RWMA-BULL-19.pdf

rwma bulls19 tt m 7678558 0000137 9 m b u l l e t i n n u m b e r b resistance wecuin miscellaneuus a i d dissimilar metals a p u b l i c a t i o n of t h e of resistance welder manufacturers association copyright resistance welder manufacturers association provided by ihs under license with rwmalicensee=ihs employees/1111111001, user=wing, bernie not for resale, 04/18/2007 10:38:30 mdtno reproduction or networking permitted without license from ihs -,-,- rwma bull*l *k m 7698558 0000l38 o m -/- resistance welding of misceiianeous und dissimilar metals titanium titanium, while one of the most abun- dant metals in the earths crust has been only recently commercially available. it, with its alloys, promises to become one of our most important structural metals. as may be seen from table 1, its weight is about half that of steel, its strength is about the same, and its melting point is higher. in addition, it possesses valuable heat- anri corrosion- resisting properties. several titanium alloys are currently being produced or under development. these include m:illory-sharon alloy l- 2850 containing c.p. titanium with less than 0.257 carbon; alloy l-2749 with 0.4 to 0.7% carbon, and alloy i,-2748 with the addition of 3 to 5% chromium. as time goes on, undoubtedly additional alloys will be produced. experienee so far indicates that most of the alloys are weldable by the resist- ance processes, some more readily thun others. these alloys, while not acutely sensitive to welding variables, are not a a easily welded as either low carbon or stainless steel. penetration and duc- tility, for instance, are a little niore dif- ficult to control. material preparation while titanium oxidizes quite readily, the srale or oxide formed at normal tem- perat.ures does not seem to have :i deleterious effect on welding. mill or hot-formed srale should be removed 1)y first sandblasting, followed by a sodium hydroxide cleaning, and finishing with a bright dip in a solution of 2% liy(r0- fluoric acid itnd 10% nitric acid, removal of grease, oils, etc. can he accomplished with carbon tetrachloride. spot welding one of the c.li:irtioteristies of titanium spot welds is the formation of tlie weld nugget. this consists of the weld nugget itself, surrounded by ti iieat- affected zone. the nugget with a pene- tration of 70-90% forms quickly, and with increase in weld time grows later- :illy, that is, to increuse the diameter. in oticr words, with the ordinary spot weld, tlie nugget grows with time both vertically and laterally, whereas, with titanium, it appea1.s to grow first ver- tically, then laterally. in one series of teood table 3. approximate composition and some physical properties of cobalt alloyb. (stainless steel, type 347 included for reference) ._ _ . . . . _ - . . i . _ _ . . _ _ _ _ - _ l-605* n-153* n-155* type 347t (iiaynes-25) . . - - . . _ _i - . - _. . (2 cobalt (co) i3 20 clironiiuni 16 20 18.5 15 ao 11.5 10 2 9 . 15 nickel 1% tungsten (w) hfolybdeniini (mo) 3 3 . . manganese (mn) 1.5 1.5 1.25 1.5 0.5 0.5 0.5 0.5 1 .o 1.0 0.85 . silicon (si) columbiuin (cb) o. i2 o. 12 0.08 o. 10 o. 12 o. 12 . . carbon (c) nitrogen (n) iron (fe) bal. (68) bal. (32) bal. (68) 2.0 _ i - _ _ .-. yield strength psi, 53,000 53,000 33,000 70.000 elongation in 2-id. % 40 45 50 60 rockwcll hardness 8-88 8-90 b-82 b-100 reaist.ancc. niicrolims 33.7 36.6 28-30 34.9 ultimate strengti psi. 114.000 115.000 86,300 155,000 per cu. in. - * heat treated 1 hr. at 2200o y air cooled. t heat treated 10 min. at 1965 f., air cooled. quality and uniform strwtiwe, and the welded parts should be cinneirled im- mediately after welding. welding. par they are all one of the most important factors for insuring sound and reproduciblc. welds is correct surface preparation. parts should be cleaned carefully on both sides, preferably by adequate pickling. the metal should be first degreased with any good commercial degreasing ma- terial, as carbon-tetrachloride. molten caustic pickling has been found mbst effective for removing the touah hot-formed s:ale. twa such methods are the “vergo“ molten caus- tic bath, and the sodium hydride proc- ess. either o these should be followed by a water quench, then l one to two minute dip in 10 to 12% h b, seam wald; c, cross-wire welds; d , spot welds; e, projection welds form alloys with iron, c*obalt, arid nickel quite readily, while on the other liaiid, it ier difficult to forin itlloys of the refrao- tory metals with c!opper or silvei how- ever, it seems possible to obtiiiii, by proper weltling c*ontiiticins, il wetting of tlie refractory niet:il!: with copper or c o p per base alloys anti tiicreby produce a satisfwtory although inc!oinplete weld. in welding refrricntory metals to iron and nickel alloys tirectly, usually these lower melting point iiiateri!is fuse at the weld interface, thcrchy wetting the re- fractory materials :mi forming small surface alloy layers. in many cases in welding tlie refrac- tory met,als to each other, it has been found desirable to interpose between the two metals a third metitl, such :is nickel or nickel :tiloy, or similtir materials cessive heat and cylindrical flat tips. -i . i i ! i i i i i l li whichalloy readily weldswith bothrefrac- tory metals to be joined together. it has been found possible also to use straight butt welding for attaching refractory metals to base metals such as iron and nickel hase alloys. zinc and zinc die castings although there are no data on produc- tion applications of resistance welding to cornmerciai zinc alloy die castings, it has been determined experimentally that these may be successfully welded. when the necessary conditions can be estab- lished, the use of resistance welding should therefore be of considerable value in fabricating various structures, by welding together diecast parts to form an assembly which could not be cast as a complete structure, or to reduce cost on . i , q of welds .f spl2cone t g li pressure -750lbs: time - 30 cycles wrent- 12000amps. . -:249“ lead-antimony alloy 1 i x 5 photomacrographs of spotwelds i i i i photomacrographs of spotwelds between ,064“ terne plate and lead or lead alloys i n lead ano lea0 alloy sheets fig. 2. socfions of spot welds in lead, load alloys and torne plate 3 copyright resistance welder manufacturers association provided by ihs under license with rwmalicensee=ihs employees/1111111001, user=wing, bernie not for resale, 04/18/2007 10:38:30 mdtno reproduction or networking permitted without license from ihs -,-,- rwma bull*ls * m 7698558 - ooool41 o m i _ _ _ - ? structures which are difficult to cast in one piece. investigations of various types of re- sistance welds in zinc die castings in- dicate that the following conditions should be observed: synchronous controls bhould he uiietl. pulsation welds appear to give lmt results. in spot welding, low welding forre must be used to avoid excessive indenta- tion; and on account of the low melting point, surface overheating should be avoided. figure 1 shows some typical resistance welds in zinc die castings. some work has also been reported on seam welding rolled zinc sheet, and it would appear that the material may be spot and seam welded under certain conditions, but specific information is lacking. - . lead and lead alloys lead and the principal lead alloys, which are used commercially mostly in sheet form, have low electrical conduc- fig. 3. flash-butt weld of hard rolled copper to 75s-t aluminum with weld section of l/%-in, by 31/4-n. tivity and correspondingly low heat conductivity. therefore, it requires re- latively low currents to raise them to the fusion temperature, and the heat is not too rapidly conducted away into the ad- jacent metal. the fact that these ma- terials also have low compressive strength makes it necessary to avoid high elec- trode forces, in order to prevent exces- sive indentation. when properly made, spot welds in pure lead are usually char- acterized by the good ductility which is found in the parent met.al and although the strength of these welds is not gen- erally high, it is usually sufficient for the purpose for which the niaterial is used. some of the lead antimony alloys show higher strength values in the welds, al- though the ductility is somewhat less. sections of spot welds in lead alloys and in lead alloy-terne plate combinations are shown in fig. 2. .machine settings will run from i00 ibs. electrode force, 9 cycles time and 5800 amperes for l!eldeti. in the nonferrous :illoys, the best welds will be made be- tmen two :tlloys which will form inter- mediate alloys, such as between monel and sonie of the bronzes. development of satisfactory pro- cedures for resistaxice welding of dis- similar metal combinations obviously involves the determination of proper settings for current, pressure and time, in addition, the following conditions need to be considered. copyright resistance welder manufacturers association provided by ihs under license with rwmalicensee=ihs employees/1111111001, user=wing, bernie not for resale, 04/18/2007 10:38:30 mdtno reproduction or networking permitted without license from ihs -,-,- _ fig. 4. flash-butf welds in various typas of joints between aluminum and copper i. relative electrical and thermal conductivity of the two metals. 2. melting points of the two metals. 3. plastic range. 4. relative thickness. these variables can be partly com- pensated for by adjustment of heat balance through electrodes or other means. xo hard and fast rules can be laid down for setting up welding procedures under such conditions, but the factors affecting each job must be studied as a whole. a practical approach to any individ- ual problem is to.consider the weld as fundamentally a metallurgical proceas. then the first step toward the solution is to mure a balanced heating effect. this should preferably be done before the design of each of the component parts is definitely fixed. furthermore there may be other important factors than heat balance to consider. therefore it is not usually economical to go into pro- duction on component purts until il, has been proved definitely that the design of each part is sound from il welding stand- point. another neceswry preliminary is to assure the reproducibility of satis- factory procedures, by providing the welder with the greatest possible degree of precise and automatic control. the recommended method o f ohtain- ing heat balance when spot welding com- binations which differ widely in heat and electrical conductivity is the use of two dissimilar electrodes, such ns one of copper alloy and one of a copper- tungsten alloy of high tungsten content. for example, combinations like copper with galvanized iron or copper with nichrome (metals of widely difrercnt electrical and heat conductivity) may be welded by using a copper-alloy electrode next to the nichrome and an electrode of an alloy rich in tungsten content next to the copper. this will give a balanced 6 heating effect, the low-resistance copper electrode in contact with the high- resistance nichrome helping to conduct away the excessive heat caused by the high resistance of the nichrome, while the heat in the low-resistance copper al- loy o f the part being welded is intensi- fied and localized by its contact with the relatively high-resistance copper-tung- steri electrode. this causes the two dis- similar metals to heat evenly to the welding temperature. a wide choice of electrode material is available, ranging from pure copper of high conductivity through the copper- tungsten alloy series to pure tungsten which has a still higher resistance. pure tungsten is seldom used except in cases where two pieces of metal of very high heat conductivity are to be welded, if the conductivities of the component parts are not widely different, a satisfac- tory heat balance may usually be ob- tained by using the same type of eiec- trodes on both sides of the joint. _ , copyright resistance welder manufacturers association provided by ihs under license with rwmalicensee=ihs employees/1111111001, user=wing, bernie not for resale, 04/18/2007 10:38:30 mdtno reproduction or networking permitted without license from ihs -,-,- c applications - .rwma bull*ls 8% e 7698558 0000143 4 e incandescent lamps. lead-in wires consisting of a piece of copper, a piece of dumet and a piece of nickel. radio and vacuum tubes. combina- tions such as molybdenum to nickel, fernico to hcci, inolyirleiiiirii, tiiiigh iriiti c!oplier to riickcl. contrd larts. ilinplior liroiize to steel, copper, silver, nickel, nichrome and others, copper to brass and com- binations of the above. telephone inatruinent park. precious metal disc, bar and point contacts to springs, seam welding bimetal bars for contacts, bronze and nickel-silver, miig- net steel to low carbon steel. electrical instruments and appliances. welding of cable wires to many types of lugs and terminals, while there is little specific data available on actual welding procedures. table 4 shows welding schedules for some typical combinations. ._ table 4. bpot weldinc; conditions for bohe combinations of dissihllah metal8 (thickness each piece, lh-in.) combination two pieces each 1/1a in. thick ._ . - - nickel-mild bteel nickel-863o steel nickcl-18/8 htuinli*m nickel .- hlonrl nickal liiniiiiil miiiiiil htilil h1i.i-i m i i i i l hiibf) hii*i*l monel . ih/x niniiiii.n monel-i nroiii.1 inconel-hlild steel inconel-8630 steel inconel-18/8 stainlwu 18/8 hiild steel 16/6-8630 steel butt-welding theoretic:ally uny combiniition that can be spot weltlcd can also be butt welded; and : i s with butt welds in most materials, flash welding is the most satisfactory method. it is generally necessary to compensate for differing electrical and thermal conductivities of the two piec.es by projecting the one with the higher conductivity further from the dies to strike a herrt balance. weld weld weld shear . time current, diam strength, cycl 14 14 17.000 14 16.000 16 14,ooo 14 18.ooo 14 17.500 .- 0.25 0.25 0.25 0.28 0.26 0.25 0.25 0.25 0.25 0.23 0.25 0.28 0.25 0.26 .-_. - 2200 2350 2700 2000 2750 2300 2460 2800 3000 2200 2300 2950 2170 24ou - - . figure 3 illustr&?s a good quality flash weld between 75s-t aluminum and hard rolled copper with a weld section of in. by 31/r in. this shows the work :is it is removed from the welder. figure 4 shows several copper-aluminum welds in tubes, bars and miscellaneous sec- tions. most of these welds have had the flash partially or wholly trimmed off. typical applications are terminal con- nections for refrigerator condensers, elertriral conductors, etc. 6 copyright resistance welder manufacturers association provided by ihs under license with rwmalicensee=ihs employees/1111111001, user=wing, bern