Complex hole shaping

1. A method for forming a complex hole through a wall of a structure, the complex hole having an outer portion having a larger cross-sectional area adjacent a first surface of the wall, the complex hole having a smaller cross-sectional area within the wall, and the complex hole having an inner portion extending between the smaller cross-sectional area and an inlet opening on a second surface of the wall, the method comprising:

automatically forming with an EDM process an entry hole in the wall extending from the first surface to a first location inside the wall;

thereafter automatically cutting the outer portion of the complex hole with an EDM process by cutting the outer portion in a direction moving from the first location inside the wall toward the first surface; and

thereafter, automatically forming the inner portion of the complex hole with an EDM process.

2. The method of claim 1 further comprising drilling the entry hole with an EDM tool having a cross-sectional area substantially equal to the smaller cross-sectional area.

3. The method of claim 2 further comprising drilling the entry hole with an EDM tool having a substantially circular cross-sectional area.

4. The method of claim 1 wherein the first location corresponds to a location of intersection of the outer portion with the inner portion.

5. The method of claim 4 further comprising advancing an EDM tool through the first surface and into the wall to the first location to form the entry hole.

6. The method of claim 5 further comprising:

retracting the EDM tool through an incremental displacement from the first location toward the first surface to a second location;

then moving the EDM tool in a direction substantially perpendicular to a longitudinal centerline of the tool along a first path corresponding to a desired shape of the outlet portion at the second location; and

iterating the above steps of retracting and then moving the EDM tool from the outer portion of the complex hole.

7. The method of claim 5 further comprising:

retracting the EDM tool from the first location toward the first surface to a second location;

then, moving the EDM tool along a first path corresponding to a desired shape of the outer portion at the second location;

next, retracting the EDM tool from the second location toward the first surface to a third location; and

thereafter, moving the EDM tool along a second path corresponding to a desired shape of the outer portion at the third location.

8. The method of claim 7 wherein the first path and the second path are in respective planes substantially perpendicular to a centerline of the EDM tool.

9. The method of claim 8 further comprising:

moving the EDM tool along the first path in a first direction; and

moving the EDM tool along the second path in an opposite direction.

10. The method of claim 9 wherein the complex hole has a centerline oblique to the first surface and the method further comprises:

while moving the EDM tool along the first path in the first direction, detecting the EDM tool exceeding a desired spacing with the wall;

terminating motion of the EDM tool along the first path in response to detecting the EDM tool exceeding the desired spacing; and

thereafter, initiating motion of the EDM tool along the second path.

11. The method of claim 10 further comprising:

detecting an open circuit condition while moving the EDM tool along the first path;

terminating motion of the EDM tool along the first path in response to detecting the open circuit condition; and

thereafter, initiating motion of the EDM tool along the second path.

12. The method of claim 2 wherein the EDM tool is a wire tool and the method further comprises rotating the EDM tool.

13. The method of claim 12 wherein the EDM tool is hollow and the method further comprises establishing a flow of dielectric through the EDM tool.

14. A method for forming a cooling hole through a wall of a structure, the cooling hole having a diffuser with an outlet of a larger cross-sectional area on a first surface of the wall, the diffuser tapering to a smaller cross-sectional area within the wall, and the cooling hole having a through-hole extending from the smaller cross-sectional area to a second surface of the wall, the method comprising:

first, drilling with an EDM tool an entry hole in the wall extending from the first surface to a location inside the wall;

then, automatically forming with the EDM tool the diffuser starting at the location inside the wall and moving toward the first surface; and

thereafter, forming with the EDM tool the through-hole.

15. The method of claim 14 further comprising forming with the EDM tool the through-hole having a constant cross-sectional area substantially equal to the smaller cross-sectional area.

16. The method of claim 15 further forming with the EDM tool the through-hole having a substantially circular cross-sectional area.

17. The method of claim 14 further comprising providing a rotating EDM wire tool as the EDM tool.

18. The method of claim 17 wherein the rotating EDM wire tool has an interior passage and the method further comprises providing a flow of dielectric through the interior passage of the rotating EDM wire tool.

19. A method of forming a cooling hole in an air-cooled component of a gas turbine engine, the component having a wall with an outer surface and an inner surface, the cooling hole having

a diffuser portion extending between an outlet opening having a larger cross-sectional area on the outer surface and a smaller cross-sectional area location inside the wall portion, and

an inlet portion extending between the smaller cross-sectional area location and an inlet opening on the inner surface, the method comprising:

drilling with an EDM tool an entry hole from the outer surface to the smaller cross-sectional area location;

then, forming the diffuser with the EDM tool by first removing material closer to the smaller cross-sectional area location and thereafter, removing material closer to the outlet opening on the outer surface, and

thereafter, removing with the EDM tool material between the smaller cross-sectional area location and the inlet opening to form the inlet portion.

20. The method of claim 19 further comprising providing a rotating EDM wire tool as the EDM tool.

21. The method of claim 20 wherein the rotating EDM wire tool has an interior passage and the method further comprises providing a flow of dielectric through the interior passage of the rotating EDM wire tool.