CA1244269A

CA1244269A - Blind rivet assembly

Info

Publication number: CA1244269A
Application number: CA000448553A
Authority: CA
Inventors: Raymond D. Lacey; Albert C. Francis; Michael Woodrow
Original assignee: Avdel Ltd
Current assignee: Avdel UK Ltd
Priority date: 1983-03-07
Filing date: 1984-02-29
Publication date: 1988-11-08
Also published as: AU564123B2; GB2136075B; FR2542396A1; DE3407464A1; GB2136075A; IT8447798A0; IT1180686B; FR2542396B1; US4580936A; JPH0331922B2; AU2527084A; JPS59166708A; GB8306188D0

Abstract

ABSTRACT
Known blind, self-plugging rivet assemblies comprise a tubular shell with an enlarged head at one end, and a stem which extends through the bore of the shell, where the stem has an enlarged head beyond the tail end of the shell. In this invention, the shell has a weakened zone formed by three slits extending along part of the shell shank and spaced apart equiangularly around it.
A stem head lies beyond the shell tail end, and has an underhead surface which is slightly convex and is bounded by a sharp end. This arrangement facilitates axial compression of the rivet assembly and subsequent outward bending of the portions of the shell between the slits to conveniently secure together two members. The stem has a pulling portion connected by a breakneck to a plugging portion which is an interference fit in the shell bore. Adjacent the breakneck the plugging portion has a cylindrical skirt which, when the rivet has been installed, and the pulling portion detached at the break-neck can be deformed outwardly to lock the plugging portion to the shell. A simple, yet effective, means of locking the plugging portion to the shell is thus provided.

Description

~LIND RIVET ASSEM~LY

This invsnti~n rslatas to a blind rivet asRembly. More parti-cularly it relates to a blind rivet assembly of the so-cQlled "aalf-plugging" typa, which comprises a tubular shell and a stQm~ and in which part of the stem remains in the shell of the installed rivet to plug the tubular shall. A blind rivst is one which can be ~et without access to the remots or blind side of tha workpiecas.

Rivets of thls general k]nd~are waIl known and have been made in a variaty of diffarent forms in order to me~t various specific : ~ requirQments~

~ Ths pressnt invention providas blind rivet asssmbly comprlsing a tubular:shall and ~3 stem; : ~
the~shall~having an elungate~ shank,:a~head at one ènd, and;a bora throughout the haad and shank~
ths shell bore havlng a radlally~`enlargbd counterbora~at~its~
15 ~ head~end and e~-aCF~ locklng~should:r~faclng towards ths hsad~:end at thq Junction of the counterbora and the r.mainder Df the bore;~

ths~shsll shank b~ing wsakened:over a~zons~which a~tends~longi- 9 tudlnally of:the shank from a po~:itlon:spac:d:from th:~ta~ snd (i.:. th: end th:reof r:mot: from th: h:ad) of~th:~sh:nk tow:rds Zo ths~h:ad snd;

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the stem extending through the bore of tha shell and having an alongate pulling portion which projects from the head end of the shell, and an alongata plugging portion connected to the pulling portion by a breakneck and disposad substantially within the shell shank bore;
the plugging portion being formed with a radially enlargad stem head at the end thereof remote From the breakneck, and di~posed bayond the tail end of the shank;
whereby, when the assembly is inserted through alignad aperturas in workpieces to be thereby riveted together so that at lea t part of the shell shank weakened zone projects beyond the workpieces on the blind side thersof, and the pulling portlon of the stem i9 pullsd with increasing tension with raspect to the shell;
firstly compression exerted by the stam head on ths~shell shank tail end oauses radial enl~rgemant of at least part of the we:kened zone of th: shell shank to form a blind head, whilst the plugging portion mo~:s through tha shell bore towards ths head end thereof;
:nd thareaft:r th: :hsll sh:nk tail end dafor:s to allow~the antry of the stem head thereinto;:
tharaaftar the part of tha plugging portion adjacent the:break-neck being deformable into locking engagement with the ~Y~h~r locking shoulder of tha shell countarbora, and tha stem baing frac- ::
turable at the braakneck to ~leav: the plugging portion plugging the :

shall bora.

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~ ~ P.291 lZ~2~;9 Other prEferred features of the invention will become apparent from the appended claims. An embodimant of the inv~ntion will now be described, by way of flxample, and with referance to the accompa-nying drawings in which :-Figures 1 and 2 are, resp0ctively a sectional ælevation of the shell, and a side elevation of the stem, for a blind rivet, prior to assembly together;
Figure 3 ia a section on the line 3 - 3 of Figure 1, Figura 4 i8 a sectional alevation showing the blind rivet assembly positionad and ready to ba sat in workpieces to be riveted, and showing part of a riveting tool for setting thæ blind rivet;
Figures 5, 6 and 7 are sectional elevations showing succesive stages in the setting of the blind rivet; and Figure~8 corresponds to Figure 7 but shows a slm~lar rivet used to rivet together workpiece of a graater total thickness.

Tha~self-plugging blind~rlvet ass~mbly 10 (Figure 4) consi~sts~
of two parts, namely, a tubular rivet;~hell 11 and a stem 12~ whlch are assembled togethsr, The rivet shell is made of alumlnium alloy and~has an elongate~
shank 13 and a ra~ially enlarged~haad 14 formed intægrally with thæ shsnk st one end (the;hesd;~end)~o~ the she11.~ The shY11 hss a b~ore 15 throughout its lsngth, the dlamete~r Df the~;bora b~5ng in~
creased at tha~head end~by a head counterbDre 16.~ Exeept fDr~this, the bore 15 is Df u m form dlamstsr (subject~to manufsoturi~ng~to~ls~
ranc~s) throu~hout its length.

~ p~291 :.

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The head counterbore 16 is shorter than the thiGkness of the head and provides a locking shoulder 17 at thH junGtion betwsen the bore 15 and counterbore 16. The locking ehoulder feces towards the head end of the shell. The tail end of the shell has a flat face 18 perpendicular to the longi$udinal axis of the shell.
The shell shank is weakened over a zone 19 which extends from a position 21 spaced awsy from the tail end face 18 and extending along the shsll shank nearly to the head 14. Ths weakened zone comprisss three longitudinsl slits 22 spaced equiangularly around the ~hank. The s~its are made as narrow as practicable in the oir-cumfersntial sensa,and define ostween adjacent Dnes of them three longitudinal struts 23 which are separated from each other by the slits and which, when the shank is subjected to axial compression, will bend outwsrdly, as will become apparent.
The tmil - end portion 24 of tha shell, between the end 21 of the weakened zone and the tail end face 18 of the shank, is of course stronger thsn the weakened zons.
The underside of the head 14 mhioh faoes towards~the tsil end of the body lS undercut to leave a circumferential seaIing lip 25 surrounding a ~lat face 26 which receives a resilient sea]ing washsr 27 (Figure 4) which assists the formation of a saal betwssn the shell head and a workpiece in whioh the~rivst is installed.
The stem 12 is also made of aluminium slloy. The stem compr ses a plugging portion 31 which,~after setting of the rivat, sarves to plug the bore of the body, and an slongatsd pulling portion 32 which is joined to the plugging portion 31 by a breaknsck 33 :

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P.291 ..,,"~..,.. ~.

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The pulling portion i5 of less sxternal diamster thsn the plugging portion, and will pa9S through the shell bore 15 without intsrfsrence.
The breaknsok i5 ths weakest part slong ths length of the stem so that, when ths stern is subjected to progressively increasing tension,it will break at the breakneck rather thsn elsewhere. The plugging portion 31 is of uniform external diameter throughout its length (subject to manufacturing tolerances) and i5 an interference fit in the bore 15 of the tubular shell 11, and is apprsoiably shorter in length than the shell shank 13.
10To enable tha plugging portion 31 to be locked to the sh~ll 11 during setting of the rivst, the part of the plugging portion adjacsnt the breakneck 33 is formsd with a cylindrical ciaavags 34 (ses FigurR
4) which extends into ths plugging portion plug in the longitudinal direction away from the brsakneck. Ths claavage has a diameter the same as, or minutely greater than, that of tha pulllng portion 32, and diffarentiate~ the part oF the plugging portion adjacent to~the break-neck into a central cylindrical core 35 of substantially the same dia-~meter as ths pulling portion 32, snd a skirt 36 which peripherally ~; surrounds the cors 357 ths skirt~being integrally joined with t:ha ra-20~ ~ mainder o~ths plugging portlon in~ths r~gion furthsr from the break~
neck than the clsevags extends. Ths skirt pre~ents an annular fsce~or~
stsp 37 which faces towards the pulling portion 32. The~skirt~is de~or~
mabls~ by means of a sultsbls rlustlng~tool~ to form~sn outwsrdly dirsctsd flange capabla o~ abutting~tha locking shouldsr 1~7 in ths ~ 25 body, and thus provides locking means;for locking ths plugging ~ ~

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P.291 :: : :: :
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portion in thc shell of ths rivet.

lhe plugging portion 31 i9 formed with a radially enlargeci head 38 at tha end remots from the br~alcnsck. This head has an underhead surfaoa 39 having an extrems diameter slightly le38 than that of the shell Rhank end face 18. In this example the underhead face 39 i9 not absolute]y flat but is in the form of a very shallow convsx cons, having an included angle of about 170 dHgress (an abso-lutely flat face would have an included angle oP 1~0 degrees). The outer edge 40 of the underhaad surface 39 is 8 sharp sdge9 and the peripheral face 41 of the head 38 i8 cylindrical i.e. of uniform dismeter throughout its length~

The shell and stem are assembled by inserting the pulling por-tion 32 of the stem into the tail end of the shell and passing it along ths bora until the plugging portion 31 meats the tail end of the shallO Sufficient force is then sxertsd to drivs the pulling portion into the bnre9 in which it is an interfersnce fit. It may be deslrable to support the sxterior of the shell in a die or other form of psriph~ral clamp, to prevent rsdial expansion of the shell as the plugging portion is dr`iven in. Th~ stem i8 thus forced into ~20 ths ShBll until th~underface 39 of the stBm head 38 contaot~ the~
end face 1a af the shell. The stem and~shell are thus aesembled9 i.e. ln the condition illustreted in Figure 4. The breakneok 33 lies eùout one third of the way along the weakened zone 15. The pulling portion 32 of tha stem projects from tha head end of th shell, 25 ~ The interfssence between the plugging;~ portion 31 and the :
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P.291 ~ . - . . .~ . . .

iLZ4~263 interior of the shell shank 13 maintains the parts of the rivet in an assembled condition ready for use.

The U8B of the assembled riv0t 10 to fastHn together apertursd workpiece members will now be described.

An apertured panel member 42 (which may be o~ a soft or easily fractured material such QS glass fibre rainforced pl~stics material) may be fastened to another apertursd member 43 (which may, for exampls~
be a metallic support member for the panel), by bringing the msmbers togethsr with their aperturss 44 in registqr and inserting the shell ghank through ths apertures until the s3aling washer 27 under ths hsad 14 abuts tha ~ace 45 of the member nearer the operator, and ths tail-end portion 24 and at least a portion of the weakened zone of the shell shank projects beyond the back or blind face 46 o~ tha;wcrkpleces.
The diameter o~ the apsrtures 44 in the panels is of caurse made very slightly larger than the external diamster of the shell shank.

Ths rivet can bA set by means~of a rivet setting tool of~ a known kind sold under the Registsred Trade Mark "AVDEL" and comprising means (not shown) f~or gripplng~and pulllng the pulllng portion~32 of the~stsm which proJsots from the hsad of~the rlvet shell. As lllu~tra-; 2Q~ ted in Figures 4, 5 and 6, ths tool has annular~anvil 47 for~abuttingthe head of the~shall and a p~roJect1n9 rim 48 for~deformlng tne locklng skirt. The tool~is offsrd up tn~the rivst so that~ths pulli~ng portion 32 passe th~ough the anvil 47 into angagement with the grip-plng snd pulling mAsns, And thA;anvil~ abutA ths shAll hsad 14.~ The 25~ tool is then operatsd~to pu11 th~e stsm axially rslstive to the rivet : :

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P.291 :

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shell, in a dir~ation to draw the plugging pDrtion 31 towards the head 14 of the ~hell with a progres6ively increasing ~orce Due to the abutmant between the faae 39 of the stem head 41 and the end face 18 of the shell tail, axial compre~eion i9 exerted on the shell Since ths weake3t portion of the shell i8 the weakened zone, it is the weakened zone which deforms first The shell shank tail portion 24 begins to move with the steM towards the shell head 14, accompanied by an outward bending of the three struts 23 at a position generally half-way batween the blind ~ace 46 Df the panel 42 which constrains the portions of the struts within it againet radial expansion and the tail portion 74 of the =hell~body (see Figure~
5) The plugging portion 31 moves through the outwardly expanded struts and into~the part of ths shank which axtends within the thick-ness of the workpiece membtrs 42 and 439 slightly~xpanding the shsnk ~radlally~ This movement of the shell tail portlon 31 with~the stem continues until the three struts are bent and forced~fixmly~into ; abutment with the blind face 46, as~ahown ln Figure G, so as to oonatitute~a bllnd h=ad 49 of~greatar~tranv=~r=e~dim=nslon~th=n th=~
=p=rture= of thc workpi=o=

~At~thi~ =t=g=, th= force r=qulr=d to~mov= th~ =h=~ t=ll~portion~
24~ns=rer~to the head 14~incr==a=s =bruptly,~to th=~=xtent th=t, by =pplylng sufficient force, th=~stem~haad~41 cau=e= the t=il end part~
24~of th= =hell to d=form outwardly, =o that the head 41 enters lnto th=~t=il end p~art 24~of th=~=hell ;

lS~ ~ Co ti~u=d oullin~ n-r=l by~t-= to~ lV brirys ~ P 2Y1 :~

1~4~Z69 _ 9 _ ths plugging portion into engagement with the projecting annular rim 4~ which projects forwardly of the anvil into the shell head counterbore 16. The rim has ~n inclined front which, as the plugging portion is dra~n towards it, engages the skirt annular faoe 37 and ~,~) 5 entHrs the cleavage 34, eo as to progressivHly deform~ th0 locking skirt 36 radially outwardly, away from the central core 35 of ths plugging portion. It theraby forms a radially enlarged locking flange 51 (Figure 7) which abuts at least the inner peripherial fldge of the locking ehouldar 17, theraby constituting an obstacla to withdrawal of the plugging portion from the body. Onca the Hkirt is fully dsformed, tha force required to pull ths stam furth~r increases sbruptly, because of the engagemsnt with tha anvil rim 48. On apply-ing sufficient further foroa, therefore~the breakneck 33 fractures, leaving tha plugging portion~31 locked ln~the body, while the pulllng portion 32 becomas detached and aan be discarded, a9 shown in Figure :
7. Tha~racture face 52;of;the plugging portion is about level with, or~just ln~side, the~facs of ths~shsll hsad. ~ ~

The rasidual tsnsion on the stem clamps the panels 42, 43 toge-ther. On the blind face 46 this clamping is transmitted through the 20 ~bllnd rivst hsad 49, which lS of~substsnt~sl~rsdlsl~sxt~nt. ~On ths ; front faca 45 tha clamping is axartad through ths shell haad sealing washer~27. It may be ~that if the residualtension is~sufficiant, khe ssaling~wssher~ls compressed sufficiently that~the rim 25 contrscts the face 45 of the panel.

The washer 2~ seals ths shell head 14 to the front~ace 45 of~

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lZ44269 ~ 10 -the panel~ aruund the ep~rture 44. The interfsrence ~it of the plug-ging porti.on 31 in the part of -the shall shank within the panels sEals the plugging portion to the shell. There is no need for the stem head 41 to seal within the shell tail portion 24 (provided it is mschanically locked therein)~ because the interior of the shell shank bore is open to the outside space through the slots 22.

In Figures 4, 5, 6 and 7, ths example rivet ass2mbly is illu-stratsd being used to fasten together two sheets 42, 43 of a total thickness (or "grip"9 as the total workpiece thickness 1s known in the art of blind riv0ting) which is about the minimum valus for which the sxampls rivet assembly can be used. One of the advantages of the rivet illustrated in Figure 4 is that it has a relatlvely wide grip range, and Figure 5 illustrates the uss of a similar rivet to ~asten together sheets havlng a grip about the maximum valus for which this rivst will work succsssfully. Figure 8 illustrates the fully installsd condition of the rivst mssembly9 and compariaon with Figure 7 ~hows~that, since a much shorter length of the struts 32 ~: produoes from the blind panal faoe, a~radially smaller blind~head~49 : results. Also ths shell shank contracts axialIy by a much smsllsr :
: 20 ~amount dug to the shortgr foldsd length of the struts. Sincs the : plugging portion has still been pullsd through tha shell bor~ until :: : : : :
the~locking skirt lies in the:shs~ll head counterbora 16, the stsm head 41 has necessarily been pulled into the shell bors by a much ~; greater distance than in the minimum grip condition illustrated in Figurs 7, P.291 1;24~26~

The maximum grip i8 daterlninHd in praotice by the limitations that in the fully ins-talled oondition, the stam head 44 cannot entar into the space within ths panels~ and that the blind head 49 must be large enough to secure the rear pansl~

When the stem 41 is pullad into the rivet shell, it i~ found that, depending on the preoise circumstances of each particular plscing operation~ the sharp leading edge of the head may cut a ring of material from thc shell tall portion 24 (most probably from ad~acent the tail end face 18 of the shell).

The means by whlch, in the foregoing embodiment, the formation ; of a blind head is achieved during setting of ths rivet, and by which the plugging portion is snabled to become disengaged~from the tail-; end portion of the rivet shell may also~be~modifled sli~ghtly, as i8 ~msntloned balow.~ A number of~sultable solutlonm~hmvm~bmen proposed in the pagt in oonnection with pull-to-sat~self-plugging blind rivets.
; ~ ; However, it i9 believed thet the aolution to this problem de~ecribed in the ~oregoing exampla offers advantages in that, on ths~one hand it~fecilitates good oontrol~ovar the~dif~farent force~; required~et~
dlfferent stages of the setting~operetlon~ and et~bhe~3eme~time~
20 enables~ 3 singla si~e o~ rivet to be varsatile in the rangs o~
thickness of~workpiece (î~.~e~ grip~rang~ which~cmn~om accommodatRd~
It~mlmo mekes mmnufacture of~the stem~end~she~ simple,;~sinc~eg described the plugging port~ion has an uniform extsrnal diamat~r~
throughout~lts~length (apart from~the head), end the shell; bore~
also~has~m uniform dlemmter throughout~its 1ength (epart from~the P.291 _ 12 -hDa(i end aountarbore). Furthr3rmore sssr3mbly of tha stam and shell i9 simple, mr3rr31y requiring the forcing of one into thr-3 othsr, The invantion i8 not restricted to the details of the foregoing sxample. For instanae the form of ths shell may be modified in various ways. In partioular, instead of having three struta 22 there could be only two, or a greater number, for axample ~ix, made by appropriataly varying tha number of slits. Furthermore, the mate-rial of the shank could be punched out to form slots. ~lternatively, the shank could meraly be formed with longitudinalshear lines or groovas eo a~ to provida longltudial weakening of ths oollapsible part of the shsnk such as to enable it, on being comprsssed axially, to split into a plurality of longitudinal ~truts which aan be bent or bowed outwardly until doubled and thereby form a radially enlargeg blind hsad, ~ ~

Tha saaling washer 47 may be omitted from beneath the shell head.

As previously mentioned, the precise form oF the stam head 38 may ba modified. Tha conical angl~ of tha underhead face 39 may ba grestsr, up to snd includ1ng the~csse where ths fscs~is flst. ~ltsr-nativgly it may be somewhat less than ths 170 degrees. ~Similarly,the psripheral faca 41 of the stem head may not be cylindricsl, but~
could taper outwardly from its lssding edge 40. ~Such taper would be slight, having an included angle~ in th~ range from 0 degreas to :
about 5 ~degrees. Variation of the~;p-ecise shape of underheari face 25~ 39 lS believad to altar the value of pulllng tension at~which ths P.291 .
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stam head initi.r~lly entera the shell ts:ll, arld variation o~ the pre-cise ahape of the r~tem head peripheral ~ace 41 i8 beliaved to alter the tension therea~ter required to pul.l the st~3m haad into the r~hell tail .

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A blind rivet assembly comprising a tubular shell and a stem;

the shell having an elongate shank, a head at one end, a tail end, and a bore through the head and shank;

the bore having a radially enlarged counterbore at the head end of the shell and a locking shoulder facing towards the head end of the shell at the junction of the counterbore and the bore;

the shell shank having a weakened zone which extends longitudinally of the shank from a position spaced from the tail end of the shank towards the head end;

the stem extending through the bore and the counter-bore of the shell and having an elongate pulling portion which projects from the head end of the shell, and an elongate plugging portion connected to the pulling portion by a breakneck and disposed substan-tially within the bore and the counterbore of the shell shank:

the plugging portion being formed with a radially enlarged stem head at the end thereof remote from the breakneck, and disposed beyond the tail end of the shank;

whereby, when the assembly is inserted through aligned apertures in workpieces to be riveted together so that At least part of the weakened zone of the shell shank projects beyond the workpieces on the blind side thereof, and the pulling portion of the stem is pulled with increasing tension with respect to the shell;

firstly compression exerted by the stem head on the tail end of the shell shank causes radial enlargement of at least part of the weakened zone of the shell shank to form a blind head, whilst the plugging portion moves through the shell bore towards the head end thereof;

and thereafter the tail end of the shell shank deforms to allow the entry of the stem head thereinto;

and thereafter the part of the plugging portion adja-cent the breakneck is deformable into locking engage-ment with the locking shoulder of the shell counter-bore, and the stem is fracturable at the breakneck to leave the plugging portion plugging the shell bore.

2. A blind rivet assembly as claimed in Claim 1, in which the weakened zone of the shell shank comprises a plurality of circumferentially spaced lines of weakness extending longitudinally of the shank.

3. A blind rivet assembly as claimed in Claim 2, in which the lines of weakness comprise slots extending radially through the shank.

4. A blind rivet assembly as claimed in Claim 1, in which the plugging portion of the stem is in interference fit in the bore of the shell shank.

5. A blind rivet assembly as claimed in Claim 1, in which the bore of the shell shank, apart from the counter-bore at the head end, is of substantially uniform diameter throughout its length.

6. A blind rivet assembly as claimed in Claim 1, in which the plugging portion of the stem, apart from -the radially enlarged head, is a substantially uniform diameter throughout its length.

7. A blind rivet assembly as claimed in Claim 1, in which the radially enlarged stem head is initially in contact with the adjacent tail end of the shell shank.

8. A blind rivet assembly as claimed in Claim 1, in which the stem head has a surface, which faces towards the shell shank, which is flat.

9. A blind rivet assembly as claimed in Claim 1, in which the stem head has a surface, which faces towards the shell shank, which surface is bounded by a sharp edge.

10. A blind rivet assembly as claimed in Claim 9, in which the surface has a diameter which is less than the external diameter of the shell shank at the tail end thereof.

11. A blind rivet assembly as claimed in Claim 10, in which, when the stem enters the shell shank, the head severs material from the adjacent part of the shell shank.

12. A blind rivet assembly as claimed in Claim 1, in which the stem head has a peripheral surface which is cylindrical or slightly tapering with its minimum diameter at the end thereof which is nearer the shell shank.

13. A blind rivet assembly as claimed in Claim 12, in which the included angle of the taper is not more than 10 degrees.

14. A blind rivet assembly as claimed in Claim 1, in which the stem head has a surface, which faces towards the shell shank, which is slightly convex.