Description Field of the invention

The present invention relates to the method used for welding the OGV Inner Ring, a component of the engines of the Airbus aircraft.

Background art

The OGV Inner Ring is a component of the engine mounted on the Airbus A350, A380, A320 and A318 aircraft. It is the stator in the Mount Ring, another component of the engine, located just behind the rotating bladed ring visible with the naked eye from outside. The latter ring is entirely made of Grade 5 Titanium (TiAl ₆ V ₄ ) and the vanes and the central ring are hand- welded to each other, using the same type of alloy by means of a manual full penetration TIG (141) welding process in mandatory inert gas chamber.

A fundamental part of the welding process is the assembly of the vanes on the central ring, which in turn consists of stubes, in a number matching the number of the vanes, specifically obtained by 5-axis turning to form the entire joint to be welded. Vanes and stubes have three slightly different shapes, for the purpose of correctly directing air. A stube and a vane constitute one of the joints to be welded, each characterized by a variable thickness in which the higher value is reached in the central section and decreases towards the ends, reaching the lowest value at the trailing edge. For a full penetration manual TIG (141) process on the thicknesses in question, it is necessary to caulk stubes and vanes creating a double V shaped joint with 30° inclination with the parts (stubes and vanes) distanced, when possible, by 1 mm. The entire process starts with the due checks of the central ring, the check of the dimensions, the classification of the vanes, the due washings with precise drying, penetrating liquids and visual inspections to ascertain the absence of surface defects. Once this is done, the central ring is fastened in a fixture fixed in a common positioner.

The fixture where the entire OGV Inner Ring is fastened and processed is a circular carpentry structure which must assure, with the aid of the welder's skills, a finished product that is dimensionally correct within the set tolerances; this is a critical operation, given the plastic deformation of GR5 Titanium. With reference to the positions of the vanes, adjustable pins exist which serve both as fixing devices and as reference points for the final check that is carried out before extracting the welded piece from the fixture.

The currently used method comprises assembling the vanes one by one by Tack Welding in the leading edge and in the trailing edge, followed by the complete welding of each individual vane before moving on to the next one.

Essential for the perfect success of the welding operation are the manual melting techniques, the rigorous treatment of Gr5 Titanium fillers, the perfect construction of the pure Argon inert gas chamber on the entire joint to be welded and, consequently, on the parts that may suffer from thermal alterations, very frequent in this metal alloy. The instruments necessary for an acceptable weld are: pure Argon diffusers or, in other types of situations, Argon Helium diffusers, connected to the related system; TIG torch connected to the welder; Amperage control pedal and welding wire made of the same Gr5 Titanium alloy.

The Argon inert gas chamber is generated by a pair of small diffusers provided with housings for leading edge and trailing edge, mutually connected by a metal spring. The TIG torch used is provided with gas-Lens with #7 ceramic nozzle, tungsten 0 2.4 WL 1% with 30° angle, flexible collet body, all connected to a welding machine with Amperage control pedal that contemplates up to 70 Ampere with indefinite pre-gas and post-gas and indefinite pressure of the diffusion connected in the opposite part. As a diffusion system, a 16-bottle box is used, equal to 1 mc of 5.0 pure Argon gas, connected to a 4-outlet unit (one 10 1/m outlet and three 50 1/m outlets). As welding wire, 0 1.6 and 0 2.4 Ti Al ₆ V ₄ certified wire is used, without any particular treatment after opening the original package.

With the method used, it is difficult to add material manually, so the operator is forced to employ Tack Welding and melting, not assuring the right mechanical and metallographic quality. Moreover, metal spring diffusers are unable to give the proper stube - vane fastening and alignment, so the welder only has one free hand and can use only the TIG torch.

Once this operation is finished, the quality of the points and the proper stube - vane alignment are checked, and the welding phase is carried out. The welding phase requires creating a sterile chamber, obtained using diffusing shoes of Titanium and Nickel alloy consisting of a sort of pincer that envelops the entire length of the joint to be welded both from the convex part and from the concave part. These diffusers have 3 inlets that operate at different pressures according to the position and the system is made of (food quality) PVC pipes 0 6 mm. This diffusion system provides filler material and gas diffusion that are not correct to assure the perfect quality of melting.

The melting operation is carried out in the following runs:

• Concave portion - trailing edge: 3 long runs by ¼ of the total length;

• Concave portion - leading edge: 2 long runs by ¾ of the total length;

· Convex portion - trailing edge: 3 long runs by ½ of the total length;

• Convex portion - leading edge: 4 long runs by ½ of the total length;

• Concave portion - leading edge: 2 long runs by ¾ of the total length.

After completing the first through the fifth run with two welding wires with different diameters, it is necessary to suspend the welding activity, detach the diffuser pincer, shut off the gas system and start grinding until reaching the root of the run number 1 and number 4 (respectively trailing edge and leading edge). The operation is fully manual and its function is to remove the unmelted base metal belonging to the joint and concurrently to re-calk the joint. Once this is done, polluted burrs and chips are checked and the other welding runs can be carried out. Once the concave part is finished, the operator proceeds with the convex part, repositioning all equipment. At the completion of the weld of each individual vane, the position is checked according to the reference pin positioned on the assembly fixture. It is necessary to consider as the correct position of the vanes a tolerance equal to +/- 5 mm on the axis Y and +/- 1 mm on the axis X. The calculation is made from the center of the vane "boss" hole to pin center. "Bosses" are parts of the vanes, created both for fastening in the fixture and for the final fastening of the entire OGV Inner Ring in the mount ring. The operations listed hitherto yield the following result excluding the radiographic examination:

- Amber - purple colored contaminations;

- Significant deformation, beyond the prescribed tolerance, of the positions of the vanes, especially in the convex part;

- Considerable alteration at all welds in the inner circumference of the entire OGV Inner Ring, a nearly black color being visible even with the naked eye over the whole surface;

- The weld requires, excluding repairs, a time exceeding three working weeks. The process used hitherto addresses the problem of color by restoring it by grinding and removing it with all base material.

The problem of the Y axis deformations is addressed as follows:

- If the vane is out of tolerance in + Y, a run undefined in the process is carried out, in the median section of the convex part of the welded joint with DC pulse current until the entire vane is within tolerance,

- If the vane is out of tolerance in - Y, the same incomplete operation is carried out in the concave part.

At the end of the welding work, the figure that is still out of tolerance is - Y, so the welder almost always has to make continuous re-melts in the concave part.

The problem of the Y axis deformations is addressed as follows: - If the vane is out of tolerance in + X, a run of approximately 50 mm, which ends in the trailing edge, is carried out,

- If the vane is out of tolerance in - X, a run of approximately 50 mm, which ends in the leading edge, is carried out,

The considerable alterations, that are already noted visually, are confirmed after inspection with numerous porosities, cavities and unmelted material within the weld. All that which is out of tolerance is repaired by removing the defective region and filling it again with the welding process until an acceptable result is obtained. The inner surface of the OGV Inner Ring is ground by hand with appropriate abrasives until obtaining a silver colored surface which, however, will be inaccurate given the removal of base material. This operation requires approximately 10 / 12 hours of work.

The problems deriving from this type of process are numerous: first of all, the acceptable machining allowance to assure a perfect weld is not specified, in the second place the change of the geometry of the joint is noted, its color has amber - purple - black contaminations, change in the position of the vanes beyond the prescribed tolerances, high noise level of the process, very high vibrations, sparks, alterations and deformations of the metal, high costs and very long working times (exceeding three working weeks) excluding repairs.

The purpose of the present invention is to propose a new welding method that uses modified instruments with respect to those currently in use, to obtain a product with perfect mechanical, metallographic and visible characteristics (unaltered silver color), with minimal energy and material consumption and markedly reducing processing times.

Description of the invention

According to the present invention, a welding system for OGV Inner Ring is obtained which provides a final product free of imperfections of every kind, manufactured through a method that markedly reduce processing times.

The stubes 2 are the aerodynamic housings obtained by 5-axis turning, whose purpose is to cause the weld to move away from the surface of the central ring 1 and hence to have less deformation, given the low thickness of the central ring 1.

The vanes 3 are the vanes to be welded to the stubes 2.

The term "TIG" is the acronym of Tungsten Inert Gas, the universal term that defines the type of weld.

Tack welding is a type of welding by points which serves as a preparatory step for the actual welding, to make it possible to control the exact position of the joint to be welded.

Advantageously, said welding method for OGV Inner Rings comprises the steps of positioning A, cleaning the welding wires B, tack welding C and welding D.

Advantageously, said positioning step A is carried out in the classification of each vane 3 at the related stube 2 positioned on the central ring 1. The most advantageous between stube 2 and vane 3 to obtain the joint is 2 mm.

Advantageously, said step of cleaning the welding wires B consists of washing said welding wires 6 in the dedicated cleaning apparatus 7 filled with cleaning liquid, preferably Multisolve MS 38, for 24 hours leaving the identifying label outside. Subsequently, the wires are extracted from the cleaning apparatus 7 and dried with paper towel and the welding wires 6 are positioned in the sterilization apparatus 8 awaiting their use.

Advantageously, said sterilization apparatus 8 is filled with pure Argon to avoid any contamination of the welding wires 6.

Advantageously, said tack welding step C has the purpose of fixing the position of all vanes 3 with respect to the stubes 2 and it is carried out with maximum Amperage of 60° via foot pedal.

Advantageously, said welding step D is carried out with maximum Amperage of 150° through the following successive runs: • concave part, trailing edge 3.b, 1 long run by 1/5 of the total length; leading edge 3. a, 1 long run by 4/5 of the total length,

• convex part, trailing edge 3.b, 3 long runs by ½ of the total length; leading edge 3. a, 4 long runs by ½ of the total length,

· concave part, trailing edge 3.b, 2 long runs by 1/5 of the total length; leading edge 3. a, 3 long runs by 4/5 of the total length.

Advantageously, the central ring 1 consists of a bladed ring made of Gr5 Titanium forged by five-axis turning and provided with a plurality of stubes 2.

Said stubes 2 are advantageously V calked with an angle of 10° to reduce the welding volume.

Advantageously, the vanes 3 are in a number matching said stubes 2 and, together, they constitute the welding joints.

Advantageously, said vanes 3 are characterized by V calking with an angle of 30°.

Advantageously, the air is correctly directed inside the motor in that there are at least three different types of stubes 2, corresponding to at least three different types of vanes 3, which form three differently shaped joints on said central ring 1.

Advantageously, it is possible to obtain the joint called "butt-joint" if each vane 3 is characterized by the end to be welded with V-shaped profile inclined by 10° while each stube 2 has vertical profile.

Advantageously, said welding technology for OGV Inner Ring is characterized by the presence of a control unit 10 for the emission of the Argon gas provided with at least six outlets lO.a, each connected to a gas supply hose connected to a different welding instrument.

Another advantage provided by the control unit 10 is the possibility of regulating the outlet pressure of the gas independently for each outlet lO.a because of the presence of a regulator lO.b and of a flow rate gauge lO.c for each outlet lO.a.

Advantageously, said welding technology is characterized by the presence of a positioning tool 4 consisting of a jaw-type gun with adjustable pressure fork, provided with a stainless steel 316L argon diffuser 4.a which serves to allow the positioning A and tack weld C operation.

Advantageously, said Argon diffuser 4.a is connected to said control unit 10 for gas emission via a screened polycarbonate hose 4.c connected to a stainless steel 316L supply nozzle 4.b.

Advantageously, all points of contacts between said positioning tool 4 and the elements to be welded have been modified by 316L stainless steel TIG welding in order to avoid any contamination.

Advantageously, the inner walls of the diffuser 4.a, belonging to the positioning tool 4, are provided with a highly porous wire mesh (4.d) which assures the atomized diffusion of the Argon gas.

Another advantage of said welding technology for OGV Inner Ring is characterized in that the welding operation D takes place thanks to the TIG torch 5 modified with 8 Gas-Lens 5. a and Tungsten 5.b with a diameter of 3.2 mm and 2% percentage of lanthanum WL.

Advantageously, said tungsten 5.b is characterized by one V-shaped end with 15° lowered by a few tenths at the top, to obtain better welding precision.

Advantageously, said TIG torch 5 is also provided with trailing shield diffuser 5.c with ceramic nozzle 5.d, connected to the control unit 10 for emission of the Argon gas through a hose 5.e.

Advantageously, said trailing shield diffuser 5.c consists of a 316L Stainless Steel tube with a diameter of 20 mm sectioned at half the circumference and its provided with a wire mesh 5.f having dimensions equal to the length of the tube, which serves to homogenize the distribution of the Argon gas.

Advantageously, the welding D is carried out using welding wires 6, made of Gr5 Titanium with at least three different diameters, preferably 1.6 mm, 2 mm and 2.4 mm.

Advantageously, said welding wires 6 are preventively kept within a cleaning apparatus 7 immersed for at least 24 in a dedicated liquid solution with cleaning function.

Advantageously, said cleaning apparatus 7 consists of a system of at least three vertical tubes in which the welding wires 6 are kept for at least 24 hours leaving the identifying label of the wire outside the cleaning liquid to avoid detachment and have non conformities in the course of qualitative inspections.

Advantageously, each tube of said cleaning apparatus 7 is provided with a 316L stainless steel cap 7. a which prevents the cleaning liquid from escaping, each tube is also connected to a tap 7.b from which the cleaning liquid comes and from which it is discharged every three washes to assure its quality.

Advantageously, said welding wires 6, are kept until their use in a sterilization apparatus 8 able to maintain them in a sterile environment of pure Argon.

Advantageously, said sterilization apparatus 8 consists of a system of at least three vertical tubes each provided with an airtight cap 8. a and connected to a valve 8.b for the inlet of pure Argon gas.

Advantageously, said welding technology for OGV Inner Ring is characterized in that it is provided with an argon gas diffuser 9 positioned in the inner surface of said central ring 1 at each stube 2, adapted to supply pure argon by the entire length of the joint during the welding step D.

Advantageously, said diffuser 9 is provided with a plurality of holes 9.b of increasing diameter and it is connected to the argon gas emission control unit 10 through a hose 9.a.

Advantageously, said welding method for OGV Inner Ring consists of a process which brings production times to a maximum of 7 working days. Another advantage offered by the present method consists of the fact that the work does not present the need for removals and re-melting due to the poor quality of the weld.

Advantageously, the system of hoses that supplies the Argon gas from the control unit 10 to the diffusion apparatuses, has optimal operation guaranteed for 6 months, upon the elapsing of which it is advisable to replace said hoses with other, new ones. Advantageously, said welding method is applicable to all the Airbus engines that have an OGV Inner Ring to be welded. Description of the figures

The invention shall be described below in at least one preferred embodiment by way of non-limiting explanation with the aid of the accompanying figures, in which:

- FIGURE 1 shows the welded OGV Inner Ring, in which the central ring 1 is seen with the stubes 2 and the corresponding vanes 3; on each joint is present, as indicated, a leading edge 3. a of the air and a trailing edge 3.b of the air.

- FIGURE 2 shows the positioning tool 4 consisting of a jaw-type gun with adjustable pressure fork, provided with the gas diffuser (4. a) modified with wire mesh 4.d, provided with supply nozzle 4.b connected to a hose 4.c.

- FIGURE 3 shows the lateral view of the trailing shield diffuser 5.c belonging to the TIG 5 torch: the supply hose 5.e provided with ceramic nozzle 5.d can be seen, as can the wire mesh 5.f for the atomized diffusion of the gas.

- FIGURE 4 shows the three orthogonal views of the cleaning apparatus 7: FIGURE 4A is the top view, FIGURE 4B is the front view and FIGURE 4C is the lateral view; shown are the three vertical tubes 7.c with the corresponding caps 7. a, under the bearing plane of the vertical tubes 7.c can be seen the tap 7.b through which the liquid cleaning solution is injected and discharged.

- FIGURE 5 shows the three orthogonal views of the sterilization apparatus 8: FIGURE 5A is the top view, FIGURE 5B is the front view and FIGURE 5C is the lateral view; the three vertical tubes 8.c are shown with the corresponding caps 8.a with silicone gaskets, the valve 8.b for the inlet of the gas in the tubes 8.c is shown laterally.

- FIGURE 6 shows a lateral view of the diffuser 9 with the gas supply hose 9. a and with the holes 9.b of increasing diameter positioned over the entire length of the diffuser.

- FIGURE 7 shows a diagram of the control unit 10 for the diffusion of the Argon gas illustrating the six outlets lO.a into which the hoses that will transmit the gas to the apparatuses will be connected; the pressure of the gas for each outlet is managed by the respective six regulators lO.b and it is indicated in the dedicated six flow rate gauges.

Detailed description of the invention

With reference to FIG. 1, the OGV Inner Ring is shown at the end of the welding process described by the present invention; the central ring 1 made of Gr5 Titanium forged by five-axis turning is shown, whereon the different stubes 2 that constitute one of the two elements of the welding joint were preventively created. The second element that constitutes said joint are the vanes 3, obviously present in the same number as the stubes 2. For each OGV Inner Ring, there are at least 3 different types of stubes 2 and vanes 3 so that it is possible to obtain differently shaped joints to direct the air exactly to the desired point. For this purpose, before each welding operation, each vane 3 must be classified by shape.

Each stube 2 is characterized by the end to be welded in V shape with the preferred inclination of 10°, while the end to be welded of each vane 3 is equally V-shaped but with a preferred inclination of 30°. Another possible weld joint, called "butt-joint", can be made with the free end of the vanes 3 in V shape with the inclination of 10° and with free end of the stube 2 with vertical profile. Each joint made will consist of a leading edge 3. a of the air and of a trailing edge 3.b of the air.

The first processing step consists of the positioning A of each vane 3, preventively classified by shape, at the related stube 2, at the optimal distance to obtain a perfectly crafted weld joint, i.e. 2 mm. This operation is made possible by the instrument represented in FIG 2, i.e. the positioning tool 4 consisting of a jaw-type gun with adjustable pressure fork, provided with a 316L Stainless Steel Argon diffuser 4.a. The latter is connected to a control unit 10 for gas emission via a polycarbonate hose 4.c connected to a stainless steel 316L supply nozzle 4.b. It is of absolute importance that the material of all contact points between the positioning tool 4 and the elements to be welded be 316L Stainless Steel, because only this material assures the absence of any contamination. FIG. 2 shows the highly porous wire mesh 4.d which coats the inner walls of the diffuser 4. a in such a way as to allow an atomized diffusion of the Argon gas coming from the control unit 10.

Once the positioning step A is carried out, the elements need to be fixed with the tack weld C, performed with a maximum Amperage of 60° via foot pedal, which is executed by means of the TIG 5 torch. FIG. 3 represents the trailing shield diffuser 5.c described by the present invention, which constitutes the innovative element with which said TIG 5 torch was modified with respect to its standard configuration.

Substantially, the trailing shield diffuser 5.c consists of a 316L stainless steel tube with a diameter of 20 mm sectioned in the longitudinal sense at half the circumference. Its function is to supply Argon gas from the control unit 10 to the welding point, as it is connected to said control unit 10 by means of a polycarbonate hose 5.e provided with ceramic nozzle 5.d. Like the other elements adapted to the diffusion of the Argon gas, the trailing shield diffuser 5.c is also provided with wire mesh 5.f, having dimensions equal to the length of the tube, which serves to homogenize the distribution of the gas.

The TIG 5 torch is also characterized by 8 Gas-Lens and tungsten with a diameter of 3.2 mm and 2% percentage of lanthanum WL. The latter has the V end with 15° angle lowered by a few tenths at the top which serves to allow greater penetration and precision and reduced loss of tungsten particles within the molten pool.

In the welding operation D, it is necessary to melt in the joint welding wires 6 also made of Gr5 titanium with at least three different diameters, to be chosen appropriately according to the point of the joint on which the welding operation is being performed. The preferred diameters to be used are 1.6 mm, 2 mm and 2.4 mm. However, before they are used, the require a cleaning and sterilization step B, which will assure a weld without any contamination. This step constitutes one of the main innovations of the present invention, in that the cleaning of the welding wires 6 has always been neglected.

With reference to FIG.4, a plan view (FIG. 4A), a front view (FIG. 4B) and a lateral view (FIG. 4C) are shown of the cleaning apparatus 7, consisting of a system of at least three vertical tubes 7.c each provided with a 316L stainless steel cap 7. a connected to a tap 7.b for the injection and discharge of the cleaning liquid. Every welding wire 6 is kept immersed in the liquid for at least 24 hours. The preferred liquid to be used is Multisolve MS 38. In addition, it is beneficial to leave outside the vertical tube 7.c the label identifying the welding wire 6 that is inserted therein, to prevent its detachment and the impossibility of recognition.

Once the welding wire 6 is extracted, the welding wire is dried with paper towel and inserted in the sterilization apparatus 8, show in FIG. 5 in plan view (FIG. 5A) in front view (FIG. 5B) and in lateral view (FIG. 5C). Said sterilization apparatus 8, which serves to contain the welding wires 6 in a sterile environment until their use, consists of a system of at least three vertical tubes 8.c each provided with an airtight cap 8. a and connected to a valve 8.b for the inlet of pure Argon gas.

After the cleaning and sterilization of the wires B, and after the tack welding C, the final welding step D can be carried out by means of the TIG 5 torch described above with a maximum amperage of 150° via foot pedal. The welding runs are carried out according to the following order:

- concave portion, trailing edge 3.b, 1 long run by 1/5 of the total length,

- concave portion, leading edge 3. a, 1 long run by 4/5 of the total length,

- convex portion, trailing edge 3.b, 3 long runs by ½ of the total length,

- convex portion, leading edge 3. a, 4 long runs by ½ of the total length,

- concave portion, trailing edge 3.b, 2 long runs by 1/5 of the total length,

- concave portion, leading edge 3. a, 3 long runs by 4/5 of the total length.

In the welding step D the Argon gas, necessary to obtain a perfectly crafted weld joint, is supplied to the welding region by means of a diffuser 9 shown in FIG. 6. It is positioned in the inner surface of the central ring 1 at each stube 2 and it is provided with a plurality of holes 9.b of increasing diameter. Obviously, it is connected to the control unit 10 for emission of the Argon gas through a hose 9. a. It is important that the total length of the diffusor 9 be equal to the entire length of the joint to be welded. FIG. 7, lastly, shows the control unit 10 for emission of the Argon gas. It is provided with at least 6 outlets lO.a of gas to which it is necessary to connect the various hoses that connect said control unit 10 to each of the gas diffusion instruments present in the system. A particular feature of the control unit 10 that is a part of the present invention consists of the fact that each of the gas outlets lO.a has a pressure that is adjustable independently of the others thanks to a regulator lO.b and a dedicated flow rate gauge for each outlet lO.a.

This technology and this method for welding assure a perfect work from the esthetic point of view as well as from the metallographic and radiographic point of view and makes it unnecessary to remove and re-melt the metal.

All these improvements of the traditional welding system for OGV Inner Ring not only allow the work to be completed without any imperfection but they also reduce the processing times from 30 to 7 working days.

Lastly, it is clear that to the invention described herein can be made modifications, additions or variations that are obvious for a person skilled in the art, without thereby departing from the scope of protection provided by the appended claims.