Abstract:
The present disclosure provides a process and a device for the orbital friction welding of blades to the drum of an axial compressor. The process consists of holding the drum on a cradle via an indexing table, the cradle being able to pivot and vertically movable so as to present different regions of its outer surface parallel to the plane of orbital motion of the blade. The blade is held in the orbital motion device by a clamping device. The inner surface of the drum is braced by supports carried by a core fixed to the cradle. The drum comprises a series of protrusions which have a blade-shaped cross section. These protrusions form faying surfaces for the blades. The blades have a plate to ensure they are satisfactorily clamped by the clamping device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit, under 35 U.S.C. §119, of European Application No. EP 11170460.7, which was filed on Jun. 17, 2011 the disclosure of which is incorporated here by reference in its entirety. 
     FIELD 
     The present teachings relate to a friction welding process for attaching blades to an axial turbomachine rotor, in particular to a drum of an axial turbomachine compressor. The present teachings also relate to a corresponding device for implementing the friction welding process and to an axial turbomachine rotor resulting from implementation of the friction welding process or use of the corresponding device. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Friction welding is a welding process in which the mechanical heat necessary for welding is generated by rubbing the parts to be joined against each other under an axial forging pressure. 
     Patent US 2003/0201305 A1 discloses a friction welding device for attaching blades to a rotor. The principle of welding disclosed in this document is based on linear friction and uses a device initially designed for linear welding that is capable of imparting a back and forth motion to a work piece relative to the substrate to which it is intended that it be welded. The movement of the work piece, i.e. the blade, is guided to define a curved path generally matching the cross-sectional profile of the blade. The purpose of the curved path is to avoid a part of the blade&#39;s contact surface with the rotor being exposed during friction and undergoing direct contact with the ambient air and uncontrolled cooling. This solution is therefore particularly suitable for highly curved blades. This process, however, requires heavy and expensive equipment, especially because of the use of linear friction welding. Indeed, reciprocating back and forth movements of the work piece are very restrictive, particularly in terms of the equipment that moves the work piece. This solution is therefore not particularly attractive on cost grounds, especially from a fixed cost point of view. 
     Patent EP 2281653 A1 discloses a method of friction welding of blades in a fan disk or a fan at the intake to an axial turbomachine. This patent focuses on the problem of the lack of control over the forging pressure at the extremities of the faying surfaces of the pieces to be welded, when the section of material below the faying surface decreases at too steep an angle. The method described is notable in that it provides for a first contact zone under the faying surface without any reduction in section, which is then followed by a second zone with the material tapering off. The welding process that is described therein is a linear friction welding process. It suggests that an orbital friction welding method can also be used, without specifying the conditions under which it can be used. As in the previous patent, this patent focuses on a linear friction welding process which necessitates expensive equipment. 
     SUMMARY 
     The present disclosure relates to a friction welding process for attaching blades to an axial turbomachine rotor. The process includes: (a) positioning the rotor so as to have a faying surface for one blade; (b) starting a frictional movement of the blade against the faying surface for the blade, essentially in a mean contact plane of the blade with the surface so as to reach a welding temperature, the rotor being held stationary in the plane of frictional movement of the blade; and (c) immobilizing the blade and forging the blade onto the rotor. Importantly, the frictional movement of the blade at the faying surface is a substantially orbital movement. 
     Advantageously, the rotor remains completely immobile during the welding operation set forth in step (b) and (c), such that step (c) affects the blade alone. 
     Generally, the blade is constantly pressed against the faying surface of the rotor during step (b). In various implementations the pressure can be increased during step (c). However, in other implementations, the pressure can be varied during step (b) and/or (c). 
     According to an advantageous embodiment of the invention, the rotor is a compressor drum that, in various embodiments, comprises a hollow body that is generally circularly symmetrical about the axis of the rotor and defining a hollow interior volume with a first aperture at the front end of the drum and a second aperture at the rear end. 
     The rotor can comprise at least two rows of blades, or alternatively at least three rows of blades. 
     According to another advantageous embodiment of the invention, step (a) comprises locating at least one support on the inside of the rotor&#39;s faying surface for the blade so as to brace the faying surface with respect to the forging pressure being exerted on the blade during step (c). The support can also brace the faying surface during step (b). 
     According to yet another advantageous embodiment of the invention, locating at least one support within the drum comprises inserting a core inside the drum, the core being designed to be the basis for the support of the opposite internal surface of the drum, the core can extend over at least half the length of the drum between the first and second apertures. 
     According to yet another advantageous embodiment of the invention, step (a) comprises locating the rotor on a cradle via an indexing table so as to angularly position the rotor about its main axis relative to the cradle. 
     According to yet another advantageous embodiment of the invention, the cradle is designed to be capable of pivoting about a transverse axis. In various embodiments, the pivoting can be perpendicular to both the main axis of the rotor and to the direction of the pressure applied to the blade against the rotor during step (c). In various embodiments, this axis is horizontal. 
     According to yet another advantageous embodiment of the invention, the cradle is movable in translation along a direction generally perpendicular to the direction of applying pressure to the blade against the rotor during step (c) and mainly within a plane containing the principal axis of the rotor. In various embodiments, this direction is vertical. 
     According to yet another advantageous embodiment of the invention, step (b) comprises gripping the blade by a clamping device provided with a means for rapid fixing. The clamping device may take the form of a cassette. In various embodiments, the clamping device comprises at least one jaw for clamping the body of the blade and further comprises a suitable opening or cavity into which the blade can be inserted. 
     According to yet another advantageous embodiment of the invention, the rotor comprises protrusions shaped to the profiles of the blades, forming faying surfaces for the blades before they are welded. 
     According to yet another advantageous embodiment of the invention, the blade comprises a plate on the part to be welded to the rotor, the plate having a protrusion whose section has a blade profile and is intended to be in contact with the faying surface for the blade. 
     The invention relates also to a friction welding device for attaching the blades to an axial turbomachine rotor. The device includes a supporting frame, a rotor support designed to hold the rotor stationary during the friction welding operation, and a blade support for holding the blade fixed for the friction movement and the forging movement towards the rotor. Importantly, the blade support is designed to impart an orbital motion to the blade. 
     According to an advantageous embodiment of the invention, the rotor support comprises a cradle pivotally mounted relative to an axis substantially horizontal and perpendicular to the forging movement direction, and the cradle comprises an indexing table designed to angularly position the rotor about its axis of rotation. 
     According to another advantageous embodiment of the invention, the cradle can comprise a mounting bed for the rotor and a bearing at a distance from the mounting bed, the bearing being able to support a shaft generally perpendicular to the mounting bed. 
     According to yet another advantageous embodiment of the invention, the cradle comprises a core designed to be secured to the indexing table and designed to act as a support for the rotor&#39;s inner surface supports. 
     According to yet another advantageous embodiment of the invention, the blade support comprises a mounting for holding a tapered clamping device for clamping the blade. 
     The invention further relates to an axial turbomachine rotor constructed using the process and/or the device described above. 
     The solution proposed by the invention has the advantage of enabling an axial turbomachine rotor axial to be made at a very reasonable cost. Linear friction welding is, in fact, commonly used for massive and compact disc rotors, commonly called bladed disks or blisks, or annular rotors, commonly called bladed rings or blings, particularly in configurations where the rotor is fixed. However, this process requires expensive equipment, particularly because of the nature of the alternating back and forth movement of the workpiece. Orbital friction welding, compared with linear friction welding, has not appeared to be the obvious way of attaching blades because of the elongated shape of the blades. In fact, with orbital friction welding where the two surfaces are usually in motion, the component of movement which is perpendicular to the main axis of the blade is capable of fully covering the mating surface. The inventors have discovered that applying an orbital friction motion to a process where the rotor is stationary, at least in terms of the plane of orbital motion, has many advantages. These include the simplification of the kinematics of the machine and its associated parts, resulting in lower equipment costs and reduced power consumption. The method of clamping the blade, however, requires particular care because of the movement in both the main X and Y directions and the spacing between the blades. For drum type rotors, special measures may be needed both for clamping as well as for supporting the hollow body of the drum. With the aim of further reducing manufacturing costs and the resulting reduction in the amount of machine time needed, clamping the blade and positioning the rotor deserve especial attention. 
     Further areas of applicability of the present teachings will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present teachings. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present teachings in any way. 
         FIG. 1  is a cross-sectional view of an axial double-flow turbomachine, with multiple rotors fitted with blades attached using the inventive process described below.  FIG. 1  includes an enlarged view of a partial section of a low-pressure compressor part of the turbomachine, the blades being attached to the compressor rotor utilizing an orbital friction welding device, shown in  FIG. 2 , structured and operable to implement the inventive process in accordance with the invention. 
         FIG. 2  is a plan and part section view of the orbital friction welding device in accordance with the invention. 
         FIG. 3  is an isometric view of a portion of a drum of the compressor shown in  FIG. 1 , as well as a blade in an orbital motion on a corresponding protrusion of the drum. 
         FIG. 4  is an isometric view of a blade clamping mechanism of the device shown in  FIG. 2 , wherein the blade is mounted and clamped in the mechanism that is structured and operable to be fixed to a structure that moves with an orbital motion. 
         FIG. 5  is a plan view of a portion of the drum with the clamping mechanism of  FIG. 4 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of drawings. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the present teachings, application, or uses. Throughout this specification, like reference numerals will be used to refer to like elements. 
       FIG. 1  shows an aero engine double-flow axial turbomachine  2 . The turbomachine  2  comprises, in order, from intake to outlet: a fan  4 , a low-pressure compressor  6 , a high-pressure compressor  8 , a combustion chamber  10 , a high-pressure turbine  11  and a low-pressure turbine  12 . Intake air is forced into the machine by the fan  4  and is then split into a primary flow through the various components mentioned above and a secondary flow through the machine outside these components, joining the primary flow at the outlet to generate propulsive thrust. 
     The low-pressure compressor  6  is illustrated in detail in the magnified portion of  FIG. 1  and comprises essentially a rotor  14  (also referred to herein as drum  14 ) and a stator  32 . The rotor  14  is formed by a hollow body  16  generally symmetrical in revolution about its axis of rotation, the hollow body  16  being provided with rows of rotor blades  18 ,  20  and  22 . The stator  32  comprises a splitter nose  34  dividing the intake stream and a wall  36  defining the primary flow and provided with rows of stator vanes  24 ,  26 ,  28  and  30 . The rows of stator vanes  24 / 26 / 28 / 30  and rotor blades  18 / 20 / 22  are arranged alternately so as to form several compression stages, each stage being formed by a rotor blade row and a stator blade row pair. 
     Dynamic sealing devices generally known to one skilled in the art are fitted between the tips of the rotor blades  18 ,  20  and  22  and the wall  36  delimiting the fluid stream of the primary flow, and between the tips of stator blades  24 ,  26 ,  28  and  30  with the hollow body  16  of the drum  14 . 
     The drum  14  is typically made of metallic material such as, for example, titanium or stainless steel. The hollow body  16  has the general shape of an ogive defining a hollow internal volume. It can be manufactured by machining from a rough forged hollow body. This rough hollow body will have a profile and a thickness close to the maximum profile and thickness of the finished hollow body  16  as shown in  FIG. 1 , in order to minimize both the amount of material to be removed and the machine time associated with this operation. 
     The rotor blades  18 / 20 / 22  are manufactured separately and then attached to the hollow body  16  of the drum  14 . In fact, although it is of course possible to machine the rotor blades  18 / 20 / 22  directly from the rough form that will eventually be the drum  14 , it is nevertheless desirable, mainly for economic reasons, for the rotor blades  18 / 20 / 22  to be manufactured separately and then attached to the hollow body  16  of the drum  14 . This is particularly true if the drum  14  has a large diameter as, in which case, the number of rotor blades  18 / 20 / 22  increases steeply and the time for to machine them from the forging would be very long, not to mention the cost of the raw material needed for the rough hollow body  16 . 
     In various embodiments, the rotor blades  18 / 20 / 22  are attached to the hollow body  16  of the drum  14  by an orbital friction welding process described herein and exemplarily illustrated in  FIGS. 2 through 5 . 
       FIG. 2  illustrates an orbital friction welding device  40  for an axial compressor drum such as the drum  14  shown in  FIG. 1 . The device  40  comprises a supporting frame  42  supporting a cradle  44  for the drum  14 . It also comprises a blade support, capable of orbital friction motion, comprising of a clamping device  68  which grips the blade  18 / 20 / 22 , a mounting  66  for the clamping device  68 , a plate  64  to which the mounting  66  is rigidly attached and an orbital motion unit  62 . This assembly is able to translate horizontally relative to the supporting frame by sliding on guide rails using a ram  70 . 
     The cradle  44  comprises a mounting bed  56  for the drum  14 , such that the drum  14  is located with a rear aperture of the drum  14  (relative to the direction of the air flow in the turbomachine) disposed on the mounting bed  56  so that the axis of rotation of the drum  14  is generally vertical. An indexing table  54  is located between the mounting bed  56  of the cradle  44  and a rear edge of the drum  14  so as to allow precise angular positioning of the drum  14  for the various blades  18 / 20 / 11  of each row. Some form of clamping (not shown) may be provided between the indexing table and the rear edge of the drum  14 . 
     The cradle  44  also comprises a mounting arm  46  disposed directly above and at some distance from the mounting bed  56 . The mounting arm  46  supports a bearing  48  for holding a shaft  50  passing through a front opening of the drum  14 . The shaft  50  is linked to a core  52  that is disposable within the hollow space of the drum  14 . The core  52  carries supports  51  that are disposable inside zones of the body  16  where the blades  18 / 20 / 22  will be joined. Locating devices  53  that are configured to clamp onto the supports  51  are designed to be fitted between the core  52  and the supports  51 . The locating devices  53  and supports  51  can have various forms. For example, in various implementations, the supports  51  can be segmented and the locating devices  53  and the clamping device  68  can be eccentric. 
     The supports  51  are configured to support the hollow body  16  of the drum  14  during friction welding, especially when the respective blade  18 / 20 / 22  is subjected to a forging pressure against the drum  14  after heating due to orbital friction motion. 
     As shown in  FIGS. 1 and 2 , the hollow body  16  of the drum  14  also comprises the faying surfaces  39  for the rotor blades  18 / 20 / 22 . As exemplarily illustrated in  FIGS. 1 and 2 , the faying surfaces  39  can have a particular geometry for optimizing the stiffness of the rotor  14  and its mass. In various embodiments, the drum  14  comprises three of faying surfaces  39 , constructed in a similar manner. Each faying surface  39  is annular in shape and consists essentially of two parts in the hollow body  16  in the shape of ribs generally perpendicular to the axis of rotation and a central part supporting the blade row. The cross-section of each faying surface  39  is shaped like the Greek letter pi (π), wherein a central part extends higher than the surrounding wall  16  in a direction generally perpendicular to the axis of rotation and is oriented toward the outside of the hollow body  16 , thereby enabling the outer surface of the central portion to be at the level of the surrounding interior shells delimiting the fluid stream (see detail in  FIG. 1 ). The inner surfaces of the shells are, in fact, at some distance from the hollow body  16  due to the height of the lip seals and the shell&#39;s necessary thickness. The internal surfaces of the shells and of the central portions of the annular zones, which delimit the fluid stream, are generally offset and aligned to ensure that the flow is perturbed as little as possible. 
     The central part of each faying surface  39  for the blades  18 / 20 / 22  comprises a generally straight or slightly curved section that corresponds to the general shape of the fluid stream of the rotor  14 . Each faying surface central part has a generally annular shape with integrally formed protrusions or stubs that form part of the blade roots. The central part of each faying surface  39  is a generally annular platform for the respective blade row. Each annular blade faying surface  39  thus forms an annular cavity inside the hollow body  16  that open towards the axis of rotation. The annular cavity is disposed within a plane passing through the axis of rotation and has an overall “U” shape, whose opening is directed towards the axis of rotation. Moreover, the annular cavities are structured receive and locate the supports  51 . 
     The cradle  44  is pivotally mounted about an axis that is generally horizontal and substantially perpendicular to the blade  18 / 20 / 22  and to the direction of forging of the blade  18 / 20 / 22  and the drum  14 . This axis is preferably arranged so as to cross the drum  14 . It should be noted, however, that this axis can be at some distance from the drum  14 . Pivoting of the cradle  44  enables the orientation of the drum  14  to be changed so as to have a blade faying surface  39  that is generally in the plane of the orbital motion of the respective blade  18 / 20 / 22 . Accordingly, the cradle  44  is pivotally mounted relative to a guide  58  configured to move vertically relative to a vertical guide  60  of the supporting frame  42 , and using the ram  70 , such as a worm driven by an electric motor. This combination of vertical movement and pivoting the cradle  44  enables the drum  14  to be positioned to weld the blades  18 / 20 / 22  of the different stages. 
     The indexing table  54  and the rotating connection of the shaft  50  of the core  52  through the bearing  48  provides easy positioning of the drum  14  for attaching each blade  18 / 20 / 22  of a blade row without having to unclamp the drum  14  and having to make other accurate and time consuming adjustments. 
     The orbital motion of the blade is generated at the plate  64  by means of eccentrics driven by electric motors (not shown) of the orbital motion unit  62 . Adjusting the phase shift between the eccentrics can change the motion imparted to the respective blade  18 / 20 / 22 . The means for creating the orbital motion can be any means that is suitable for creating such orbital motion that is known to someone skilled in the art. 
       FIG. 3  illustrates the principle of orbital friction welding between a blade  18 / 20 / 22  and the drum  16 . Each respective blade  18 / 20 / 22  comprises a plate  23  near the end of a side of the blade intended to be welded to the drum  14 . The plate  23  is essentially a means for clamping and positioning the blade  18 / 20 / 22 , especially in a plane parallel to the orbital motion. In various embodiments, a protrusion  37  is provided under the plate  23  on the side of the plate  23  that is to be welded to the drum  14 . In various implementations, the protrusion  37  can have a section whose profile is essentially the same as the profile of the respective blade  18 / 20 / 22 . The protrusion  37  has a front surface which is brought into contact with a front surface of the corresponding protrusion  38  of the faying surface  39 . The blade  18 / 20 / 22  and the corresponding front surface of the protrusion  37  of the plate  23  are moved along a generally orbital path of small radius so that the surface remains largely in contact with the surface of the corresponding protrusion  38  of the faying surface  39 . The general orientation of the blade  18 / 20 / 22  remains constant. This movement is accompanied by pressure between the contact surfaces of the protrusions  37  and  38  so as to generate homogeneous heating of the entire interface area through a uniform tangential speed. This heating generates a forging or welding zone  19 . Once the desired temperature is reached, the movement is stopped in a reference position and a forging force is exerted on the blade  18 / 20 / 22 , pressing it against the drum  14  to form the weld. 
     After welding, machining may then be necessary to remove the interface material that has been pushed to the outside, commonly called flash, and to remove the plate  23 . In various implementations, the machining is adaptive, such that it adapts to the surface of the blade  18 / 20 / 22  thus formed in the vicinity of the weld so as to avoid any spring-back related to the machining. 
     It should be noted that the presence of the protrusion  37  under the plate  23  is optional in view of the machining operation that follows. 
     It should also be noted that the presence of the protrusion  38  on the drum  14  is also optional. However, it facilitates the machining operation that follows. 
       FIGS. 4 and 5  illustrate in detail the blade clamping device  68  and the mounting  66  for the blade clamping device  68 . The clamping device  68  is generally designed to fit in the space between the blades  18 / 20 / 22  and consists essentially of a first part  681  and a second part  682 . The first part  681  is the body of the device  68  and the second part  682  is a clamp or jaw designed to be placed under pressure to clamp the blade plate  23  against the body  681  of the device  68 . A clamping means, for example, a screwing means such as bolts  74  are arranged transversely near a front face of the device  68 . Other such clamping means, such as a thermal shrink-tightening, are also conceivable. The clamp  682  is structured and operable to ensure accurate positioning of the blade  18 / 20 / 22 , especially at the end to be welded to the drum  14 , essentially in the plane of orbital motion. The positioning of the blade  18 / 20 / 22  in the blade&#39;s axial or main direction can be provided by clamping, or by the clamping device  68  providing a shoulder and/or support at the end of the blade on the bottom of the clamping device  68 . Each of the first and second parts  681  and  682  of the clamping device  68  can have a taper that matches, at least partially, the outer surface of the blade  18 / 20 / 22 . The clamping device  68  comprises a means of rapid fixing to the mounting  66 . In various embodiments, the rapid fixing means comprises at least two studs  72  extending generally parallel to the main direction of the blade  18 / 20 / 22  and structured to enter corresponding holes  76  in the mounting  66 . Each stud  72  comprises a shoulder at a free end structured and operable to engage with a rapid clamping means (not shown) located on the mounting  66 . The rapid clamping means can be any suitable rapid clamping means known to those skilled in the art. 
     It should be noted that the implementation of the clamping device  68  and the mounting  66  can take many forms. 
     The description herein is merely exemplary in nature and, thus, variations that do not depart from the gist of that which is described are intended to be within the scope of the teachings. Such variations are not to be regarded as a departure from the spirit and scope of the teachings.