GB944613A - Improvements in electrolytic machining apparatus - Google Patents

Abstract

In an electrolytic machining apparatus, a control system is effective to stop relative movement between an electrode and a workpiece and to cut-off the D.C. supply to the electrode and workpiece in response to minor transient changes in the D.C. supply due to short circuiting between the electrode and workpiece, the control system being substantially insensitive to a gradual change in, or steady state conditions of, the D.C. supply. In the arrangement shown, the control grid of a gas-filled valve 2D21 is normally biased so that the valve is non-conducting. This control grid is connected through a high-pass filter C3, C2, L1, a potentiometer R1, a capacitor C1 and conductors 63 to the electrode and workpiece. Under transient conditions due to a spark between the electrode and workpiece, a signal is applied to the control grid causing the valve to conduct. A relay RY6 is now energized and closes its contacts A to cause the energizing of a relay RY5, a signal lamp S and a thermal delay relay TDR. The relay RY5 closes contacts E to complete a holding circuit for itself, opens contacts B to cut-off the supply to the relay RY6 and the valve, and closes contacts C <PICT:0944613/C3/1> and D to cause the stopping of the movement between the electrode and workpiece, e.g. by causing the de-energizing of a drive motor (not shown) and to cause the interruption of the D.C. supply to the electrode and workpiece. After a short delay, the relay TDR opens its contacts F to interrupt the holding circuit for the relay RY5 so that the control system automatically returns to normal and permits the manual operation of a conventional starting system (not shown) to re-start the apparatus after the fault condition has been removed. The control system described also functions when the D.C. supply to the electrode and workpiece fails, to prevent mechanical damage to the electrode.