Abrasive flow machining process for a meridionally divided turbine housing, and a masking fixture used in said process
An abrasive flow machining process for a meridionally divided turbine housing for a turbocharger employs a fixture installed in the axial bore of the housing to force the abrasive medium to flow substantially 360° about the circumference of the volute, and to shield the portion of the divider of the turbine housing volute located proximate the turbine housing inlet.
1 . 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.
2 . The process of claim 1 , wherein the first portion of the second angular sector is adjacent the first angular sector.
3 . The process of claim 2 , wherein the first angular sector occupies between 30° and 60° of the circumference.
4 . The process of claim 2 , wherein the throttling step comprises producing a gradient of flow restriction within the first portion of the second angular sector with increasing circumferential distance from the first angular sector.
5 . The process of claim 4 , wherein throttling of the flow within the second portion of the second angular sector is uniform over the second portion, and wherein the fixture geometry produces the throttling.
6 . The process of claim 1 , wherein an axial width of each slot increases progressively in a circumferential direction over a first portion of the second angular sector and is uniform over a second portion thereof.
7 . The process of claim 6 , wherein the throttling behavior is defined by first and second axially spaced slots in the fixture, wherein the first and second slots are respectively aligned with the first and second scrolls of the turbine housing.
8 . The process of claim 6 , wherein the axial width of each slot begins to increase immediately adjacent an end of a blocking area.
9 . The process of claim 6 , wherein the axial width of each slot reaches a maximum at a circumferential location approximately opposite a blocking area.
10 . The process of claim 6 , wherein the axial width of each slot remains substantially constant over a remaining 180° of the second angular sector.
11 . The process of claim 1 , wherein the fixture comprises a surface that mates with a convex contour of a turbine housing shroud to establish a substantially gap-free engagement.
12 . The process of claim 1 , wherein the fixture includes an alignment marker, and the fixture is oriented during installation such that a blocking area begins at an end of a tongue defined between the inlet pipe and the volute.
13 . The process of claim 1 , wherein the slots extend circumferentially over an angular sector occupying between 300° and 330° of a circumference of the fixture.
14 . The process of claim 1 , wherein a blocking area of the fixture occupies between 30° and 60° of the circumference.
15 . The process of claim 1 , wherein the first slot is wider than the second slot.
16 . The process of claim 1 , wherein the first and second slots have equal axial slot widths.
17 . The process of claim 1 , wherein the fixture is inserted into the axial bore in a direction opposite to the direction of abrasive flow.