description of the Related Art
When performing a drilling operation using an electric discharge machining system, it has not heretofore been possible to automatically determine whether or not a hole have been formed. Operator experience or visual detection has been required to determine the completion of a hole.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a drilling confirmation apparatus for an electric discharge machining system which can automatically, correctly, and easily detect when drilling of a hole through a workpiece has been completed.
In order to achieve the above object, the drilling confirmation apparatus of the present invention comprises average machining current detecting means for detecting an average machining current between a workpiece and an electrode, machining speed detecting means for detecting a machining speed, operational means for dividing the detected average machining current by the detected machining speed and outputting the division result, and drilling detecting means for detecting a decrease in output signal value from the operational means.
As described above, according to the present invention, the average machining current between a workpiece and an electrode is divided by a detected machining speed, i.e., a relative feed speed between the workpiece and the electrode, to obtain a signal corresponding to a machining area. Completion of drilling is detected when the signal corresponding to the machining area decreases. Therefore, completion of machining of a hole through a workpiece can be correctly, easily, and automatically detected.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a drilling confirmation apparatus according to an embodiment of the present invention;
FIG. 2 is a cross-sectional view showing an electrode of a wire discharge machining apparatus machining a hole through a workpiece; and
FIG. 3 is a graph illustrating respective changes in average machining current, machining speed, signal corresponding to a machining area and a delay signal in the embodiment with respect to a machining depth.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a drilling confirmation apparatus of an electric discharge machining system according to an embodiment of the present invention. In this embodiment, electric discharge drilling is performed by applying a machining voltage between a workpiece 1 and a drilling electrode 2. A DC power source 3 supplies the machining voltage via a current limiting resistor 5 and a transistor 4. The transistor 4 acts as a switching element which is turned on/off by a controller (not shown).
Prior to the explanation on the arrangement of the main portion of the apparatus of the present invention, the operational principle of the present invention will be briefly described. The value of a signal representing an electric discharge machining area S abruptly decreases from a specified value during machining to zero when electric discharge drilling is completed. The present invention is based on this fact. According to the present invention, drilling is deemed to have been completed when an abrupt decrease in the machining area S is detected. More specifically, a change in the machining area S during machining is monitored by utilizing a conventionally known relationship, S=K.multidot.IT/F (K is a constant), where S is the machining area, F is the machining speed, and IT is the machining current. Monitoring of the value of S will thereby detect the completion of drilling.
The main portion of the apparatus of the present invention will be described with reference to FIG. 1. One end of a resistor 11 and one end of another resistor 13 are connected to two ends of the current limiting resistor 5. The resistors 11 and 13 are connected in series with resistors 12 and 14, respectively. These resistors 11-14 detect a voltage V1 between nodes 15 and 16
REFERENCES:
patent: 4146770 (1979-03-01), Dinsdale et al.
patent: 4415791 (1983-11-01), Yamada et al.
Evans Geoffrey S.
Fanuc Ltd
Leung Philip H.
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