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Old 09-06-2009, 08:19 AM
Fawteen Fawteen is offline
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Default Welding - MIG Welding

MIG Welding

Equipment

A MIG welder, aka a wire welder, consists of a power unit, ground lead, welding lead and optionally, a regulator for shielding gas. You have a few decisions to make when choosing a MIG welder:

Voltage:

The two common operating voltages are 110 Volts AC (VAC) or 220 VAC.

110VAC has the advantage plugging into any common household outlet, no special receptacles or wiring required. (Note: the circuit used should be capable of 20 amps minimum, check the breaker for that circuit). 110VAC units are also cheaper to purchase. The main disadvantage of 110VAC units is that they are only capable of welding relatively thin materials, 1/8th to ¼ inch max. Also, they are less efficient and therefore more expensive to operate.

220VAC units are much more versatile and will weld anything a stick welder will. The disadvantage is that you’ll need a 220 welder outlet. Most homes have 220 service for a stove or clothes dryer, so it’s usually just a matter of having an electrician run a separate circuit for the welder. Check the paperwork on the specific welder, but usually a 50 Amp circuit is plenty.

I highly recommend the 220VAC unit, you’ll be happier in the long run.

Gas Shielding or Flux-core wire:

Electric welding, be it MIG, TIG or Stick, requires that the arc be shielded from the atmosphere to prevent impurities and oxidation from the oxygen in the air from contaminating the weld.

With a MIG welder, you have two choices: Flux-core wire, which has a chemical component that creates a shielding gas when it burns, or a gas bottle and regulator which flows a cone of shielding gas around the arc from a separate orifice in the torch handle.

I have never dealt with flux-core wire, so have very little knowledge of it. As with most things, there are folks that love it and folks that hate it. I’ll leave the discussion of advantages and disadvantages to someone with direct experience. The only thing I’m aware of is that you avoid the cost of a regulator and bottle rental on the initial purchase. I expect flux-core wire would be more expensive than solid wire, which may offset some of the cost advantage.

Gas shielding is more expensive initially but IMHO easier to use. You also have the advantage of matching the shielding gas to the material being welded. For general mild steel work, you can use Stargon, which is a mixture of 25% CO2 and 75% Argon. This is the cheapest gas mix. If you plan to weld aluminum or stainless, you must use pure Argon.

Again, I have never used flux-core wire, so I can’t state this with certainty, but it is my feeling that solid wire is less likely to cause feeding problems, will work better on materials that are less than perfectly clean, and comes in a variety of compositions that may not be available in flux core.

Wire Feed Mechanism

There are two primary ways of feeding wire to the torch: Feed-through and spool gun.

In a feed through rig, the spool of wire and wire drive apparatus are contained in the control unit and the wire is pushed through the torch cable in a sheath very similar to the clutch or brake cable on a motorcycle. The advantages of this are that you can mount a larger spool of wire, the torch handle is much lighter and more maneuverable, and the entire mechanism is lest costly. The disadvantages are a minor tendency for jams, especially when feeding aluminum wire or if the cable gets kinked, and contamination of the liner. What I mean by this is that if you’ve been welding mild steel and change over to aluminum, residue from the steel wire will contaminate the aluminum wire and compromise the quality of the weld.

Spool guns contain the spool of wire and the drive apparatus in the torch handle. This is particularly handy when you change between stainless, aluminum and mild steel a lot as there is no liner contamination to worry about. It is also less susceptible to jamming. Disadvantages are cost (nearly as much as the machine for smaller units), weight of the torch and lack of maneuverability due to the size of the torch.


Equipment Summary

Based on my experience, I feel that the home shop will be best served by a 220VAC unit, with feed-through wire delivery and a gas regulator. You may wish to start with flux-core and add the gas regulator later if you find the flux-core doesn’t work for your application. $500-$700 should put you in business.

Techniques

MIG welding is probably the easiest method of electric arc welding to learn. Once you have the correct wire and shielding gas, the only adjustments you need to make are wire feed speed and heat range. It is important to note that it is very easy (and common for beginners) to create a weld that LOOKS perfect, but has no penetration or strength. A strong weld with good penetration looks good: A good-looking weld is not necessarily strong.

Setting up to weld with a MIG is pretty simple. Find a clean spot to attach the ground lead, turn on the welder (and gas, if you’re using it) check that there’s an inch or so of wire sticking out of the torch, place the tip of the wire near the work and pull the trigger.

The ideal situation is enough heat to form the weld without blowing through or warping the work, and wire speed just fast enough to maintain the arc. If the arc goes out and the wire has burned back to the nozzle (and usually, stuck to it…) you need to turn up the wire speed. If the wire is sticking to the work and pushing the torch away from the work, you need to slow the wire down. You can also change the heat range in some cases to correct these issues, but it’s usually best to pick the heat range to match the material and adjust the wire speed to fit. A good indicator of correct settings is how the welder sounds: you should get a steady “frying bacon” sound when things are set up correctly.

Once you’ve established the puddle, keep point of the arc in the puddle and either draw or push it along the joint, weaving side-to-side in a “Z” pattern to advance the weld. The wire should never actually touch the puddle. The arc is what transfers metal from the wire to the weld. Two things will determine the amount of metal transferred: The distance from the wire to the weld puddle (“stickout”) and the speed of travel of the torch. You’ll need to experiment with both to get the weld bead you’re looking for. Note that increasing the stickout increases the heat and penetration to some extent.

If welding different thicknesses, concentrate the arc on the thicker piece, wiping onto the thinner piece briefly to get the puddle to bridge the gap. You should see a sort of half-moon shape as the two pieces are joined by the weld puddle.

If welding a fillet into an angled joint, start on the upper side and walk the puddle down to the lower side until you see the half-moon, and then continue down the joint working from the upper side to the lower side.

Vertical up-welding can be done with a MIG fairly easily. Two tips: A little less heat to keep the puddle from sagging and running out of the weld, and “stitch” welding. Make a quick spot weld, stop for a second to let it cool and solidify, make another spot, etc.

NOTE: When stopping a weld, do so by pulling the torch back from the work, NOT by letting go of the trigger. Pull it back until the arc stops, let go of the trigger, wait for it to cool then approach the work, hit the trigger, tack another weld, etc.

I should probably do a separate article on material prep but for right now, I’ll just make a couple of points:

CLEAN! – Grind the surfaces to be welded down to clean, shiny metal, removing all the rust, scale and oxidation.

TIGHT! – Get that joint to fit as tight mechanically as you can. That’s not to say you CAN’T weld across a gap, but in general a tight joint is a strong joint.

BEVEL! – The most common cause of bad joints is insufficient penetration. If you’re welding thick pieces, bevel the joint into a V shape and weld from both sides to ensure complete penetration.
The Following 4 Users Say Thank You to Fawteen For This Useful Post:
gokart14 (05-17-2010), lukasdlf (08-09-2013), uaweldercod (11-11-2017), Yukon (11-17-2011)
 

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