Nuts & Bolts

Craft & Technique •

WHEN IT COMES TO WELDING aluminum, which of the following truisms are memorable to you, dear reader? A. You can't weld aluminum. B. You can't gas weld aluminum. C. You have to use hydrogen in order to gas weld aluIts minum. D. You must use blue glasses in order to gas weld aluminum. E. GTAW (TIG) is the only way to weld aluminum! After considerable research—from reading many old welding texts and interviewing old welders, to contacting the Aluminum Association—and having used gas to weld aluminum since 1976, these truisms seem to be untrue. Answer A is partially true. You simply cannot weld some aluminum alloys, like 2024 and 7075. Answers B and E come from some electric welding schools, simple misinformation, and some rather aggressive "electric-machine" welding suppliers. Answer C is a legacy from World War II, where the entire civilian population was pressed into wartime materiel production, ultimately producing more than 300,000 aircraft in 4.5 years! In these aircraft plants, women welders in crews as large as 50 produced parts and followed methods approved by the plants' management. In 1941, however, and before Pearl Harbor, Alcoa (the nation's only aluminum producer) reported that oxyacetylene was the most popular method of aluminum welding in the U.S. By 1947, though, the leading welding books of the day were mysteriously stating that oxyhydrogen was "more suitable for aircraft aluminum welding because it

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Aircraft Aluminum Gas Welding

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MARCH 2000

gas. When wartime rationing came about and acetylene was specified for shipyard cutting torches and other steelwork, the electrolysis plants were moved to the aircraft factories, where everyone gladly used the tools and history; tradition, tools, and methods materials given them and never felt the need to ask the KENT WHITE reason why. Lastly we address answer D. In the 1940s aluminum welders borrowed the now-antiquated blue glasses (cobalts) from the steel foundries, but through the 1930s and '40s, many welders wore no safety eyewear at all for gas welding! In the days when movies cost a nickel, $3.50 for a set of goggles was expensive! r '?*Vj

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Gas History Using oxyacetylene to weld a jetaircraft component. (Photo: Alcoa)

was cleaner." That's not quite true. Paul Dickerson, chief consultant to the Aluminum Association, says the largest prewar aluminum welding operations were in the cookware industry, and it used the economy-of-scale electrolysis method to break river water into H 2 and O2 for welding

Key Words OFW—oxy-fuel welding (gas welding or torch welding) GTAW (also called TIG)—gas tungsten arc welding GMAW (also called MIG)—gas metal arc welding HAZ—heat affected zone Planishing—smoothing by hammering or rolling Metal finishing—smoothing by metal removal (filing, sanding, etc.)

Developed right at the turn of the century (that last one, not this one) the oxyacetylene torch remains pretty much the same unit we use today. With the advent of welding fluxes around 1913, it became possible to torch-weld aluminum, stainless, Inconel, Monel, cast iron, magnesium, and titanium. In November 1942, a couple of creative men at Northrup cobbled up the first "heliarc" (which became tungsten inert gas or TIG, which then begat GTAW for gas tungsten arc welding.) In a few years, together with "wire feed" or MIG, for metal inert gas (now GMAW for gas-metal arc welding), these new welding methods helped pioneer the application of exotic new metals vital to supersonic flight. However, for nearly half a century prior and half a century since, the common oxy-fuel torch has been a significant mainstay in the aluminum joining processes.

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1. A P-51 wing root fairing. Where is that lady today who made this beautiful gas weld 50 years ago? 2. The author using oxyacetylene to weld the two halves of a P-51 header tank together. 3. This Luscombe wheelpant was pressed in halves and then joined by oxyacetylene welding, leaving the weld bead exposed. 4. This leading-edge air intake on EAA's B17, Aluminum Overcast, shows two types of welding methods: TIG, which are the large stressrepair "worms" at the corners, and OFW, which are the original factory welds, lying flat and barely visible, surrounding the opening.

Torch vs. TIG OFW's chief advantages over GTAW are economy, speed, penetration, workability, wind resistance,

and that its small, flat weld beads re-

quire minimal planishing and metal finishing. OFW's disadvantages are flux cleanup, larger HAZ, and that fewer alloys and heavy thicknesses

lend themselves well to the process. Gas welding aluminum alloys, stainless, and titanium, etc. requires special fluxes to keep oxygen out of the molten puddle the same way the

inert gases, such as helium and argon, do with GTAW. However, these fluxes allow excellent weld penetration to the root side, something only expensive back-purging enables GTAW to equal. Until 1994 Boeing gas welded thin aluminum sheet at its Welded Duct Facility, when the flux industry as a whole finally bogged down in MSDS, OSHA, and EPA entanglements. Boe-

ing now employs the back-purge GTAW method, where each duct is filled with inert gas prior to welding. As I understand it, Marietta Corp. in Maryland still uses OFW, as do vari-

ous other facilities. When you consider the purchase of a fully equipped electric machine and the cost of consumables, such as tungsten, argon, and electricity, against the cost of a torch and its gas and some fluxes, there might be a nice cost savings with the torch. Even if the electric box can weld tinfoil 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. It will weld thick metals (those over .125 inch) much better, and it makes life a bit simpler when welding com-

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Sport Aviation

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Craft & Technique

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plex 4130 engine mounts and lift struts. What about MIG? The wire-feed GMAW (what we thin-sheet metal guys often call the "manure spreader") does okay on thick metal, and it leaves a high bead with some sort of penetration. An expensive, digital turbo double-backflip model does thick stuff absolutely beautifully, and on the best machine a virtuoso might be able to do an outside corner 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 backside showing penetration, and the edge view shows bead thickness. (Welds by author)

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

Welding, Brazing & Soldering

By definition, brazing and soldering do not melt the parent metal— they join by surface adhesion of the melted 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 define them in other esoteric ways. I'll try to cover them all for you: the temperatures and alloys; the fluxes, hardnesses, and brittleness; yield

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and tensile strengths; and the fillet colorations. Divided by temperature, soldering is generally defined on brass, copper, steel, stainless, and aluminum alloys as melting in the range up to 850° F. Brazing goes from there upwards to slightly below the melting point of the parent metal. Welding, of course, is right at the melting point. If the parent

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metal does not melt, but is bonded by the melted filler, then the process is not welding! Braze welding is another misunderstood term. It occurs so close to the melting point of the parent metal that when using the same

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This interesting photo is of a 1942 Ryan fuel tank (ID tag extant, but not shown) with the weld seam running vertically next to a brazed-in fuel fitting, with inspector's stamp just visible. (A braze is typically darker than a weld.) ;

filler on two similar but different aluminum alloys, one will weld and the other will braze. For example, if we're using a brazing filler of 1140° F on 6061, which melts at 1100° F, we'd be welding it because the 6061 is molten at 1140° F. If we used the same process on 3003 (which melts at 1195° F), we'd be brazing. Haven't we all seen those helpful fellows at the swap meets who hawk the latest upgrade of a marvelous "mystery metal" that "welds, brazes and solders" every white metal part ever made, and all we need to do it is a propane torch? And when we get home the magic evaporates and

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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 of some big parts-production facility, so for quality results avoid flea-market zingers, 3-in-l pot metal alloys, and various Lumi-braze zinc-bearing materials because their chief use is to repair cheap die-cast parts or to manufacture heat exchangers. One common failure of these materials occurs when one planishes aluminum sheet so joined by hammering or rolling, and the subsequent cracks arch observant eyebrows. Note, one must completely remove areas erroneously joined in this fashion or attempted fixes will spread the infection. In general, brazing materials are brittle and hard (high tensile but low yield strength), and on aluminums they are darker gray in color. Joint design is also important for both brazed and soldered construction, because we need plenty of surface area for the bond to achieve requisite strength. For this reason,

Fuel Gas Acetylene Propane Mapp Natural Gas Hydrogen

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high corrosion resistance and therefore needs a corrosive flux. For the most part solders are dark gray and soft, with fair tensile and sometimes a fair yield strength. It's unusual to find aluminum solder, but a new one that uses a noncorrosive flux has superseded the old alloy and flux combination from the 1940s. The new stuff won't join 5000-series alloys, but it is certainly applicable to nice repairs on radiators as it flows just as well on aluminum as it does on copper.

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oxygen consumption. The choice of a fuel such as propane, MAPP, or natural gas might be based on simple cost alone, but it's wise to consider that the excess oxygen makes the cost rise again, if you don't use an injector-type torch to lower that oxygen consumption.

Tools of the Trade

Virtually any torch may be considered viable, but I tend to avoid giant "railway" torches and tiny jewelry torches. Most torches are fine, some are really good and comfortable, and a few might be considFuel Gases The fuel gas chart indicates only ered for specialty work. (Out of my some of the significant oxy-fuel cost extensive collections I have occadifferences between hydrogen and sionally selected a Victor cutting acetylene. That torch to nicely weld .050-inch 3003 acetylene is much for my students' considerable enterhotter should suf- tainment.) Torch tip selection is always one fice. Using hydrosize larger than one would normally gen requires a completely sepa- choose for the same thickness of rate tank, regula- steel sheet. The "formula of thumb" tor, hose, and for this is three-quarters of the metal torch because thickness equals the tip orifice diammixing acetylene eter. (Please don't ask me to translate residues with hy- your Smith 00 tip size to decimal, drogen gas invites because all of the torches will want a explosive disaster. translation, too.) Hoses of choice are light and flexFurther, hydrogen doesn't pro- ible, to allow out-of-position work These young ladies are welding parts for the P-39 duce soot, which and long periods that require a Airacobra. (Photo courtesy Bell Aircraft) we can use as a steady hand. Because of the low except for welds, butt joints are rough temperature indicator when pressures required, regulators may annealing aluminum sheet. Hydro- not be accurate at the low end, and strictly taboo. The fluxes for solders and brazes, gen's benefits may be fuel production one will need to twiddle with the whether corrosive or noncorrosive, cost (if an electrolysis plant is feasi- torch lit to establish the best flame. are also special for that particular ble) and a slightly cleaner weld zone Do this with the torch valves wide operation and depend on the alloy, appearance because of the absence of open, setting the largest, best flame for the tip. Glance back at the gauges the required bond strength, and carbon in the flame. •.r', the world's only hands-free, completely automatic intercom vox 1 Individual volume controls for pilot and co-pilot 1 Stuck mic indicator 1 Speaker Amplifier output 1 Expandable up to 8 headsets 1 Entertainment input with SoftMute™ • Easy to install Remote volume control capability

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