Electrical discharge wire cutting machines remove material from a workpiece by spark erosion as a wire electrode is fed from a spool or similar supply through the workpiece. During a cutting operation, it is necessary to deliver current to the moving wire electrode. To insure good electrical conduction between a power supply and a moving wire electrode, a current pick-up is used. Delivery of current pulses from a power supply to a wire electrode just above and below the cutting zone is provided by actual physical contact between the wire electrode and the current pick-up.
The erosion of the central bore of the current pick-up enlarges the bore making it possible for the wire electrode to be centered temporarily in the bore out of contact with the current pick-up. When this occurs, there is no electrical contact between the wire electrode and the carbide current pick-up. The center lines of these guides are offset relative to the centerline of the bore of the carbide current pick-up causing the wire electrode to bear against the inner surface of the bore of the current pick-up.
This deformation is caused, at least in part, by rubbing of the wire electrode over an edge where a tapered inlet and outlet merge with the bore. The deformation of the wire electrode is believed to be caused by work hardening of one side of the wire electrode surface due to engagement between the wire electrode and the inner peripheral surface of the longitudinal bore of the current pick-up and the edges in the bore. This deformation can affect the cutting accuracy of the electrical discharge wire cutting machine since deformation of the wire electrode results in a "bowing" of the wire electrode in the cutting region. |
