IL35234A - Bimetal rivets - Google Patents

Description

Bimetal riveta I The use of special alloys and metals for rivets has been increasing over recent years. This is especially true where high strength at elevated temperature is required, as for example, in the aircraft and aerospace industries. In these applications also light weight has always been of considerable importance.

For such applications titanium and titanium alloys have found much favour.

Other alloys have also been found favourable but all these, including the titanium alloys, present a common problem. A material which offers satisfactory strength properties is usually - *,« difficult to rivet by conventional methods. They do not have sufficient ductility and are not readily formable into a rivet head. This oflen results in the formation of an unsatisfactory rivet or the actual splitting of the head during riveting.

It is therefore an object of the invention to provide a rivet of a high strengh alloy such as those of titanium on which it would be pos sible to form a satisfactory rivet head.

In accordance with this invention, there is provided a bimet. rivet having a head and shank section composed of metal having relatively high shear and tensile strengths and a tail section compos of a relatively ductile and formable material, the head and shank section being integral with the tail section at a pair of interfaces of the sections. ~ The invention is more particularly described hereafter with reference to the accompanying drawings, wherein: - Figure 1 is a cross- section through a riveted joint showing one bi-metallic rivet before driving and one after driving under one set of conditions^ Figure 2 is a cross - section through a riveted joint showing one bi-metallic rivet before driving and one after driving under another set of conditions; Figure 3 is a cross- section through a riveted joint showing bi-metallic rivets having a spherical interface; ' ' Figure 4 is a cross- section through a riveted joint showing bi-metallic rivets having an alternate embodiment of curved interface; Figure 5 is a cross- section through a riveted joint showing bi-metallic rivets having an annular interface.

Referring now more particularly to Figure 1 and Figure 2, . being there are seen plates 1 and 2 in the process of trrc-rrg joined together by rivets 3. A flat or counter- sunk head rivet is shown in Figure 1, while a button head rivet is shown in Figure 2. Our invention may be adapted to any style of rivet head, as will become evident from what follows. The body or shan k/of the rivet 4 is joined to the tail section 5 at interface 6. It fs evident that in each Figure, one rivet is shown before driving and one after driving. The location of the interface 6 is shown before driving and 6a after driving. After driving, the driven head appears at 7, the lower portion of the rivet at 8, and the upper portion at 9· In previous constructions attempts have been made to heat treat the tail section 5 of the rivet, which was composed of a single metal, in order to render it more ductile and formable. This, however, resulted in a gradual change in properties of the rivet shank and not a sudden change. Consequently, when the rivet was driven, the upsetting action of the shank was not uniform and the rivet did not completely fill the rivet hole at the upper section 9 as shown on Figure 1. To develop its proper maximum strength, the rivet shank or body should completely fill the rivet hole as shown at 9 in Figure 2, as is well known to those skilled in the art.

Attempts have been made to overcome this by using a washer between plate 2 and head 7 to facilitate formation of the head in a difficult to- deform rivet shank. Use of the rivets of the present invention, of course, eliminates the need for a washer, enables a satisfactory head 7 to be provided, as well tory as a satisface-feyr rivet bearing in the rivet hole, as shown at 8 and 9 in Figure 2.

For the shank, or body section 4 of the rivet, materials having a shear strength of up to^l 80, 000 pounds per square inch, a tensile strength of up to 300, 000 pounds per square inch at room temperature and an acceptable strength at temperatures Og. as high as 1000 degrees F, may be used.

Materials used for the tail section 5, besides being ductile and readily formable, should be compatible with the material used for the shank section 4 insofar as being capable of joining integrally with one another at an interface 6 by means of friction welding or other integral forming processes known in the art. Materials so have been discovered that may be/combined to form the unusual rivet of the invention are tabulated below.

TABLE I Head and Shank Section Tail Section 3 and 4 Pure Titanium Columbium Alloy Cb-lZr " " Cb-lOW " " Cb-752 Tantalum Alloy FS 60 Zirconium Alloy Zirconium 2 Pure Vanadium Pure Molybdenum Ti-8Al-lMo-IV Same as above for all materials.

Ti-6Al-6V-2Sn Same as above for all materials.

Ti-13V-llCr-3Al Same as above for all materials H-11 A- 286 Stainless Steel - Monel VascoMax 300 A-286 Stainless Steel - Monel Vasco 300 designates Vanadium Alloys Steel Co' s alloy consisting of approximately 18 % nickel, 9 % cobalt, 0. 5 % molybdenum, 0. 6% titanium, 0. 1 % aluminium and 0. 02 % carbon.

The chemical composition of materials represented by the other material symbols used herein may be found in the publication DMIC Memorandun 232 dated February 1 , 1968, entitled "Designatio: of Alloys for the Aerospace Industry (Revised)" and published by Defense Metals Information Center, Battelle Memorial Institute, Columbus, Ohio 43201.

The actual configuration of the interface 6 between the two different metals is important. As stated above, this joint may be formed by any integral joining proces s such as friction welding, metallurgical bonding of the pressure, vacuum or diffusion type, as well as fusion welding by means of electron or laser beams.

Various configurations which we have shown to be particularly advantageous are shown in Figure 3, Figure 4 and Figure 5. In each case, the interface before driving is shown at 6 and after driving at 6a. It should be noted that in all instances the interface must bear a definite relation insofar as position is concerned to thepilates 1 and 2. For the flat or plane interface shown on Figure 1 and Figure 2 it is essential that it lie within the confines of the outside planes of the sheets which define the grip of the rivet. In the case of the configurations shown on Figure 3, Figure 4 and Figure 5, the interface must lie substantially within the grip- of the rivet as described more fully below. , All of the configurations shown in Figure 3, Figure 4 and Figure 5 provide a greater surface ar ea between shank section 4 and tail section 5, thus providing for a stronger integral joint. In addition to forming a satisfactory head 7 including expansion of the tail section 5 into the opening in plate 2 as shown, they all facilitate the upsetting of the shank 4 as discussed above and described more fully below.

Thus, in Figure 3 there is shown a spherical interface 6 which is convex as to shank section 4 and concave as to tail section 5. With this configuration it has been discovered that a good head 7 may be formed while also providing form improved expansion of the shank 4 into the holes in plates 1 and 2 as shown.

In the configuration of Figure 4 there is provided what is called a male and female type of interface. This comprises a substantially deeper penetration of the shank section 4 into the tail section 5 than that provided in Figure 3. The shank sect i on protrudes a considerable distance beyond the outer surface of plate 2 and hence the riveting action produce s a greater upsetting effect upon shank section 4 insuring more compl filling of the hole s in plates 1 and 2 by the rivet shank.

In the annular configuration shown in Figure 5, the shank section extends through the entire length of the rivet and the tail section is positioned concentrically around the outside of the shank section. The tail section likewise penetrates into plate 2 in this configuration. Upon formation of the rivet head 7 there is seen an expansion of the shank section 4 to completely fill the holes in plates 1 and 2 and also an upset of the shank section 4 outside the plate. The rivet head formed in a tail section surrounds this upset portion of the end of the shank section and also penetrates inside the hole of plate 2, thus producing a vastly superior head.

Of the three configurations disclosed herein it is evident that Figure 3 is the simplestand most economical to manufacture, whereas Figure 5 is the most difficult. The decision as to which configuration to use is a question of economic s coupled with the stringency of the requirements of the application, and degree of resistance to expansion of the material used in the shank. All have their advantages, as disclosed above and, it is submitted, are novel and distinct with respect to one another.

The integral forming processes which may be used to form the joint between the two sections of the rivet, employing these configurations, are the same as thosedisclosed for the flat plane interface of Figure 1 and Figure 2 described above.

In connection with bimetal fasteners where the individual sections are composed of materials having substantially different chemical compositions, for instance, the combinations hereinabove recited, the fasteners may be subjected to heat treatment after the sections are welded together, with the result that the head and shank material is hardened to a relatively high shear strength while the tail material remains or is made appreciably lower in shear strength and with sufficient ductility to be readily formed or upset without cracking.

The required union can be accomplished if the head and shank section is subjected to heat treatment and the tail section also subjected to heat treatment separately prior to welding so that the head and shank section is treated to have a relatively high shear strength and said tail section is pretreated so as to have appreciably lower shear strength and sufficient ductility to be readily formed or upset without cracking. When the sections are heat treated separately prior to welding it is pos sible to use materials of the same composition for both sections or of substantially different compositions for the two sections.

Examples of materials where the same material is used for both sections and may be heat treated as aforesaid are: Ti-6A1 -4V, Beta III (Ti- 1 1. 5 Mo-6Zr-4. 5Sn), Ti-8Mo-SV- 2Fe- 3Al , and Beta C (Ti- 3Al -8V-6.Cr-4Mo-.4Zr).

Examples where the two sections are of different materials " and are treated before welding, are: Ti- 6A1 -4V for the head and shank section; and Pure Titanium, Ti-3Al - 2, 5V, Beta III (Ti- 1 1. 5 Zr- .5 Sn Mo-62n*4rȣrr), / -8Mo-8V-2Fe- 3Al , or Beta C (Ti-3Al -8V-6Cr-4Mo-4Zr) for the tail section.

Further examples of materials of like or nearly like chemical composition heat treated to different conditions as separate parts prior to welding, are as follows: HEAD AND SHANK SECTION TAIL SECTION 6A1-4V titanium solution treated 1625 6A1-4V titanium annealed 1 hr lO^1 WQ-aged 100C° 4 hrs.10~4AC 1325° 1 hr 10-4 AC Betta III titanium (nominal composition Beta III titanium solution 11.5 Mo-6Zr-4.5Sn) solution treated treated 1275-1300 5 min. 1325-1350° 5 min. 10~4 WQ aged 900° lO^4 WQ - aged 1100° -4 4 hrs. 10~4 AC 4 hrs. 10 raised to 1175 1-1/2 hrs. 10^ AC 8Mo-8V-2Fe-3Al titanium solution 8-8-2-3 titanium hot rolled, treated 1425° 5 min. 10~4 WQ, - straightened and ground aged 900° 4 hrs lO^4 AC Beta C titanium (nominal composition Beta C titani oum solution 3Al-8V-6Cr-4Mo-4Zr) cold dr,awn 39% treated 1500 mins. and aged 900 4 hrs AC " * - AC The above mentioned heat treated conditions would not be obtainable by heat treating the above metals after welding.

Additional examples of metals and their heat treatment before welding are as follows: HEAD AND SHANK SECTION TAIL SECTION 6A1-4V titanium solution treated 1625 1 hr Pure Titanium "4 WQ - aged 1000° 4 hrs 10~4 AC Betta III titanium golution treated 1275-1300 5 min. ~4 WQ-aged 1100° 4 hrs. lO^4 raised to 1175°l-l/2 hrs. 10~4AC 8-8-2-3 titanium hot rolled, straightened and ground Beta C titanium solution treated 1500 15 mins. lO^ AC In the above examples: AC stands for Air Cool WQ stands for Water Quench - is degree of vacuum expressed in Torr units.

Claims (3)

WHAT WE CLAIM IS:

1. A bimetal rivet comprising, a solid head and shank section of a metal having a high shear and tensile strength at room temperature and up to at least 1000 degrees F, a tail section of a ductile and readily formable metal being compatible with th metal of the head and shank sections for integral union therewith, the shank of said head and shank section and said tail section being of the same diameter , said tail section and the shank of said head and shank section being united end to end and forming an interface between their meeting ends, said interface being positioned within the grip length of said rivet, said interface comprisin a friction welded joint, said head a«d shank section comprised entirely of an alloy selected from the group consisting of T1-6A1-4V, IV Ti-8Al-IMo-i¥, and Ti-.13V-llCr-3Al^ and said tail section comprised entirely of a metal selected from the group consisting of titanium, vanadium, molybdenum, Cb-lZr, Cb-752, Cb-lOW-lOTa, tantalum FS60 Z and eirconium 2.

2. A bimetal rivet as claimed in Ctlaim 1 said head and shank section comprising entirely the alloy H-11 and said tail section comprising entirely an alloy selected from the group consisting of A-286 stainless Monel steel and Η.ΟΒΒΊ, said interface comprising a" friction welded joint.

3. A bimetal rivet as claimed in Claims 1 or 2, said head and shank section comprising entirely VascoMax 300 and said tail section comprising entirely an alloy selected from the group consisting of A-286 stainlee steel and moneli . A bimetal rive* as claimed in Claims 1, 2 or 3, said interface comprising an integral welded Joint. 5» In a method of making a bimetal rivet having a solid bead and shank section and a solid tail section of the same diameter, hea treating the head and shank section separately from the tail section to high shear and tensile strength, heat treating the tail section separately to be ductile and readily fo mable, and friction weldin said sections together end to end into an integral unity V