High quality resistance spot welds were produced by welding through epoxy adhesive on titanium alloys. Weldbond joints were consistently stronger than those of either mechanical fasteners, structural adhesive bonds, or mechanical fasteners with adhesive at the joint interface. Weldbond joints and/or spot weld joints showed superior strength at all temperature ranges as compared to other joints tested

Fields, D.

English

NASA Technical Reports Server

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ABSTBBCT 
This paper presents a digest of work performed under Contract F33615-714-1099 
f o r  the Pabrioation Branch, Xaau8aoGuring Teohnology Mvision, BFML, Air Force 
Sgsterna Command, Wright Patterson Air Foroe Base, Ohio. Dafa d i s o ~ a e d  within 
the scope of this paper resulted primarily from this program &io& established 
the basic parameters f o r  joining titanium alloy urring the resistance spot weld- 
adhesive bonding (Weldbonding prooess) , 
The writer wishee t o  gratefully saknowledge the technioal and adn~inietrativei 
efforts of Mr, Frerdrick B, Miller, A i r  Form Mansger f o r  the Weldbond Program, 
and Mr. G a i l  E, Eiohelmen, Bot- Chief, Mstals Branch, AFML. The ef for t s  of 
both Mr. Miller and Mr. Eichelmsa have omtributed greatly t o  the advanoement 
of Weldbonding from a specimen stage t o  a fUl saale produotion process, 
INTRODUCTION 
Beginning i n  1965, experimenbl work at Lookheed-Georgia Company i n  resistance 
welding through high strength strwtural adhesives produced a prooesa whereby 
exceptionally high mechanical strength properties oould be obtained in aircraft 
jo in ts  fabricated from aluminum alloy8, Conti&d work with adhesive formulatiom, 
and continued Improvement in  weldips teohniquea further advawed the repeatability 
of the process t o  a point where large scale 
https://ntrs.nasa.gov/search.jsp?R=19740022815 2020-03-17T15:09:32+00:00Z
In  July, 1969, the Fabrication Brmch, Manufacturing Technology Division, A i r  
Force Materials Laboratory awarded a contract t o  Locl&eed.Georgd.a Company 
- f o r  the purpose of building and testing a f u l l  scale aluminum aircraft fuselage - .  
section joined by the spot weld-edhesive bon- (WeXdbon&hg) process. 
Results from the successful oompletion of the program encoursged the continued 
development of a weldbonding technology that would encompass other materials 
and other conditione. 
Many military amraft operate under conditions of stress and tempersture 
that are beyond the design limits of aluminum alloy, regardbee of the 
joint  fastening system used. Deve lopn t  and u t i l i ea t ion  of the weldbonding 
process in titanium alloys would grea%ly inarease the ueefulnees of the 
! weldbonding process for the military customer. 
The overall objective of the program diauusaed herein was t o  further advance 
manufacturing methods related processes of weldbond In high e t r e e h ,  heat and 
corrosion resistant alloys. 
In order t o  establish baeiu jo in t  s t a t i o  strength d t e r i a  for  weldbonded 
titanium joints  at room and elevated temperatures end t o  establish weldability 
using various adhesives, the following program objectives were outlined: 
c 
1. Select an adhesive f o r  optiPaum uormpatibility with weldbmdbg of 
titanium alloy. 
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2 
2, Establish resistance spotweld schedules and obtain certifioatione 
of weldbond joints  t o  meet minimum requirements of MIL Specification 
mfw-6858c 0 
3. Fabricate and join single and multiple spot lap aad butt shear joints 
t o  establish basic static strewh of weldbonded Joints in titanium 
4. Compare static strength of multiple and single row weldbond joints  with 
conventional resistanoe spot weld joints,  and t o  similar specimens joined 
by mechanical fasteners and by etructuraladhesim bonding, 
5. Record and document data related t o  weldability of titanium aelng high 
temperature type adhesives and compare joint  strength at room and 
elevated temperature 
I 
TITANIUM 
Titanium sheet material type 6Al+ in the solution treated condition in 
th ichesses  of O.aQ5" and 0,063*1 was used in one series of tests during this 
program, Thitanium sheet material type 6 6 1 4 V  in the annealed condition in 
thicknesses of 0.020" snd O,O25" was used in other tes te  during this program, 
3 
f 
The following mechanical fasteners were used t o  join speoimena made during 
this program: 
1, 5/52" diameter Hilok Universal head, stoak No, STSAF004-05-02. 
2. 5/52" diemeter Hilok Flush head, stoak No, sTSAF01~05UV02. 
3 . 5/32'' diameter Hilok nut, stook Bo, STSAEOO7-05. 
.1 
The following adhesives were seleated from sewral asndidate sdhesiws and 
were used t o  j o b  the specimns teeted during this program: 
J 
1. 3M Company Adhesive lE3419. The adhesiw is a one part, lo@ eolids 
thermosetting heavy liquid, The adhesive is lwt grey in oolor. 
The adhesive base is a 1 ~ d i f i 8 d  epoxy reeia. Reommended aure 
procedure f o r  optimum resu l t s  i e  350.F 
\ 
f o r  60 minuba. 
2. 3M Company Adhesive type E2214 Hi-Flex, The adhesive is a one part, 
lo($ 60lid8, thermose t tw liquid adhesive, The aolor is l igh t  grey. 
Reoomrmsnded cure temperature is 25O.F f o r  60 minutes, 
A Sciaky, three phase9 variable pressure resietanae spot welder shown 
in Figure 1 was used t o  join all  welded aad weldbonded tensi le  specimens 
4 -. 1335 
tested during this program. 
with turret heads and axtomatic electrode dressers. 
The welder is rated at 150 KVA and is equipped i’ 
A Tiniua Olsen testing machine ahawn in Figure 2 was used throughout the 
program. 
accuracy of two percent of indioated load. 
with an Olsen Atcotran reoorder, a model S-1 Eleotronic Ertensamster, and a 
type D-2 Defleotometer. 
The machine is rated at 60,000 pound capacity and bas a test 
 the^ testing machine waa equipped 
The testing machine was also equipped with a 
Mazshall Electr ic  Furllanoe, serial number 6510742, for  an elevated t e m P Z % =  
ture testing range 78.F t o  1800.F. 
I 
DESIGN OF TEST PBRBHETHis 
TEST IlESIGN LOGIC 
Design of t e s t  parameters fer evaluation of a ta t io  strength of weldbond 
joints  in titauium alloy required that f i r a t  coneideration be given t o  
probable use of the developed proceea. Shoe a high peroentage of 
Manium used in military aircraft would involve areas either erposed 
t o  high stress and/or elevated te?nperatwea, strength at elevated temperatures 
would have t o  be given prime oonaideration, where titanium would be used 
in structures not exposed t o  elevated temperature, generally the ohoice 
would be made because of better strength t o  weight advantages of titanium as 
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5 -  132% 
b 
compared t o  aluminum or other alloys. 
in this  program with stre&h/weight considerations paramount. 
Joint  thicbess ra t io s  were selected 
Real is t ic  evalwtion of weldbonded jo in t s  in titanium required that where- 
ever possible weldbond jo in t  strength would be compared direct ly  t o  st 
of other type joints. Jo in ts  were designed uti l izing spot welds only, 
mechanical fasteners only, mgchanioal fasteners with adhesive, and structural 
adhesive bond only. 
were kept ident ical  in order t o  obtain a direct  strength comparison at room 
Jo in t  oonfigurstions, jo in t  overlap, and jo in t  thickness 
and elevated temperatures, 
. .  
6 
m i c a 1  test specimen design for multispot, double row weldbond and fastener 
bond joints is shown in Fig\l,Ees 3 through 5. Elevated temiperature test 
specimens were of the same essential configuration except they were made 
18 inches long in order t o  allow for heating of the specimen within the 
specimen gage length during testing. 
,e.'- 
t 
WEIS sc-s 
In  order t o  obtain weldbond titeniMl joint strangth data 
campaxed qualitativeu and quantitativdy with other j procresses , 
basic welding echedules were needed. Hachine schedule setups we- made 
t o  establish adhesive wrtldability, correct spot weld nwget diameter and 
penetration, and other criteria a8 required by Military Sgeoification MIL- 
W-6858c. It w a s  necessary t o  vary weld schedule setups as various types of 
adhesive8 were tested. Weld current and weld pressure settings were found 
t o  differ with variation i n  a d h e e i ~  type and/or viecoeity. 
WED CERTIFICATION 
Weld certifioatione were obtained for  the follawing joint combinations 
tested within the scope of thgs prograar. 
1. Titanium type 6 a l 4 V  in the annealed condition, 0.025" thiek 
weldbonded to  titanium 6 a l 4 V  in the solution treated oondition, 
0,063" thick. 
2. Titanium type 6 A l d V  in the eolution treated condition, 0.045* 
thick weldbonded t o  titanium type 6a1+ in the aolution treated 
condition, 0.063" thiok. 
3. Titanium 
titanium 
AMs4300 (Commercially Pure) 0.025" thick weldbonded t o  
6Al-4V in the solution treated condition, 0.063" thiok. 
- ZE1= 
8 -  
Weld certifioations met Class A requirements for  Group C, (titanium) 
alloys, MIGW-6858C, Welding, Reeistanoe Spot and Seam, 
was encountered in obtaining oertif ied sohedulee in the oomwrctially 
pure titanium t o  type 6 a l d V  joints. This diffioulty was due primsrily 
t o  the differenoe i n  welding oharebteriatios of the fm, alloys and not 
t o  the effect  of adhesive at the joint  interfwe, 
Some diffioulty 
' 
Preliminary cleaning and welding tests were =de at the beginning of this 
program t o  determine if resietanoe welding could be acoamplished in titanium 
that had been ohsmically cleaued for  struotuzal metal bonding. A l l  attempts 
were unsuccessful as kasured by standard weld oertifioation requirements 
of MIL-W-6858C. It waa determined tbrrt the pgeeivaticrn treatment (inmereion 
in  Trisodium Phospate (Ha PO ) used prior t o  bonding inhibited the passage of 3 4  
welding current during the welding operation and oauiwd highly emgtio weld 
quality. 
Since high strength bonds could be whieved on par ts  olesned for  meistame 
welding, (except for  passivation the two oleaniag prmeeses were essentially 
the same), a l l  weldbondin@ amomplished within the soope of thia progrem 
was done on parts cleaned by the ohemtcal prooess wed for  resistanoe welding. 
9 
A d h e s i v e  weldability as disowsed herein relates t o  the oompatibility 
and/or incompatibil%ty of the adhesive w i t h  the resistance welding 
process, and conversely, the effecrt of the welding prooess on the adhesive, 
First  requirement of any adhesive candidate fo r  the weld through procees 
of weldbonding is that the adhesive have the oapability of being moved 
under pressure of the welding electrodee in order fo r  metal t o  metal 
contact t o  0c)cur at the jo in t  interfaoe. 
A second requirement fo r  an adhe6ive candidate wae that the heat result ing 
from the epot weld would eauacr only limited detrimental effeot on the 
t 
strength of the bond. The strength of the bond fi titanium alloy joints ,  
the adhesive and/or oohesive failure o w t e r i s t i o s  of the adhesive a l l  
entered in to  the final selection of the adhesive. 
Final selection of the adheeives wed during this progrem was based an 
overal l  weldbond properties at room and elevated temperatures as related 
t o  titanium weldbond joint strength, 
A listing of the adhesives aareened for use during t h i e  program and 
resul ts  of the screening are detailed 88: follows, 
- %37( - 
10 
2. 
3. 
L 
4. 
5. 
3M Company epoxy adhesive type Xa3919 is a r o l l  coatable paste adhesive. 
a 3 9 1 9  is a temperature resistant, 7i$ solids version of 0 1 3 0  adhesive 
f i l m ,  XA39lg exhibited adequate weldabilitp and fair strength at 350.F 
temperature, but showed poor lep shear strength at EO- temperature, 
3M Compaay  epoxy type Xa34lO is a one part, 1 0 6  solids, theaaoeetting 
l iquid adhesive advertised as being resis tant  t o  temperatures up t o  350.F. 
XA3410 exhibited fair weldability, but showed low strength at al l  
temperatures . 
3M Company adhesive XA3435 is a one part, 1 0 s  solids, thermosetting 
liquid advertised as offering euperior strength up t o  and including 
350.F temperature. a3435 showed good weldability but exhibited only 
fair strength at a l l  tempersk~res, 
3M Company adhesive type E3419 is EL one part, lo@ solids, thermosettiqg 
heavy liquid advertised as ha- exceptioaally high strength properties 
from -40 t o  350.F. T h i s  adhesive exhibited excellent weldability on 
titanium alloy 6A11qV and showed ffir t o  good strength at elevated tem- 
perature and at room temperature, EC3419 was one of the adhesives selected 
f o r  use during this program. 
3M Company adhesive type E2234 Hi-Flex is a paste epoxy adhesive J i th  
f i l l e r  designed fo r  use from -40 t o  25O.F. T h i s  adhesive exhibited 
excellent 
and elevated temperature, 
weldability and showed cohesive type failures both at room 
Room temperature shear strength i n  titanium 
32aik 11 - 
joints  was superior t o  al l  others teeted. EC22l4 was selected f o r  use 
in this program. 
6, Bysol Corporation adhesive bD[IE347 and ADlQj73, sad WbittaJEer Corporation 
adhesive X6800 were a l so  mbjeoted t o  p re lhhmry  feet8 
but exhibited adhesive failures with low lap eheer strength at room 
temperature. 
titaPi\mP joint8 
FABRICATIOX AND JOI- OF SpEcIMElos 
Specimens used f o r  preliminary evaluation of adhesives were finger panel type. 
These specimens were stamped from titanium sheet stook and are of the type 
normally used f o r  process oontrol t sne i le  testing 88 required by Military 
Specifiaation NIcW-6858C and Federal Specification MMK-132. x 
Specimens used t o  obtain the final t e a t  r e m l t e  were sheaxed from titanium 
eheet and machined t o  the co&igurations shown in Figure 3.. 
TELPSIrn TESTS 
Room temperature s t a t i o  tensile tea t8  were performed on the Tiniue-Olaen 
tensi le  testing machine ahown in Figure 2. Test load pounds were all  within 
a ran&e of 500 t o  12,000 pounds which allowed a test machine accuracy of two 
percent of indicated load, 
.. 1394 
12 
Load deflection ourves were obtained f o r  eecth of the testa.  Ultimate strmqth, 
ykeld strength, and geruent elongationwere obtained f o r  each speclipasn. Yield 
strength was determined using the 0 . 8  offaet method. 
Figures 3 through 5 show goint description end a ta t io  shear strength of the 
specimens teated during this progmxn. 
Elevated temperature static tensi le  tests were made on the Tiniue-Olsen 
tes t ing machine aebg the Maxsbsll specimen fumme as shown in Figure 2. 
Welded, weldbonded, adhesive bonded, meahanically fastened, and mechanically 
fastened and bonded apecimens w e r e  subjected t o  various temperatures under 
load t o  failure. Static shear strength and mechsnical propertiea of the 
j o i n t s  at different temperature levels are shown b Figures 3 through 5.  
FIGURE 3 - STATIC SBEBR 
STRENGTH, BUTP SHEBB 
DOUBIlE ROW, MULTISPOT 
WEWBOETD, 0.045" TO 
0,063" 
OVER 
SPEC V I m I  LAP 
NO. IN. IN. 
18-1 1.50 1.50 
18-2 
18-3 
18-4 
18-5 
816-6 
18-7 
1- 
18-9 
18-10 
18A-1 1-50 1-50 
1BA-2 
23 
18A4 
.37 None 11100 4933 RT 2214 'RB 
11150 4955 
10950 4866 
10740 4773 
10830 4813 
?io& 4924 
10730 4768 
10720 4764 
Average log00 4847 
108% a 2 2  
2?2?24857 
.37 None 10270 4564 7 5 0 '  2214 'dia 
9940 4417 200. 
10070 4475 200. 
%So 4200 325. 
. 
. 9490 4217 325. 
JORlT PXTCR 
C W .  IN. 
-045 e75 
.063 
To 
.045 .75 
,063 
'Po 
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13 
DIA XOIZ 
2 PLACES 
SPEC uIm-9 
NO. IN. 
20-1 1.50 
20-2 
20-3 
20-4 
20-5 
20-6 
20-7 
20-8 
20-9 
20A-1 1.x 
20A-2 
20~-3 
20A-4 
EQA-5 
3vEri 
LAP W E  FASTWADLBS; 
L'J. DIST. FIA. LBS. IN. 
1.50 *37 5/ 6710 
32 7200 
FUGH 6740 - 7685 
7750 
7120 
7440 
8050 
I22 
1 - 3 3  .37 6530 
F l B H  6750 
6895 
5865 
6940 
Average 7665 
5, 
32 
HEAD 
FIGURE 4 - STATIC SHEgR SlTtEKGTH, BUTP SEWR DOUBliE 
ROW, I!lUIEIPIE FASTEETEB, 0.045" TO 0.063n 
I 
5 .  
1 
J 
-- 
SPEC 
NO. 
24-1 
24-2 
24-3 
24-5 
24-7 
24-4 
24-6 
24-8 
24-9 
24-10 
24A-1 
24A-2 
24A-3 
24A-5 
24A-4 
' -  
m 
IT<. 
1.3 
- 
1.s 
FIGURE 5 - SI! 
PEEL TESTS 
In order to t e s t  the combined strength of both the bond and the spot weld, 
peel specimens typical of those shown in Figure 6 w e r e  tested in a peel test 
fixture a t  room temperature. 
I I I I I I I  
FIGURE 6 - D I A G U  SHOWIXG TymCAL PEEL STREKGTE 
OF WELDBOKIBD JOIrJTS Ill TITANIUM 
TEST IiESULTS ANALYSIS 
ROOM AND EI;EVBTED TENPERA!PU€E TEST RESCTIIPS 
Comparative strength of the different joining methods i s  shown in Figures 
7 and 8. Strength of the Joints is plotted in  ultimate load pounds versus 
temperature in order t o  obtain a direct  strength comparison of the various 
joining techniques. 
DOUBLE ROW, 0.045" TO 0.063" TITANIUM 
16 1434 
r -  
F I G m  8 - COPPARATIVE J O I N T  STRENGTEI, BUTI' SBEBR 
S~~ ROW, 0.025" TO 0.063" TITANIUM 
Weldbond joints show a superior strength at  room temperature i n  al l  joint  
types tested. 
the greatest superiority in weldbond strength as compared t o  other joining 
methods . 
The double row, and double row multiple spot type joint  showed 
Spot-welds were inferior only t o  the weldbond joint at room temperature in 
a l l  categories tested. Mechanioal fasteners plus adhesive showed the third 
highest strength properties at room temperature in al l  joint  categories 
except in the single row, O,O@to 0.06~condition. Structural adhesive 
bond j o i n t s  were inferior t o  a l l  other type joints tested a% room temperature. 
Weldbond strength at elevated temperahaices varied not only with the tempera- 
ture but also 88 a function of the type adhesive wed and the type of joint  
design wed. As shown i n  Flgum 7 and Pigme 8, weldbond joint type double 
row, multiple spot, exhibited a definite strength superiority from room 
temperature through 325.F. 
. 
b 
Weldbond Joint8 and/or apot-reld j o i n 9  ware wrperior in strength in all 
categories from room tempera- t o  400V as oaaDpared t o  other join- rnsthoda. 
The structural adhesive bond joints made with EC22l4 HI Flex adhesive los t  - 
approrimately 5@ of 
hesive bonded jo in ts  
their effeotive strength at 2OO0k. The strwtural ad- 
made with EC3419 reteiaed approximately 5 6  of Wir 
DISCUSSION 
H i g h  quality reeietanoe spot-welds meeting the requirements of Military 
Specification MIL-W-6858C were prodwed when welding through epoxy adheslve 
on titanium alloys. 
weldbonding tltaslum 
Weldbond Jo in t s  were 
Bo speaial ~~ m o d l f l ~ t l o n s  were required for 
alloys 0 
I 
prodwed that were oonsistently strbPnger than those of 
either meohanlcal fasteners, strwturel adhesive bonds, or meuhanloal fastenere 
with adhesive at the joint interfecre. Weldbond joirhts and/or mot weld joints 
showed superior strength at a l l  temperature rangem as aosnpared t o  other joints 
teated. 
A d h e s i v e s  having a strength above 3000 psi  at 4OO.F need t o  be developed for 
weldbonding in order t o  mhleve optimum joint efflolency in tltanlum alloys at 
elevated temperatures. 
The oombined peel a t r e e h  of spot welds and adhesive bond joints was approxi- 
mately five tlmea greater than that of a bond'jolnt alone. 
18 


Development of the weldbond process for joining titanium

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