Abstract:
A disclosed resin transfer molding tool includes a mold defining an internal cavity of a fixed geometry and a bladder configured to be received within the internal cavity and define a flexible interface surface for surrounding a molded article. The bladder is fillable with a fluid material to exert a pressure on a surface of the molded article within the mold.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/886,761 filed Oct. 4, 2013. 
     
    
     BACKGROUND 
       [0002]    A resin transfer molding process begins with a fibrous pre-form that is inserted into a rigid mold die piece mold. In the mold, resin is injected at a low temperature into the pre-mold and cured. The curing process changes the resin into a pre-ceramic polymer material. The pre-ceramic polymer material is rigid and allows the part to be removed from the mold tool and pyrolized at very high temperatures. The pyrolized process at high temperature is conducted outside of the tool and converts the pre-ceramic polymer into a ceramic material. During the pyrolysis operation, a significant amount of polymer shrinkage occurs as it is converted into a ceramic material. The significant amount of shrinkage causes porosity including pores and cracks formed within the ceramic matrix. 
         [0003]    After the first pyrolysis process, additional polymer infiltration processes are utilized to fill the pores and cracks that exist in the ceramic matrix from the first process. Additional cycles of the polymer infiltration and pyrolysis process are executed to increase the density and reduce the porosity within the part. However, each high temperature pyrolysis process causes distortion of the part and prevents the part from being reinserted into the original rigid tool utilized to inject resin into the pre-form. Accordingly, the current practice is to simply dip a part into resin, remove from the resin, and pyrolize outside of a rigid tool. However, such processes do not retain sufficient amount of liquid resin within the cores, voids and cracks of the ceramic part to adequately fill and provide the desired density of the completed part. Moreover, such a process often results in significant amounts of pre-ceramic polymer on outer surfaces of the ceramic part that must be machined or otherwise removed prior to the next pyrolysis operation. 
         [0004]    Accordingly, it is desirable to develop a re-infiltration process to inject resin into a ceramic part to fill voids that minimizes the use of excess resin and provides for the more efficient infusion of resin into the cracks and voids formed within the part. 
       SUMMARY 
       [0005]    A resin transfer molding tool according to an exemplary embodiment of this disclosure, among other possible things includes a mold defining an internal cavity of a fixed geometry, and a bladder configured to be received within the internal cavity and define a flexible interface surface for surrounding a molded article. The bladder is fillable with a fluid material to exert a pressure on a surface of the molded article within the mold. 
         [0006]    In a further embodiment of the foregoing, the internal cavity is larger than the desired completed molded article in at least one dimension. The bladder is configured to fill any gap between the internal cavity and a molded article. 
         [0007]    In a further embodiment of any of the foregoing, a resin injecting device is configured for injecting resin into a molded article within the bladder and mold. 
         [0008]    In a further embodiment of any of the foregoing, a vacuum device is configured to apply a vacuum pressure to a molded article received within the bladder while within the mold. 
         [0009]    In a further embodiment of any of the foregoing, the resin transfer molding tool includes a pressure application device for applying a pressure to fluid within the bladder when received within the mold. 
         [0010]    In a further embodiment of any of the foregoing, the pressure application device is configured to apply pressure to fluid within the bladder in a cyclic manner. 
         [0011]    In a further embodiment of any of the foregoing, the pressure application device is configured to apply pressure to the fluid with the bladder in a static manner. 
         [0012]    In a further embodiment of any of the foregoing, the bladder is configured to receive the molded article before insertion into the mold. 
         [0013]    In a further embodiment of any of the foregoing, the bladder includes a reinforcement element defining a desired geometry of the bladder. 
         [0014]    In a further embodiment of any of the foregoing, the fluid within the bladder is a pre-ceramic resin. 
         [0015]    A flexible resin transfer tool according to an exemplary embodiment of this disclosure, among other possible things includes a first mold including a first internal cavity for receiving a pre-mold and infusing resin into the pre-mold to form a ceramic article, a second mold defining a second internal cavity including a fixed geometry, a bladder receivable within the second internal cavity that defines a part cavity for receiving the ceramic article. The bladder includes a variable internal and external geometry for filling gaps between the second internal cavity and the ceramic article and a resin injection device for injecting resin into voids in the ceramic article within the bladder and the second internal cavity. 
         [0016]    In a further embodiment of the foregoing, the bladder is fillable with a pre-ceramic resin for applying a pressure to a surface of the ceramic article to hold uncured resin within the ceramic article until cured. 
         [0017]    In a further embodiment of any of the foregoing, the flexible resin transfer tool includes a pressure application device for applying a pressure to fluid within the bladder when received within the mold. 
         [0018]    In a further embodiment of any of the foregoing, a vacuum device is configured to apply a vacuum pressure to a molded article received within the bladder while within the mold. 
         [0019]    In a further embodiment of any of the foregoing, the pressure application device is configured to apply pressure to fluid within the bladder in a cyclic manner. 
         [0020]    In a further embodiment of any of the foregoing, the pressure application device is configured to apply pressure to the fluid with the bladder in a static manner. 
         [0021]    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. 
         [0022]    These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a schematic view of an example flexible resin transfer molding tool. 
           [0024]      FIG. 2  is a schematic view of an example bladder for the disclosed resin transfer and polymer infiltration process. 
           [0025]      FIG. 3  is a schematic representation of a disclosed method of resin transfer molding and polymer infiltration and pyrolysis to form a ceramic article. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Referring to  FIG. 1 , an example resin transfer molding tool for polymer infiltration and pyrolysis operation includes a mold  12  that defines an internal cavity  26  that receives a ceramic article  22  that is enclosed within an inflatable bladder  14 . The inflatable bladder  14  fills gaps  35  between the outer geometry and shape of the ceramic article  22  and the part cavity  26  defined by the mold  12 . 
         [0027]    The mold  12  includes conduits that communicate resin as is indicated schematically at  16  and that provide a vacuum into the part cavity  26  to remove air to allow for the better infusion of resin into the ceramic article  22 . The example tool  12  also includes a pumping device  20  that fills the bladder  14  to provide the desired pressure against the exterior surfaces of the ceramic article  22  and provide the pressure infusion of resin  18 . A controller  24  is provided to control the resin impregnation  18 , filling of the bladder by the pump  20 , and the vacuum source  16 . 
         [0028]    Referring to  FIG. 2  with continued reference to  FIG. 1 , an example bladder  14  is illustrated and defines an internal part cavity  34  that receives the ceramic article  22 . The bladder  14  includes an internal cavity  28  that is fillable with a liquid such as a pre-ceramic resin utilized to exert a pressure force on the external surfaces of the ceramic article  22 . The internal cavity  34  includes internal surfaces  30  that engage the exterior surfaces of a ceramic article  22 . The bladder  14  also may include a reinforcement structure  32  to define a general overall shape that corresponds with the desired ceramic article geometry. 
         [0029]    The bladder  14  is configured to receive liquid materials, such as a pre-ceramic resin, communicated by the pump  20 . Pre-ceramic resin is utilized to fill the bladder and apply pressure against the ceramic article  22  to hold resin  18  within the ceramic article  22 . The bladder  14  conforms to the ceramic article  22  to enable use of a common tool  12  while accommodating part to part variation caused by the various heat treating processes executed during fabrication of the ceramic article  22 . In this example, the bladder  14  is made from a silicon rubber or similar flexible material that is compatible with the temperatures required for the low temperature curing conducted within the mold tool  12 . 
         [0030]    In traditional resin transfer molding operations, the ceramic article is formed within a first mold by infusing resin into a fiber pre-mold. Once the fiber pre-mold is impregnated with the desired amount of resin, it is cured for a predetermined time to form a pre-ceramic polymer. Curing within the first mold occurs at a relatively low temperature of between 100° C. and 200° C. The pre-ceramic polymer soaked pre-form is then completed in during a pyrolysis operation where the pre-ceramic polymer is treated at very high temperatures to transform the pre-ceramic polymer to a ceramic material. The temperatures are typically between 850° C. and 1800° C. The high temperatures encountered during the pyrolysis operation can distort the resulting ceramic article. Distortions of the ceramic article are not typically uniform or substantially repeatable and therefore prevent the reuse and reinsertion of the pyrolized ceramic article into the original mold tool. This is because the original tool is a rigid structure and cannot accommodate the variations in geometry that occur during processing between various ceramic articles. 
         [0031]    Moreover, after the pyrolysis operation, substantial voids and porosity may be encountered within the initial ceramic article. The repeated polymer infiltration and pyrolysis operations typically utilized to increase the density and reduce the porosity of a ceramic article only increase the deformation of the ceramic part. Moreover, the polymer infusion and pyrolysis process can be inefficient because a substantial amount of the liquid resin is not capable of being maintained within the ceramic article during the pyrolysis operation. 
         [0032]    The example device and method utilizes the fluid filled bladder  14  to accommodate and fill gaps  35  between the ceramic article  22  and the internal surfaces of the mold tool  12  to allow for reinsertion of a pyrolized ceramic article back into an example second mold tool  12 . The bladder  14  is filled with a liquid material that can be utilized to exert a desired pressure against the surfaces of the ceramic article  22  to maintain the resin within the voids, cracks and other openings within the ceramic article  22  during an initial curing process. The bladder  14  maintains a pressure against surfaces of the ceramic article  22  until completion of the curing process. Because a substantial amount of the resin can be maintained within the ceramic article  22  that is encased within the fillable bladder  14 , the number of repeated cycles required to obtain a ceramic article  22  of a desired density can be substantially improved. 
         [0033]    Referring to  FIG. 3  with continued reference to  FIG. 1 , the example method  54  begins with a fiber pre-form  36  inserted into a first mold  38 . The first mold  38  includes a cavity  40  that defines a desired initial geometry and shape of a completed ceramic article. The first mold  38  includes a vacuum source  44  and a resin injection device  42  that is controlled by a controller  46 . As appreciated, although a vacuum source  44  is disclosed; other processes that do not utilize a vacuum are within the contemplation of this disclosure for the initial resin impregnation of the pre-form  36 . 
         [0034]    Within the first mold  38 , as is indicated schematically at  56 , resin is impregnated into the pre-form  36  and allowed to cure to form the pre-ceramic polymer. The pre-ceramic polymer impregnated pre-form  36  is then removed from the first mold  38 . Subsequently the pre-ceramic polymer impregnated preform,  36 , is processed at elevated temperatures  58 , into a ceramic article  48 . 
         [0035]    The ceramic article  48  is then installed into the bladder  14  as is indicated at step  60 . The bladder  14  and ceramic article  48  are then inserted into the second mold  12  that includes an inner cavity  26  that is larger than the cavity  40  of the first mold. The larger inner cavity  26  provided by the second mold  12  accommodates the bladder  14  along with variations in the ceramic article  48 . The bladder  14  is fillable to fill any gaps  35  that may exist between the internal surfaces of the cavity  26  defined by the mold tool  12  and the ceramic article  22 . 
         [0036]    Once the bladder  14  and ceramic article  48  are inserted into the second mold  12 , a resin impregnation process is executed where resin from a resin source  18  is injected into the ceramic article  48  under pressure. A vacuum may be applied to the ceramic article  48  from the vacuum source  16  to draw resin into the ceramic part  48  and fill any cracks and voids that may exist within the initial ceramic article  48 . 
         [0037]    The bladder  14  is filled with a fluid that is compatible with the temperatures incurred during the resin impregnation process. In one example, the bladder  14  is filled with resin to exert pressure on the external surfaces of the ceramic article  22  to force and hold resin into the cracks and voids. The resin may be pumped into the bladder  14  at an increasing pressure until a desired static pressure is obtained and maintained at that desired static pressure. 
         [0038]    In another example, resin is pumped into the bladder  14  in a cyclical manner to provide a pumping action that further infuses resin into cracks, openings and voids in external surfaces of the ceramic article  48 . The cyclical pressure exerted by the pump  20  and, thereby, on the surfaces of the bladder  14  on the external surfaces of the ceramic article  48  aid in resin flow through the part with or without the aid of the vacuum applied by the vacuum source  16 . The cyclical pumping action provided by the bladder  14  can provide significant improvements in resin impregnation during the initial load temperature curing process executed as schematically indicated at  62  within the second mold  12 . Pressure exerted by the bladder  14  is maintained until the resin is cured. 
         [0039]    Once this initial and subsequent resin impregnation and pre-ceramic polymer conversion process is complete, the ceramic article  48  and bladder  14  are removed from the second mold  12 . Upon removal of the ceramic article  48 , the resin that had been subsequently injected into the voids and cracks, and converted into pre-ceramic polymer, requires pyrolization to be converted into the desired ceramic material. The pyrolysis process as generally indicated at  64  includes high temperature heat treatment of the ceramic article  48  as is known in the art. In this example, the heat treatment process  64  exerts a heat indicated schematically by arrows  52  on to the ceramic article  48 . The heat treatment process indicated at  64  can be conducted with the bladder  14  remaining on the part, such that the bladder  14  will encounter the extreme heat and be destroyed such that it may be removed after the pyrolysis process. 
         [0040]    The bladder  14  may also be removed prior to the pyrolysis operation and reused. The bladder  14  is removed from the ceramic article  48  prior to the pyrolysis operation, such that it may be reused for this part or another ceramic article in subsequent resin injection processes as are schematically shown at  62 . A vacuum may be applied to the bladder  14  to aid in removal from the ceramic article  48 . 
         [0041]    In another example, the bladder  14  is destroyed during the heat treatment or pyrolysis process and a second or subsequent bladder is utilized for subsequent processes. 
         [0042]    Once the pyrolysis process  64  is complete, the part may undergo a repeated pyrolysis operation as is indicated at  66  to repeat the resin injection in the second mold  12  with a bladder  14  to infuse resin into any remaining cracks, voids and pores. The process can be repeated as is indicated at  66  until a ceramic article of a desired density and porosity is achieved as is indicated at  68  to achieve a completed ceramic article  50 . 
         [0043]    Accordingly, the example device and method allows resin injection pressures and vacuum that is in excess of atmospheric pressures to fill the deep voids, pores and cracks within a ceramic article after an initial resin injection and pyrolysis process. 
         [0044]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the scope and content of this disclosure.