GB1169042A - Electrochemical Machining - Google Patents

Abstract

1,169,042. Electro-chemical machining. ASSOCIATED ENG. Ltd. Sept. 11, 1967 [Sept. 16, 1966, No.41564/66. Heading C7B. [Also in Division G3] In a method of electro-chemical machining, changes in electrolyte composition are compensated by changes in the operating temperature of the electrolyte so as to maintain the conductivity of the electrolyte substantially constant. If the conductivity rises above a desired value the electrolyte is cooled and if the conductivity falls below a desired value the electrolyte is heated. Upper and lower temperature limits may be imposed for maintaining the conductivity at which limits it is arranged that a visible or audible warning is given. At these temperature limits the electrolyte composition may be adjusted automatically or manually by adding water or concentrated electrolyte in order to vary the temperature at which the required conductivity is achieved. The warning signals may be used to stop the machining operation until the electrolyte composition has been adjusted. The temperature limits may be determined by a thermostat, by specific gravity measurements or by continuous monitoring of the chemical composition of the electrolyte. The temperature control may be by a heating and cooling system which (a) is on or off (b) operates such that the rate of heating or cooling is proportional to the error in conductivity or (c) operates in a stepwise fashion as the error in conductivity changes. Alternatively, there may be only a cooling system. In carrying out the method, the workpiece and tool may be maintained in fixed positions or there may be relative advance between them. The applied voltage and the advance rate may be maintained constant or both of these parameters may be varied in accordance with a predetermined programme. Fig. 1 illustrates a method of machining. Fig. 2 (not shown) is a block diagram of conductivity measuring and electrolyte temperature control apparatus wherein one of two spaced coils of a conductivity cell (20) is energised by an oscillator (21). The output from the other coil effects control whereby a water valve (29) or steam valve (30) can be operated to cool or heat the electrolyte. Fig. 3 (not shown) is a block diagram showing an electrical resistance thermometer (40) a temperature indicator controller (41) and a moving coil instrument (42) with a pointer which, when one of the above mentioned temperature limits is reached, engages one of the contacts (44 or 45) to initiate action.