Blind fastener

Abstract

A fastener includes a sleeve, a core bolt, and an insert. The sleeve includes a tubular portion and an internal thread. The core bolt includes a cylindrical portion, a threaded portion having an external thread, and a screw tail between the cylindrical portion and the threaded portion. The core bolt is disposed within the sleeve and the external thread engages the internal thread. The insert is disposed within the sleeve and surrounds a portion of the core bolt. The insert abuts and is retained between the internal thread and the screw tail in a pre-installed position. The insert is compressed between the internal thread and the tail by a mounting movement of the core bolt while generating a compressive load on the sleeve. The insert deforms concurrently with a ball portion in the sleeve and facilitates formation of the ball portion in response to the compression.

Description

[0001] Cross-reference to related applications

[0002] This application is related to and claims the benefit of commonly owned, co-pending U.S. Provisional Patent Application No. 63 / 352,780, filed on June 16, 2022, and entitled “BLIND FASTENER,” the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present invention relates to fasteners, and more particularly, to blind fasteners for securing together carbon fiber reinforced composite workpieces that are exposed to lightning strikes. Background Art

[0004] Blind fasteners are often used to fasten multiple workpieces together when there are only limited physical or visible accesses on one side of the workpiece. There is a trend toward using carbon fiber reinforced composites for aircraft structures because these materials have good strength-to-weight ratios, stiffness, and resistance to fatigue-induced damage. There is also a trend toward natural and hybrid laminar wing designs to achieve higher fuel efficiency. Such wings typically have thinner cross-sections with limited accesses inside the wing.

[0005] Aircraft are often struck by lightning. This is particularly important for carbon fiber reinforced composite structures, which have inherently low electrical conductivity, and because metal fasteners are often the primary path for lightning currents that are not fully distributed across the skin of a composite aircraft. In such situations, lightning currents can create hazardous ignition sources through arcing between fasteners and the composite structure. While the primary hazard from a lightning strike is fastener arcing, which creates a potential ignition source for fuel vapor, Joule heating of materials, plasma activity, and evaporation of material along the fastener / structure assembly can produce substantial physical damage to the fasteners and surrounding structure.

[0006] Carbon fiber reinforced composites are typically composed of a combination of a binding polymer (commonly referred to as a matrix) and high-strength carbon fibers. The orientation of the carbon fibers, the matrix-to-fiber ratio, and the composition of both the fibers and the matrix can be adjusted to achieve specific target properties for a particular application. The mechanical, electrical, and environmental properties of carbon fiber reinforced composites can also be affected by various types of additives introduced into the binding matrix.

[0007] A wide range of manufacturing techniques have been developed, but many of them use a layered manufacturing process that involves combining fibers into unidirectional or woven fabric layers that are then stacked one on top of the other in a quasi-isotropic stack, for example at 0°, +60°, or -60° relative to each other. In some cases, the matrix is ​​combined with individual layers. In other cases, the matrix is ​​poured into the stack after the individual layers have been stacked. Manufacturing techniques continue to evolve to reduce costs, but two-dimensional stacking is more common than three-dimensional stacking. Variants of two-dimensional stacking techniques are commonly used to manufacture aircraft structural sections, such as fuselages and wings. Although some techniques enable large-scale integration of features, it is still necessary to mechanically join subsections with fasteners to form assemblies. This is especially true when subsections are constructed from different materials.

[0008] One of the challenges is that subsections or individual parts have inherently isotropic mechanical and electrical properties that are a product of the stacked, layered nature of their construction. As a result, the development of composite aircraft has led to a greater need for mechanical fasteners that are electrically compatible with composite structures by being significantly less conductive than those used in metallic aircraft; and therefore more susceptible to lightning damage. Anisotropic resistance properties and elevated contact resistance directly impact current paths and resulting electric fields within the electrical connection areas in the aircraft sections joined by the fasteners. These electrical irregularities also directly impact the electromagnetic response of the aircraft to high frequency waves.

[0009] The trend toward greater use of carbon fiber reinforced composites and natural and hybrid laminar wings creates a need for blind fasteners with low inherent contact resistance between components of the fastener assembly itself and between the fastener and the surrounding composite structure. Such fasteners will enable lightning currents to pass from one structural element to another and through the surrounding structure with relatively little adverse effects. As currents and electric fields evolve within the aircraft structure, low electrical continuity between the fastener surface and the internal joint caused by the interface resistivity will be critical to influencing the current distribution. Summary of the invention

[0010] In some embodiments, a fastener includes: a sleeve including a first end and a second end opposite to the first end, a tubular portion having an outer surface, an inner surface, an inner thread formed in the inner surface at the second end, and a head positioned at the first end; a core bolt including a first end of the core bolt and a second end opposite to the first end, a cylindrical portion proximate the first end of the core bolt, an outer threaded portion proximate the second end of the core bolt, and a runout between the cylindrical portion and the threaded portion, wherein the core bolt is configured to be disposed within the sleeve, and wherein the outer thread is configured to engage the sleeve in a threaded manner and an insert configured to be disposed within the sleeve and around a portion of the core bolt proximate its second end, wherein the insert is sized and shaped to abut the internal threads of the sleeve and the threaded end of the core bolt and be retained between the internal threads and the threaded end when the fastener is in a pre-installed position, wherein the insert is configured to be compressed between the internal threads of the sleeve and the threaded end of the core bolt by the installation movement of the core bolt relative to the sleeve, while generating a compressive load on the sleeve by the installation movement of the core bolt, and wherein the insert is configured to deform simultaneously with the ball portion in the sleeve in response to compression of the insert and promote formation of the ball portion.

[0011] In some embodiments, the core bolt includes an exterior surface, wherein the insert is configured to fill a gap between the exterior surface of the core bolt proximate its second end and the interior surface of the sleeve proximate the second end of the tubular portion of the sleeve, and wherein the insert is configured to provide a conductive path between the sleeve and the core bolt. In some embodiments, the sleeve is comprised of steel. In some embodiments, a first coefficient of friction between the interior surface of the sleeve and the exterior surface of the core bolt and a second coefficient of friction between the interior surface of the sleeve and the exterior surface of the insert are selected to promote sliding contact between the sleeve and the core bolt and between the sleeve and the insert during installation of the fastener.

[0012] In some embodiments, the sleeve comprises a first layer located on an outer surface of the sleeve, wherein the first layer comprises a first hardness, and a second layer located on an inner surface of the sleeve, wherein the second layer comprises a second hardness, and wherein the second hardness is greater than the first hardness. In some embodiments, the first layer is a coating. In some embodiments, the coating is composed of a metal-based coating. In some embodiments, the coating is selected from the group consisting of silver, gold, nickel, cadmium, copper, and lead or alloys thereof. In some embodiments, the coating is composed of bronze. In some embodiments, the second layer is composed of an oxide layer. In some embodiments, the sleeve comprises a third layer located above the second layer. In some embodiments, the second layer is composed of carbon, and the third layer is composed of nitrogen and carbon.

[0013] In some embodiments, the insert is comprised of copper. In some embodiments, the insert is comprised of Monel alloy. In some embodiments, the insert comprises a coating. In some embodiments, the coating is selected from the group consisting of silver, gold, and nickel. In some embodiments, the sleeve comprises a strip annealed portion proximate the insert. In some embodiments, the core bolt comprises a head at a first end thereof, and wherein the head of the sleeve comprises a recess sized and shaped to receive the head of the core bolt. In some embodiments, the head of the sleeve is configured to be mounted in an accessible hole in a plurality of workpieces, and wherein the ball portion is configured to be positioned on a blind side of the workpiece.

[0014] In some embodiments, a fastener comprises: a sleeve having a first end and a second end opposite to the first end, a tubular portion having a head positioned at the first end, a first portion close to the first end and having a first inner diameter, a second portion adjacent to the first portion and having a second inner diameter smaller than the first inner diameter of the first portion, a third portion close to the second end and having an internal thread, and a step positioned between the first portion and the second portion; a core bolt comprising a first end of the core bolt and a second end opposite to the first end, a cylindrical portion close to the first end of the core bolt, an externally threaded portion close to the second end of the core bolt, and a screw tail between the cylindrical portion and the externally threaded portion, wherein the core bolt is configured to be installed The invention relates to a method for manufacturing a fastener for a screw threaded engagement member comprising: placing the fastener in the sleeve and surrounding a portion of the core bolt near its second end, wherein the insert is sized and shaped to abut against a step of the sleeve and a tail of the core bolt and be retained between the step and the tail when the fastener is in a pre-installed position, wherein the insert is configured to be compressed between the internal thread of the sleeve and the tail of the core bolt by the installation movement of the core bolt relative to the sleeve, while generating a compressive load on the sleeve by the installation movement of the core bolt, and wherein the insert is configured to deform simultaneously with a ball portion in the sleeve in response to compression of the insert and promote formation of the ball portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 and Figure 2 are perspective views and side elevation views, respectively, of some embodiments of core bolts employed by the fasteners of the present invention;

[0016] Figures 3 to 7 are perspective, side elevation, and cross-sectional perspective and side elevation views of some embodiments of sleeves employed by fasteners;

[0017] Figure 8 are perspective views of some embodiments of inserts employed by fasteners;

[0018] Figures 9 to 15 To adopt Figures 1 to 8Various perspective, side elevation, and cross-sectional perspective and side elevation views of some embodiments of the core bolt, sleeve, and insert fasteners shown in FIG.

[0019] Fig.16 and Fig.17 for Figures 9 to 15 side elevation views and cross-sectional side elevation views of some embodiments of the fasteners shown in , the fasteners being pre-installed in a plurality of workpieces; and

[0020] Fig.18 and Fig.19 for Figure 16 to Figure 17 0014] Side elevation views and cross-sectional side elevation views of some embodiments of the fasteners shown in FIG. 1 , the fasteners being fully installed in a plurality of workpieces. DETAILED DESCRIPTION

[0021] As shown, for example, in Fig.10 In some embodiments, the fastener 10 includes a core bolt 12, a sleeve 14, and an insert 16. In some embodiments, the sleeve 14 is sized and shaped to receive the core bolt 12 and the insert 16, which will be described in further detail below.

[0022] refer to Figure 1 and Figure 2In some embodiments, the core bolt 12 includes a first end 18, a second end 20 opposite the first end 18, and a shank portion 22 between the first end 18 and the second end 20. In some embodiments, the shank portion 22 includes a cylindrical portion 24, which includes an outer surface 25. In some embodiments, the cylindrical portion 24 is close to the first end 18. In some embodiments, the shank portion 22 is a smooth cylindrical shank portion. In some embodiments, the shank portion 22 has a first diameter. In some embodiments, the shank portion 22 includes a threaded portion 26. In some embodiments, the threaded portion 26 is close to the second end 20. In some embodiments, the threaded portion 26 includes an external thread 28. In some embodiments, the external thread 28 has an outer diameter. In some embodiments, the outer diameter is smaller than the first diameter of the shank portion 22. In some embodiments, the core bolt 12 includes a screw tail 30. In some embodiments, the screw tail 30 is positioned between the cylindrical portion 24 and the threaded portion 26. In some embodiments, the core bolt 12 is configured to be disposed in the sleeve 14. In some embodiments, the core bolt 12 includes an annular groove 32. In some embodiments, the annular groove 32 is adjacent to the screw tail 30. In some embodiments, the core bolt 12 includes a first head 34. In some embodiments, the first head 34 is proximate to the first end 18. In some embodiments, the first head 34 is a flush head. In some embodiments, the core bolt 12 includes a second head 36. In some embodiments, the second head 36 is positioned at the first end 18. In some embodiments, the second head 36 is a spline head. In some embodiments, the second head 36 is configured to be engaged by a fastener installation tool. In some embodiments, the second head 36 is removably attached to the first head 34. In some embodiments, the second head 36 is removably attached to the first head 34 by a neck portion 37. In some embodiments, the second head 36 is removed from the fastener 10 at the neck portion 37.

[0023] refer to Figures 3 to 6 In some embodiments, the sleeve 14 includes a tubular portion 38. In some embodiments, the tubular portion 38 includes a first end 40, a second end 42 opposite the first end 40, a first portion 44 proximate the first end 40 and having a first inner diameter, and a second portion 46 proximate the second end 42. In some embodiments, the sleeve 14 includes an interior surface 66. In some embodiments, the second portion 46 includes an internal thread 48. In some embodiments, the internal thread 48 is positioned on the interior surface 66 of the second portion 46 of the sleeve 14. Figure 7In some embodiments, the sleeve 14 includes a third portion 50 adjacent to the first portion 44. In some embodiments, the third portion 50 includes a second inner diameter that is smaller than the first inner diameter of the first portion 44. In some embodiments, the sleeve 14 includes an annular step 52. In some embodiments, the annular step 52 is positioned between the first portion 44 and the third portion 50. In some embodiments, the sleeve 14 does not include the annular step 52.

[0024] In some embodiments, the sleeve 14 includes a head 54. In some embodiments, the head 54 is positioned at the first end 40 of the tubular portion 38. In some embodiments, the head 54 is an enlarged head. In some embodiments, the head 54 includes a recess 56. In some embodiments, the recess 56 is sized and shaped to receive the first head 34 of the core bolt 12. In some embodiments, the sleeve 14 includes an outer surface 58. In some embodiments, the outer surface 58 of the tubular portion 38 of the sleeve 14 includes an outer diameter. In some embodiments, the outer diameter of the outer surface 58 is sized and shaped to enable the sleeve 14 to be installed in the aligned holes of the plurality of workpieces 110, 112.

[0025] refer to Figure 8 In some embodiments, the insert 16 includes a first end 60, a second end 62 opposite the first end 60, and an inner surface 63. In some embodiments, the inner surface 63 of the insert 16 forms an orifice 64. In some embodiments, the orifice 64 extends from the first end 60 of the insert 16 to the second end 62. In some embodiments, the insert 16 includes an outer surface 65. In some embodiments, the insert 16 has a tubular shape. In some embodiments, the shape of the inner surface 63 is cylindrical. In some embodiments, the insert 16 has an inner diameter. In some embodiments, the inner diameter of the insert 16 is greater than the outer diameter of the external thread 28 of the core bolt 12. In some embodiments, the insert 16 has an outer diameter. In some embodiments, the outer diameter of the insert 16 is less than the minimum inner diameter of the sleeve 14. In some embodiments, the insert 16 is made of copper. In some embodiments, the insert 16 is made of In some embodiments, the insert 16 is coated with a highly conductive coating. In some embodiments, the coating is composed of a conductive metallic material. In some embodiments, the coating is composed of silver. In some embodiments, the coating is composed of gold. In some embodiments, the coating is composed of nickel. In some embodiments, the coating is composed of cadmium. In some embodiments, the coating comprises a low coefficient of friction. In some embodiments, the coefficient of friction is less than 0.50.

[0026] refer to Figures 9 to 15In some embodiments, the first diameter of the cylindrical portion 24 of the core bolt 12 is sized and shaped to enable the core bolt 12 to be installed in the sleeve 14. In some embodiments, the external threads 28 of the threaded portion 26 of the core bolt 12 are complementary to the internal threads 48 of the sleeve 14 and are configured to threadingly engage the internal threads of the sleeve. In some embodiments, the core bolt 12 is configured to be engaged by a fastener installation tool. In some embodiments, the insert 16 is disposed in the sleeve 14. In some embodiments, the insert 16 surrounds at least a portion of the threaded portion 26 of the core bolt 12. In some embodiments, the insert 16 completely surrounds the threaded portion 26 of the core bolt 12.

[0027] refer to Fig.16 and Fig.17 In some embodiments, the fastener 10 is configured to be installed in the aligned holes 115, 117 of a plurality of workpieces 110, 112. In some embodiments, the fastener 10 is assembled and pre-installed in the plurality of workpieces 110, 112. In some embodiments, the workpiece 110 includes an accessible side 113. In some embodiments, the workpiece 112 includes a blind side 114. In some embodiments, the accessible side 113 is opposite the blind side 114. In some embodiments, the installer of the fastener 10 does not have physical or visible access to its blind side 114. In some embodiments, each of the aligned holes 115, 117 of the workpieces 110, 112 includes an inner diameter. In some embodiments, each of the workpieces 110, 112 is composed of a composite material. In some embodiments, each of the workpieces 110, 112 is composed of substantially composite materials. In some embodiments, the insert 16 is sized and shaped to abut and be held between the internal threads 48 of the sleeve 14 and the screw tail 30 of the core bolt 12 when the fastener 10 is in a pre-installed position. In some embodiments, the insert 16 is sized and shaped to abut and be retained between the annular step 52 of the sleeve 14 and the threaded end 30 of the core bolt 12 when the fastener 10 is in the pre-installed position.

[0028] refer to Fig.18 and Fig.19In some embodiments, during installation of the fastener 10, the insert 16 is compressed between the annular step 52 of the sleeve 14 and the threaded end 30 of the core bolt 12 by the installation movement of the core bolt 12 relative to the sleeve 14, and the compression is performed simultaneously with the installation movement of the core bolt 12. In some embodiments, the length of the insert 16 is configured so that the total volume of the insert 16 is complementary to the total volume of the gap located between the inner surface 66 of the sleeve 14 and the outer surface 25 of the core bolt 12, so as to fill the gap between the core bolt 12 and the sleeve 14 when the fastener 10 is fully installed in the workpiece 110, 112. In some other embodiments, during installation of the fastener 10, the insert 16 is compressed between the inner thread 48 of the sleeve 14 and the threaded end 30 of the core bolt 12 by the installation movement of the core bolt 12 relative to the sleeve 14, and the compression is performed simultaneously with the installation movement of the core bolt 12, thereby generating a compressive load on the sleeve 14.

[0029] In some embodiments, the insert 16 is configured to be compressed between the internal threads 48 of the sleeve 14 and the threaded end 30 of the core bolt 12 by the installation movement of the core bolt 12 relative to the sleeve 14, while generating a compressive load on the sleeve 14 by the installation movement of the core bolt 12. In some embodiments, the insert 16 is configured to deform simultaneously with the ball portion in the tubular portion 38 of the sleeve 14 in response to the compression of the insert 16 and promote the formation of the ball portion 70. In some embodiments, the insert 16 is configured to act as a bearing during the installation process and fill the gap between the inner surface 66 of the sleeve 14 and the outer surface 25 of the core bolt 12 to form a conductive path between the core bolt 12 and the sleeve 14. In some embodiments, after the fastener 10 is installed in the workpiece 110, 112, the second head 36 is removed from the fastener 10 at the neck portion 37. In some embodiments, the first head 34 of the core bolt 12 is flush with the accessible side 113 of the workpiece 110. In some embodiments, the head 54 of the sleeve 14 is flush with the accessible side 113 of the workpiece 110 .

[0030] In some embodiments, sleeve 14 is made of A286 (AISI 660) steel. In some embodiments, A286 steel is austenitic precipitation hardening stainless steel. In some embodiments, sleeve 14 is made of 300 series stainless steel. In some embodiments, sleeve 14 is made of 304L stainless steel. In some embodiments, sleeve 14 is made of 316L stainless steel. In some embodiments, sleeve 14 is made of copper-nickel alloy. In some embodiments, steel is modified to include a soft layer on the outer surface 58 of sleeve 14. In some embodiments, the term "soft" as defined herein means that the layer on the outer surface 58 of sleeve 14 has a hardness of less than Rc 30 on the Hardness Rockwell Scale (Hardness Rockwell Scale) C.

[0031] In some embodiments, the steel is modified to include a hard layer located on the interior surface 66 of the sleeve 14. In some embodiments, the term "hard" as defined herein means that the layer on the interior surface 66 of the sleeve 14 has a hardness of 8.0 to 8.5 on the Mohs scale. In some embodiments, the sleeve 14 includes a band annealing portion 72. In some embodiments, the first layer on the exterior surface 58 of the sleeve 14 includes a first hardness. In some embodiments, the second layer on the interior surface 66 of the sleeve 14 includes a second hardness. In some embodiments, the second hardness of the interior surface 66 of the sleeve 14 is greater than the first hardness of the exterior surface 58 of the sleeve 14. In some embodiments, the band annealing portion 72 is adjacent to the insert 16. In some embodiments, the sleeve 14 includes a selectively soft conformal exterior surface, a selectively hard interior surface, and an annealing portion between the first end 40 and the second end 42 adjacent to the insert 16. In some embodiments, the band annealing portion 72 is band annealed by a laser or a radio frequency induction coil. In some embodiments, the strip annealed portion 72 facilitates forming the ball 70 against the surface of the blind side 114 of the workpiece 112 throughout all clamping ranges of the fastener 10 .

[0032] In some embodiments, the outer surface 58 of the sleeve 14 is coated with a soft, highly conductive coating. In some embodiments, the coating has sufficient electrical conductivity. In some embodiments, the coating is galvanically compatible with the sleeve 14. In some embodiments, the coating is galvanically compatible with the workpieces 110, 112. In some embodiments, the coating conforms to the inherent microtexture of each of the inner surfaces formed by the corresponding holes in the workpieces 110, 112. In some embodiments, the coating is composed of a metal-based coating. In some embodiments, the coating is composed of silver. In some embodiments, the coating is composed of gold. In some embodiments, the coating is composed of nickel. In some embodiments, the coating is composed of cadmium. In some embodiments, the coating is composed of copper. In some embodiments, the coating is composed of lead. In some embodiments, the coating is composed of an alloy. In some embodiments, the coating is composed of bronze.

[0033] In some embodiments, the outer surface 58 of the sleeve is uncoated. In some embodiments, the outer surface 58 of the sleeve 14 is microtextured. In some embodiments, the microtexture of the outer surface 58 of the sleeve 14 complements the inherent microtexture of the inner surface of the hole forming each of the workpieces 110, 112. In some embodiments, the microtexture is 25 micro-inches to 40 micro-inches.

[0034] In some embodiments, the inner surface 66 of the sleeve 14 includes a layer having a higher surface hardness than the hardness of the untreated inner surface 66. In some embodiments, the inner surface 66 of the sleeve 14 has a surface hardness of 8.0 to 8.5 on the Mohs scale. In some embodiments, the first coefficient of friction between the inner surface 66 of the sleeve 14 and the outer surface 25 of the core bolt 12 and the second coefficient of friction between the inner surface 66 of the sleeve 14 and the outer surface 65 of the insert 16 are selected to promote sliding contact between the sleeve 14 and the core bolt 12 and the insert 16 during installation of the fastener 10. In some embodiments, the first coefficient of friction is less than 0.5. In some embodiments, the second coefficient of friction is less than 0.5. In some embodiments, the friction at the interface between the inner surface 66 of the sleeve 14 and the outer surface 25 of the core bolt 12 and the friction at the interface between the inner surface 66 of the sleeve 14 and the outer surface 65 of the insert 16 are reduced by the presence of the oxide layer. In some embodiments, the oxide layer includes a high hardness. In some embodiments, the oxide layer has a hardness of 8.0 to 8.5 on the Mohs scale. In some embodiments, the inner surface 66 of the sleeve 14 comprises a double layer. In some embodiments, the double layer of the inner surface 66 of the sleeve 14 includes nitrogen and carbon in the first layer and includes carbon in the second layer. In some embodiments, the first layer of the inner surface 66 of the sleeve 14 is the innermost layer. In some embodiments, the first layer of the inner surface 66 of the sleeve 14 is the outermost layer. In some embodiments, the second layer of the inner surface 66 of the sleeve 14 is the innermost layer. In some embodiments, the second layer of the inner surface 66 of the sleeve 14 is the outermost layer. In some embodiments, the microhardness of the inner surface 66 of the sleeve 14 with the double layer increases two to three times compared to the inner surface 66 of the untreated sleeve 14. In some embodiments, the microhardness of the inner surface 66 of the sleeve 14 is 8.0 to 8.5 on the Mohs scale.

[0035] In some embodiments, a thick hard oxide layer is selectively grown on the inner surface 66 of the sleeve 14. In some embodiments, the selectively grown thicker oxide layer on the inner surface of the sleeve 14 produces sufficient protection to prevent surface damage and results in lower friction. In some embodiments, the thick oxide layer is slowly formed at high temperatures. In some embodiments, the oxide layer grows to a thickness of several microns to provide a hard layer. In some embodiments, the hard layer separates the metal counterparts of the core bolt 12 and the insert 16 from the metal counterparts of the sleeve 14 during the sliding action of the core bolt 12 and the insert 16 relative to the sleeve 14, thereby avoiding surface damage and wear and high friction. In some embodiments, the hard layer has a corundum-like fine grain structure, thereby producing a hard surface of up to 9.0 on the Mohs scale on the outer surface 58 of the sleeve 14.

[0036] It should be understood that the embodiments described herein are merely exemplary in nature, and that many changes and modifications may be made thereto by those skilled in the art without departing from the scope of the present invention. All such changes and modifications including those discussed above are intended to be included within the scope of the present invention.

Claims

1. A fastener, comprising: A sleeve comprising a first end and a second end opposite to the first end, A tubular portion having: external surface, Internal surface, internal threads formed in the interior surface at the second end, and a head positioned at the first end; Core bolt, which contains a first end of the core bolt and a second end opposite to the first end, a cylindrical portion proximal to the first end of the core bolt, an externally threaded portion proximate the second end of the core bolt, and a screw tail, which is located between the cylindrical portion and the threaded portion, wherein the core bolt is configured to be disposed within the sleeve, and wherein the external threads are configured to threadingly engage the internal threads of the sleeve; and an insert configured to be disposed within the sleeve and to surround a portion of the core bolt proximate the second end thereof, wherein the insert is sized and shaped to abut and be retained between the internal threads of the sleeve and the screw tail of the core bolt when the fastener is in a pre-installed position, wherein the insert is configured to be compressed between the internal thread of the sleeve and the thread tail of the core bolt by the installation movement of the core bolt relative to the sleeve, while generating a compressive load on the sleeve by the installation movement of the core bolt, and The insert is configured to deform simultaneously with the ball portion in the sleeve and facilitate formation of the ball portion in response to compression of the insert.

2. The fastener of claim 1 , wherein the core bolt includes an outer surface, wherein the insert is configured to fill a gap between the outer surface of the core bolt near its second end and the inner surface of the sleeve near the second end of the tubular portion of the sleeve, and wherein the insert is configured to provide a conductive path between the sleeve and the core bolt.

3. The fastener of claim 1, wherein the sleeve is comprised of steel.

4. The fastener of claim 3, wherein a first coefficient of friction between the interior surface of the sleeve and the exterior surface of the core bolt and a second coefficient of friction between the interior surface of the sleeve and the exterior surface of the insert are selected to facilitate sliding contact between the sleeve and the core bolt and between the sleeve and the insert during installation of the fastener.

5. The fastener of claim 4, wherein the sleeve comprises a first layer located on the outer surface of the sleeve, wherein the first layer comprises a first hardness, and a second layer located on the inner surface of the sleeve, wherein the second layer comprises a second hardness, and wherein the second hardness is greater than the first hardness. The fastener of claim 5 , wherein the first layer is a coating.

7. The fastener of claim 6, wherein the coating is comprised of a metal-based coating.

8. The fastener of claim 6, wherein the coating is selected from the group consisting of silver, gold, nickel, cadmium, copper, and lead or alloys thereof.

9. The fastener of claim 6, wherein the coating is comprised of bronze.

10. The fastener of claim 5, wherein the second layer is comprised of an oxide layer.

11. The fastener of claim 10, wherein the sleeve includes a third layer located above the second layer.

12. The fastener of claim 11, wherein the second layer is comprised of carbon and the third layer is comprised of nitrogen and carbon.

13. The fastener of claim 1, wherein the insert is comprised of copper.

14. The fastener of claim 1 wherein the insert is comprised of monel.

15. The fastener of claim 1, wherein the insert comprises a coating.

16. The fastener of claim 15, wherein the coating is selected from the group consisting of silver, gold, and nickel.

17. The fastener of claim 4 wherein said sleeve includes an annealed portion adjacent said insert.

18. The fastener of claim 1, wherein the core bolt includes a head at the first end thereof, and wherein the head of the sleeve includes a recess sized and shaped to receive the head of the core bolt.

19. The fastener of claim 1, wherein the head of the sleeve is configured to be mounted in accessible holes in a plurality of workpieces, and wherein the ball portion is configured to be positioned on a blind side of the workpiece.

20. A fastener comprising: A sleeve comprising a first end and a second end opposite to the first end, A tubular portion having: a head positioned at said first end, a first portion proximate the first end and having a first inner diameter, a second portion adjacent to the first portion and having a second inner diameter smaller than the first inner diameter of the first portion, a third portion proximate the second end and having internal threads, and a step positioned between the first portion and the second portion; Core bolt, which contains a first end of the core bolt and a second end opposite to the first end, a cylindrical portion proximal to the first end of the core bolt, an externally threaded portion proximate the second end of the core bolt, and a screw tail, which is located between the cylindrical portion and the external threaded portion, wherein the core bolt is configured to be disposed within the sleeve, and wherein the external threads are configured to threadingly engage the internal threads of the sleeve; and an insert configured to be disposed within the sleeve and to surround a portion of the core bolt proximate the second end thereof, wherein the insert is sized and shaped to abut and be retained between the step of the sleeve and the tail of the core bolt when the fastener is in a pre-installed position, wherein the insert is configured to be compressed between the internal thread of the sleeve and the thread tail of the core bolt by the installation movement of the core bolt relative to the sleeve, while generating a compressive load on the sleeve by the installation movement of the core bolt, and The insert is configured to deform simultaneously with the ball portion in the sleeve and facilitate formation of the ball portion in response to compression of the insert.

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