Abrasive flow machining process for a meridionally divided turbine housing, and a masking fixture used in said process

A process for treating a meridionally divided turbine housing, the turbine housing comprising an inlet pipe partitioned by a center wall into a first inlet conduit and a second inlet conduit for conducting two separate fluid streams into the turbine housing, a volute connected to the inlet pipe and extending from the inlet pipe circumferentially about a center axis of the turbine housing, an annular nozzle passage connected to the volute and extending radially inwardly therefrom with respect to the center axis, and an axial bore connected to the nozzle passage and extending axially to a discharge opening, the turbine housing further comprising a divider disposed within the volute so as to divide the volute into a first scroll and a second scroll, the first scroll being connected to the first inlet conduit and the second scroll being connected to the second inlet conduit, the process comprising the steps of:

• causing a medium comprising a pressurized abrasive fluid to flow in one direction between the inlet pipe and the discharge opening via the nozzle disposed therebetween;
• blocking a flow of the medium through the nozzle in a first angular sector that extends partially about a circumference of the turbine housing, the first angular sector being adjacent the inlet pipe, wherein a geometry of a fixture is configured to substantially prevent abrasive flow through said portion of the nozzle corresponding to the first angular sector;
• throttling the flow of the medium through the nozzle in a second angular sector that begins at a point adjacent the first angular sector and extends about a remainder of the circumference, wherein the throttling step comprises producing a circumferential gradient of flow restriction within the second angular sector such that the flow is restricted to a greater degree in a first portion of the second angular sector and is restricted to a lesser degree in a second portion thereof, and wherein the blocking and throttling steps are accomplished exclusively by the geometry of the fixture, which is installed in the axial bore or the turbine housing, the fixture comprising circumferentially non-uniform features configured to produce the blocking and throttling behavior as defined above, and
• wherein the fixture comprises a tubular side wall having a pair of axially spaced, circumferentially coextensive slots defining the throttling behavior.