Patent EA-001993-B1 (EA)
Title: Method and arrangement for the electrochemical machining of a workpiece
Inventor: ALTENA HERMANUS S J
IPC: B23H7/16
Filed: 1999-03-25
Abstract: 1. A method of electochemically machining a workpiece (2) by means of an electrode (3), comprising the steps of bringing the workpiece and the electrode into contact with one another, setting a working distance (dw) between the electrode and the workpiece while keeping a gap (4) between the workpiece and the electrode filled with an electrolyte, and passing an operating current through the electrolyte in the gap via the electrode and the workpiece in order to machine the workpiece, wherein the working distance (dw) is set by increasing, initially from a situation of contact between the electrode (3) and the workpiece (2), a distance (d) between the electrode and the workpiece by a first distance (d1) to form an increased distance, detecting whether the contact between the electrode and the workpiece is broken, and increasing the increased distance between the workpiece and the electrode by a second distance (d2) if the detecting shows that the contact between the electrode and the workpiece is broken. 2. A method as claimed in claim 1, wherein the first distance (d1) is a predetermined distance and the first distance (d1) is comparatively small with respect to the second distance (d2). 3. A method as claimed in claim 2, wherein the distance (d) between the workpiece (2) and the electrode (3) is increased by a third distance (d3), after which the electrolyte (5) in the gap is renewed by flushing, upon which the workpiece and the electrode are again brought into contact with one another if the contact between the electrode and the workpiece is found not to be broken after the predetermined distance (d1) has been set. 4. A method as claimed in claim 1, wherein the steps of bringing the workpiece (2) and the electrode (3) into contact with one another and setting the working distance (dw) between the electrode and the workpiece are repeated periodically. 5. A method as claimed in claim 1, wherein as a result of the operating current(I) material of the workpiece (2) is dissolved, and during the passage of an operating current through the electrolyte (5) the electrode (3) and the workpiece are moved towards one another (FF) in accordance with an estimate of a dissolution rate (Vf) at which the material is dissolved. 6. A method as claimed in claims 4 or 5, wherein the dissolution rate (Vf) is estimated on the basis of a relative displacement (d4) between the electrode (3) and the workpiece (2) between two contacting phases. 7. A method as claimed in claim 1, wherein contact between the electrode (3) and the workpiece (2) is detected by connecting a current-limited voltage source (21) between the electrode and the workpiece and monitoring a voltage difference between the electrode and the workpiece. 8. A method as claimed in claim 7, wherein the voltage source (21) supplies a voltage between 1 and 3 V. 9. A method as claimed in claim 1, wherein the electrolyte comprises NaNO3. 10. A method as claimed in claim 1, wherein the working distance (dw) is smaller than 50 μm. 11. A method as claimed in claim 10, wherein the first distance (d1) lies between 2 and 10 μm and the second distance (d2) lies between 5 and 30 μm. 12. An arrangement for electrochemically machining a workpiece (2) by means of an electrode (3), in which a working distance (dw) is set between the electrode and the workpiece while the gap (4) between the workpiece and the electrode is filled with an electrolyte (5) wherein the workpiece is machined by passing an operating current (I) through the electrolyte in the gap via the electrode and the workpiece, said arrangement including a base (6) for positioning the workpiece, a holder (7) for positioning the electrode, an actuator (8) for moving the holder and the base with respect to one another, a detection device (20) for detecting contact between the electrode and the workpiece, and a control unit (30) for controlling the actuator, wherein the control unit (30) is adapted to set a distance (d) between the electrode and the workpiece by a first distance (d1) starting from a situation of contact between the electrode and the workpiece, to detect whether the contact between the electrode and the workpiece is broken, and to increase the distance (d) between the workpiece and the electrode by a second distance (d2). 13. A control unit (30) for controlling an actuator in an arrangement (1) for electrochemically machining a workpiece (2) by means of an electrode (3), wherein the control unit (30) is adapted to set a distance (d) between the electrode (3) and the workpiece (2) by a first distance (d1) starting from a situation of contact between the electrode and the workpiece, to detect whether the contact between the electrode and the workpiece is broken, and to increase the distance (d) between the workpiece and the electrode by a second distance (d2).