Patent ID: 9346108
Filing Date: 2016-05-24
CPC Classification: B23C,B23Q,Y10T

Claim Text:
1. A method for machining a helical bore of a two-lobe stator for a progressive cavity machine, said helical bore having a longitudinal axis, a desired profile along the longitudinal axis, a minor diameter, a major diameter, and a helically varying radial axis along said longitudinal axis defining a helix pitch, said profile being defined, at any axial position along said longitudinal axis, by the area swept by a circle of diameter equal to said minor diameter being translated along said radial axis by an equal displacement amount on either side of said longitudinal axis, said method comprising: a) providing a tubular stator body with a cylindrical bore centred on said longitudinal axis and having a diameter not less than said minor diameter, a first machining device, and a second machining device, each machining device sized to slidingly engage the stator body along said minor diameter; wherein the first machining device comprises a milling head coupled to an end of a shaft, the milling head mounting a rotary cutter arranged for rotation about a first axis transverse to said longitudinal axis by a drive mechanism; and wherein the second machining device comprises a cutting head coupled to an end of a shaft, the cutting head comprising a journal member for mounting a whirling cutter for rotation about a second axis substantially parallel to said longitudinal axis but radially offset therefrom by a selectively variable degree between a minimal and maximal separation of the second axis from the longitudinal axis; and wherein the shaft of the second machining device has an outer diameter that is substantially the same as the minor diameter of the bore, and wherein the whirling cutter is configured to cut to a diameter measured perpendicular to the second axis is substantially equal to the outer diameter of the shaft of the second machining device; b) driving the first machining device through the bore so that said rotary cutter follows a helical path with said helix pitch; c) milling a first helical groove along said helical path in the stator body during b); d) angularly offsetting the first axis of the rotary cutter of the first machining device with respect to the radial axis after c); e) driving the first machining device through the bore along said helical path after d); f) milling a second helical groove in the stator body during e); g) increasing a radial depth of cut of the rotary cutter of the first machining device and repeating b) thru f) without over cutting the desired profile; h) driving said second machining device through the bore so that the whirling cutter follows said helical path with the second axis of said whirling cutter intersecting said radial axis; i) milling the stator bore to a diameter equal to said minor diameter with a plurality of cutting elements extending from the cutting head; j) translating the cutting head along said radial axis by said displacement amount during h) or translating the cutting head along said radial axis by said displacement amount by incrementally indexing the whirling head prior to one or more repetitions of h).