Patent EA-001749-B1 (EA)
Title: Method of and arrangement for electrochemical machining
Inventor: AGAFONOV IGOR L
IPC: B23H3/02
Filed: 1999-03-29
Abstract: 1. A method of electrochemically machining an electrically conductive workpiece (2) which comprises applying electrical machining pulses between the workpiece (2) and an electrically conductive electrode (6) while supplying electrolyte between the workpiece (2) and the electrode (6) wherein, the machining pulses alternate with electrical passivation pulses of the same polarity as the machining pulses, the voltage of the passivation pulses having an amplitude which is inadequate to dissolve the workpiece (2) and a passivation film on the workpiece (2). 2. A method as claimed in claim 1, which comprises adjusting the amplitude of the voltage of the passivation pulses at least once during electrochemical machining, by changing the amplitude of the passivation pulses in a series of successive passivation pulses until a resistance value measured between the workpiece (2) and the electrode (6) has reached a maximum, and after measuring the resistance value continuing electrochemical machining with an amplitude of the passivation pulse which corresponds to the maximum of the resistance value. 3. A method as claimed in claim 2, which comprises dividing the passivation pulses into time slices and for each individual time slice, changing the instantaneous amplitude of the voltage of the passivation pulses until the resistance value measured between the workpiece (2) and the electrode (6) has reached a maximum during the individual time slice, thereafter, continuing electrochemical machining with passivation pulses whose instantaneous amplitude varies in accordance with the amplitude found for each time slice and corresponding to the maximum of the resistance value in said time slice. 4. A method as claimed in claim 1,2 or 3 which comprises keeping a space between the workpiece and the electrode (6) which is smaller during the machining pulses than during the passivation pulses. 5. A method as claimed in claim 4, which comprises oscillating the workpiece (2) and the electrode (6) relative to one another so that the space between the workpiece (2) and the electrode (6) reaches a minimum during the machining pulses. 6. A method as claimed in claims 1 to 5, which comprises in time intervals between the successive machining pulses, applying electrical pulses of opposite polarity between the workpiece (2) and the electrode (6), wherein said opposite polarity electrical pulses have a voltage amplitude that does not exceed the amplitude at which the electrode 6) begins to dissolve in the electrolyte. 7. A method as claimed in claim 1,2, 3, or 5, which comprises in time intervals between the successive machining pulses, alternating the passivation pulses with electrical pulses of opposite polarity, wherein said opposite polarity electrical pulses have a voltage amplitude that does not exceed the amplitude at which the electrode (6) begins to dissolve in the electrolyte. 8. An arrangement for electrochemically machining an electrically conductive workpiece (2) comprising: an electrode (6); means (4, 40) for positioning the electrode (6) and the workpiece (2) in a spatial relationship so as to maintain a gap (5) between the electrode and the workpiece; means (3) for supplying electrolyte into the gap (5); a first electric power supply source (14), which is electrically connectable to the electrode (6) and the workpiece (2) to supply machining pulses to the workpiece (2) and the electrode (6); a second electric power supply source (16) of the same polarity as the first power supply source (14) and having an output voltage which is controllable by means of a control signal, which second power supply source (16) is electrically connectable to the electrode (6) and the workpiece (2) to supply passivation pulses to the workpiece (2) and the electrode (6); means (20, 24) for alternately connecting the first (14)and the second (16) power supply source to the workpiece (20 and the electrode (6); means (28, 44) for generating a varying control signal for changing the output voltage of the second power supply source (16) during successive passivation pulses; means (18, 30, 26, 28) for measuring during the successive passivation pulses the electrical resistance of the gap (5) between the workpiece (2), for storing resistance information values, the gap at said instant and for storing corresponding control signal values of the control signal at said instant; and means (28) for calculating a maximum value from the resistance information values, and means (28, 44) for maintaining the control signal for the second power supply source (16) at the control signal value which corresponds to the maximum value. 9. An arrangement as claimed in claim 8, wherein the means (28, 44) for generating the varying control signal include means for changing the output voltage of the second power supply source (16) at different instants within the time span of one passivation pulse; the means (18, 30, 26, 28) for measuring and storing are adapted to store resistance information values which are representative of the instantaneous resistance of the gap (5) at the different instants within the passivation pulse and to store corresponding control signal values of the control signal at the different instants; and the means (28) for calculating are adapted to calculate individual maximum values from the resistance information values of corresponding instants within successive passivation pulses and to generate a control signal having an instantaneous value which, at the different instants, is equal to the control signal values which correspond to the individual maximum values. 10. An arrangement as claimed in claim 9, wherein further comprises means (8, 10) for changing the distance between the electrode (6) and the workpiece (2) so that said distance is smaller during the supply of the machining pulses than during the supply of the passivation pulses. 11. An arrangement as claimed in claim 10, wherein further comprises means (8, 10) for producing an oscillating movement between the workpiece (2) and the electrode (6), and means (22) for synchronizing the means (20, 24) for alternately connecting the first (14) and the second (16) power supply source with the oscillating movement of the workpiece (2). 12. An electrical power supply source for use as claimed in claim 1 comprising: a first electric power supply source (14), which is electrically connectable to the electrode (6) and the workpiece (2) to supply machining pulses to the workpiece (2) and the electrode (6); a second electric power supply source (16) of the same polarity as the first power supply source (14) and having an output voltage which is controllable by means of a control signal, which second power supply source (16) is electrically connectable to the electrode (6) and the workpiece (2) to supply passivation pulses to the workpiece (2) and the electrode (6); means (20, 24) for alternately connecting the first and the second power supply source to the workpiece (2) and the electrode (6); means (28, 44) for generating a varying control signal for changing the output voltage of the second power supply source (16) during successive passivation pulses; means (18, 26, 28, 30) for measuring, during the successive passivation pulses, the electrical resistance of the gap (5) between the workpiece (2) and the electrode (6), for storing resistance information values which are representative of the resistance of the gap (5) at said instant and for storing corresponding control signal values of the control signal at said instant; and means (28) for calculating a maximum value from the resistance information values, and means (28, 44) for maintaining the control signal for the second power supply source (16) at the control signal value which corresponds to the maximum value. 13. An electrical power supply as claimed in claim 12, wherein the means (28, 44) for generating the varying control signal include means for changing the output voltage of the second power supply source (16) at different instants within the time span of one passivation pulse; the means (18, 30, 26, 28) for measuring and storing are adapted to store resistance information values which are representative of the instantaneous resistance of the gap (5) at the different instants within the passivation pulse and to store corresponding control signal values of the control signal at the different instants; and the means (28) for calculating are adapted to calculate individual maximum values from the resistance information values of corresponding instants within successive passivation pulses and to generate a control signal having an instantaneous value which, at the different instants, is equal to the control signal values which correspond to the individual maximum values.