Deformable sleeve nut and a method of manufacturing

Disclosed is a method of manufacturing a deformable sleeve nut that includes selectively strain hardening only a first portion of a material blank while not strain hardening a second portion of the material blank, then, after strain hardening the first portion of the material blank, internally threading the first portion of the material blank to define a nut portion and machining the second portion of the material blank to define a deformable sleeve portion that includes an end portion and a bulbing portion positioned between the end portion and the nut portion, where the bulbing portion is constructed to bulb outwardly and form a load bearing flange when the bulbing portion is compressed between the end portion and the nut portion. Also disclosed is a deformable sleeve nut made with this process.

BACKGROUND

Blind fasteners and clamps are widely used. Applicant's OSI-Bolt® Fasteners is a type of blind fastener that is used in both composite and metallic airframe application as both a primary and secondary fastener. (Primary fasteners are subjected to more severe joint loads than secondary fasteners.) Blind type fasteners, where the blind side clamping surface is inserted through the fastener opening before engaging the blind side clamping surface, are popular because, unlike two-piece fastening systems that require where access to both sides of the fastener, the installation of a blind type fastener can often be facilitated from just one side of the fastener opening. This can simplify installation, particular when robotic installation is used, and also permits using blind fasteners in application where access to one side of the opening is restricted or unavailable, for example, in a closed structure such as some aircraft wings.

In situations where access to both sides of the blind fastener is restricted, if a failure occurs on the blind side, it can be difficult and time consuming to remove the failed fastener and replace it with a new fastener. There is a need for improved blind fasteners that reliably perform as expected.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

For the purposes of promoting an understanding of the principles of what is claimed, reference will now be made to embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the claims is thereby intended. Any alterations and further modifications in the illustrated device, and any further applications of the principles disclosed and illustrated herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates.

Referring toFIG. 1, a prior art OSI fastener is illustrated as fastener50. Fastener50includes bolt60, body70, nut80and sleeve90. Sleeve90is also illustrated inFIGS. 2 and 3and nut80is also illustrated inFIGS. 4 and 5. After inserting fastener50into an opening and securing body70from rotating, rotation of bolt60relative to body70compresses sleeve90between body70and nut80causing sleeve90to bulb outwardly generating an enlarged flange that forms an enlarged clamping surface that cannot pass through the opening. Continued rotation of bolt60relative to body70moves the enlarged flange into contact with the part(s) being claimed and applies a clamping force between the enlarged flange from sleeve90and head72on body70.

Fastener50requires a non-rotating interface between body70, sleeve90and nut80because only body70can be secured from rotation during installation (nut80and sleeve90are inserted through the fastener hole and are not accessible in a “blind” installation). Thus, securing body70from rotating should also secure nut80from rotating, otherwise nut80could rotate with bolt60rather than compressing and advancing sleeve90to complete installing the fastener due to threaded engagement with bolt60. To enhance a non-rotating interface, the end of body70that contacts sleeve90, both ends of sleeve90and the end of nut80that contacts sleeve90may be knurled or otherwise include features that interlock sleeve90, nut80and body70to reduce or prevent relative rotation between these components during installation. This is shown as knurling82on nut80inFIGS. 4 and 5and knurling92on sleeve90as shown inFIGS. 2 and 3.

Fastener50utilized separate sleeve90and nut80structures because these components generally require different material characteristics. Sleeve90generally requires significant ductility to permit the formation of an enlarged flange while nut80generally requires significant strength to prevent internal threads from being stripped by bolt60and be sufficiently hard such that nut80does not significantly deform when a load is applied while, at the same time, sleeve90does deform. With separate components, material selection for sleeve90and nut80can be separately optimized for a particular application. A ductile material can be selected for sleeve90while a stronger, heat treated (hardened) material can be used for nut80. For example, Applicant uses a material such as titanium or steel that has been hardened by heat treating to construct nut80while a malleable material, such as a solution treated AISI 304 Stainless Steel, is used for sleeve90.

Applicant has identified that the two piece construction for nut80and sleeve90, while addressing the required physical characteristics for these components, may cause other problems. Slippage between nut80and sleeve90results in a failed installation, because there is no alternative mechanism to hold nut80against rotation of bolt60. This can be a significant problem if slippage occurs after partial expansion of sleeve90, so that fastener50cannot be easily removed but installation cannot be completed without scrapping fastener50, which may require cutting fastener50off. There is a need for an improved nut and sleeve combination that reduces the occurrence of failed installations.

Applicant has identified that by combining the nut and sleeve structure into a single structure, failure modes that previously occurred at the junction between the nut and sleeve structures can be significantly reduced or eliminated. However, the problem of different material performance requirements for these structures remains. Applicants solution to this problem is to selectively strain harden the portion of a material blank that is used for the nut portion while not strain hardening the remaining portion of the material blank that is utilized to form the deformable sleeve portion of the combined structure.

Referring toFIG. 6, process100is illustrated. Process100is a manufacturing process to produce a deformable sleeve nut that combines functions similar to nut80and sleeve90in a unitary structure constructed from a single piece of material. Process100begins with step102where a first portion of a material blank is selectively strain hardened while a second portion of the material blank is not strain hardened. Strain hardening process such as extruding and roll forming can be used in step102. Process100continues with step104where the first portion of the material blank is machined and internally threaded to define a nut portion of the deformable sleeve nut. In step106, the second portion of the material blank is machined to define a deformable sleeve portion. In step108, a transition between the nut portion and the deformable sleeve portion is machined. The transition can be conical in shape or any other desired geometry. In step110, the outer surface of the material blank, including the nut portion and the deformable sleeve portion, is machined to have a constant outer diameter.

It should be understood that steps104,106.108and/or110in process100may be performed in any desired sequence and/or at the same time. For example, the material blank may require a boring operation that passes through both the first and second portions as part of forming the nut portion and the deformable sleeve portion. Similarly, the outside surface could be formed before internal features are formed.

Referring toFIGS. 7 and 8, material blank120is illustrated. Material blank120has a length L1and an outer diameter OD1. Material blank120is a continuous piece of a single material such as AISI 304 Stainless Steel. Other materials that are acceptable to use as material blank120include 300 and 400 series stainless steels and A 286 Precipitation Hardening Alloy.

Referring toFIG. 9, partially cold worked material blank130is illustrated. Partially cold worked material blank130includes cold worked portion132, un-worked portion136and head138with transition134located between cold worked portion132and un-worked portion136. Cold worked portion132is formed by a trapped extrusion process performed on a solution treated material blank120. Transition134may be partially cold worked, but is less cold worked than cold worked portion132. Head138is formed by cold working after cold worked portion132is formed. Head138is primarily formed to aid in orienting and handling cold work blank130during subsequent steps such as machining.

Referring toFIGS. 10 and 11, deformable sleeve nut140is illustrated. Deformable sleeve nut140includes nut portion142, transition portion144and deformable sleeve portion146. Deformable sleeve nut140has an outer surface147that has a diameter OD3. Deformable sleeve nut140may have a constant diameter OD3across substantially its entire length. Nut portion142is internally threaded with internal threads148defining major diameter150. In the illustrated embodiment, transition portion144includes conical taper152that has a vertex angle VA, although the conical transition geometry is not limiting. In the illustrated embodiment, vertex angle NA is approximately equal to 15 degrees. In other embodiments, vertex angle VA can vary from between 10 degrees and 25 degrees. In yet other embodiments, vertex angle VA can vary from between 5 degrees and 90 degrees.

Deformable sleeve portion146also defines and includes internal diameter154, insert recess156and end wall158. In the illustrated embodiment, internal diameter154is approximately equal to major diameter150. Insert recess156may be constructed and arranged to receive a plastic insert that may assist deformable sleeve portion146to preferentially bulb outwardly while potentially blocking deformable sleeve portion146from buckling inwardly upon application of a compressive force. While not illustrated, end wall158may optionally include geometries such as knurling to reduce or eliminate rotation against a body such as body70.

Referring now toFIG. 12, fastener200is illustrated. Fastener200includes deformable sleeve nut140, bolt160, body170and insert180. Bolt160includes external threads162, head164and engaging portion166that is constructed and arranged to interface with an external tool to rotate bolt160. Bolt160also optionally includes break groove168positioned between engaging portion166and head164. Break groove168may be constructed and arranged to fracture when sufficient torque is applied to engaging portion166, such as may be encountered when fastener150is fully installed as described below.

Body170defines bore172through which bolt160passes. Body170also includes tapered end174and head176, which head176defining engaging portion177and surface178. Engaging portion177is constructed and arranged to interface with an external tool to secure the relative position of body170when bolt160is rotated. Tapered end174may optionally include anti-rotation features such as knurling, which is shown inFIG. 12.

Insert180is positioned in insert recess156. Insert180may define a substantially cylindrical shape. Insert180may be constructed from a relatively easily deformable material (compared to deformable portion146) such as plastic. Insert180may be constructed and arranged to substantially fill the space between bolt160and deformable sleeve nut140defined by insert recess156. Insert180may have sufficient compression strength to encourage deformable portion146to bulb outwardly when compressed while potentially blocking deformable sleeve portion146from buckling inwardly upon application of a compressive force.

Fastener200is installed by inserting it into an appropriate sized opening, securing body170and deformable sleeve nut140from rotating by securing engaging portion177with an appropriate tool and then rotating bolt160relative to body170utilizing a tool engaged with engaging portion166to cause deformable sleeve nut140to advance along bolt160toward body170, thereby compressing deformable sleeve portion146between nut portion142and tapered end174on body170. This causes deformable sleeve portion146to bulb outwardly and fold upon itself to form an enlarged flange.

Referring now toFIG. 13, fastener200is shown as installed through overlapping plates201and202as installed fastener200′. Installed deformable sleeve nut140′ has been advanced toward body170sufficiently that deformed sleeve portion146′ has bulbed outwardly and advanced up tapered end174, thereby expanding the internal diameter of deformed sleeve portion146′. Deformed insert180′ is positioned inside bulbed flange190formed by deformed sleeve portion146′. Overlapping plates201are clamped together between bulbed flange190and surface178on head176.

Referring toFIG. 14, a chart of the hardness distribution along the length of deformable sleeve nut140is illustrated. The X-axis of the chart shows the relative position, measured in inches, long the length of deformable sleeve nut140where hardness was tested. The Y-axis of the chart shows the measured Knoop hardness, measured with a500gload. The chart includes the results of 5 different specimens, each made of AISI 304 Stainless Steel, each having been subject to partial 33% cold working. Samples 1 through 3 were manufactured from one heat of raw material. Samples 4 and 5 were manufactured from a different heat of raw material. The location “0” starts at the threaded end of deformable sleeve nut140, with larger measurement progressively advancing along the length of deformable sleeve nut140toward deformable sleeve portion146.

As illustrated inFIG. 14, the method of partially cold working the material blank resulted in selectively hardening the portion of the blank cold worked. With nut portion142averaging approximately twice the hardness of deformable sleeve portion146, with a distinct transition in the hardness at transition portion144.

Additional testing also revealed that the ratio between the maximum and minimum measured hardness varies based on the size of the deformable sleeve nut produced (smaller deformable sleeve nuts are manufactured using smaller material blanks). Testing on ¼ inch diameter deformable sleeve nuts subjected to partial 33% cold work measured hardness ratios (max/min) of 1.85, 1.91, 1.92 and 1.87. Conversely, testing on 3/16″ diameter deformable sleeve nuts subjected to partial 33% cold work measured hardness ratios (max/min) 2.31, 2.53, 2.79. In subsequent installation testing on the 3/16″ diameter deformable sleeve nuts, the corebolt occasionally fractured during the installation process, indicating that the amount of cold work might need to be reduced for the 3/16″ parts compared to the ¼″ parts. Based on this data, nut portion142should be at least seventy-five percent harder than the hardness of deformable sleeve portion146but no more than one hundred and fifty percent harder.

Table 1, below, reports additional measured hardness ratios for ¼″ sleeves and 3/16″ sleeves subjected to partial 33% cold work.

All the specimens listed in Table 1 where determined to have been adequately work hardened, but, as already discussed, some of the 06 parts ( 3/16″ OD) might require less hardening. The difference between the equipment used, i.e., tensile tester vs. header, is the speed of the extrusion process. The header is much quicker at cold working the parts, around 60 pieces a minute, while the tensile tester (in an R&D lab) took around 15-20 seconds to extrude a single blank. There were also differences in the material lots tested. Lot #20361 was wire in solution treated condition while the rest of the lot numbers were bar stock which was machined to the correct size before solution treating the blanks. (All specimens were solution treated before cold working.)

While the claimed subject matter has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. All changes and modifications that come within the spirit of the disclosure are desired to be protected by the claims.