Motorcycle frame being TIG...
Motorcycle frame being TIG welded togther.
Gas Tungsten ARC Welding
When it comes to working on motorcycles Gas Tungsten ARC welding, more commonly known as TIG (tungsten inert gas) or Heliarc welding, is the uh, hot set up. TIG welders produce heat by drawing an electric arc between a tungsten electrode and the base metal. The heat creates a molten puddle into which a filler rod is fed as needed. A shielding gas, most often Argon or Helium, hence the term Heliarc, shields the welding puddle from oxidation. TIG welding is an excellent, in some cases the only, way to successfully weld materials like stainless steel, aluminum and titanium, which are all nice materials to use when you're building motorcycles, which is one reason why TIG welders see widespread use throughout the industry, especially in custom and race shops.
Perfected in the early 1940's, primarily to work on aircraft, early TIG machines were expensive and a little esoteric so only specialty welding shops and factories had them. But over the years they've become quite affordable and can now be found in every welding shop and in fact many dealerships where they're used to repair everything from broken cylinder fins to cracked frames.
TIG welding does present some problems, especially at the OEM level. For starters becoming a proficient TIG welder requires lot's of patience, a good deal of practice, and some natural talent, it is an art in every sense of the word so good TIG men are a little hard to find, and by the same token are generally paid a premium for their skills. It's also a fairly time consuming way to weld. If you're a small production run company, or only building a few hundred bikes at a time then having a few guys do nothing but stitch things together, makes perfect sense, and I think we'd all agree it also lends the finished product, be it a custom fuel tank, or a chassis a certain cachet. However if you're an OEM churning out widgets by the thousands then a robotic MIG welder that works morning, noon and night, as well as Sundays and holidays makes a lot more economic sense.
Gas Metal ARC Welding (GMAW)
What's that you've never heard of GMAW? I'm not surprised, the term's a little obscure, so we'll call it by its more popular acronym, MIG, (Metal Inert Gas).
In MIG welding an electric arc is created between the base metal and spool of wire that's fed through a gun like handle. An inert gas, usually Argon, Helium or Carbon Dioxide is used to shield the weld, the choice of the gas being dependent on the metal you're working with. Because the process is easy to learn and the spools can hold up to several thousand feet of wire the MIG process is very popular in production and repair shops, many motorcycle components including frames and fuel tanks are MIG welded either by robots or humans and the process can be used on steel and aluminum.
Early on MIG welders or "Squirt Guns" got kind of a bad rap. This was largely because the inexpensive bikes from Japan were stitched together with MIG welds and while the welds were structurally sound, they weren't very attractive. It wasn't unusual to see errant bits of wire left in the weld for example and the welds sometimes looked as if they'd been made by someone that in the middle of an on the job training program. Nevertheless, you rarely saw them break, at least not during normal use. Robotic MIG welders have largely replaced the human component and the process itself has been much improved over the years so these days it takes a trained eye to spot a MIG weld, and yeah, there are an awful lot of MIG welds on new motorcycles.
As an aside because a MIG machine is versatile, you can join everything from sheet metal, to steel plate with them, easy to use and relatively inexpensive to buy and run, they have become the most commonly used production welders in the world. Furthermore because inexpensive 110V machines are available, along with flux cored wire, which eliminates the need for a shield gas, many serious do-it-yourselfers have some sort of MIG welder in the garage.
ARC Welding
When many of us think of welding the DC ARC weld is what first comes to mind, usually along with a mental picture of manly men welding huge slabs of steel together to produce manly things like air craft carriers and bridges. ARC welders are intense, lots of heat is created and big welds can be made, but they can also be used to weld steel as thin as 1/16 of an inch thick, if you know what you're doing. If you don't you'll do more damage with an ARC or "stick" welder in five minutes than you can repair in a week.
ARC welders work by producing an electrical arc between the metal you're welding and the metal you're adding to the weld. A metal electrode is placed in an insulated holder that's connected to the positive terminal of a generator or rectifier capable of producing enough current to jump the gap between the electrode and the base metal. The base metal is connected to the ground side. When the electrode is struck against the base metal an arc is drawn which provides the heat needed to create a molten puddle. The electrode also melts and is used to fill the weld. Typically the electrode or rod is covered with a hard flux that gives the arc some stability and protects the finished weld. The slag from the flux must be manually cleaned from the weld after it cools off. ARC welds can be made using AC or DC current, and the polarity may be straight or reverse as the situation warrants.
ARC welding has a place, albeit a limited one in motorcycle construction and repair, however because the equipment is bulky, and the skills somewhat difficult to master it's of limited use and popularity. That being said it's my favorite form of welding and I've earned many a nice paycheck sticking everything from steel piers to dump truck bodies together with an old gas engine driven Lincoln ARC welder.
Down The Road
Whether or not future motorcycles will feature as many welded joints as current ones do is debatable. For sure gluing the things together would be cheaper, and yeah, there is some movement in that direction, in fact my 1994 DR 350 Suzuki has its aluminum swing arm stuck together with some sort of epoxy, and I understand some of the current aluminum sport bike frames are also constructed using glued joints.
However at least in the near term I think that welding will remain the preferred method of construction, it's proven technology, and it works extremely well which are reason enough at the OEM level. As for me, I've always enjoyed looking at the properly welded joints that keep my bikes together. Somehow a bike that was put together like some giant model car kit just wouldn't be the same.