Plastic and nonmetallic article shaping or treating: processes – With severing – removing material from preform mechanically,... – Dividing work to form plural articles
Reexamination Certificate
1998-12-17
2001-01-23
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With severing, removing material from preform mechanically,...
Dividing work to form plural articles
C264S219000, C264S225000, C264S267000, C029S889700, C425S110000
Reexamination Certificate
active
06177038
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application relates to U.S. patent application Ser. No. 09/162,832, now U.S. Pat. No. 5,914,060, entitled “Method of Laser Drilling an Airfoil”, by Jeffrey D. Flis et al.; Ser. No. 09/162,614, now U.S. Pat. No. 5,928,534, entitled method for “Reducing Void Volumes in Cavities for Laser Drilling”, by Jeffrey D. Flis et al.; Ser. No. 09/213,591 entitled “Method and Material for Processing a Component for Laser Machining”, by Foster Philip Lamm et al.; Ser. No. 09/213,690 entitled “Method for Disposing a Laser Blocking Material on the Interior of an Airfoil”, by Gordon M. Reed et al.; Ser. No. 09/213,592 entitled “Tool for Disposing Laser Blocking Material in an Airfoil”, by Christopher P. Jordan et al.; and Ser. No. 09/213,593 entitled “Fixture for Disposing a Laser Blocking Material in an Airfoil”, by Gordon M. Reed et al.
DESCRIPTION
1. Technical Field
This invention relates to a method for positioning an airfoil during part of the process for laser machining an airfoil where the airfoil has internal passages for cooling air. More particularly, the method relates to positioning the airfoil during the step of disposing material in the passage for blocking a laser beam from striking the interior as a hole is drilled to the cavity through a wall of the airfoil and to a method of making a mask for positioning the airfoil.
2. Background of the Description
Airfoils for gas turbine engines are disposed in a flow path for working medium gases. Examples of such airfoils are turbine blades and turbine vanes. The airfoils are bathed in hot gases as the gases are flowed through the engine. Cooling air is flowed though passages on the interior of the airfoil under operative conditions to keep the temperature of the airfoil, such as a turbine vane or turbine blade, within acceptable limits.
In addition, the airfoil may have cooling air holes extending from the interior to the exterior of the airfoil. The cooling air holes are small and may have diameters that are in a range of eleven to seventeen mils (0.011-0.017 inches). The holes are drilled in predetermined patterns and are contoured to ensure adequate cooling of the airfoil.
The cooling air holes duct cooling air from passages on the interior of the airfoil through the hot walls to the exterior. The cooling air provides transpiration cooling as the air passes through the wall and, after the air is discharged from the airfoil, provides film cooling with a film of air on the exterior. The film of cooling air provides a barrier between the airfoil and the hot, working medium gasses.
One way to drill the holes uses a laser to direct a beam of coherent energy at the exterior of the airfoil. The intense radiation from the laser beam burns through the wall of the airfoil, leaving behind a hole which provides a satisfactory conduit for cooling air. As the laser beam penetrates through the airfoil wall into an interior cavity, the laser beam may strike adjacent structure on the other side of the cavity causing unacceptable damage to the airfoil. Accordingly, blocking material may be disposed in the cavity to block the laser beam from striking walls bounding the cavity after the beam penetrates through the airfoil wall.
One approach is to leave disposed within the airfoil the ceramic casting core around which the blade is poured during the manufacturing process. The ceramic core provides a suitable blocking material. The ceramic core is subsequently removed by well known leaching techniques. This approach is described in U.S. Pat. No. 5,222,617 entitled “Drilling Turbine Blades” issued to Gregore, Griffith and Stroud. However, the presence of the core after casting prevents initial inspection of the interior of the airfoil. The ceramic material may also be difficult to remove once the cooling air holes are drilled. In addition, the core is not available for use with the airfoil during repair processes which may require redrilling of the cooling air holes.
Another example of a blocking material is wax or a wax-like material. The material is melted so that it may easily flow into interior passages, such as the leading edge passage of the airfoil. The temperature of the molten material above its melting point, may exceed two hundred and fifty degrees Fahrenheit (250°). The molten material may be poured by hand or injected into the cavity or may even be sprayed or painted on the surface to be protected. However, the molten material may severely scald personnel working with the material. Moreover, the operation is time consuming if such material is poured by hand into the airfoil. In addition, the wax may extend between two closely adjacent cooling air holes. The wax adjacent the first hole, which blocks the laser beam as the second hole is drilled, may melt as the first hole is drilled by the laser beam. This causes a void to form in the wax. As a result, the energy from the laser beam at the second hole may not be sufficiently dissipated by the wax as it passes through the portion of the passage having the void. Damage may occur to the airfoil as the second hole is drilled because the beam, after it penetrates through the wall at the second hole, may strike the interior wall of the airfoil.
One wax-like blocking material which uses an additive to avoid forming voids is discussed in U.S. Pat. No. 5,049,722, issued to Corfe and Stroud, entitled “Laser Barrier Material And Method Of Laser Drilling.” In Corfe, a PTFE (polytetrafluoroethylene) wax-like material is disposed in a wax base. The PTFE helps avoid the formation of voids. Disposing such material on the interior of a leading edge passage is particularly difficult for some airfoils. Often the leading edge passage has no connection during fabrication with the is exterior of the airfoil. It is a blind or dead end passage prior to the drilling operation except for small impingement holes which place the passage in gas communication with an adjacent passage. The adjacent passage also has an opening for receiving cooling air which is flowed to the leading edge passage. Accordingly, personnel must carefully pour the molten material in the inlet opening and manipulate the airfoil to avoid bubbles in the material in the leading edge passage.
Still another approach is to use a masking agent, such as an epoxy resin, which is disposed in the airfoil in a fluid state. The epoxy resin is disposed in the airfoil by simply pouring the resin into the airfoil. The epoxy resin is at room temperature and poses no scalding hazard to personnel. The epoxy resin is further processed to harden the fluid and cause it to become a more solid material similar to the PTFE wax mentioned in U.S. Pat. No. 5, 049,722. However, the resin is relatively viscous compared to molten wax and has difficulty in flowing through small connecting passages on the interior of the airfoil.
It may be particularly difficult in some airfoils to dispose such material on the interior of a leading edge passage. Often the leading edge passage has no connection during fabrication with the exterior of the airfoil. It is a blind or dead end passage prior to the drilling operation except for small impingement holes which place the passage in gas communication with an adjacent passage. The adjacent passage also has an opening for receiving cooling air which is flowed to the leading edge passage. Accordingly, personnel must carefully pour the molten material in the inlet opening and manipulate the airfoil to avoid bubbles in the material in the leading edge passage and manipulate the airfoil to avoid the formation of voids. The material does have the advantage of being easily removed by heating the material to a temperature that vaporizes the material.
Another approach is to use a thixotropic medium that comprises materials for dispersing laser light. This approach is discussed in U.S. Pat. No. 4,873,414 issued to Ma and Pinder entitled “Laser Drilling of Components”. A particular advantage of this medium is that it emits light when contacted by the laser light. Monitoring the light reflected from the component
Boucher Kenneth M.
Dolan James F.
Funk Stanley J.
Jordan Christopher P.
Nehez, Sr. William A.
Fleischhauer Gene D.
Silbaugh Jan H.
Staicovici Stefan
United Technologies Corporation
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