Patent Publication Number: US-2011056078-A1

Title: method of producing a rotor component or a stator component

Description:
BACKGROUND AND SUMMARY 
     The present invention relates to method of producing a rotor component or a stator component. More particularly, the component comprises a disc-shaped element with a plurality of radially projecting and circumferentially spaced air foil projections, or blades. The invention aims for attaching a ring-shaped band, or shroud, radially outside and in interfering contact with the blade tips. 
     The shroud is adapted to counteract leakage from a pressure side to a suction side of the blade and vibrations during operation. Such leakage is associated with efficiency losses, and the vibrations are associated with an increase in fatigue cracks. The invention is not to be regarded as being limited to this use but can also be used in other applications. 
     The component can be used in both static applications (stators) and dynamic applications (rotors). The component can also find application in both turbines and compressors. For rotors, the component is commonly referred to as a “blisk” (blade integrated disk) or a “bling” (bladed ring). The blade is often called a guide vane when applied in stators and is intended in operation to guide or deflect a gas flow. When applied in rotors, the blade is usually used for both guiding and power transmission. 
     The stator component or rotor component can, for example, be arranged in a gas turbine or jet engine. The areas of application of the component are, for example, in engines for vehicles, aircraft, power plant equipment for vessels and power stations for electricity production. 
     It is desirable to achieve a cost-efficient manufacturing of a stator component or rotor component, and especially for applying a shroud radially outside of a disc-shaped element with a plurality of radially projecting and circumferentially spaced blades. It is particularly desirable to create conditions for a final weight reduction of the component. 
     A method according to an aspect of the present invention comprises the steps of
         providing a disc-shaped element with a plurality of radially projecting and circumferentially spaced blades, an intermediate ring with an inner surface adapted for contacting tips of said blades, and an external ring with an inner surface adapted for contacting an outer surface of the intermediate ring,   moving the intermediate ring co-axially in relation to the disc-shaped element to an operative position, in which it is located radially outside the blades, and   moving the external ring co-axially in relation to the intermediate ring to an operative position, in which it is located radially outside the intermediate ring.       

     According to a preferred embodiment, the external ring comprises a composite structure. This feature creates conditions for a weight reduction and a high tensile strength of the final component. Further, it can be operated in higher speed ranges due to the lower weight of the external ring. The external ring preferably comprises the composite structure prior to the assembly of the ring to the disc-shaped element. According to a preferred alternative, carbon fibers are used in the composite structure. 
     According to a further preferred embodiment, the intermediate ring comprises a metal material. The intermediate ring is preferably substantially thinner than the external ring. The thickness of the intermediate ring is preferably less than 50% and especially less than 25% of the thickness of the external ring. The intermediate ring creates conditions for an improved assembly of the external composite ring. 
     According to a further preferred embodiment, the method comprises the steps of providing the intermediate ring with excess material adapted for providing the intermediate ring with an increased rigidity during said movement, and moving the intermediate ring with the excess material in relation to the disc-shaped element to said operative position. The excess material creates conditions for a further improved assembly of the external composite ring. This is especially advantageous when the excess material is provided with an external conical surface for interaction with the external ring during said relative movement. After having positioned the intermediate ring in said operative position, the excess material is removed. 
     Other advantageous features and functions of various embodiments of the invention are set forth in the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained below, with reference to the embodiments shown on the appended drawings, wherein 
         FIG. 1  shows a disc-shaped element in a perspective view, 
         FIG. 2  shows a first manufacturing step in-a-cut view, wherein an intermediate ring is applied on the disc-shaped element, 
         FIG. 3  shows a second manufacturing step in a cut view, wherein an external ring is applied on the intermediate ring, 
         FIG. 4  shows the external ring in its operative position in a cut view, wherein excess material has been removed from the intermediate ring in a third manufacturing step, 
         FIG. 5  shows an enlarged cross section view of the disc shaped element provided with the external ring in its operative position. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a disc-shaped element  1 , which comprises a central part  2 , what is known as a hub, and a plurality of circumferentially spaced blades  3  which are arranged on a circular path and projecting in the radial direction from the hub. Thus, the blades  3  are attached to the hub  2 . Each of the blades  3  has a blade root  4  and a blade tip  5  disposed opposite the root, see  FIG. 2 . 
       FIGS. 2-4  show consecutive manufacturing steps for attaching a shroud  10  (external ring) to the blades  3 . 
     A work piece  6  comprises a first part  7 , which is configured to form a continuous intermediate ring and a second annular part  8  forming excess material to be removed later. The excess material  8  is adapted for providing the intermediate ring with an increased rigidity during assembly. In other words, the excess material is adapted so that the intermediate ring will sustain an application force during assembly. 
     The excess material  8  is unitary with the intermediate ring. In other words, the excess material  8  is in one piece with the intermediate ring  7 . The intermediate ring  7  comprises a metal material, preferably a lightweight material such as titanium or aluminium. Thus, the intermediate ring  7  forms a supporting metal ring. 
     The intermediate ring  7  comprises a cylindrical inner surface adapted for contacting the blade tips  5  of the disc-shaped element  1 . The method comprises the step of moving the work piece  6  (comprising the intermediate ring  7 ) co-axially in relation to the disc-shaped element  1  to an operative position, in which it is located radially outside the blades  3 . The axial movement is illustrated by means of an arrow. 
     More specifically, the method comprises the step of moving the intermediate ring  7  with the excess material in relation to the disc-shaped element  1  to said operative position. The second part (the excess material)  8  is provided with an external conical surface  9  (tapered surface) for interaction with the external ring  10  during a next step. 
     A continuous external ring  10  (or shroud) preferably comprises a composite structure  17 , see  FIG. 6 . The composite structure  17  comprises a circumferentially wound fiber structure. The composite material is lightweight, has a high strength and stiffness and a low coefficient of thermal expansion. Composite materials can provide a ring which is self-supporting at very high rotational speeds while minimizing its radial thermal growth. 
     The external ring  10  is provided with an inner surface  12  adapted for contacting an outer surface of the intermediate ring  7 . The external ring  10  is provided with an inner diameter substantially equal to an outer diameter of the intermediate ring  7 . 
     The method comprises the step of moving the external ring  10  co-axially in relation to the intermediate ring  7  to an operative position, in which it is located radially outside the intermediate ring. More specifically, the method comprises the step of applying a pressure in an axial direction on the external ring  10  in order to move it to said operative position. A separate annular pressure application means  11  is used for applying the pressure on the external ring. 
     Thus, the method comprises the sequential steps of first moving the intermediate ring  7  co-axially in relation to the disc-shaped element  1  to its operative position and then moving the external ring  10  co-axially in relation to the intermediate ring  7  to its operative position. 
     The method preferably comprises the step of providing the pressure application means  11  with an internal conical surface configured for interaction with the external conical surface of the excess material  8  during said movement. 
     Preferably, the method comprises the step of moving the external ring  10  while the fiber structure  17  is in a preloaded state. 
     The method preferably comprises the step of providing an adhesive (preferably glue) on the contacting surfaces of the external ring  10  and the intermediate ring  7 . In addition to providing a fastening function in the applied state, the adhesive also forms a lubrication during assembly. 
     The method further comprises the step of removing the excess material  8  after having positioned the external ring  10  radially outside the intermediate ring  7 . This removed excess material is indicated with phantom lines in  FIG. 4 . More specifically, the method comprises the step of removing the excess material  8  after having positioned the intermediate ring  7  in said operative position relative to the disc-shaped element  1 . The extra material  8  is preferably removed in a machining process. 
       FIG. 4  shows the external ring  10  applied in its operative position radially outside and in interfering contact with the intermediate ring  14 . The excess material  8  has been removed in  FIG. 4 . The external ring  10  is held in place by interfering contact. 
       FIG. 5  shows a cross section view of the final rotor comprising the external ring  10 . The external ring  10  comprises a composite fiber structure  17 . The fibers are preferably glued together. The composite fiber structure  17  may comprise an OMC (Organic Matrix composite material) or MMC (metal matric composite material). OMC comprises a thermosetting resin, such as an epoxy, polyester or polyamide, and usually cures or hardens in the presence of a catalyst, such as heat or pressure. Alternatively, the matrix component of an OMC can be provided in the form of a thermoplastic resin, such as polycarbonate or polysulfone. The matrix component of an MMC material may comprise metals such as aluminium, titanium, titanium aluminide and the like. The fibers of OMC and MMC are typically formed from boron, graphite or carbide. 
     The invention is not in any way limited to the above described embodiments, instead a number of alternatives and modifications are possible without departing from the scope of the following claims. 
     For example, some of the method steps may be performed in a different order. According to one example, the external ring may first be applied radially outside the intermediate ring and thereafter, they may in unison be applied on the disc-shaped element. 
     Further, the blade tips may be provided with an external conical surface (tapered surface) for interaction with the intermediate ring during assembly. According to an alternative, or complement, the intermediate ring may be provided with an internal conical surface (tapered surface) for interaction with the blade tips during assembly.