TECHNICAL FIELD

The present invention relates to a welding method comprising providing a metal object intended to be welded at at least one weld region to at least one metal device.

BACKGROUND

It is a well known fact that when welding metal objects together, the weld joint can provide a structural weakness, for example in attracting stress concentrations, in the resulting assembled unit. Especially in gas turbine engines, for example where vanes are welded at their ends and extend through a gas flow channel, it is important to provide weld joints that are able to withstand structural stresses under extreme conditions, in particular high temperatures. At the same time, where the gas turbine engine is used for airplane propulsion purposes, it is of course important to keep weight of structural components, including weld joints, as low as possible.

SUMMARY OF THE INVENTION

It is an object of the invention to increase structural performance of welded metal parts.

It is an object of the invention to allow reduced weight of welded metal parts while the structural integrity thereof is retained or increased.

These objects are reached by a welding method comprising providing, a metal object intended to be welded at at least one weld region to at least one metal device, characterized in that it comprises providing by metal deposition at least one metal buildup element at the weld region, and thereafter welding the metal object to the metal device, at least a part of the metal buildup element forming at least a part of the weld joint.

As mentioned further below, the method is advantageously applied in production or repair of a gas turbine engines, for example where blades or vanes are welded to a metal device such as a structure or a structural portion in the form of an outer casing or a hub of an engine part, or where blades or vanes are welded to a metal device such as a base or a platform which mates with a recess in an outer casing or a hub. Providing the metal object intended to be welded can include producing the metal object in a number of alternative manners, as exemplified below, which metal object presents at least one designated weld region, i.e. a region of the metal object where the weld joint is to be formed when the object is welded to the metal device.

The metal buildup element is produced by metal deposition after the provision of the metal object, and is therefore provided by additional material. The metal buildup element serves as a reinforcement at the weld region. Thereby, more material is presented at the region of the intended weld joint, providing a wider welding joint compensating for any reduction in structural properties caused by the welding.

Since the weld reinforcements are produced separately by metal deposition, other steps in the production are independent of the reinforcement production. This means that the metal object itself can be produced in a manner providing a high structural integrity.

For example, in the case of blades for rotating parts or vanes for stationary parts for gas turbine engines, a less advantageous alternative to the invention is producing the blades or vanes by casting the blades or vanes, whereby the blades or vanes are designed so that they present a thicker portion at one or both of their ends, after which the blades or vanes are welded to a structural portion, such as an outer casing, of the engine part, whereby the thicker portion forms a part of the weld joint. A problem with such a solution, avoided by the invention, is that casting processes usually gives as a result that the material of the objects are structurally inferior than the material of objects produced in other manners, such as forging. Therefore, more material has to be used for objects produced by casting, which adds weight to the finished product, which is often a disadvantage, for example in the case of gas turbine engines for airplane propulsion applications.

Instead, with the invention, the metal object can be produced in a manner, for example involving forging, providing a higher structural integrity than that of casting. Another advantage with involving forging sheet metal in the provision of the metal object is that the dimensional tolerances thereof are better that in the case of casting. Such an improvement of the tolerances contributes to possibilities of reducing weight of the metal object. More generally, the provision of the metal object can advantageously include any suitable wroughting measure. In gas turbine engine applications, the material used for the metal object could be for example a suitable titanium, nickel, steel or aluminum alloy.

The metal deposition can be carried out by a variety of alternative processes, known in the art of metal deposition, and could involve building up a three dimensional geometry in metal by using a welding source, (weld build-up or weld deposition), including for example laser beam, electron beam, or gas tungsten arc welding (GTAW), (also known as tungsten inert gas (TIG) welding), at which the material could be fed in any suitable manner, for example in the form of a wire or powder. More specific metal deposition examples include laser cladding and direct laser forming. In gas turbine engine applications, the material fed could be for example a suitable titanium, nickel, steel or aluminum alloy.

Although weld deposition is known from EP 1260300 A2 for the production of vanes for gas turbine engines, it is not known to be used to overcome the problems mentioned above specifically arising at joining by welding. The welding of the metal object to the metal device can be done in a variety of manners known per se in the art of welding, and could involve for example laser beam, electron beam, or GTAW (TIG). Notwithstanding what has been mentioned above concerning advantages of forging being included in the provision of the metal object, within the scope of the invention, the metal object can be provided in a variety of manners. For example, as an alternative to forging at least one sheet metal workpiece, the step of providing the metal object can comprise a metal extrusion process for producing a plurality of metal objects with a constant cross-sectional shape, or even producing the metal object by casting. An advantage with involving a metal extrusion process is that it is a relatively simple and cheap manner of production, still providing good structural properties.

The metal object may be a hollow structure, and at least one of the at least one metal buildup element can be located on the outside of the metal object, or alternatively on the inside of the metal object. In some embodiments, the method comprises providing by metal deposition at least two metal buildup elements at the weld region, at least one of the metal buildup elements being located on the inside of the metal object, and at least one of the metal buildup elements being located on the outside of the metal object.

Advantageously, the metal object is a vane for a stationary part of a gas turbine engine. Such a stationary part would normally present a central axis and the vane could be adapted to extend at last partly radially in relation to the central axis. Thereby, the weld region could be located at an end of the vane forming an inner or an outer end of the vane in the stationary part. The metal device could be for example an inner portion or an outer portion of the stationary part. Alternatively, the metal device could a base or a platform which is intended to mate with a complementary recess in an inner portion or an outer portion of the stationary part. The inner and outer portion is herein also referred to as a hub and an outer casing, respectively. In alternative embodiments, the metal object is a blade for a rotatable part of a gas turbine engine, the weld region being located at an end of the blade forming an inner or an outer end of the blade in the rotatable part.

DESCRIPTION OF THE FIGURES

Below, the invention will be described in detail with reference to the drawings, in which

- fig. 1 shows a schematic perspective view of a metal object intended to be mounted on a metal device,

- fig. 2 shows a cross-sectional view of the metal object, with the section oriented along the line H-II in fig. 1,

- fig. 3 shows a cross-sectional view of the metal object, with the section oriented along the line IH-III in fig. 2, - fig. 4 shows a cross-sectional view corresponding to the one in fig, 3, after a further production stage of the metal object,

- fig. 5 shows a view corresponding to the one in fig. 1, of the metal object at the same stage in production as shown in fig. 4,

- fig. 6 shows a cross-sectional view corresponding to the one in fig. 4, after another production stage of the metal object,

- fig. 7 shows a cross-sectional view corresponding to the one in fig. 6, of the result of a further alternative embodiment of the invention,

- fig. 7a and 7b show side views of a metal plate with metal buildup elements in an alternative method of providing the result in fig. 7, - fig. 8 and fig. 9 show cross-sectional views corresponding to the one in fig. 6, of respective results of additional embodiments of the invention, and

- fig. 10 shows a view corresponding to the one in fig. 5, of the result of a yet another alternative embodiment of the invention. DETAILED DESCRIPTION

Fig. 1 shows a schematic perspective view of a metal object 1 in the form of a vane intended to be welded to a metal device in the form of a hub, herein also referred to as an inner portion, in the production of a stationary part of a gas turbine engine. Alternatively or in addition, the vane could be intended to be welded to a metal device in the form of an outer casing of the stationary part, the outer casing being herein also referred to as an outer portion. As can be seen in fig. 2, the vane is a hollow structure with an aerofoil shape. The vane is produced from two forged sheet metal pieces 2, 3, which have been joined by welding at the leading edge 4 and the trailing edge 5 of the resulting vane 1.

The vane 1 is to be welded to the hub at a weld region 6 (fig. 1 and fig. 3) at one end of the vane 1, which vane end will be the inner end of the vane when mounted in the stationary part of the gas turbine engine. The weld region 6 is formed by the end surface 6 at the inner end. As can be seen in fig. 4 and fig. 5, before welding, a metal buildup element 7 is provided on the weld region 6 by metal deposition. The metal buildup element 7 surrounds the inner end of the vane. As an alternative, a plurality of metal buildup elements 7 can be provided along the inner end of the vane 1.

As depicted in fig. 6, after the production of the metal buildup element 7, the vane is welded to the hub 8, so that the weld joint follows the entire inner end of the vane 1, and the metal buildup element 7 forms a part of the weld joint. As can be seen in fig. 6, the hub 8 presents a protruding portion 81 which is complementary to the inner portion of the vane 1.

Fig. 7 depicts an alternative embodiment of the invention, where two metal buildup elements 7 are located on the inside of the vane 1. This will eliminate the risk of the metal buildup elements 7 disturbing a gas flow in the gas turbine engine. The embodiment depicted in fig. 7, the metal buildup element 7 is provided before the two forged sheet metal pieces 2, 3 (fig. 2) are joined.

Fig. 7a and fig. 7b depicts steps in an alternative method of providing the metal buildup elements 7 as presented in fig. 7. As can be seen in fig. 7a ₅ before the single metal object 1, in the form of a flat metal plate, is forged to the form of a vane, the metal buildup elements 7 are provided at the weld region. Thereafter, the plate is forged so as to provide the form as depicted in fig. 7b, whereupon the ends of the forged plate is joined by welding to form the trailing edge 5 of the vane.

Fig. 8 depicts a further alternative of the invention, where a metal buildup element 7 is located on the inside of the vane 1, and a further metal buildup element 7 is located on the outside of the vane 1. This will reduce any tendency for deformation of the vane 1 as a result of the metal deposition. Similarly to the embodiment depicted in fig. 7, in the embodiment depicted in fig. 8, at least the inner metal buildup element 7 is provided before the two forged sheet metal pieces 2, 3 (fig. 2) are joined.

Fig. 9 depicts a yet another alternative of the invention, similar to the one described above with reference to fig. 1 - fig- 6, with the exception that the hub 8 does not present any protruding portion which is complementary to the inner portion of the vane 1.

Reference is made to fig. 10. As has been mentioned above, the invention is of course also applicable for the purpose of joining the outer end of the vane 1 to an outer casing, which outer end is the upper end in fig. 10. Thereby, similarly to what has been described above concerning the inner end of the vane 1, a metal buildup element 7 can be provided at the outer end of the vane 1 before welding the vane to the outer casing.