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---
title: MIG welding
---
Recently, I took a MIG welding class at [Artisan's
Asylum](https://artisansasylum.com) in Somerville, MA. I wanted to document what
I learned so that I can refer back to it in the future, so here it is!
<!--more-->
## Safety
There are four primary hazards:
1. **Burns.** You're dealing with liquid metal, so the work piece will remain
hot even after you finish a weld. Also, small balls of molten steel will fly
away from the work area and can burn through clothing and footwear, or ignite
flammable objects nearby. Precautions: welding jacket, welding gloves, face
mask, eye protection. Scan the surrounding area for fire hazards before
welding.
2. **Electric shock.** MIG welding is an electrical process in which current is
passed between the welding wire and the ground clamp. Precautions: don't weld
in damp areas.
3. **Radiation.** Ultraviolet light emitted from the arc can damage eyesight.
Precautions: welding face shield, preferably an auto-darkening one, though a
small amount of exposure will occur due to the delay between the arc flash
and the sensor activation, mostly a concern when you spend 40 hours a week
welding.
4. **Asphyxiation.** MIG welding typically uses a gas mix called C25, a mix of
75% argon and 25% carbon dioxide, in order to displace oxygen from the work
area which would oxidize the molten steel and prevent a solid weld from
forming. As the gas mix displaces oxygen, welding in an enclosed area could
result in hypoxia. Precautions: weld in a well-ventilated area. The welding
shop at A^2 has an exhaust system.
## Mechanics
There are two primary controls on the welding machine: voltage (a proxy for
temperature) and feed speed. There's a chart on the welding machine with
recommended settings for types and thicknesses of sheet metal. Some machines
have an "auto feed" setting which tends to work fairly well.
Don't weld anything galvanized, as the zinc will vaporize and can cross the
blood-brain barrier causing neurological damage.
There are three common gauges of welding wire: 0.023", 0.030", and 0.035". 030
is a good general purpose wire. When you switch out a reel, be sure that the
feed rollers are fitted for the correct gauge. The number facing out on the reel
is the groove in use, regardless of whether it's actually on the same side of
the number or the opposite side.
To reduce friction on the sleeve that holds the welding wire inside the gas
cable, try to avoid sharp loops, similar to how a garden hose can kink.
You want to keep the nozzle about 3/8" away from the work piece.
After a weld, slag and ash may accumulate on the surface. This can be brushed
off with a wire brush or ground down for a cleaner surface.
The welding tip is where the current is transferred from the electrode running
down the cable into the welding wire. It's relatively easy for the tip to become
damaged and require replacement; it's a 15-cent consumable part so not a big
deal. To replace, pull off (don't unscrew) the sheath from the end of the
nozzle, unscrew the tip, and screw a new one in. The inner diameter of the
sheath may also accumulate slag buildup over time which can easily be cleaned
out using the tapered end of MIG welding pliers.
To warn people nearby, announce "welding" before starting a weld.
Two directions for welding: push and drag. Not much difference between them
other than what you can see: drag allows you to see the bead you're laying while
push allows you to see where you're going.
## Tack Welds
Useful for tacking a piece in place before laying a bead. With about 3/8" of
wire protruding from the tip, place the tip against the work surface, and
depress the trigger for about 1 second.
## Beads
A bead can be produced by dragging the end of the welding wire along the work
piece. The bead should be about twice as wide as the work piece is thick; e.g.
for 1/8" steel the bead should be about 1/4" wide. The width can be controlled
by regulating the speed at which you drag the nozzle across the work surface.
A nicer bead can be laid by using a circular motion, which also produces the
aesthetically pleasing waves.
The height of the bead should be fairly low, as the larger the angle between the
sheet metal and the bead, the less sturdy the weld will be.
## Fillets
This is basically just a bead laid to join two pieces at a right angle. Use the
same basic technique, but you'll be bumping then nozzle up against the side and
bottom pieces in order to be close enough to the work area right at the join.
## "Series of tacks"
Can be useful when welding very thin stock that welding a bead might melt right
through. This works by using the thermal capacity of the previously welded tack
to help absorb some of the heat. Place the wire right up against the previous
tack for optimal heat dissipation.
## Fill-in
You can fix a hole by placing a bunch of dots inside it. It won't look super
pretty, you'll almost certainly need to grind it down afterwards, and it won't
be very strong. You could use it as an aesthetic (rather than structural) fix
e.g. if it'll be painted over afterwards.
|
