Welding advice

[georgebarr]

I am new to MIG welding and tried it a couple of times using mild steel tubing (1/8" thick) on some projects. I have noticed that as the welds cool, the mild steel begins to warp. I heard that tack welding (welding small area) should be done to secure the two pieces in position before putting a bead of weld over the entire weld area. What is the technique or secret I should be using? Should I wait to allow the tacks to cool (for how many minutes) before welding long beads? Should I avoid welding long beads? Should I be looking at the spark and making sure it hits the exact area I want to weld?

Any advice for a beginner is appreciated. I would like to get near expert welding results if possible.

[bcromwell]

For metal that thin you can't do 'long beads' , Stagger and do 1/2 - 1" beads.

Also what amperage are you running? (If your machine has a four position switch, take the machine amperage and divide by 4 to tell you what each postions amperage is)

[JFettig]

yah, he is right, and tacking is a technique, you want to tack both ends together at least, and even the middle in a few places if you need.

I know I have layed long beads on stuff like that but most of the time it tends to warp.

Jon

[HuFlungDung]

George,

You're new to MIG but want near expert results? Don't we all?

Anyways, you are going to get some warping. But, the voltage and wirespeed are very closely tied together, so you have to play with the settings a bit to figure out the lowest heat setting that you can use to still get a good bond.

At low settings, the weld metal is going to transfer in globules, at quite high settings, spray transfer may begin to occur. Spray transfer creates a beautiful weld, but dumps lots of heat into it, too

Globular transfer does not sound nearly as nice, its kind of like water spitting in a hot skillet. However, this is most likely the mode you will be in, due to using lower wirespeed and voltage settings. Proper settings will result in a rapid-fire crackling sound.

Inert gas flux is required for a lower spatter and better looking weld, as well. There are three, or so, mixes of inert gas (that I am familiar with) used for steel welding. These all have an effect on the "heat" of the process. Talk to your gas supplier about the best choice for what you want, which is low heat, thin material welding.

The proper wire speed setting will keep the melt zone a 1/4 inch or so away from the copper tip of the MIG gun. This melt zone distance should increase as you increase the voltage, to prevent overheating the tip and the subsequent sticking of the wire inside of it.

For an .035 wire size, using what we call "MIG Mix Gold" inert gas, you can begin at 15volts about 160 inches per minute wire speed. If you use smaller wire, you can decrease these settings further.

[ESjaavik]

Try this once:
Take a 10mm steel rod and make it a bit pointed. Tack it to a thick steel plate. Ask someone to grab it at the top, not too close of course. Then at full amperage quickly run a bead around it. I'm sure you'll get a surprised face as a reward. I did this and the guy started laughing. The rod wagged like a dog's tail.

Try to lay the two pieces close at the end you start welding, and with some space between them at the other end. When you get this right, they will meet each other as you get to the other end. Then they will contain less strain than if you tack them. When you tack them they will not be allowed to contract and that leaves you with more strain in the finished material. And if you have to grind off a lot of bead after you're finished, you have put in too much metal and thus heat, try with less the next time.

Go buy this book: "Modern Welding" Althouse, Turnquist, Bowditch, Bowditch. ISBN 0-87006-668-4.
It's not cheap, but the best coverage I've seen on welding. Also covers soldering and brazing.

[trubleshtr]

For more proffesional looking welds, also prepare the metal joints first by beveling the edges that you intend on joining. Clamp everything, and leave it clamped until things are cool enough to handle.Proper grounding is critical to smooth flow of current aswell, make sure there are no rust or painted surfaces you are trying to cross. If you are welding outside (or with a fan blowing on/near you) try to weld elsewhere, or block the wind, The sheilding gases used easily blow away and affect the welding process, and can contribute to welds that fail later in life. If you are getting splatter and feel you have the right settings you can buy anti-spatter (goop) that you dunk the tip of the mig gun in. If you don't have a gas set-up for your mig, use Flux cored wire, and you will get similar results to using gas.
As an industrial machine builder, I try to stick to the above rules, I have been welding close to 10 years and I still have days where I have to shake my head after welding.
bcromwell and huflungdung have good advice also that should be practiced to get nice welds.....
good luck

[doug6949]

All of the above is sound advice. To that I will add the need for practice. Close fitting joints help minimize the pull. It is not uncommon to tack the entire assembly before any welds are completed.

You will get significantly better welds with MIG (metal inert gas) if your metal is absolutely clean and free of mill scale. Flux core wire is more tolerant to surface contamination. You did not say which process you are using.

[Mortek]

To minimize warpage and pull, tack both ends, then use a method called backstepping. Lets say you are making a 12 inch long weld. Start your first weld 3 inches from where you would normally end the long weld. When you've welded that 3 inches, go three inches in front of the start of the 1st weld and weld to the start of the 1st weld and so on. Tacking also helps.

[georgebarr]

I am using gasless mig welding. My mig is a 220V mig and is rated as being able to weld 1/4" thick metals (I am assuming 1/4" is the thickness of one of the pieces and not the thickness of both pieces combined). My question is can I weld mild steel that is upto 3/8" thick? Also, will tack welding (w/o using beads of welds or intermittent welds) be good and strong enough for mild steel w/o putting welding beads?

[HuFlungDung]

George,
how many amps is your machine rated at? What diameter wire is it rated to handle?

With multipass welding it is of course, possible to weld greater thicknesses. However, that being said, you should weld at a higher heat setting (higher voltage and wirespeed) when welding thicker materials to avoid cold lap and brittle joints. A bit of base metal preheat can help avoid brittle weld joints, too.

One simple test to determine if your heat setting is right, is to weld a couple of sample pieces of mild steel ("iron") together on one side only (a simple butt weld). Then, clamp the piece in a vice right near the weld zone. Hit it with a hammer. If it immediately breaks out beside the weld, then the base metal was too cold. This can be remedied by either preheating, or welding at a higher heat.

Of course, you will always succeed at breaking the piece off eventually when doing this test, but by observing the amount of stretching in the weld zone as the piece bends over, this gives you an idea of the ductility of the weld joint. For mild steels, you would expect the joint to stand some bending, as opposed to just snapping off immediately.

[InventIt]

Good way to test a weld Hu, U never cease to amaze me with your knowledge of this stuff.

George, when your welding you want to move the wire from one piece to the other in a cicular pattern. Make little circles from one piece to the other. Go slowly so the heat has enough time to penatrate and make a pool of molten metal.

Try this to get a really nice weld, set your pieces up so you can weld straight up and down. Start from the top and draw your bead down the piece. Let gravity keep the bead flowing and work your torch in a zig-zag pattern like I said. Practice, Practice, Practice...

[georgebarr]

HuFlungDung,
I have a Clarke 220V 180Amp MIG uisng 0.35 wire size with gasless flux core wire.

InventIt,
What do you mean by circular pattern, moving from one piece to the other, in a zig zag pattern? Are you saying to create small circular patterns (say about 3/8" dia. circles) starting on one piece (in a 2 piece joint) and slowly moving to the second piece (using circular motions all the time)? That sounds very similar to when I took a Acetylen/Oxygen welding class back in 1985 in high school. Any similarities with the 2 techniques (MIG vs. ACEY/OXY)? Any more advice? I plan to weld something on Saturday.

Thanks,