MIG welding has come up again, what to buy, etc. I thought my experience as a long time welder might help the discussion. Since this is my experience your mileage may vary.
First of all, even though most folks call any type of wirefeed welding MIG welding, MIG welding really means using a solid wire and a shielding gas. And, in fact, MIG, which stands for Metal Inert Gas, is no longer used. GMAW is the acronym now. Gas Metal Arc Welding. I'm gonna use MIG if I mean solid wire and shielding gas. Welding with fluxcore wire is not MIG welding, though it is a type of wirefeed welding.
Even though I own two wirefeed machines, that are both capable of MIG welding, I find that I use my little 125 volt machine whenever possible. This is because it is light and easy to move as well as, and more importantly, being very easy to use. My 300 amp machine is a wonderful machine too but it only gets used when necessary. It is a large and heavy machine. It is smarter than me too.
My small MIG welder is a Lincoln SP125 Plus that I bought used about 20 years ago. The big machine is a Miller but I don't remember the model. I bought it used too. I wasn't that worried about buying used machines because they were both high quality machines. In any case I want to talk mostly about the small machine.
With the Lincoln I have welded steel and aluminum and brazed steel. That's correct, brazed. The thickest steel I have welded with the machine is 3/8" thick.
Welding with this machine is pretty easy and this is mostly because it is a high quality machine and the voltage and wire speed are infinitely adjustable. The controls can be set just the way I want for a particular situation and this is an immense help. For welding steel in the thickness ranges the machine is made for the guide on the inside of the door that covers the wire spool is plenty good. For welding outside of these parameters I rely on my years of experience welding with this machine to get the results I want and need.
For example, I use mostly .023 solid wire, not .030 wire. Using thinner wire has two advantages, it is good for thinner work when you are trying to put less heat into the work but also is better when welding thicker steel because you can get the thinner wire hotter than .030. The disadvantage is that it takes more passes that .030. So, depending on the job I will switch between the two.
When welding steel that is thicker that 1/4" or if the steel is cold then I pre-heat the work. I use a propane weed burner for this task most of the time. For steel 3/8" thick I get the work really hot. Not only is this necessary to get good and proper penetration it keeps me warm in the winter. Kinda sucks when welding thick stuff in the summer though.
I tend to use fluxcore wire for dirty work and work done outside because I don't need to worry as much about wind blowing away the shielding gas(ses) and because dirty metal welds better with fluxcore. I should point out that I NEVER make substandard welds on purpose. The welds I do must always be stronger than the parent metal, parent metal meaning the metal being welded. When I need to weld on dirty stuff it is usually because I am building up worn away surfaces like the bottom of the bucket on my backhoe. Places where I need thicker metal. Or when I am trying to repair a lawn mower deck that is badly rusted out and it is hard to get all the rust ground out and my neighbor is too cheap or can't afford to buy a new one and I'm doing the job for free. Dirty work is also work done when I have tried to grind out all the dirt and corrosion but think it is likely I will still find some small pockets of dirt and rust. The fluxcore wire is better able to handle these small pockets without making porous welds. Porous welds are brittle and break easy. Oil contamination is a major cause of weld porosity. This is because of the hydrogen that is in the oil. At welding temperatures the hydrogen will come out of the oil and dissolve into the molten steel. When the steel cools and hardens some of the hydrogen will come out of solution and cause porosity. Some will also stay dissolved. And the weld will become brittle for both reasons.
The 125 volt machines are not meant for aluminum but it can be done. Without a spool gun. Spool guns are mainly used for aluminum because it is difficult to push small diameter aluminum wire more than a few inches. So pushing small diameter aluminum wire through a 10 foot long whip is problematic. A 25 foot long whip even more so. That's why I have two Python whips for my big Miller, one for aluminum and one for steel. Both 25 feet long. Python whips pull the wire and work in concert with the rolls in the welder that push the wire. There is more than one brand of pull whips. Cobra whips are probably the most recognized. And the 125 volt machines really don't have the amperage to weld aluminum. But it can be done.
I have welded aluminum with my small Lincoln. I used the smallest diameter wire. I used 4043 alloy. It is harder to push without "birdnesting" than 5356 wire because it is softer. (Bridnesting happens when the wire cannot be pushed into the whip so it just piles up in a big tangle that resembles a bird nest.) But the welds I needed to do required 4043 alloy wire. I did this by using a teflon liner in the whip and keeping the whip as straight as possible. I adjusted the wire feed rolls to such a light pressure that the wire would stop feeding before it could birdnest. I pre-heated the work so that it was very hot, and welded away. I was welding 1/4" thick aluminum castings that needed to be built up due to casting defects. I later machined the areas built up with the welds. I found no porosity. I'm sure I could have welded 1/4" plate too with the same procedure. This would have made the plate soft and weaker if it was a 6000 series alloy but if I was welding a 5000 series alloy, like 5052, and using 5356 wire, the pre-heat would have made no difference to the strength of the parent metal.
I only attempted the aluminum welds with my small welder because at the time I didn't yet have my big Miller and I couldn't get my TIG torch into the bores that needed to be built up. But I did it and it worked well. And if I can do it then someone else could too.
I have TIG brazed a lot of steel parts. TIG brazing is usually done with silicon bronze wire. There are other wires available and I have used some of them. Like aluminum bronze. But MIG brazing is a thing too. I have done this using silicon bronze wire. I needed to braze some steel assemblies. Silicon bronze wire was specified. The job required many inches of brazing so I decided to try using my little Lincoln machine instead of the TIG machine. At one time, soon after I bought the Lincoln, I took a 1 day class on MIG welding from a very well respected instructor. The class was worth every penny. This class taught me how to MIG braze. So when a job came up a couple years after I took the class I was prepared to try MIG brazing an actual money paying job.
Since it had been some time since I had attempted MIG brazing I burned some wire on practice pieces to get proficient again. It didn't take long, it is easy. I used my teflon lined whip and had to pre-heat the work. But I got the job done, the beads looked good and were good.
So, my experience with a 125 volt machine has taught me that using a high quality machine can help a person make high quality welds. This is because of the way the machine can be adjusted and because the machine is so consistent. When adjusted a certain way the adjustment stays that way. It doesn't drift off of the adjustment. So when I adjusted the drive rolls to just barely push the aluminum wire the rolls kept that adjustment. And the voltage stays constant as the machine warms up. And the wire speed doesn't vary. My experience has also taught me that I can make good welds that are beyond the usual capabilities of the machine if certain things are done. Being able to make good welds within the envelope that the machine is made for helps when going outside of that envelope. Once a person learns what a good weld is and how to make them then using certain techniques that enable the machine to make good welds beyond its usual capability is possible without much extra effort.
Cheers,
Eric
