CA1154619A - Blind rivet assembly - Google Patents

Abstract

BRW/js IMPROVED BLIND RIVET ASSEMBLY

ABSTRACT

A blind rivet assembly is disclosed. The rivet assembly comprises a mandrel, a rivet body, a buckling sleeve and a locking collar. The sleeve, rivet body and collar are slidably disposed about the mandrel with the buckle sleeve disposed adjacent one end of the body and the mandrel extending through the body and beyond the other end of the body. The buckle sleeve has a generally cylindrical configuration such that when subjected to a pulling force, the sleeve buckles out-wardly from the mandrel, slides about the rivet body and engages a work piece.

Description

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l BACKGROU~ID OF ~HE INVE~lTIO~l

2 l. Field_of the Invention

3 The present invent~on relates to blind fastener

4 assemblies, and more specifically, to a blind rivet as~embly having ~ a buckle sleeve.
6 2. Prior Art 7 Blind rivets are we~l known in the prior art and are ~ used to fasten components when only one side of the workpiece is g accessible. Such type of rivets generally comprise three pieces:
ta) a stem or mandrel having a bulb-forming head at one end and l serrations at the other end for engagement by a pulling tool, 12 tb) a tubular body s~rrounding the mandrel and having a flanged 13 head, and (c) a locking collar encircling the mandrel near the 14 body head. In use, the head portion of the mandrel and the 15 surrounding body together are inserted through a hole in the 16 workpiece. A riveting tool including a pulling head is used 17 to translate the mandrel axially away from the workpiece. During 18 such translation, the bulb-forming elements of the mandrel head l9 expand the rivet body laterally to form a "blind b~lbn on 20 the hidden side of the workpiece. The pulling head then forces 21 the locking collar into a groove in the mandrel to lock the headed, 22 ac~essible end of the body to the stem. Finally, the stem 23 portion of the mandrel extending from the workpiece is broken 24 off to ~omplete the installation.
2B Recently a four-piece ~ripple sleeve" type rivet assembly ~6 has been devised which provided certain advantage5 in bllnd fastene Xq assemblies. In the ripple sleeve configuration, the sleeve and 28 rivet body are specifi~ally configured such that as the mandrel is 29 pulled through the workpiece, the rivet ~leeve begin~ to slide ~nd 30 expand l~terally over the tapered tail portion of the body member 31 without any bulb formation until the forward end of the sleeve 32 engages the workpiece. ~

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~ 416~9~, 1 However, a number of problems exist with ~uch type of assembly.
2 More specifically, the rippling action on which bulb formation 3 and propagation depend has proved to be difficult to control.
4 Moreover, the sleeve makes inltial contact with the workpiece over a narrow region immediately around the e~ge of the hole 61 exerting high pressure and tending to extrude into the gap between 7 ¦ the workpiece and the shan~ portion of the rivet hody. While t ¦ such a configuration may prove useful in connection with certain ~ ¦ materials and in certain stress situations, there is a long felt need for a fastener assembly which could produce a substantially 11 reduced stress on a structure made of synthetic material, thereby 12 ¦ not impairing the integrity of the structure. This is especially 13 I significant in aerospace applications which are now using a 14 I wide range of newly developed different materials and which 15 ¦ must be joined in a specific manner. Furthermore, to the above 16 I shortcomings, it is believed that a ripple sleeve type fastener 17 I assembly is susceptible to a reverse foLding sequence, thus 18 substantially weakening the workpieces so joined. Furthermore, 19 I the ripple sleeve rivet requires a complex tail geometry on the 20 ¦ rivet body requiring expensive secondary manufacturing operations 21 ¦ on the excessively long tail end of the body member. Given the 22 act that simplicity and weight are of special importance in 2~ the aerospace industry, there is a need for a blind fastener 24 assembly which has these attrlbutes.
The present invention overcomes the above-referenced 26 problems and provides a means for joining pie~es together ~uch 27 that improvements in strength and in integrity are achieved.
~8 In addition, the blind fastener assembly of the present inven~ion is relatively straight forw~rd ~n its configur~tion, light weight, and easy to ~n~tall utilizing conventional equipment.

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11546~9 1 5~M~ARY OF THE INVENTIO~
_ When a strong axially force is exerted on the end of 3 a hollow cylinder so as to put i. under compression, the 4 compressed column will buckle outwards at some random location around the cylinder. If ~he cylinder wall is of uniform thick-6 ness, buckle finally results in a radially projecting flange 7 around the circumference. This flange is generally skewed, 8 but by the use of the specific configuration of the present 9 invention, an annular flange i5 obtained having a certain, prede-termined configuration. In the past, blind rivets were not able li to achieve a reliable control for the buckle. However, the 12 present invention utilizes a stepped, hollow cylindrical buckle 13 sleeve having two different wall thickness portions arranged such 14 that buckle will occur at the circumerentially uniform divide 15 between the two wall thickness portions Iwith the resultant flange 16 being partially made up of the entire length of the thicker wall 17 portion on one side, and of an adjoining roughl~ equal, length lB increment from the longer and thinner wall portion of the cylinder 19 on the other side of the flange.
The present invention i5 directed to a blind rivet 21 fastening assembly which has a specific configuration such that 22 controlled buckling is achieved. The buckling sleeve mem~er as 23 broadly described above, is a long, hollow cylinder and can 24 come in a variety of different configur~tions. Preferably, a configuration which has two different thicknesses is used;
~S more specifically, a two-stepped model which has a centrally 27 spaced thinner wall portion separating two thicker end portions.
28 A step or shoulder is formed on the outside surface separatiny 29 the thinner wall portion ~nd the thicker wall portion at one 30 end, and a deep counter bore produce5 a step or ~houlder on the 31 nner surface at the other end.

~ llS4619 1 ~he rivet ~ody is designed with a tail section which aids 2 in controlling the buckling of 'che slee~e member. The ~ail ~ection 3 s configured so as to minimize problems due to eceentricity of 4 he bores in ~he sleeve and the rivet body and to assure a fully

5 eveloped primary buckling of the sleeve prior to arly contact with

6 ~he workpiece.

7 ¦ In addition to improvements in the ~uckle sleeve and ~ ~he rivet body, the assembly of the present invention utilizes 9 ~r, improved configuration for the mandrel for separating the ~hrow 10 ~way portion of the mandrel from the section whi~h remains so as to 11 ~roduce a clean, brittle fracture break instead of a cup-and-cone 12 ~reak of ductile fracture. The configuration of the m~ndrel is 13 uch that it eliminates the objectionably sharp residual burr 14 urrounding the fracture surface found on rivets of the prior art.
Yet another improvement in the mandrel involves an 16 lement referred to herein as a dummy notchn. This dummy notch 17 is formed adjacent to a brea~notch in such a way that the break-18 otch is flanked by both the dummy notch on one side and a lock-19 roove for the locking collar on the other slde. This enables the andrel of the present invention to fulfill a known metallurigical 21 ondition for raising the fracture strength of the breaknotch 22 ithout changinq the breaknot~h dlameter.
23 The novel features which are believed to be eharateristic ~4 f the invention, both as to its organization and method of opera-~5 ion, together with further obje~tives and advantages thereof, 26 ill be better l~nderstood from the following dèscription considered 27 n ~onnection with the accompanying drawings in which presently ~.8 referred embodiments of the invention are illustrated by way 29 f example. It is to be expressly understood, however, that the rawings are for the purpose of illustrat~on and description only 331 nd are not intended as a defin tion of the limits of the invention.

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1 BRIEF DESCRIPTION OF THE DR~INGS
FIGURE 1 is a oross-sectional view 3howing one embodi-3 ¦ment of the bl ind fastener assembly of the present invention.
4 ¦ FTGURE 2 shows the embodiment of PIGURE 1 in ~ first ~ lintermediate positlon.
6 ¦ FIGURE 3 shows the embodiment of FIGURE 1 in a 7 ¦second inter~ediate position.
~ ¦ EIGU~L 4 shows the embodiment of FIGU~E 1 wherein the 9 ¦buckle sleeve engages a surf ace of the workpiece.
10 ¦ FIGURE S shows the embodiment of FIGURE l in the flnally 11 ¦f ormed condit io n. ;~
12 ¦ FIGURE 6 shows a second embodiment of the rivet body of 13 ¦the present invention.
14 ¦ FIGURE 7 shows a third embodiment of the rivet body of 15 ¦the present invention.
1~ I FIGURE 8 shows a fourth embodiment of the rivet bod~ of 17 ¦the present invention.
18 i FIGU~E 9 shows both primary and secondary buckling o~
19 Ithe fourth embodiment of the present inventlon.
20 I FIGURE 10 is an enlarged view of the tail section of the 21 Irivet body of the first embodiment of the present invention.
22 ¦ FIGURE ll is an enlarged view of the first embodiment 23 ¦of the present invention prior to the throw away end of the mandrel ~4 ¦being removed.
25 ¦ FIGURE 12 shows the formation of hidden notches in the 26 ¦stem 5hank 5ection o~ the mandrel of the present invention.
27 ¦ FIGURE l~A an alternate conf iguration for the breaknotch.
28 ¦ FIGURE 13 al~o ~how~ the hidden notche5 formQd in the 29 ¦tail seetlon of the .~ndrel o the preRent inventlon.
30 ¦ FIGURE 14 shows the formation of the fracture in the 32 mandrel of the present invention.
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6~9 FIGURE 15 shows a cross-sectional view of another embocliment of the blind fastener assembly in accordance with -the present inventlon.
FIGURE 16 is an enlarged view showing the rear end of the rivet body and the forward end of the separate buckle sleeve of the embocliment of FIGURE
15.
FIGURES 17-20 show consecutive steps of buckle formation during installation of the blind 10 fastener assembly of FIGURE 15. ~ :
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1 DETAILED DESCRIPT~ON OF THE INVENTION
. . _ 2 Referring first to FIGURES 1-4, the fir6t embodiment 3 of the improved blind fastener assembly of the present invention is shown. The fastener ~ssembly 10 includes a generally solld 5 rod-shaped mandrel 12, a tubular rivet body 14, a buckle sle~ve ~ 16 and a locking collar 18. The mandrel 12 is slideably disposed 7 in the body 14 and sleeve 16, with the sleeve 16 at one end of

8 body 14 and the locking collar 18 at the other end thereof.

9 The mandrel 12 has an enlarged or flared stem head 20

10 at one end thereof f~rmed on a first section 12a. Head 20 is

11 configured to circumferentially engage sleeve 16. An intermediate

12 section 12c of mandrel 12 forms a shoulder 13 with section 12a,

13 and a plurality of pulling members 22 shown in phantom line are

14 located adjacent the other end 12b thereof. Pulling members 22

15 are configured to be engaged by an associated pulling tool 2~ such

16 as that illustrated and described in U.S~ Patent No. 3,915,055.

17 It is to be understood, however, that a wide variety of pulling

18 members and associated pulling tools ~re within the scope o the 1~ present invention. Mandrel 12 also has an inwardly extending 20 groove 26 of reduced cross-sectional diameter, compared with 21 sections 12a, 12b and 12c into which locking collar 18 is forced 22 as hereinbelow ~escribed. Adjacent the groove 26 is a breaknotch ~3 section 28 which is configured such that ~ection 12b of the mandrel 24 can be separated as also herelnbelow descrlbed.
Rivet body 14 has a generally tubular configuration and 26 includes an enlarged head 30 ~djaoent one end thereof, an inter-27 mediate ~hank portion 32, and R tail section 3B adjacent the other Z8 end ~hereof. Tail 38 i~ ~pecifically de5igned 50 ~6 to engage the 29 buckle sleeve 16. ~n the prefe~red embodi~ent, the ~hank portion 31 32 extend~ through allgned openings ln a pair of workpieces 34 . I
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1 ¦and 36. More specifically, the tail ~ection 38 of the body 14 2 ¦is formed, in the first embodiment, of two arched ~ections 40 3 ¦and 42. As one can see~ arched ~ection 40 has a ~omewhat l~rger 4 ¦diameter than ~rched section 42.
5 ¦ The buckle sleeve 16 has a generally tubular configura-6 ¦tion and includes a central thin walled section 44, a first thicXer 7 ¦end section 46 and a second thicker end section 4B. End sections 8 ¦ 46 and 48 are configured to form external and internal shoulder 5 ¦areas adjacent each end of the buckle sleeve 16. While not to be 1~ ¦limited to any specific method of construction, the internal ledge 11 ¦of shoulder 60 adjacent end 48 can be made by boring out the sleeve 12 ¦16 such that the diameter of the sleeve 16 is smaller adjacent the 1~ ¦rivet body 14. The external ledge or shoulder 72 adja~ent section 14 46 can be made by trimming the sleeve 16 so as to remove material from the o~ter surface thereof. Note that end 54 of sleeve 16 16 abuts directly against tail 38 in an end-to-end config~ration.
17 To install the first embodiment of the blind fastener 18 assembly 10 of the present invention in a pair of workpieces

19 34 and 36, a hole is drilled through workpiece~ 34 and 36. The hole in workpiece 36 is countersunk at area 50. Assembly 10 is 21 then inserted as one can see. The hole through the workpieces 22 34 and 36 is large enough to permit the stem head 20 of the mandrel 12 as well as the bu~kle sleeve 16 to pass therethrough. The rivet 24 body also passes through the opening, but is ret~ined by the X5 enlarged head 30 which engages the counter~unk area 50 in workpiec 26 36. Other means for limiting the travel of assembly 10 through 27 the workpiece i5 also within the scope of this invention.
28 An axial force is exerted on mandrel 12 by means of 29 pulling tool 24. More ~peci~i~ally, the pulling tool 24 engages 30 ¦ the pulling members 22, as illustrated and described with ~1 I . ' ~
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1 ¦reference to FIGURES 3-S of UOS~ Patent No. 3,915,055, for 2 ¦e~ample, This teehnique and the associated tool are ~onventional 3 ¦and thus a more detailed description of how an axial force is 4 ¦applied ~o the mandrel 12 will not be set forth ~n ~ny great ~ ¦detail herein. One can see, nowever, that a region 24a of 6 ¦the pulling tool 24 bearing upon the enlarged head 30 of the 7 ¦rivet body 14 serves mainly to contain the locking collar 18 8 ¦which bears the reaction force transmitted through the tool 9 ¦anvil 56 during pulling of the mandrel ~2. The cylindrical 10 ¦anvil member 56 within the tool 24 also provides an axial force 11 lon locking collar 18, thus forcing it against a tapered surface 12 153 and into recess or cavity 52 of the rivet body 14.
1~ ¦ Referring to FIGURE 1, one can see the assembly 10 14 ¦disposed through workpieces 34 and 36, prior to any forces being 15 ¦applied. As is shown, mandrel 12 extends through both workpieces 16 134 and 36 such that end 12b is gripped by the pulling tool 24.
17 ¦AS mandrel 12 is advanced axially by pulling tool 24, the second 18 ¦end section 48, and more specifically end 54 of the buckle ~9 ¦sleeve 16, is caused to press against arched section 42 of tail

20 ¦section 38. Further advance~ent of the mandrel 12 through the

21 ¦workpieces 34 and 36 as shown ln Y~GURE 2, causes an outward

22 ¦buckling of the buckle sleeve 16 to occur adjacent the second : ~;

23 ¦end section 48 thus forming a first outwardly extending ~nnularly

24 ¦shaped buckle 58. This buckling ls encouraged by the differences

25 lln thickness between second end sectlon 48 and 1ntermediate

26 ¦section 44. Thus, buckle 58 is found adjacent shoulder 60 as

27 ¦~een in ~IGURE 2. Note th~t buckle 58 ls formed of the entire 2~ ¦length of the thicker end ~ection 48 and a roughly equal length 2330 lincrem C of the thinner welled section i4, 521~

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~154619 1 Continued advancements of the mandrel 12 through the 2 blJdy 14l as shown in FIGURE 3, causes the buckle 58 to flex 3 f ~rther axially outward from the mandrel 12 so as ~o form a generally flat surface 62. As illustra~ed in FIGURE 4, further advancement of the mandrel 12 causes the buckle sleeve 16 to 6 flex further outward and to slide outwardly over the first and 7 second sections 40 and 42 and down ~he rivet body 14 thereby 8 engaging workpiece 34. In this manner, generally flat ~urface 9 ¦62 contacts the workpiece 34. Because of this fact, problems of point pressure associated with ripple ~leeves are substantially l; eliminated. This means that materials such as ceramics, plastics, 12 as well as metals and the like can be used as workpieces 34 ~nd 36.
13 Refereing now to FIGURE 5, the mandrel 12 has been 14 pulled through the workpieces 34 and 36 such that shoulder 13 is caused to abut against the tail 38 of the rivet body 14 16 simultaneously as lockgroove 26 comes ~nto alignment with cavity 17 52 and the collar is stuffed. This limits the travel of the 18 mandrel 12 and further extraction of mandrel 12 causes the distal ~9 end 12b to break off as hereinbelow described. As one can see, in the preferred embodiment a second buckle 70 is formed in the 21 buckle sleeve 14 adjacent the ~houlder 72 so ~s to form a trough 22 74 between buckle 58 and buckle 70. Uniformity of buckle 70, as 23 described abovel is encouraged by placement o~ shoulder 72 adjacent 24 thin walled section 44.
By the use of the configurat~on of the fir~t embodiment 2) of the present invention, problems of eccentricity of bores ;~ in both the buckle 51eeve 16 and the rivet body 14 ~re overcome, 2B ~ore eccentricity results in a blind h~ad which lacks roundness 29 and may only be partlally ~eated ~qainst t~e workpiece. In extreme cases, a croo~ed bl~nd he~d wlll be such ns to prevent 3Z 1~ 9.

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1154~;19 1 the s'ide of 51eeve 16 into contact with the ~s~ocia~ed workpiece.
2 However, by the use of the assembly 10 of the presen~ invention, 3 this is substantially overcome. Thus, a very stable, final 4 configuration (FIGURE 51 results which produces ~ Rymmetrical and ~ery strong blind head 76 with minimal pressure on he composite ~ ¦ material of workpiece 34. This is achieved by three processes 7 ¦ which occur more or less simultaneously during the formation o , ¦ buckle 58; to wit: rotation, pivoting and slide. Bore eccentricity 9 ¦ causes these processes to develop at nonuniform rates around the 0 ¦ periphery of the mating end of the buckle sleeve 16 with differen-11 ¦ tial rates of slide heing the most problematic of the three 12 ¦ processes. To control the slide problem, a ~stepped" form is 13 ~ designed into the tail section 3~ of the body 14. The depression 14 , or step is formed between the two domes o~ arcs 40 and 42. The 15 ¦ step serves to ensure that portions of the buckle sleeve 16 adja-16 ~ cent section 48 do not exhibit early slide over body 14 until 17 I the other lagging portions of 5ection 48 catch up. Thus, the slid 18 of sleeve 16 is temporarily stopped while the other two processes, rotation and pivoting, eontinue until the buckling wall of the buckle sleeve 15 rotates through an angle equal to or greater 21 than 90 deyrees as shown in FIGURE 3. Under the deformative force 22 of installation, the mating end surface 54 of section 48 of sleeve ~3 16 which is somewhat malleable, takes on the shape of the double ~4 arch of sect~ons 40 and 42 on the tail 38 of body member 14. This 2B shape is indicated in FIGURE 4 ag grooves 64.
26 When the result~ng symmetry obtained by the dela~ of 27 slide is completed, the slide process is re5umed in a uniform

28 manner untll the broad face or 8urace 6~ of the blind head 76

29 makes contact with the workpiece at area 66 as shown in FIGURE
4. Distribution of the force of contact over the broad footprint 332 ~
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11546~L9 1 ¦of the contacting ~urface 62 allows for ~ low pre5Bure in pounds 2 ¦per sq~are inch making it relatively impos6ible to damage the 31 workpiece 34 and/or 36.
¦ While the stepped radius form for the tail 3B~ as ~hown 5 ¦in PI~URE 4, is preferred, other configurations for ~ail 38 ~re 6 ¦also within the ~cope of the present invention.
7 ¦ Refereace is now made to ~IGURE 6 in which a second 8 ¦alternate configuration for the tall 6ection 38 is shown. In ¦this configuration, rivet body BO has a first annular section 82 lO ¦a second annular section 84 joined by an intermediate section 11 ¦86 thereby forming a step therebetween. Mandrel 81 extends 12 ¦thro~gh the rivet b~dy 80 and the buckle sleeve 88 as in the 13 ¦first embodiment of the present invention. The formation of a 14 ¦step between ~he first and second sections 82 and 84, respectively, ~;
15 ¦also prevents problems of eccentricity a!g discussed hereinabove.
1~ In this manner, end 92 formed on the thicker se~tion 90 engages 17 the second ann~lar section 84 and causes the buckle sleeve 88 18 to flex outwardly therefrom as the mandrel 81 is withdrawn.
19 As the sleeve section 9O buckles outward from the mandrel 81, it ZO ¦will remain in the ~tep region 85 until the configuration of 21 IFIGURE 3 is achieved. Ultimately, an outwardly extending ~ection 22 lor buckle is formed which is caused to engage the workpiece 34.
23 ¦ In FIGURE 7 a third variation is shown. In this embodi-24 ¦ment, the rivet body 94 and buckle ~leeve 88 are formed with 25 ¦~andrel 95 passing therethrough. The rivet body 94 has a generally 26 round or convex arched top 9Ç terminating in an ~rched concave ~!7 ~ection 98. The thicker section 1~2 of ~leeve 100 ad~acent end 104 28 would lnitially be di~posed on top 96. As the mandrel 95 is 29 withdrawn, sleeve 100 would bu~kle outward ~nd ~lide down adjacent

30 the workpiece 34 as shown in FIGURE 7. ~hile this configuration

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~ 6~9 ~ ¦ is not believed to be as effective in con~rolling eccentricity 2 ¦as the first embodiment, a good Nfootprint~ with ~orkpiece 34 3 ¦ is still achiev.?d.
4 ¦ Referring now to FIGURE 8, one can see a fourth ¦embodiment for the rivet body 106. In this embodiment~ body 106 6 ¦is formed with a first round sec'ion 108 and a second inclined 7 ¦section 110 extending outwardly therefrom. Buckle sleeve 112 8 would initially mate with sectie~ln 108. Continued withdrawal of 9 ¦mandrel 118 would thus result in the buckle formed as i n FIGURE
8 where a single fold and much extension of the ~ody tail beyond 11 ~he workpiece's inaccessible surface 34 indicating that minimum 12 grip ins~allation is achieved. By the same logic in FIW RE 9, 13 the double fold and little body tail protrusion indicate maximum 14 grip installation.
Referring now to FIG~RES 10-14, the fracturing of section 16 12b of the mandrel 12 from section 12c is illustrated. Referring 17 first to FIGURE 10, one can see that the mandrel 12 has progressed 18 hrough the rivet body 14. When the mandrel 12 has been further ~9 ithdrawn, as in FIGURE 11, shoulder 13 is engaged by the tail 8 such that further withdrawal of mandrel 12 is lnitially pre-21 ented. Simultaneously, the spring loaded tool shroud 24a around 22 he locking collar 18 allows the tool anvil 55 to move in the pposite direction o~ mandrel travel causing the collar 18 to 24 e stuffed into the now adequate void provided by ~lignment of he mandrel lockgroove 26 and the recess 52. Further pull on 26 he mandrel 12 encourages fracture at a first hidden groove or 27 rea~notch 126 preformed ln the breaknotch section 28. Prior art 2 ivets which used this type of concealed breaknotch on the mandrel 29 ¦~xhlbi a sh~rp, forw~rd pointLng kn1fe edged burr peripberrlly 32 1 12, ., 461~ 1 1 formed around the fracture ~urface, giving possible rise to both 2 pre-installation and post installation problems. The former 3 problem usually shows ~p as premature stem fracture since the 4 forward pointing burr tends to gore into the loc}cing collar ~ as the ~andrel advances. As a result, the prior art stem may 6 break below the workpiece surface and the locklng collar 7 may not be properly stuffed. In the event that acceptable break B and collar stuffing are obtained, the latter problem ~ppears as ~ an objectionably sharp burr protrusion above the workpiece surface.
10 ~ot infrequently, this knife edge protrusion has to be removed 11 by a secondary shaving operation which adds expense to the installa-12 tion process. Secondly, shaving may be possible on aircraft 6kins ~ made from metals, however shaving can be very damaging for new 14 eneration skins made from graphite/epoxy composite materials.
It can be seen in ~IG~RE 14 tlat the present invention 16 eliminates the sharpness from the burr 134 surrounding the fracture 17 surface 140. This is achieved by a unique manufacturing process 18 referred to as a reversal of roll form. More specifically, the 19 form which appeared on the throwaway portion of the stem on prior 20 art is now incorporated on the retained portion of the stem 12c 21 of the present invention. As shown in ~IGUP~E 14, the ~harp burr 22 and cup shape 134a now appear on the throwaway pintail portion 12b ~3 of the mandrel 12. More acceptable alignment between the rounded 24 urr surface 134 and the ~racture surface 140 results from the ~5 improved manufacturing oper~tion.
26 ¦ FIGURE 12 explain~ this improvement ln the product and 27 ¦rel~ted manufacturing operation by showing the breaknotch angles ~8 ¦and shoulder burr rolllng ~equence. Prior ~rt reversed the 29 ¦location of ~he 40/20 degree ~ngles of the bre~knotch form as 30 ¦shown. In the present invention, by incorporatinq the larger 40 332 degree angle on the lockgroove 26 ~ide of the notch 12~ ~ont~ining 1 13.

~154619 1 the first radially larger annular burr 132, the root of the 2 notch 126 ~here rac~ure is to occur is initially ~epar~ted from 3 centerline of the notch a greater distance than that which 4 w~uld be realized from the smaller 20 degree angle. Under burr 5 flattening pressure, the larger burr 132 tends to elongate 6 axially across the breaknotch 126 and to overrun beyond the 7 centerline of the notch 126. However, the arrangement of the 8 angles as shown in FI~E 12 assures less overrun than if the 9 angles were reversed so that in the final run there is better 1~ alignment between the burr periphery and the fracture s~rface.
11 Instead of using dissimilar angles, a symmetric notch with 30 12 degree angles on each side as shown in FIGURE 12a is s~ill in 13 keeping with thls improvement, and the ~orkable range of values 14 for the included notch angle is 45 degrees to 70 degrees.
Concerning bure flattening sequence, in the past, this 16 was done with a pair of flat tools 130 and the mandrel was rolled 17 between them. The tools were arranged such that the higher burr 18 132 was flattened before the lower b~rr 132a; the first burr 132 lg flattened thus spanning the notched orifice 126 with a sharp leading edge and with a rounded cavity beneath. However, in the Xl present invention, the lower burr 132a is deliberately flattened 2~ first as shown in FIGURE 12 causing the sharp leading edge and 23 the rounded undercavlty 134a to appear on the throwaway pintail 24 portion 12b of the mandrel 12 as seen in ~GVRE 14. Sub~equent ~5 flattening of the higher burr 132 force5 it to flow into the 26 undercavity 134a with the rounded form 134 remaining on the useful 27 portion 12c of the mandrel 12 ~fter fracture. Thus ~harpne~s ~nd 28 excessive protrusion are eliminated making a secondary shaving 29 opetation unnecessary. The ~tepped face roll~ng tools 130 shown ~n FIG~RE 12 pres~ the Bpar5e material contained in the 5maller 1~ 14.

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1 burr 132a below the mandrel diameter to make sure that the sharp 2 burr and undercavity are formed on the throwaway pintail portion 3 2c of the ~andrel 12. Travel of the mandrel 12 through tools 4 30 causes third and fourth burrs 132b to form the second hidden ~ notch 128.
6 I F~GURE 13 shows the finished view of the region at the 7 ¦end of the rolling operation. Observe that both the dummy notch 8 ¦128 and the breaknotch 126 are concealed and the lockgroove 26 9 ¦alone remains open. The slightly reduced diameter at the 10 ¦region of the concealed breaknotch 126 lowers the frictional 11 ¦drag against the lockcollar 18 facilitating slide into the 12 ¦lockgroove 26 without aggravating premature stem break problems.
13 ¦ Finally, with respect to the dummy notch 128, it is a 14 ]cnown principle that auxiliary notches imposed on the two sides 15 of a test notch, raise the strength level at which the test 16 notch will fail. One such auxiliary not:ch is provided by the 17 lock groove 26 so that a dummy notch 12B on the other side of 18 ~he break notch 126 fulfills the criter:ia for raising the fracture 19 strength for a given break notch diameter. With this improvement ; ~ -~
2~ maximum possible strength i5 extracted from the mandrel 12 to 21 resist any tendency toward premature stem breaX while retaining 22 a small enough breaknotch diamter to restrict a clean fracture ~3 to the root of the breaknotch 126 without carrying away a portion 24 of the lockgroove shoulder with the fracture.
Another improvement of the assembly 10 of the present 26 invention relates to the configuration of the countersunk portion 27 50 in workpiece 36 and the associated enlarged head 30 of body 14 28 In the preferred embodiment, a straight walled, shallow counter 2g bore 124 (see FIGURES 10 and 11) in the head 30 of rivet body ~O 14 serves to confine locking collar lB and also serves to conceal 15.

,.11., ~5~6~9 1 I the slightly projecting rounded burr 134 thus eliminating any 2i protrusion above necessary flushness limits associated with 3~ aerospace technology.
4 ¦ Having thus described several embodiments of the present ¦ invention~ it should therefore be understood that other changes 6 ¦ and modifications can be made without departing from the true 7 scope and spirit of this ~nvention as recited in tlle appended a claims. For example, in the preferred embodiment, mandrel 12 9 has knurled section regions 120 and 122 formed along the length thereof. One of these knurled regions 120 within the body member 11 14 provides friction to hold the preassembled rivet components 12 a~ainst inadvertent dissembly during handling or installation 13 ¦and the other exposed knurl 122 prevents the locking collar 18 14 ¦from inadvertently falling off the mandrel 12 before installation.
15 ¦ Yet another embodiment 10' of the inventive "buckle 16 ¦bolt" blir~d rivet assembly is shown in FIG~R~S 15 through 20.
17 There, the mandrel 12 has the same conflguration as in the 18 earlier embodiments, and the rivet body 14' has substantially 19 ¦the same double arched or double domed configuration as in 2~ ¦the embodiments of FIGURES 1-5, 10, and 11. As an option, the 21 lend dome may have a small flat 144 against which the buc~le 22 ¦sleeve abutts. The buckle sleeve 16' is similar to the sleeve 23 ¦16 shown in earlier embodiments, but now is provided with an 24 ¦outer step 145 in addition to an inner step 146 near the forward 25 ¦or buckle forming end 48' of the buckle sleeve.
26 ¦ Advantageously, but not necessarilyj a small counter-27 ¦bore 147 may be formed in tha end of the rivet body 14' 2~ ¦beneath the first or end dome 42~o As that dome is formed 29 ¦during the manufacturing process, a burr 148 may be produced 30 ¦at the leading edge of the counterbore 147. If the counter-31 ¦bore 147 were not present, this burr might extend into the ~2 //
16.

11S46~L9 1 the fon~ard opening of the rivet body 14' and interfere with ~ the initial assembly of the rivet body onto the mandrel 31 12. The counterbore 147 eliminates this potential problem.
4 Advantageously the radial thickness re of the forward end 48' of the buckle sleeve 16' (FIG~RE 16) is greater 6 than the base thickness rd of the first or end dome 42' on 7 the rivet body 14'. ~his aids in assuring that initial 8 partial buckle formation will occur while the end 48' of the 9 ¦sleeve 16' is still abutting agAinst the end dome 42'.
Preferably, the outer step 145 is situated sli~htly 11 "behind" or further away from the forward end 48' of the 12 buckle sleeve 16' than the inner step 146. The outer step 145 13 i5 formed by reducing the outside diameter of the buckle sleeve 14 16' in a re~ion 149 extending from the forward end of the buckle sleeve to the location of the step 145. From there 16 rearward, the buckle sleeve 16' has a thicker outside diameter 17 ¦correspondin~ to the central walled section 44 in the earlier 18 ¦embodiments. Some typical dimensions for an illustrative 19 ¦"buckle bolt" asse~bly 10' are as follo~s:
20 I Mandrel diameter: .133 inch 21 ¦ Rivet body inside dlameter: .136 22 ¦ Rivet body 14l maximum outside diameter: .190 23 I End dome 42' base thickness rd: .017 24 ¦ Counterbore 147 inside diameter: .142 25 ¦ Length of counterbore 147: .015 26 ¦ Buckle sleeve end radial thickness~re: .022 27 ¦ Buckle sleeve 16' forward end inside 28 ¦ diameter: .134 29 I Buckle sleeve forward end 149 outside 30 ¦ diameter: .177 31 Distance of inner step 146 from buckle 32 sleeve forward end: 050 ,,.11,.~

2 1l Inside diameter of buckle sleeve rearward 3 of inner step 146: 147 inch 4 Distance of outer step 145 from buckle sleeve forward end: .070 6 Outside diameter of buckle sleeve at 7 location of wall section 44: .183 8 The double step arrangement of the sleeve 16' aids 9 in pre-formation of the buckle prior to contact with the workpiece 34, 36. This stepped buckle formation is shown in 11 ¦FIGURES 17 through 20.
12 ¦ As the mandrel 12 initially is pulled during the 13 installation process, a partial buc~le 150 begins to form ~4 while the forward end 48' of the sleeve 16' is still abutting a~ainst the first or end dome 42'. This is aided slightly 16¦ by a tendency c~f the forward end 48' to bite into the 17 ¦counterbore 147 as buckle ormation first be~ins. The bucklc 18 ¦150 itself forms at a region between the inner ste~ 146 and 19 ¦the outer step 145. The presence of these two steps substan-20 ¦tially elimin~tes nonuniformity or skewing of the buckle being 21 ¦formed. That is, the buckle radius at any particular time 22 ¦during buckle formation is uniform around the entire periphery 23 ¦of the sleeve 16', and ls also uniformly spaced from the 24 ¦forward end of the buckle sleeve.
25 ¦ After the buckle lS0 has partially formed as shown 26 ¦in FIGURE 17, continued pulling of the mandrel 12 results in 27 ¦the sleeve end 48' sliding up toward and ahutting against the 28 ¦second dome 40', as shown in FIGURE 18. The second dome I ~ ¦provides additional resistance so that as the mandrel 12 is 30 ¦pulled further, bulb or buckle formation is essentially ~ 321// 1~.

~.~ 54619 ¦lcompleted, as shown in FIGURE 19~ The second dome also prevents 2~flaring or radial spreading of the forward end of the buckle 3 sleeve.
As the mandrel 12 is pulled even further, the now 5 ¦essentially completely formed buckle 150' slides over the 6 Ithe second dome 40' and advances along the outside of the 7 ¦rivet body 14' (as shown in FIGURE 20) until it comes in 8 contact with the workpiece 34p 36. Preformation of the buckle 9 results in broad area contact with the workpiece, making the inventive blind rivet especially useful with composite work-'~1 ¦piece materials such as graphite/epoxy. Unlike the prior art, 12 there is no initial contact of the workpiece by the forward 13 end of the buckle sleeve, following by rotation of that end 14 ¦as the blind bulb is formed. Such prior art blind bulb 15 ¦formation tended to gouge the workpiece, and thus was ~¦
16 ¦particularly damagin~ to a graphite/epoxy matrial. Although 17 ¦not shown, installation is completed when the shoulder 13 18 ¦contacts the end of the rivet body 14' and the locking collar 19 18 1s inserted into the lock groove 26 (similar to FIGU~E 5).
Finally, the projecting end of the mandrel 12 is broken away.

19.

Claims (9)

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

1. A blind rivet assembly of the type having a mandrel with an enlarged head at one end, and having a rivet body and a separate buckle forming sleeve dispos-able about said mandrel with the rear end of said buckle sleeve against said enlarged head and the forward end of said buckle sleeve abutting against the rear end of said rivet body, said assembly being useful for fastening a workpiece from one side thereof, the improvement wherein:
the rear end of said rivet body has a double domed configuration including an end dome extending forwardly from said rivet body rear end and having a minimum diameter at said rear end and a maximum diameter where the end dome terminates and a second dome begins, said second dome extending with increasing diameter forwardly from the termination of said end dome, said buckle sleeve having a central walled section and having a forward end section which abuts against the end dome of said rivet body, the inner diameter of said central wall section being greater than the inner diameter of said forward end section so that there is an internal shoulder at the rear of said for-ward end section, the radial thickness of said forward end section being greater than the radial thickness of said central walled section, the length of said rivet body being greater than the thickness of said workpiece, so that during installation, as said mandrel is translated forwardly while counterforce is exerted axially rearwardly on said rivet body, said buckle sleeve will begin to buckle while said forward end section is still abutting against said rivet body first dome, said buckle initially forming in the vicinity of said internal shoulder, con-tinued mandrel translation causing said buckle sleeve to slide over said end dome into abuttment with said second dome, the increased resistance of said second dome to forward movement of said buckle sleeve resulting in continued buckle formation as said mandrel is translated further forward, so that said buckle is substantially completely formed against said second dome, further continued forward translation of said mandrel causing said substantially fully formed buckle to expand over said second dome and to translate axially along the exterior of said rivet body into firm abutting relation-ship with said workpiece.

2. A blind rivet assembly according to claim 1 wherein the inner diameter of said buckle sleeve forward end section is substantially the same as the inner diam-eter of said rivet body, each of said inner diameters being slightly greater than the outer diameter of said mandrel.

3. A blind rivet assembly according to claim 1 wherein the outer diameter of said buckle sleeve forward end section is less than the outer diameter of said central walled section so that there is an external shoulder at the rear of said forward end section, said external shoulder being situated a greater distance further from the forward end of said buckle sleeve than is said internal shoulder, said buckle initially forming in the region between said internal shoulder and said external shoulder.

4. A blind rivet according to claim 1 wherein a shallow counterbore is provided at the interior of the rear end of said rivet body, beneath said end dome.

5. A blind rivet assembly according to claim 1 wherein said assembly further includes a locking collar, and said mandrel has a locking groove which receives said locking collar during installation of said assem-bly, said mandrel having a section which is removable after installation, the further improvement wherein:
said mandrel has a breaknotch formed adjacent said locking groove, said breaknotch being configured to aid in the formation of a clean break between said removable section and the remainder of said mandrel, said breaknotch being formed from two angled sections, the angle of the first section being approximately 40 degrees and the angle of the second section being approximately 20 degrees, said first section being closest to said locking groove, and the range of values for the included angle of the breaknotch being 45 degrees to 70 degrees.

6. A blind rivet assembly according to claim 5 wherein instead, the angle of the first and second sec-tion each is approximately 30 degrees, and the range of values for the included angle of the breaknotch is 45 degrees to 70 degrees.

7. A blind rivet assembly according to claim 5 wherein said first angled section is formed with a first burr and said second angled section is formed with a second burr, said first burr being greater in diameter than said second burr.

8. A blind rivet assembly according to claim 5 wherein there is formed within said breaknotch first and second flattened burrs with said first burr being shorter than said second burr and being situated in said breaknotch above said second burr, said first burr extending from the side of said breaknotch on said removable section.

9. A blind rivet assembly according to claim 5 wherein said mandrel also has a second notch which is a dummy notch configured to raise the fracture strength of said breaknotch.