GB2109726A

GB2109726A - Producing a new edge on an airfoil blade for a gas turbine engine

Info

Publication number: GB2109726A
Application number: GB08231115A
Authority: GB
Inventors: Harold Maynard Sharon
Original assignee: United Technologies Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1981-11-16
Filing date: 1982-11-01
Publication date: 1983-06-08
Also published as: DE3241948C2; BR8206595A; DE3241948A1; FR2516417A1; JPS5890420A; MX159380A; JPH029504A; CA1214926A; FR2516417B1; GB2109726B

Abstract

In a process for the production of a new edge on the aerofoil edge of a gas turbine blade, one side face is cut using a first cutting tool (Fig. 3) to form the desired angle and thickness between opposed blade surfaces and then the leading edge of the blade is cut by a second cutting tool (Fig. 5) to provide an aerodynamically efficient blade contour. Two separate hand held tools are used in the forming process. <IMAGE>

Description

SPECIFICATION Apparatus and process for producing a new edge on an airfoil blade particularly the fan blade for a gas turbine engine This invention relates to cutting tools for reshaping the airfoil edge of a blade or vane particularly the fan blade for a yas turbine engine.

It has become well known that the fan efficiency is dependent to a great extent on the airfoil shape of the fan and particularly on the shape of the leading edge of the airfoil. Recent studies have indicated that a thinner and well rounded leading edge will significantly improve the fan performance and efficiency. Routinely this would be accomplished by reworking the fan in an overhaul shop or by returning the fan to the manufacturer for establishing a desired new configuration. It is desirable to form this leading edge without the need for returning the blade to the manufacturer for a complete reshaping.

Instead it is hoped that the leading edge can be reshaped in the field without any significant downtirne for the engine.

Also in the manufacture of new blades no two blades are precisely alike in shape and it is thus impossible to machine the leading edges of the blades to the precise dimensions and contours desired by cams or computer controlled machines.

They must be hand-crafted to the precision desired and suitable tools for hand forming this edge are needed. Such tools would also have use in refurbishing the blade after a period of use in which the normal wear and tear erosion spoils the shape of the leading edge.

A feature of the invention is a set of cutting tools with which to manually rework the edge of the blade to the desired new thinness and to establish an aerodynamically rounded contour for the edge. Limiting means are included in the cutting tools to ensure the reshaping of the edge to The desired contour within acceptable limits.

Another feature is the process by which the edge may be worked in two steps to produce the new thin contour desired.

Accorcling to the invention the edge of the blade or vane is cut to size by a two step process in which the first step involves cutting one side surface of the blade adjacent to the radius of the edge with a first cutting tool to establish the desired relation of the surface of the chord of the blade and to establish the desired blade thickness and the second step involves cutting the leading edge and a very short distance back on each side of the blade by using a second tool to create the desired radius or curvature at the edge and to establish the precise thickness desired for the blade closely adjacent to the leading edge. These tools may be carbide tool bits in suitable holders which ensure the proper cutting action with respect to the chord of the blade.

The foregoing and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of the preferred embodiments thereof as shown in the accompanying drawing.

Fig. 1 is a sectional view showing the original contour of the leading edge.

Fig. 2 is a sectional view as in Fig. 1 showing the new thinner contour after the completion of the cutting operation.

Fig. 3 is a side view of the first tool and holder used.

Fig. 4 is a plan view showing the location of the cutting tool in this holder.

Fig. 5 is a side view of the second tool holder.

Fig. 6 is a plan view showing the location of the cutting tool in the second holder.

Fig. 7 is an enlarged view of the desired edge after the first cutting operation.

Referring first to Fig. 1 the original leading edge is relatively thick and has a leading edge curvature 2 that blends with the opposite surfaces 4 and 6 of the blade adjacent to the leading edge. The leading edge thickness may be about 1.27 mm at the point 8 on the blade. A preferred leading edge contour is shown in Fig. 2 where the leading edge 2' has a curvature necessarily on a smaller radius, and the thickness between the opposite surfaces 4' and 6' at the point 8' is about 0.76 mm.

The present invention is directed to tools for reshaping the leading edge to such a contour as that of Figure 2 and to a process that makes it possible to do this shaping in the field.

To accomplish this the leading edge of the airfoil is worked on successively by two tools, the first one cutting only one surface of the blade adjacent to the leading edge and the second tool cutting the leading edge and either or both surfaces closely adjacent thereto. The first tool as shown in Fig. 3 has a handle 12 to the end of which is fastened a mounting block 14 in which is supported a carbide tool bit 1 6 having a cutting edge 18. A pin 20 is also supported in the block.

The pin and the cutting edge make an angle of about 1400 to the handle as shown and also make an angle of about 14" to one another in the mounting block. The cutting edge of the tool is parallel to the pin and also on the centerline of the pin as shown. Although the angle 140 is given for a particular tool it will be understood that this angle is in fact set to conform to the desired angle between the opposed fan blade surfaces adjacent the leading edge. This angle may vary depending upon the particular blade being operated on. One fan blade for example that has been treated by a device of this character had an angle of 14" between the opposed surfaces and thus the tool angle is set at 100 when viewed normal to the cutting face. The tool angle is less than the blade angle since the tool is used at an angle to the blade edge.At the upper end of the notch 22 formed between the tool bit and the pin is a second pin 24 substantially at right angle to the pin 20 and in a position to limit the edge of the fan blade as it enters the slot and is operated on by the tool. Set screw 34 retains the pin 24 in position.

The tool bit is removable by releasing a clamping screw 26 extending through a clamping block 28. This block has a recess 32 to accept the tool bit. In use the tool is held against the edge of the blade with the handle at an angle of about 5 to the edge. This allows the user to hold the handle without hitting his hands against the blade.

This in effect makes a cutting angle for the tool bit of about 1350 to the blade edge or about 450 to a perpendicular to this edge and this is enough to permit good cutting action on the side of the blade being cut and also to allow the tool to ride over portions of the blade edge that may be slightly thicker. The trailing pin 35 is in a position to engage the leading edge of the blade if the handle is raised to form too high an angle with the leading edge. This limits the cutting action to the desired angle. Cutting with this tool is continued until the leading edge is in contact with the pin 24 during cutting action on the entire length of the fan blade.

The result is a fan blade shape as shown in Fig. 7.

The edge of the blade is then further shaped by the second cutting tool. This tool is shown in Figs.

5 and 6 has a handle 40 to the end of which is attached a mounting block 42. This block has a coverplate 43 defining with the block a slot to receive therein a tool bit 44 which is clamped by bolts 47 acting against a set screw 46 to hold the plate against the tool bit. The block and plate have notches 48 therein to expose the cutting edge of the tool bit as shown. The mounting block in this arrangement is at about 1300 to the axis of the handle for the same purpose as in the first tool.

This tool is found to cut best at this angle.

The cutting tool bit in this case is differently shaped. It has a V notch 50 therein terminating in the curvature 52 desired for the edge of the blade.

The opposite sides 54 and 56 of the notch extending from the base curvature are formed as cutting surfaces for about two-thirds of the length of the notch to about the point 62 and the remainder of the sides are ground so as not to perform a cutting action but only to ride on the opposite sides of the blade to locate the tool bit proper!y with respect to the chord of the blade.

When the tool is in use it functions in the same manner as the first tool. The cutting edges produce the desired leading edge curvature 2' on the blade and the desired angle of the opposed blade surfaces 4' and 6' closely adjacent to the leading edge. The edges of the tool bit ride on the sides of the blade and assure the proper angular relation of the surfaces of the blade to each other and to the chord of the blade.

These tools are utilized in carrying out the process of the invention which essentially includes cutting back one side surface of the blade for a distance back from the leading edge to form the desired angle and thickness between the opposed blade surfaces and subsequently with the second tool cutting the leading edge itself to form the desired contour. It has been found that by practicing this process it is possible to reshape the blade so that it will have the desired curvature on the leading edge and the desired thickness of the blade adjacent to the leading edge that will provide significantly better performance of the blade in use.

Although the invention has been shown and described with respect to a preferred embodiment thereof, it should be understood by those skilled in the art that other various changes and omissions in the form and detail thereof may be made therein without departing from the scope of the invention.

Claims

1. Process for the formation of a thinner edge on a fan blade characterized by the steps of: cutting back one side surface of the blade a distance back from the leading edge to form the desired angle and thickness between the opposed blade surfaces and then; cutting the leading edge of the blade to form an aerodynamically efficient contour.

2. The process according to claim 1 characterized in that the second cutting operation is guided by a part of the blade surface cut by the first operation and by the opposed blade surface.

3. The process according to claim 1 characterized in that the first cutting operation cuts a surface wider from the leading edge than the second cutting operation.

4. The process according to claim 1 characterized in that the first cutting operation is performed by a cutter making the desired blade angle with a guide pin (20) that engages the blade surface opposite to the cutter.

5. The process according to claim 4, characterized in that the position of the blade between the pin (20) and cutter is limited by a stop (24) engaging with the edge (2) of the blade.

6. A cutting tool for use in producing a new leading edge angle on a blade in carrying out the process of claims 1-5 characterized in including: a mounting block (14), a handle (12) extending from said mounting block (14) a tool bit (16) secured in said block (14) and having an exposed cutting edge (18), a pin (20) in said block (14) forming a notch with said cutting edge and making the desired blade edge angle with the cutting edge (18) with the blade edge (2) positioned between said cutting edge (18) and pin (20), and means (24) adjacent the base of the notch for limiting the depth of movement of the blade edge (2) into said notch.

7. A cutting tool according to claim 6 characterized in that the block (14) has clamping means (26) for releasably holding the tool bit (16) in position.

8. A cutting tool according to clairn 6 characterized in that the limiting means is a second pin (24) at a substantial angle to the first pin (20) and located at the base of the notch.

9. A cutting tool according to claim 6 characterized in that the angle of the handle (12) with the mounting block (14) is such as to position the cutting edge (18) of the tool at an angle of about 135 to the blade edge (20).

10. A cutting tool for use in producing a new leading edge on a blade in carrying out the process of claims 1-5, characterized in including: a mounting block (42), a handle (40) extending from said mounting block (42), and a tool bit (44) secured in said block (42) and having an exposed cutting edge for engagement with the edge (2') of a fan blade, said block (42) being so positioned that the cutting edge of the tool bit (44) when the tool is in use makes an angle of about 1200 with the blade edge (21).

11. A cutting tool for use in producing a new leading edge contour on a blade in carrying out the process of claims 1-5 characterized in including: a mounting block (42), a handle (40) extending from said mounting block (42) and a tool bit (44) secured in said block (42) and having a V notch (50) therein contoured to the desired blade edge shape and the angle between the blade surfaces adjacent said edge, said bit (44) having noncutting surfaces thereon remote from the edge cutting portion of the notch to guide the tool bit (44) by contact with the opposed surfaces of the blade.

12. A cutting tool according to claim 11, characterized in that the non-cutting surfaces are at the outer ends of the V notch (50) and the cutting portions (54, 56) of the tool bit (44) extend approximately two-thirds of the length of the notch (50), on both sides thereof.