GB2132512A - Welded stator vane assemblies for turbomachines - Google Patents

Abstract

A method of manufacturing a welded stator vane assembly for a turbomachine. The method comprises the steps of providing radially spaced inner and outer slotted members 38, 40 and a plurality of vanes 14 each of which has end fittings 64, 66 at each end. The end fittings 64, 66 are slotted into the slots 48, 52 of the inner and outer members 38, 40 and the end fittings are welded to the members 38, 40. In effect, the slotted members 38, 40 define a plurality of "spacers" 70 between the slots 48, 52 interconnected by the metal of members 38, 40 that define the base of the slots 48, 52. Subsequently, this metal is machined away to expose the welds and leave two concentric rings interconnected by the vanes. The rings consist of alternately end fittings and "spacers". <IMAGE>

Description

SPECIFICATION Welded stator vane assemblies for turbomachines This invention relates to a method of manufacturing a welded stator vane assembly for turbomachines.

One known method of manufacturing such assemblies is to forge the aerofoil shaped stator vanes with integral platforms at the radially inner and outer ends of the vanes. These stator vanes are assembled in a jig to form an annular ring with adjacent platforms abutting each other. The platforms are welded together where they abut each other. Conventionally, the platforms are welded using focussed electron beams and each weld joint shrinks causing the whole assembly to shrink circumferentially and radially. Each weld shrinks by about the same amount (typically 0.006 ins. (0.15 mm) in a circumferential direction), therefore, in the past the incentive has been to reduce the number of welds as much as possible.

To cater for the shrinkage of the assembly, the jig is designed to allow individual vanes to move radially inwards. This requires a multiplicity of sliding clamps urged by springs radially inwards.

During use weld splatter and debris can cause the sliding parts of the jig to become jammed. This makes it difficult to build up the loose assembly of vanes in the jig both prior to, and during, clamping the vanes in the jig.

Assembling the loose vanes into the jig is very time consuming. It can take an experienced workman many hours to build up a complete set of individual vanes to produce an accurate loose assembly of vanes which, after welding, will shrink to exactly the correct size. Because the inner and outer circumferences of the complete assembly are dictated by the sum of the circumferential widths of all the platforms, the individual platforms have to be ground or machined to extremely close tolerances. Even so, the sum of all the tolerances make it difficult to construct a complete assembly to an accurate dimension without using specially sized platforms to adjust the size of the final assembly.As a consequence of this, the cost of manufacture is greatly increased because of the expense of machining to close tolerances, making specially sized components and the time spent matching and adjusting sets of stator vanes to produce a suitable assembly.

Another area of high cost is the individual cost of making each stator vane with integral inner and outer platforms. In order to arrive at the correct spacing of the stator vanes using the known method of welding the platforms together, it is usual to upset the ends of the vanes to produce wide platforms. This further adds to the cost of the forging.

An object of the present invention is to provide a method of manufacturing welded stator vane assemblies which is cheaper and simpler to assemble than that described above.

The invention as claimed enables one to produce a much cheaper initial forging for each vane because the end fixings can be very small in the circumferential direction and do not require upsetting. This can reduce the cost of individual forgings by as much as 30% or more. The overall size of the assembly is more readily determined by the diameters of the intermediate members and does not require lengthy matching and rebuilding of loose components. Providing all vanes are within a predetermined tolerance, then individual tolerances are accommodated during assembly and have less effect on the size of the assembly as a whole.

The final product of the method of the present invention reveals that at least twice the number of welds are carried out than with the present known method described above. As pointed out above, previously known disadvantages of shrinkage point strongly towards the need to reduce the number of welds. The present invention as claimed reverses this trend and exploits the fact that the common structure that interconnects the spacers serves the important functions during welding, firstly it locates accurately the spacers and determines the total shrinkage and secondly it acts as a filler of the welding joint to lessen the effects of shrinkage.

The present invention as claimed exploits a further advantage of interconnecting the spacers with a common structure and that is that it would be impossible to position accurately in space loose spacers and stator vanes without complicated jigs with sliding parts that could become jammed. All that is required in the method of the present invention is to allow the inner and outer members to rest on a flat surface during assembly of the loose components and then finally clamp them in position for welding.

The present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 illustrates schematically a plan view of a prior known jig for manufacturing welded stator vane assemblies in accordance with a known method.

Figure 2 illustrates schematically a crosssectional view along the line Il-li of Figure 1.

Figure 3 illustrates schematically a plan view of a jig for welding stator vane assemblies for gas turbine engines in accordance with the method of the present invention.

Figure 4 illustrates a cross-sectional view taken along line lV-lV of the jig of Figure 3.

Figure 5 illustrates an end view of one of the vanes of the stator vane assembly shown in Figures 3 and 4 looking in a direction along the slots, and, Figure 6 illustrates a side view of the vane of Figure 5.

To appreciate the complexity of welding in accordance with a prior known method, reference is made to Figures 1 and 2. In Figure 1 the prior known jig comprises a base plate 10, on which are mounted a plurality of radially movable clamping members 12. There is one clamping member 12 clamping member 12 is mounted on needle roller bearings 16 and is movable radially inwards by means of a cylindrical member 18 which pushes on the cams 20 of each clamping member 12. In this way the cylindrical member 18 pushes all of the members 12, in unison, in a radial inwards direction.

Each stator vane assembly comprises an aerofoil shaped vane 22 which has integral tip and root platforms 24, 26 extending circumferentially.

The vanes 14 are produced by forging and are machined to the final profile prior to putting them into the jig. The platforms 24, 26 of adjacent vanes are welded together by electron beams (shown schematically by the arrows A and B).

Impingement plates 28 are positioned each side of the vanes to prevent the electron beams damaging the stator vane assembly.

As the welding is effected, diametrically opposed vanes are welded in sequence so that the whole assembly shrinks in a controlled manner. It will be seen that with this known jib, as shown in Figures 1 and 2, there are many movable parts and needle roller bearings 16 which can become jammed (and often do) by weld materials and other debris falling down between the clamping members 12. Furthermore, the final size of the stator vane assembly is totally determined by the shrinkage of many loose parts urged radially inwards by the cylindrical member 18 and the cams 20. The jig is also very complex and expensive to manufacture and, in addition, the welds have to be dressed manually because the weld bead is exposed to the fluid flow annulus of the gas turbine engine.

In order to understand the method of welding according to the present invention, attention is drawn to Figures 3 to 6. Referring to Figure 3, it will be seen that the jig comprises a base plate 30 which has two concentric cylindrical flanges 32, 34 which define two coplanar abutment faces.

The stator vane assembly to be welded comprises two hollow cylindrical members 38, 40 which are located concentrically on the abutment faces 36, 37 by means of clamps and registers 42, 44 mounted on the base plate.

The outer cylindrical member 40 has a conical bore 46 which has slots 48 which extend along the length of the bore at an angle of about 1 50 to the axis. Similarly, the inner cylindrical member 38 has a conical outer surface 50 which faces toward, and converges with, a conical bore 46 of the outer member 40. The outer surface 50 of the inner member 38 is also provided with slots 52 which extend axially along the surface 50.

Referring in particular to Figures 5 and 6, it will be seen that the slots 48 and 52 are parallelsided, that is to say the circumferentially confronting surfaces 54, 56 of slots 48 and the circumferentially confronting surfaces 58, 60 of the slots 52 are parallel with each other. In addition, one of the circumferentially facing surfaces 54 on each slot 48 lies in the same radial plane as one of the surfaces 58 of each slot 52.

The widths of the slots 52 is slightly smaller than the width of the slot 48. Accordingly, each of the slots can be machined either by milling or broaching by indexing each member 38 or 40, as the case may be, to a suitable parallel-sided milling cutter or broach. The slots 48, 52 are machined at an angle of about 1 50 to the axis of the assembly.

Each stator vane to be welded comprises a vane 52 which is provided at each of its ends with an end fitting and are dimensioned to fit into the respective slots 48 or 52. It will be seen that the remaining metal that lies between each of the slots 48, 52 constitutes a spacer and that each of the spacers 68, 70 is connected together by a common structure, namely the material of the members 38, 40 defining the base of the slots 48, 52.

The dimensions of the slots 48, 52 and the end fittings 64, 66 and the machining tolerances are established in one plane at one end of the members 38 and 40 and to prevent the individual vanes becoming jammed at different positions axially in the members 38 and 40, the base of the slots 48, 52 are machined with a small taper relative to the faces of the end fittings 64, 66 that face towards the base of the slots. This taper is shown more particularly in Figure 6.

Referring once again to Figures 3 and 4, the stator vanes to be welded are dropped into each of the slots 48, 52 with the members 38, 40 held loosely by the clamps 42. When a complete assembly of vanes has been loaded into the slots, the clamps 42 hold the assembly in the jig loosely.

Spring clips 74 are used to urge each of the vanes 14 down against the abutment surfaces 36, 37.

With the assembly lightly clamped in the jig, electron beam welding is initiated.

Electron beam welding of each end fitting 64 to the member 40 is achieved by directing a focussed beam E of electrons at the bore 46 to effect a weld between the parallel faces of the end fittings and the sides of the slots. Similarly, welding of the end fittings 66 to the inner member 38 is achieved by directing a beam of focussed electrons at the surface 50 and effecting a weld between the end fittings 66 and the sides of the slots 52. During the welding step, shrinkage of the assembly is controlled by the dimensions of the slotted rings that are used to make up the inner and outer members 38, 40. The common structure linking the "spacers", that is to say the material of the inner and outer members 38. 40 that forms the base of the slots 48, 52, also acts as a filler and thereby tops up each weld join.

Although there are twice as many welds to effect compared to the assembly shown in Figures 1 and 2, it has been found that the shrinkage of the components 38, 40 can be more readily controlled.

The welded assembly at this stage of the method comprises a plurality of vanes welded into two slotted rings. The next step of the method is to machine away at least part of the common structure which links together the spacers so that the final assembly comprises two concentric rings each comprising alternately an end fitting 64, 66 and spacers 68, 70. By machining away the common structure, the welds are exposed so that one can examine whether full penetration of the weld has been achieved. This makes inspection far simpler. Subsequently, additional features such as for example additional flanges may be provided on the completed assembly after some common structure has been removed.

Referring to Figure 6, it will be seen that a small recess 80 has been provided in the inner and outer members 38, 40. It will be noted that each end fitting 64, 66 does not include such a recess. The reason for this is that when each vane 14 is loaded into the slots 48, 52, the end fittings 64, 66 define a discontinuity in the vicinity of this circumferential recess 80 so that automatic equipment may be used which is responsive to discontinuities in order to locate the region where the weld is to be effected and to lock the electron beam onto this region in order that the weld may be carried out automatically. This type of location of weld regions is well known and does not in itself form part of this invention.

In the above example the inner and outer members 38,40 are each machined from a unitary body and the "spacers" 70 are constituted by the metal of the members 38,40. However, whilst this is the preferred mode of construction, it is to be appreciated that it may be possible, with some designs of stator assembly, to provide separate spacers and to mount them on a common backing structure, for example, by spigots or adhesively fixing them. It is felt, however, that this latter mentioned mode of construction would not take advantage of the good points of the mode of construction to Figures 3 to 6.

The advantages gained by the present invention can be appreciated by comparing the simplicity of the jig of Figures 3 and 4 with the complexity of the jig of Figures 1 and 2. Bearing in mind that sixty or more stator vanes constitute a typical stator vane assembly, it will be appreciated that the machining tolerances, and assembly, is very much simplified compared with prior known methods of welding. Contrary to normal belief doubling the number of welds does not exacerbate the problems of shrinkage because the unitary members 38, 40 control the shrinkage.

The jig of Figures 3 and 4 is provided with cylindrical impingement blocks 81,82 to arrest the electron beam as it breaks through the stator vane assembly.

Claims (14)

1. A method of manufacturing a welded stator vane assembly comprising the steps of: (a) providing radially spaced inner and outer members, the outer member comprising a hollow body which comprises a plurality of spacers spaced circumferentially around an inward facing surface of a common structure that interconnects all the spacers in a fixed relationship with each other, and the inner member comprising a body which comprises a plurality of spacers spaced circumferentially around an outward facing surface of a common structure that interconnects all the spacers of the inner member in a fixed relationship with each other;; (b) providing a plurality of stator vanes each of which comprises a vane with a circumferentially extending end fixing at each end of the vane, one of the end fixings of each vane being shaped and dimensioned in a circumferential direction to fit between, and abut against, two spacers of the outer member and the other end fixing of each stator vane being shaped and dimensioned to fit between, and abut against, two spacers of the inner member; (c) inserting the vanes between the inner and outer members, each vane having an end fixing located between, and abutting against, two spacers of the outer member and an end fixing located between and abutting against two spacers of the inner member; (d) effecting welds between the end fitting and the spacers whilst allowing the inner and outer members to shrink circumferentially; and (e) removing at least part of the common structure that interconnects the spacers of the inner and outer members thereby to leave inner and outer rings consisting of, alternately, spacers and end fixings, interconnected by the vanes.

2. A method according to Claim 1 wherein the outer member comprises a unitary body with a circular cross-section bore and a plurality of circumferentially spaced recesses extending along the bore, and the said spacers are defined by the material of the member that is located circumferentially between the recesses.

3. A method according to Claim 1 or Claim 2 wherein the inner member comprises a unitary body with a circular cross-section outer profile and a plurality of circumferentially spaced recesses extending along the profile, and the said spacers are defined by the material of the member that is located circumferentially between the recesses.

4. A method according to any one of Claims 1 to 3 wherein the spacers and end fixings are shaped to define conical surfaces, and the conical surfaces converge to define an annular converging fluid flow passage across which the vanes extend.

5. A method according to Claim 2 or 3 wherein the mutually circumferentially confronting faces of each recess are substantially parallel to each other.

6. A method according to any one of Claims 2, 3 or 5 wherein each recess in the outer member faces a recess in the inner member, and one of the mutually circumferentially confronting surfaces of each recess in the outer member lies in the same plane as one of the mutually circumferentially confronting surfaces of a recess in the inner member.

7. A method according to Claim 6 wherein the said plane is a radial plane of the assembly.

8. A method according to any one of Claims 2, 3, 5, 6 or 7 wherein the recesses extend in a direction at an angle to the axis of the assembly.

for each stator vane 14 to be welded. Each

9. A method according to any one of Claims 2, 3, 5, 6, 7 or 8 wherein a tapered gap is formed between the base of each recess and the surface of the end fitting that faces the base of the recess.

10. A method according to any one of the preceding claims wherein the welding steps is carried out using focussed electron beams.

11. A method according to any one of the preceding claims wherein the common structure is removed by machining away the material interconnecting the spacers.

12. A method according to any one of the preceding claims further including the steps of providing a co-planar circumferential recess in a surface of the spacers prior to welding, thereby to form a discontinuity which forms an aid to locating the weld line during the welding step.

13. A method according to any one of the preceding claims further including the step of welding a ring to the final inner or outer member thereby to form a flange thereon.

14. A welded stator vane assembly for a turbomachine when made by the method according to any one of Claims 1 to 13.