Metal deforming – Process – Tube making or reshaping
Reexamination Certificate
2000-04-03
2001-07-31
Larson, Lowell A. (Department: 3725)
Metal deforming
Process
Tube making or reshaping
Reexamination Certificate
active
06266991
ABSTRACT:
BACKGROUND OF THE INVENTION
The fatigue lives of metal structures and machinery can be enhanced by a hole coldworking method which creates a beneficial compressive residual stress at hole edge. Such a method is especially usefull in the manufacturing of airframe structures. Several prior art methods are available to enhance fatigue lives of holes, for example, split sleeve method described in U.S. Pat. No. 3,566,662, seamless sleeve method described in U.S. Pat. No. 4,164,807, stress coining method described in U.S. Pat. No. 3,895,922, split mandrel method described in U.S. Pat. No. 4,665,732, shape memory effect sleeve method described in U.S. Pat. No. 4,433,567, and my recent invention described in U.S. Pat. No. 5,943,898 which utilizes a tubular seamless sleeve made of shape memory alloy having a superelasticity property. The disadvantages of the prior art of hole coldworking methods including split sleeve, split mandrel, stress coining, and seamless sleeve were discussed in my previous invention of U.S. Pat. No. 5,943,898. The split sleeve method is the common method currently used in the aerospace industry. The disadvantages of the prior art of split sleeve and split mandrel methods are associated with the creation of a ridge and shear discontinuity in the bore of a coldworked hole. The prior art of shape memory effect sleeve method requires to cool down a sleeve to cryogenic temperatures; therefore the method is impractical for the application to productions. All of the aforementioned disadvantages of the prior art of coldworking methods were eliminated by my previous invention of U.S. Pat. No. 5,943,898, which utilizes a tubular seamless sleeve made of shape memory alloys having a superelasticity property. However, shape memory alloys are much more expensive comparing with the other metals for airframe structures. Furthermore, hole coldworking is usually performed manually; there is a trend in the aerospace industry for the automation of hole coldworking to reduce labor cost and maintain consistent quality.
SUMMARY OF THE INVENTION
The present invention described herein is an improvement of my previous invention of U.S. Pat. No. 5,943,898. The improvement makes the expensive seamless sleeve made of shape memory alloys become reuseable for saving material cost, and become amiable to manufacturing automation for reducing labor cost and maintaining consistent quality.
A tubular seamless reusable sleeve coldworking method and apparatus utilizing shape memory alloys (abbreviated hereinafter as SMA in this document) having a superelasticity property is invented and described hereinafter to enhance the fatigue lives of holes. The tubular seamless SMA sleeve coldworking method eliminates the final reaming step of the prior art of split sleeve and split mandrel coldworking methods described in U.S. Pat. Nos. 3,566,662 and 4,665,732. In contrast to the prior art of seamless sleeve coldworking method described in U.S. Pat. No. 4,164,807, the diameter of the seamless SMA sleeve shrinks, owing to the superelasticity property of SMA, after hole expansion, to a size smaller than the diameter of the coldworked hole to ease the removal of the seamless SMA sleeve. Hence the present invention not only shortens manufacturing time to reduce labor cost, creates higher beneficial compressive residual stress at hole edge than the split sleeve and split mandrel method, but also reduces material cost via the reusable sleeve.
In general, the method of coldworking holes of this invention comprises the steps of assembling a pre-lubricated tubular seamless sleeve made of SMA having a superelasticity property and the associated parts to the coldworking mandrel pulling means, securing firmly said sleeve in the mandrel pulling means, pushing the mandrel forward through the sleeve, inserting the mandrel and sleeve into a hole to be coldworked in an associated workpiece, holding the sleeve in the hole while retracting the mandrel backward from the workpiece, thereby expanding the sleeve to contact with hole wall and thereby compressing the materials of the sleeve and the hole in a radial direction taken from the center axis of the hole, and removing the sleeve, whose diameter shrinks to a size sufficiently smaller than the coldworked hole, out of the coldworked hole. The apparatus uses a pre-lubricated tubular seamless sleeve made of SMA having a superelasticity property, a mandrel having a major and a minor diameter portions, an end-cap with rough surface, an adapting-spacer with rough surface complementary to the end-cap, and an extension tube. Said sleeve is reusable. Said adapting-spacer is an assembly consisting of a spacer with rough surface, a bearing, and an screw-threaded adapter.
It is therefore an object of the present invention to provide a hole coldworking method which eliminates the need for the final reaming of holes, thereby shortens manufacturing time and reduces labor cost, and thereby better improves fatigue life of holes than the prior art methods of coldworking.
It is a further object of the present invention to make the costly seamless SMA sleeve become reuseable to save material cost, and become amiable to manufacture automation for reducing labor cost and maintaining consistent quality.
REFERENCES:
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patent: 3895922 (1975-07-01), Phillips
patent: 3943748 (1976-03-01), King, Jr.
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patent: 4164807 (1979-08-01), King, Jr.
patent: 4423619 (1984-01-01), Champoux
patent: 4433567 (1984-02-01), Mead
patent: 4665732 (1987-05-01), Hogenhout
patent: 4956991 (1990-09-01), Noonan
patent: 5127254 (1992-07-01), Copple
patent: 5943898 (1999-08-01), Kuo
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