Abstract:
An exemplary mold assembly includes a mold providing a cavity, and a heating element configured to heat a first portion of the mold at a first rate to melt a first amount of metal powder within the cavity, and further configured to heat a second portion of the mold at a different second rate to melt a second amount of powder within the cavity. The heating element includes a portion on a first side of the cavity and a portion on an opposing, second side of the cavity. The heating element is configured to receive the mold such that the heating element extends circumferentially about an entire perimeter of the mold.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/461,280, which was filed on 1 May 2012 and is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates generally to casting a component and, more particularly, to casting using metal powder. 
         [0003]    Conventional casting techniques involve heating a metal to form liquid metal, and then moving the liquid metal into a mold cavity. The liquid metal cools and hardens within the mold cavity to form a cast component. 
         [0004]    There are several problems with conventional casting techniques. As an example, completely filling the mold cavity with liquid metal is difficult, especially when casting components having relatively complex geometries. Incomplete fills may result in undesirable voids and weak areas in the cast component. 
       SUMMARY 
       [0005]    A mold assembly according to an exemplary aspect of the present disclosure includes, among other things, a mold providing a cavity, and a heating element configured to heat a first portion of the mold at a first rate to melt a first amount of metal powder within the cavity, and further configured to heat a second portion of the mold at a different second rate to melt a second amount of powder within the cavity. The heating element includes a portion on a first side of the cavity and a portion on an opposing, second side of the cavity. The heating element is configured to receive the mold such that the heating element extends circumferentially about an entire perimeter of the mold. The heating element is configured to heat the first portion at the first rate and second portion at the second rate without moving the mold. The heating element is configured to control a cooling of the mold by shutting off a first area of the heating element before another second area of the heating element without moving the mold relative to the heating element. 
         [0006]    In a further non-limiting embodiment of the foregoing mold assembly, the heating element may comprise an induction furnace coil. 
         [0007]    In a further non-limiting embodiment of either of the foregoing mold assemblies, the first area comprises at least one first coil of the induction furnace coil, and the second area comprises at least one other second coil of the induction furnace coil. 
         [0008]    In a further non-limiting embodiment of any of the foregoing mold assemblies, the shutting off is a sequential shutting off of the at least one first coil before the at least one second coil. 
         [0009]    In a further non-limiting embodiment of any of the foregoing mold assemblies, the mold is a reusable mold. 
         [0010]    In a further non-limiting embodiment of any of the foregoing mold assemblies, the mold is configured to hold the melted metal powder as the melted metal powder cools. 
         [0011]    In a further non-limiting embodiment of any of the foregoing mold assemblies, the heating element comprises an induction furnace coil configured to shut off individual coils to control a cooling of the mold. 
         [0012]    A cast component assembly according to another exemplary aspect of the present disclosure includes, among other things, a component. At least a portion of the component is formed from a metal powder that has been melted and cooled within a mold cavity without moving the component relative to the mold cavity. The metal powder has been melted using a heating element on a first side of the component and a second heating element on an opposing, second side of the component. The heating element is configured to receive the mold such that the heating element extends circumferentially about an entire perimeter of the mold. The metal powder is cooled at different rates by shutting off a first area of the heating element prior to a second area of the heating element. 
         [0013]    In a further non-limiting embodiment of the foregoing mold assembly, the heating element comprises an induction furnace coil. 
         [0014]    In a further non-limiting embodiment of either of the foregoing mold assemblies, the first area comprises at least one first coil of the induction furnace coil, and the second area comprises at least one other second coil of the induction furnace coil. 
         [0015]    In a further non-limiting embodiment of any of the foregoing mold assemblies, the shutting off is a sequential shutting off of the at least one first coil before the at least one second coil. 
         [0016]    In a further non-limiting embodiment of any of the foregoing mold assemblies, the portion is formed from metal powder that has been completely melted. 
         [0017]    In a further non-limiting embodiment of any of the foregoing mold assemblies, the component is a turbomachine component. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0018]    The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows: 
           [0019]      FIG. 1  shows a cross-sectional, schematic view of an example turbomachine. 
           [0020]      FIG. 2  shows a flow of an example method of forming a component of the turbomachine of  FIG. 1 . 
           [0021]      FIG. 3  shows an example component formed according to the method of  FIG. 2 . 
           [0022]      FIG. 4  shows a mold used in the method of  FIG. 2 . 
           [0023]      FIG. 5  shows an example furnace for heating the mold of  FIG. 4 . 
           [0024]      FIG. 6  shows an exploded view of the mold of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  schematically illustrates an example turbomachine, which is a gas turbine engine  20  in this example. The gas turbine engine  20  is a two-spool turbofan gas turbine engine that generally includes a fan section  22 , a compressor section  24 , a combustion section  26 , and a turbine section  28 . 
         [0026]    Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans. That is, the teachings may be applied to other types of turbomachines and turbine engines including three-spool architectures. 
         [0027]    In the example engine  20 , flow moves from the fan section  22  to a bypass flowpath B or a core flowpath C. Flow from the bypass flowpath B generates forward thrust. The compressor section  24  drives air along the core flowpath C. Compressed air from the compressor section  24  communicates through the combustion section  26 . The products of combustion expand through the turbine section  28 . 
         [0028]    The example engine  20  generally includes a low-speed spool  30  and a high-speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36 . The low-speed spool  30  and the high-speed spool  32  are rotatably supported by several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively, or additionally, be provided. 
         [0029]    The low-speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low-pressure compressor  44 , and a low-pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a geared architecture  48  to drive the fan  42  at a lower speed than the low-speed spool  30 . 
         [0030]    The high-speed spool  32  includes an outer shaft  50  that interconnects a high-pressure compressor  52  and high-pressure turbine  54 . 
         [0031]    The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A, which is collinear with the longitudinal axes of the inner shaft  40  and the outer shaft  50 . 
         [0032]    The combustion section  26  includes a circumferentially distributed array of combustors  56  generally arranged axially between the high-pressure compressor  52  and the high-pressure turbine  54 . 
         [0033]    In some non-limiting examples, the engine  20  is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6 to 1). 
         [0034]    The geared architecture  48  of the example engine  20  includes an epicyclic gear train, such as a planetary gear system or other gear system. The example epicyclic gear train has a gear reduction ratio of greater than about 2.3 (2.3 to 1). 
         [0035]    The low-pressure turbine  46  pressure ratio is pressure measured prior to inlet of low-pressure turbine  46  as related to the pressure at the outlet of the low-pressure turbine  46  prior to an exhaust nozzle of the engine  20 . In one non-limiting embodiment, the bypass ratio of the engine  20  is greater than about ten (10 to 1), the fan diameter is significantly larger than that of the low pressure compressor  44 , and the low-pressure turbine  46  has a pressure ratio that is greater than about 5 (5 to 1). The geared architecture  48  of this embodiment is an epicyclic gear train with a gear reduction ratio of greater than about 2.5 (2.5 to 1). It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans. 
         [0036]    In this embodiment of the example engine  20 , a significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. This flight condition, with the engine  20  at its best fuel consumption, is also known as “Bucket Cruise” Thrust Specific Fuel Consumption (TSFC). TSFC is an industry standard parameter of fuel consumption per unit of thrust. 
         [0037]    Fan Pressure Ratio is the pressure ratio across a blade of the fan section  22  without the use of a Fan Exit Guide Vane system. The low Fan Pressure Ratio according to one non-limiting embodiment of the example engine  20  is less than 1.45 (1.45 to 1). 
         [0038]    Low Corrected Fan Tip Speed is the actual fan tip speed divided by an industry standard temperature correction of Temperature divided by 518.7̂0.5. The Temperature represents the ambient temperature in degrees Rankine. The Low Corrected Fan Tip Speed according to one non-limiting embodiment of the example engine  20  is less than about 1150 fps (351 m/s). 
         [0039]    Referring to  FIGS. 2 to 6  with continuing reference to  FIG. 1 , the gas turbine engine  20  includes a component  60  formed according to a component forming method  64 . The component  60  is a compressor case of the gas turbine engine  20  in this example. The method  64  could be used to form various other types of components, including other turbomachine components, such as exhaust ducts, and components of other assemblies, such as automotive assemblies. 
         [0040]    The method  64  includes a step  68  of positioning a metal powder  72  in a mold cavity  76 , a step  80  of melting the metal powder  72  in the mold cavity  76 , and a step  84  of cooling the metal powder  72  after the melting. The melted metal powder hardens when cooled to form the component  60 . 
         [0041]    The positioning step  68  involves any technique suitable for communicating this metal powder  72 , in powder form, into the mold cavity  76 . In one specific example, the metal powder  72  is poured into the mold cavity  76 , and mold  88  providing the mold cavity  76  is vibrated to settle the metal powder within the mold cavity  76 . The metal powder  72  may be compressed or uncompressed within the mold cavity  76 . 
         [0042]    The melting step  80 , in one example, involves heating the mold  88  and the metal powder  72  within an induction furnace  92 . In such an example, the mold  88  having the metal powder  72  within the mold cavity  76  is placed within a crucible  96  of the furnace  92 . Current is then moved through a heating element, such as induction furnace coils  98  surrounding the crucible  96 , to add thermal energy to the mold  88  and the metal powder  72 . Areas of the mold  88  may be heated at different rates to achieve a desired melt of the metal powder within the mold cavity  76 . 
         [0043]    The induction furnace  92  may be a vacuum induction furnace. In such example, a vacuum may be drawn on the area within the crucible  96  such that the mold  88  having the metal powder  72  is within the vacuum. A vacuum environment helps reduce the likelihood of trapped gasses and oxygen contamination. Other example induction furnaces may incorporate a conventional vacuum or vacuum hot press. 
         [0044]    In other examples, energy assisted metal flow, such as pressure, ultrasound, centrifugal forces, and other methods as appropriate may be used to enhance the molten metal fluidity inside the mold  88 . 
         [0045]    The heating of the mold  88  and the metal powder  72  is controlled to provide a quiescent melt of the metal powder  72 . In some examples, all the metal powder  72  within the mold cavity  76  is heated to, or beyond, the liquidus point. That is, all the metal powder is completely melted, not some portion of the metal powder. 
         [0046]    Heating the metal powder  72  below the liquidus point forms a metal slurry, which conforms to the shape of the mold cavity  76 . The example metal slurry includes spherical solidus particles, which limits undesirable dendrite growth and facilitates better metal flow. The metal slurry is then cooled to provide the component  60 . The cooling in the step  84  is controlled to reduce areas of high stress in the component  60 . Controlling the cooling rate may include sequentially shutting off some of the coils  98  before others of the coils  98  to cool some areas of the mold cavity  76  and metal slurry at different rates than other areas. 
         [0047]    Once cooled, the component  60  is removed from the mold  88  and may be trimmed and the surfaces finished prior to installation within the gas turbine engine  20 . 
         [0048]    In this example, the metal powder  72  is a metal powder alloy, such as Inconel 625, and the mold  88  is graphite. Some or all of the surfaces of the mold cavity  76  may be lined with a protective material, such as a high purity alumina. 
         [0049]    The example mold  88  includes several separate pieces  88   a  to  88   d.  Some or all of the mold pieces  88   a  to  88   d  may be reused to mold components in addition to the component  60 . Utilizing multiple pieces  88   a  to  88   d  facilitates a mold cavity having a relatively complex geometry, and filling such the mold cavity with the metal powder  72 . Relatively complex geometries include thin walled panels. 
         [0050]    Filling the mold cavity  76  may take place in stages as the mold pieces  88   a  to  88   d  are assembled to from the mold  88 . For example, the portions of the mold cavity  76  provided by the piece  88   d  may be filled with the metal powder  72  prior to assembling the remaining pieces  88   a  to  88   c.    
         [0051]    In some examples, select areas of the mold cavity  76  are filled with component strengthening structures  102 , such silicon carbide fibers. The metal powder  72  surrounds these structures  102  during the step  68 . The structures  102  are typically located at areas of potential weakness in the component  60 . The structures  102  are held in position by the component  60  after the component  60  is formed. 
         [0052]    In some examples, select areas of the mold cavity  76  are filled with other items, such as sensors  106 , such as isotope markers. The metal powder  72  surrounds these sensors  106  during the step  68 . The sensors  106  are held in position by the component  60  after the component  60  is formed. 
         [0053]    In some examples, threaded inserts, studs, fittings, etc., are placed in the mold cavity  76 . The powdered metal  72  surrounds these components during the step  68 . The components could also be co-molded or over-molded with the powdered metal  72 . 
         [0054]    In some examples, different types of metal powder  72  may be used within the mold cavity  76 . For example, areas of the mold cavity  76  that correspond to projected weak areas of the component  60  may be filled with a relatively high-strength metal powder, whereas other areas are filled with a relatively low-strength (and lower cost) metal powder. 
         [0055]    Features of the disclosed examples include a method capable of producing components having relatively complex geometries due to the elimination of run length limitations associated with filling a mold cavity with a liquid material. 
         [0056]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.