Originally Posted by Scooper

I'm not a welder, but my understanding is that TIG offers much better results for welding thin walled chromoly tubing than MIG. The usual advice is that MIG is much more difficult to do clean work and avoid burning through thin walled tubing.

MIG welding chromoly tubing | BikeForums

Originally Posted by CliffordK

When I put together my cargo bike. I thought I'd mig it due to speed...

I found that I was blowing far too many holes in the thin metal (ok, so I am good at blowing holes in stuff). And my welds were quite ragged.

The second half of my welds were tigging, and they turned out much nicer with fewer problems.

Anyway, the bicycle tubing is mighty thin, and tig welding just seems to work better. Do the factories use some kind of automated tig welders?

Originally Posted by fietsbob

no usually they just train a lot of people to do the work, thats why so many bikes come out of Asia, low labor cost.

Originally Posted by Brian25

Tig welding generally gets much better penetration/ much stronger welds than mig welding.

Originally Posted by MassiveD

The actual answer is:

1) When you are trying to do critical welds you want to eliminate cold start problems. This is when you start welding if the method is such that you can't separate heat input and filler addition, then you get bad welds. With Tig you can heat the weld pool to the point where you add filler independent of the rate at which you add filler. You can adjust heat and filler rates independent of each other and on the fly.

There are a lot of starts and stops in bike welding as you work around the tube, or make tacks to hold parts and reduce distortion. Later you have to burn through the tacks.

2) for the same reasons as above you can control heat and filler as you progress around the tube. You may run into structures like plate drops where you need to pump in a little more heat, or as you progress around the tube, the overall heat in the part goes up, and you need to lower the heat. Constant independent control is a must.

3) There are more filler rods available to work with odd alloys in tubes for TIG.

4) Torch is more configurable, and can be made smaller as it does only one thing, pour on the arc.

5) Shielding is more accurate and adjustable, with more control features, and more structural formats. Custom gas lenses as an example.

All that said some of these limits can be overcome through MIG configuration, though that is not a home shop thing as much as TIG. You are basically forced to come up with custom TIG configs just to get going, while in MIG it is more something on bikes that might be done as part of a robotics set-up.