US3384563A

US3384563A - Method of radiusing the edge of an aperture electrolytically

Info

Publication number: US3384563A
Application number: US473634A
Authority: US
Inventors: Taylor John
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1964-08-27
Filing date: 1965-07-21
Publication date: 1968-05-21
Anticipated expiration: 1985-05-21
Also published as: GB1025297A

Description

May 21, 1968 J. TAYLOR 3,

METHOD OF RADIUSING THE EDGE OF AN APERTURE ELEC'IROLY'IICALLY Filed July 21, 1965 2 Sheets-Sheet 1 liiv Inventor Attorneys May 21, 1968 .1. TAYLOR 3,384,563

METHOD OF RADIUSING THE EDGE OF AN APERTURE ELECTROLYTICALLY Filed July 21, 1965 2 Sheets-Sheet 2 3,384,563 METl-IUD OF RADIUSENG THE EDGE OF AN APERTURE ELECTROLYTICALLY John Taylor, Derby, England, assiguor to Rolls-Royce Limited, Derby, Derbyshire, England, a British company Filed .luly 21, 1965, Ser. No. 473,634 Claims priority, application Great Britain, Aug. 27, 1964, 35,239/ 64 6 Claims. (Cl. 204143) This invention concerns electrolytic machining and in particular a method of smoothing the sharp edge(s) of an aperture within a metal workpiece.

The invention is particularly applicable to the smoothing or radiusing of the sharp edge(s) which are left after machining lade roots on turbine or compressor rotor discs for gas turbine engines. If these edges are left sharp on such components they are liable to initiate cracks and thus cause breakdown of the engine. It has previously been proposed to radius these edges by means of an abrasive string used manually but such a method is expensive, time consuming and not particularly satisfactory.

According therefore to the present invention there is provided a method of smoothing the sharp edge(s) of an aperture within a metal workpiece comprising providing a nozzle-electrode assembly, the nozzle of which is the same shape as, but of somewhat larger internal dimensions than, said aperture, disposing said assembly adjacent said aperture, causing electrolyte to How continuously through said nozzle-electrode assembly and into said aperture such that it passes over the sharp edge(s) of said aperture, and making said workpiece electrically positive relative to said assembly whereby the sharp edge(s) of said aperture is or are removed by electrolytic action.

Thus it is possible to smooth or radius the sharp edges which are left after machining the blade roots on turbine or compressor rotor discs electrolytically and it has been found that this method is most suitable for this application.

Preferably the nozzle-electrode assembly comprises an outer tubular structure of electrically non-conductive material within which there is disposed an electrically conductive rod or plate which is made electrically negative with respect to said workpiece.

In a preferred method the electrolyte is caused to flow continuously whilst the workpiece and electrode are electrically biased relative to one another. This is most important if accurate results are to be obtained since, should the electrolyte fiow stagnate deep etching may occur at the points of stagnation and a smooth edge will not be obtained.

Preferred electrolytes are those containing sodium ions and thus solutions of sodium chloride, sodium sulphate or sodium nitrate may be used.

The invention is illustrated merely by way of example in the accompanying drawings, in which:

FIGURE 1 is a general view of apparatus which may be used in employing the method according to the present invention,

FIGURE 2 is a detailed side elevation of part of the apparatus shown in FIGURE 1,

FIGURE 3 is a sectional view on line 3-3 of FIG- URE 2,

FIGURE 4 is a sectional View on line 44 of FIG- URE 3, and

FIGURE 5 is a view similar to FIGURE 3 of an alternative form of nozzle-electrode assembly used in machining a gas turbine engine turbine rotor disc.

Referring to the drawings and particularly to FIG- URES 1 to 4 thereof there is shown a tank containing electrolyte 11. A work table 12 is disposed within "ice tank 10 and clamped thereon is an annular metal workpiece 13 having formed therein eight circular holes 14 having sharp edges which it is desired to smooth or radius.

Slidably mounted on the table 12 is a support 15 having a clamp 16 fixed thereto. Clamp 16 rigidly holds a tube 17 therein, the tube 17 communicating with and being fixed to an annular manifold 18. Projecting from and communicating with annular manifold 18 are eight tubular extensions 19 to the lower ends of which are attached electrically non-conductive tubular nozzles 20. Fixed within and connected to the tubular extensions 19 are metal electrodes 21. Set screws 22 threaded within apertures in the tubular extensions 19 make electrical contact with the electrodes 21. The electrically non-conductive nozzles 20, together with the metal electrodes 21, constitute nozzle-electrode assemblies.

As seen in FIGURES 1 and 2 the upper end of tube 17 has fixed thereto a flexible pipe which communicates with the outlet side of a pump 31. The inlet side of pump 31 communicates by a further flexible pipe 32 with the outlet from tank 10 from which it receives electrolyte. Pump 31 is driven by an electric motor 34 and, when in operation, pumps electrolyte continuously from the tank 10 through tube 17 and thus through tubular nozzles 20. Electrolyte which has flowed through nozzles 20 passes over table 12 and into the electrolyte 11 within tank 10 to be used again by recirculation.

To radius the sharp edges of holes 14, the nozzleelectrode assemblies constituted by tubular nozzles 20 and electrodes 21 are disposed closely adjacent the upper ends of holes 14, as clearly seen in the figures. It will be noted, particularly from FIGURES 3 and 4, that the internal dimension of each tubular nozzle 20 is somewhat larger than that of the hole 14 which it is desired to machine and it will also be noted that the shape of each tubular nozzle 20 is identical with that of each hole 14. The pump 31 is actuated by electric motor 34 and a continuous flow of electrolyte therefore fiows through tubular nozzles 20 and into apertures 14, the electrolyte being forced over the sharp edges of holes 14 due to the relative sizes and shapes of tubular nozzles 20 and holes 14. The workpiece 13 is made electrically positive with respect to electrodes 21, the electrodes 21 being made electrically negative by connecting electrical leads to the set screws 22. Electrolytic action takes place and the sharp edges of the apertures 14 over which the electrolyte flows are machined away by this electrolytic action, the sharp edges thereby being smoothed or radiused.

The method is particularly suitable for use in machining apertures within turbine rotor and compressor rotor discs of gas turbine engines and a modified electrode for use in such an arrangement is shown in FIGURE 5. In FIG- URE 5 there is shown a turbine disc which has been machined to provide a fir tree blade root 41 having an enlarged radially inner end 42. The aperture formed at the radially inner end 42 has sharp corners as a result of the machining process and these are liable to initiate cracks if left sharp. A generally elliptical tubular nozzleelectrode assembly 43 is provided as shown in FIGURE 5, the nozzle being of the same shape as but somewhat larger than the aperture formed at the radially inner end 42. As in the embodiment of FIGURES l to 4, the nozzle-electrode assembly comprises an electrically non-conductive outer tubular portion 44 and an inner electrode 45 which is made electrically negative with respect to the turbine rotor disc 40. The sharp edges of the aperture at the radially inner end 42 are now removed by electrolytic action in the manner described above with reference to FIGURES 1 to 4.

It will be appreciated that the arrangement described above may be employed in any location in which it is present invention it is imperative that the electrolyte fiow should not be allowed to stagnate since if this happens deep etching is liable to take place at the point of stagnation and the smoothing or radiusing operation is thereby hindered.

I claim: I

1. A method of smoothing the sharp edge of an aperture within a metal workpiece comprising providing a nozzle-electrode assembly, the nozzle of which is the same shape as, but of somewhat larger internal dimensions than, said aperture, disposing said assembly adjacent said aperture, causing electrolyte to flow continuously through said nozzle-electrode assembly and into said aperture such that it passes over the sharp edge of said aperture, and making'said workpiece electrically positive relative to said electrode whereby the sharp edge of said aperture is removed by electrolytic action.

2. A method of smoothing the sharp edge of an aperture within a metal workpiece comprising providing a nozzle-electrode assembly comprising an outer tubular nozzle structure of electrically non-conductive material and an electrically conductive electrode member disposed within said outer tubular nozzle structure, said nozzle being the same shape as, but of somewhat larger internal dimensions than, said aperture, disposing said assembly adjacent said aperture, causing electrolyte to flow continuously through said nozzle and into said aperture such that it passes over the sharp, edge of said aperture, and making said workpiece electrically positive relative to said electrode whereby the sharp edge of said aperture is removed by electrolytic action.

3. A method of smoothing the sharp edge of an aperture within a metal workpiece comprising providing a nozzle-electrode assembly, the nozzle of which is the same shape as, but of somewhat larger internal dimensions than, said aperture, disposing said assembly adjacent said aperture, causing electrolyte to flow continuously through said nozzle-electrode assembly and into said aperture such that it passes over the sharp edge of said aperture, and making said workpiece electrically positive relative to said electrode whereby the sharp edge of said aperture is removed by electrolytic action, said electrolyte flowing continuous ly whilst the workpiece and nozzle-electrode assembly are electrically biased relative to one another.

4. A method of smoothing the sharp edge of an aperture within a metal workpiece comprising providing a nozzle-electrode assembly, the nozzle of which is the same shape as, but of somewhat larger internal dimensions than, said aperture, disposing said assembly adjacent said aperture, causing electrolyte containing sodium ions to flow continuously through said nozzle-electrode assembly and into said aperture such that it passes overthe sharp edge of said aperture, and making said workpiece electrically positive relative to said electrode whereby the sharp edge of said aperture is removed by electrolytic action.

5. A method of smoothing the sharp edge of an aperture within. a metal workpiece comprising providing a nozzle-electrode assembly, the nozzle of which is the same shape as,'but of somewhat larger internal dimensions than, said aperture, disposing said assembly adjacent said aperture, selecting electrolyte from the class including sodium chloride, sodium sulphate and sodium nitrate solutions, causing the electrolyte to flow continuously through said nozzle-electrode assembly and into said aperture such that it passes over the sharp edge of said aperture, and making said workpiece electrically positive relative to said electrode whereby the sharp edge of said aperture is removed by electrolytic action.

6. A method of smoothing the sharp edge of an aperture within a gas turbine rotor disc comprising providing a nozzle-electrode assembly, the nozzle of which is the same shape as, but of somewhat larger internal dimensions than, said aperture, disposing said assembly adjacent said aperture, causing electrolyte to flow continuously through said nozzle-electrode assembly and into said aperture such that it passes over the sharp edge of said aperture, and making said workpiece electrically positive relative to said electrode whereby the sharp edge of said aperture is removed by electrolytic action.

References Cited UNITED STATES PATENTS 3,309,294 3/1967 Goodwin 204l43 FOREIGN PATENTS 703,838 2/1954 Great Britain.

ROBERT K. MIHALEK, Primary Examiner.

Claims

1. A METHOD OF SMOOTHING THE SHARP EDGE OF AN APERTURE WITHIN A METAL WORKPIECE COMPRISING PROVING A NOZZLE-ELECTRODE ASSEMBLY, THE NOZZLE OF WHICH IS THE SAME SHAPE AS, BUT OF SOMEWHAT LARGER INTERNAL DIMENSIONS THAN, SAID APERTURE, DISPOSING SAID ASSEMBLY ADJACENT SAID APERTURE, CAUSING ELECTROLYTE TO FLOW CONTINUOUS-