MIG welding comes up periodically, here. My assumption has always been that many bikes are MIG welded since TIG is time consuming, and somewhat difficult, and a lot of bikes do not look carefully welded, right up to the 400 dollar frame level (meaning manual welding, probably MIG, is being used). Also there are some parts on suspension bikes where there are long flat runs that could easily be automated. Also, welders like a challenge and good welders can turn almost any process to any task, someone out there is clever enough to pull it off so people considering MIG or stick can probably assume that even if it is rarely done it is certianly possible.
That said, I thought some people might enjoy these Marchetti MIG welding machines:
Thanks for the answer, but there wasn't a question. Just plunking this in the archives for the next time someone asks the question. I do TIG, stick, and gas welding. And wish I had MIG on occasions when I need to lay down a lot of steel.
Actually they sell tig torches for cnc instalation, I was just ordering a new torch from CK and during my web search I came across them, can't remember by whom. Part of my point about welding is that the moment one thinks in catagories there is someone or something out there doing the very thing that someone else says isn't done.
Not sure what they use the CNC TIG for, but fusion welding is one thing a machine could easily do, though the way bikes are welded with pulse doing a lot of the work, it probably isn't impossible to have something that wire feeds also like the weak hand. The advantage to TIG is that it separates out the heating and the feeding. The problem with MIG is that there is the possibility of cold starts. The TIG with CNC could spend a few seconds creating the puddle, then pulse, dip, pulse did, etc... WIth MIG the wire is the electrode, which creates certain challenges, someone has probably solved. Say by having a tig come in and nail the puddle then weld the rest with a MIG head. But all that is just my imaginings.
Just to add....
I have been talking with a manufacturer in Taiwan and they quoted me around 50 bucks for a cromo road frame I designed.
The thing is that they claim it is TIG welded. So at this price they may be blowing smoke, but who knows. I guess I will know a bit more when I get the sample.
in small runs (1000's of units) it's cheaper to have a semi experienced crew TIG welding sub-assemblies with a master welder overseeing, teaching, filling pinholes and fixing other f-ups than paying for everything that goes into semi or fully automated assembly. Automation is for tens of thousands of units. Something as simple as size range (imagine you offer a small med and large) would make full automation difficult. A good example of a MIG'd robo-welded aluminum bike frame would be those crap full suspension MTB's they sell at k-mart (magna, huffy etc..) they use the same rear end no matter what size, and the front end is just a bit longer.
The chunk666 bikes are all stick or MIG, some are brazed with prefluxed rod.
I would agree with you WF. The only thing is that the Marchetti stuff doesn't look that expensive. Too expensive for small numbers, but something short of Walmart. Marchetti is a premium maker of supplies sold by Strawberry Cycles, who sells stuff to the good and the great in the custom field, if surely not these MIG welders. Walmart does not equally well penetrate a lot of countries so possibly in some place like Italy the wally world level bikes are smaller scale and medium nicer.
I do think some of the chinese stuff is hand MIG welded. Just from the look of the bead. Badly done TIG, really bad, looks like they guy couldn't get it going, there is lots of different sized and spaced stuff. The badly welded frames of a not quite Surly level, look like a good smooth bead that didn't penetrate well enough, kinda like someone put a necklace of string around the tube. That tends to be the last thing that comes together with TIG. If you have it together to make effortlessly nicely spaced dimes, then it should be possible to get the setting and pace right for the right penetration. Meanwhile the typical MIG weld, looks casually as if it was expertly done, but the penetration is likely wrong. Anyway, there is a lot of welding, with a lot of machines, and I have only seen some of it, mileage may vary.
the worst I have seen if the SE draft and lager track bikes. looks like someone stuck the tubes together with chewing gum, some joins have no penetration and some are cooked crispy. the drop outs are probably hearth brazed, with a slug of pre-fluxed low fuming bronze filler dropped inside the tube..of course that method has been around for a bit, but they can't seem to get it right, shine a flashlight up the chainstay tube from the purge hole in the BB and you can see light all around the DO tabs...eeek!
to top this off they powder coat it really thick so the weld beads and other imperfections get "lost in the paint" so to speak...
But they ship warranty frames overnight so shops still sell 'em...