Patent Publication Number: US-2023158759-A1

Title: Locking hole plug for sealing holes in composite structures

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application to U.S. patent application Ser. No. 16/049,317 filed on Jul. 30, 2018, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present teachings relate to the field of composite structures formed from composite materials and, more particularly, to rework and repair of composite structures. 
     BACKGROUND 
     Composite materials such as composite fiber reinforced polymer are commonly used in various industries for their advantages of weight, strength, rigidity, moldability into complex contoured shapes, etc., compared to some other materials. In the aerospace industry, composite fiber reinforced polymers (referred to herein collectively as “carbon composite” for simplicity) are commonly used to form various aircraft structures or portions of structures such as fuselages, wings, empennages, etc. The carbon composite can include multiple layers of carbon fiber sheets laminated together using a resin adhesive, matrix, or binder. To complete a carbon fiber assembly that includes the carbon composite, an outer shell or skin panel (i.e., skin) can be attached with fasteners to an inner frame that can include metal stringers and ribs. 
     While carbon composites provide a robust strength and durability, rework and/or repair of fatigued, damaged, or other regions or areas is occasionally required. A region to undergo rework may be caused, for example, by physical contact with other objects, gradual wear, material or manufacturing defects, wind damage, lightning strike, chemical damage, fatigue, or other causes. In other cases, the region may result from rework of the structure, for example, from installing additional framework that supports the composite layer. The region may include only surface damage to the skin or may extend further into the carbon composite. 
     In some cases, depending on surrounding structures, the composite resin can be reworked or repaired by removing the damaged area, applying a fiber patch and an epoxy resin with a curing agent, curing the resin, then sanding and finishing the fiber patch and surrounding areas to complete the repair. Generally, a vacuum force is applied to the fiber patch during the resin cure to compact the two or more fiber layers that make up the fiber patch by removing air and volatile gases from within and between the laminated layers, and to remove excess resin. 
     Improved structures, methods, and kits for repairing composite structures would be a welcome addition to the art. 
     SUMMARY 
     The following presents a simplified summary in order to provide a basic understanding of some aspects of one or more implementations of the present teachings. This summary is not an extensive overview, nor is it intended to identify key or critical elements of the present teachings, nor to delineate the scope of the disclosure. Rather, its primary purpose is merely to present one or more concepts in simplified form as a prelude to the detailed description presented later. 
     In an implementation of the present teachings, a hole plug includes a flange having a first diameter, wherein the flange is positioned at a first end of the hole plug, a bevel extending from, and intersecting, the flange at an angle, a shank extending from the bevel away from the flange to a second end of the hole plug opposite the first end, the shank including a second diameter that is smaller than the first diameter and a plurality of longitudinal grooves defined by the shank and oriented around an exterior of the shank. The hole plug further includes a plurality of nubs positioned on, and extending from, the exterior of the shank, wherein the plurality of nubs are positioned between the plurality of longitudinal grooves. 
     Optionally, the plurality of nubs each include a radius and a tangent of each radius parallel to a longitudinal axis of the hole plug intersects the flange within the first diameter. The hole plug can further include a circumferential notch defined by the shank, wherein the circumferential notch is positioned between the plurality of longitudinal grooves and the flange. The plurality of nubs can each include a first height that is parallel to a longitudinal axis of the hole plug. The plurality of longitudinal grooves each have a second height that is parallel to the longitudinal axis of the hole plug and greater than the first height, and the plurality of longitudinal grooves can be positioned closer to the first end and the second end of the hole plug than the plurality of nubs. The second end of the hole plug can include a chamfered surface, and the plurality of longitudinal grooves can extend into the chamfered surface. 
     Additionally each nub can define a radius, such that the plurality of nubs define a plurality of radii. Each radius can include a tangent that is parallel to a longitudinal axis of the hole plug, and each tangent of each radius intersects the flange within the first diameter. 
     In an implementation, the hole plug can have a third diameter through a first nub, through the shank, and through a second nub that is opposite the first nub, and the third diameter can be less than the first diameter and greater than the second diameter. The hole plug can be formed from a single piece of material, and the single piece of material can be maraging steel. The hole plug can have a surface roughness, wherein an average roughness centerline “R a ” of the surface roughness is from 250 microns (μm) to 400 μm. Further, 
     In another implementation of the present teachings, a composite fiber assembly includes a composite laminate and a skin overlying the composite laminate, the composite laminate and the skin having a hole therethrough, wherein a first diameter of the hole through the skin is larger than a second diameter of the hole through the composite laminate. The composite fiber assembly further includes a hole plug within the hole, the hole plug having a flange having a third diameter, wherein the flange is positioned at a first end of the hole plug, a bevel extending from, and intersecting, the flange at an angle, a shank extending from the bevel away from the flange to a second end of the hole plug opposite the first end. The shank includes a fourth diameter that is smaller than the third diameter and a plurality of longitudinal grooves defined by the shank and oriented around an exterior of the shank. The hole plug further includes a plurality of nubs positioned on, and extending from, the exterior of the shank, wherein the plurality of nubs are positioned between the plurality of longitudinal grooves, and wherein the composite laminate physically contacts the hole plug between the flange and the plurality of nubs. 
     Optionally, the plurality of nubs each comprise a radius and a tangent of each radius parallel to a longitudinal axis of the hole plug intersects the flange within the third diameter. The hole plug can further include a circumferential notch defined by the shank and the circumferential notch is positioned between the plurality of longitudinal grooves and the flange. The plurality of nubs can have a first height that is parallel to a longitudinal axis of the hole plug, the plurality of longitudinal grooves can each have a second height that is parallel to the longitudinal axis of the hole plug and greater than the first height, and the plurality of longitudinal grooves can be positioned closer to the first end and the second end of the hole plug than the plurality of nubs. The hole plug can further include a chamfered surface at the second end, wherein the plurality of longitudinal grooves extend into the chamfered surface. 
     Another implementation of the present teachings includes a method for reworking a region of a composite resin assembly having a composite laminate and a skin overlying the composite laminate. The method includes defining a hole within the region of the composite resin assembly, wherein the hole comprises a first diameter within the skin and a second diameter within the composite laminate, and the first diameter is larger than the second diameter, applying an adhesive to a plurality of grooves defined by a shank of a hole plug, fully inserting the hole plug into the hole, wherein the hole plug is recessed within the skin, curing the adhesive, and subsequent to curing the adhesive, completing the reworking of the region. The completing of the reworking of the region can optionally include applying a vacuum bag to the region subsequent to curing the adhesive and applying a vacuum force to the region and to the hole plug. The applying of the vacuum force to the region can debulk one or more repair layers overlying the hole plug. The method can further include forming a cant on the composite laminate, partially inserting the hole plug into the hole, wherein nubs extending from the shank of the hole plug rest on the cant, and applying the adhesive to a notch that encircles the shank of the hole plug. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in, and constitute a part of this specification, illustrate implementations of the present teachings and, together with the description, serve to explain the principles of the disclosure. In the figures: 
         FIG.  1    is a side view of a hole plug in accordance with an implementation of the present teachings. 
         FIG.  2    is a plan view or top view of the hole plug of  FIG.  1   . 
         FIG.  3    is a bottom view of the hole plug of  FIG.  1   . 
         FIG.  4    is a cross section of a composite fiber assembly having a area for repair or rework. 
         FIG.  5    depicts the  FIG.  4    structure after forming or shaping a hole therethrough. 
         FIG.  6    depicts the  FIG.  5    structure after partially inserting a hole plug into the hole. 
         FIG.  7    depicts the  FIG.  6    structure after fully inserting the hole plug into the hole. 
         FIG.  8    depicts the  FIG.  7    structure during repair or rework. 
         FIG.  9    depicts the  FIG.  8    structure after completing the repair or rework. 
         FIG.  10    depicts the  FIG.  9    structure after drilling out the hole plug and lining a resulting fastening hole with a liner. 
         FIG.  11    is a functional block diagram depicting a hole plug within a hole of a composite laminate. 
         FIG.  12    is a flow chart of a method for repairing or reworking a workpiece. 
     
    
    
     It should be noted that some details of the figures have been simplified and are drawn to facilitate understanding of the present teachings rather than to maintain strict structural accuracy, detail, and scale. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary implementations of the present teachings, examples of which are illustrated in the accompanying drawings. Wherever convenient, the same reference numbers will be used throughout the drawings to refer to the same or like parts. It will be understood that the structures referenced herein may include additional features which are not depicted for simplicity, while various depicted structures may be removed or modified. 
     As discussed above, a vacuum force can be applied to a surface area during repair of a carbon composite. The vacuum force debulks the two or more fiber layers by removing air and volatile gases from within and between the laminated layers, and removes excess resin. 
     As discussed above, some structures can include a carbon composite covered by a hard skin panel to form a composite fiber assembly. The composite fiber assembly can include a pair of adjacent or parallel surfaces that form a hollow area or gap between the adjacent surfaces. This construction can impede or prevent access to the back side of the surface undergoing repair or rework (i.e., the repair surface). When this hollow area has a high volume or is open to the inflow of air or other gases, a vacuum force on the repair surface during the cure of the repair patch can be difficult or impossible to establish and, if applied, can result in the repair patch lifting away from the repair surface. 
     The present teachings thus include a hole plug that can be positioned through the laminated layers of the carbon composite. The hole plug fills the opening through the carbon composite and simplifies the repair of the structure. 
       FIG.  1    is a side view,  FIG.  2    is a bottom view, and  FIG.  3    is a top view of a hole plug  100  in accordance with an example implementation of the present teachings. The hole plug design includes various features for use with carbon composites such as multilayer carbon fiber resin structures as described below. It will be appreciated that the hole plug  100  depicted in the figures is an exemplary implementation, and that other implementations may include other features that have not been depicted for simplicity, while various depicted features may be removed or modified. 
     The hole plug  100  in the implementation of  FIG.  1    includes a first or upper surface  102  at a first end of the hole plug  100 , a second or lower surface  104  at a second end of the hole plug  100 , and a body  106  positioned between the upper surface  102  and the lower surface  104  (i.e., between the first end and the second end). The upper  102  and lower  104  surfaces can be planar or generally planar, and parallel or generally parallel with each other. The body  106  includes a flange  108  that can intersect the upper surface  102  at an angle of about 90°±5° and has a thickness  110 . The body  106  further includes a bevel  112  that intersects the flange  108  and a shank  114  that intersects the bevel  112 . The bevel  112  can have an angle of about 100°±5° relative to a longitudinal axis A that extends through a center of the hole plug  100 , or another angle that matches a countersink of the hole it is being used to fill as described in more detail below. A bevel  112  with an angle of less than 95° or greater than 105° can result in a poor adhesive bond with the carbon fiber laminate, and may result in leakage of air around the hole plug  100  upon the application of a vacuum during use. The shank  114  can be generally parallel with the longitudinal axis A. 
     The shank  114  defines a notch  116  that can encircle an entirety of the shank  114  around the longitudinal axis A, thus providing a circumferential notch. Two linear edges of the notch  116  can intersect to form an angle theta 1 (θ 1 ) of about 45°±5°. The shank  114  further defines, at least in part, a plurality of grooves  118 . Each groove  118  has a height that is parallel to the longitudinal axis A and a width that is perpendicular to the longitudinal axis A, where the height is greater than the width, and thus form longitudinal grooves  118 . The plurality of grooves  118  extend along a majority of the shank  114  parallel to the longitudinal axis A. Further, the plurality of grooves  118  extend into a chamfered surface  120  or chamfer  120 , and thus the chamfer  120  defines a portion of each of the plurality of grooves  118 .  FIG.  3    depicts eight grooves  118  generally equally spaced around the circumference of the hole plug  100 , and thus a center of each groove  118  is spaced from each of two adjacent grooves  118  by 45° around the circumference of the hole plug  100 . Two linear edges of each groove  118  can intersect to form an angle theta 2 (θ 2 ) of about 97.2°±5°. 
     The hole plug  100  further includes a plurality of locking detents, bumps, retention members, or nubs  122  (hereinafter, collectively, “nubs”) that extend from the shank  114 .  FIGS.  1  and  3    depict one nub  122  positioned between each pair of adjacent grooves  118 . The nubs  122  are generally equally spaced around the circumference of the hole plug  100 , and thus a center of each nub  122  is spaced from each of two adjacent nubs by 45° around the circumference of the hole plug  100 . Each nub  122  can include, for example, a spherical sector, a spherical slice, a hemisphere, etc., having a radius, such that the plurality of nubs define a plurality of radii. As depicted in  FIG.  1   , a tangent T of the radius of each nub  122  that is parallel to the longitudinal axis A intersects the bevel  112  within an outside diameter D 1  ( FIG.  2   ) of the flange  108 . In another aspect, a width W of the hole plug  100  through the longitudinal axis A and through a pair of nubs  122  that are positioned on opposite sides of the shank  114  is less than the outside diameter D 1  of the flange  108 . Additionally, a circumference of the hole plug  100  around a midpoint of the nubs  122  (generally circumferentially around width “W” in  FIG.  1   ) is less than a circumference of the hole plug  100  around the outer vertical surface of the flange  108 . Moreover, an outside diameter D 4  ( FIG.  3   ) of the shank  114  is less than the outside diameter D 1  of the flange  108 . 
     The midpoint of the nubs  122  depicted at the width W in  FIG.  1    should be the approximate middle of the hole plug  100  between upper surface  102  and lower surface  104 . In this aspect, “W” in  FIG.  1    refers to the middle or midpoint of the hole plug  100 , where 50% of an overall height of the hole plug  100  is above midpoint W and 50% of the overall height of the hole plug  100  is below midpoint W. As depicted, the plurality of grooves  118  are positioned closer to the first surface  102  at the first end and to the second surface  104  at the second end of the hole plug than are the plurality of nubs  122 , which aids in dispersing a sealant (e.g., adhesive) as described below. 
     The surface of the chamfer  120  intersects the surface of the shank  114  and the lower surface  104  as depicted in  FIG.  1   , and forms an angle theta 3 (θ 3 ) with the lower surface  104 . The angle θ 3  can be about 131°±5°. 
     With regard to use, the hole plug  100  can be designed so that the diameter D 1  of the flange  108  (e.g., the diameter D 1  of the upper surface  102 ) is larger than the minimum diameter of the hole for which it is used (i.e., the hole through the carbon fiber resin laminate) and smaller than the largest diameter of the hole through the exterior surface (i.e., the hole through the exterior skin) of the composite fiber assembly. Further, the thickness  110  of the flange  108  must have a sufficient thickness to withstand the loads and/or forces that it will undergo during installation as described below. The bevel  112  (e.g., the angle and height of the bevel  112 ) is designed to match a countersink of the hole for which it is designed. 
     The notch  116  can be included to facilitate bonding at an interface of the bottom of the skin. The notch  116  provides an additional adhesive carrier or receptacle that at least partially attaches the hole plug  100  to the carbon fiber laminate. Similarly, grooves  118  running parallel to the shank  114  and to the longitudinal axis A are designed as an additional adhesive carrier or receptacle for attachment to the carbon fiber laminate. Both the notch  116  and grooves  118  can also provide some frictional resistance to maintain the hole plug  100  in place prior to curing of the adhesive. The grooves  118  should extend both above and below the nubs  122  so that the adhesive is carried through the length of the hole that receives the hole plug  100 . 
     The nubs  122  are sized to be sufficiently large to maintain the hole plug  100  within the hole in the carbon fiber laminate but small enough to prevent damaged to the carbon fiber laminate as they pass through the hole. The length of the chamfer  120  and the angle θ 3  of the chamfer are designed to ease installation of the hole plug  100  into the hole in the carbon fiber assembly during repair. A minimum length of the body  106  (i.e., the total length of the hole plug  100 ) is designed for ease of installation of the hole plug  100 , but also helps prevent the nubs  122  from breaking or fracturing off of the shank  114  during installation. 
     A surface roughness of the hole plug  100  contributes to the mechanical bond of the adhesive to the hole plug  100 . In an implementation, the hole plug  100  can have a surface roughness, wherein an average roughness centerline “Ra” of the surface roughness is from 250 microns (μm) to 400 μm. 
     The hole plug  100  can be formed, for example, using an additive manufacturing process such as a three dimensional (3D) printing process. The 3D printing process can include laser sintering of a metal or metal alloy, such as maraging steel. In another manufacturing process, the hole plug  100  can be formed using a molding process of a metal, metal alloy, or a suitable synthetic such as a polymer. The hole plug  100  can be formed as a single solid structure or single piece of material, although other constructions, such as formation from two or more materials or layers, or the formation of a hollow hole plug  100  to reduce weight, are contemplated. The surface roughness described above can result form the 3D printing process, molding process, or another formation process, or can result from a separate method act such as one or more of chemical etching, mechanical etching, or chemical-mechanical etching. 
     Various uses and techniques for using the hole plug  100  in accordance are contemplated. An example use is depicted in  FIGS.  4 - 9   .  FIG.  4    is a cross section depicting a composite resin assembly  400  (e.g., a carbon fiber assembly  400 ) including a rigid outer layer or skin  402  and a carbon fiber laminate  404 . The carbon fiber laminate  404  of  FIG.  4    includes four carbon fiber layers  404 A- 404 D, but it will be appreciated that a carbon fiber laminate can include two or more carbon fiber layers, and may include 100 or more layers. The carbon fiber assembly  400  includes a region  406  to undergo rework or repair (hereinafter, generally referred to collectively as rework). The region  406  to undergo rework may result from damage, maintenance, reconstruction, or reinforcing of the carbon fiber assembly, or any another cause. For purposes of illustration,  FIG.  4    further depicts a surface or layer  408  that prevents access to the back surface  410  of the carbon fiber laminate  404 , where the back surface  410  and the layer  408  are separated by a gap  412 . Access to the back surface  410  is typically required to properly establish a vacuum from the skin  402  side of the carbon fiber assembly  400 . The layer  408  may include a plurality of layers and may be part of the carbon fiber assembly  400  or another surface. 
       FIG.  5    depicts the  FIG.  4    structure after forming or shaping a hole  500  through the skin  402  and carbon fiber laminate  404  of the carbon fiber assembly  400 . As depicted, the portion of the hole  500  through the skin  402  has a larger diameter D 2  than the diameter D 1  of the surface  102  of the flange  108  ( FIG.  2   ) of the hole plug  100 . Further D 2  is larger than a diameter D 3  of the portion of the hole  500  through the carbon fiber laminate  404 . Further, the carbon fiber laminate  404  around the hole  500  can include a sloping face  502  (i.e., cant  502 ) that forms a countersink for the hole  500 , where the cant  502  approximates or matches the bevel  112  of the hole plug  100 . The hole  500  can be formed using, for example, a drill bit and countersink tool known in the art (not individually depicted for simplicity). 
     The measurements of the  FIG.  4    structure, particularly the carbon fiber assembly  400  and the hole  500  therethrough, can be used to determine the shape of the hole plug  100  used for the rework. In one implementation, the hole plug  100  can be formed by 3D printing after forming the hole  500 . In another implementation, the hole plug  100  can be formed prior to forming the hole  500 , where the hole  500  is shaped to match the hole plug  100 . After forming the shaped hole  500  and the hole plug  100 , an adhesive material  600  can be applied to the grooves  118  of the hole plug  100 . The hole plug can then be placed either completely into the hole  500  as depicted in  FIG.  7   , or partially into the hole  500  as depicted in  FIG.  6   . In the position of  FIG.  6   , the elongated portion of the shank  114  below the nubs  122  stabilize the hole plug  100  within the hole in the carbon fiber laminate  404 . In the position of  FIG.  6   , additional adhesive  600  can be placed around the hole plug  100 , for example, around and/or into the notch  116 , after which the hole plug  100  is inserted fully into the hole  500  as depicted in  FIG.  7   . Excessive adhesive is removed to result in a structure similar to  FIG.  7   . 
     As depicted in  FIG.  7   , the hole plug  100  is designed so that the tops of the nubs  122  (i.e., the upper edges between surface  102  and the midpoint W,  FIG.  1   ) are positioned at or near the level of the back surface  410 . The nubs  122  thus prevent the hole plug  100  from falling or popping out of the hole  500  prior to the curing of the adhesive  600 , even under the force of gravity or the application of a certain amount of vacuum force. In one aspect, the nubs  122  loosely secure or “lock” the hole plug  100  onto the composite laminate  404 , possibly in the absence of cured or uncured adhesive or other discrete mechanical attachments, and thus can be referred to as a “locking” hole plug. Further, the upper surface  102  of the hole plug  100  is at a level that is below the exposed upper surface  700  of the skin  402  so that the rework region  406  can be continuous and level with the exposed upper surface  700  after completion of the rework. The elongated portion of the shank  114  between the bottom of the nubs  122  and the chamfer  120  ensures that a sufficient amount or volume of adhesive is carried within the grooves  118  by the hole plug  100  through the hole in the carbon fiber laminate  404  and to the back surface  410  to properly bond the hole plug  100  to the carbon fiber laminate  404 . After forming the  FIG.  7    structure, the adhesive  600  is cured, thereby bonding the hole plug  100  to the carbon fiber layers  404 A- 404 D of the carbon fiber laminate  404 . 
     Subsequently, additional processing can be performed to rework the region  406  that includes the hole plug  100 . The rework can include applying one or more repair layers  800  to the region  406  as depicted in  FIG.  8   . A vacuum assembly  802 , which may include a vacuum bag  804 , a vacuum nozzle  806 , and a vacuum line  808  connected to a vacuum  810  can be applied to the region  406 . The vacuum assembly  802  may be used to debulk the one or more repair layers  800 , and to remove excess resin as the one or more repair layers  800  are cured. After curing the one or more repair layers  800 , the vacuum assembly  802  is removed from the upper exposed surface  700  of the skin  402 , and additional processing is performed on the repair layer  800  and skin  402  to result in the completed structure of  FIG.  9   . The hole plug  100  thus remains part of the carbon fiber assembly  400 . 
     With regard to the structure depicted in  FIGS.  4 - 9   , the region  406  to undergo rework or repair may be a solid surface such that the structure of  FIG.  9    is completed. In another implementation, the region  406  of  FIG.  4    can be or include a damaged region around a fastening hole. In this implementation, the fastening hole can be temporarily filled and sealed using the hole plug  100  and repaired as described above with reference to  FIGS.  4 - 8    result in the structure of  FIG.  9   . Subsequently, the structure of  FIG.  9    can be further processed, for example, by drilling out and/or otherwise removing the hole plug  100  to result in the fastening hole  1000  of  FIG.  10   . In an implementation, the fastening hole  1000  can be lined with a liner  1002 , for example, to protect the carbon fiber laminate  404  or to prepare the fastening hole  1000  for insertion of a fastener (not individually depicted for simplicity). 
     It will be appreciated that the figures have been simplified and are drawn to facilitate understanding of the present teachings and are not to scale. 
       FIG.  11    is a functional block diagram depicting a composite laminate  1100  having a first hole  1102  therethrough, and a hole plug  1104  positioned within the first hole  1102 . The composite laminate  1100  can be or include one or more layers, for example, one or more carbon fiber layers. The  FIG.  11    structure further depicts a skin  1106  that can be a solid shell that overlies and covers the composite laminate  1100 . The skin  1106  can have a second hole  1108  therethrough. The hole plug  1104  can be inserted through the second hole  1108  to result in the positioning of the hole plug  100  within the first hole  1102 . A first width or first diameter D 5  of the first hole  1102  is smaller than a second width or second diameter D 6  of the second hole  1108 . The hole plug  1104  of  FIG.  10    includes a flange  1110 , a bevel  1112  extending from the flange  1110 , and a shank  1114  extending from the bevel  1112 . The shank  1114  can include a notch  1116  that can extend partially or completely around a circumference of the shank  1114 . The shank  1114  further includes a plurality of grooves  1118  extending longitudinally along a height of the shank  1114 . A plurality of nubs  1120  and a chamfer  1122  extend from the shank  1114 . 
       FIG.  12    is a flow chart depicting a method  1200  for reworking a workpiece such as a fiber resin assembly  400  which may be a carbon fiber assembly  400  according to an implementation of the present teachings. The method  1200  can proceed by operation or use of one or more of the structures depicted in the figures described above, and thus is described with reference to  FIGS.  1 - 9   ; however, it will be appreciated that the method  1200  is not limited to any particular structure or use unless expressly stated herein. It will be appreciated that while the method  1200  is described as a series of acts or events, the present teachings are not limited by the ordering of such acts or events. Some acts can occur in different orders and/or concurrently with other acts or events apart from those described herein. Further, a method in accordance with the present teachings can include other acts or events that have not been shown for simplicity, while other illustrated acts or events can be removed or modified. 
     In an implementation, a rework area of a workpiece  400  is processed to define a hole  500  within the workpiece as at  1202 . The hole  500  can have a first diameter D 2  through a first region (e.g., skin  402 ) of the workpiece  400  that is larger than a second diameter D 3  through a second region  404  (e.g., a carbon fiber laminate  404 ) of the workpiece. The second region  404  of the workpiece can be formed to define a cant  502 . A hole plug  100  is formed, for example, using 3D printing, a molding process, or another suitable process as at  1204 . The hole plug  100  can be formed after forming the hole  500  based on measurements of the hole  500 , or the hole  500  can be formed to match the dimensions of an existing hole plug  100 . The hole plug  100  can include a flange  108  having a third diameter D 1  that is smaller than the first diameter D 2 . 
     Subsequently, as at  1206 , adhesive  600  is applied to grooves  118  of the hole plug  100 , and the hole plug  100  is partially inserted into the hole  500  as at  1208 . In an example implementation, the hole plug  100  is partially inserted such that a lower edge of nubs  122  around a shank  114  of the hole plug  100  rest on the second region such as the cant  502 . With the hole plug  100  partially inserted into the hole, additional adhesive  600  can be applied to the hole plug  100 , for example, to a notch  116  as at  1210 . The notch  116  and grooves  118  thus provide a carrier for the adhesive  600  as it is inserted into the hole  500 , thereby spreading or dispersing a sufficient volume or quantity of the adhesive  600  to other portions of the shank  114  and the workpiece to ensure bonding of the hole plug  100  to the workpiece  400 . Next, at  1212 , the hole plug  100  is fully inserted into the hole  500 . When fully inserted, an upper surface  102  of the hole plug  100  is recessed within an exposed upper surface  700  of the skin  402 . Next, at  1214 , a vacuum bag  804  is applied to a region  406  of the workpiece  400  including the hole plug  100  and one or more repair layers  800 . Subsequently, a vacuum force can be applied to the workpiece  400 , the one or more repair layers  800 , and the locking hole plug  100  as at  1216 . The application of the vacuum force can debulk the one or more repair layers  800  that overlie the workpiece  400  and the locking hole plug  100 , as at  1218 . At  1220 , the adhesive  600  is cured, either passively using a timed cure at ambient temperatures or by performing active processing acts such as heating the adhesive  600 , exposing the adhesive to ultraviolet light, etc. Subsequently, additional processing of the region  406  can optionally be performed to complete the rework as at  1222 . The rework can include one or more of applying additional layers and adhesives, sanding and/or curing the additional layers  800 , applying a vacuum to the additional layer  800  using a vacuum assembly  802 , painting or otherwise finishing the workpiece  400 . The rework can also optionally include drilling out and removing the hole plug  100  to form a fastening hole  1000 , lining the fastening hole  1000  with a liner  1002 , and/or other processing acts. 
     A hole plug according to an example implementation of the present teachings thus provides a structure and technique for reworking a workpiece. The hole plug is secured within a hole defined by the workpiece such that processing of the workpiece can be performed. The processing of the workpiece can include the application of a vacuum force to the rework area during a cure and/or other processing of a repair layer. 
     Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the present teachings are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. For example, a range of “less than 10” can include any and all sub-ranges between (and including) the minimum value of zero and the maximum value of 10, that is, any and all sub-ranges having a minimum value of equal to or greater than zero and a maximum value of equal to or less than 10, e.g., 1 to 5. In certain cases, the numerical values as stated for the parameter can take on negative values. In this case, the example value of range stated as “less than 10” can assume negative values, e.g. −1, −2, −3, −10, −20, −30, etc. 
     While the present teachings have been illustrated with respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the spirit and scope of the appended claims. For example, it will be appreciated that while the process is described as a series of acts or events, the present teachings are not limited by the ordering of such acts or events. Some acts may occur in different orders and/or concurrently with other acts or events apart from those described herein. Also, not all process stages may be required to implement a methodology in accordance with one or more aspects or implementations of the present teachings. It will be appreciated that structural components and/or processing stages can be added or existing structural components and/or processing stages can be removed or modified. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. Furthermore, to the extent that the terms “including,” “includes,” “having,” “has,” “with,” or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” The term “at least one of” is used to mean one or more of the listed items can be selected. As used herein, the term “one or more of” with respect to a listing of items such as, for example, A and B, means A alone, B alone, or A and B. Further, in the discussion and claims herein, the term “on” used with respect to two materials, one “on” the other, means at least some contact between the materials, while “over” means the materials are in proximity, but possibly with one or more additional intervening materials such that contact is possible but not required. Neither “on” nor “over” implies any directionality as used herein. The term “conformal” describes a coating material in which angles of the underlying material are preserved by the conformal material. The term “about” indicates that the value listed may be somewhat altered, as long as the alteration does not result in nonconformance of the process or structure to the illustrated implementation. Finally, “exemplary” indicates the description is used as an example, rather than implying that it is an ideal. Other implementations of the present teachings will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present teachings being indicated by the following claims. 
     Terms of relative position as used in this application are defined based on a plane parallel to the conventional plane or working surface of a workpiece, regardless of the orientation of the workpiece. The term “horizontal” or “lateral” as used in this application is defined as a plane parallel to the conventional plane or working surface of a workpiece, regardless of the orientation of the workpiece. The term “vertical” refers to a direction perpendicular to the horizontal. Terms such as “on,” “side” (as in “sidewall”), “higher,” “lower,” “over,” “top,” and “under” are defined with respect to the conventional plane or working surface being on the top surface of the workpiece, regardless of the orientation of the workpiece.