US3166971A

US3166971A - Riveting by electric discharge

Info

Publication number: US3166971A
Application number: US71324A
Authority: US
Inventors: Robert L Stoecker
Original assignee: Air Reduction Co Inc
Current assignee: Airco Inc
Priority date: 1960-11-23
Filing date: 1960-11-23
Publication date: 1965-01-26
Anticipated expiration: 1982-01-26

Description

Jan. 26, 1965 R. L.. s'roEcKER 3,166,971

RIVETING BY ELECTRIC DISCHARGE Filed Nov. 23. 1960 2 Sheets-Sheet 2 INV EN TOR.

Y longitudinal of the rivet.

United States Patent() 3,166,971 RIVETING EY ELECTRIC DISCHARGE Robert` L. Stoecirer, Florham Park, NJ., assignor to Air Reduction Company, Incorporated, New York, N.Y.,

a corporation of New York Filed Nov. 23, 1960, Ser. No. 71,324 2 Claims. (Cl. 85-65) This invention relates to riveting by electric discharge. It is especially concerned with improved methods and apparatus useful in blind rivetingi.e., the riveting of work of which one surface is exposed but the other is concealed or is at least inaccessible.

Various methods of blind riveting, utilizing rivets of generallycup-like form, have heretofore been proposed. In one method there is placed at the inner extremity of the rivet cavity a charge of explosive which, after the rivet is seated in its apenture in the work to be riveted, is suit`- `ably provoked into explosion-Le., the violent chemical the obvious disadvantage of hazard, not merely as to each of the Iindividual rivets but also as` to their collective storage and transport. In themelting method there is the ditiicultyofcontrol over the directions of iiow of In both the melting and variousy the melted' material. mechanical methods there is the unlikelihood of final signiiicant clamping or binding pressure on the work` In some mechanical methods there is required the use foreach rivet of a new tool which will be destroyed in the process of setting that rivet-and so on.` i i It isan object of myinvention" to provide method" of riveting, which may beblind riveting equally as per-l missibly as not, which is free of the hazard inherently present in the use of explosives. It is an object Vto'provide a method which imposes no need for special measures to control the direction of iiow of material. It is `an object to` provide `a method by the use of which thereis developed a final large clamping or binding pressure, longitudinal of the rivet, on the work. It is an object to provide a method which, practiceable in an elementary manner essentially without any apparatus at all, also lends itself to a highly eihcient manner of practice with a simple, single and permanent tool.

It is an object to provide a method of riveting, permissibly blind riveting, by the use of which there is de` veloped not only a nal `large bindingpressure longitudinalof the rivet on the work, but `also a highly advantageous iinal substantial'pressure of the wall of the rivet against coniinesfof the aperture in which the rivet has been set. i p p Itis a general object to pro-vide a simple, inexpensive and otherwise improved method of riveting,l

It is` anohject to provide a simple and otherwise improvedmeans for deforrning a rivet intohighly effective relationshiptowork, of which one face may be concealed or inaccessible.

It ismanother objecttoprovidc a simple, inexpensive and' otherwise improvedrivet adapted to be blindly set into highly effective relationship to such work. p

Other` and allied` objects willappear fromthe follow? ing description andthe appended claims.

ICC

In practicing the methods, and in utilizing the means and the rivet, according to my invention I make kuse of the pressure developed, within a material inert` as to chemical explosion, by the disruption thereof `occasioned by effecting the abruptdisch'arge of a quantity of elec tricity therethrough. Typically and preferredly the discharge will he the discharge of an electrical capacitor previously charged to a voltage more than sufficient to effect the electric breakdown of the material. Typically the discharge is an arc discharge.

There is, of course, already known thebroad `concept of metal deformation by discharge of a charged `electrical capacitor. I have found, however, that in the setting of rivets this broad method of metal deformation produces unexpected advantageous results, besides affording eX- ceptional simplicities. And my invention ofcourse fur` ther involves various more specilic features not` at all contemplated or disclosed by the capacitor-discharge metal-deformation art of which I am aware,

In the description of my invention hereinafter set forth reference is made to the accompanying drawing, in which:

FIGURE 1 is a view, partly in vertical cross-section and partly in elevation, `illustrating an elementary manner of practicing my invention;`

FIGURE 2 is a` cross-sectional view of the rivet of FIGURE l after its having been set;

FIGURE 3 is a View, partly in vertical cross-section and partly in elevation, illustrating an elementary alternative manner of practicing my invention; ,i

FIGURE 4 is an enlarged elevational viewof theend of the rivet, taken along the line 4-`4,'of FIGURE 3;

FIGURE 5 is a cross-sectional view of the rivet of FIGURE 3 after its having been set;

FIGURE 6 is an enlarged elevational View of the end of the set rivet, taken along the line 6 6, of FIGURE 5;

FIGURE 7 is a cross-sectional view of a tool which may be used fori the more efficient practiceof my invention in one manner, the tool being in position close to but still out of contact withthe rivet to beset, together with a schematic diagram of the power supply to which that tool may be connected;

FIGURE 8 is a view similar in` nature to part of FIGURE 7 but illustratingthe tool and rivet immediately after the latter has been set; i

FIGURE 9 is a cross-sectional view of a tool or gun which may vbe Aused for the more elicient practice of my` invention in an alternativegmanner, the gun being in position close to but still out of Contact with the rivet to be set, together with a schematic diagram of the power supply to which that gunmay be connected;

FIGURE 10 is a similar view in nature to part of FIG- URE 9 but illustrating the gun and rivet immediately after the latter has been set; and

FIGURE 11` is a cross-sectional fview of a rivet generally similar to that of FIGURE 9 but illustrating a moditica-tion of my invention in respect to the loading of the i rivet.

A typical rivet with which my invention may be` practiced appears as 10 in FIGURE 1.4 It may beco'nsidered as generally cup-shaped,` having the relatively thin side`` wall 12, a bottom (in cup terms) endl 11, a flare or liange I3 at the upper end, and a cavity 14. In FIG* URE l the rivet is illustrated as havingbeen already seated in an aperture 3 in work which may, for example, compriseinner and outer vertically disposed flat sheets, 1 and` 2 respectively, of metal which are to be riveted togetherthe rivet, however, not yet being` `set (ie, expanded into final binding relationship to the work) in that aperture.

The rivet and `its cavity are elongatedA (relative to most` typical cup proportions) so that when the rivet is` seated (i.e., when its flare 13 rests against the exposed face 6 ycharge persist for any extended period of time. therefore, `desirable that the quantity of electricity disof the work) the cavity 14 extends substantialy beyond the inner or concealed face 5 of the work. The rivet will be of electricallyconductive material having good ductility or at least exhibiting that characteristic under the impulsive 'action described below.

It may be appropriate here to stress that there is intended no limitation of the are of the rivet to a flat flange such as shown inYFIGURE l. Thus, by way of alternative example FIGURE 3 (the showing of which is hereinafter detailedly'discussed) Shows a different form of are in a rivet which, of course, may still be characterized as generally cup-shaped. The primary function of the flare, of whatever form, is, of course, the provision on the rivet of a shoulder or equivalent surface which will finally exert an inward force on the exposed face 6 of the work in opposition to an outward force to be exerted on the concealed face 5 as will hereinafter be described. Indeed, it is to be understood generally that the rivet may be altered within wide limits in respect of shape, proportions, etc.V without defeating the applicability of my invention to the task of setting it.

To make of the rivet a member adapted to be set by electrical-capacitor discharge in accordance with my invention there is placed within its cavity 14 a material, inert as to chemical explosion, and of limited dielectric strength. Choice of this material is more fully discussed below; it will here be convenient to mention, as a simple initial example, a Wax (of Viscosity such that it is capabie of being displaced under relatively light pressure but in the absenceof pressure will remain in its position throughout various orientations of the rivet) into which has been mixed a quantity of common salt (NaCl) to lower its dielectric strength appropriately. In carrying out my invention as contemplated in the illustration of FIGURE 1,

a loading 15 of this material may initially almost but not necessarily completely till the cavity 14. The insertion of the loading into the cavity is usually most conveniently carried outbefore the seating of the rivet in the aperture 3, though it may, if desired, be performed thereafter.

With the rivet resting in seated position in the aperture, i

I effect between a point within the rivet cavity and the bounding surface of the cavity an abrupt electric discharge through the material of the loading 15, disrupting thatniaterial along the line therethrough taken by the discharge. This discharge may be effected with the aid of a simple electrode introduced into the cavity, preferably almost centrally thereof, to that point. Thus, FIG- URE l shows an electroderZti in the form of a hard, straight wire, for example of tungsten, of which the lefthand end portion is surrounded by a sheath 19 of insulation starting just to the right of the very extremity of the electrode; this lefthand end portion may be introduced approximately centrally of the cavity to a point 16 therein which lies preferably within but relatively near the inner limit of the aperture 3 in the work. The introduction of the electrode may displace some of the material of the loading 15, and even though the cavity was not initially quite lled by the loading it may be assumed to be substantially lled after the introduction of the electrode.

The work of the rivet deformation to be performed bythe discharge is, of course, inherently limited in magnitude, and furthermoreY its effective performance depends on initial abruptness of the discharge; it is accomplished in an extremelyminute interval of time. It is, therefore, wholly unnecessary-and for obvious practical reasons of preservationof the` rivet and work against destruction, safety to the operator, conservation of power consumption and the like Vit is altogether undesirable-that the dis- It is,

charged be a pre-established quantity only-such as that stored in an electrical capacitor previously charged to a suitably selected voltage.

Accordingly, in FIGURE 1 the other of the electrode (righthand) end 2@ is shown as being in` slight spaced to effect the discharge, after having manipulated the electrede to the position in which it is illustrated in FIGURE l, it is necessary only to lower its righthand end into contact with the lug 21. A generally cylindrical blocl; 18 of insulatin 7 material secured about the electrode is shown as a linger piece by which the electrode may be manipulated in these manners. v

The discharge effected as a result of bringing the electrode into contact with the lug 21 is yan arc which disrupts the material of the loading 15 along the line taken therethrough by the discharge; under the circumstances illustrated in FIGURE l e.g., wherein the outward extent of the loading 1S is to a distance from the inner end of the cavity very substantially greater than the cavity diameter this line will be from the exposed left--y hand tip end of the electrode 20 to some point on Vthe side surface of the cavity (i.e., on the inner surface of the rivet wall 12) generally opposite that tip end. disruption creates within the affected portion of the material an extremely sudden burst of energy, the Vexpansive" force of which is transmitted through the remaining portion of the material to the entirety of the bounding surface of the cavity.

It is true that as shown in FIGURE 1 that bounding surface is discontinuous-de., the cavity is to a considerable extent openat the outer end; the expansive force is so strong and abrupt, however, that it does its work on the various areas of the cavity surface with relatively little wasteful dissipation outwardly through the opening afforded at the outer end of the rivet. It is fur-ther true that the path of the discharge is not symmetrically positioned within the cavity, either longitudinally (which, of course, it cannot be, in view among other things of the inherent dissimilarity of the innerV and outer end portions of vthe cavity) or even transversely (since it will occur to some one peripheral point or region on the side surface); I have, however, observed that notwithstanding these facts the Veffect of the energy burst is not only a highly useful'one for its purpose in its relatively general and not thin-shelled, compression of the Y material outwardly against the boundary of the cavity'. Whatever its precise nature may be, however, I have found that `the expansive force generated as above described has served-as illustrated in FIGURE Z-both to create in the wall of the rivet a bulge 17 which exertsV a longitudinal force component as well as a transverse one on the inner rim 4 of the aperture, and further yto expand the wall of the rivet within the aperture 3 into a state of pressure against confines of the aperture-eg., ery of the aperture in the inner portion 1 of the work and in part of the outer portion 2. I have further found that the force components exerted by the bulge onl the rim 4, and thestate yof pressure-of the expanded wall against confines of the aperture, are continuing phenornena.

The inner rim 4 of the aperture is effectively a part: of the inner face 5 of the work as well as being a parti of the aperture 3, and accordingly the effect of the longitudinal force component thereon is to exert an outward pressure Von the inner face 5 in opposition. to the inwardl against the periph-VV a force exerted on the exposed face 6 by the flare 13 of the rivet-ie., to elfect a clamping of the work between the bulge and the flare. The effects of the transverse force component on the rim 4 are to preclude the rivet from working laterally within the aperture, and to minimize tendencies of the two portions of the work to creep transversely (i.e., in a direction parallel to their faces) relatively to each other. In thesefnctions the transverse force component on the rim is aided by the expansion of the rivet Wall into a state of pressure against contines of the aperture, which expansion and state of pressure in this case extend to be effective on those confines to a substantial longitudinal extent within the outer workpiece 2 as well as throughout the inner workpiece 1.

In the method above described with reference to FIGURES 1-2 the are discharge is brought about by suddenly applying a suitable electric charge to an already positioned electrode. FIGURES 3-6 illustrate an alternative method of bringing about the discharge, They also illustrate the use of a rivet altered from that of FIGURES 1 2 in respect of the continuity of its inner end portion and in the nature of the bulge which will be produced by the discharge-and, for the primary purpose of showing the independence of my invention from specic rivet shapes, a different form of rivet flare.

Thus, the rivet of these figures, designated as lil', may have a flare in the form of a truncatedly conical flange 13 (for the receiving of whichthe exposed face 6 of the work will desirably be conically `countersunk around the aperture, as indicated at 6'). The more basic alteration of the rivet 10 from the rivet 10 of earlier figures is effected by the making of a number (for example, three) of very thin (for example, several mils thick only) longitudinal cuts through the rivet, preferably in planes each containing the rivet axis, from the inner end of the rivet for a distance outwardly, preferably to limits which when the rivet is seated will lie within the aperture 3 but relatively near its inner extremity; the effect of the making of these cuts is to create within the rivet wall and inner end a double number of slits 9 converging at the center of that inner end, asbest seen in FIGURE 4, though leaving the inner end of the rivet and of its cavity still substantially closed and well probfed against loss of the loading therethrough.

In conformity both with the now-less-resistive rivet structure and with the altered method to be used in bringing about the arc discharge the loading of the rivet, which may, for example, be with the same material as in the case of FIGURES 1-2 but is now designated at may be confined to a region of the cavity adjacent the inner end--for example, from the inner end for a distance somewhat less than the diameter of the cavity. As` before there Will be employed the capacitor 23, again charged `to a voltage more than `sufficient when applied between a point in the ,loading and the rivet to effect the electrical breakdown of the loading, arid again having its righthand lug 22 connected to the rivet as by the conductor 24 and the outer work portion 2.

p In this case, however, before the introduction of the electrode into the cavity,` or at least before its lefthand end comes into proximity with the loading 15its righthand end will have been brought into and thereafter maintained in contactwith the lefthand lug 21 of the charged capacitor. While this contact is still being maintained the electrode will be moved progressively leftwardly, preferably substantially centered transversely of the cavity, FIGURE 3 illustrating the electrode. at an intermediate position in the course of this movement. When the `lefthand end of the electrode has reached at least the very 'close vicinity of the loadingilS` (the exact point depending on various parameters including the dielectric constant of the loading material) there will occur an abrupt discharge from the tip of the electrode to and through the loadingin this case to some point or region on the end surface of the cavity. i

Again the discharge is an are the effect of which is to disrupt the material of the loading along the line taken therethrough by the discharge, though that line has been seen to be specifically repositioned from that taken through the material of earlier figures. Again the disruption creates within the material an extremely sudden burst of energy, the expansive force of which is transmitted through the material. In this case, however, because of the limitation of quantity of the loading and because of the presence of the slits 9, the effect of that force will be principally conned to the several jaws 8 which have been formed by, and between,- the slits 9.

. The typical effect of the expansive force on the rivet itl is illustrated in FIGURES 5 and 6. As seen therein, that force has served to rock each of the jaws` 8 away from the rivet axis, generally in the manner of causing each of them to pivot first about a bending region 7 at the outward extremity of the slits 9, and then to pivot further about the inner rim 4 of the aperture 3. The main part of each of the jaws 8 is, of course, a part of the rivet wall l2, and thus again it may be considered that in the rivet wall there has been created a bulgethough, of course, in this case the bulge is not reentrant to the original rivet configuration, and is peripherally interrupted by the noW-triangularly-widened slits 9. Again the bulge exerts a longitudinal force component as well as a transverse one on the inner rim 4 of the aperture-though the further action, of earlier figures, of expanding the wall of the rivet within the aperture (i.e., substantially outwardly of the rim 4) is not usually performed to a very appreciable extentand again those force components on the rim 4 are continuing phenomena.

It may be mentioned that the failure to effect any expansion at all, at a rim or otherwise, of the FIGURE-3` rivet within the portion-2 part of the aperture 3 is effectively substituted for, in preventing rivet working and work-portion creeping,7 by the truncatedly conical flare i3 and its seating against the corresponding countersinking at 6 of the exposed face of the work.

From the FIGURES (2, 5 and 6, as well as others not yet described) illustrating the loaded rivet after it has been set in the Work by the discharge there has been omitted any showing of remnant material of the loading (l5 or 15). This has been purely for simplicity of illustration, and is not to be taken as implying that there will not be'remnant material. There will be, since the breakdown will have consumed or altered the state of only a modest portion of the loading, the rest of which will have served the function of pressure transmission and may be harmlessly and unimportantly left within the rivet cavity (FIGURE 2) or at least partially adhering to the inner surfaces of the jaws 8 (FIGURES 5-6).

While the general method of my invention may indeed be carried out in Various manners, such as those described above, Without the aid of apparatus specially adapted thereto, nevertheless its practice can `by the use of such apparatus be made more facile, safer for the operator, andmore eiiicient. In FIGURES 7-8 and in FIGURES 9-l0 I have shown two embodiments of such apparatus, and these may now be described.

Attention is first invited to FIGURES 7 and 8. Herein the rivet has the fully closed inner end of the FIGURE-l rivet I() yet, by way purely of example, has the truncatedly conical flare I?!` of the FIGURE-3 rivet 10'; it is designated as lili), andmay, of course, be initially seated in the aperture 3 in the work 1-2 just like the rivet l0 of FIGURE 3. It may be provided with an almost-full loading l5 of material, quite analogously to the rivet 10 of FIGURE 1. `In these figures the apparatus specially adapted to the practice of my invention comprises a tool, designated generally as Btl, which may be manipulated in the vicinity of the rivet;V a relatively stationary power supply, designated generally as S01; and suitable cabling interconnecting that tool and that power supply. The functions of the tool, beside effecting an essentially coniplete closing of the rivet cavity, are those of aptly positioning the electrode both transversely and longitudinally of the cavity, and of controlling the supply of energy to the electrode; the tool may be most conveniently described starting with'the electrode, which is centrally contained therein.

The electrode, designated as Ztl', may again typically be of material such as tungsten. It is surrounded by and secured in a relatively thick sleeve 31 of insulating material, which in turn issurrounded by and secured in a metallic jacket 33. The outer (lower-shown) end of the electrode projects below the outer end of the jacket 33 by just the distance by which the electrode is to penetrate into the cavity 14 of the rivet; this is desirably a distance such that when the jacket 33 is brought into contact with the outer face of the rivet, the tip of the electrode will have been brought toa point within the cavity which lies within Vbut relatively near the inner limit of the aperture 3 in the work. Immediately adjacent the jacket 33 the outer end of the sleeve 3l may be slightly inset, so as to insure that it will not interfere with intimate contact of the jacket 33 with the rivet; in its central portion, how-- ever, the sleeve 31 is provided with an outward extension 32 about the electrode, of diameter just freely to lit within the cavity 3. The outward extent of this extension is desirably such as to bring its extremity, when the jacket 33 is brought into Contact with the rivet face, only partially within the work-portion-Z part of the aperture 3-i.e., to leave free of insulation the major part of the longitudinal extent of the cavity which lies within the entire aperture 3 of the work. The inner extremities of the jacket 33 and sleeve 31 may be substantially in alignment with each other, but the inner extremity of the electrode Ztl' will extend slightly beyond that of the sleeve.

In its longitudinally central region the jacket 33 may be provided with an enlarged-diameter portion 35, and inwardly beyond that portion it may be provided with external threading 37. Onto this threading, though not fully into abutment against the shoulder 36 formed at the inward extremity of the central portion 35, may be screwed an internally threaded metallic cap 4h, the central portion of which is formed into a reduced-diameter extension 38 directed away from the electrode, jacket and sleeve. In the space between the latter and the main part of the cap, and lying against the shoulder 39 of` the cap formed between its threading and the cap extension 38, there may be positioned a disc 41 of insulating material; through this disc there may project toward the electrode the extremity 59 of a cable conductor 60 hereinafter more fully referred to-that extremity being for example Vfolded over against the disc, and being held in tight contact with the inner end of the electrode when the cap is screwed in place on the jacket.

The portions of the tool 30 thus far described will be recognized as not only a cavity-closing and electrodepositioning means, but as also a means for detachably securing the electrode in electrically connected relationship to the cable conductor 60. The other extremity of the cable conductor 60 lies in the power supply Sti; there it serves to connect (subject to a control hereinafter described) the electrode with one terminal 21 of a capacitor 23', of which the other terminal 22 is connectible to the rivet in manner described below.

In the power supply there is comprised a D.C. source 5I of appropriately high voltage for charging the capacitor 23'; the grounded (or groundable) terminal 52 of the voltage source being connected to the capacitor terminal 22, and the high-voltage terminal 54 of the source Vbeingconnected to the capacitor terminal ZI through the charging resistor 55. Itwill be understood that the source will keep the capacitor charged through the resistor at all times excepting through each minute interval during which theV capacitor is being discharged through the cable conductor 60 Vand through a brief recovery period (whose duration is, of course, established by choice of the value of the resistor) immediately following each such discharge.

For the purposes of my invention the effectiveness of the arc discharge of the chargedcapacitor is a function not only of the energy content Vof the charged capacitor, but also of the abruptness with whichthat energy is released through the discharge-ie., the shortness of the period of time within which the discharge will be substantially completely effected. Thatl abruptness is militated against by the resistance, and even more by any inductance, effectively present in the series circuit through which the discharge occurs. It is true that the resistance eiiectively present in that circuit is usually most importantly contributed to by the eitective resistance of the path of the arc proper, so that more than ordinary measures to reduce the resistance of conductor portions of that circuit are not called for. These exists, however, no such pragmatic limitation on the worth of minimizing to the greatest extent possible the eiective inductance.

Even small values of effective inductance, although allowing the discharge to remain aperiodic as it should be, nevertheless lengthen the duration of its single pulse, while higher values not only lengthen that pulse further, but when great enough render te discharge oscillatoryi.e., cause some of the energy to be withheld from the already-slowed initial pulse and to be released only in successive pulses of alternating directions-all to the serious detriment of the desired abruptness. In the preferred practice of my invention I minimize the inductance as much as possible-with a high preference, at

least to the point of insuring aperiodicity or" the dis-1 charge, and very desirably as much further as can be practically achieved.

This minimization may be accomplished by employing for the circuit from the'capacitor to the electrode and rivet-or, stated reversely, for the circuit from electrode to rivet via the capacitor-a pair of coaxial conductors. Accordingly, in FIGURE 7 I have shown the conductor eti, leading from electrode to capacitor terminal 2l', as forming the inner one of a pair of such conductors, of which the outer one is a tubularly formed conductor 61--the space between the conductors being lled with any suitable insulation 63. VTo preserve the coaxiality of the circuit right to the electrode and rivet, the tubular conductor 61 may be mechanically and electrically connected to the cap extension 38-it, of course, being readily observable that the cap, and the jacket V3:3 to which it in turn is mechanically and electrically connected, are in coaxial relationship to the electrode 20' to which the conductor 60 is electrically connected as above described. The connection of the tubular conductor 6l to the cap extension 3S is readily effected by fitting the former about the latter with a slight are as indicated at 62 and, for example, soldering the are'to the exterior of the main part of the cap V4t).

The connection from the capacitor terminal 22 to the rivet, above described as far as the .jacket 33, is, of course, completed between the outer end of that jacket and the outer face of the rivet by the physical contact of those two elements eiected by movement of the tool 3@ to bring the electrode 26 into itsabove-'described operative relationship to the rivet. r

It is desirable that, as an adjunctive action to bringing r the electrode into that operative relationship and completing the connection of capacitor terminal 22'` to the rivet as just described, there be brought about the completion of the circuit from the capacitor terminal 21 to'YV the electrode-fwhich circuit it is desirable to maintain naccomplish such energization of the coil 66 it may be connected between a relatively low-voltage terminal 53 may include, in freely surrounding relationship to the jacket 33` and the cap 4d and the outer end portion of the cable formed by the coaxial conductors 6i) and 61, a cylinder 42 of insulating material. Through most of its length from its outer end inwardly this cylinder. may be provided with an `axial bore 43 just freely accommodating the jacket 33 and cap 49, and of a length somewhat greater than the combined length of those elements. Communicating with this bore 43 and passing through the remainder of the cylinder may be a somewhat smaller axial bore 45, between which and the bore 43 there intervenes the shoulder 44, the outer end portion of the cable 60-61 lying partially within the bore 43 and partially within the bore 45. Within the bore 43 in surrounding relationship to that cable portion there` may be provided a helical compression spring 46 whose extremities bear respectively on the shoulder 44 and on the main portion of the cap 4t? (permissibly through the tlare 62 of the tubular conductor 61). The spring 46, of course, biases outwardly of thecylinder 4Z the assembly consisting of the jacket, the cap, the end portion of cable 60-61 and the electrode Ztl insulatedly carried within the jacket. A

limit for the response of this assembly to this bias may be provided by one or more screws 47 threaded radially through the cylinder 42 near its outer end to extend slightly into its bore 43, there to intercept and be impinged on by the shoulder 34 forming the outer extremity of the enlarged central portion 35 of the jacket 33. This limit may establish a normal position, for the assembly relative to the cylinder, wherein the jacket 33 will extend a `short distance outwardly from that cylinder.

The contact above discussed and to which the conductor 64 will be electrically connected may be formed by the outer extremity of a suitable stiit wire 49 passing, for example slightly diagonally, from a short distance outwardly of the outer extremity of the cylinder 42 through the cylinder to a region 48 therewithin `relatively near the inner (upper-shown) extremity of the cylinder. This region 48 may form the inner end portion of a radial bore 69 in the cylinder, and from it to the inner cylinder extremity there may extend a further and stepped bore 68. The conductor 64 may extend into the bore 68 to overlap the wire 49 in the region 66, there to be clamped against that wire by the screw 69' threaded into the radial bore 69.

The point of emergence of the wire 49 from the cylinder may be close enough to the cylinder laxis so that the contact formed by its extremity will be aligned with a marginal portion of the rivet face when the sleeve extension 32 is aligned. with the rivet cavity 14. The distance of extension of the wire 49 outwardly from the cylinder will, however, be somewhat less Ithan the normal such` distance of the jacket 33; thus when the tool is manipulated merely to bring the end of the jacket into contact with the rivet (and the sleeve extension into the rivet cavity and the electrode into its operative position) the contact formed by the outer extremity of wire 49 will still be free of electrical connection with the rivet face. But if thereupon pressure toward the work be exerted on the cylinder 42, the spring 46 will be compressed and the cylinderand contact will move toward the work until the contact touches the rivet face-thereupon completing the circuit for energization of the coil 66, from that coil through the conductor 64, the wire 49, the rivet face, the jacket 33 and cap 4t), and the conductor 61 to i the grounded source terminal 52.

FIGURE 7 hasillustrated the condition of the appa ratus at a late point `in the movement of the tool toward its iinal operative position. FIGURE 8 illustrates the conditionimmediately following the completion of that movement,` and of the further movement of the cylinder 42 just described `as serving to energize the coil 66. That energization will have caused the closure of the switch formed by the contacts 67 (which, although not appearing in FIGURE 8, would if appearing be shown closed), thus completing the connecting of the charged capacitor between the electrode and the rivet (analogously to the lowering of the electrode 20 into contact with the capacitor terminal 21 in the case of FIGURE l) Iand bringing about the disruptive discharge ofthe capacitor through the loading 15. That discharge `will in turn` have brought about the setting of the rivet; that setting will be quite analogous to the setting of the rivet 10 in the case of FIGURE l, with two exceptions. One is `that the expansion of the rivet wall 12 into contact with contines of the aperture 3, though occurring as previously within the work-portion-l part of the aperture, will have been precluded by the truncatedly conical flare from extending into the work-portion-Z part; that is a dierence from which any unfavorable effects `are precluded (as above brought out in a rather similar connection in the case of FIGURE 3) by the action of that flare itself in cooperation with the associated countersinking of the work face` 6. The other exception is that the essentially complete closing of the rivet cavity `14 prior to the occurrence ofthe arc discharge will have created a slightly more ecient set of conditions, either resulting inthe formation of a slightly greater bulge 17, or permitting the use of slightly less energy for the discharge, or the like.

It will be appreciated that the use of the specially adapted apparatus of FIGURES 7-8 carries out the method of my invention in a specic adaptation of the mannerbroadly disclosed in connection with FIGURES l-Z. FIGURES 9-10, to which reference isnow invited, show specially adapted apparatus whose use carries out the method in a speciiic adaptation of the manner broadly disclosed in connection with FIGURES 3 6.

In FIGURES 9-10 the rivet is shown as having the thinly slitted inner end `of the FIGURE-3 rivet 10 yet, by way of example, the flat iiare 13 of the FIGURE-l rivet; it is designated as and may be provided with the limited loading 15 of material quite analogously to the rivet 1W of FIGURE 3. In these figures the apparatus specially adapted tothe practice of my invention com# prises a tool or gun designated generally as 70; again a power supply, which may be generally like that of FIGURE 7 but is designated generally as 50 because ol one speciiic elaboration; and again cabling 60-61 and 64; interconnecting the tool or gun 70 and the power supply.

The gun 70 may be most conveniently described starting with its main exterior member. This may be a` rela` tively long metallic barrel 71, for example of diameter slightly less than the outer diameter of the rivet flare. Secured immediately within the barrel maybe a lining cylinder 74 of insulating material, having throughout a little over half its length starting with its outer (leftshown) end a bore 75 identical with that of the rivet cavity;` its bore 76 throughout the remainder of its length may be somewhat enlarged. The outer extremity of the lining cylinder 74 may be slightly inset relative to that of the barrel 71; the opposite extremities of `the two may, for example, be flush with one another. At the last mentioned extremity of the barrel 71 the barrel may be provided with external threading 72; onto this threading maybe screwed an internally threaded metallic cap 80, the central portion of which is formed into a reduced-diameter extension 78 directed away from the barrel. In the space between the extremity of the barrel (and lining cylinder) and the cap, and lying against the shoulder 79 of theicap formed between its threading and the crap extension 78, there may be positioned a disc 81 of insulating material; through this disc there may project to within the lining cylinder the end portion 59 of the cable conductor 6l), which conductor may be iden- Y tical with that in FIGURE 7.' In this instance the end portion 59 may pass on through and be folded over against the surface of a metallic disc S2, whose'periphery 83 may be bevelled Vto rest against corresponding bevelling 77 on, and just within the extremity of, the lining cylinder n 74; the folded-overV end portion 59 of the conductor may Vbe'soldered or otherwise secured to the surface of the disc 82. k

Within and havingA a free t to the bore 75 there may be carried a sleeve 91 of insulating material, centrally within which is imbedded or otherwise secured the electrode 2.0, again for example of tungsten wire. At their outer extremities the sleeve and electrode may for example be unitarily formed into a conical shape. FIGURE 9 illustrates the sleeve and electrode as inwardly withdrawn into the lining cylinder 74, for example so that the outer 'extremity of the electrode is just flush with the outer V86 there may be secured about the sleeve 91 a collar 87, for example of metal. The diameters of

discs

85 and 86 and of collarv 87 will, of course, fit freely within the enlarged bore 76. The entire assembly of electrode, sleeve, discs and collar will be urged outwardly by a fairly powerful helical compression spring 84 contained within the enlarged .bore 76 between, and having its extremities bearing against, :the discs 85 and82. The spring 84 will also serve electrically to interconnect those discs, and thus to connect the electrode with the conductor 60. Y

To arrange for externally controllable longitudinal movement of the internal assembly of electrode, sleeve, discs and collar, there may extend freely into a hole 88 in the wall of the collar, and freely through an elongated aperture 92 in lining cylinder 74 and barrel 71, a screw 89 threaded inwardly through a cylinder 93 which surrounds and is freely slidablealongrthe barrel 71-the effect of the screw 89 being to interlock that assembly and that slidable cylinder as to longitudinal movement. FIG- 'URE 9 illustrates that assembly and that cylinder as being held, against the force of the compressed spring84, in a retracted position; such holding may be accomplished byoutward linger pressure on a linger piece 94 extending for example downwardly from the cylinder 93. To facilitate the establishment and maintenance of that finger pressure a handle 99 may be secured about and extend downwardly from the barrel 71 a little inwardly from the retracted position of the cylinder 93.V

As its outer/extremity the barrel 71 may have secured coaxially thereabout an outwardly extending cup-shaped flange 73 of internal diameter shaped just freely to embrace the flange or are 13 of the rivet 100'; the outward (i.e., leftward) extent of the flange will be limited so as not quite to abut against the work surface 6 when the outer extremity of barrel 71 is moved into contact with the rivet face and thus iso as not to interfere with that contact.

The contemplated manner of mechanically manipulating the gun 70is` to move it, while maintaining the internal assembly and thus the electrode 20Vin retracted position, to bring the flange 73 into surrounding relationship to the rivet liare 13 and the extremity of -the barrel 71 into con- ,tact with the rivetface-FIGURE 9 illustratingV the gum f ina position just prior to the completion of this movement-and then suddenly to release the finger pressure from the linger piece 94. Thereupon the internal assembly including the electrode 20 will be abruptly propelled by the spring 34 into the rivet cavity C14-for a distance lixed by the impactive abutment of the outer end of collar S7 against the shoulder formed within the lining cylinder 74% by the inner extremity of the bore 75.

While the power supply Sil may be generally like the power supply 50 of FIGURE 7, it is necessary in this case to control it in a somewhat different manner-since it is desired that the potential of the charged capacitor 23 be already applied to the electrode at the time of release of the linger piece 94. Accordingly, instead of an arrangement such as that of the contact wire 49 of FGURE 7 there may be employed a switch which will be closed, to apply that potential to the electrode, when the internal assembly including electrode 20" is retracted Vby linger pressure on the linger piece 94. Such a switch may be conveniently provided, for example by mounting, in a suitable slot 98 formed in the handle 99 immediately underneath the barrel 71, a small normally open switch 9e of encased variety throwable -to closed condition, against the force of an internal over-center spring, by

light pressure on a limitedly movableplunger 97. This switch may be mounted in the slot in an orientation such that the plunger 97 will be outwardly directed and may be impinged on, when the slidable cylinder 93 is retracted, by a small downward extension 9S formed from vthat cylinder-the plunger 97, when moved inwardly' by the cylinder extension 95, constituting the limiting stop for retraction of the cylinder 93 and the internal assembly ing i in .response to the closed condition of the switch 96 *Y which in turn is being maintained by the retracted linger l piece 94, and is a condition desired to be continued at least until immediately after the completion of the abrupt propulsion of the internal assembly including the electrode 20" which will occur upon release of that linger piece.` It will be appreciated, however, that in the absence of appropriate measures the coil 66 will be deenergized, and the contacts 67, therefore, constrained to open, forthwith upon the rrelease of the linger piece. To preclude a premature opening of the contacts 67, the releasing action of the relay 65 may be delayed for a brief. interval, following any Vopening, of switch 96, suliicientV to allow time for the completion of the propulsion just mentioned. Such a delay may be accomplished in any known manner, typical of which I have shown associated with the armature of the relay an air dash-pot 162 which will freely permit upward movement, but will appro-` priately retard any downwardmovement, of that armature.

It will already have been appreciated that in the ap- .paratus of FIGURE 9 the barrel 71 and cap 80 perform the same functions as did jacket 33 and cap 4) of FIG- URE 7, the outer tubular conductor 61 of the coaxial pair 6ft-61 being secured on and electrically connected to the i cap StB-in manner quite analogous to that )above described in connection with cap 40.

FIGURE l0 illustrates the condition of the apparatus i following the completion ofthe forward propulsion of t-he internal assembly including the electrode 20 and the discharge of the capacitor 2.3 to andthroughV the loading 15' which will, of course, occur at or minutely, prior to that completion of propulsion. The Vaction'of that discharge will kbe fully understood from the above descripitsai tion of action presented in connection with FIGURES 3-6, Athere being in general only the distinctions that the movement of the electrode is now effectedpropulsively, at a much more rapid rate, and'` under uniformly duplicable conditions.

It will be understood that, in distinction to the limited dielectric strength possessed byV the loading or 15 within the rivet cavity, the dielectric strengths of the various insulating members (e.g., sleeve 31, disc 41, insulation 62, etc. in FIGURES 7-8; sleeve 91, lining cylinder '74, discs S1 and 86, insulation 62, etc. in FIG- URES 9-10) which support and insulate the electrode and the conductor 60 in the apparatusv of FIGURES 7-8 and 9-11 will each be high.

It is to be understood that the arrangements of apparatus of FIGURES 7-8 and 94-10 and the components thereof are typical only, and may be Widely varied or elaborated upon. Simply as one example there may be mentioned the relay 65 which, While for conciseness of illustration shown as of a simple solenoid type (in one case, with mechanically delayed release), may, of course, be of any appropriate variety-for example,` when utilizing quite high voltages, of an ignitron or other highvoltage-switch type (permissibly, in the delayed-release case, with purely electrical or still other release-delay means).

The capacity of the

capacitor

23 or 23 and the voltage to which` it will be charged of course determine the er1- ergy which is available for release in the discharge of the capacitor- Which energy will be understood, in accordance with Well-known physical laws, to be proportional to the first power of that capacity and to the second power of that voltage. Choice of the magnitude of that energy, and thus in turn of the capacity and voltage, is determined by such factors as the easewith which the rivet to be set may be deformed, in turn involving the structural strength of its cavity, is ductility, etc.; the abruptness with which the discharge is eifected, in turn influenced by such factors as the inductance of the discharge circuit, discussed above; the significant losses of discharge energy, which in general are those represented by that serial part of the discharge which may occur not Within the material of the loading but instead at the switch contacts in the process of their closure (in the case of the method as typilied by FIGURES 1 2) or from the approaching electrode tip to the surface of the material (in the case of the method as typied by FIGURES 36); and the choice of material for the

loading

15 or 15.

I may give the following as examples of typical orders of magnitude of various parameters. With aluminum rivets of essentially maximum available ductility and of the type shown in FIGURES 9-10 and having a wall of approximately 1/32 in thickness, and with the use of a simple petroleum derived oil as the material of the loading 15 (the rivet being seated in a substantially vertical position, as shown for the different form of rivet in FIG- URES 7-8, to retain the oil at the inner end of the cavity) I have successfully expanded the rivets to such iinal state as disclosed in connection With FIGURES 3-6 or 9-10 by the discharge of a 54-rnicrofarad capacitor previously charged to a voltage of 1,000 volts. Again, with rivets of similar material but of the type shown in FIGURES l-Z and having a Wall thickness of approximately %4 and with the use of a saturated solution of common salt (NaCl) in Water as the material of the loading 15 (the seating, of course, again holding the rivet substantially vertical to maintain the lling of the cavity by the material) I have successfully expanded the rivets to such final state as disclosed in connection With FIGURES 1-2 by the discharge of a 154-micr0farad capacitor previously charged to a potential of 1,000 volts. The inductance of the discharge circuit has been sufliciently minimized so that the discharges have been aperiodic, and oscillographic observation of their durations has indicated substantial completion of their single pulse in a time period of the order of 50 micro-seconds.

It will already be appreciated that the choice of material for the loading is a very wide one, to say the least. It should of course have a dielectric' strength low enough so that the voltage required to break it down, considered as applied in the particular manner to the material in the particular configuration Which will be used, is less than the voltage to which the capacitor will be charged. It may be a single material which meets these specifications (such as the oil mentioned above for the FIGURES 9-10 type of rivet); alternatively it may consist of a rst component to which a second has been added for reduction of an otherwise excessively high `dielectric strength (such as the Water above mentioned for the FIGURES 1-2 type of rivet, With the addition of common salt). It may be a highly fluid material (such as the salt-saturated Water), or a somewhat viscous but still iluid material (such as the oil), When the rivets may always be vertically or near-vertically seated; alternatively, to permit any orientation of the seated rivet, it may be a much more viscous material such as the salt-or otherwise-impregnated Wax mentioned early hereinabove, or a suitably impregnated grease. When two or more components are used, one or more may be in true solution in the other (such as the salt in the water); alternatively one or more may be merely dispersed through and in suspension in the other (such as the salt in the grease).

When two or more components are used with one or more dispersed in particle form through but not in true solution in the other component or vehicle, the dispersed one or ones may be chosen to be electrically conductive, such as fine metallic particles; in this case, while some of the breaking down or disruption must and, of course, will be an arc occurring in the relatively nonconductive vehicle, the disruption considered as an entirety will Vin large measure include the vaporization, brought about by the momentary gross overheating, of the dispersed conductive particles.

A variation of the subject matter of the preceding paragraph Which may be successfully employed is the constitution of the multi-component material not by one or more components dispersed in particle form throughout the other, but rather by one in a suitably disposed solid and unitary form Within the other. This variation I have illustrated in FIGURE l1, which shows a sealed but unset rivet alternative to that of FIGURES 9-10. The basic rivet proper may be quite identical to that of those iigures and is, therefore, again designated as and in the cavity of the rivet at its inner end may be a quantity for example of pure grease or Wax, similar in extent to the loading 15' of those earlier iigures-but to it there has been added, extending through it from the central region of the inner end of the cavity, for example to its outer surface, a conductive component 115" consisting of a ne (for example, about l-mil) wire. In this case the disruption Will comprise principally the vaporization, brought about by the momentary gross overheating, of the conductive tine wire 115". It may be mentioned that the manner of securing this Wire at the center of the inner end of the rivet is not critical; the Wire may, for example, be cemented in the hole formed by the intersecting slits 9 since the cement, even though initially insulating the Wire from the rivet, Will, of course, itself be broken down in the discharge, which preferentially occurs therethrough.

In the FIGURE-l1 loading material one of the components is, of course, Wholly solid-and it will be understood that with any of the general types of material mentioned above, Whether consisting of a single component, or of a plurality with one or more either dissolved in or dispersed in particle form through the other, or of a plurality with one or more contained in unitary form or forms Within the other, the entire material may, if desired, be solid.

While I have disclosed my invention with reference to particular examples thereof, I intend no unncessary 1 5` limitations thereby. Modications in many respects will be suggested by my disclosure to those skilled in the art, and such modifications will not necessarily constitute departures from the spirit of the invention or from its Scope, which` I undertake to define in the claims set forth below.

I claim:

1. A rivet seatable in an aperture in work to be riveted and adapted to be blindly deformed in any deposition of said rivet into binding relationship to that Work by the abrupt discharge of a quantity of electricity, comprising a generally cup-like electrically conductive member having a shoulder means at one end and having an elongated cavity opening at the shouldered end and extending substantially beyond they inner face of the Work and at least substantially closed at the inner end thereof, and a material of limited dielectric strength in said cavity which is self-retaining therein in inverted positions ofV said rivet, said material being inert as to chemical eXplosion but susceptible of electric disruption by an -abrupt electrical discharge and comprising a highly viscous substance of a relatively high dielectric strength and a substance of relatively low dielectric strength dispersed throughout said viscous substance, the respective proportions of said substances being such as to render said material of a dielectric strength such that an abrupt electrical discharge through the material results in trans? mission of an expansive force to said cup-like member, and the outward extent of said material within the cavity being to a distance from the inner end of the cavity substantially greater than the cavity diameter whereby the rivet extremity of an electric discharge through the material to the rivet from an electrode inserted into contact withIthe material will be caused to be a point on the side surface of the cavity.

2. A rivet seatable in an aperture in Work to' be riveted and adapted to be blindly deformed in any depo- CID sition of said rivet into binding relationship to that work' by the abrupt discharge of a quantity of electricity, comprising a generally cup-like electrically conductive member having a shoulder means at one end and having a cavity opening at the shouldered end and extending substantially beyond the inner face of the Work to dene a Wall, and at least substantially closed at the inner end thereof, said cavity Wall having a portion removed near said inner end to provide a weakened Wall portion to facilitate the expansion of said Wall, and a material, self-retaining in said cavity and inverted positions of said rivet, which is inert as to chemical explosion but susceptible of electric disruption, said material comprising a highly viscous substance of a relatively high dielectric strength and a substance of relatively low dielectric strength dispersed throughout said viscous substance, the respective proportions of said substances being such as to render said material of a dielectric strength such that an abrupt electrical discharge through the material results in transmission of an expansive force to said cup-like member.

References Cited in the tile of this patent UNITED STATES PATENTS 2,327,763 Burrows Aug. 24, 1943 2,387,742 Burrows Oct. 30, 1945 2,415,560 Higley Feb. 1l, 1947 2,438,976 Lautmann Apr. 6, 1948 2,492,579 Kahn Dec. 27, 1949 2,843,861 Gandy July 22, 1958 OTHER REFERENCES k Hydrospark Forming, The Tool Engineer, March 1960, pp. s1, s2. Y

Explosion Forming with Electricity; Mechanical Engineering, vol. 81, No. 11, Nov. 1959, ASME.

Claims

1. A RIVET SEATABLE IN AN APERTURE IN WORK TO BE RIVETED AND ADAPTED TO BE BLINDLY DEFORMED IN ANY DEPOSITION OF SAID RIVET INTO BINDING RELATIONSHIP TO THAT WORK BY THE ABRUPT DISCHARGE OF A QUANTITY OF ELECTRICITY, COMPRISING A GENERALLY CUP-LIKE ELECTRICALLY CONDUCTIVE MEMBER HAVING A SHOULDER MEANS AT ONE END AND HAVING AN ELONGATED CAVITY OPENING AT THE SHOULDER END AND EXTENDING SUBSTANTIALLY BEYOND THE INNER FACE OF THE WORK AND AT LEAST SUBSTANTIALLY CLOSED AT THE INNER END THEREOF, AND A MATERIAL OF LIMITED DIELECTRIC STRENGTH IN SAID CAVITY WHICH IS SELF-RETAINING THEREING IN INVERTED POSITIONS OF SAID RIVET, SAID MATERIAL BEING INERT AS TO CHEMICAL EXPLOSION BUT SUSCEPTIBLE OF ELECTRICAL DISRUPTION BY AN ABRUPT ELECTRICAL DISCHARGE AND COMPRISING A HIGHLY VISCOUS SUBSTANCE OF A RELATIVELY HIGH DIELECTRIC STRENGTH AND A SUBSTANCE OF RELATIVELY LOW DIELECTRIC STRENGTH DISPERSED THROUGHOUT SAID VISCOUS SUBSTANCE, THE RESPECTIVE PROPORTIONS OF SAID SUBSTANCES BEING SUCH AS TO RENDER SAID MATERIAL OF A DIELECTRIC STRENGTH SUCH THAT AN ABRUPT ELECTRICAL DISCHARGE THROUGH THE MATERIAL RESULTS IN TRANSMISSION OF AN EXPANSIVE FORCE TO SAID CUP-LIKE MEMBER, AND THE OUTWARD EXTENT OF SAID MATERIAL WITHIN THE CAVITY BEING TO A DISTANCE FROM THE INNER END OF THE CAVITY SUBSTANTIALLY GREATER THAN THE CAVITY DIAMETER WHEREBY THE RIVET EXTREMITY OF AN ELECTRIC DISCHARGE THROUGH THE MATERIAL TO THE RIVET FROM AN ELECTRODE INSERTED INTO CONTACT WITH THE MATERIAL WILL CAUSED TO BE A POINT ON THE SIDE SURFACE OF THE CAVITY.