Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
1998-05-11
2001-10-23
Young, Lee (Department: 3729)
Abrading
Abrading process
Utilizing fluent abradant
C451S036000, C451S559000
Reexamination Certificate
active
06306011
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a system to radius and smooth a microhole, such as a microhole in a fuel injection nozzle.
2. Description of Related Art
In many applications, such as fuel injector nozzle tips, carburetor jets, cooling air flow through turbine engine components, lubricating oil metering for precision bearings and the like, metering of flow rates is of very great importance. However, due to manufacturing artifacts, it is of great difficulty. Even minute variations in manufacturing tolerances can produce substantial variations in flow resistance and flow.
Parts having fluid flow orifices are made by a wide variety of casting and machining procedures. For example, high quality investment castings are frequently employed for the manufacture of such parts. Even the high quality parts will have variations in dimensions, particularly wall thicknesses attributable to slight core misalignments or core shifting, and other variations in surface conditions, including surface roughness, pits, nicks, gouges, blow holes, or positive metal. In the extreme case, a very slight crack in a core can lead to a thin wall projecting into an internal passage. All these artifacts will substantially impede fluid flow.
Commonly employed machining methods, such as conventional drilling, electrical discharge machining and even less usual techniques as laser, electron beam and electrochemical techniques are not sufficiently precise to avoid the generation of substantial variations in flow resistance. Probably, the most precise of these, electrical discharge machining, will not produce perfectly uniform flow resistance because non-uniform EDM conditions are inevitable and may produce variations in size, shape, surface finish and hole edge conditions.
Such deviations are necessarily tolerated within broad limits and the attendant compromises in design freedom, performance and efficiency are accepted as unavoidable. For example, the delivery of fuel charges to internal combustion engines by pressurized fuel injection requires metering of flow through injector nozzles. The more precisely the flow can be regulated, the greater the fuel efficiency and economy of the engine operation.
At present, the design of such fuel injector nozzles is often based on the measurement of the actual flow resistance. The nozzles are segregated into different ranges of flow parameters to provide at least approximate matching of components within a range of deviation from defined tolerances. The inventory requirements for the matching of components is quite substantial and therefore very costly. In addition, a substantial number of components must be rejected as out of allowable deviations and must be reworked at considerable expense or discarded.
With diesel fuel injector nozzles, it has been found desirable to radius the inlet side of the injector microholes in order to eliminate stress risers and pre-radius the upstream edge to minimize changes in emissions over the design life of the nozzle. Conventional abrasive flow machining can effectively produce radii on microholes, but fine control of the final injector flow rate has been impossible to achieve. The high, putty-like viscosity and highly elastic character of conventional abrasive flow media are too radically different from the characteristics of diesel fuel to permit either in-process gauging or adaptive control of this process. Furthermore, the very small quantity of abrasive flow media required to produce the desired radius limits process resolution.
Briefly, in abrasive flow machining (AFM) of microholes the flow rate of the material does not correlate well to the flow rate of the target liquid. Therefore, the actual calibration of a microhole is a step-by-step fine tuning process. After radiusing and smoothing the microhole with AFM, the target liquid or calibration liquid is tested in the microhole, the microhole is further worked and the target liquid or calibration liquid is again tested, etcetera, until the target liquid tests correctly.
The aforementioned problems were overcome to a considerable degree with the system disclosed in PCT Publication WO 97/05989. This publication discloses the use of a liquid abrasive slurry having rheological properties. When the flow rate of the slurry through the microholes of a nozzle reaches a predetermined flow rate, the process stops and the microholes are properly radiused and smoothed.
SUMMARY OF THE INVENTION
The present invention embodies a system to radius and smooth a microhole which is based upon a statistically meaningful correlation between the time a liquid abrasive slurry flows through a microhole and the increase in calibration fluid flow rate. When the abrasive liquid slurry reaches a predetermined target time the microhole is properly calibrated.
In the system of the invention, a microhole is preconditioned with a liquid abrasive slurry at a first station. The flow rate of a calibration fluid through the preconditioned microhole is measured at a second station. At a third station the liquid abrasive slurry flows through the microhole a predetermined time. This predetermined time, at the third station, is based upon the measured flow rate of the calibration fluid at the second station. The correlation between the target increase in calibration flow rate and the slurry flow time is based upon prior experience with substantially the same slurry/calibration fluid
ozzle/microholes. Subsequently, at a fourth station the flow rate of the calibration fluid through the microhole is measured and this determines whether or not the microholes have been properly calibrated. The liquid slurry flow stations may be the same station or separate stations and the calibration flow stations may be the same or separate stations.
In a preferred embodiment, workpieces having microholes to be radiused and smoothed are removably secured in fixtures. The fixtures are each secured in a nest. Each nest is secured in a platform. The platform indexes the workpieces through a plurality of treatment stations.
In a particularly preferred embodiment, the platform is a carousel which rotates in an indexed fashion. An upper base plate is positioned over the carousel. Reciprocating rams having feed nozzles for carrying fluids, such as pneumatic air, liquid abrasive slurry and calibration fluid are ganged in the upper base plate. A lower base plate is positioned under the carousel and supports tooling fixtures. When a ram, nest and tooling fixture are aligned a treatment station is defined. When a workpiece is moved (indexed) into registration with a ram, the ram moves with a feed nozzle engaging the workpiece
est and the nest moves and engages the tooling fixture. The fluid flows through the microholes in the workpiece and is discharged through the lower tooling fixture.
A programmable controller controls the movement of the carousel, the rams and the actuation of the feed nozzles.
The invention finds utility in the radiusing, polishing and smoothing of microholes in any workpiece, e.g. fuel injector nozzles, spinerettes. Although the preferred embodiment of the invention is described in reference to the radiusing and smoothing of microholes, it also includes the smoothing and polishing of non-circular apertures, i.e. rectangular slots, squares, elliptical configurations, etc. The square area of the non-circular apertures would typically be less than approximately 3 mm
2
.
Any relative motion between the workpieces and the rams is within the scope of the invention. The workpieces can travel on any linear or curvilinear path. The workpiece can be fixed and the rams move along paths both parallel (linear) to the workpieces and perpendicular (reciprocal) to the workpieces. Alternatively, the rams can be fixed and the workpieces move both parallel and perpendicular to the rams.
REFERENCES:
patent: 2310488 (1943-02-01), Guite
patent: 2365152 (1944-12-01), Stearman
patent: 3153882 (1964-10-01), Millhiser
patent: 3521412 (1970-07-01), McCarty
patent: 3634973 (1972-01-01), McCarty
patent: 3769
O'Shea Liam
Perry Winfield B.
Wright Mark
Dynetics Corporation
Samuels , Gauthier & Stevens, LLP
Trinh Minh
Young Lee
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