Most of you guys have a MIG welder and know how to use them. However, since we're getting so many new members, I thought it a good idea to share a few procedures that many may not be familiar with. Some may just be starting out with a new MIG welder. The information is not "cut in stone" since there are many ways to setup a MIG machine, but these procedures have served me well for over 30 years --
So before we get to actual welding, here are few things that must be understood before you strike that first arc. Most importantly is getting the machine ready to weld. New machines come with good manuals, but they are only a guide; fine tuning the machine is left up to the operator.
First step is to make sure that the welder polarity is setup properly for the MIG/Gas process. This is important since the polarity requirements change when moving from flux core to gas -- and vise versa
There should be a tag inside the welder to indicate what connections must be set for converting to the proper polarilty. Hard to believe but many welding problems can be traced to this critical step. You won't like the look of your welds if the polarity doesn't match the process. Many guys have beaten their heads on the wall for days trying to figure out what they were doing wrong -- when in fact their only problem was a polarity issue.
Another critical step is to choose the correct feed roller. The roller grooves are matched to the wire size. In my case I used a spool of .023" wire, which must be fed to the MIG gun by the MIG feed motor with the appropriately sized .023" roller. Getting the roller mixed up will cause the wire to feed improperly (either skipping or jamming) in the gun.
Critical at this stage is the feed roller pressure on the wire. The setting is adjusted by a spring loaded clamp that ensures that wire feeds smoothly. The manufacturer usuall lists an approximate setting in the manual, but the best way to adjust the pressure is to observe the wire being fed into and out of the gun. If the spool of wire skips, then more pressure is needed. The spool should rotate smoothly and evenly and the wire should exit the gun in the same manner. The trick is to find the spot where the spool just begins to track smoothly and not exceed that feed roller pressure setting, because too much pressure will damage the wire and may cause it to "birdsnest" before entering the hose.
Next step is to make absolutely sure that the tip on the gun matches the wire in the machine. The tip is the electrical connection to the wire and if too loose, will cause very spotty welds and spattering.
Of note here is that there is a spring retainer on the end of the MIG gun (toward the back of the brass fitting). The nozzle is held in place by this spring. However, the nozzle will only screw off the gun in one direction only.
On most new MIGs the spring and nozzle have a very tight friction fit, so the design only allows the nozzle to be removed when turned in the clockwise direction (When facing the front of the MIG nozzle). If the nozzle is forced off in the opposite direction, the spring retainer will get damaged and will have to be replaced before another nozzle can be refitted.
One of the most useful tools in maintaining a MIG gun is a set of MIG pliers. This tool functions to remove stuck nozzles and tips, offset cut MIG wire to the correct length for starting a weld, and to clean the nozzle itself. These are just a few uses; the least of which is that the tool also functions as a good needle nose plier.
Removing a nozzle -
Cutter jaws provide the required wire offset for easy arc startup
seating a new tip --
Cleaning (reaming) the nozzle
Lastly, a good spatter gel will aid greatly in extending the life of a nozzle. Simply dip the tip of the gun into the gel and weld spatter won't clog the nozzle as readily. Although the gel is mostly used for flux core welding (which produces more spatter), it's a good idea to dip the welding tip a few times when using gas. It will extend the life of the tip and nozzle.
At this point I'm ready to weld something, but I need to dial in the heat and feed in order to get a good solid weld. The goal is to get the welder setup for adequate pentration and to provide enough wire feed to get a good even bead. When all these things come together, you can hear a consistent "buzzing" or "sizzling" sound from the end of the MIG gun without producing very much spatter.
First item is to take a piece of scrap metal from your project. In my case it's a piece of a rocker panel. This will ensure that you dial in the welder for that specific alloy -- because alloys differ and you want to setup the machine to work at its optimum.
The thickness is 20ga steel, and based on some convention, the approximate gas flow is between 12 and 20 Cubic Feet per Hour (CFH). If you're working in a garage with stable air, then 12-15 CFH is a good starting point. If you're outside in a slight breeze, then 16-20 CFH may be appropriate; when the wind is blowing you may need to go to even higher flow rates. This is a judgement call.
NOTE: Also, the proper gas flow is read from the regulator gauge ONLY when the trigger is pulled on the MIG gun -- hence the gauge setting will have to indicate at least 18-20 CFH (or more depending on the regualtor) of static pressure in order to get a 12-15 CFH flow rate when the gun trigger is pulled.
The first heat setting is also a judgement call. Many machines include an approximate setting guide for heat/feed based on a material thickness chart supplied with the welder. I don't use that --
Here's my "quick and dirty" method.
My first attempt is designed to find the lowest heat setting at which I can still burn
a hole through the material with the wire speed set at medium feed -- without moving the gun at all. (In my case the feed dial goes to 10, so I choose 5 as the feed setting). I could still burn a hole at heat range 3 and wire feed range 5. --- Sorry for the bad pic -- clearly though this heat range is too high for 20ga steel because it burned a nice BIG hole almost immediately.
Next step is to dial down the heat setting to range number 2 and keep the feed set at range 5
This time you can see that there is no hole, but a lot of spatter and hardly any penetration --
Clearly now there is too much feed -- so I dial down from range 5 to range 2.5 (half of 5 -- I use this "halving" method to get within a useable range)
Here we have some good results -- heat range 2 and feed range 2.5. The bead is smoothing out, and the penetration looks good.
Judging from the pic, the bead has good penetration (so the heat is good), but still a bit uneven. That means that the feed is a bit too fast.
To remedy the problem, I take the feed range from 2.5 down to 2 -- while the heat range range is still kept at 2.
This bead "sizzles" nicely, and is very even (the top bead in the pic). The penetration is perfect and it looks very good cosmetically --
Penetration is 100% from underneath
This is a good setting to start welding 20ga steel -- now I need to try this setting on some new 20ga that will eventually be welded onto the existing 20ga alloy in the car.
I layed down two very nice beads on the new alloy with the same settings (heat set on range 2 and feed set on range 2) -
Penetration is also very good --
So now these heat/feed and CFH settings will be written in my welding log for future reference --
Just for demonstration purposes, to show what happens when the gas flow is not right, I set the CFH flow down to 5 CFH -- notice the burn-through. It's critical that CFH be followed as recommended.
Hope this helps some of you get that machine "dialed in" correctly.