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How to Mig Weld: Welding Tips

A guide for beginners and beyond

How to mig weld

Obviously it’s safety first when you’re learning to weld. That is common sense, but I say that so you’re sure to remember: welding is dangerous. Welders throw sparks; they set things on fire. Make sure anything in the area around you that could possibly ignite is removed. If you are outside, near grass or bushes, wet them with a hose.

Some welding safety tips:

Practice welding, then practice more

When you are ready to start, practice welding on scrap metal that is close to the thickness of the metal you are going to repair. This is usually 20 or 22 gauge “stock material” which is available at metal scrap yards.

In welding, practice is essential and it will show up in your final effort. You definitely want your technique in place before you weld a live project on valuable metals, a car, or other items.

Welding Systems

A MIG welder has two cables. One is the ground. It looks like an alligator toothed clamp – like car “jumper cables”. This lead must be attached either to the metal you intend to weld, or near the piece you are welding for proper grounding.

The other lead from the MIG welder has the electrode and its handle with the “welder on” and wire feed button. The tip will have a gas outlet if your MIG uses tanks.

When you press the button, wire (and gas, with a MIG with tanks) will be fed from a spool in the machine through the feed line and to the handle you hold in your hand and, as importantly - electricity will flow from that electrode.

A MIG with a tank attachment will force CO2/Argon into the arc as the weld is created. This gas helps keep the air surrounding the weld uniform, creating a better weld in the process. A gasless mig welder uses a shielded wire electrode. The outer coating of this shielded wire creates its own gas as it burns in much the same way a tank provides a gas source.

Preparing the Surface

Electricity travels most efficiently through clean metal, so preparing the surface to weld is as important as the weld itself. Cut out all the rust and use a wire brush to clean all the surfaces. Use a welding primer if necessary.

First, the procedure is pretty simple - when you press the switch on the handle, you will strike an arc—an electrical contact—between the metal and the electrode. Start the arc by holding the electrode 1/8" from the welding surface.

Once the arc is lit, the metal gets molten hot. New metal is fed from the electrode, and a puddle forms on the work pieces. This puddle is molten steel. When you weld, you are joining metals within this puddle. It all boils down to how well you can control that puddle.

When you strike the arc, the hooded shield that protects your eyes must be in place or you won’t see a thing.

The bright light will not only hurt your eyes, it could cause more permanent eye damage. Practice pulling the welding hood into place until you’re comfortable. Eye protection is imperative. You can also hold the electrode in place, pull on the hood, and then start the arc. Whatever you want to do is fine, so long as your eyes are covered when you start welding. You will see everything as you weld even though you can’t see through the shield under natural light.

Techniques and Welds Types

Spot or Tack Welding: To create a tack, hold the electrode in an area for no more than a couple of seconds. Hold tip in one spot about 1/8" above the metal. Too long will burn a hole in metal. Proceed to next position for the next tack or spot, on and on. Spot and tack welding can be done on a seam or though holes made in the overlaid stock to be attached.

Creating A Seam or Butt Weld: When you are doing long seams, your hand motion will be in small oval movements. These movements are small circular motions away from you one side on the work piece and toward you on the other. Remember that you are actually moving a molten puddle of metal along a predetermined path. Think of it a “fanning or pulling a drop of water” – it’s pretty much the same principle. Keep repeating this motion into the joining metals about 1/8" to 3/16" from the top of previous circular always working toward your standing position. Never do this type weld without tacking the entire length with spots no more than 6" apart maximum.


Mig Welding Feed Rate & Voltage

Once the work material and wire type etc has been fixed you have three variables:

The three interact and there will be combinations that work -- and those that don't.

The voltage setting is the main control for penetration but the other two parameters have some effect. The feed rate sets the arc length. Your movement controls the smooth transfer on metal to the work piece.

The first two parameters are a compromise because the ideal “settings” will usually vary from part of the weld to another. You can vary your motion to compensate to some extent. Low voltage will mean low penetration and the weld will sit on the job instead of soaking in. Too much voltage will mean penetrating right through and making a hole.

Most MIG welders have little choice of voltage, so try as many as you can. Having fixed the voltage we now adjust the feed rate. The easiest is to drag the gun along some scrap of similar thickness to the work piece and adjust till you get a smooth arc. If you can hear it - you don't even need to watch it.

Start fast and slow it down. When the rate is fast you get a series of pops. The wire hits the job and short-circuits without maintaining an arc. The wire then melts and the process repeats when the new piece hits the metal. It doesn't seem to do any harm.

There will be a range of speeds were you have a steady arc. You will have to experiment a bit.

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