Abstract:
A method for shaping a component cast from a titanium alloy including firstly heating the component to a plastic temperature such that it becomes plastically deformable and subsequently subjecting the component to a deformation process to thereby plastically deform the component to a desired geometric shape.

Description:
This invention claims the benefit of UK Patent Application No. 1117183.2, filed on 6 Oct. 2011, which is hereby incorporated herein in its entirety. 
     FIELD OF THE INVENTION 
     The present disclosure relates to a method of shaping or reshaping a cast component. 
     BACKGROUND TO THE INVENTION 
     It is well known to form components by casting methods using molten metals, and that the casting may deform as it cools due to shrinkage. In particular it may bend and/or twist as it cools. Where the casting is heat treated to remove inherent stresses built up in the casting as it was formed and cooled, the casting may further deform. 
     The dimensional accuracy of the component may be achieved by machining to the correct dimensions. However, because of the inherent strain in the component, this may result in further distortions as any weakened portions of the component yield to the inherent stresses. This makes machining difficult and increases cost and time and requires the part to have a greater level of restraint during machining. 
     Alternatively the component may be deformed by bending, pressing or other mechanical working method, literally forcing it to take up the desired shape. Mechanical working is very unsatisfactory as the mechanical strain introduced during manipulation is often found to relax over time. The consequence of this is that material of the component creeps during its operational life and hence the component may change shape and no longer conform to desired dimensions, despite it being dimensionally accurate upon completion of its manufacture. This results in operational non-conformance which is highly problematic for the functioning of mechanical hardware, especially those used for flight. 
     Mechanical working may introduce further residual strain in the component. For many applications the presence of high internal stress and strain will not be an issue. 
     However, for other applications it is, and may increase the chance of the component having a shortened operational life. 
     Typically this problem is resolved by either accepting the reduced life, or making the component from thicker material so that it can deal with higher loads (i.e., the operational load plus the residual stressed present in the component). However, increasing the material thickness may compound the problem. 
     Additionally, if the casting is large and rigid, the equipment required to mechanically work the component must be capable providing a great deal of force, and hence are highly specialist and expensive pieces of equipment (for example, large hydraulic presses.) 
     Hence a method and apparatus which enable the shaping or reshaping of cast components which do not increase the residual stress and/or strain in the component, and which does not require the use of expensive equipment is highly desirable. 
     STATEMENTS OF INVENTION 
     Accordingly there is provided a method for shaping a component cast from a titanium alloy comprising the steps of: heating the component to a plastic temperature such that it becomes plastically deformable; and subjecting the component to a deformation process to thereby plastically deform the component to a desired geometric shape. 
     Thus distortions in the component can be corrected without inducing further stress or strain in the component, and with the application of a relatively low force compared to known processes. 
     Other aspects of the invention provide devices, methods and systems which include and/or implement some or all of the actions described herein. The illustrative aspects of the invention are designed to solve one or more of the problems herein described and/or one or more other problems not discussed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples of the present disclosure will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  shows a component mounted between a first example of a deformation member and a base member; 
         FIG. 2  shows a perspective view of one example of the component; 
         FIG. 3  shows a perspective view of an alternative example of the component; 
         FIG. 4  shows a perspective view of an alternative example of the component; 
         FIG. 5  shows an alternative arrangement to that shown in  FIG. 1 ; and 
         FIG. 6  shows of a component mounted between a second example of a deformation member and a base member. 
     
    
    
     It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings. 
     DETAILED DESCRIPTION 
       FIG. 1  shows a component  10  mounted on base member  12  with a deformation member  14  placed upon the component  10 . The component  10  is a casing made by a casting process from a titanium alloy. The titanium alloy may be titanium 6-4. In the example shown the casting  10  is a section of at least part of an exhaust duct for a gas turbine engine. The casting  10  is substantially “L” shaped in cross-section, and extends in a direction into and out of the page as shown in  FIG. 1 . That is to say, it has the general form of a “L” beam, as shown in  FIG. 2  and  FIG. 3 . The cast component  10  may extend in a planar direction, as shown in  FIG. 2 , or may be curved, as shown in  FIG. 3  and  FIG. 4 . As shown in  FIG. 3  and  FIG. 4  the component may have at least one wall which is double curved such that it is “S” shaped, or have a single curve. 
     The deformation member  14  is configured to engage with at least a part of the surface of the casing component  10 . In the example of  FIG. 1  the deformation member  14  is in communication with a pneumatic or mechanical ram  16  (which may comprise a lever arrangement) configured to press down on the deformation member  14 . However, the ram mechanism  16  is optional, and in other examples the weight of the deformation member  14  acting under the force of gravity is sufficient to provide adequate force on the casting  10 . The deformation member  14  comprises a substantially rigid body  18 . 
     The rigid body of the deformation member  14  is provided with location features  20  for engagement with the surface of the component  10 , the location features  20  defining the desired component geometric shape of the component  10 . The cast component  10  is provided with a first set of location pads  22  for engagement with the location features  20  of the rigid body  18 . As shown in  FIG. 3  the location pads  22  may take the form of substantially square raised regions, or substantially circular raised regions. 
     Alternatively, as shown in  FIG. 4 , the location pads  22  may take the form of substantially rectangular raised regions which extend along a surface of the component  10 . The location pads may be spaced apart at intervals of at least 25 mm but no more than 250 mm. The base member  12  is provided with location features  30  for engagement with the surface of the component  10 , the location features  30  defining the desired component geometric shape. The component  10  is also provided with location pads  32  for engagement with the location features  30  of the base member  12 . 
     An alternative arrangement is shown in  FIG. 5 . This arrangement is substantially as that shown on  FIG. 1 , except the base member  12  is provided with a location feature  30  on a plurality of surfaces of the base member  12 . In this example the location features  30  are provided on surfaces which are at right angles to one another to match the shape of the casting  10 . A second ram  36  is provided as a deformation member  38  at an angle to the vertical direction (as shown in the figures), and is configured to apply a force at an angle to the direction of force applied by deformation member  14  under the force of gravity and/or as applied by the first ram  16  (in examples where the first ram  16  is present). In the example shown the second ram  36  deformation member  38  is orientated at 90 degrees to vertical direction, and is configured to apply a force at right angles to the direction of force applied by deformation member  14  under the force of gravity and/or as applied by the first ram  16  (in examples where the first ram  16  is present). In alternative examples (not shown) the second ram  36 , or further rams, may be provided such that they can apply a force in a direction substantially opposite to the direction of the first ram  16 , with the second or further ram being offset from the first ram  16 . 
     An alternative arrangement is shown in  FIG. 6 . This is similar to the example shown in  FIG. 1  except that the deformation member  14  in this example is a vessel  40  having a flexible wall  42  which defines a cavity  44 , the cavity  44  at least partially filled with a plurality of weights  46 . In this example, the deformation member  14  will conform to the surface of the component  10  and hence location pads  22  on the surface of the component in contact with the deformation member  14  are not required. 
     In  FIG. 1 ,  FIG. 5  and  FIG. 6  the deformation member  14 , component  10  and base member  12  are mounted relative to one another such that the deformation member  14  exerts a force on the component  10  in at least a substantially vertical downward direction, where downward is from top to bottom as shown in the figures. In the example shown in  FIG. 5 , the second ram  36  exerts a force on the component  10  in a direction at an angle to the vertical direction. 
     In another example, the base member  12  is configurable to alter the orientation of the component  10  relative to the deformation member  14 , to thereby change the direction in which the deformation member  14  exerts a force on the component  10 . 
     The surface of the location pads  22 , 32  may be at right angles (i.e. perpendicular) to the direction of the load path. That is to say, the surface of the location pads should be configured such that they are perpendicular to the direction in which a force is to be applied to the component  10 . This prevents movement of the component  10  relative to the deformation member  14  and/or base member  12  as a result of force applied during the deformation process. 
     In the examples of  FIG. 1 ,  FIG. 5  and  FIG. 6 , the surface of the deformation member  14  and/or base member  12  may be made from a ceramic or other high temperature capable material that is inert with respect to the material of the component  10 . 
     The assembly of component  10 , deformation member  14  and base member  12  are placed in a furnace  50  at least during the shaping or reshaping process. 
     The method of the present disclosure, that is to say the method for shaping or reshaping a component cast from a titanium alloy, comprises the following steps. 
     The actual geometric shape of the component  10  prior to being shaped is determined, for example by measurement. The actual geometric shape is compared to the desired geometric shape. The region, or regions, of the component to apply force(s) to achieve the desired geometric shape are determined. The magnitude of the force or forces required to achieve the desired geometric shape are determined. The direction relative to the surface of the component to apply the required force or force(s) to achieve the desired geometric shape is determined. 
     The component  10  is then placed on the base member  12 , and the deformation member  14  is placed upon the component  10 . Rams  16 ,  36  (for example as shown in  FIG. 1  and  FIG. 5 ) are positioned as required. In examples where location pads  22 , 32  are provided on the component  10 , and location features  20 , 30  are provided on the deformation member  14  and base member  12  respectively, there may be a gap between at least some of the location pads  22 , 32  and their respective location features  20 , 30 . This is because the component  10  does not at this stage, i.e. pre-deformation, have the desired geometry, and so all the features of the component  10  may not line up with all the corresponding features of the deformation member  14  and base member  12 . 
     The assembly of component  10 , deformation member  14  and base member  12  are heated in the furnace  50  to the component&#39;s  10  plastic temperature such that it becomes plastically deformable. For a component  10  made from titanium 6-4, the plastic temperature is above 800° C. In particular, it is at least 820° C. and no more than 860° C. The component  10  is then subjected to a deformation process to thereby plastically deform the component  10  to a desired geometric shape. 
     The deformation process comprises the step of applying the predetermined force(s) in the predetermined direction(s) to the at least one predetermined region of the component  10  while the component  10  is at the plastic temperature. The component  10  is held at plastic temperature at least until the deformation process is complete. At least one region of the component  10  is deformed such that it conforms to the desired geometric shape, while the remaining regions of the component  10  may not be deformed. The temperature of the component  10  is then reduced to below the plastic temperature. 
     The force is applied by the deformation member  14  which, as described above, is configured to engage with at least a part of the surface of the component  10 . A pneumatic or mechanical ram  16  may act upon the deformation member  14  to provide at least part of the required force. In examples where location pads  22  are provided on the component  10 , the force is communicated from the deformation member  14  to the location pads  22 , and reacted at these locations by the base member  12 . In examples where location pads  22 , 32  are provided on the component  10 , and location features  20 , 30  are provided on the deformation member  14  and base member  12  respectively, the force is communicated from the location features  20  of the deformation member  14  to the location pads  22  of the component, and reacted at these locations by the base member  12  location features  30 . 
     In the examples shown in  FIGS. 1 ,  4  and  5  the deformation member  14  exerts a force on the component  10  in a substantially vertical direction. In alternative examples the base member  12  is configurable to alter the orientation of the component  10  relative to the deformation member  14 . 
     In all examples, the component  10  is bent and/or twisted during the deformation process such that the component  10  is deformed to conform to the features of the base member  12 . Where the deformation member  14  is a rigid body, for example as described with reference to  FIG. 1 , the component  10  is also deformed to conform to the features of the deformation member  14  during the deformation process. 
     The component  10  may be bent and/or twisted in one or more deformation processes, either in the same or different orientations as required to achieve the desired shape. 
     The volume of the component  10  remains substantially constant throughout the deformation process. The density of the component  10  remains substantially constant throughout the deformation process. The surface area of the component  10  remains substantially constant throughout the deformation process. 
     Additionally the topographical geometry of the component  10  remains substantially constant throughout the deformation process. That is to say, while the component  10  may be bent and/or twisted, the surface of the component  10  will not be distorted. That is to say, while the shape of the substrate which defines the component body may alter during the deformation process, distances between fixed points on the surface of the component will remain substantially constant. Likewise the wall thickness of the component will remain substantially constant. 
     The method of the present disclosure enables titanium or titanium alloy parts to be reworked, adjusted, shaped or reshaped such that they have the desired shape. In practice it has been found that components can be made to within 0.1 mm of their required dimension. 
     A component  10  made from a Titanium alloy, and in particular Titanium 6-4, has very little rigidity at elevated temperatures. The method of the present disclosure provides the advantage of limiting and controlling the amount of displacement when the part is heated. 
     The process produces a very stable part that will be less likely to deform in use and over time, and which may be machined with a reduced risk of deformation during the machining process. 
     Parts that have distorted during machining may also be corrected using this procedure. For example, this may be a repair or as a way of stabilising the part during manufacture. 
     The examples of the present disclosure have been described with reference to the manufacture of at least part of an exhaust duct for a gas turbine engine, where the part has an “L” shaped cross section. However, the apparatus and method are equally applicable to other components, having a different cross section, for applications other than for an exhaust for a gas turbine engine. 
     The foregoing description of various aspects of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person of skill in the art are included within the scope of the invention as defined by the accompanying claims.