Progressive cavity pump/motor stator, and apparatus and method to manufacture same by electrochemical machining

An apparatus for use in machining a helically-lobed profile in the interior of tubular work-piece to produce a progressive cavity pump stator comprising:

• an electrode having a lobed-shaped portion;
• a drive bar arranged to move the electrode along a linear path while simultaneously rotating the electrode about an axis parallel to the linear path such that the electrode can electrochemically machine a helical lobed profile in the interior of the tubular work-piece to produce a stator suitable for a progressive cavity pump or motor;
• a device for establishing a flow path for directing an electrolyte in a first space between the electrode and the work-piece such that an electrical power supply can establish an electric current through the electrolyte in the first space between the electrode and the work-piece,
• wherein the flow path also includes a space defined behind the electrode as the electrode moves along the linear path such that electrolyte can be used to roughen the interior surface of the work-piece after the machining by the electrode and wherein the electrode is maintained within the work-piece for a sufficient duration of time to achieve said roughened interior surface.

An apparatus for use in machining the interior profile in the bore of a progressive cavity pump stator comprising:

• a cathodic electrode shaped to machine helical lobes in a tubular work-piece;
• a drive bar arranged to move the cathodic electrode along a linear path, while simultaneously rotating the cathode about an axis parallel to the linear path;
• an electrical power supply connected to the cathodic electrode, and connectible to a tubular work-piece disposed along the linear path and arranged so that the cathodic electrode can pass axially along the interior of the tubular work-piece, whereby the power supply can establish an electric current through the cathodic electrode and the work-piece, as the cathodic electrode passes along the interior of the work-piece;
• and
• a flow path for directing electrolyte past the cathodic electrode, between the cathodic electrode and the work-piece;
• wherein the flow path includes a space defined between a portion of the drive bar and the work-piece, behind the cathodic electrode as the cathodic electrode moves along the linear path;
• and
• including an electrical conductor, connected to the electrical power supply and exposed to the space, whereby an electric current is established, through electrolyte within the space, between the conductor and the work-piece;
• the space being sufficiently long, in the direction of the linear path, that the electric current established in the space can etch, and thereby roughen the finished interior surface of the work-piece after machining thereof by the cathodic electrode,
• wherein the cathodic electrode is maintained within the tubular work-piece for a sufficient duration of time to achieve the roughened finish of the interior surface of the work-piece.