METHOD OF SURFACE TREATMENT FOR DOVETAIL IN GAS TURBINE ENGINE FAN BLADE

Abstract

A method of surface treating a dovetail in a blade includes the steps of providing a burnishing operation along circumferential sides of the dovetail. Next, shot peening is provided at axial ends of the dovetail. A fan blade made by the method is also claimed.

Description

BACKGROUND

This application relates to a surface treatment method for treating a dovetail in a blade.

Gas turbine engines are known, and typically have a fan delivering air to a compressor. From the compressor, the air passes downstream into a combustion section where it is mixed with fuel and burned. Products of that combustion pass downstream over turbine rotors which in turn drive the fan to rotate.

The fan may include a plurality of separate blades mounted into a rotor. The blades have an airfoil which moves the air, and a radially inner portion, known as a dovetail, which is received within a slot in the rotor.

The dovetail is subject to high stress during operation of the gas turbine engine. Thus, it presents challenges to a designer of a fan blade.

One method that has been proposed to address the stresses applied into the dovetail is to utilize a burnishing operation on the dovetail. A burnishing operation will induce stresses within the part. These induced stresses are residual compressive stresses that can be induced into the part to a desired depth. The induced stresses counter applied stresses during operation to result in an overall lower stress level.

The burnishing operation does provide good control over the level of induced stresses and the depth into the material. However, burnishing typically requires a somewhat flat surface, and thus, complex surfaces may not be candidates for burnishing.

Once a burnishing operation has been applied to a part, surfaces that have not been burnished may have increased stresses or other changes which may be undesirable.

SUMMARY

A method of surface treating a dovetail in a blade includes the steps of providing a burnishing operation along circumferential sides of the dovetail. Next, shot peening is provided at axial ends of the dovetail. A blade made by the method is also claimed.

These and other features of this application will be better understood from the following specification and drawings, the following of which is a brief description:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a fan blade.

FIG. 1B shows the fan blade mounted into a rotor.

FIG. 2 shows a first method step according to this invention.

FIG. 3 shows a subsequent step.

DETAILED DESCRIPTION

FIG. 1A shows a fan blade 20 having an airfoil 18 extending radially outwardly of a dovetail 24. The airfoil can be said to have a leading edge 21 and a trailing edge 22. The dovetail 24 has circumferential side surfaces 100, and axial ends 102 and 104. As can be appreciated from FIG. 1A, the axial ends 102 and 104 are not regular surfaces, but have complex curved shapes. The circumferential sides 100 have generally regular shapes along an axial length.

FIG. 1B shows the fan blade 20 mounted within a slot 17 in a rotor 16. As can be appreciated, the sides 100 receive a good deal of stress when the rotor 16 is rotating, as the rotational force is transmitted through the sides 100. The ends 102 and 104 do not receive the same forces. As shown, the circumferential sides 100 have a more regular surface than the ends 102 and 104.

In order to surface treat the fan blade dovetail to withstand such forces, a first surface treatment step, burnishing, is shown in FIG. 2. The term burnishing can be generally described as bringing a tool into contact to physically treat surfaces on a workpiece.

A burnishing operation with a burnishing tool, shown rather schematically at 50, has surfaces 104 brought into contact with the side surfaces 100. The burnishing tool 50 may provide low plasticity burnishing. One known low plasticity technique is disclosed in U.S. Pat. No. 6,415,486. Other burnishing operations can be used however.

As shown in FIG. 2, in a generic burnishing operation, the tool 50 is controlled with the computer numerical control (CNC) positioning control 56, and a pressure control 58. Broadly speaking, once the selected area 100 of the dovetail has been identified, a desired magnitude of compression from the tool surfaces 52 and a residual desired stress distribution are determined. The pressure is controlled against the surfaces to form zones of deformation having a deep layer of compressive stress. The pressure can be varied to achieve a desired residual stress distribution, and a magnitude of compression within the dovetail 24.

While burnishing works very well on the circumferential side surfaces 100, it is not as effective for the ends 102 and 104. Since the ends 102 and 104 have complex surfaces, they are not as easily treated with the burnishing technique. In addition, the burnishing of the sides 100 does result in undesirable stress distribution at the ends 102 and 104.

Thus, FIG. 3 shows a step subsequent to the FIG. 2 step. In FIG. 3, shot peening masks 62 are mounted to enclose the ends 102 and 104. Shot peening tool 60 delivers particles 64 against the ends 102 and 104. The shot peening process is shown somewhat schematically in FIG. 3, however, a worker of ordinary skill in the art would recognize how to provide shot peening to the surfaces 102 and 104.

After the two-step method is complete, the fan blade 20 has been surface treated at both of its ends 102/104, and the sides 100 of the dovetail such that it will provide effective operation in the challenging environment of the gas turbine engine.

In addition, as an initial optional step prior to the FIG. 2 step, the entire dovetail may be initially shot peened prior to the burnishing.

The blade as disclosed above is for use as a fan blade. It is believed the teachings of this application would have most success when utilized on blades that will exist in lower temperature portions of a gas turbine engine. However, it is possible that blades in higher temperature regions may also benefit from the methods. In addition, the methods may have application in blades having air foils and dovetails for use in applications other than gas turbine engines. Thus, while the invention might have most application in fan blades and lower pressure compressor sections, it may also have application in other locations.

Although an embodiment has been disclosed, a worker of ordinary skill in the art would recognize that certain modification would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims

1. A method of surface treating a dovetail in a blade comprises the steps of:

providing a burnishing operation along circumferential sides of said dovetail; and

then providing shot peening to axial ends of said dovetail.

2. The method as set forth in claim 1, wherein said burnishing operation is low plasticity burnishing.

3. The method as set forth in claim 2, wherein said burnishing technique includes a body which is brought into contact with the circumferential sides of said dovetail, said body being controlled by a position control and a pressure control to apply a desired stress distribution and compressive load within the dovetail along said circumferential sides.

4. The method as set forth in claim 1, wherein the entire dovetail is subject to a shot peening process prior to the burnishing operation.

5. The method as set forth in claim 1, wherein said axial ends are not regular surfaces, but have complex curved shapes

6. The method as set forth in claim 5, wherein said circumferential sides have a more regular shape.

7. The method as set forth in claim 1, wherein said blade is for use in a gas turbine engine.

8. The method as set forth in claim 7, wherein said blade is a fan blade.

9. A blade comprising:

an airfoil extending radially outwardly from a dovetail, the airfoil having a leading edge and a trailing edge; and

said dovetail having circumferential sides, and axial ends, with said circumferential sides being surface treated by a burnishing operation, and said axial ends being surface treated by shop peening; and

said axial ends having complex curved shapes, and said circumferential sides having generally regular shapes along an axial length.

10. The blade as set forth in claim 9, wherein said blade is for use in a gas turbine engine.

11. The blade as set forth in claim 10, wherein said blade is a fan blade.