GB2270644A - Apparatus for the electrochemical machining of components - Google Patents

Abstract

Apparatus for electrochemically machining a blade having cambered aerofoil surfaces includes at least one pair of electrodes 6, 7 each electrode having an operative surface which is the inverse of a finished surface of the blade, and structures for supporting each electrode. The apparatus further includes a pair of pivoted levers, 13, 14 for displacing the electrodes in opposite directions through a circumferential arc about an axis 15 and between operative and inoperative positions relative to the blade. A power-operated extendible ram 26 is coupled to the levers whereby each electrode may be displaced between the operative and inoperative positions. <IMAGE>

Description

APPARATUS FOR THE ELECTROCHEMICAL MACHINING OF COMPONENTS This invention relates to apparatus for the electro-chemical machining of components made of metal such as aerofoil shaped blades of the kind used in gas turbine engines.

The cambered surfaces of an aerofoil shaped blade such as a shrouded aerofoil of the kind used in the compressor and turbine stages of a gas turbine engine are difficult to machine by conventional metal cutting processes such as milling and grinding.

Electro-chemical machining provides a method for producing both surfaces-of such blades in a single operation and to a very high degree of accuracy and surface finish.

It is an object of the present invention to provide an improved apparatus for electro-chemical machining both surfaces of an aerofoil shaped blade, eg a shrouded aerofoil for a gas turbine engine, in a single operation.

Electro-chemical machining is a well-known form of metal removal and is basically an electro-plating process except that the metal that should adhere to the plate is not allowed to adhere to the workpiece but instead is carried away by the electrolyte. The basic action requires that a positive electrode (anode), provided by a workpiece, and a negative electrode (cathode) provided by a shaped tool, are separated by an electrolyte and are energised by low-voltage direct current. When the current flows electrons and ions move from the anode to the cathode. In the electro-chemical machining process the ion-rich electrolyte does not allow any of the removed metallic debris to attach itself to the cathode but carries it away. Thus, the charged particles leave the anode and pass through the electrolyte, whereupon the electrolyte forces the particles away.Erosion takes place at the anode until it is formed into the shape of the cathode with clean burr-free edges.

According to of the invention apparatus for electro-chemically machining a blade having cambered aerofoil surfaces includes: mounting means for mounting said blade, at least one pair of electrodes, each electrode having an operative surface which is the inverse of a finished surface of the blade, support means for supporting each said electrode, first displacement means for displacing said electrodes on said support means in opposite directions through a circumferential arc about an axis and between operative and inoperative positions relative to the blade, and second displacement means coupled to said first displacement means and acting along a plane extending through said axis and blade whereby each said electrode may be displaced between said operative and inoperative positions.

Preferably the second displacement means comprises a power-operated extendible ram.

At least one of said pair of electrodes may comprise a major electrode member and a plurality of minor electrodes mounted for movement relative to the major electrode member.

The invention will now be described by way of example only with reference to the accompanying diagrammatic drawing in which: Figure 1 shows, in line form, an apparatus for electro-chemically machining a blade having cambered aerofoil surfaces, Figure 2 illustrates a plan view of the blade and electrodes shown in Figure 1, Figure 3 illustrates a plan view of an alternative blade and electrode arrangement to that shown in Figure 2, and Figure 4 illustrates a side elevation of the apparatus shown in Figure 3.

Referring to Figure 1, a blank of a blade 1 to be provided with cambered aerofoil surfaces, in this case a shrouded aerofoil of a kind for use in a gas turbine engine, is shown as being mounted in jaws 2,2 of an electro-chemical machining apparatus indicated generally by the line 3.

It will be understood that the apparatus is of a form known in the art and is provided with the usual electrolyte fluid pumping system and electrical DC power source which enables the blade to be connected to a positive terminal and the electrodes to be connected to a negative terminal. The blade 1 is provided with shrouds or flanges 4,5 whereby the blade may be mounted with a number of similar blades so as to form an annular array in a gas turbine engine. As can be seen in Figure 2 a pair of electrodes 6,7 each provided with a surface having a mirror image of the required cambered aerofoil surface of the finished, machined blade 1 are located adjacent the blade and are screwed to support members 8,9 which are provided with flanges 11,12 whereby connection may be made with levers 13,14.These levers 13,14 are mounted for rotational movement about an axis 15, and act in the manner of clamps which open and close as required. Following conventional practice, each electrode is provided with a sleeve 16,17 of insulating material to prevent continued electro-chemical action between the electrode and the surfaces of the flanges 4,5 of the blade 1.

At a position along the length of each lever 13,14 is provision for pivotal connection to one end of a link 18,19, the other end of which is pivotable connected to the end of an arm 21,22 slidable in bearings 23,24 and extending from the face 25 of an extendible and contractible ram 26 forming part of the electro-chemical machining apparatus 3. As can be seen in Figure 1 downward movement of the ram 26 will draw downwardly both arms 21,22 together with their pivotal connections to links 18,19 thereby causing links 18,19 to pivot the levers 13,14 about axis 15 and so opening the electrodes 6,7 to positions 6a,7a out of place relative to the blade 1.

In operation, after placing a blade blank in positions in jaws 2 the ram 26 will be contracted and the electrodes 6,7 opened apart to enable a blade 1 which is to be finish machined to be secured in position in the jaws 2,2. The ram will then be extended to place the working surfaces of the electrodes 6,7 in close proximity to the blade 1 whereupon, the blade 1 and electrodes 6,7 are connected to the DC electrical power source after the electrolyte fluid pumping system has been started up. During the following machining operation the electrodes continue to move along the circumferential path to a position where the DC supply is automatically switched off. At this point the manufacture of the blade is complete and its concave and convex surfaces, leading and trailing edges, shrouds and fillet radii between the blade and shrouds are all machined to the required accuracy and finish.

It will be seen that the mechanism described provides a means of driving a pair of electrodes through a circumferential path into and out of engagement with the surfaces of an aerofoil shaped blade using a power source having a linear output, and this is of particular importance in the case of the manufacture of a shrouded aerofoil where the outer shroud would restrict movement of an electrode moving along a path normal to the surface of the blade. The apparatus may, however, be adapted to accommodate a wide range of aerofoil type components from short high pressure compressor vanes to long low pressure turbine rotor blades.

An alternative embodiment of the invention is shown in Figure 3 where a blade blank 1, having shrouds or flanges 4,5 and leading and trailing edges 31,32 is mounted in jaws (not shown) and multiple element electrodes 33,34 have been brought into working engagement with it. These electrodes comprise main elements 35,36 supporting pivot rods 37 on which are mounted eccentric cranked levers 38. Slidably mounted to the sides of the main elements 35,36 are four leading edge electrode blocks 39-42 and two trailing edge electrode blocks 43,44. The short arms of levers 38 are coupled to the blocks whilst their long arms are coupled to wedge section electrode blocks 45-48 which are of U-form in side elevation as can be seen in Figure 4.

The blocks 45,46 are associated with the leading edge of the blade blank whilst blocks 47,48 are associated with the trailing edge of the blade blank and they are spring-loaded to the positions shown in Figure 3.

In operation after placing the blade blank in position in the mounting jaws with the multiple element electrodes 33,34 opened apart, the electrodes are coupled to the DC power supply after the electrolyte fluid pumping system has been started up. The electrodes 33,34 are then advanced towards the blank and this movement continues until at a pre-determined distance from the surfaces of the blades the leading edge and trailing edge electrodes 39-44 are stopped.

The leading and trailing edges of the blank are thus brought to final finish. Further movement of the main electrode elements 35,36 will continue the machining of the side surfaces of the blank, and pivot rods 37, moving with the electrode elements 35,36 will cause the cranked levers 38 to pivot about rods 37 and press the wedge shaped electrode blocks 45-48 into further machining contact with the blank 1 thereby finish machining the radiussed root fillets between the blade 1 and the shrouds or flanges 4,5.

It will be understood that with suitable design a pair of multiple element electrodes can be used for the purpose of making very intricate blade shapes. Indeed, a combination of a single electrode and multiple element electrode may be employed as a pair of electrodes in some instances.

Claims (7)

1 Apparatus for electro-chemically machining a blade having cambered aerofoil surfaces including: mounting means for mounting said blade, at least one pair of electrodes, each electrode having an operative surface which is the inverse of a finished surface of the blade, support means for supporting each said electrode, first displacement means for displacing said electrodes on said support means in opposite directions through a circumferential arc about an axis and between operative and inoperative positions relative to the blade, and second displacement means coupled to said first displacement means and acting along a plane extending through said axis and blade whereby each said electrode may be displaced between said operative and inoperative positions.

2 Apparatus as claimed in claim 1 wherein said second displacement means comprises a power-operated extendible ram.

3 Apparatus as claimed in claims 1 or 2 wherein the blade having cambered aero-foil surfaces is a shrouded aerofoil for use in a gas turbine engine.

4 Apparatus as claimed in any preceding claim wherein the first displacement means comprise a pair of levers pivoted at their one ends for rotational movement about said axes.

5 Apparatus as claimed in any preceding claim wherein at least one of the electrodes comprises a major electrode member and a plurality of minor electrode members mounted for movement relative to the major electrode member.

6 Apparatus for electro-chemically machining a blade having cambered aerofoil surfaces as described herein with reference to Figures 1 and 2.

7 Apparatus for electro-chemically machining a blade having cambered aerofoil surfaces as described herein with reference to Figures 1, 3 and 4.