Floorpan welding help needed

[NashBronco]

So I have screwed in new floor pans (from TBP) and now I need to plug weld them in. I am new to welding and have a Miller 211. I am running gas and using .23 wire.

I have been practicing my plug welding on clean scrap pieces and keep ending up with “undercut” on the edges of my welds. The scrap pieces are 16 gauge and I have set my welder anywhere between 3.25-4.5 and wire speed around 40-50. My welds look better when I have the amps set in the 4.25 range but they still have undercut on the sides. Am I moving too slow? Amps to low/high? Wire speed issue?

Any advice on how to fix an undercut issue? Happy to post pictures of that helps.

Thanks, Houston

 

[Apogee]

What are you using for cover gas? Straight CO2 or 75/25 CO2/Argon mix? 100% C02 tends to provide a bit more penetration as it runs hotter than the mix.

With the .023 wire, I would expect to have the voltage a little lower than 4, but that's not to say you can't make it work where you're at. Undercutting the toes of the weld is generally a function of too much heat and/or poor welding technique. I would start by turning down the voltage, adjusting the wire speed to match so that you get that nice bacon sizzle sound while welding on a test piece of material, and then working on your technique. Shorten your arc length by keeping the tip nice and close to the material and hold the gun angle close to perpendicular to the spot weld to get uniform arc length around it. Depending on the size of the spot weld, I will sometimes do a little swirl with the tip to get good penetration without undercutting or burn through. This is one of those don't move too fast or slow type of things...think Goldilocks...you want it just right.

FWIW, I'm not a professional welder, but my brother has a Miller 211 (nice machine) and I usually run a Miller XMT304 CC/CV with remote feeder, and a lot of it just comes down to practice. There are some great Youtube videos on MIG welding techniques and other online resources that I wish were available when I learned to weld in high-school 20+ years ago. Otherwise, if you have a community college near you with a welding department, those classes can bring you up to speed relatively quickly and cheaply and can be a great way to not only get the skill, but the theory behind it.

Tobin

 

[NashBronco]

Thanks Apogee. I am using 75/25 mix. I have abosolutly no doubt that you hit the nail on the head with poor welding technique!! I have reached out to a few community colleges and the only classes they offer are full semester type classes. That’s a little more time than I can devote right now. I may put an add on Craigslist services to see if someone can come by my place and teach me on my machine.

I am probably not getting perpendicular enough and too much wire out. I’ll work on those today. I also thought 4 was a little high. I’ll keep tinkering with it. After all that’s the fun of it.

 

[Apogee]

Spot/plug welds can be inherently difficult, because there's very little time to actually get a feel for how the machine is running. I would practice butt, lap and tee welds first to get a better feel for the machine, how it starts, etc, and then move into spot/plug welds. With a spot weld, you want to get good penetration without undercutting or burning through, so I usually start in the center of the hole to strike the arc, and then circle the puddle if it's large enough. A nice, hot, flat spot weld will have better penetration and strength than a big, tall, cold one, and it will be easier to clean up afterwards with less grinding/sanding/etc.

If you don't have an auto-darking hood, I would highly recommend one, especially for sheet metal work. It's not to say you can't do it with a normal helmet, but all the start/stopping can get a bit tedious with flipping your hood up and down, especially if you don't have decent head gear. I love the light-weight old school helmets, but find that I don't put one on very often anymore.

Also, take care of your body. The UV will give you a sunburn you if you let it, so put on sun screen and cover what you can with your clothing. Position your body so that you're not inhaling the fumes as best you can...this is critical if you might ever weld anything with zinc/galvanize/cadmium/etc, such as fasteners. Most of all, have fun and burn some wire. If you have an excuse to build a welder cart, tool cart, shelving, etc, now's the time to do it and call it practice.

 

[bronkenn]

I run a Millermatic 180 and I find the .035 wire does a better job at plug welding. The Millers have a weld setting recommendation chart on them that is pretty close, Like Apogee recommends I also do a little swirl motion as I weld. Comes out pretty good with less grinding when done. Some welds require a two part weld sequence where I'll start a spot weld. stop and then finish the weld. I don't know why but sometimes I do this and the spots come out good. Experiment a bit and should be fine. Ken

 

[Wyflyer]

I recommend a 2 or 3 setting on the heat. 3 for a small hole fill, and 2 for larger ones.
Maybe back it up with a flat piece of copper on the backside.
A plug weld should just be a small 'zap' and it's done, maybe 1 second duration

 

[rspd505]

Like others have said use a short burst. I try to start my weld in about the 2 o’clock point of the hole and about 2/3 of the way to the edge. Strike the arc and watch the puddle, make a small “C”. You’ll push the puddle around to fill the hole. This whole process will take about a second or less.

 

[nvrstuk]

I just burned 4 %'s of .023" wire in my Miller 222doing sheetmetal, spots, gas tank mods and built new floor pans...practice , practice and...

Try different patterns and heat/ wire speed settings and WRITE THEM DOWN as you weld ! Important!!

This way you can compare 8 practice spot welds with 1/2 dozen strings changes and remember and compare-very important to run multiple spot welds with each setting. Good luck. I used to teach HS kids how to weld decades ago! . Not saying I'm great, but I can sure make them good welders thru technique and a systematic approach!! Good luck, you'll get it.