Abstract:
One exemplary embodiment of this disclosure relates to a transfer molding assembly. The assembly includes a die having a molding cavity interconnected with a reservoir. The assembly further includes a heater operable to heat the die, and a load plate configured to move under its own weight to transfer material from the reservoir into the molding cavity.

Description:
STATEMENT REGARDING GOVERNMENT SUPPORT 
     This invention was made with government support under Contract No. N-00019-12-D-0002 awarded by the United States Navy. The government has certain rights in this invention. 
    
    
     BACKGROUND 
     Ceramic material, glass material and other high temperature-resistance materials can provide desirable properties for use in relatively severe operating environments, such as in gas turbine engines. Often, such materials are used in ceramic matrix composites, such as fiber-reinforced silicon carbide composites. Such composites are typically fabricated using techniques such as polymer impregnation and pyrolysis (PIP), chemical vapor deposition (CVD), and chemical vapor infiltration (CVI). Ceramic matrix composites also include fiber reinforced glass and glass-ceramic composites. Such composites are typically formed by hot pressing. 
     Another known technique for forming composites is transfer molding. In a typical transfer molding process, a fiber preform is provided into a die, and a softened glass or glass/ceramic material is impregnated into the preform using a hydraulically driven ram. 
     SUMMARY 
     One exemplary embodiment of this disclosure relates to a transfer molding assembly. The assembly includes a die having a molding cavity interconnected with a reservoir. The assembly further includes a heater operable to heat the die, and a load plate configured to move under its own weight to transfer material from the reservoir into the molding cavity. 
     In a further embodiment of any of the above, the material softens as the material is heated by the heater, and wherein the softened material is transferred into molding cavity under the weight of the load plate. 
     In a further embodiment of any of the above, the material is rigid before the heater heats the material, the rigid material resisting movement of the load plate under its own weight. 
     In a further embodiment of any of the above, the assembly includes a control rod, and an injection ram configured to translate along the reservoir under the weight of the load plate. The control rod supports the load plate above the injection ram before the heater softens the control rod. 
     In a further embodiment of any of the above, the material received in the reservoir is a first material, and wherein the control rod is made of a second material different than the first material. 
     In a further embodiment of any of the above, the heater is configured to heat the first material to a transfer molding point before the second material reaches the transfer molding point. 
     In a further embodiment of any of the above, the heater is configured to heat the first material to a transfer molding point before the second material reaches a working point. 
     In a further embodiment of any of the above, the heater is configured to heat the first material to a transfer molding point before the second material reaches a softening point. 
     In a further embodiment of any of the above, the first material and the second material are glass-based materials. 
     In a further embodiment of any of the above, the first material has a lower viscosity than the second material at a first temperature. 
     In a further embodiment of any of the above, the reservoir is located above, relative to a direction of gravity, the cavity. 
     In a further embodiment of any of the above, the assembly includes a controller, the heater including a chamber having a plurality of heating elements, the heating elements in communication with the controller and configured to generate heat in the heater. 
     In a further embodiment of any of the above, the load plate is configured to move solely under its own weight to transfer material from the reservoir into the molding cavity. 
     Another exemplary embodiment of this disclosure relates to a method of transfer molding. The method includes heating a first material such that the material softens and is injected into a preform under the weight of a load plate. 
     In a further embodiment of any of the above, the method includes supporting the load plate with a control rod, and releasing at least a portion of the weight of the load plate in response to the first material reaching a predefined temperature. 
     In a further embodiment of any of the above, the control rod is made of a second material configured to soften at a higher temperature than the first material. 
     In a further embodiment of any of the above, the first material and the second material are glass-based materials. 
     In a further embodiment of any of the above, the first material has a viscosity at or below 10 2.6  poises at a temperature of about 1500° C., and wherein the second material has a viscosity above 10 2.6  poises at a temperature of about 1500° C. 
     In a further embodiment of any of the above, the second material has a viscosity of about 10 7.6  poises at a temperature of about 1500° C. 
     The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings can be briefly described as follows: 
         FIG. 1  illustrates an example transfer molding assembly. 
         FIG. 2  graphically illustrates the relationship between viscosity and temperature for two example materials. 
         FIG. 3  illustrates another example transfer molding assembly. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates an example assembly  20  that can be used in conjunction with a method for processing a process-environment-sensitive material (hereafter “material”), which is a material that is formed into a desired article geometry at high temperatures in a controlled environment, such as under vacuum and/or inert cover gas (e.g., argon). Such materials require high temperatures to enable formation and consolidation into the desired geometry and a controlled environment to manage reactions that can undesirably alter the chemistry of the material. 
     In non-limiting examples, the material can be a ceramic-based material, a glass-based material or a combination of a ceramic/glass-based material. One example includes silicon carbide fiber reinforced ceramic-glass matrix materials. The ceramic-glass matrix can be lithium-aluminosilicate with boron or barium magnesium aluminosilicate, for example. The fibers can include one or more interface layers, such as carbon or boron nitride layers. These and other process-environment-sensitive materials can be rapidly processed into an article using the assembly  20 . 
     In the illustrated example, the article being formed is an annular engine component. Example annular components include turbine rings, rub strips, seals, acoustic tiles, combustor liners, shrouds, heat shields, etc. It should be understood that this disclosure is not limited to annular articles, and extends to articles having other shapes. 
     In this example, the assembly  20  provides a transfer molding assembly. The assembly  20  includes a chamber  24  and a plurality of heaters  26 ,  28  provided therein. It should be noted that although two heaters  26 ,  28  are illustrated, there may be any number of heaters, including only one heater. The heaters  26 ,  28  are configured to provide heat H, which raises the temperature within the chamber  24 . While only one chamber  24  is illustrated, the assembly  20  could include additional chambers. 
     The chamber  24  is connected, through a port  30 , to a gas environment control device  32 , which is in turn in communication with a vacuum pump  34  and/or a pressurized gas source  36 . The gas environment control device  32  is controlled by command of a controller  38 , which is configured to control evacuation of, and process gas flow into, the chamber  24 . Thus, for a given process having a predefined controlled gas environment, the controller  38  can purge the interior of the chamber  24  of air, evacuate the interior to a desired pressure and/or provide an inert process cover gas to a desired pressure. 
     The assembly  20  further includes a support plate  40  located within the chamber  24 , which may be supported by a plurality of legs  42 . A die  44  is provided on the support plate  40 . In this example, the die  44  includes a molding cavity  46  and a reservoir  50  above, relative to the direction of gravity G, the molding cavity  46 . The molding cavity  46  is in fluid communication with the reservoir  50 , as will be appreciated from the below. 
     In  FIG. 1 , a fiber preform  48  is provided in the molding cavity  46 , and a material  52  is placed in the reservoir  50 . An injection ram  54  is provided above the material  52 . The injection ram  54  is shaped to correspond to the shape of the reservoir  50 , and to travel within the reservoir in the direction of gravity G. The injection ram  54  in one example is sealed against the side walls of the reservoir  50  to prevent the material  52  from escaping during injection. Optionally, there may be an exit port at the bottom of the reservoir  50 , or at the bottom of the molding cavity  46 , for directing excess material  52  away from the preform  48 . 
     A load plate  56  is provided above the injection ram  54 , and is in direct contact with the injection ram  54  in this example. The load plate  56  may be rigidly attached to the injection ram  54  in some examples. In other examples, however, the load plate  56  is moveable relative to the injection ram  54 . The weight and/or size of the load plate  56  can be adjusted depending on the properties associated with the particular material being worked upon. 
     Before heat is applied to the die  44 , the material  52  may be a plurality of rigid glass cutlets. These rigid cutlets resist the weight W of the load plate  56 . In order to inject the material  52  into the preform  48 , the controller  38  activates the heaters  26 ,  28  to increase the temperature within the chamber  24 . In response, the temperature of the material  52  rises, which decreases the viscosity of the material  52 , and the material  52  softens. 
     The softened material  52  is injected into the fiber preform  48  under at least a component of the gravitational weight W of the load plate  56 , via movement of the injection ram  54  in the downward direction. The load plate  56  is unforced by a mechanical actuator (such as that commonly associated with a hot press assembly). In other words, the softened material  52  is injected solely under the weight of the load plate  56 . After injection, the preform  48  and the material  52  provide are allowed to cool, and may undergo further processing, as needed, to prepare the article for use. 
     The chamber  24  provides a controlled gas environment for the application of heat, which could otherwise cause undesired reactions in the material (e.g., the preform  48 , or the material  52 ) or degrade the die  44  or other structures of the chamber  24 , particularly if the die  44  is made of graphite. 
     While the assembly illustrated in  FIG. 1  may be effective, the material  52  may be prematurely injected into the preform  48  depending on a number of factors, including the composition and properties of the material  52 . In particular, in some instances, the weight W of the load plate  56  may urge the glass  52  into the preform  48  before the material  52  has been heated to viscosity to avoid or limit damaging the preform  48 . Thus, the force of the flow into the preform  48  could alter the fiber orientations of the preform  48 , or even physically damage the fibers. 
     The relationship between viscosity and temperature for an example material M 1  is illustrated in  FIG. 2 . In one example, the material M 1  is used as the material  52  in  FIG. 1 , and as the material  152  in  FIG. 3 . The material M 1  in one example is a glass-based material, which is initially in the form of glass cutlets. The material M 1  experiences softening at a temperature of about 750° C. (about 1382° F.), wherein the material M 1  has a viscosity V 1  of about 10 7.6  poises (about 580 reyn). This point is illustrated in  FIG. 2  as the “Softening Point,” which is associated with a viscosity at which uniform fibers (e.g., 0.55-0.75 mm [about 0.02-0.03 inches] in diameter and 23.5 mm [about 0.93 in] long) in a material (e.g., such as silicate fibers) elongate under their own weight at a rate of 1 mm (about 0.04 inches) per minute. 
     As the temperature of the material M 1  continues to rise, the material M 1  achieves a working point viscosity V 2  of about 10 4  poises (about 0.15 reyn), at temperature T 2  of about 1100° C. (about 2010° F.). The “Working Point” illustrated in  FIG. 2  corresponds to a viscosity level where a material is soft enough for hot working. 
     Finally, the material M 1  reaches a viscosity of 10 2.6  poises (about 0.006 reyn) at V 3 , at which point the material M 1  is in a substantially fluid state such that it is acceptable for glass transfer molding. The viscosity V 3  is reached at about 1500° C. in this example, and is referenced as a “Transfer Molding Point.” Any viscosity at or below V 3  is acceptable for transfer molding. It should be understood that the illustrated material M 1  is only one example material, and materials having other characteristics come within the scope of this disclosure. 
       FIG. 3  illustrates another example assembly  120  according to this disclosure. To the extent not otherwise described or shown, the reference numerals in  FIG. 3  correspond to the reference numerals of  FIG. 1 , with like parts having reference numerals preappended with a “1.” 
     In the assembly  120  of  FIG. 3 , a plurality of control rods  158 ,  160  are configured to delay a force transfer from the load plate  156  to the material  152 . In particular, the control rods  158 ,  160  support the load plate  156  above the injection ram  154  before the material  152  is heated. That is, before heating, there is an initial clearance C between an upper surface  154 U of the injection ram  154  and a lower surface  156 L of the load plate  156 . 
     In one example, the control rods  158 ,  160  are made of a material M 2 , illustrated in  FIG. 2 , and the material  152  is made of the material M 1 . With reference to  FIG. 2 , the material M 2  of the travel control rods  158 ,  160  is initially rigid, and does not reach the softening point viscosity V 1  until temperature T 3 , which is the temperature for preparing the material M 1  of the material  152  for transfer molding at the viscosity V 3 . 
     At a minimum, the material M 2  is selected such that it has a viscosity greater than V 3  at temperature T 3 . In another example, the material M 2  has a viscosity of about V 2  at temperature T 3 . In still another example, the material M 2  is rigid and has a viscosity above the softening point viscosity V 1  at temperature T 3 . 
     At any rate, in the example of  FIG. 3 , the weight W of the load plate  156  does not transfer to the injection ram  154  until a point at which the material  152  has reached an acceptable transfer molding viscosity V 3 . 
     In one example, the first material M 1  is a Corning Glass Works (CGW) 7070 glass, and the second material M 2  is CGW 7913 glass. This disclosure is not limited to these two particular glass types, however, and it should be understood that other materials come within the scope of this disclosure. 
     In either of the example assemblies  20 ,  120 , the expenses typically associated with transfer molding, such as purchasing a relatively expensive hot press (including the corresponding hydraulics, etc.), are eliminated. The transfer molding assembly and method discussed herein allow for passive injection by the weight of the load plate  56 , rather than active injection by way of a hydraulic actuator. Accordingly, this disclosure can be relatively easily incorporated into a chamber (e.g., a furnace) which is relatively more available, and less expensive than a hot press, which in turn reduces manufacturing costs, etc. 
     Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. Further, it should be understood that terms such as “above,” “downward,” etc., are used herein for purposes of explanation, and should not otherwise be considered limiting. Also, as used herein, the term “about” is not a boundaryless limitation on the corresponding quantities, but instead imparts a range consistent with the way the term “about” is used by those skilled in this art. 
     One of ordinary skill in this art would understand that the above-described embodiments are exemplary and non-limiting. That is, modifications of this disclosure would come within the scope of the claims. Accordingly, the following claims should be studied to determine their true scope and content.