You have to use the right tools and procedures for what you want to do.
First off, welding sheetmetal (thin stuff) is kind of tough to do, no matter what. There is a fine line between not enough 'heat' and instantly blowing a hole right through the metal. And you also have to manage the heat input carefully or you'll end up with a very warped piece of sheetmetal.
Next, FCAW usually does have more spatter than GMAW. It's just one of the ways the two processess are different.
And FCAW usually burns 'hotter' than an equivalent 'size' of solid GMAW wire, so it will usually enable you to weld slight thicker steel (with the same machine) than you could with GMAW.
Most of this should be covered in your manual (if from any of the 'decent' welding companies), so RTFM applies here.
Next, 'cheap' welders (machines) are often tougher to use because they have a rather limited power output in the first place and they also have a rather limited power adjustment in the second place. Run the machine at one of its 'sweet spots' on the appropriate thickness of steel and it can give OK results. Try to run that machine on a much different thickness of steel and you can be in for a difficult time trying to make any sort of 'good' weld.
Example time. All of this is for steel.
Lincoln L-56 solid wire GMAW, using short-circuit transfer (as almost no 'small' machine has the power output and voltage output to run in spray-mode transfer).
0.025 wire at 100 ipm WFS and 15-16V in short-circuit transfer mode gives about 35 amps using C25 gas, about 80 amps at 17-18V and 250 ipm WFS.
Everything else the same but use 100% CO2 as the shielding gas and you have to run at 17V for that 30 amp output, and 19V for the 80 amp output.
0.030 wire at 75 ipm and 15-16V gives about 35 amps using C25, about 70 amps at 150 ipm and 16-17V, and about 130 amps at 300 ipm and 20-21V.
Using CO2, that same 0.030 solid wire needs about 17V at 75 ipm to give that 35 amp output, 18V at 150 ipm for the 70 amp output, and 22V at 300 ipm for the 130 amp output.
Let's look at a 'typical' FCAW wire used in the 'small' machines. Lincoln NR-211-MP (E71T-11) in 0.035 size (diameter).
At 50 ipm and 14-15V you have about 30 amps.
At 70 ipm and 15-16V you have about 60 amps.
At 110 ipm and 16-17V you have about 115 amps.
At 150 ipm and 17-18V you have about 130 amps.
At 200 ipm and 18-19V you have about 155 amps.
At 275 ipm and 20-21V you have about 155 amps (wire is running at approx max current saturation and will not really get any more amperage no matter how much voltage and WFS you run).
All in the manual, or in this case the Welding Procedures section of the Lincoln catalog.
So with only two voltage adjustment settings, how close do you think you can get to the desired/proper welding parameters? And will those parameters be even close to what is needed to weld the thickness of metal you happen to be dealing with?
General welding rule-of-thumb is 1 amp per 0.001 material thickness (single pass welds).
So if the machine in use even has the guts/snot/power to run the parameters, that 0.025 solid wire GMAW and C25 gas will maybe be 'adequate' to weld about 14 gauge steel, the 0.030 wire maybe about 10-12 gauge material (about 1/8 inch thick).
That 0.035 FCAW NR-211-MP wire can maybe go to about 1/4 inch thick (multi-pass).
You have to use the right tools for the job. In this case the welder (machine) and the wire (size and type) and the parameters.
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