US3559449A

US3559449A - Explosively actuated rivet gun

Info

Publication number: US3559449A
Application number: US777088A
Authority: US
Inventors: John C Steinmetz
Original assignee: VSI Corp
Current assignee: Shared Technologies Fairchild Telecom Inc
Priority date: 1968-11-19
Filing date: 1968-11-19
Publication date: 1971-02-02
Anticipated expiration: 1988-02-02

Abstract

A BARREL ASSEMBLY OF AN EXPLOSIVELY ACTUATED RIVET GUN INCLUDES A BARREL HOUSING AND AN INNER, LONGITUDINALLY DISPLACEABLE BARREL WITHIN THE HOUSING. A TRANSLATABLE IMPACTING HAMMER IS DISPOSED WITHIN THE INNER BARREL FOR STRIKING A RIVET FORMING PUNCH AT THE MUZZLE END OF THE GUN. PORTING IN THE INNER BARREL PROVIDES FOR ITS MOVEMENT IN RESPONSE TO GAS PRESSURE TOWARD THE BREECH END OF THE GUN AND THE VENTING OF EXPOSIVE GENERATED GASES. AN IMPACTING HAMMER RETURNPORT IN THE INNER BARREL ADMITS GASES AHEAD OF THE IMPACTING HAMMER TO FORCE IT BACK TO THE BREECH END OF THE GUN. THE PORTING ALSO PRODUCES GAS BIASING OF A NOSE ASSEMBLY AGAINST THE SHEETS BEING RIVETED TO ELIMINATED THE EFFECT OF GUN RECOIL. THE IMPACTING HAMMER, THROUGH INERTIA SEPARATION, PROLONGS THE TRANSFER OF ITS UPSETTING IMPACT TO A RIVET. THE FORMING PUNCH HAS A FRUSTO-CONICAL RECESS FOR UPSETTING AND CONSTRICTING EXPANSION OF A RIVET. THE NOSE ASSEMBLY HAS A UNIVERSALLY ROTATABLE HEAD WITH A PARABOLIC MIRROR THAT IS MAINTAINED OUT OF ALIGNMENT WITH A LIGHT SOURCE ON THE BREECH ASSEMBLY UNTIL THE NOSE ASSEMBLY IS PROPERLY ALIGNED, WHEREUPON LIGHT REFLECTED FROM THE PARABOLIC MIRROR ENERGIES A PHOTOSENSITIVE ELEMENT TO UNLOCK THE GUN''S TRIGGER. ADDITIONAL INTERLOCKS PREVENT GUN FIRING UNTIL A RIVET BUCKING BAR AND A FORMING DIE ARE IN PROPER POSITION. AN ADJUSTABLE VOLUME EXPANSION CHAMBER CONTROLS EXPLOSIVE PRESSURE ON THE IMPACTING HAMMER AND, THEREFORE, THE UPSETTING IMPACT TRANSFERRED THROUGH THE FORMING PUNCH TO A RIVET.

Description

Feb. 2, 1971l J. c. sTElNME-rz 3,559,449

ExPLosIvELY ACTUATED RIVET GUN Filed Nov. 19, 196e l s sheets-sheet 2 vZ22* g fw pff /X/x//m/ m ///wlf////S Feb, 2, 1971 y J. c. STEINMETZ I EXPLOSIVELY ACTUATED RIVET GUN Filed Nov. 19, 1968 3 Sheets-Sheet 5 Arme/ufr;

U.S. Cl. 72-430 51 Claims ABSTRACT F THE DISCLOSURE A barrel assembly of an explosively actuated rivet gun includes a barrel housing and an inner, longitudinally displaceable barrel within the housing. A translatable impacting hammer is disposed within the inner barrel for striking a rivet forming punch at the muzzle end of the gun. Porting in the inner barrel provides for its movement in response to gas pressure toward the breech end of the gun and the venting of exposive generated gases. An impacting hammer return port in the inner barrel admits gases ahead of the impacting hammer to force it back to the breech end of the gun. The porting also produces gas biasing of a nose assembly against the sheets being riveted to eliminated the effect of gun recoil. The impacting hammer, through inertia separation, prolongs the transfer of its upsetting impact to a rivet. The forming punch has a frusto-conical recess for upsetting and constricting expansion of a rivet. The nose assembly has a universally rotatable head with a parabolic mirror that is maintained out of alignment with a light source on the breech assembly until the nose assembly is properly aligned, whereupon light reflected from the parabolic mirror energies a photosensitive element to unlock the guns trigger. Additional interlocks prevent gun firing until a-rivet bucking bar and a forming die are in proper position. An adjustable volume expansion chamber controls explosive pressure on the impacting hammer and, therefore, the upsetting impact transferred through the forming punch to a rivet.

The present invention relates to an explosively actuated tool for setting rivets which is particularly useful for setting rivets fabricated from hard material.

The effectiveness of a riveted joint is dependent on the shear strength of the rivet. With high shear strength rivets, smaller holes in the fastened sheets may be used while maintaining the riveted joints integrity. The overall effect of high strength rivets results in lightweight riveted structures. Additionally, the use of high strength rivets results in substantially improved joint fatigue life. Therefore, rivets fabricated from such high strength materials as titanium or steel alloys are highly desirable in weight critical structures such as found in aircraft.

An effective riveted joint also requires that the set rivet itself have substantial fatigue resistance. Hard materials such as titanium and certain steel alloys, however, are brittle and extremely difficult to upset without creating fatigue life limiting structural tiaws. As a consequence of these characteristics, la rivet head formed by a sharp, distinct blow of suflicient magnitude to upset the hard material of the rivet has heretofore produced cracking and lines of weakness in the formed head and proximate shank portions. Riveted joints employing hard rivets set by uncontrolled impact also tend to unevenly deform the sheet through which the rivet extends, as the sheet tends to expand to a greater extent adjacent where the rivet end is upset. This uneven sheet expansion reduces joint fatigue life by overexpansion near the formed head and insutlicient expansion of hole walls in the balance of the joint.

Because of the ditliculties encountered with hard rivet United States Patent O materials in producing an effective riveted joint, prior art developments have been directed to high pressure, squeeze setting of hard rivets. This high pressure, squeeze setting slowly applies a setting force on both ends of the rivet. While effective, this method of riveting has limited application. The equipment necessary to apply the extremely large compressive forces through both ends of a rivet must, of necessity, be large and expensive because the equipment must span large distances in reaching interior areas Vto be riveted. These large distances require the equipment to be extremely large to have the strength required to withstand the large flexure loads produced by the setting force. Moreover, the equipment is only useful, because of its size, for riveting large, relatively llat subsections which are susceptible to fabrication away from the final assembly of which they form a part. In aircraft air frame fabrication, for example, the production of subassemblies of this type is possible for only a small proportion of the total air frame.

Therefore, there is a demand for a hand or portable tool which can eiectively produce a high strength riveted joint employing rivets fabricated from hard materials. Such a tool cannot employ the squeeze technique because of the weight and size of the tool required to apply the necessary compressive force and the requirement for applying such a force on either end of the rivet well within the panels being riveted.

The present invention provides an explosively actuated impact tool lwhich may be used to set a wide variety of rivets. In its preferred form, the present invention provides an explosively actuated impact tool which is capable of upsetting rivets fabricated from hard materials, such as titanium or certain steel alloys, to produce an eifectively riveted joint.

In one form, the present invention contemplates an explosively actuated tool or gun for setting rivets which maintains a nose of the gun rmly against the structure being riveted during the upsettingof a rivet, notwithstanding the tendency of the gun to recoil. The gun includes a barrel having a bore for receiving an impacting hammer disposed for translation from the breech end of the barrel toward the barrels muzzle end in response to the -ring of an explosive charge. A forming punch or hammer at the muzzle end of the gun is disposed to be struck by the impacting hammer, translate in a bore of the nose and impart an upsetting force to a rivet. Means is provided for receiving an explosive charge at the breech end of the barrel such as a breech plug disposed in a breech block. Means is also provided for selectively firing an explosive charge disposed in the explosive charge receiving means. The nose is mounted at the muzzle end of the barrel for abutting against the surface of the structural sheet surorunding the rivet to be formed. The nose is coupled to the barrel such that gas generated by the detonation of an explosive charge biases or urges the nose against the sheets While allowing the barrel to recoil.

In one embodiment of the present invention, the forming punch has a frusto-conical recess and the nose has an annular constricting flange disposed on the sheet side of the forming Ipunch. The frusto-conical recess of the forming punch acts on the end of a rivet to constrict its radial expansion into the shape of the frusto-conical recess While the annular, inwardly directed constricting flange restrains the expansion of a collar-like forming die which may be employed with the rivet.

Means may also be `provided to prevent tiring of the explosive charge and the consequent upsetting of a rivet unless the resulting impact force is directed axially of the rivet. Such means may include a universally rotatable or pivotable head, the Iposition of which determines the position of the noses bore. The rotatable head may have a sheet abutting surface and be mounted for limited rotation in a socket. The means may further include a. parabolic mirror, a light source, a photosensitive element and a firing interlock. The parabolic mirror is carried by the head to reflect light from the light source to the photosensitive element when the gun is in proper alignment. The photosensitive element is in circuit with the firing interlock, which may be a solenoid on the path of the guns trigger, to prevent firing until the photosensitive element senses light reflected from the parabolic mirror. In order to prevent inadvertent firing, means may be provided to positively maintain the parabolic mirror out of alignment with the photosensitive element until the gun is properly aligned with the axis of the rivet to be set. Such means may include a spring mounted on a stationary portion of the nose and urging against the mirrors mount. Alternately, the parabolic mirror may be maintained out of alignment with the photosensitive cell by providing an inclined end at the muzzle end of the inner barrel which normally maintains the mirror out of alignment by bearing against a nose sleeve that carries the rotatable or pivotable head. Additional interlocks which prevent gun firing until -a forming die and a bucking bar are properly placed may be provided.

It has been found, in upsetting rivets fabricated from hard materials with an explosively actuated rivet setting gun or tool, that the requisite upsetting force required to upset the rivet must Ibe imparted to the rivet over a relatively prolonged period of time. `Stated alternately, the use of an impacting member which acts as a unitary mass on the forming punch with sufficient force to upset the rivet with a single blow produces cracking and oftentimes the disintegration of the hard rivet material being upset.

Accordingly, it is preferred in applications where the rivet gun is used for upsetting hard rivet materials to have the impacting hammer transfer the requisite upsetting force over a prolonged period of time relative to the time, estimated as a part of a millisecond, that a unitary hammer of the same mass traveling at the same speed would act. This may be accomplished by fabricating the impacting hammer from individual cylindrical segments which are held together through, for example, a split pin disposed within the hammer along its longitudinal axis. This form of the impacting hammer apparently produces an inertial lag from the leading to the trailing segments as the impacting hammer is accelerated by the explosive charge. On striking the forming punch, the leading segments are decelerated before the trailing segments to prolong the period of impact.

An alternate form of an impacting hammer which prolongs the period of impact employs a heavy, fluid-like filler. This form of the impacting hammer has an axial cavity of progressively reduced cross section toward the leading end of the impacting hammer. The interior of the cavity is filled with a heavy fluid-like material, such as mercury, which lags because of its inertia as the impacting hammer accelerates down the barrel toward the forming punch. Upon striking the forming punch, the body of the impacting hammer begins to decelerate rapidly while the fluid-like material moves rapidly toward the leading end of the impacting hammer. As the fluid moves toward the leading end of the impacting hammer, it encounters the areas of reduced cross section to decelerate and impart a delayed and prolonged impact force through the body of the hammer to the forming punch.

An embodiment of the present invention employs means for varying the initial expansion volume of the expanding gases produced by the ignition of the explosive charge. This means allows for adjustment of the ultimate impact force felt by the rivet and therefore admits to greater flexibility of the gun. Such means may include a chamber having an adjustable sealing element disposed within it. 'Ille chamber is in gas communication between the explosive charge and the impacting hammer with the gases generated by the charge. The adjustment of the volume of the chamber adjusts the effective pressure acting against the muzzle end of the impacting hammer. Preferably, the seal element includes a dish or cup-shaped member which is capable of expanding radially against the walls of the chamber to seal the chamber in response to the pressure generated by the explosive charge.

The rivet setting tool or gun of the present invention has a nose which remains in abutting contact with the sheet or panel being riveted because the nose is urged against the sheet by expanding, relatively high pressure gases from the detonated explosive charge. This stabilizing facility of the gun avoids the adverse effects of recoil during the setting of rivets.

The unique barrel construction of a preferred form of the present invention results in a very simple and economical gun. By the unique porting of the slidable barrel, spent gases produced by the explosive charge are reliably vented to atmosphere when the barrel moves toward the breech end of the gun. Moreover, the Iporting produces impact hammer return to its prefiring position by accelerating the hammer from the muzzle end of the barrel toward the breech end of the barrel after the setting of a rivet.

In its preferred form, the rivet setting tool or gun of the present invention is particularly useful in setting rivets of very hard material, such as rivets fabricated from titanium or steel alloy. The tool is lightweight and portable and therefore may be readily used in difficult access areas or considerably inboard of large panel sections. By utilizing an explosive charge, sufficient force is available to upset the head of even the hardest rivets, thereby avoiding the use of squeeze pressure setting of hard rivets. The frusto-conical recess of the impacting hammer constrains the radial expansion of the rivet head being formed in such a manner that unacceptable formed head cracking and weakening are avoided. With the frustoconical configuration, for example, there is no tendency of the forming rivet head material to extrude into an annular space between an impacting member and a stationary constraining sleeve or die which is a characteristic of at least one prior art impact rivet gun presently known to the inventor and which, it is thought, leads to rivet failure. The unique construction of the impacting hammer to develop a sustained impact is also important in the formation of a sound riveted joint with hard rivet materials.

Another advantage of an embodiment of the present invention resides in the safety means for preventing the firing of the explosive charge when the barrel of the gun is not in proper alignment with the axis of the rivet to be upset. The rotatably or pivotally mounted head of the gun reliably indicates alignment of the axis of the barrel and the axis of the rivet by enabling the parabolic mirror carried by the head to reflect light from the light source to the photosensitive element. Until proper alignment, however, the photosensitive element cannot be energized to release the locking means and `fire the explosive charge. The provision of firing interlocks which prevents gun firing until a bucking bar and a forming die are properly positioned is also significant in assuring proper rivet setting.

Another unique advantage of an embodiment of the present invention resides in the facility for adjusting the expansion volume of the gases generated by the explosive charge. This facility allows the velocity of the impacting hammer to be reduced 0r increased to adjust the forming force imparted by the forming punch to the rivet. Variations in rivet material characteristics and size may, therefore, be compensated for.

These and other aspects, features and advantages of the present invention will become more apparent from the following description, appended claims and drawings in which:

FIG. 1 is a foreshortened, side elevational view, partly in hal-f section, of a preferred embodiment of the present invention;

FIG. 2 is a sectional view vtaken along line 2-2 of FIG. 1;

FIG. 3 is a fragmentary sectional view taken along line 3 3 of FIG. 1;

FIG. 4 is a fragmentary sectional view taken along line 4-4 of FIG. 1;

FIG. 5 is a fragmentary half-sectional view of an alternate embodiment of the setting end of the gun of the present invention which illustrates the position of a rivet to be set just prior to the impacting hammer striking the depicted forming punch;

FIG. 6 is a half-sectional view similar to FIG. 5, illustrating the terminal stages of rivet upset produced with the rivet gun of the present invention;

FIG. 7 is a fragmentary view, partly in half section, of an alternate embodiment of the nose assembly of the present invention together with a rivet to be set; and

FIG. 8 is a schematic circuit diagram of the various interlock or safety means of the present invention.

A preferred rivet setting gun or tool 10 of the present invention is illustrated in FIG. 1. In general, rivet gun 10 includes a barrel assembly 12 which slidably mounts a nose assembly 14. The barrel assembly is received on a breech assembly 16. A firing pin assembly 18 in the breech assembly is capable of firing an explosive charge 20. A pistol grip firing assembly 22, including a trigger KJ and a hammer 26, is provided for actuating firing pin assembly 18 to detonate explosive charge 20. An impacting hammer 28 is disposed within a bore 30 of an inner barrel 32 of the barrel assembly 12. The inner barrel is capable of limited longitudinal movement within the barrel assembly in response to gas pressure. A forming punch or die 34 is normally disposed at the muzzle end of barrel assembly .12 within nose .assembly 14 for limited translation. The impacting hammer is constructed to impart a sustained impact on forming punch 34 to prevent failure of riveted joints -which is a particularly acute problem with hard rivet materials. In order to control the velocity of impacting hammer 28 to that required for the proper upsetting of a rivet by forming punch or die 34, an expansion chamber assembly 36 is provided.

The improved rivet gun illustrated in FIG. 1 also has means for preventing the guns firing until bore 30 of inner barrel 32 is properly aligned. In general, these means include a parabolic mirror 38 mounted through a mirror mount or arm 40 on a ball-like, universally rotatable or pivotable head 42 of nose assembly 14, a light source 44, a photosensitive element 46 and an interlock solenoid 48 in circuit with the photosensitive element. A sheet abutting face or surface 50 of ball member 42 and the noses bore 52 provide the means for accurately aligning the nose assembly. Light source 44 and photosensitive element 46 are contained in a sighting bore 54 of a housing 56.

Before describing in further detail the construction of the preferred embodiments of the present invention, a brief description of operation will be presented in order to facilitate the understanding of the more detailed description which follows. In prering position, impacting hammer 28 resides at the breech end of bore 30 in inner barrel 32. Forming punch 34 receives the end of a rivet to be upset (as illustrated for an alternate embodiment Expanding gases from the detonated charge 20 act against the end of impacting hammer 28 to accelerate the impacting hammer toward the forming punch or die 34. The accelerating pressure is controlled by the volume in expansion chamber assembly 36. Gas acts against nose assembly 14 to maintain this assembly rmly against the sheets surrounding the extending end of the rivet. The hammer will continue on its course until striking forming punch or die 34 with a sustained impact to upset a rivet in a manner illustrated in FIG. 6.'Simultaneous with the forming operation, gas from the charge will begin to act on impact hammer 28 to return the hammer to the breech end of the gun. Gas will also move barrel 32 toward the breech end of the gun to exhaust spent gases from bore 30 and the expansion volume of expansion chamber assembly 36.

With this brief description in mind, a more detailed description will now be presented.

Barrel assembly 12 includes an outer barrel housing 58 disposed annularly around inner barrel 32. This housing has a first section 60 and a second section 62. Section 60 is attached to section 62 at threads 64. Section 60 is mounted to breech assembly 16 at threads 66. An inner barrel return spring 68 is disposed about barrel 32 within section 6.2 of housing 58. This spring urges against a shoulder 70 of section k60 and an annular flange 72 which extends radially from barrel 32. The spring urges inner barrel 32 toward the muzzle end of the gun. An annular O-ring 74 is disposed in flange 72 to provide a seal against leakage of explosive generated gases.

A longitudinal annulus 76 is present between housing section 62 and the outside of barrel 32 toward the muzzle end of the barrel. Annulus 76 is in pressure and gas communication with bore 30 of barrel 32 through a pair of pressurizing ports 78. A second longitudinal annulus is disposed between section 62 and the outside of barrel 32 at the extreme muzzle end of barrel 32. This longitudinal annulus is in pressure and gas communication with the bore 30 of barrel 32 through pressurizing ports 78 and a pair of impacting hammer return ports 82. Annulus -80 is in communication with pressurizing ports 78 through annulus 76 and a plurality of passages 84 in an annular guiding flange 86 of barrel 32. These passages and guiding flange are best illustrated in FIG. 2. A pair of exhaust ports 87 at the breech out of barrel 32 provide for the exhausting of spent explosive charge generated gases as will subsequently become more apparent. The inner diameter of housing section 60 at the breech end of barrel 32 is reduced to provide a gas seal between this housing section and the barrel and prevent leakage through exhaust ports 87.

Nose assembly 14 includes an annular mounting collar 88 which is disposed for limited longitudinal translation on a reduced diameter section 90 of housing section 62. A radial, annular shoulder 92 of mounting collar 88 is exposed to gas pressure within annulus 80 to urge the nose assembly against a sheet of material being riveted. An O-ring 94 in reduced diameter section 90 provides a gastight seal between mounting collar 88 and this section. A compression spring 96 is also disposed in annulus 80 to slightly bias nose assembly 14 longitudinally away from barrel assembly 1-2.

The nose assembly also includes ball member 42 as a universally rotatable head. The ball member or head has a spherically curved surface 98 which rotates in a spherical socket or seat 100 of mounting collar 88. The extreme forward or muzzle end of mounting collar 88 is swedged around spherical surface 98 to retain ball member or head 42 in place. To allow a limited amount of rotational movement in aligning gun 10, an annular recess 102 is provided within ball member or head 42 to allow the head to rotate with respect to the extreme muzzle end of barrel 32. An annular relief section 104 is also provided for head 42 to clear the extreme muzzle end of mounting collar 88. Sheet abutting face 50 of head 42 is normal to bore 52 which extends through the longitudinal center of the head. An annular collar or constricting ange 106 extends radially inward to define the mouth of bore 52 and to constrict a forming collar or die employed with some hard rivets. An enlarged section 108 of bore 52 extends longitudinally inward from constricting ilange 106 to merge into annular recess 102. This enlarged section 108 of bore 52 allows for limited, captive longitudinal movement of forming punch 34 within head 42. Mirror mount or support arm 40 extends upwardly from head 42 to support parabolic mirror 38, to be described in detail subsequently.

A spring 110 is disposed between mirror mount 40 and mounting collar 88 to urge the parabolic mirror out of reflective alignment from photocell 46 until sheet abutting face or surface 50 rests against a sheet.

Breech assembly 16 may take any number of forms. Briefly, however, the assembly illustrated includes a breech coupling member 112 which is threadedly received on the male threads of housing section 60 of barrel assembly 12. A cylindrical, annular chamber 114 is disposed within this coupling member to allow for limited translation of barrel 32 and to communicate exhaust ports 87 with a pair of discharge ports 116 (shown in FIG. 3). Discharge ports 116 open into chamber 114 through the wall of coupling member 112. A threaded boss 118 extends from coupling member 112 for receiving a cylindrical breech block 120. A breech plug 122 is disposed within a bore in boss 1118. Breech plug 122 includes a head 124 for abutting against a rearward, radial shoulder of boss 118. Beech plug 122 also has a cylindrical counterbore 125 for receiving the rim of cartridge 20. In the embodiment illustrated, explosive charge is in the form of a cased cartridge. However, it should be understood that pellet-type charges may also be employed with the explosively actuated, rivet setting gun of the present invention. Breech plug 122 also includes an annular groove 126 about its cylindrical periphery. An expansion port 128 opens into groove 126 for communication with the chamber of the expansion chamber assembly 36, to be subsequently described in detail. Breech plug 122 also has a cartridge receiving bore or chamber 130 which extends for the longitudinal length of the breech plug and opens into bore 30 of barrel 32 as well as into expansion port 128. The muzzle end of breech plug 122 has an accurately machined, reduced diameter section 132 for telescopic, gastight receipt in bore 30 of barrel 32.

Firing pin assembly 18 is received in breech block 120. Firing pin assembly 18 is maintained in its position illustrated by a compressori spring 134 which acts against an annular ange 136 of the assembly. A cylindrical extending portion 138 normally extends to the rear of breech block 120. A firing pin 140 extends inwardly from inner cylindrical portion 142 of the firing pin assembly for striking the rim of cartridge 20 in a standard manner. A bore 144 in breech block 120 admits to limited longitudinal movement of the firing pin assembly to detonate charge 20.

-Piston grip tiring assembly 22 is responsible for striking cylindrical extending portion 138 and thrusting firing pin 140 into the rim of explosive charge cartridge 20. This assembly includes a handle or grip body 146 with a hammer 26 pivotally mounted through a pin 148 within a recessed portion 150 of handle 146. A cap 152 is attached on the face of hammer 26 to strike cylindrical extending portion 138. A leaf spring 154 extends from its mounting in a recess in the body of handle 146 to bias hammer 26 in the direction of firing pin assembly 18. Trigger 24 is pivotally mounted to the body of handle 146 by a pin 156. A trigger return spring 158 biases trigger 24 into the position illustrated in FIG. 1. This spring abuts against a spring block 160 which is mounted to the body of the handle portion. Hammer 26 is normally maintained in its cocked position by a sear 162 which is integrally formed will trigger 24. This gear has a reduced transverse cross section as indicated most clearly in FIG. 4. Hammer 26 has a recess 164 along one of its sides for reviewing sear 162 when trigger 24 is pulled. When trigger 24 is pulled, sear 162 rotates clockwise from its engagement with the body of hammer 26 into recess 164. Hammer 26 will then rotate clockwise under the influence of spring 154 to strike cylindrical extending portion 138 of firing pin assembly 18 to extend firing pin 140 into the rim of explosive charge cartridge 20.

Impacting hammer 28 includes a plurality of cylindrical segments 166 which are held together by a split retention pin 168 of standard construction. This retention pin is compressed when segments 166 are assembled over it to exert, through hoop stress, an outwardly directed, retention force on the walls of the axial bores of segments 166 to hold the segments with the pin. The leading segment, indicated by reference numeral 170, is of smaller diameter than the balance of the segments in order to facilitate the admission of gas through impacting hammer return ports 82 to force the hammer to the breech end of barrel 32. The trailing segment of segments 166, indicated by reference numeral 172, mounts an expansion ring 173 which is in elastic contact with the wall of bore 30 of barrel 32. The frictional drag created by this expansion ring is sufficient to retain impacting hammer 28 at the breech end of barrel 32 upon its return from the muzzle end of the barrel.

The segmented construction of impacting hammer 28 allows for a prolonged or sustained impact on forming punch 34 to spread the inertial effect of the impacting hammer over a period of time in excess of that which would be presented by an impacting hammer of equal mass but of homogeneous construction. While the operation or elfect of the impacting hammer is not completely understood, it is postulated that as the impact hammer accelerates down the barrel toward the muuel end, small air gaps develop between the segments because of inertial lag. Upon striking forming punch or die 34, these air gaps tend to cause the segments to act as discrete masses. The resulting impact produces a large amount of upsetting energy which is transferred through the forming punch or die with sufficient force per unit of time to upset a rivet, but over a long enough period of time to prevent fracture or other structural defects in the formed rivet.

FIG. 5 illustrates a suitable construction of forming punch or die 34. Forming punch or die 34 includes a frusto-conical recess 174 which converges inwardly of the face of punch 34, indicated by reference numeral 175, toward the breech end of the tool. This recess includes an inwardly disposed impacting face 176 which is normal to the axis of the forming punch. The tapered flank or side of recess 174, indicated by reference numeral 178, serves to constrict the radial expansion of a rivet while its end is being upset and to determine the nal shape of the formed rivet end. An enlarged cylindrical portion 180 of forming punch 34 is slidably disposed in an enlarged section 182 of the nose sections axial bore. Enlarged section 182 corresponds to enlarged section 108 of nose assembly bore 52 of the embodiment illustrated in FIG. 1. A cylindrical driving portion 184 extends longitudinally toward the breech end of the barrel from enlarged cylindrical portion 180 and is slidable in bore 30 of barrel 32. An inwardly directed radial ilange 186 serves to constrict a rivet forming collar of the rivet being upset. This ange corresponds to flange 106 of the FIG. l embodiment. Because of the rapid change in cross-sectional area between driving portion 184 and enlarged cylindrical portion 180, stress risers may occur in this transitional zone of cross-sectional area which may cause failure of forming punch 34. To prevent this eventuality, it is preferred that driving portion 184 be separate from enlarged cylindrical portion 180. Alternately, the enlarged cylindrical portion may include the driving portion without reduction 9 in diameter between the two, as will be described with reference to FIG. 7.

In setting hard rivets, such as rivets may from titanium, forming punch or die 34 determines to a great extent the soundness of the resulting joint.

Where weight is an important factor, the size of the upset end of rivet should be as small as is possible to produce desired joint preload. Accordingly, the axial distance between face 175 and impacting face 176 should be as small as is consonant with the development of a head that will withstand the tensile stress of preload. The depth of recess 174 should also be relatively small if face 175 is not to strike constricting flange 186 and cause tool damage. (See FIG. 6 which illustrates the desired spacing between face 175 and flange 1186 in the nally upset rivet head.)

The diameter of impacting face 176 is also important in producing an optimum formed rivet head. This diameter should be slightly greater than the unformed diameter of the rivet to be formed. However, the diameter of the impacting face cannot be too great relative to the diameter of the unformed rivet shank if forming cracks and lines of weakness in the formed rivet head are to be avoided.

Still another consideration in forming eifective riveted joints with forming punch 34 is in the included angle of tapered constricting flank 178. If this included angle is too small, structural iiaws in the formed head develop with head size diameters which are sufficient to sustain required joint preload. On the other hand, when the included angle is too large, the reaction force of the rivet head, being upset causes the forming punch to recoil away from the head before it is completely and eifectively formed. The reaction force problem is particularly acute when a forming collar or die is used because it causes constricting ilange 1106 of the FIG. 1 embodiment or constricting flange 186 of the FIG. 5 embodiment to jump olf the sheet and lose the forming collar. With the loss of forming collar constraint, the forming collars function of preventing sheet failure from rivet expansion is lost because, at a minimum, the collar expands too much and, at the maximum, the collar fails. Moreover, even with permissible collar expansion, a longer and therefore heavier rivet is required for an effective joint because less rivet material is otherwise available to expand the wall of the hole in the sheets containing the rivet.

The considerations discussed above in relation to forming punch 34 are more particularly set forth below. With reference to FIG. 5, the included angle of ank 178 should be about 60. The diameter of impacting face 176 should be about 1.06 times the unformed diameter of the hard rivet shank. The diameter of bore 232 (the internal diameter of iange 186) should be from about 1 to about 1.05 times the unstressed diameter of the forming collar or die. The depth of recess 174 should be about 0.225 times the diameter of impacting face 176. The diameter at the mouth of recess 174 should be about 1.26 times the diameter of the impacting face.

These relationships are shown in the table below where:

nt-:included angle of flank,

al1=diameter of the impacting face,

dzzdiameter of the vmouth of the recess,

D1=unformed diameter of the rivet shank,

D2=outside diameter of the forming collar,

D3=the internal diameter of the constricting flange, and l1|=depth of the recess.

TABLE Item: Value oc 60 d1 I1.06D1 D@ to 1.05D2 lh d2 1.26d1 D2 1.42D1

In order to control the velocity of impacting hammer 28 as it progresses down barrel 32 toward `forming punch or die 34, expansion chamber assembly 36 is provided. As was previously mentioned, this expansion chamber assembly allows for the control of the volume and hence the pressure of the expanding gases generated by the discharge of explosive charge or cartridge 20.

The chamber assembly is integral with breech coupling member 112. The chamber has a duct y188 in register with annular groove 126 and, hence, with cartridge receiving chamber 130 through radial expansion port 128. Duct 188 opens into an enlarged chamber 190. A plug 192 caps an end of chamber 190. A piston ',194 closes the other end of the chamber.

Piston 194 is mounted on a lead screw 196 which is received in threads at the end of a body A198 of the expansion chamber assembly. A calibration wheel 200 engages the threads of lead screw 196 and is constrained against axial movement with respect to body 198 by its receipt in a narrow slot 202 in the body. Rotation of calibration wheel 200 produces longitudinal, axial movement of piston 194 which in turn produces a greater or lesser expansion volume of chamber 190.

Piston 194 includes a sealing element 204 which may be made of phosphorus-bronze. This sealing element is cup or dish-shaped such that its wall, proximate the walls of chamber 190, may expand in response to the pressure generated by explosive charge 20 and seal the low-pressure side of the chamber. A back-up or support member 206 mounts seal 204 and provides pressure ntegrity for the seal. These elements are made separate in order to increase the life of the piston.

One unique safety interlock of the present invention includes photosensitive cell or element 46 of well known construction. Housing 56 is provided for receiving this photosensitive element. This housing is mounted on breech block through a mounting bracket v207. Annular light source 44 is disposed within sighting bore 54- of housing 56, as is the photosensitive element. Sighting bore 54 includes an enlarged light guide portion 208 to columnate the light emanating from source 44 into a beam for striking parabolic mirror 38 mounted on arm or mount 40 of nose assembly 14. Arm 40, and hence universally rotatable head or ball member 42 of nose assembly |14, is normally maintained askew from the axis of the gun in order to prevent light from light source 44 from being reflected from the parabolic mirror to the light sensitive element of photocell 46. When sheet abutting surface or face 50 is normal to the axis of barrel 32, light reflected from parabolic mirror 38 will strike the light sensitive element of photocell 46.

As illustrated in FIG. 8, photocell 46 and light source 44 are part of a circuit for controlling the element of interlock solenoid 48. This element, indicated by reference numeral 210, is normally disposed in the rotational path of trigger 24, as illustrated in FIGS. l and 4. A power source, such as a DC battery 212, is in series circuit with light source 44. This power source also provides the power for an amplifier 214 which ampliies the signal from photocell 46. The resultant amplified signal energizes a coil 216 of a relay l21-8 when the circuit from the coil to ground is completed. The energization of this coil closes normally open contacts 220 of the relay to establish a circuit to the coil of solenoid 48 through a current limiting resistor 222.

Thus, when photocell 46 does not generate current, because light reilected from parabolic mirror 38 does not strike it, contacts 220 are open and the coil of solenoid 48 is out of circuit. As a consequence, element 210 of solenoid 48 is in the path of trigger 24. However, when light from light source 44 vreflects off parabolic mirror 38 and photocell 46 receives the reflected light, contacts 220 close to withdraw element 210 from the path of trigger 24 to allow the ring of explosive cartridge charge 201. With the exception of light source 44, photosensitive cell 46 and solenoid 48, the balance of the circuit elements 1 1 shown in FIG. 8 associated with gun alignment, may be contained in a power pack 224 in handle or grip body 146. FIG. 8 also illustrates additional ring interlocks which will be described with reference to FIG. 7.

FIG. 5 illustrates an alternate embodiment of the nose assembly for the improved rivet gun of the present invention. This figure also illustrates to a better extent the construction of the muzzle end of barrel assembly 12. The modified nose assembly, indicated by reference numeral 226, does not include the universally rotatable head previously described. The nose assembly is mounted for limited translation on reduced diameter section 90, the muzzle end of barrel assembly 12. The nose assembly includes an annular mounting collar 228 disposed about the reduced diameter portion of barrel assembly 12. As in the previously described embodiment, an annular shoulder 230 of the nose assembly is responsive to gas pressure within annulus 80 to urge the nose assembly against a sheet when the gun is fired. Enlarged diameter section 182 of the noses bore permits limited longitudinal movement of forming punch 34. Inwardly directed radial flange 186 serves to confine forming punch 34 within bore 182 and to constrict the radial expansion of a forming collar. This flange also defines a reduced diameter portion 2-32 of the noses bore and a part of a sheet abutting face or surface 234 of nose assembly 226.

As in the embodiment described in FIG. 1, compression spring 96 serves to bias slightly the nose assembly towards the muzzle end of the gun and to buffer the impact of the radial shoulder, of which shoulder 230 is a part, on the end of reduced diameter section 90` of barrel housing 58 (shown in FIG. 1). Gas from annulus 76 passes through passages 84 and into annulus 80 for urging against shoulder 230. This gas also passe through irnpacting hammer return ports 82 for the return of the impacting hammer to the breech end of barrel 32 after the setting of a rivet. O-ring 94 provides a sliding seal between mounting collar 228 and reduced diameter portion 90.

FIG. 6 illustrates an alternate form of an impacting hammer of the present invention which is generally indicated by reference numeral 236. The impacting hammer includes a cylindrical body portion 238 and a cap portion 240. Cap portion 240 is received as by an interference fit into a bore 242 within the body portion. The bore forms a part of a cavity 244 which is partially filled with a heavy fluid-like material such as mercury, shown by reference numeral 245. The leading portion of cavity 244 has a plurality of stepped, cylindrical sections 246 of progressively reduced diameters. These sections are joined by frusto-conical transition shoulders 248. The cap also has a plurality of progressively reduced diameter, cylindrical sections 250 joined by frusto-conical transition shoulders 252. The cylindrical sections in the cap form a part of cavity 244.

It has been found that transition sections, such as indicated at 248 between the reduced diameter sections of cavity 244, act to prolong the impact provided by impacting hammer 236 on forming punch 34 by progressively arresting the motion of the mercury toward the muzzle end of the cavity after body 238 is decelerated by its striking of forming punch 34. The mercury acts on the transition sections to impart a force to the body represented by the product of the arrested mercurys mass and deceleration. The transition sections in the cap also act to distribute the impact of the mercury over a sustained period when the impacting hammer strikes the breech plug at its return from the muzzle end of the barrel. In this instance, the steps act to prevent too sudden an impact on the breech plug. One embodiment of the present invention which has been tested on high strength titanium of this weight.

As in the case of impacting hammer 28, impacting hamrivets employs an impacting hammer weighing approximately 68 grams with the mercury constituting 18 grams 12 mer 236 has a reduced diameter section 254 to present an annular shoulder 256 to gases admitted through irnpacting hammer return ports 82. An expansion ring (not shown, but similar to the one shown in FIG. l by reference numeral 173) may be used to arrest impacting hammer 236 at the breech end of barrel 32.

FIG. 7 is directed to an alternate embodiment of the rotatable or pivotable head of the present invention and illustrates, as well, additional firing interlocks which sense the presence of a forming collar and a bucking bar often used in riveting. Only those portions of the rivet gun of the present invention which are germane to these embodiments of the invention are shown and described.

In general, the embodiment illustrated in FIG. 7 includes an inner barrel 258 disposed for limited longitudinal movement Within a barrel housing that includes section 260. Barrel housing section 260 corresponds to second section 62 of the FIG. l embodiment. A modified nose assembly 262 is provided which includes a nose proper defined by a sleeve 264, a universally rotatable or pivotable head 266, and a mounting collar 268. A modified forming punch or die 269 is disposed for limited longitudinal movement within sleeve 264. A firing interlock circuit 270 prevents gun firing until a bucking bar and forming die are sensed.

As in the previously described embodiment, inner barrel 258 has an annular guiding flange 271 proximate its muzzle end for maintaining alignment of the inner barrel within the barrel housing. A plurality of longitudinally extending gas passages 272 are disposed within flange 271 to allow gas to pass and bias sleeve 264 of nose assembly 262 against the sheets being riveted and to return the impacting hammer to its prefiring position. To effect gas communication for this purpose, a plurality of circumferentially disposed ports 274 pass through inner barrel 258 into a longitudinal annulus 276. Annulus 276 is defined by the outer circumferential wall of inner barrel 258 and the inner wall of barrel housing section 260.

A ange 278 on inner barrel 258 is disposed proximate pressurizing ports 274 towards the breech end of the gun. This flange receives an O-ring 280 in sealing engagement with the inner wall of housing section 260 to effect a gas seal between annulus 276 and the breech end of the gun.

An inner barrel return spring 282 biases inner barrel 258 towards the muzzle end of the gun by engaging ange 278 and the barrel housing. (The engagement of return spring 282 with the barrel housing may be effected as in the embodiment illustrated and described with reference to FIG. l.)

The muzzle end of barrel 258 is inclined at a slight angle to the normal of the longitudinal axis of the barrel as indicated by reference numeral 284. This inclined or angled end of barrel 258 urges against sleeve 264 to cant nose assembly 262 with respect to the axis of barrel 258 and normally maintain the longitudinal axes of the barrel and the sleeve out of alignment. When the sleeve and the barrel are aligned, a space is developed between the two. This space acts as the impacting hammer return port of the previously described embodiments.

A reduced diameter section 286 of barrel housing section 260 is threaded for securely receiving a mounting collar 268. These threads are indicated by reference numeral 288. Pivotable head 266 is carried by the mounting collar through mating receipt of a spherical bearing surface 289 of the head in spherical seat 290 of collar 268. As in the previously described embodiment, the outer end of collar 268 is swedged over spherical bearing surface 289 to retain pivotable head 266 with the collar. In this embodiment, both collar 268 and head 266 are retained with barrel housing section 260 and thus are not capable of limited longitudinal movement with respect to the barrel housing. `It is sleeve 264 which is capable of longitudinal movement and gas biasing against the sheets. But as before, head 266 is capable of pivotal or rotational movement to align the gun.

Pivotable head 266 has a sheet abutting face or surface 291 and a parabolic mirror 292. The parabolic mirror is supported by an arm 294 of the pivotable head. The mirror is maintained out of alignment with a light source and a photosensitive cell by the forced inclination of sleeve 264 and the latters carried head 266 effected by the inclination of barrel end 284. The photosensitive cell and light source are illustrated and described with reference to FIGS. 1 and 8.

Sleeve 264 receives forming punch or die 269 for limited translational movement therein. The sleeve has an external flange 296 which meets a reduced diameter section 298. The external flange provides a stop for retaining the sleeve With the pivotable head. Return spring 282 acts through angled muzzle end 284 to normally maintain flange 296 against head 266 and to positively maintain sleeve 264 and forming punch 269 out of alignment with barrel 258. The outer muzzle end of sleeve 264 has a sheet abutting surface which is defined in part by an annular, radial constricting flange 300. The flange bounds a bore 302 for the rivet to be upset. Flange 300 keeps forming punch 269 in sleeve 264 and retains a forming collar or die to be described. The external or extreme outer end of bore 302 is enlarged for receiving an annular indexing flange of the forming die. The inner end of sleeve 264 is larger in outside diameter than barrel 2.58, as indicated at 304, to provide a surface for the-gas biasing of sleeve 264 against a sheet to be riveted. The inner end of sleeve 264 also has a retaining iiange 305 for forming punch or die 269. The retaining flange defines a bore large enough for the passage of the impacting hammer.

IForming punch 269 is of a generally cylindrical configuration and therefore avoids the problem of stress risers occasioned by variations in cross-sectional area. As in the previously described forming punch, forming punch 269 has a frusto-conical recess 30-6 with an impacting face 308 at right angles to the axis of the punch. The impacting face meets a tapered Hank 310 which diverges from the face towards the outer end of the forming punch.

lSleeve 264 is translatable within pivotable head 266, towards the breech end of the gun from its stop position against the head, but carries the head for pivoting within mounting collar 268.

The particular conguration of the bore of sleeve 264 allows the use of a forming die having an external indexing flange. The forming die is indicated by reference numeral 312 and its indexing ange is indicated by reference numeral 314. When properly oriented on a rivet 316, the indexing flange is towards the manufactured head of the rivet. If the forming die were inadvertently inverted it would not be received in bore 302 of sleeve 264. When properly received in the bore, a circuit is completed to ground by the engagement of the cylindrical outer surface of forming die 312 with a contact 318 of circuit 270. Contact 318 and the forming die, then, act as a switch, as shown schematically in FIG. 8 by reference numeral 320.

The sensing of the presence of a bucking bar 322 on the manufactured head of the rivet will now be described. When forming punch 269 is placed over the end of the rivet to be formed, it is displaced toward the breech end of the gun. In doing so, it engages inwardly directed retaining flange 305 of sleeve 264 which in turn engages muzzle end 284 of inner barrel 258. T he sleeve will then move towards the breech end by overcoming the force of inner barrel return spring 282 to allow ange 278 to actuate a switch 324 of circuit 270. Switch 324 is disposed in barrel housing section 260. As indicated in FIG. 8, the closing of switch 324 completes the circuit from the coil of relay 218 to ground, enabling the closing of contacts 220 and the withdrawal of element 210 from the trigger 24.

The operation of the presently preferred embodiments of the present invention will initially be described with specific reference to lFIGS. 1, 5, 6 and 8. Nose assemblies 14 14 and 226 will both be referred to in this operational description, as well as impacting hammers 28 and 236.

An explosive charge 20 is placed in cartridge receiving chamber of breech plug 122 by unscrewing the barrel assembly together with breech coupling member 112 from breech block 120. The gun is then placed over the extending portion of a rivet 316 which extends from a pair of

sheets

326 and 328 to be joined. A standard bucking bar 322 is used to abut the preformed or manufactured head of the rivet and, therefore, to maintain the rivet Within the holes in the sheets. A forming collar or die 330 is inserted over the shank of the rivet and engaged by annular constricting flange 186 of nose assembly 226. At this stage, the nose portion of the gun and the rivet to be driven `appear as in FIG. 5.

With particular reference to the embodiment of the invention shown in FIGS. 1 and 8, hammer 26 is cocked to bring sear 162 against the shank of the hammer and out of engagement with recess 164. The operator may maintain finger pressure on trigger 24 but the gun will not fire until light from light source 44 strikes parabolic mirror 38 and is reflected therefrom and received by photosensitive cell 46. In the embodiment illustrated in FIG. 1, this will not occur until sheet abutting face 50 is normal to the axis of barrel 32 to axially align rivet 316 With the barrels axis. Alignment is impossible until this condition occurs because spring 110 normally keeps mirror 38 out of reflective alignment with photooell 46. At this point, a circuit is completed to the coil of relay 218 to close normally open .contacts 220 and establish a circuit to solenoid 48, circuit completion being possible in the absence of

switches

320 and 324. With a circuit established, solenoid 48 withdraws its element 210l from the path of trigger 24. Trigger 24 may then be depressed to rotate about pin 156 in a clockwise direction to bring sear 162 into register with recess 164, allowing hammer 26 to strike firing pin assembly 18.

When hammer 26 strikes firing pin assembly 18, tiring pin will strike the rim of explosive charge 20) to detonate the charge. Gases from the charge will be admitted through port 128 into duct 188 and urge against the rear impacting hammer 28 (or impacting hammer 236 in the case of the FIG. 6 embodiment). The volume of chamber has been present by rotating calibration Wheel 200 either clockwise or counterclockwise to increase or decrease its volume. The gas -will act on the impacting hammer to accelerate it towards the muzzle end of barrel 32 at a rapid rate. As the impacting hammer passes pressurizing ports 78, gas is admitted into annulus 76 to urge against ange 72 to begin the retraction of barrel 32 toward the breech end of the gun. Gas will also be admitted through impact hammer return ports 82 at about the time the impacting hammer strikes forming punch or die 34.

The forming punch will then feel a sustained impact. In the instance where impacting hammer 236 is used, the sustained impact is occasioned by mercury 245 within the hammer continuing progressively forward and encountering frusto-conical transition shoulders 248 of body 238. Mercury 245 will eventually till that portion of the cavity bounded or defined by stepped, cylindrical sections 246, as indicated in FIG. 6. The sustained impact effect on forming punch or die 34 will also be present when impacting hammer 28 is used because of the discrete action of its cylindrical segments.

When the impacting hammer strikes forming punch 34, inward face 176 will strike the end of the rivet and begin the upsetting process. As upsetting proceeds, the rivet will expand radially against flank 178 of the forming punch while being displaced into the rounded portion of forming collar or die 330. Owing to this impact, the rivet will also uniformly swell against the walls of the holes in the sheets in which it is inserted. A iinally formed rivet is shown in FIG. 6 at about the end of the impact from impacting hammer 236.

During the upsetting of the rivet, nose assemblies 14 and 226 will be maintained firmly against the sheets being riveted. In the FIG. l embodiment, gases admitted through ports 78 will urge against shoulder 92 to gas bias collar 88 and its carried head 42 against the sheets while barrel housing 58 and barrel 32 are experiencing recoil. In the FIG. 5 embodiment, gas will act against shoulder 230 to urge nose assembly 226 against the sheets during gun recoil.

At about the time that the rivets being upset or formed, the gases admitted through impacting hammer return ports 82 surround the reduced diameter portion of the impacting hammer, leading segment 170 for impacting hammer 28, and reduced diameter section 254 for impacting hammer 236, to act on the shoulder thereof and accelerate the hammer toward the breech end of barrel 32. Barrel 32 will be at the breech end owing to gas pressure acting on flange 72. With the barrel at the breech end, spent gases generated by the explosive charge -will vent through exhaust ports 87 and discharge ports 116. After venting, inner barrel return spring returns barrel 32 to the muzzle end of the gun. The impacting hammer progresses down the barrel toward the breech end and strikes the exposed end of breech plug 122. Expansion ring 173 prevents the impacting hammer from bouncing toward the muzzle end of the barrel after the impacting hammer strikes the breech plug.

The embodiment of the invention illustrated in FIG. 7 operates as follows.

An operator places nose assembly 262 against sheet 326 with rivet 316 and forming die 312 registered in bore 302 of sleeve 264. As was previously mentioned, the forming die can only enter bore 302 when indexing flange 314 is against the sheet to be riveted. With sleeve 264 and forming punch 269 over the end of the rivet to be formed, the forming punch pushes the sleeve and the inner barrel towards the muzzle end of the gun to close switch 324 when annular constricting flange 300y is with the sheet abutting surface of universally pivotable head 266. The operator then must orient the gun such that the axis of the bore of barrel 258 is coaxial with the axis of the bore of sleeve 264. Upon proper alignment, mirror 292 will be in position to reect light from a light source to a photosensitive element to release the trigger interlock, as described with reference to FIG. l. The alingment of the bore axes of barrel 258 and sleeve 264 will develop a space between the barrels muzzle end and the sleeve which acts to admit gas generated by the explosive charge to pass in ahead of the impacting hammer and return it to its prefiring position. Gas passing through passages 272 will also urge sleeve 264 against the sheet, notwithstanding gun recoil. Relative movement between sleeve 264 and head 266 is possible in the ring position because external ange 296 is displaced from pivotable head 266. Thus, for gas biasing purposes of the nose against a sheet, sleeve 264 replaces the mounting collars and rotatable heads of the previous embodiments in their translation capacities.

The alignment of the axes of the bores of sleeve 264 and barrel 258, the closing of switch 324 by flange 278', and the completed circuit to ground through contact 318 allow the gun to be fired in the manner of the FIG. 1 embodiment. Thus, tiring is only possible when an operator manipulates the gun to align the axes of barrel 258 and sleeve 264, an operation which assures against inadvertent gun discharge. Moreover, unless the forming collar or die and the bucking bar are sensed by contact 318 and switch 324, respectively, ring is impossible.

In all the embodiments of the present invention, the frusto-conical recess in forming

punches

34 and 269, and constricting

anges

106, 186, 300 materially add to the rivet setting ability of the rivet gun. As previously described, the frusto-conical recesses constrain radial expansion of the formed rivet head in a manner which prevents rivet failure. The constricting ange is always in proper position because of nose biasing and therefore forming collar failure from excessive expansion is overcome and the collar is always in proper position to prevent sheet failure from excessive rivet formed head expansion in the sheets.

What is claimed is:

1. An explosively actuated rivet setting gun comprising:

(a) a barrel having a breech end and a muzzle end;

(b) means for receiving an explosive charge at the breech end of the barrel;

(c) means for closing the breech end of the barrel and for introducing an explosive charge to the explosive charge receiving means;

(d) means for selectively firing an explosive charge in the explosive charge receiving means;

(e) an impacting hammer disposed in the barrel for translation from the breech end toward the muzzle end in response to the tiring of an explosive charge by the firing means;

(f) a nose mounted on the gun for limited longitudinal movement at the muzzle end of the barrel, the nose including a sheet abutting surface for abutting against the exposed side of a sheet through which an end of a rivet to be set extends and a bore for receiving the end of the rivet;

(g) means responsive to gas pressure generated by the detonation of the explosive charge to urge the nose against the sheet during recoil of the setting gun; and

(h) a forming die at the muzzle end of the barrel disposed to be struck by the impacting hammer and in turn to strike the end of a rivet extending into the bore of the nose.

2. The rivet setting gun claimed in claim 1 wherein the forming die has a frusto-conical recess dening an impacting face normal to the axis of the forming die for striking an end of a rivet to be upset and a tapered i'lank converging from the impacting face to the muzzle end of the forming die to conne radial expansion of the rivet to be upset.

3. The rivet setting gun claimed in claim 2 wherein:

(a) the nose includes an annular, radial ange extending inwardly toward the axis of the noses bore from the sheet abutting surface for constricting the radial expansion of a forming collar utilized with the rivet, the radial flange defining a reduced diameter portion of the noses bore; and

(b) the forming die is disposed longitudinally inward of the radial flange for limited longitudinal movement in the noses bore.

4. The rivet setting gun claimed in claim 3 wherein:

(a) an outer barrel housing is provided, the Outer barrel housing encasing the barrel; and

(b) the nose urging means includes at least one pressurizing port in the barrel, the pressurizing port being in pressure and gas communication with the nose between the barrel housing and the barrel to urge the nose against the sheet.

t5. The rivet setting gun claimed in claim 4 wherein the impacting hammer includes at least two inertia portions coupled together such that upon acceleration from the breech end toward the muzzle end of the barrel one of the portions will lag behind the other and upon striking the forming die a sustained impact will be delivered to the forming die.

6. The rivet setting gun claimed in claim 5 wherein the impacting hammer inertia portions comprise a plurality of segments longitudinally coupled together.

7. The rivet setting gun claimed in claim 5 wherein the impacting hammer inertia portions comprise:

(a) a body having a longitudinal cavity of progressively reduced transverse cross sectional area toward the muzzle end of the impacting hammer; and

(b) a heavy fluid-like material partially lling the cavity.

8. The rivet setting gun claimed in claim 5 including an expansion chamber assembly having an expansion v 17 chamber, means for adjusting the volume of the expansion chamber, and means for communicating the expansion chamber with the gases generated by the detonation of the explosive charge between the breech end of the barrel and the explosive charge receiving means.

9. The rivet setting gun claimed in claim 8 wherein:

(a) a universally rotatable head is disposed on the muzzle end of the gun, the noses bore extending through the head and being rotatable therewith; and

(b) means is provided for preventing tiring of the gun until the noses bore is coaxial with the axis of the barrel.

10. The rivet setting gun claimed in claim 1 including:

`(a) an outer barrel housing encasing the barrel, the

barrel being disposed for limited longitudinal movement in the barrel housing between a rst and a second position, the rst position being toward the nose and the second position being away from the nose;

(b) biasing means for urging the barrel toward its r-st position; and

(c) the nose urging means includes at least one pressurizing port associated with the barrel and the nose to urge the nose against the sheet with expanding combustion gases from the explosive charge after the impacting hammer reaches a predetermined point in the barrel.

11. The rivet setting gun claimed in claim 10 wherein the nose urging means includes an annulus between the outer barrel housing and the barrel in pressure communication with the port and a surface of the nose such that gases produced by the ring of the explosive charge act against the surface to urge the nose against the sheet.

12. The setting tool claimed in claim 11 including at least one impacting hammer return port at the muzzle end of the barrel in communication with the annulus for admitting gases generated by the explosive charge into the barrel to return the impacting hammer to the breech end of the barrel.

13. The rivet setting gun claimed in claim 12 including:

(a) at least one gas exhaust port at the breech end of the barrel which is normally closed by the barrel housing; and

(b) at least one gas discharge port disposed in the gun for communication with the exhaust port when the barrel is in its second position and to vent gases generated by the explosive charge to atmosphere.

14. An explosively actuated tool for setting a rivet fabricated from hard material comprising:

(a) a barrel assembly having a barrel housing, a barrel, a muzzle end and breech end, the barrel being mounted in the barrel housing for limited longitudinal movement therein, a barrel return spring disposed to act between the barrel housing and the barrel to urge the barrel in the direction of the muzzle end, at least one pressurizing port through the wall of the barrel intermediate the ends of the barrel, means outside the barrel to pressure communicate the pressurizing port with the muzzle end of the barrel assembly, at least one impacting hammer return port at the muzzle end of the barrel communicating the bore of the barrel with the pressure communication means, and means to vent the barrel of explosive generated gases when the barrel moves towards the breech end;

(b) a nose mounted at the muzzle end of the barrel assembly for longitudinal translation thereon, the nose having a surface in pressure communication with the pressure communication means such that upon sensing of a pressure generated by the gases formed in the ring of an explosive charge the barrel moves longitudinally away from the nose, and a bore for receiving an end of a rivet extending from the sheet;

(c) a breech block assembly normally closing the breech end of the barrel assembly and attached to the barrel housing, ythe breech block assembly having means for receiving an explosive charge and means for introducing an explosive charge to the receiving means;

(d) means for igniting an explosive charge received in the receiving means;

(e) a forming die disposed for longitudinal translation in the noses bore, the forming die having a frustoconical recess converging toward the exposed end of the forming die and an impacting face normal to the axis of the forming die for respectively constraining the expansion of the end of a rivet to be upset by the tool and striking such rivet end; and

(f) an impacting hammer disposed for translation in the bore of the barrel between the breech end and the muzzle end, the impacting hammer having at least two inertial masses coupled together such that upon striking the forming die at the muzzle end a sustained impact is imparted thereto, the impacting hammer being capable of returning to the breech end after striking the forming die by pressure generated by the gases formed in the tiring of an explosive charge admitted through the impacting hammer return port.

15. The explosively actuated tool claimed in claim 14 wherein the impacting hammer includes:

(a) a body portion having an axial cavity which progressively reduces in transverse cross-sectional area toward the muzzle end thereof; and

(b) a heavy fluid-like material partially iilling the axial cavity.

16. The explosively actuated tool claimed in claim 15 wherein the breech end of the cavity has a cross-sectional area which progressively reduces toward the breech end.

17. The explosively actuated tool claimed in claim 15 wherein the progressively reducing transverse cross-sec tional area at the muzzle end of the impacting hammer is defined by a series of progressively reduced diameter cylindrical sections.

18. The explosively actuated tool claimed in claim 17 wherein:

(a) the progressively reduced diameter cylindrical sections are joined by frusto-conical transition shoulders;

(b) the body portion has a reduced diameter section at the muzzle end of the impacting hammer to present an impacting hammer return surface at the juncture of the reduced diameter section and the balance of the impacting hammer; andy (c) means is provided to compressively engage the Wall of the barrels bore to retain the impacting hammer at the breech end of the barrel upon return from the muzzle end thereof.

19. The explosively actuated tool claimed in claim 18 wherein:

(a) the breech end of the cavity has a series of progressively reduced diameter cylindrical sections joined together by frusto-conical transition shoulders; and

(b) the heavy fluid-like material is mercury.

20. The explosively actuated tool claimed in claim 14 wherein the impacting hammer is dened by a plurality of cylindrical segments longitudinally coupled together such that upon acceleration toward the muzzle end progressive segments toward the breech end lag behind segments toward the muzzle end.

21. The explosively actuated tool claimed in claim 20 wherein the cylindrical segments are coupled together through a longitudinal pin which exerts a radial, outwardly directed force on the walls of the bores in the segments in which the pin is disposed.

22. The explosively actuated tool claimed in claim 21 including:

(a) means to compressively engage the wall of the barrels bore to arrest the impacting hammer at the breech end of the barrel upon return from the muzzle end thereof; and

(b) the segment at the muzzle end of the impacting hammer has a reduced diameter to present a surface for gas from the impacting hammer return port to act upon.

23. The rivet setting tool claimed in claim 14 wherein:

(a) the nose assembly includes a universally pivotable head mounted at its end, the sheet abutting surface being on the universally pivotable head; and

(b) aligning means is provided including:

(i) a parabolic mirror mounted on the universally pivotable head;

(ii) a source of light for directing a beam of light at the parabolic mirror;

(iii) a photosensitive cell disposed to be energized by light reflected from the parabolic mirror; and

(iv) means to prevent the actuation for the firing means until the photosensitive cell generates a tiring signal in response to light from the light source being reflected from the parabolic mirror.

24. The rivet setting tool claimed in claim 23 including: biasing means urging against the universally pivotable head to normally position the parabolic mirror such that light from the light source reected from the parabolic mirror will not strike the photo sensitive cell until the bore of the nose assembly is coaxial with the bore of the barrel.

25. The rivet setting tool claimed in claim 24 including a housing mounted on the tool having a bore, the photosensitive cell and the light source being mounted in the bore such that light emanating from the light source is directed as a beam toward the muzzle end of the `barrel assembly.

26. The rivet setting tool claimed in claim 25 wherein:

(a) the firing means includes a trigger; and

(b) the firing prevention means includes a solenoid in circuit with the photosensitive cell having an element responsive to the energization of the solenoids coil, the solenoid being mounted such that its element is in the path of the trigger until the solenoids coil is energized.

27. The rivet setting tool claimed in claim 14 wherein:

(a) the nose includes a universally pivotable head mounted to the barrel assembly at such assemblys muzzle end, the bore of the nose being in the pivotable head;

(b) means is provided to normally maintain the bore of the nose out of axial alignment with the bore of the barrel; and

(c) means is provided to prevent actuation of the ring means until the bore of the nose is coaxially aligned with the bore of the barrel.

28. The rivet setting tool claimed in claim 27 wherein the means to maintain the bore of the nose out of axial alignment with the bore of the barrel includes:

the muzzle end of the barrel and an inner end of the nose being normally in abutting relationship with the abutting surfaces such that the bore of the nose is out of alignment with the bore of the barrel until the tool is aligned by pivoting the nose with the pivotable head, with respect to the barrel.

29. The rivet setting tool claimed in claim 28 wherein the nose includes a sleeve having the noses bore, the forming punch being slidably disposed within the sleeve, and the inner end of the nose in normal abutting relationship with the muzzle end of the barrel is on the sleeve.

30. The rivet setting tool claimed in claim 29 wherein the sleeve is slidable in the pivotable head and has an outer end extending beyond a sheet abutting surface thereof such that sucient compressive engagement of the sleeve on a sheet causes the outer end of the sleeve to become flush with the sheet abutting surface by displacing the barrel and barrel return spring towards the breech end of the tool.

31. The rivet setting tool claimed in claim 30 wherein:

the nose includes a mounting collar xedly secured to the barrel housing and rotatably receiving the pivotable head;

the sleeve displaces the barrel against the return spring to maintain the bore of the sleeve normally out of alignment with the bore of the barrel.

32. The rivet setting tool claimed in claim 31 including:

means for preventing the actuation of the ring means until the sensing of the correct position of a bucking bar; and

means for preventing the actuation of the ring means until the sensing of the correct position of a forming collar used with the rivet.

33. The rivet setting tool claimed in claim 32 wherein the means to prevent actuation of the firing means until the bore of the pivotable head is coaxially aligned with the bore of the lbarrel includes:

(a) a parabolic mirror mounted on the pivotable head;

(b) a source of light for directing a beam of light at the parabolic mirror;

(c) a photosensitive cell disposed to be energized by light reflected from the parabolic mirror; and

(d) means to prevent actuation of the ring means until the photosensitive cell generates a firing signal in response to light from the light source being reflected from the parabolic mirror.

34. An explosively actuated rivet setting gun compris- (a) a barrel assembly having a barrel with a muzzle end and a breech end, a pressurizing port intermediate the ends of the barrel, and means in communication with the pressurizing port for communicating the pressurizing port with the muzzle end of the barrel;

(b) a nose mounted to the barrel assembly at the muzzle end for limited longitudinal translation thereon, the nose assembly having a pressure surface in pressure communication with the pressurizing port through the communicating means such that upon the presence of a pressure generated by the gases formed in the firing of an explosive charge the nose assembly is urged away from the barrel assembly, a flat sheet abutting surface for abutting against the sheet of material to be riveted, yand a bore for receiving an end of a rivet extending from the sheet;

(c) means for receiving an explosive charge at the breech end of the rbarrel;

(d) means for closing the breech end of the barrel and for introducing an explosive charge to the explosive charge receiving means;

(e) means for selectively firing an explosive charge in the explosive charge receiving means;

(f) an impacting hammer disposed in the barrel for translation from the breech end toward the muzzle end in response to the ring of an expolsive charge by the firing means; and

(g) a forming die at the muzzle end of the barrel disposed to be struck by the impacting hammer and in turn to strike the end of a rivet extending into the bore of the nose.

35. The explosively actuated rivet setting gun claimed in claim 34 wherein the nose includes an annular mounting collar slidably disposed about the barrel assembly at the muzzle end thereof and in gastight relationship therewith.

36. The explosively actuated rivet setting gun claimed in claim 35 wherein the barrel assembly includes a barrel housing which receives the barrel and the communicating means includes an annulus betwen the barrel housing and the barrel in pressure Comunication with the pressurizing port and the noses pressure surface.

37. The explosively actuated rivet setting gun claimed in claim 36 wherein:

(a) the nose is received for limited longitudinal movement on the barrel; and

(b) at least one impacting hammer return port is provide at the muzzle end of the barrel in pressure and gas communication with the annulus.

38. An explosively actuated rivet setting gun comprismg:

(a) a barrel having a breech end and a muzzle end;

(b) means for receiving an explosive charge at the breech end of the barrel;

(c) means for closing the breech end of the barrel and for introducing an exposive charge to the charge receiving means;

(d) means for ring an explosive charge in the explosive charge receiving means;

(e) an impacting hammer disposed in the barrel for translation from the breech end toward the muzzle end in response to the firing 0f an exposive charge by the firing means;

(f) a forming die at the muzzle end of the barrel disposed to ibe struck by the impacting hammer, the forming die having a frusto-conical recess defining an impacting face normal to the laxis of the forming die for striking the end of a rivet t0 be upset and a tapered flank converging from the impacting face to the muzzle end of the forming die to confine radial expansion of the rivet to be upset; and

(g) means to retain the forming die with the gun.

39. The explosively actuated rivet setting gun claimed in claim 38 wherein the included angle of the forming die ank is about 60.

40. The explosively actuated rivet setting gun claimed in claim 39 wherein the depth of the forming die recess is about 0.225 times the diameter of the impacting face.

41. The explosively actuated rivet setting gun claimed in claim 40 wherein the diamteer of the impacting face of the forming die is about 1.06 times the unformed diameter of the shank of the rivet to be upset.

42. The explosively actuated rivet setting gun claimed in claim 41 wherein the means for retaining the forming die with the gun includes an annular radial constricting flange at the muzzle end of the gun, the constricting flange defining a bore for the passage of the shank of a rivet to be upset and for constricting the radial expansion of a forming collar used with such rivet, the diameter of such bore -being about 1 to 1.05 times the diameter of the forming collar.

43. The rivet setting gun claimed in claim 40 wherein the impacting hammer comprises a plurality of tandemly aligned cylindrical segments and means for coupling the segments together such that upon striking'the forming die each of the segments acts relatively independent of the other segments to effect a sustained impact on the forming die.

44. The rivet setting gun claimed in claim 43 wherein the segments are attached together through a longitudinally disposed split retention pin received in holes in the segments.

45. The rivet setting tool claimed in claim 40 wherein the impacting hammer has an axial cavity, is partially lled with a heavy fluid-like material and the muzzle end of the axial cavity converges in cross-sectional area toward the muzzle end.

46. The rivet setting gun claimed in claim 45 wherein the converging portion of the axial cavity of the impacting hammer is defined by a series of cylindrical sections of progressively reduced diameters.

47. The riveting gun claimed in claim 46 wherein the heavy fluid-like material is mercury.

48. An improved explosively actuated rivet setting tool comprising:

(a) a `barrel having a breech end and a muzzle end;

(b) an impacting hammer disposed for movement between the breech end and the muzzle end of the barrel;

(c) a forming die disposed `at the muzzle end of the barrel for striking a rivet upon being impacted by the impacting hammer;

(d) means for receiving an explosive charge at the breech end of the barrel;

(e) breech means at the breech end of the barrel for closing such end of the barrel, the breech means being operable in the loading of an explosive charge into the receiving means;

(f) means for firing an explosive charge received in the receiving means; and

(g) means for adjusting the expansion volume between the impacting hammer and the receiving means to vary the velocity of the impacting hammer.

49. The improvement claimed in claim 48 wherein the expansion volume adjusting means includes a chamber in gas communication with the explosive charge receiving means and an adjustable element disposed in the chamber for varying the volume of the chamber.

50. The improvement claimed in claim 49 wherein the adjustable element includes a cup-shaped metal seal, the walls of the cup-shaped seal being deformable against the walls of the chamber in response to the pressure generated by the firing of the explosive charge.

51. The improvement claimed in claim 50 wherein the adjusting element includes a support member attached to the metal seal on the latters low pressure side.

References Cited UNITED STATES PATENTS 3,050,732 8/1962 Termet 227-10 3,239,121 3/1966 Kopf 227-10 3,248,032 4/1966 Bochrnan 227-8 3,275,209 9/ 1966 Hansen 227-10 3,341,101 9/ 1967 Butler 227-10 JOHN F. CAMPBELL, Primary Examiner GENE P. CROSBY, Assistant Examiner IU.S. Cl. X.R.

P04050 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pltevnt N0 3,559,449 Dated February 2 1971 A Inventor(s) John C. ASteinmetz i It is certifiea that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the specification: Column 5, line 32 "KJ" should l -2+. Column 7 line 60 "piston" should be pistol Column 8, line 1, "gear" should be -sear. Column ll, line 34', Hpasse" 'should b e --passes. Column ll, line 71. after "titanium" insert r--riv'ets employs an impacting hamme weighing approximately 68 grams with the mercury constitutl' 18' grams". Column 11,4 lines 74 and 75 -delete "rivets employs an impactinghammer weighing approximately 68 grams with the mercury constituting 18 grams,

Signed-rand sealed this 2nd day of November l 971 (SEAT-ly Attest:

EDWARD M.FLETCHER',JR. ROBERT GOTTSCHALK Attestng Officer Acting Commissionerof Patent.