nuts & bolts craft &...

Nuts & Bolts

Craft & Technique

WHEN IT COMES TO WELDINGaluminum, which of the fol-lowing truisms are memo-rable to you, dear reader?A. You can't weld aluminum.B. You can't gas weld alu-

minum.C. You have to use hydrogen

in order to gas weld alu-minum.

D. You must use blue glassesin order to gas weld alu-minum.

E. GTAW (TIG) is the only way toweld aluminum!After considerable research—from

reading many old welding texts andinterviewing old welders, to contact-ing the Aluminum Association—andhaving used gas to weld aluminumsince 1976, these truisms seem to beuntrue.

Answer A is partially true. Yousimply cannot weld some aluminumalloys, like 2024 and 7075. AnswersB and E come from some electricwelding schools, simple misinfor-mation, and some rather aggressive"electric-machine" welding suppli-ers. Answer C is a legacy from WorldWar II, where the entire civilianpopulation was pressed into wartimemateriel production, ultimately pro-ducing more than 300,000 aircraftin 4.5 years!

In these aircraft plants, womenwelders in crews as large as 50 pro-duced parts and followed methodsapproved by the plants' manage-ment. In 1941, however, and beforePearl Harbor, Alcoa (the nation'sonly aluminum producer) reportedthat oxyacetylene was the most pop-ular method of aluminum weldingin the U.S. By 1947, though, theleading welding books of the daywere mysteriously stating that oxy-hydrogen was "more suitable for air-craft aluminum welding because it

• • - - • - • " : t

AircraftAluminum

Gas WeldingIts history; tradition, tools, and methods

KENT WHITE

Using oxyacetylene to weld a jet-aircraft component. (Photo: Alcoa)

was cleaner."That's not quite true. Paul Dicker-

son, chief consultant to the Alu-minum Association, says the largestprewar aluminum welding opera-tions were in the cookware industry,and it used the economy-of-scaleelectrolysis method to break riverwater into H2 and O2 for welding

Key WordsOFW—oxy-fuel welding (gas

welding or torch welding)GTAW (also called TIG)—gas

tungsten arc weldingGMAW (also called MIG)—gas

metal arc weldingHAZ—heat affected zonePlanishing—smoothing by ham-

mering or rollingMetal finishing—smoothing by

metal removal (filing, sanding,etc.)

gas. When wartime rationingcame about and acetylenewas specified for shipyardcutting torches and othersteelwork, the electrolysisplants were moved to the air-craft factories, where every-one gladly used the tools andmaterials given them andnever felt the need to ask thereason why.

Lastly we address answerD. In the 1940s aluminum weldersborrowed the now-antiquated blueglasses (cobalts) from the steelfoundries, but through the 1930sand '40s, many welders wore nosafety eyewear at all for gas welding!In the days when movies cost anickel, $3.50 for a set of goggles wasexpensive!

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Gas HistoryDeveloped right at the turn of the

century (that last one, not this one)the oxyacetylene torch remainspretty much the same unit we usetoday. With the advent of weldingfluxes around 1913, it became possi-ble to torch-weld aluminum, stain-less, Inconel, Monel, cast iron,magnesium, and titanium.

In November 1942, a couple ofcreative men at Northrup cobbledup the first "heliarc" (which becametungsten inert gas or TIG, whichthen begat GTAW for gas tungstenarc welding.) In a few years, togetherwith "wire feed" or MIG, for metalinert gas (now GMAW for gas-metalarc welding), these new weldingmethods helped pioneer the applica-tion of exotic new metals vital to su-personic flight. However, for nearlyhalf a century prior and half a cen-tury since, the common oxy-fueltorch has been a significant main-stay in the aluminum joiningprocesses.

92 MARCH 2000

*>?•

Torch vs. TIGOFW's chief advantages over

GTAW are economy, speed, penetra-tion, workability, wind resistance,and that its small, flat weld beads re-quire minimal planishing and metalfinishing. OFW's disadvantages areflux cleanup, larger HAZ, and thatfewer alloys and heavy thicknesseslend themselves well to the process.

Gas welding aluminum alloys,stainless, and titanium, etc. requiresspecial fluxes to keep oxygen out ofthe molten puddle the same way the

inert gases, such as helium and ar-gon, do with GTAW. However, thesefluxes allow excellent weld penetra-tion to the root side, somethingonly expensive back-purging en-ables GTAW to equal.

Until 1994 Boeing gas welded thinaluminum sheet at its Welded DuctFacility, when the flux industry as awhole finally bogged down in MSDS,OSHA, and EPA entanglements. Boe-ing now employs the back-purgeGTAW method, where each duct isfilled with inert gas prior to welding.As I understand it, Marietta Corp. inMaryland still uses OFW, as do vari-

1. A P-51 wing root fairing. Where isthat lady today who made this beau-tiful gas weld 50 years ago?2. The author using oxyacetylene toweld the two halves of a P-51header tank together.3. This Luscombe wheelpant waspressed in halves and then joined byoxyacetylene welding, leaving theweld bead exposed.4. This leading-edge air intake onEAA's B17, Aluminum Overcast,shows two types of welding meth-ods: TIG, which are the large stress-repair "worms" at the corners, andOFW, which are the original factorywelds, lying flat and barely visible,surrounding the opening.

ous other facilities.When you consider the purchase

of a fully equipped electric machineand the cost of consumables, suchas tungsten, argon, and electricity,against the cost of a torch and its gasand some fluxes, there might be anice cost savings with the torch.Even if the electric box can weld tin-foil to crankcases, it won't solder,braze, anneal, and do hot working.And it still won't like windy ramps,breezy shops, or dirty material. Itwill weld thick metals (those over.125 inch) much better, and it makeslife a bit simpler when welding com-

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Craft & Technique T.

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What about MIG? The wire-feedGMAW (what we thin-sheet metalguys often call the "manurespreader") does okay on thick metal,and it leaves a high bead with somesort of penetration. An expensive,digital turbo double-backflip modeldoes thick stuff absolutely beauti-fully, and on the best machine a vir-tuoso might be able to do an outsidecorner on .063 after much practice.

This series of photos compares TIG to torch on the same sheet of material,having a large gap of .060". "TOP" is the welded side, "ROOT" is the back-side showing penetration, and the edge view shows bead thickness.(Welds by author)

(It's just like anything else, dearreader—practice, practice!)

Welding, Brazing & SolderingBy definition, brazing and solder-

ing do not melt the parent metal—they join by surface adhesion of themelted filler metal. They seem anal-

ogous to really good hot-melt glues.Books define the three "hot metal"joining methods by melting points,and "inside" industry experts definethem in other esoteric ways. I'll tryto cover them all for you: the tem-peratures and alloys; the fluxes,hardnesses, and brittleness; yield

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and tensile strengths; and the filletcolorations.

Divided by temperature, solder-ing is generally defined on brass,copper, steel, stainless, and alu-minum alloys as melting in therange up to 850° F. Brazing goesfrom there upwards to slightly be-low the melting point of the parentmetal. Welding, of course, is right atthe melt ing point. If the parentmetal does not melt, but is bondedby the melted filler, then the processis not welding!

Braze welding is another misun-derstood term. It occurs so close tothe melting point of the parentmetal that when using the same

This interesting photo is of a 1942Ryan fuel tank (ID tag extant, butnot shown) with the weld seam run-ning vertically next to a brazed-infuel fitting, with inspector's stampjust visible. (A braze is typicallydarker than a weld.) ;

filler on two similar but differentaluminum alloys, one will weld andthe other will braze. For example, ifwe're using a brazing filler of 1140° Fon 6061, which melts at 1100° F,we'd be welding it because the 6061is molten at 1140° F. If we used thesame process on 3003 (which meltsat 1195° F), we'd be brazing.

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Craft & Technique

the durned stuff just won't work?Cheer up. That alloy was quite

possibly leaked out the back door ofsome big parts-production facility,so for quality results avoid flea-mar-ket zingers, 3-in-l pot metal alloys,and various Lumi-braze zinc-bearingmaterials because their chief use isto repair cheap die-cast parts or tomanufacture heat exchangers. Onecommon failure of these materialsoccurs when one planishes alu-minum sheet so joined by hammer-ing or rolling, and the subsequentcracks arch observant eyebrows.Note, one must completely removeareas erroneously joined in this fash-ion or attempted fixes will spreadthe infection.

In general, brazing materials arebrittle and hard (high tensile butlow yield strength), and on alu-minums they are darker gray incolor. Joint design is also importantfor both brazed and soldered con-struction, because we need plenty ofsurface area for the bond to achieverequisite strength. For this reason,

Fuel Gas

AcetylenePropaneMappNatural GasHydrogen

Combustion RatioOxygen to Fuel Gas

2.55.04.02.00.5

These young ladies are welding parts for the P-39Airacobra. (Photo courtesy Bell Aircraft)

except for welds, butt joints arestrictly taboo.

The fluxes for solders and brazes,whether corrosive or noncorrosive,are also special for that particularoperation and depend on the alloy,the required bond strength, andwhether the part can be rinsed cleanafterwards. For example, 5052 has

high corrosion resistance and there-fore needs a corrosive flux.

For the most part solders are darkgray and soft, with fair tensile andsometimes a fair yield strength. It'sunusual to find aluminum solder,but a new one that uses a noncorro-sive flux has superseded the old al-loy and flux combination from the1940s. The new stuff won't join5000-series alloys, but it is certainlyapplicable to nice repairs on radia-tors as it flows just as well on alu-minum as it does on copper.

Fuel GasesThe fuel gas chart indicates only

some of the significant oxy-fuel costdifferences between hydrogen and

acetylene. Thatacetylene is muchhotter should suf-fice. Using hydro-gen requires acompletely sepa-rate tank, regula-tor, hose, andtorch becausemixing acetyleneresidues with hy-drogen gas invitesexplosive disaster.Further, hydro-gen doesn't pro-duce soot, whichwe can use as a

rough temperature indicator whenannealing aluminum sheet. Hydro-gen's benefits may be fuel productioncost (if an electrolysis plant is feasi-ble) and a slightly cleaner weld zoneappearance because of the absence ofcarbon in the flame. ••.<- • ) , . • :

The fuel gas chart also gives thegeneral fuel consumption relative to

Flame Temp F°Oxy-Fuel

55904580530046004820

oxygen consumption. The choice ofa fuel such as propane, MAPP, ornatural gas might be based on sim-ple cost alone, but it's wise to con-sider that the excess oxygen makesthe cost rise again, if you don't usean injector-type torch to lower thatoxygen consumption.

Tools of the TradeVirtually any torch may be con-

sidered viable, but I tend to avoid gi-ant "railway" torches and tinyjewelry torches. Most torches arefine, some are really good and com-fortable, and a few might be consid-ered for specialty work. (Out of myextensive collections I have occa-sionally selected a Victor cuttingtorch to nicely weld .050-inch 3003for my students' considerable enter-tainment.)

Torch tip selection is always onesize larger than one would normallychoose for the same thickness ofsteel sheet. The "formula of thumb"for this is three-quarters of the metalthickness equals the tip orifice diam-eter. (Please don't ask me to translateyour Smith 00 tip size to decimal,because all of the torches will want atranslation, too.)

Hoses of choice are light and flex-ible, to allow out-of-position workand long periods that require asteady hand. Because of the lowpressures required, regulators maynot be accurate at the low end, andone will need to twiddle with thetorch lit to establish the best flame.Do this with the torch valves wideopen, setting the largest, best flamefor the tip. Glance back at the gaugesto see the approximate right pres-sure. Set the flame neutral, or if the

96 MARCH 2000

regulators creep, slightly feathered(carburizing) to avoid the oxidizingflame completely.

Aluminum OFW flux must be ofthe highest quality, and strictly spec-ified as a welding flux, not as a braz-ing or soldering flux. Brazing fluxesgive a poor weld appearance and re-alloy the weld with zinc from thezinc chloride they contain, whichmakes the aluminum parent metalweak and brittle. The proper alu-minum OFW fluxes from the olddays have mostly disappeared, but afew years ago TM Technologies re-vived the original Alcoa formula andit is now sold under the TM Tech-nologies label, along with others forwelding, soldering, and brazing.

Aluminum welders must use spe-cial safety eyewear to protect themand provide a clear view throughthe yellow-orange flare given off bythe incandescing flux. In the 1940swelders borrowed cobalt melter'sglasses from steel foundries, andthey were still available until the1980s. However, the lack of protec-tion from impact, ultraviolet, in-frared, and blue light caused severeeyestrain—and eye damage. Alu-minum welders also borroweddidymium eyewear, developed forglassblowers in the 1960s, untilmany complained of eye problemsfrom excessive infrared and bluelight, as well as insufficient shading.

In 1989 TM Technologiespatented a new green glass, designedespecially for aluminum OFW. Itcuts the flare and provides requiredprotection from ultraviolet, infrared,blue light and impact, according toANSI Z87-1989 safety standards. Asof this writing, this eyewear has noknown peer, and no complaints.(For more information, call TM Tech-nologies at 530/292-3506.)

ProceduresNote: The following procedure is

for oxyacetylene because of themore technical nature and variedavailability of hydrogen. The rules

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Craft & Technique

are simple. Follow them or fail!Open the oxygen bottle fully to seat the upper

packing, and then just crack the acetylene. Choose atorch tip one size larger than would be used on steel.For example, if you choose a 00 (double ought) tip for.040 steel sheet, move up to an O tip for .040 alu-minum sheet.

If the material is oily, clean it with solvent, lacquerthinner, or alcohol. Either 70 or 95 percent denatured al-cohol is an excellent solvent for cleaning. MEK and ace-tone are toxic and expensive, but acetone works well. Inthe presence of an electric arc, such as GTAW or GMAW,MEK converts to phosgene gas, which is a nasty com-panion for most bipeds!

Just prior to welding, use a stainless toothbrush toscrub off the invisible oxide film on both sides of thesheet. Flux either the rod (or wire) or the part—or in ex-treme cases, both. The flux will be a white powder thatwill be mixed 1/3 with either 2/3 really clean water or al-cohol. Safety precautions such as eye protection, ade-quate ventilation, and keeping one's head out of thefumes are naturally recommended. Choose the properfiller metal for the alloy to be welded.

The hollow, flux-filled rod was made available years

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Welds using the sameprocess I have describedhere: A, B, and C showviews of one oxyacetyleneweld on new .050" 3003,with the top, the root, andthen the same weld's rootside after planishing in thewheeling machine.D. The root side of a weldon 6061, using 5356 filler.E. This I do for the amuse-ment of my students—us-ing a Victor 100 modelcutting torch to weld3003 .125" thicknesssheet.

ago, but, aside from thequestionable alloy, it hadthe persistent bad habit ofneatly dividing itself ,building up the edges ofthe joint without joiningthem together. Then, aftersetting the used rod aside,the flux would spill out ofthe open end.

Get the best fit-up possible to avoid large gaps wherethe two sheets meet, and select filler metal no thickerthan the panel to be welded. Set regulators to full closed(knobs wound OUT) and torch wide open—no, not somuch the knobs fall off! Add acetylene with the regula-tor till you feel a breeze on your cheek, light the torch(preferably away from cheek), and then add oxygen toget a loud flame. Next, set the flame down to what youfigure you need, which will vary with application. Applyflux and set flame a bit hot for tacking, then apply tacks1 to 1.5 inches apart. Don't worry if distortion or stresscauses some tacks to crack.

(Note: TM Technologies offers a professional 1.75-hour video, shot with two cameras with special lensesthat show the OFW process clearly.) When you com-plete the tacks, weld the panel completely from oneto the other, or, if distortion is nasty, planish theseam a bit—after you first clean off the flux. You can

control distortion somewhat by clamping, joint de-sign, hammering, or prying as you go. Chill blocks,while good for GTAW, are detrimental for OFW be-cause of the additional heat required. When con-structing tanks, for instance, and you need to weld90-degree corners, just use the radius bend joint de-sign where a 45-degree radius bend on each panel al-lows for stiffness against distortion.

Cleanup—Getting Stuff to StickFlux cleanup begins with hot (180° F) water and a

stainless steel brush immediately after welding, followedby a liberal fresh-water rinse. The amount of cleanupwill be minimal if only the filler was fluxed. You canrinse tanks and similar enclosed parts in this fashion or,as an additional precaution, soak them in the followingmanner for 5 to 10 minutes: 1 gallon Technical GradeHNO3 (nitric acid—58-62 percent) at 39.5° (chemists'lingo for temperature-density)—added to 1 gallon cleanwater, either hot or cold.

Any flux residue left in voids or pinholes can be apainter's nightmare in six weeks. If any particular area issuspect, play a neutral flame over it; a yellow-orange in-candescence betrays residue. As mentioned previously,an invisible oxide film appears nearly instantly on alu-minum alloys. Proper scrubbing with an etching solu-tion and waiting no longer than 20 minutes to prime,seal, or fill will avoid such sundry unpleasantness as lift-ing, peeling, or blistering. A good acid etch also ensuresagainst any small traces of flux residue.

The simple economics of aluminum OFW have en-sured its longevity. Today, some professional tankbuilders often don't leak-test the parts produced usingOFW because their experience has proved its reliability.Conversely, tanks they produce using GTAW may havean average leak count of six or seven, and thus must betested. Workability of the H AZ can either make, or liter-ally, break the job. Planishing to remove distortion alsosaves cleanup and paint prep time, as well as increasingthe strength of the weld-softened area.

Just follow the rules and take time to practice thiscentury-old art, and if the parts don't turn out prettydarn nice, they can always be used to cook sand dabs!

Kent White, an EAA technical counselor, achieved MasterTechnician's status atHarrah's Auto Collection in 1976,where he restored metal components for aircraft and autos. Hestarted his own metal restoration company in 1977, and nowteaches, writes, and develops tools for metalworking—andstill pounds out parts. He can be reached at 17167 SalmonMine Rd., in Nevada City, CA 95959; 530/292-3506 or e-mail www.tinmantech.com. He encourages any welder ormetalworker to contact him in regard to preserving the tradi-tions of aircraft metalworking. •

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