Abstract:
An improved retention pin assembly and method of forming a pin assembly that uses a melt in a pocket without a metallurgical joint having been formed. The assembly can be generated by a method of forming a joint which includes providing a metal shaft and a member that is operable to receive the shaft. A pocket is formed within the member which operates to receive a melt pool. Next the shaft is inserted into apertures in the member. A welding or melting operation is then performed to create a melted portion that occupies the pocket. A joint is created using a retention pin.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is claims priority to U.S. Provisional Patent Application No. 61/780,746 filed Mar. 13, 2013, the contents of which are hereby incorporated in their entirety. 
     
    
     GOVERNMENT RIGHTS 
       [0002]    This application was made with government support under N00019-96-C-0176 awarded by the United States Navy. The government has certain rights in the application. 
     
    
     FIELD OF TECHNOLOGY 
       [0003]    An improved retention pin, and more particularly, a pin and method of forming a pin assembly that uses a melt in a pocket without a metallurgical joint having been formed. 
       BACKGROUND 
       [0004]    Traditionally mechanical fasteners are used to mechanically link two or more articles together. Mechanical fasteners come in various shapes and sizes and they have a variety of constructs. The type of construct depends in part on the environmental conditions in which the fastener system must operate. Some may operate in high stress, shear, compression or tension conditions, and some may operate in high temperature, low temperature, or just ambient temperature conditions. Thus, depending on the circumstances, the design of fastener system may be changed. 
         [0005]    One style of mechanical fastener includes rivets. A problem with rivet type fasteners is that rivet heads have been known to be liberated into engines, causing damage. This is because the rivet construct may not have tightly controlled material strength and structural integrity. This in part may be because the quality of the rivet is subject to the quality of work of the operator who forms the rivet. If a rivet has been unknowingly overworked, it may not have the fatigue life that was assumed. Thus, rivet constructs are not dependable or desirable to use in engines, or other locations or machinery, where potentially causing damage to the machinery is an issue. 
         [0006]    It would be helpful to provide an improved mechanical joint. Such a joint could be formed by a welder who melts a retention pin only into a pocket. The welder can watch the molten metal flow into the pocket to know that he has finished the forming operation. The fatigue properties of the melt-formed pin may be the same as the solution heat treated form of the pin material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    While the claims are not limited to a specific illustration, an appreciation of the various aspects is best gained through a discussion of various examples thereof. Referring now to the drawings, exemplary illustrations are shown in detail. Although the drawings represent the illustrations, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an example. Further, the exemplary illustrations described herein are not intended to be exhaustive or otherwise limiting or restricted to the precise form and configuration shown in the drawings and disclosed in the following detailed description. Exemplary illustrations are described in detail by referring to the drawings as follows: 
           [0008]      FIG. 1  illustrates a schematic view of a gas turbine engine; 
           [0009]      FIG. 2  illustrates a side sectional view of a seal assembly having a pinned connection; 
           [0010]      FIG. 3  illustrates a side sectional view of a joint assembly, where the joint has not yet been welded; and 
           [0011]      FIG. 4  illustrates a side sectional view of the joint assembly, where a melt has been formed without creating a metallurgical joint. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    An exemplary embodiment includes a retention pin and method of forming a seal assembly which may be used where seals are employed. Such a pin could be used on any conceivable assembly, not just to retain leaf seals on turbine engine nozzle guide vanes, the example shown herein. Thus, it will be appreciated that the seal assembly, and methodology, could be used in other applications, for example, in machinery where it is helpful to provide an improved joint using a retention pin, particularly where it is desirable to not use a rivet assembly. 
         [0013]    Traditionally a rivet could be used to secure multiple members together. However, rivets are generally forbidden from being used near the main flow path of gas turbine engines. Thus, an exemplary embodiment overcomes this problem by providing a method and construct that has the requisite retentive functionality of a rivet without a rivet construct being used. This is accomplished by providing a headed pin that has a distally opposed smaller diameter end that is melted by a welder. The molten pin metal flows into a countersink or bore-like pocket in the underlying component. The molten pin metal immediately cools to fill the pocket. Excess solidified metal can then be ground flush with the surface into which the pocket was formed if desired for clearance with the environment. 
         [0014]    Another exemplary embodiment provides a retention pin assembly having molten metal that has quickly cooled when it contacted the underlying part&#39;s surface, thereby precluding any melting of the underlying surface. This produces a mechanical joint rather than a metallurgical joint. The pin is free to rotate because there is no metallurgical joint. This also makes it very simple to remove the pin, such as would be done during an engine overhaul, without altering the underlying component; a simple drill is used to remove the pin material in the pocket and the pin can be pulled out of the components that it was retaining together. Thus, a serviceable retention pin assembly is contemplated. 
         [0015]      FIG. 1  illustrates a gas turbine engine  10 , which includes a fan  12 , an intermediate pressure compressor and a high pressure compressor,  14  and  16 , a combustor  18 , a high pressure turbine, an intermediate pressure turbine, and a low pressure turbine,  20  and  21  and  22 , respectively. The high pressure compressor  16  is connected to a first rotor shaft  24  while the intermediate pressure compressor  14  is connected to a second rotor shaft  26  and the fan is connected to a third rotor shaft  42 . The shafts extend axially and are parallel to a longitudinal center line axis  28 . 
         [0016]    Ambient air  30  enters the fan  12  and is directed across a fan rotor  32  in an annular duct  34 , which in part is circumscribed by fan case  36 . The bypass airflow  38  provides engine thrust while the primary gas stream  40  is directed to the combustor  18  and the high pressure turbine  20 . The gas turbine engine  10  includes an improved retention pin assembly  50  for retaining a leaf seal that is operable to direct hot combustion gases onto rotor blades of the turbine  20 . 
         [0017]    With reference to  FIG. 2 , a retention pin assembly  50  can be used with a leaf seal assembly  52  for use in hot combustion gas pathways of a gas turbine engine  10 . It will be appreciated that the pin assembly  50  may be used in other applications where it is desirable to provide an improved seal. The seal assembly  52  includes a first member  54  having an upwardly extending wall  56 . A depending member  58  extends from the wall  56  and forms a rest for a leaf seal  60  to engage. 
         [0018]    The seal assembly further includes a base  62  with a u-shaped portion  64  having a first upwardly extending support  66  and a second upwardly extending support  68 . The supports are shown integral with the base  62 . The base  62  and the member  54  are made of metal that is operable in gas turbine engine type environments. The supports  66  and  68  have apertures  70  for receiving a shaft of a retention pin. The apertures  70  are slightly larger than the diameter of the shaft so as to permit movement of the shaft relative to the supports  66  and  68 . 
         [0019]    The pin assembly  50  includes a retention pin  72  having a shaft  74 , a head  76 , and a melted end  78 . The melted end  78  resides loosely within a conic shaped void  80  that is formed within the support  66 . It will be appreciated that the void&#39;s shape can vary, and could include other shapes such as, but not limited to, round, stepped, or elliptical. Washers  82  can be provided adjacent the head  76 . The leaf seal  60  is retained at an aperture  84  by the shaft  74  of the pin  72 . 
         [0020]      FIG. 3  illustrates a first step in the process of manufacturing a retention pin assembly  50  having a melt end  90  to form the locking feature of the pin  72  relative to the base  62 . The first step includes providing a leaf seal  60  and inserting a pin  72  through an aperture  70  in support arm  66 . The pin  72  is then passed through the aperture  84  of the leaf seal  60 . An opposing end  90  of the pin  72  includes an elongated portion that passes through aperture  70 . A sufficient amount of material at the melt end  90  of the pin  72  should be present so as to provide a sufficient amount of volume of melt  78  that consumes the conic void  80  in the support  66 . 
         [0021]      FIG. 4  illustrates the next step of forming the assembly where the retention pin  72  now becomes loosely, mechanically joined to the support arm  66  and  68 . This is accomplished by heating, via welding or some other means, the melt end  90  of the pin  72 . This melting step may continue until a melt  78  or pool of material fills the conic shaped void  80 . The welding does not, however, cause any metallurgical displacement or connection between the support  66  and the pin  72 . Once the pool of melted material  78  is cooled, the pin  72  is not rigidly affixed to the base  62 . Instead the pin  72  may be able to rotate within the aperture  70 . As shown in  FIG. 4 , the melt  78  has smooth exterior surface  92  that is nearly flush with the surface  94  of the base  62 . This may be accomplished by use of a finishing step, such as grinding, so as to provide a smooth surface to enhance clearance within passageway  98  (see  FIG. 2 .). The pin  72  can be constructed of any material that can be melted using a welder. The melt-formed pin head material can have the same material properties as the remainder of the pin that was not melted if the pin was in the solution heat treated condition prior to weld melting of the smaller end. 
         [0022]    The retaining pin  72  has a residual, axial load after forming. The residual load results from the thermal expansion of this pin  72  during melting, with negligible expansion of the underlying components being retained together due to their relatively large mass relative to the pin, followed by thermal contraction of the pin upon release from heat input from the welder. The net result is a small load. This axial load is customizable in that the length, cross sectional area, and material conductivity of the pin  72  are customizable features that can be exploited to limit heat input into the pin, thus allowing a tailoring of expansion of the pin with resulting tailoring of the residual axial load in the pin following cool down. 
         [0023]    It will be appreciated that the retention pin  72  is customizable in size to accommodate any requirement. The melted material  78  completely fills the pocket or void  80 , thereby maximizing the use of the material to provide retention. 
         [0024]    The voids  80  into which the pin  72  is melted can be undercut, such that the melted portion  90  cannot be liberated even in the event that the pin were to be severed or worn-through during fielded operation. In an alternative embodiment, both ends of the pin  72  could be melted into opposing pockets if desired, and undercuts could be utilized on both ends to preclude liberation of either of the headed ends of the pin. 
         [0025]    It will be appreciated that the aforementioned method and devices may be modified to have some components and steps removed, or may have additional components and steps added, all of which are deemed to be within the spirit of the present disclosure. Even though the present disclosure has been described in detail with reference to specific embodiments, it will be appreciated that the various modifications and changes can be made to these embodiments without departing from the scope of the present disclosure as set forth in the claims. The specification and the drawings are to be regarded as an illustrative thought instead of merely restrictive thought.