IL31827A - Fastener including expander means and joint including the same - Google Patents

Description

FASTENER EXPANDER MEANS ANO THE SAME This invention relates to a fastener pin for making an interference fit with the nominally cylindrical wall of hole in a metal and to the resulting Especially in the aircraft but not exclusively it has become increasingly important to utilize a fastener in a Joint which provides together with least physical interruption of the it has become critioally important not only to design to the classical considerations of shear and bearing strengths but also to consider the effects on the workpiece Itself of its interaction with the reaso for this is the proportional relationship between stress corrosion and the compressive stress exerted by the workpiece on the Still another ance to or cyclic A tight Joint is more fatigue resistant than a relatively looser and fatigue strength a major factor in aircraft As a current in the Boeing the is expected to take off with a loaded gross weight of approximately The tare weight of the airplane itself is expected to be on the order of will thereby be noted that this modern airplane is expected to lift a payload of approximately the same order of magnitude as its own Not only does this require highly stressed Joints and structural members forming to their optimal but it must be expected that these Joints will be cycled many The aircraft will cost many millions of dollars and its mercial life must It is stipulated that its life cycle will have to be a roximatel four times lon er than of aircraft to be which are to perform under the circumstances indicated will in general have to be very tight ing substantial clamping forces even more involving tight fits between the shank of the fastener and the wall of the hole in which it One typical example of a fit for this purpose is called the inter wherein the diameter of the shank of a fastener greater than the nominal diameter of the hole in which it is be Interference fits are not new per and are frequently utilized where a tight fit is desired between the workplace and the Such fits have involved a number of very serious problems in the no the least of which results from the standards ship to which the holes are and to which the ers themselves are If the interference is then it possible to damage the into which shank forcibly the springback force of the workplece will be and lead to increased Stress corrosion is a problem in all interference fits and with the hoop It is therefore desirable to have reduced hoop force on the but still have a tight Still another problem resides in the surface finish of both the hole and of the fastener Surface ities become stress concentration regions wherein fatigue failures resulting from many hundreds of thousands of cycles are likely to cause incipient It is an object of this nvention to provide a means forces between wall of the workpiece and the fastener are reduced while still providing a good tight in which the structural properties of the of the wall are in which the hole in the workpiece optimally rounded and in which the same is burnished so as to provide a smooth finish for ith a truly cylindrical It is a further object of this invention to provide a wherein a fastener can be plated with a relatively delicate in which the forces between the wall of the hole in the workpiece and the plating are whereby the plating which remains contiguous tween the wall of the workpiece and the general structure of the fastener pin alon the shank is maintained in an optimal This invention contemplates a fastener pin for makin an interference fit with the cylindrical wall of a hole in a metal workpiece and for during the insertion o the pin into the a temporary and localized expansion of the wall to a diameter greater than that of the shank with which the interference fit will be and to such an extent that the metal immediately surrounding the where the localized expansion occurs is compressed beyond its compressive after which at least a portion of the axial extent of the wall of the hole is permitted return toward its original thereby to embrace in an interference fit at least a portion of said The pin includes a cylindrical a head on the pin on the first end thereofi and fastening means at the other end than the of the hole through which it is to be and the shank has a diameter which is greater than said diameter of the A section is disposed adjacent to the fastening means which constitutes a surface of revolution in the zone between the lateral dimension arid the said shank The tangent to the generator line of the surface of revolution makes an acute angle with the central which acute angle faces toward headed deflector section free from expander is in the nature of a bead or extending around the fastener disposed between the deflector section and the The deflector section comprises a solid annular projection extending to a diameter greater than that of the shank as the pin is forced into the hole in the the fastening means passes through the hole without The deflector section enlarges the hole to at least the diameter of the and the sectio therea ter enlarges the hole locally compressing the material beyond its yield point as the expander section moves beyond the the expanded material contracts upon the shank to form an interference fit at least some properties of the metal at the wall of the hole being different than which would have resulted had the interference fit with the shank been formed without the said localized The invention also comprehends the Joint produced by said fastener with the together with additional fastening means such as or which bear against one side the workpiece while head of the fastener pin bears against the other side of the The above and other features of this invention will be fully understood from the following detailed description and the accompanying in 1 is a side elevation of the presently preferred embodiment of the invention showing a portion of the fastener entering a workpiece preparatory to making a joint according to the 2 is a elevation partly in cutaway section showing a first stage in the of the joint of shows the result of further insertion of the device of 1 into the shows the device of 1 fully inserted the workpiece and further Illustrates considerations relating to grip range 5 shows the presently preferred joint of 6 and are side partl in cutaway of other embodiments of the 8 is a diagram illustrating a feature of the and a illustrating a feature of the The invention as shown in 1 includes a metal piece 10 which may comprise a plurality of pieces such as sheets or a sheet and a bracket to be joined together fe a fastener which fastener 11 includes a pin Th pin has a central 13 which is intended to be aligned with the axis of a hole Ik extending through the workplace into the pin is to be The hole has a nominal diameter 15 which is the diameter of the hole in its relaxed and undisturbed Other diameters are also shown will be described The pin a circularly cylindrical 16 which is sometimes described as a being a pure cylinder on central axis At on end of the shank there is a head 17 which is shown as a typical sink type intended to fit in a countersink 18 in the It be understood that other types of heads such as flat fillister and the could be used in which cases the countersink will eliminated from the At the opposite end of the pin there is a fastening 20 which in the preferred embodiment shown is a The thread has a major diameter 21 which the greatest diameter of the This major diameter is less than the nominal diameter of the hole so that it will pass freely through the The relationships between the various dimensions in 1 have been magnified and gerated for purposes of It will also be noted that the diameter of the shank 16 is greater than the nominal diameter 15 order that there will be an interference fit between the circular shank and the wall of the Because is desired to insert cylindrical shank into the cal wall of hole with an interference it is obviously necessary to expand the wall of the hole in order to get the shank In order to so the least damage the workpieoe and to the vantage Of the resulting there is provided a tor section which deflector section begins adjacent to the thread 21 at a region no farther radially outward than the 21 of the and whic continues in a generally convex or conical mode to a diameter which is at least as great as the diameter 26 of the This flector is best shown in as extending diameter 21 to diameter 26 adjacent to the fastening Immediately contiguous to the deflector there is an expande section This expander section in two an initial portion which is contiguous to and continuous with the deflector section and a secondary tion 32 which is contiguous to the portion and also the straight The deflector section constitutes a surface of ion in its the tangent to generator line making an acute angle with the central which acute angle faces toward the head The seotion is free of discontinuities suoh as portions of the threads and the The expander section also is a surface of revolution and it comprises a solid annular pro ection tending to a diameter 33 which greater than that of the shank It is common practice for interference fits to Involve a difference of diameters on the order of approximately inches in holes of approximately inch nominal This interference dimension varies with the size of the hole tout these standards are generally known and followed the and are generally plicable to this In the instant it has been found important to attend to the class of physical property best illustrated in which shows an illustrative example of a metal material having properties of compressive stress pressive The shown is generally typical of the aluminum alloy known as T The dimensions the compressive stress component are pounds per square and those of compressive strain are in inches per The typical and portions of this overly simplified curve which is also generally similar to curves for other metals and are a proportional region which essentially a straight line terminating at a yield point beyond which there is a region with a different it is a short of should the material be stressed beyond the yield for example to points 38 or the material on the release of stress will return back down respective curves or the tinction representing residual effects nature of work hardening and the like which among other things a lesser residual or hoop stress on an article responsive to the residual It is a feature of Invention that the expander section has its diameter sufficiently large relative to the diameter 15 of the wall of the hole that when the fastener pin pressed into the there is a local compression of the material beyond its yield as the expander section moves beyond the expanded re ion the ex anded material contracts back uon the shank to an interference fit at least some physical properties of the material of the wall of the hole being different from those which would have resulted had the interference with the shank been formed without the localized expansion beyond the yield This can readily be understood by reference to 8 the material had been compressed by the expander section to points such as 38 or on the the material would have returned back onto the shank along curves 40 or instead of along curve thereby lessening the springback compressive hoo forceson the device itself while still Joying certai advantages of burnishing and the like which are yet to be a fastener for a hole diametrical difference between 33 and 26 on the order of inches in a plate of 351 aluminum has been found to provide the aforesaid The initial portion 31 is preferably a continuous circu curve in an axial length on the order of about The secondary portion 32 is preferably a conical taper on the order of two degrees conical angle and on the order of inches in The deflector and expander sections are preferably continuous with each blending without The generator line of the initial portion has a tangent between the means and the secondary to merge toward ism with the central The secondary portion and the initial portion are preferably continuous with each and the second portion meets the cylindrical shank at a small angle of about included conical An advantage of the invention is illustrated in wherein a shank and an expander section are shown which bear a plating of cadmium or other relatively soft of plating Such materials can also minum and various of the noble It is noted that in general these platings are galled in interference generally in proportion to the springbaok forces exerted by the wall of the By these springbaok forces it will be found that the plating between the shank and the wall of the hole is left relatively undisturbed and smooth and will be in better shape than were the expander section not It is generally and schematically shown in 9 that there is a region where the plating is removed from th expander section because this is the region where the roughest treatment is between the workplece and the fastener this expander tion also serves to expand and burnish the wall of the hole and also modify the physical property of the springbaok of th material such that as the material returns back to embrace the the springbaok force less than it would have been had the expander portion not stressed the Wall of the hole beyond the yield result of that there is a lesser drag betwee the wall of the hole and the and consequently there is less damage plating on the There is a still further vantage the use of the expander The fastener can readily be turned or ground to a true circular By expanding all of the material contiguous to hole to a condition beyond its yield it will be found that all of this then being in the plastic will retur back to approximately a true circular that of the whereby a hole whic is initially slightly of round in the workpieoe will actually turn to a true round con iguration and smoothly and evenly the cylindrical shank of the fastener The use of this device is shown in The first step is shown in 2 with the fastener means serted into the hole in the workpieoe and the bottom end of the workpieoe hole beginning to bear on the flector As the fastener pin is thrust further conditions of 3 begin to wherein the material is deflected b the deflector and then is further expanded by the expander and then begins to tract on the secondary portion of the expander section and upon the cylindrical shows a consideration of grip It is of that the entire length of the wall of the hole be but this is not Por the maximum grip range is indicated by line a medium grip range by line and a minimum grip range by line These represent the back surfaces of of different the dimensions being greatly exaggerated for purposesof 5 shows the device more in The total length of the expander and deflector sections will ordinarily not exceed inches on a fastener of practical and it will therefore be understood how exaggerated the drawings without such major features could not be illustrated at grip would have the end of the hole lately adjacent the fastening Minimum would have the expander section passed entirely through the and grip would at the back of the The axial extent of treated hole wall which returns to shank diameter obviously can fastening means also an additional portion which will hold the fastener pin in the This is in 5 as a nut 55 threaded onto the fastening the nut having a counterbore to clea any incomplete threads on the fastening means and also any projecting portion o the deflector and expander Threaded means are not the only way to hold the device For shows that instead of the fastener means portion a the end of the pin threaded or otherwise It could be made of material suitable to be headed to a such as by bein struck with hammer or rivet shows the use of a ring groove with a snap ring 59 other means engaged The fastening means is in every case completed by a means either of the self material or of an auxiliary part which bears against side of the workpiece while the head bears against the other invention thereby provides optimum functions resulting from working the material of the workpiece in plastic to treat the wall of the hole in whioh the fastener pin to be fitted by placing It in sion beyond its yield point so as to reduce the hoop stresses on the material as it returns to form an Terence doing less damage to plating on the smoothing and burnishing the wall of the and generally beneficially treating the material of both the fastener and of the of the workpieee so as to produce a of optimum insufficientOCRQuality

Claims (1)

1. WHAT IS CLAIMED IS: 1. A structural joint comprising: a workpiece having a pair of opposite surfaces comprised of a plurality of overlappin contiguous metal elements, each of the elements having a respective hole, the holes being axially aligned to form a continuous passage extending between said surfaces defined by respective walls of the holes and having a central axis, the metal of which the elements are made having the inherent physical property of a compressive stress-compressive strain relationship in which a yield point exists such that, when compressive forces are exerted beyond said yield point and are then relaxed, the material returns to a different strength and size than would result were the yield point not exceeded, and is said to be cold-worked", a unitary metallic combined metalworking tool and fastener pin in the said hole comprising a cylindrical shank having a central axis coincident with that of the passage, a solid annular expander section on said pin contiguous to the cylindrical shank and extending radially beyond the shank, fastener means at one end of the fastener pin, and a head at the other end, said expander section including an initial portion which is a smooth surface of revolution facing and sloping toward the fastener means with a progressively increasing diameter as it extends axially away from said fastener means, and a return portion contiguous and directly connected to both the initial portion and to the cylindrical shank, and having no diameter less than that of the cylindrical shank, the return means facing and sloping toward the head, the expander section lying closer to the fastener means than the cylindrical shank, and having a greatest diameter greater than that of the cylindrical shank, the head bearing against the workpiece surface at one end of the passage, the expander section being adjacent to the other end of the passage, some part of the expander section having contacted the passage wall at the said other end and the major portion of the axial length of the walls of the holes forming an intimate and substantially continuous interference fit with the cylindrical- shank., and the fastener means including means in abutment with the workpiece surface at said other end of the passage, the joint having been produced by selecting the said greatest diameter of the expander section relative to the initial diameter of the passage so that expansion of the wall to the diameter of the expander section by expansive force exerted by the expander section will coldwork the metal which bounds said wall and upon release of said expansive force, the wall would, absent restraint, return to a diameter which is larger than the initial diameter of the passage prior to exertion of said expansive force and smaller than that of the expander section, and selecting the diameter of the cylindrical shank so as to be greater than said new diameter, and pressing the fastener pin into the passage until the fastener means projects beyond said other end of the passage and the head bears against the workpiece surface at said one end of the passage, thereby passing the expander section axially through the major portion of the length of the passage, burnishing said walls on the way, and inserting the cylindrical shank in the passage in intimate and substantially continuous interference fit with the workpiece throughout the major proportion of the axial length of the holes without further expansion of the walls after passage of the return portion, the metal of the workpiece contiguous to the cylindrical shank being coldworked by the expander section and thereby having a greater tensile · strength than material laterally farther removed from the passage. 7. A structural joint according to claim 6, in which the said greater tensile strength of material contiguous to the cylindrical shank is substantially uniform axially throughout the said major portion of the axial length of the holes. 8. A structural joint according to claim 6, in which the fastener means includes a thread on the said combined metalworking tool and fastener pin. 9. A structural joint according to claim 6, in which the fastener means includes a recess in the said combined metalworking tool and fastener pin for receiving and retaining a laterally-extending element. 10. A structural joint according to claim 6, in which the fastener means comprises a deformable section on the said combined metalworking tool and fastener pin for forming an upset head. 11. A structural joint according to claim 6, in which the combined metalworking tool and fastener pin includes a deflector section between the fastener means and the initial portion having a diameter less than that of the cylindrical shank, the deflector section and initial portion being contiguous and without discontinuity between them. 12. A structural joint according to claim 11, in which the generator of the initial portion of the expander section bends toward parallelism with the central axis. 13. A structural joint according to claim 6, in which the generator of the initial portion of the expander section bends toward parallelism with the central axis. 1 . A structural joint according to claim 6, in which the generator of the initial portion is a continuous convex arc. 15. A structural joint according to. claim 14, in whic the return portion is a frusto-conical taper. ΐβ. A structural joint according to claim Ik, in which the return portion is non-concave. 17. A fastening pin substantially as herein described with reference to the accompanying drawings. 18. A joint substantially as herein described with reference to the accompanying drawings.