Patent Application
20090274526
1. Technical Field
The present invention relates in general to mechanical fasteners and, in particular, to an improved system, method, and apparatus for removing failed fasteners from structures that are fabricated from composite materials.
2. Description of the Related Art
Some structures, such as the wing skins of high performance aircraft, are formed from composite materials rather than from metals or metal alloys. Composite materials offer a number of advantages over metals, such as a very high strength to weight ratio. Composite materials also have some disadvantages, including lower hardness and durability compared to metallic materials. Because of these disadvantages, composite materials are not suitable for use as all structural components. For example, metallic fasteners (e.g., bolts, screws, etc.) are required to join some structural elements.
Unfortunately, even metallic fasteners are capable of failing due to improper installation or extended service over time. There is a conventional procedure for removing a failed fastener from composite materials. This approach requires a technician to hand-drill a pilot hole in the failed fastener, and then remove the fastener with a conventional tool that is commonly referred to as an “EZ-Out.”
This conventional removal procedure does not always work. When this method fails, the technician must drill out the failed fastener at an even deeper level until the head of the fastener breaks off from the threaded portion of the bolt. Where and how the head breaks off from its shank is very unpredictable. Such fastener breakage often leaves sharp burrs on the fastener shank that must be pulled through the composite materials. The sharp burrs cause damage to the inner surfaces of the hole that the fastener was in. The damaged hole must then be repaired or re-worked to accept an oversized fastener at considerable additional cost.
Currently, this process requires technicians with the highest level of skill available. All of the foregoing drilling and repair operations are performed “free hand” with little or no radial support or rigid guidance for the precise control and alignment of the cutting tools used. Such operations may be relegated to the mechanics on the shop floor using whatever tools and/or methods they are comfortable with. As a result, there is a high level of variation in the success and quality of the operations performed. Thus, an improved system, method, and apparatus for removing failed fasteners from structures would be desirable.
Embodiments of a system, method, and apparatus for removing failed fasteners from structures are disclosed. The invention removes failed fasteners by removing the head of the fastener, rather than relying on the head to break off, in a controlled manner that offers precise support and alignment for the cutting tools used by a technician. The invention is particularly well suited for applications involving structures that are fabricated from composite materials.
In one embodiment, the invention comprises a drill guide, interchangeable drill bushings and a cutting tool. The drill guide is designed to mount virtually anywhere on an underlying structure using existing fasteners and receptacles formed in the structure. This design permits the drill guide to be rigidly attached to the structure so that the cutting tool can be positioned and supported directly over the failed fastener. After the drill guide is mounted, cobalt or other suitable drill bits are extended through a selected one of the drill bushings to drill a pilot bole in the failed fastener. After the pilot hole is formed at the appropriate diameter and depth, the cutting tool is used through the drill bushing to cut off the head of the failed fastener without contacting the surrounding composite materials. Advantageously, the mounted drill guide does not have to be re-positioned as all operations required to remove the failed fastener are accomplished through the drill bushings contained in the drill guide.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.
So that the manner in which the features and advantages of the present invention are attained and can be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings. However, the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.
Referring to
In one embodiment, the invention comprises a structure such as an assembly having two structural components 11, 13 (
A guide 21 is positioned on the structure. The guide 21 has a body 22 that generally extends in a longitudinal or “x” direction. The guide 21 is mountable directly to the structure with at least one of the structure fasteners 17 (e.g., two are shown securing guide 21 to the structure). The guide 21 has a width that extends in a lateral or “y” direction.
A plate 25 is mounted to the body 22 with fasteners and also extends in the x direction. The plate 25 secures one or more sliding washers 27 (e.g., two shown in
As shown in
The sliding washers 27 are slidably mounted and captured within the slot 29, which has a width extending in the y-direction in the guide 21. The sliding washers 27 are movable in the x-direction relative to the guide 21. As shown in the drawings, at least two sliding washers 27 may be provided in one embodiment, and each sliding washer 27 is countersunk 28 (
Referring now to
In one embodiment, the cutting tools may be provided with a stop 43 (
The guide 21 also has means for locking a motion of the master bushing 23 relative to the guide. In one embodiment, the means for locking comprises a split sleeve 33 (
The invention certainly may comprise a stand-alone apparatus or tool that is adapted for removing fasteners from structures. In addition, the invention comprises a method of removing fasteners from structures. In one embodiment, the method accurately removes fouled fasteners from underlying structures. The guide is provided with interchangeable drill bushings to ensure proper cutting tool alignment and centrality throughout the process. For example, the invention may be provided with tools for removal of fasteners having a ⅜-inch diameter, and kits for multiple other sizes, including 3/16-inch, ¼-inch, 5/16-inch, ⅜-inch, etc. diameters.
In operation, the method may comprise mounting the guide to the structure utilizing the existing fasteners already located in the structure. Using a drill with an appropriate driver 51 (e.g.,
In one embodiment, a ¼-inch SFR drill bushing may be mounted in the master bushing 23. A ¼-inch ball end carbide rotary file may be used to relieve or remove the drive slots formed in the head on the fastener to be removed. This allows for an uninterrupted drill start. A slow speed (e.g., 300 to 400 rpm) hand drill motor may be used for all fastener sizes. After relieving the fastener head drive slots, the SFR drill bushing may be changed to a #30 SFR drill bushing.
For example, for ⅜-inch fasteners, the fastener to be removed may then be drilled to form a pilot hole therein with a #30 cobalt twist drill bit. After the #30 pilot hole is established, the SFR drill bushing may be changed to a 7/32-inch SFR drill bushing, and the fastener then drilled with a 7/32″ cobalt (or other style) twist drill bit. At this stage, the technician may try using a #4 EZ-Out for removal of the fastener. In cases where the threads of the fastener are stripped, this procedure will remove the fastener. However, if the preceding step is unsuccessful, then the nut plate that secures the fastener is the problem (i.e., the nut plate spins). This will require the removal of the fastener head from its shank by cutting in order to complete the removal of the fouled fastener. The SFR drill bushing may be changed to a 5/16-inch SFR drill bushing, and the fastener drilled with a 5/16-inch cobalt twist drill bit. The 5/16″ SFR drill bushing is then removed from the master bushing 23 and the head from the fastener is then removed utilizing the piloted countersink tool 41 (
The invention has numerous advantages over conventional failed fastener removal techniques. For example, the invention provides a controlled method of removing failed fasteners by cutting off the fastener head without leaving a burr on the fastener parts, or potentially damaging the underlying composite materials. This system allows for accurate, rigid location and support of cutting tools used in the removal of failed fasteners. This invention aids the technicians performing the removal, and also reduces the associated risks by cutting off the fastener head instead of relying on the head to break off.
The invention provides a well-defined and repeatable removal process that allows suspect fasteners to be removed from composite materials without requiring expensive and time consuming rework of the composite material. The removal system mounts over the suspect fastener and provides a set of guides and bushings that allow a pilot hole to be made in the suspect fastener to an appropriate and repeatable diameter and depth. When necessary, a specialized cutting tool is applied using the same set of guides and bushings to remove the head without damaging the composite material. This method does not leave a burr or otherwise damage the composite material in which the fastener was installed.
While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.
