Patent Publication Number: US-2022212276-A1

Title: Contact matrix for grounding a ceramic component during electrical discharge machining

Description:
FIELD 
     The present subject matter relates generally to electrical discharge machining ceramic components, such as ceramic matrix composite components. 
     BACKGROUND 
     Electrical Discharge Machining (EDM) is sometimes used to machine features in ceramic components, such as Ceramic Matrix Composite (CMC) components for gas turbine engines. For example, EDM can be used to drill cooling holes in CMC high-pressure turbine nozzles. One challenge with drilling features in CMC components via EDM, or ceramic components generally, is that such components are not typically electrically grounded in an efficient and/or effective manner. Typically, a metallic fixture or other metallic structure is used to electrically ground CMC components during EDM. Due to the surface irregularity of the metallic structure and the CMC component, many times only a limited number of contact points are made between the rigid CMC component and the rigid metallic grounding structure. Due to the surface potential or Schottky barrier, the electrical resistance at these contact points can be considerable, which creates bottlenecks of electrical current that obstructs or even fails the electrical grounding process by point overheating and/or arcing. Inefficient and/or ineffective electrical grounding of a CMC component during EDM is undesirable. For instance, ineffective electrical grounding can result in pitting at the grounding contact points. 
     Accordingly, methods that address one or more of the challenges noted above would be useful. 
     BRIEF DESCRIPTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one aspect, a method is provided. The method includes electrical discharge machining a ceramic component while a contact matrix is positioned so that electrically conductive contacts of the contact matrix engage the ceramic component and so that an electrically conductive member of the contact matrix is in electrical conduction to a grounding structure. 
     In another aspect, a contact matrix for facilitating electrical grounding of a ceramic component undergoing electrical discharge machining. The contact matrix includes an electrically conductive backbone. The contact matrix also includes compliant and pressurized electrically conductive contacts extending outward from the electrically conductive backbone. At least some of the compliant and pressurized electrically conductive contacts are biased into engagement with the ceramic component so that the at least some of the compliant and pressurized electrically conductive contacts are in electrical conduction to the ceramic component. Moreover, at least one of the electrically conductive backbone and at least one of the compliant and pressurized electrically conductive contacts are in electrical conduction to a grounding structure. 
     In another exemplary aspect, a method is provided. The method includes positioning a contact matrix between a ceramic matrix composite component and a grounding structure. The contact matrix has an electrically conductive backbone and compliant and pressurized electrically conductive contacts extending outward from the electrically conductive backbone. The method also includes electrical discharge machining the ceramic matrix composite component while the contact matrix is positioned therebetween so that the compliant and pressurized electrically conductive contacts are biased into pressurized engagement with the ceramic matrix composite component and so that the electrically conductive backbone or at least one of the compliant and pressurized electrically conductive contacts is in electrical conduction to the grounding structure. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  is a schematic cross-sectional view of an exemplary gas turbine engine according to various embodiments of the present subject matter; 
         FIG. 2  provides a perspective view of a turbine nozzle segment according to an example embodiment of the present subject matter; 
         FIG. 3  provides a schematic cross-sectional view of a CMC component undergoing electrical discharge machining and also depicts a contact matrix positioned engaged with the CMC component for providing electrical grounding according to an example embodiment of the present subject matter; 
         FIG. 4  provides a close-up schematic view of one contact of the contact matrix of  FIG. 3  engaging the CMC component; 
         FIG. 5  provides a close-up schematic view of an alternative configuration of a contact of a contact matrix engaging a CMC component; 
         FIG. 6  provides a schematic view of another example configuration of a contact matrix according to an example embodiment of the present subject matter; 
         FIG. 7  provides a schematic view of another example configuration of a contact matrix according to an example embodiment of the present subject matter; 
         FIG. 8  provides a schematic cross-sectional view of a CMC component undergoing electrical discharge machining and also depicts the contact matrix of  FIG. 7  positioned engaged with the CMC component for providing electrical grounding; 
         FIG. 9  provides a schematic view of another example configuration of a contact matrix according to an example embodiment of the present subject matter; 
         FIG. 10  provides a schematic view of another example configuration of a contact matrix according to an example embodiment of the present subject matter; 
         FIG. 11  provides a close-up schematic view of one contact of the contact matrix of  FIG. 10  engaging a CMC component; 
         FIG. 12  provides a schematic view of another example configuration of a contact matrix according to an example embodiment of the present subject matter; and 
         FIG. 13  provides a flow diagram of a method according to one example embodiment of the present subject matter. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention. As used herein, the terms “first,” “second,” and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. The terms “upstream” and “downstream” refer to the relative direction with respect to fluid flow in a fluid pathway. For example, “upstream” refers to the direction from which the fluid flows and “downstream” refers to the direction to which the fluid flows. 
     As used herein, a “ceramic component” is a component formed of ceramic-based materials. Ceramic-based materials encompass both homogeneous ceramic materials as well as ceramic composite materials, such as Ceramic Matrix Composite (CMC) materials. CMC materials generally include a ceramic fiber reinforcement material embedded in a ceramic matrix material. As one example, the ceramic fiber reinforcement material and the ceramic matrix material of a CMC material can both be formed of SiC. SiC/SiC CMC components are particularly suitable for high-temperature applications, such as for high-temperature components of aviation gas turbine engines and land-based gas turbine engines used in the power generation industry. SiC fibers can also been used as a reinforcement material for a variety of other ceramic matrix materials, such as, without limitation, titanium carbide (TiC), silicon nitride (Si3N4), and alumina (A1203). 
     Aspects of the present disclosure are directed to methods of Electrical Discharge Machining (EDM) ceramic components, such as CMC components for gas turbine engines. Particularly, disclosed herein is a contact matrix or matrix of electrical contacts that can be positioned between a CMC component and a grounding structure to facilitate efficient and effective electrical grounding of the CMC component during EDM of the CMC component. The contact matrix includes a plurality of contacts that contact or otherwise engage the CMC component. The electrically conductive contacts can be coupled with a backbone. The contacts can be directly connected or attached to the backbone or they can be coupled thereto, e.g., by means of a pin housing and/or a spring. The backbone can be electrically conductive and can be rigid or flexible. Further, the backbone can be straight or can be contoured complementary to the CMC component and/or the grounding structure. 
     Further, the contacts can be compliant and pressurized contacts such that they engage the rigid CMC component with spring-like action. In this way, numerous contacts can be biased into engagement with the CMC component and/or the grounding structure to accommodate the irregularity of the rigid surfaces. As one example, the compliant and pressurized contacts can be electrically conductive bristles. Each electrically conductive bristle can extend from a bristle stem to a bristle tip. The elasticity in a compressed bristle stem can exert contact pressure of the bristle tip to the rigid CMC surface. In this way, the bristles can maintain engagement with the rigid CMC component during EDM. As another example, the compliant and pressurized contacts can be electrically conductive spring-loaded pins. The spring-loaded pins can include an electrically conductive pin and a compressible spring. Compression of the spring behind the pin can exert contact pressure of the pin to the rigid CMC surface. The compressed spring maintains the pin into engagement with the rigid CMC component during EDM. 
     Notably, the contacts can provide pathways for electrical current to pass from the contact matrix to the CMC component or vice versa. Accordingly, the contacts are in electrical conduction to the CMC component when they are biased into engagement with the CMC component. The contact matrix can also be in electrical conduction to a grounding structure, such as a fixture of an EDM system. In this way, electrical current can be passed from the grounding structure to the contact matrix and then from the contact matrix to the CMC component during EDM. It is also possible for electrical current to be passed from the CMC component to the contact matrix and then from the contact matrix to the grounding structure. 
     Advantageously, the contact matrix can significantly increase the number of pathways in which the CMC component can be electrically grounded, which can lead to more efficient and effective electrical grounding of the CMC component during EDM. These numerous pathways increase flow capacity of electrical current to allow EDM at high power. With better electrical grounding, a smoother burn or sparking without contact overheat or arcing can be achieved during EDM, which can result in reduced cycle times and scrap and minimizes the risk of broken tool electrodes, among other benefits. 
       FIG. 1  provides a schematic cross-sectional view of a gas turbine engine in accordance with one example embodiment of the present subject matter. For the depicted embodiment of  FIG. 1 , the gas turbine engine is a high-bypass turbofan jet engine  10 , referred to herein as “turbofan  10 .” As shown in  FIG. 1 , the turbofan  10  defines an axial direction A (extending parallel to a longitudinal centerline  12  provided for reference), a radial direction R, and a circumferential direction extending in a plane orthogonal to the axial direction A three hundred sixty degrees around the longitudinal centerline  12 . 
     The turbofan  10  includes a fan section  14  and a core turbine engine  16  disposed downstream from the fan section  14 . The core turbine engine  16  includes a substantially tubular outer casing  18  that defines an annular core inlet  20 . The outer casing  18  encases, in serial flow relationship, a compressor section including a booster or low pressure (LP) compressor  22  and a high pressure (HP) compressor  24 ; a combustion section  26 ; a turbine section including a high pressure (HP) turbine  28  and a low pressure (LP) turbine  30 ; and a jet exhaust nozzle section  32 . A high pressure (HP) shaft or spool  34  drivingly connects the HP turbine  28  to the HP compressor  24 . A low pressure (LP) shaft or spool  36  drivingly connects the LP turbine  30  to the LP compressor  22 . 
     The fan section  14  includes a variable pitch fan  38  having a plurality of fan blades  40  coupled to a disk  42  in a spaced apart manner. As depicted, the fan blades  40  extend outward from the disk  42  generally along the radial direction R. Each fan blade  40  is rotatable relative to the disk  42  about a pitch axis P by virtue of the fan blades  40  being operatively coupled to a suitable actuation member  44  configured to collectively vary the pitch of the fan blades  40  in unison. The fan blades  40 , disk  42 , and actuation member  44  are together rotatable about the longitudinal axis  12  by LP shaft  36 . 
     Referring still to  FIG. 1 , the disk  42  is covered by a rotatable front nacelle  48  aerodynamically contoured to promote an airflow through the plurality of fan blades  40 . Additionally, the fan section  14  includes an annular fan casing or outer nacelle  50  that circumferentially surrounds the fan  38  and/or at least a portion of the core turbine engine  16 . The nacelle  50  may be supported relative to the core turbine engine  16  by a plurality of circumferentially-spaced outlet guide vanes  52 . Moreover, a downstream section  54  of the nacelle  50  may extend over an outer portion of the core turbine engine  16  so as to define a bypass airflow passage  56  therebetween. 
     During operation of the turbofan  10 , a volume of air  58  enters the turbofan  10  through an associated inlet  60  of the nacelle  50  and/or fan section  14 . As the volume of air  58  passes across the fan blades  40 , a first portion of the air  58  as indicated by arrows  62  is directed or routed into the bypass airflow passage  56  and a second portion of the air  58  as indicated by arrow  64  is directed or routed into the annular core inlet  20  and into the LP compressor  22 . The pressure of the second portion of air  64  is then increased as it is routed through the high pressure (HP) compressor  24  and into the combustion section  26 , where it is mixed with fuel and burned to provide combustion gases  66 . 
     The combustion gases  66  are routed through the HP turbine  28  where a portion of thermal and/or kinetic energy from the combustion gases  66  is extracted via sequential stages of HP turbine stator vanes  68  that are coupled to the outer casing  18  and HP turbine rotor blades  70  that are coupled to the HP shaft or spool  34 , thus causing the HP shaft or spool  34  to rotate, thereby supporting operation of the HP compressor  24 . The combustion gases  66  are then routed through the LP turbine  30  where a second portion of thermal and kinetic energy is extracted from the combustion gases  66  via sequential stages of LP turbine stator vanes  72  that are coupled to the outer casing  18  and LP turbine rotor blades  74  that are coupled to the LP shaft or spool  36 , thus causing the LP shaft or spool  36  to rotate, thereby supporting operation of the LP compressor  22  and/or rotation of the fan  38 . 
     The combustion gases  66  are subsequently routed through the jet exhaust nozzle section  32  of the core turbine engine  16  to provide propulsive thrust. Simultaneously, the pressure of the first portion of air  62  is substantially increased as the first portion of air  62  is routed through the bypass airflow passage  56  before it is exhausted from a fan nozzle exhaust section  76  of the turbofan  10 , also providing propulsive thrust. The HP turbine  28 , the LP turbine  30 , and the jet exhaust nozzle section  32  at least partially define a hot gas path  78  for routing the combustion gases  66  through the core turbine engine  16 . 
     It will be appreciated that, although described with respect to turbofan  10  having core turbine engine  16 , the present subject matter may be applicable to other types of turbomachinery. For example, the present subject matter may be suitable for use with or in turboprops, turboshafts, turbojets, industrial and marine gas turbine engines, and/or auxiliary power units. 
     In some embodiments, components of turbofan  10  can be formed of a composite material. For example, components within hot gas path  78 , such as components of combustion section  26 , HP turbine  28 , and/or LP turbine  30 , can be formed of a CMC material, which is a non-metallic material having high temperature capability. For instance, turbine blades and turbine nozzles can be formed of CMC materials. Other components of turbine engine  10  also may be formed from CMC materials or other suitable composite materials. 
     Exemplary matrix materials for such CMC components can include silicon carbide, silicon, silica, alumina, or combinations thereof. Ceramic fibers can be embedded within the matrix, such as oxidation stable reinforcing fibers including monofilaments like sapphire and silicon carbide (e.g., Textron&#39;s SCS-6), as well as rovings and yarn including silicon carbide (e.g., Nippon Carbon&#39;s NICALON®, Ube Industries&#39; TYRANNO®, and Dow Corning&#39;s SYLRAMIC®), alumina silicates (e.g., Nextel&#39;s 440 and 480), and chopped whiskers and fibers (e.g., Nextel&#39;s 440 and SAFFIL®), and optionally ceramic particles (e.g., oxides of Si, Al, Zr, Y, and combinations thereof) and inorganic fillers (e.g., pyrophyllite, wollastonite, mica, talc, kyanite, and montmorillonite). CMC materials may have coefficients of thermal expansion in the range of about 1.3×10 −6  in/in/° F. to about 3.5×10 −6  in/in/° F. in a temperature range of approximately 1000-1200° F. 
       FIG. 2  provides a perspective view of a turbine nozzle segment  80  according to an exemplary embodiment of the present subject matter. For this embodiment, the turbine nozzle segment  80  is formed of a CMC material, such as one or more of the CMC materials noted above. The turbine nozzle segment  80  is one of a number of nozzle segments that when connected together form an annular nozzle assembly of a gas turbine engine, such as e.g., the turbofan  10  of  FIG. 1 . The nozzle segment  80  includes vanes  82 , such as e.g., stator vanes  68  of the turbofan  10  of  FIG. 1 . Each vane  82  or airfoil and extends between an outer and inner band  84 ,  86 . Notably, the vanes  82  define a plurality of cooling holes  88 . Cooling holes  88  provide film cooling to improve the thermal capability of the vanes  82 . The cooling holes  88  can be fluidly connected to one or more fluid passageways that extend internally through the vanes  82 . The cooling holes  88  as well as other features of the turbine nozzle segment  80  can be machined via an EDM process. 
       FIG. 3  provides a schematic cross-sectional view of a CMC component  200  undergoing EDM. For instance, the CMC component  200  can be the turbine nozzle segment  80  of  FIG. 2  and the feature being machined into the CMC component  200  via EDM can be one of the cooling holes  88 . It will be appreciated that other CMC components, or more generally ceramic components, can be machined via EDM using the inventive concepts disclosed herein. 
     Generally, to machine a feature into the CMC component  200 , an electrode tool of an EDM system is guided proximate to the CMC component  200  submerged in a dielectric fluid. A pulse generator of the EDM system causes the voltage between the electrode tool and the CMC component  200  to increase, which ultimately causes electrical discharges or sparks that remove material from the CMC component  200 . A series of rapidly recurring electrical discharges are made until the desired feature in the CMC component  200  is formed. For safe and effective EDM operation and handling of the CMC component  200 , it is necessary to electrically ground the CMC component  200  during EDM for the efficient conduction of electrical current with minimum contact resistance. In accordance with the inventive aspects of the present subject matter, a contact matrix  100  is provided to facilitate efficient and effective grounding of the CMC component  200  during EDM. 
     As depicted in  FIG. 3 , the contact matrix  100  is positioned such that it engages the CMC component  200  and a grounding structure  300 , e.g., to facilitate electrical grounding during the EDM process. The grounding structure  300  can be a metallic fixture operable to hold the CMC component  200  during EDM, for example. Generally, the contact matrix  100  decreases the electrical contact resistance or the Schottky barrier between the CMC component  200  and the grounding structure  300 , which facilitates efficient and effective electrical conduction between the CMC component  200  and the grounding structure  300  during EDM. 
     The contact matrix  100  includes a backbone  110  and a plurality compliant and pressurized contacts  120 . The backbone  110  and the compliant and pressurized contacts  120  are both formed of an electrically conductive material. The backbone  110  can be any suitable shape. For instance, the backbone  110  can have a rectangular shape as shown in  FIG. 3 . In some embodiments, the backbone  110  can have a helical shape. Accordingly, the backbone  110  can be a helical wire rope in some embodiments. In some embodiments, the backbone  110  can be a rigid electrically conductive member. In other embodiments, the backbone  110  can be a flexible electrically conductive member. Further, in some embodiments, the backbone  110  can be a straight member. In other embodiments, the backbone  110  can be a curved or arcuate member. 
     For the depicted embodiment of  FIG. 3 , the electrically conductive backbone  110  is the electrically conductive member of the contact matrix  100  that engages the grounding structure  300 . As this is a conductive-to-conductive material interface (e.g., metal-to-metal), the Schottky barrier is not present and electrical current can flow with low contact resistance from the backbone  110  to the grounding structure  300  even despite the limited number of contact points CG 1 , CG 2  between the irregular surface of the backbone  110  and the irregular surface of the grounding structure  300 . In other embodiments, as will be explained further herein, the electrically conductive member of the contact matrix  100  that engages the grounding structure  300  can be other suitable members, such as a set of the electrically conductive contacts  120 . 
     Each of the electrically conductive contacts  120  are connected to and extend outward from the backbone  110 . In this way, the backbone  110  acts as the central hub of the contact matrix  100 . The contact matrix  100  can have any suitable number of contacts  120 . Accordingly, the contacts  120  engaged with the CMC component  200  can multiply the capacity of surface current flow of the CMC component  200  by N times, wherein N is the number of contacts of the contact matrix  100  engaging the CMC component  200 . For instance, as shown in  FIG. 3 , each contact  120  engaging the irregular surface of the CMC component  200  creates an electrical conduction pathway or contact point between the CMC component  200  and the contact matrix  100 . As depicted, a first contact  120  engaging the CMC component  200  creates a first contact point C 1  or first conduction pathway, a second contact  120  engaging the CMC component  200  creates a second contact point C 2  or second conduction pathway, and so on to the Nth contact  120  that engages the CMC component  200  to create an Nth contact point CN or Nth conduction pathway between the CMC component  200  and the contact matrix  100 . 
     For this embodiment, the contacts  120  are compliant in that they may each plastically and/or elastically deform or bend when engaged with a component or structure. For the depicted embodiment of  FIG. 3 , the contacts  120  include a plurality of electrically conductive bristles. The bristles can be steel bristles, for example. As shown, the contacts  120 , or bristles in this embodiment, deform or bend when they engage the CMC component  200 . The deformation of the bristles causes the bristles to engage the CMC component  200  with spring-like action such that the bristles are biased into contact with the CMC component  200 . Stated another way, the contacts  120  apply pressure to the CMC component  200 . Contact pressure is present between the bristle tips and CMC surface. This ensures engagement of the contacts  120  with the surface of the CMC component  200  during EDM. With the contact matrix  100  engaged in electrical conduction to the grounding structure  300  and the contacts  120  engaged with the CMC component  200  during EDM, electrical current can effectively pass from the grounding structure  300  to the contact matrix  100  and then to the CMC component  200  via the contacts  120  or vice versa. It is typical for the electrical current to flow from the grounding structure  300  to the CMC component  200  via the contact matrix  100 . 
       FIG. 4  provides a close-up schematic view of one contact  120  of the contact matrix  100  of  FIG. 3  engaging the CMC component  200 . As shown, the contact  120  has a stem or first end  122  and a tip or second end  124 . The first end  122  is connected to the backbone  110  of the contact matrix  100  and the second end  124  is not connected to the backbone  110 . When the contact matrix  100  is moved into position, e.g., between the CMC component  200  and the grounding structure  300 , the contact  120  engages the CMC component  200 . Consequently, the contact  120  transitions from a relaxed state (represented by the dashed line  120 A) to an engaged state (represented by the solid line  120 B). The contact matrix  100  is positioned such that the distance between the backbone  110  and the CMC component  200  is less than the length that the contact  120  extends outward from the backbone  110  in its relaxed state. Accordingly, when the contact  120  engages the CMC component  200  and deforms, the contact  120  engages the CMC component  200  with spring-like action, which provides contact pressure for contact reliability. 
     Particularly, in the engaged state, the contact  120  can undergo both plastic and elastic deformation. For instance, a portion of the contact  120  extending from the first end  122  to some point outward of the first end  122  may plastically deform (i.e., permanent deformation) and a portion from the point outward to the second end  124  may elastically deform (i.e., non-permanent deformation). The portion of the contact  120  that elastically deforms may apply pressure or a force on the CMC component  200 , which thus biases the contact  120  into engagement with the CMC component  200 . The biased engagement of the contact  120  of  FIG. 4  with the CMC component  200  maintains the contact  120  and the CMC component  200  in electrical conduction during EDM. Thus, a reliable electrical conduction pathway for electricity to flow from the contact matrix  100  to the CMC component  200  is provided during EDM. It will be appreciated that all or some of the other contacts  120  of the contact matrix  100  of  FIG. 3  can engage the CMC component  200  in a similar manner as described above with respect to the contact  120  of  FIG. 4 . 
     In some embodiments, the contacts  120  of the contact matrix  100  can be configured in a different manner than those shown in  FIGS. 3 and 4 . For instance, one or more of the contacts  120  can be configured as shown in  FIG. 5 . In  FIG. 5 , the electrically conductive contact  120  has a first end  122  and a second end  124 . For this embodiment, the first end  122  and the second end  124  are connected to the backbone  110  of the contact matrix  100 . When the contact matrix  100  is moved into position, e.g., between the CMC component  200  and the grounding structure  300 , the contact  120  engages the CMC component  200 . As a result, the contact  120  transitions from a relaxed state (represented by the dashed line  120 C) to an engaged and compressed state (represented by the solid line  120 D). The contact matrix  100  is positioned such that the distance between the backbone  110  and the CMC component  200  is less than the length that the contact  120  extends outward from the backbone  110  to its apex  126 . Accordingly, when the contact  120  engages the CMC component  200  and deforms, the contact  120  engages the CMC component  200  with spring-like action, which provides contact pressure for contact reliability. 
       FIG. 6  provides a schematic view of another example configuration of the contact matrix  100 . For this embodiment, the plurality of electrically conductive contacts  120  include a first set  130  of electrically conductive compliant contacts and a second set  140  of electrically conductive compliant contacts. The compliant contacts of the first set  130  alternate with the compliant contacts of the second set  140  in this example embodiment. As shown, the electrically conductive compliant contacts of the first set  130  extend outward from the backbone  110  a first predetermined length L 1  in a first direction D 1 . The electrically conductive compliant contacts of the second set  140  extend outward from the backbone  110  a second predetermined length L 2  in the first direction D 1 . Notably, the first predetermined length L 1  is greater than the second predetermined length L 2 . In other embodiments, the plurality of electrically conductive contacts  120  can include more than two sets of compliant contacts having predetermined lengths. By varying the length of the compliant contacts of the sets, the spring action applied to the CMC component  200  by the compliant contacts can be varied. Further, varying the length of the compliant contacts of the sets allows for additional margin in positioning the contact matrix  100  relative to a CMC component (and in some instances, a metallic grounding structure). 
     With reference now to  FIGS. 7 and 8 , another example configuration of the contact matrix  100  is provided. For this embodiment, the plurality of electrically conductive contacts  120  include a first set  130  of electrically conductive compliant contacts and a second set  140  of electrically conductive compliant contacts. The compliant contacts of the first set  130  extend from the backbone  110  along a first direction D 1  and engage the CMC component  200 , e.g., as shown in  FIG. 8 . The compliant contacts of the second set  140  extend from the backbone  110  along a second direction D 2  and engage the grounding structure  300 , e.g., as shown in  FIG. 8 . Accordingly, for this embodiment, the electrically conductive member of the contact matrix  100  that is in electrical conduction to the grounding structure  300  is the second set  140  of compliant contacts. In some embodiments, the second direction D 2  is opposite the first direction D 1 . In other embodiments, the second direction D 2  is not opposite the first direction D 1 . 
     As shown, the first and second sets  130 ,  140  of compliant contacts can have different predetermined lengths similar to the embodiment shown in  FIG. 6 . However, it will be appreciated that the compliant contacts of the first and second sets  130 ,  140  of the embodiment of  FIGS. 7 and 8  can have all the same length or can have compliant contacts having different lengths randomly arranged with respect to the backbone  110 . 
       FIG. 9  provides a schematic view of another example configuration of the contact matrix  100 . For this embodiment, the backbone  110  is curved or contoured. In this manner, the contacts  120  can contour to the surface or surfaces of the CMC component  200  and/or the grounding structure  300 . This can provide a greater surface area of contact, which can ultimately effectively ground the CMC component  200  during EDM. The backbone  110  can be contoured to any suitable shape. In some embodiments, the backbone  110  is flexible such that the contact matrix  100  can be manipulated relative to the CMC component  200  and/or grounding structure  300 . In other embodiments, the backbone  110  is preformed into the desired contour shape and is rigid. 
     With reference now to  FIGS. 10 and 11 ,  FIG. 10  provides a schematic view of another example configuration of the contact matrix  100 .  FIG. 11  provides a close-up view of one of the contacts  120  of the contact matrix  100  of  FIG. 10 . For this embodiment, the plurality of electrically conductive contacts  120  are spring-loaded pins. As will be explained below, each spring-loaded pin includes an electrically conductive pin and a spring connected thereto. The spring of a given spring-loaded pin provides the compliance to account for the surface irregularity of the CMC surface. The spring also provides the contact pressure for maintaining the pin in contact with the irregular and rigid CMC surface for contact reliability. 
     As shown best in  FIG. 11 , the depicted contact  120 , or electrically conductive pin  150  in this example embodiment, is connected with a spring  152 . The spring  152  extends between a first end  154  and a second end  156 . The pin  150  is connected with the spring  152  at its first end  154 . Particularly, the first end  154  of the spring  152  is received within a recess defined by the pin  150 . The pin  150  can be any suitable shape. Further, the pin  150  and the spring  152  are enclosed within a housing  158 . The housing  158  can be formed of an electrically conductive material. The housing  158  can be connected to or formed integrally with the backbone  110 . The spring  152  can contact or sit relatively flush with the base of the housing  158  or the backbone  110  at its second end  156 . The housing  158  includes one or more stops  160  that retain the pin  150  relative to the housing  158 . The spring  152  can be coupled with a post  162 . The post  162  can assist in maintaining the orientation of the spring  152  and the pin  150 . Each contact  120  in the depicted embodiment of  FIGS. 10 and 11  can be configured in the same manner shown in  FIG. 11 . 
     Notably, for this embodiment, the pin  150  is movable along a first direction D 1 . Particularly, when the pin  150  is not engaged with a surface of the CMC component  200  (or in some instances a metallic grounding structure), the spring  152  is in a relaxed state. When the contact matrix  100  is moved into position such that the pin  150  engages the CMC component  200 , the CMC component  200  applies a force on the pin  150 . The applied force on the pin  150  causes the spring  152  to compress, and consequently, the pin  150  is moved toward the backbone  110  of the contact matrix  100  along the first direction D 1 . When compressed, the spring  152  is in a compressed state. The spring  152  is shown in the compressed state in  FIG. 11 . When compressed, the pin  150  in turn exerts a force on the CMC component  200  as the spring  152  seeks to return to its relaxed state. Thus, the pin  150  is biased into engagement with the CMC component  200 . With the contacts  120 , or spring-loaded pins  150  in this embodiment, engaged with the CMC component  200  during EDM, electrical current can effectively pass from the grounding structure  300  to the contact matrix  100  and then to the CMC component  200  via the contacts  120 . This facilitates efficient and effective grounding of the CMC component  200  during EDM. 
       FIG. 12  provides a schematic view of another example configuration of the contact matrix  100 . For this embodiment, like the embodiment of  FIGS. 10 and 11 , the plurality of electrically conductive contacts  120  are spring-loaded pins. However, in this embodiment, the backbone  110  is curved or contoured. In this manner, the contacts  120 , or spring-loaded pins in this embodiment, can contour or be oriented to the surface or surfaces of the CMC component  200  and/or the grounding structure. This can provide a greater surface area of contact, which can ultimately effectively ground the CMC component  200  during EDM. The backbone  110  can be contoured to any suitable shape. In some embodiments, the backbone  110  is flexible such that the contact matrix  100  can be manipulated relative to the CMC component  200  and/or grounding structure. In other embodiments, the backbone  110  is preformed into the desired contour shape and is rigid. 
     In some embodiments, a contact matrix can include different types of compliant contacts. As one example, in some embodiments, a contact matrix can include both bristles and spring-loaded pins. 
       FIG. 13  provides a flow diagram of a method ( 400 ) of electrical discharge machining a ceramic component according to one example embodiment of the present subject matter. For instance, the method ( 400 ) can be used to electrical discharge machine a CMC component, such as the CMC turbine nozzle segment of  FIG. 2 . Particularly, the method ( 400 ) can be used to electrical discharge machine a cooling hole in the CMC turbine nozzle segment of  FIG. 2 . The method ( 400 ) can be used to electrical discharge machine other ceramic components as well. 
     At ( 402 ), the method ( 400 ) includes electrical discharge machining a ceramic component while a contact matrix is positioned so that electrically conductive contacts of the contact matrix engage the ceramic component and so that an electrically conductive member of the contact matrix is in electrical conduction to a grounding structure. For instance, as shown in  FIG. 3 , the contact matrix  100  can be positioned between the ceramic component (the CMC component  200 ) and the grounding structure  300 . The electrically conductive contacts  120  of the contact matrix  100  engage the ceramic component (the CMC component  200 ). The electrically conductive member of the contact matrix  100 , which in  FIG. 3  is the electrically conductive backbone  110 , is in electrical conduction to the grounding structure  300 . Specifically, the backbone  110  is contacting or otherwise engaged with the grounding structure  300 . Accordingly, during EDM, electrical current can pass from the grounding structure  300  to the contact matrix  100  via the backbone  110 . The electrical current can then pass from the backbone  110  to the electrically conductive contacts  120  of the contact matrix  100  and to the ceramic component (the CMC component  200 ). The contacts  120  engaged with the ceramic component provide many electrical grounding pathways for electrical current to flow to the CMC component during EDM, which as noted, can provide efficient and effective grounding of the ceramic component during EDM. 
     In some implementations of method ( 400 ), the electrically conductive contacts are compliant electrically conductive contacts that are biased into engagement with the ceramic component. For instance, in some implementations, the compliant electrically conductive contacts are bristles, e.g., as shown in the embodiments of  FIGS. 3 through 9 . In other implementations, the compliant electrically conductive compliant and pressurized contacts are spring-loaded pins, e.g., as shown in the embodiments of  FIGS. 10 through 12 . 
     In some implementations, the electrically conductive member of the contact matrix is one or more of the electrically conductive contacts. In such implementations, the one or more of the electrically conductive contacts engage the grounding structure. As one example, as shown in  FIGS. 8 and 9 , a first set  130  of the electrically conductive contacts extend from the backbone  110  and engage the ceramic component (the CMC component  200 ). In such implementations, the electrically conductive member of the contact matrix  100  is a second set  140  of the electrically conductive contacts. As depicted, the electrically conductive contacts of the second set  140  extend from the backbone  110  and engage the grounding structure  300 . In some implementations, as shown in  FIG. 8 , the first set  130  of the electrically conductive contacts extend from the backbone  110  in a first direction D 1  and the second set  140  of the electrically conductive contacts extend from the backbone  110  in a second direction D 2  that is opposite the first direction D 1 . 
     In other implementations, the electrically conductive contacts are connected to and extend outward from a backbone. In such implementations, the electrically conductive member of the contact matrix is the backbone, e.g., as shown in  FIG. 3 . 
     In some implementations, the electrically conductive contacts are coupled with a rigid backbone. In some implementations, the electrically conductive contacts are coupled with a flexible backbone. In some implementations, the electrically conductive contacts are coupled with a backbone that is contoured complementary to the ceramic component, e.g., as shown in  FIG. 9 . In some implementations, the electrically conductive contacts are coupled with a backbone that is straight, e.g., as shown in  FIGS. 3 and 8 . 
     In some implementations, at least one of the electrically conductive contacts has a first end and a second end. In such implementations, the first end is connected to a backbone of the contact matrix and the second end is not connected to the backbone, e.g., as shown in  FIG. 4 . In other implementations, at least one of the electrically conductive contacts has a first end and a second end. In such implementations, the first end and the second end are connected to a backbone of the contact matrix, e.g., as shown in  FIG. 5 . 
     Further, in some implementations, the electrically conductive contacts include a first set of electrically conductive contacts and a second set of electrically conductive contacts. In such implementations, the electrically conductive contacts of the first set extend outward from a backbone a first predetermined length in a first direction and the electrically conductive contacts of the second set extend outward from the backbone a second predetermined length in the first direction, wherein the first predetermined length is greater than the second predetermined length. Such an implementation is depicted in the embodiment of  FIG. 6 . 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 
     Further aspects of the invention are provided by the subject matter of the following clauses: 
     1. A method, comprising: electrical discharge machining a ceramic component while a contact matrix is positioned so that electrically conductive contacts of the contact matrix engage the ceramic component and so that an electrically conductive member of the contact matrix is in electrical conduction to a grounding structure. 
     2. The method of any preceding clause, wherein the ceramic component is a ceramic matrix composite component. 
     3. The method of any preceding clause, wherein the electrically conductive contacts are compliant and pressurized electrically conductive contacts that are biased into pressurized engagement with the ceramic component. 
     4. The method of any preceding clause, wherein the compliant and pressurized electrically conductive contacts are bristles. 
     5. The method of any preceding clause, wherein the compliant and pressurized electrically conductive contacts are spring-loaded pins. 
     6. The method of any preceding clause, wherein the electrically conductive member of the contact matrix is one or more of the electrically conductive contacts, and wherein the one or more of the electrically conductive contacts engage the grounding structure. 
     7. The method of any preceding clause, wherein the electrically conductive contacts are connected to and extend outward from a backbone, and wherein the electrically conductive member of the contact matrix is the backbone. 
     8. The method of any preceding clause, wherein a first set of the electrically conductive contacts extend from a backbone and engage the ceramic component. 
     9. The method of any preceding clause, wherein the electrically conductive member of the contact matrix is a second set of the electrically conductive contacts, and wherein the second set of the electrically conductive contacts extend from the backbone and engage the grounding structure. 
     10. The method of any preceding clause, wherein the first set of the electrically conductive contacts extend from the backbone in a first direction and the second set of the electrically conductive contacts extend from the backbone in a second direction that is opposite the first direction. 
     11. The method of any preceding clause, wherein the electrically conductive contacts are coupled with a backbone, and wherein the backbone is flexible. 
     12. The method of any preceding clause, wherein the electrically conductive contacts are coupled with a backbone, and wherein the backbone is contoured complementary to the ceramic component. 
     13. A contact matrix for facilitating electrical grounding of a ceramic component undergoing electrical discharge machining, the contact matrix comprising: an electrically conductive backbone; and compliant and pressurized electrically conductive contacts extending outward from the electrically conductive backbone, wherein at least some of the compliant and pressurized electrically conductive contacts are biased into engagement with the ceramic component so that the at least some of the compliant and pressurized electrically conductive contacts are in electrical conduction to the ceramic component, and wherein at least one of the electrically conductive backbone and at least one of the compliant and pressurized electrically conductive contacts are in electrical conduction to a grounding structure. 
     14. The contact matrix of any preceding clause, wherein the compliant and pressurized electrically conductive contacts are bristles. 
     15. The contact matrix of any preceding clause, wherein the compliant and pressurized electrically conductive contacts are spring-loaded pins. 
     16. The contact matrix of any preceding clause, wherein the ceramic component is a ceramic matrix composite component. 
     17. The contact matrix of any preceding clause, wherein the at least one of the compliant and pressurized electrically conductive contacts is in electrical conduction to the grounding structure. 
     18. The contact matrix of any preceding clause, wherein the electrically conductive backbone is in electrical conduction to the grounding structure. 
     19. The contact matrix of any preceding clause, wherein a first set of the compliant and pressurized electrically conductive contacts extend outward from the electrically conductive backbone along a first direction and engage the ceramic component and a second set of the compliant and pressurized electrically conductive contacts extend outward from the electrically conductive backbone along a second direction and engage the grounding structure, wherein the first direction is opposite the second direction. 
     20. A method, comprising: positioning a contact matrix between a ceramic matrix composite component and a grounding structure, the contact matrix having an electrically conductive backbone and compliant and pressurized electrically conductive contacts extending outward from the electrically conductive backbone; and electrical discharge machining the ceramic matrix composite component while the contact matrix is positioned therebetween so that the compliant and pressurized electrically conductive contacts are biased into pressurized engagement with the ceramic matrix composite component and so that the electrically conductive backbone or at least one of the compliant and pressurized electrically conductive contacts is in electrical conduction to the grounding structure.