IMPROVED SWAGED COLLAR FASTENER

Abstract: Predetermined limits are attained for the peak loads encountered when a composite assembly of workpieces (12) is secured with a swaged collar fastener (10), by disposing cavities in the cylindrical wall (32) of the fastener collar to receive material flow during the swaging operation. Rotation between the collar and pin (16) of the fastener (10) is precluded by disposing abutting portions on the pin (16), which interface against the swaged material of the collar. Fastener cost reductions are achieved by decreasing the volume of a post-swage scrap portion on the pin (16) and by concurrently fabricating grooves thereon with a rolling die, for various functional purposes. Swaging toll malfunction is avoided by eliminating land surfaces adjacent to grooves (38) on the pin (16) through which pull is applied thereto with the tool (16).

Description: The invention relates to a fastener device according to the preamble part of claim 1. A fastener device as known from US-A-4 221 152 includes a headed pin with locking grooves disposed thereon and a collar having a cylindrical wall. When such fasteners are utilized to secure a composite assembly of workpieces, the pin is disposed into aligned holes through the workpieces to be secured in the composite assembly and the collar is disposed about the pin over the locking grooves thereof. Then the cylindrical wall of the collar is radially compressed into the locking grooves to affix the collar on the pin. Various tools are available for this collar wall compression operation with the most common being a swaging tool which pulls the pin in one direction while forcing a swage anvil over the collar in the other direction to forceably clinch the workpieces of the composite assembly together while affixing the collar to the pin. The pull is applied to the pin through a pintail disposed on one end thereof, which is broken off and discarded as scrap, after the collar has been affixed to the pin. A similar fastener device is known from WO87/00891. One problem encountered with known fastener devices of that type is that vibrations passing through the composite assembly can cause the fastener collar to turn on the fastener pin. Where annular locking grooves are utilized on the fastener pin, the collar loosens to eliminate the clinching force. In a high vibration environment the collar loosening would occur in a relatively short time. Where helical locking grooves are utilized on the pin, the collar will only turn in one direction but any such turning will immediately eliminate the clinching force. When the pin is fabricated from expensive materials, such as titanium alloys, the use of a pintail thereon is always viewed with some apprehension because it serves no useful purpose after the collar is affixed to the pin and is discarded as scrap. It is an object of the present invention to reliably preclude rotation between a fastener collar and a fastener pin after affixment therebetween his been accomplished to secure a composite assembly with a swaged collar fastener. It is another specific object of the present invention to reduce the unit cost of a swaged collar fastener. Said object can be achieved - according to the characterizing part of claim 1 by including at least one abutting portion on the fastener pin locking grooves which interfaces against the swaged collar when torque develops between the fastener collar and fastener pin. Reduced unit cost of a swaged collar fastener are accomplished by significantly reducing the diameter of the pintail on the fastener pin relative to the diameter of the locking grooves thereon or concurrently fabricating the locking grooves thereon with pull grooves on the pintail thereof as a single operation, according to claims 6, 8 and 9. Embodiments of the fastener device according to the invention will be described in connection with the drawings. In the drawings is : Figure 1 a partially cross section of workpieces, a fastener device and a swaging tool just before a fastener collar is affixed on a fastener pin, Figure 2 the arrangement of Figure 1 with the fastener collar being radially compressed, Figs 3a, 3b, 4a, 4b detail variations of the fastener collar, Figure 5 a partially cross sectional view of one preferred composite assembly embodiment, Figure 6 a side view of one preferred fastener pin embodiment, Fig 7 to 11 cross section detail variations of the fastener pin of Fig 6, related to section-planes 7-7, 8-8, 9-9, 10-10, 11-11, and Figure 12 a side view of another preferred fastener pin embodiment. A fastener device 10 is arranged in Figure 1 with a plurality of workpieces 12 to illustrate the relative disposition thereof when a pull-type swaging tool 14 is utilized to fabricate a composite assembly 15 as in Figure 2. A fastener pin 16 having a substantially cylindrical shank 18 extending along a longitudinal axis 20 between a head 22 and a pintail 24, is disposed through aligned holes 26 in the workpieces 12. Locking grooves 28 are arranged about the longitudinal axis 20 between the head 22 and pintail 24 on the fastener pin 16 and a fastener collar 30 having a cylindrical wall 32 arranged about the longitudinal axis 20, is disposed about the fastener pin 16 at a location over the locking grooves 28. The swaging tool 14 includes jaws 36 which contract radially about the longitudinal axis 20 to grip the pintail 24. Pull grooves 38 are arranged about the longitudinal axis 20 on the pintail 24 and mesh into teeth 40 arranged on the jaws 36 when those jaws 36 are contracted by movement of a collet 42 along the longitudinal axis 20 away from the pintail 24. An axial pull is thereby exerted on the pintail 24 and a swage anvil 44 moves simultaneously with the collet 42 but in the opposite direction over the fastener collar 30 to radially compress the cylindrical wall 32 thereof into the pin locking grooves 28, as illustrated in Figure 2. Such relative movement between the collet 42 and the swage anvil 44 causes forces to be applied across the workpieces 12 which are thereby clinched together. A breakneck groove 45 is disposed about the longitudinal axis 20 on the fastener pin 16, between the locking grooves 28 and the pintail 24. The minimum diametral portion of the fastener pin 16 is defined by the breakneck groove 45 and as the axial pull is increased after the collar swaging operation, the yield point of the minimum diametral portion is exceeded to snap off the pintail 24. Other swaging operations are known and include such operations for a fastener device which has no pintail 24 on the fastener pin 16. At least one cavity 46 is arranged on the fastener collar 30 for the purpose of limiting the peak loads attained throughout the composite assembly 15 during the collar swaging operation. These cavities 46 are defined in the fastener collar 30 by at least 2 oppositely located and substantially radial portions extending into and/or through the cylindrical wall 32 thereof relative to the longitudinal axis 20. As compression on a material in one direction is increased, stress also builds within the material in all directions other than the direction of compression. The material will flow in those other directions to limit the stress attained in the direction of compression. Therefore, by controlling the volume and number of the cavities 46, as well as the arrangement thereof on the fastener collar 30, a radial compression stress limit can be established thereby for the collar swaging operation. For the swaging tool 14 fastener collars 30 illustrated in Figures 3a, 3b, 4a, 4b would be most appropriate. At least one axially elongated groove 48 and at least one annular groove 50 are disposed as cavities 46 in the cylindrical wall 32 of the fastener collar 30. In Figs 3a, 3b grooves 48 and 50 are disposed exteriorly on the fastener collar 30, while in Figs 4a, 4b such grooves 48 and 50 are disposed interiorly on the fastener collar 30. The cavities 46 could be disposed both exteriorly and interiorly on the fastener collar 30 and also, could penetrate through the cylindrical wall 32 thereof. The fastener collar 30 has a cylindrical bore 51 therethrough and include a bearing flange 52 which interfaces against one of the workpieces 12. The annular grooves 50 on the fastener collars 30 of Figs 3a, 3b, 4a, 4b are located next to the flange 52 so as to be accessible to axial material flow throughout the total movement of the swage anvil 44 between the initial and final positions thereof illustrated in Figures 1 and 2 respectively. Although the axially elongated grooves 48 would continue to be evenly spaced about the periphery of the fastener collar 30 for other types of swaging tools, for the radially contracting type and the circumferential roll type of swaging tool, the annular grooves 50 would be evenly distributed along the longitudinal axis of the fastener collar 30. Furthermore, the annular groove 50 could be extended into the flange 52 or be disposed in the flange 52, such as with an undercut (not shown). To provide an anti-rotation feature between the fastener pin 16 and fastener collar 30, the locking grooves 28 on the fastener pin 16 are configured to have at least one abutting portion thereon for interfacing against the fastener collar 30 to preclude relative rotation therebetween when torque develops within the assembled fastener device 10. One locking groove configuration for achieving the anti-rotational feature is illustrated in Figure 5 where the locking grooves 28 are helical and at least one annular groove 54 is disposed amongst the locking grooves 28 to render the helical path thereof discontinuous. Because material from the fastener collar 30 is compressed into the annular grooves 54 when the workpieces 12 are secured by the fastener 10 as illustrated in Figure 5, each discontinuity of the locking grooves 28 at the annular groove 54 becomes an abutting portion 58 which interfaces against the fastener collar 30 when torque develops therein relative to the fastener pin 16. Furthermore, grooves (not shown) extending parallel to the longitudinal axis 20 could be disposed into either annular or helical locking grooves 28 for obtaining discontinuities in the annular or helical path thereof. Another locking groove configuration for achieving the anti-rotation feature of the invention is illustrated in Figure 6 where a fastener pin 16 similar to that illustrated in Figures 1 and 2 is shown to have locking grooves 28 which are annular. However, these annular locking grooves 28 are disposed into at least one non-cylindrical surface portion 60 on the fastener pin 16 and therefore, each locking groove 28 includes at least one surface eccentricity, as shown in Figures 7 through 11. Because material from the fastener collar 30 is compressed into the locking grooves 28 when workpieces 12 are secured by the fastener 10 as illustrated in Figure 2, each such non-cylindrical surface portion 60 becomes an abutting portion 58 which interfaces against the fastener collar 30 when torque develops therein relative to the fastener pin 16. Because the fastener pin 16 is commonly fabricated from an extruded blank, the non-cylindrical surface portions 60 thereon can easily be incorporated as part of the extrusion process. Cross-sectional views through the crest 62 of each individual locking groove 28 are shown in Figures 7 through 11 to illustrate some of the contour configurations that the non-cylindrical surface portions 60 could have. For the non-cylindrical surface portions 60 of the locking groove 28 in Figure 7, the cross sectional configuration is elliptical. Of course, the greater the difference between the major and minor diameters of the elliptical configuration, the greater is the eccentricity of the non-cylindrical surface portions 60. In Figure 8, the non-cylindrical surface portion 60 is a spline 64 axially aligned on the fastener pin 16. Although a key type spline 64 is shown whereon adjacent faces are at right angles, the surface contour of the spline 64 could be more gradual. Additionally, or instead of spline 64, an axially aligned key slot 66 can be provided. A triroundular cross section configuration is illustrated for the non-cylindrical surface portions 60 of the locking groove 28 in Figure 9. The non-cylindrical surface portions 60 of each round in Figure 9 is more pronounced than necessary for most anti-rotation collar applications and any number of rounds can be utilized as illustrated in Figure 10 where the cross section configuration is scalloped. As was discussed in regard to Figure 8, the non-cylindrical surface portions 60 need not be raised and consequently, at least one flat 68 can be disposed therefor, as illustrated in Figure 11. In Figure 12 the fastener pin 16 shown in Figures 1 and 2 is modified to have a pintail 24 of substantially reduced diameter relative to the diameter of the locking grooves 28. Because of this reduced diameter, the volume of the pintail 24 is appreciably reduced and of course, this reduction in volume is reflected in the fabricating blank of the fastener pin 16. Therefore, the cost of the material contained in each such fastener pin 16 will be reduced, especially when the material is very expensive, as is the case for titanium which is commonly the material of fasteners 10 in the aerospace industry. The pitch of the pull grooves 38 on the pintail 24 can also be reduced in proportion with the reduced diameter and if the same number of pull grooves 38 are utilized, the length of the pintail 24 will also be reduced to accomplish a further reduction in the volume of the pintail 24. However, it should be noticed that the volume of the pintail 24 reduces in proportion to the square of its reduction in radius but only in direct or linear proportion to its reduction in length. Obviously, the jaws 36 of the tool 14 must be modified for compatability with the reduced diameter of the pintail 24 and the pull grooves 38 of decreased pitch thereon. To facilitate such modifications, helical pull grooves 38 may be utilized to provide for teeth 40 on the jaws 36 that can be readily fabricated with a conventional tapping operation. Furthermore, both material and manufacturing costs can be economized where either or both the locking grooves 28 or pull grooves 38 are machined on the fabricating blank of the fastener 10. Such economies are accomplished by rolling both the locking grooves 28 and the pull grooves 38 concurrently on the fabricating blank with a die. Such rolling produces grooves having crests of greater diameter than the diameter of the fabricating blank, which will therefore contain less material due to its reduced diameter in anticipation of such crests. Furthermore, the concurrent rolling process serves to condense groove fabrication into a single manufacturing operation. Of course, either helical or annular grooves can be rolled concurrently. After the pintail 24 is snapped off during the collar swaging operation, it moves progressively along the axis 20 toward being ejected from the swaging tool 14 as illustrated in Figures 1 and 2, where it is designated pintail 24'. The fastener 10 to which the swaging tool 14 is applied, initially relocates the pintail 24' along the axis 20 to a position where it has not cleared the jaws 36. Of course, the distance pintail 24' is relocated in the jaws 36 along the axis 20 depends on the length of the pintail 24' and the particular design of the swaging tool 14. Conventionally, a land surface 70 is disposed on each pintail 24 between the pull grooves 38 and the breakneck groove 45, which can cause the tool 14 to malfunction. As can be understood by observing the portion of the pintail 24' within the jaws 36, the teeth 40 will not mesh properly into the pull grooves 38' if the land surface 70' is oversized or raised with dirt. Therefore, the jaws 36 will remain ajar and the pull force sustainable thereby on the fastener 10 to which the swaging tool 14 is applied, will be inadequate for the desired collar swaging operation. One aspect is to eliminate the land surface 70' by extending the pull grooves 38' thereover to become discontinuous at the breakneck groove 45, as shown in Figures 6 and 12. The teeth 40 can then mesh into the pull grooves 38' over the full length of the pintail 24' to permit the retention thereof in the jaws 36, without causing the tool 14 to malfunction when gripping the pintail 24 on the next fastener 10 to which the collar swaging operation is being applied.

Claims: A fastener device (10) for securing a composite assembly (15) of workpieces (12), comprising: a fastener pin (16) having a shank (18) extending along a longitudinal axis (20) of said fastener device between a head (22) and locking grooves (28) about said axis; and a fastener collar (30) having a substantially cylindrical wall (32) about said axis, said fastener collar (30) being affixable to said fastener pin (16) by radially compressing said cylindrical wall (32) into said locking grooves (28), characterized in that said locking grooves (28) are configured to provide at least one abutting portion (58) which interfaces against said fastener collar (30) to preclude rotation therebetween. The fastener device of claim 1, characterized in that said abutting portion (58) results from said locking grooves (28) being disposed into at least one non-cylindrical surface portion (62) on said fastener pin (16). The fastener device of claim 2, characterized in that each said non-cylindrical surface portion (62) is a spline (64). The fastener device of claim 2, characterized in that the cross sectional configuration of said non-cylindrical surface portions (62) is elliptical or scalloped or triroundular or includes at least one flat segment (68). The fastener device of claim 1, characterized in that said abutting portions include discontinuities in said locking grooves (28). The fastener device of claim 5, characterized in that said fastener pin (16) includes a pintail (24) disposed on the opposite end thereof from said head (22) to provide means for pulling said fastener pin (16) with a swaging tool to radially compress said collar (30) into said locking grooves (28), said pintail (24) having a substantially reduced diameter relative to the diameter of said locking grooves (28) to appreciably reduce the volume of material in the blank from which said fastener pin (16) is fabricated. The fastener device of claim 5, characterized in that said locking grooves (28) are helical and said discontinuities therein result from at least one annular groove (58) disposed about said axis amongst said helical locking grooves (28) and/or from at least one elongated groove (66) parallel to said axis. The fastener device of claim 7, characterized in that said fastener pin (16) includes a pintail (24) disposed on the opposite end thereof from said head (22), said pintail (24) having pull grooves, preferably helical pull grooves (38), thereon about said axis, said pull grooves (38) and said helical locking grooves (28) being fabricated concurrently using a rolling die to thereby economize on both material and manufacturing costs. The fastener device of claim 1, characterized in that said fastener pin (16) includes a pintail (24) disposed on the opposite end thereof from said head (22) and having pull grooves (38) thereon about said axis, and an annular breakneck groove (45) about said axis is disposed between said pull grooves (38) and said locking grooves (28), said pull grooves (38) extending to said breakneck groove (45) for eliminating any land surface on said pintail (24) adjacent to said breakneck groove (45) and thereby permitting said pintail (24) to move progressively toward ejection from the swaging tool without causing the tool to malfunction when gripping subsequent fastener pins (16).

Inventors: DAHL, WARREN
Applicants: SPS TECHNOLOGIES, INC.
Application year: 1988
Main classification: F16B19
IPC codes: F16B19