This is a free basic guide on how to weld using a metal inert gas
MIG welding is the process of using electricity to melt and join pieces of metal
together. MIG welding is generally regarded as one of the easiest type of
welding to learn.
You can download this MIG Welding Guide by right clicking the link below and
choosing 'Save Target':
this printable Free Guide to
Welding is a skill that needs to be developed over time, with a
piece of metal in front of you suitable protection and a welding torch in your
View the videos below to see a customers review and setup guide for the Pro-Mig250 Mig Welder
1. WHAT IS
MIG welding was
developed in the 1940's and 60 years later the general principle is still very
much the same. MIG welding uses an arc of electricity to create a short circuit
between a continuously fed anode (+ the wire-fed welding torch) and a cathode (
- the metal being welded)
produced by the short circuit, along with a non-reactive (hence inert) gas
locally melts the metal and allows them to mix together. Once the heat is
removed, the metal begins to cool and solidify, and forms a new piece of fused
A few years ago
the full name - Metal Inert Gas
(MIG) welding was changed to Gas Metal Arc Welding (GMAW) but if you call it
that most people won't know what the you are talking about - the name MIG
welding has certainly stuck.
MIG welding is useful because you can
use it to weld many different types of metals: carbon steel, stainless steel,
aluminium, magnesium, copper, nickel, silicon bronze and other alloys.
are some advantages to
The ability to join a wide range of metals and thicknesses
? All-position welding capability
good weld bead
minimum of weld splatter
? Easy to learn
Here are some
MIG welding can only be used on thin to medium thick metals
? The use of an inert gas makes this type of welding less portable
arc welding which requires no external source of shielding gas. Produces a
less controlled weld as compared to TIG
(Tungsten Inert Gas Welding)
2. HOW DOES THE
MIG WELDER WORK?
MIG welder has a couple of different parts. If you open one up you will be
able to see something like the pictures below
Inside the welder you will find a spool of
MIG wire and a series of rollers that pushes the wire out to the welding torch.
There isn't much going on inside this part of the welder, so it's worth it to
take just a minute and familiarize yourself with the different parts. If the
wire feed jams up for any reason you will want to check this part of the machine
out. On larger power MIG welders you the wire feed unit can be separate as in
pictures below. A welder with internal feed assembly is commonly known as a
compact MIG welder.
The large spool
of wire should be held on with a tension nut. The nut should be tight enough to
keep the spool from unravelling so to avoids over-run (birds nesting) when
trigger released, but not so tight that the rollers can't pull the wire from the
If you follow
the wire from the spool you can see that it goes into a set of rollers that pull
the wire off of the big roll, this then pushes the wire up to the torch to the
tip ready for welding.
The Gas Supply
Assuming you are using a shielding gas with your
MIG welder there will be a cylinder of gas behind the MIG. This is either
100% Argon or a mixture of CO2 and Argon. This gas shields the weld as it forms.
Without the gas your welds will look brown, splattered and just generally not
very nice. Open the main valve of the cylinder and make sure that there is some
gas in it. Your gauges should be reading between 0 and 2500 PSI in the tank and
the regulator should be set between 15 and 25 PSI depending on how you like to
set things up and the type of welding torch you are using. When welding in areas
with a draught you may need to run more gas pressure to avoid getting porosity
in the weld.
passes through the rollers it is sent down a set of hoses which lead to
the welding torch. The hoses carry the charged electrode and the argon gas.
The welding torch is the business end of things. It's where most
of your attention will be directed during the welding process. The
consists of a trigger that controls the wire feed and the flow of electricity.
The wire is guided by a replaceable copper tip that is made for each specific
welder. Tips vary in size to fit whatever diameter wire you happen to be welding
with. Most likely this part of the welder will already be set up for you. The
outside of the tip of torch is covered by a metal shroud which protects the
electrode and directs the flow of gas out the tip of the torch.
The earth clamp is the cathode (-) in the circuit and completes
the circuit between the welder, the welding torch and the project. It should
either be clipped directly to the piece of metal being welding or onto a metal
welding table like the one pictured below.
The earth clamp
must be making good contact with the piece being welded for it to work so be
sure to grind off any rust or paint that may be preventing it from making a
connection with your work.
1. This is the
spool of wire that feeds the welder. The wire comes off the spool, is pushed
through the feeder and travels out to the welding torch.
2. These are the rollers that pull the wire off the spool and send it out to the
1. Wire being
fed through the rollers
2. Tensioning Adjustment
negative lead from the welder onto your project or, in this case, the welding
3. SAFTEY GEAR
MIG welding can be a pretty safe thing
to do so long as you follow a few important safety precautions. Because of MIG
welding produces lots of heat and lots of harmful light, you need to take a few
steps to protect yourself.
light that is generated by any form of arc welding is extremely bright. It will
burn your eyes and your skin just like the sun will if you don't protect
yourself. The first thing you will need to weld is a
welding helmet. I am wearing an auto-darkening welding mask below. They are
really helpful if you are going to do a lot of welding and make a great
investment if you think you will be working with metal often. Manual masks
require you to jerk your head dropping the mask into position or require to use
a free hand to pull the mask down. This allows you to use both your hands to
weld, and not worry about the mask. Think of protecting others from the light as
well and use a welding screen if it's available to make a border around
yourself. The light has a tendency to draw on lookers who might need to shielded
from being burned too.
gloves and leathers to protect yourself from molten metal splattering off of
your work piece. Some people like thin gloves for welding so you can have a lot
of control. In
TIG welding this is especially true, however for MIG welding you can wear
you feel comfortable with. The leathers will not only protect your
skin from the heat produced by welding but they will also protect your skin from
the UV light produced by welding. If you are going to be doing any amount of
welding more than just a minute or two you will want to cover up because UV
burns happen fast!
you are not going to wear leathers at least make sure that you are wearing
clothing made from cotton. Plastic fibers like polyester and rayon will melt
when they come into contact with molten metal and will burn you. Cotton will get
a hole in it, but at least it won't burn and make hot metal goop.
not wear open toed shoes or synthetic shoes that have mesh over the top of your
toes. Hot metal often falls straight down and I have burned many holes through
the tops of my shoes. Molten metal + hot plastic goo from shoes = no fun. Wear
leather shoes or boots if you have them or cover your shoes in something
non-flammable to stop this.
in a well ventilated area. Welding produces hazardous fumes which you shouldn't
breathe in if you can avoid it. Wear either a mask, or a respirator if you are
going to be welding for a prolonged amount of time.
DO NOT WELD GALVANIZED STEEL. Galvanized steel contains a zinc
coating that produces carcinogenic and poisonous gas when it is burned. Exposure
to the stuff can result in heavy metal poisoning (welding shivers) - flu like
symptoms that can persist for a few days, but that can also cause permanent
Molten metal can spit several feet from a weld. Grinding sparks
are even worse. Any sawdust, paper or plastic bags in the area can smolder and
catch fire, so keep a tidy area for welding. Your attention will be focused on
welding and it can be hard to see what's going on around you if something
catches fire. Reduce the chance of that happening by clearing away all flammable
objects from your weld area.
Keep a fire
extinguisher beside the exit door from your workshop. CO2 is the best type for
welding. Water extinguishers are not a good idea in a welding shop since you are
standing next to a whole lot of electricity.
auto-darkening helmet and a suitable cotton based jacket are essential to keep
4. PREPARING FOR
Before you start
welding make sure things are properly setup at both the welder and on the piece
you are about to weld.
Check to make sure that the valve to the shielding gas is open
and that you have around 14LPM flowing through the regulator. The welder needs
to be turned on, ground earth clamp attached to your welding table or to the
metal directly and you need to have the right combination of welding power and
wire feed speed
While you can pretty much just take a
MIG welder, squeeze the trigger and and touch it to your work piece to weld
you won't get a great result. If you want the weld to be strong and clean,
taking 5 minutes to clean your metal and grind down any edges that are being
joined will really help your weld.
In the picture below an angle
grinder is being used to bevel the edges of some square tube before it gets
welded onto another piece of square tubing. By creating two bevels on the
joining edges it makes a little valley for the weld pool to form in. Doing this
for butt welds (when two things are pushed together and joined) is a good idea.
Gloves should be
worn but this is a staged picture on the left. The right hand picture shows a
neat bevelled edge which is required for your work prior to welding
5. LAYING A BEAD
Once your welder
is set up and you have prepped your piece of metal it's time to start focusing
on the actual welding
If it's your
first time welding you might want to practice just running a bead before
actually welding two pieces of metal together. You can do this by taking a piece
of scrap metal and making a weld in a straight line on its surface.
Do this a couple
of times before you start actually welding so that you can get a feel for the
process and figure out what wire speed and power settings you will want to use.
Every welder is
different so you will have to figure these settings out yourself. Too little
power and you will have a splattered weld that won't penetrate through your work
piece. Too much power and you might melt right through the metal entirely.
below show a few different beads being laid down on some 1/4" plate. Some have
too much power and some could use a little more. See the image notes for the
process of laying a bead is not too difficult. You are trying to make a small
zig zag with the tip of the welder, or little concentric circles moving your way
from the top of the weld downward. I like to think of it as "sewing" motion
where I use the tip of the welding torch to weave the two pieces of metal
laying beads about an inch or two long. If you make any one weld too long your
work piece will heat up in that area and could become warped or compromised, so
it's best to do a little welding in one spot, move to another, and then come
back to finish up what's left in between.
What are the right settings?
If you are experiencing holes in your work than your power is
turned up too high and you are melting through your welds.
If your welds
are forming in spurts your wire speed or power settings are too low. The torch
is feeding wire out of the tip, it's then making contact, and then melting and
splattering without forming a proper weld.
You'll know when
you have settings right because your welds will start looking nice and smooth.
You can also tell a fair amount about the quality of the weld by the way it
sounds. You want to hear continuous sparking. Some welders says it sounds like
an egg frying!
1. These settings are pretty good.
2. Not enough power, not enough wire feed.
3. Good wire feed, not enough power.
4. Good wire feed, not enough power.
5. It takes a little while to get comfortable, don't be afraid to make some test
welds to get a feel for it.
1. These are similar power and feed settings, but tested on a
much thinner sheet of steel plate. As you can see the weld
has penetrated very deeply and is starting to deform the piece.
You can see some curling on the sides of the plate.
1. Too much power has created a burn hole in the metal
Once you've got
your method tested out a bit on some scrap, it's time to do the actual weld. In
this photo I am doing just a simple butt weld on some square stock. We've
already ground down the edges of the surfaces that are going to be welded so
that the seam where they meet makes a small "v".
We are basically
just taking the welder and making our sewing motion across the top of the seam.
It's ideal to weld from the bottom of the stock up to the top, pushing the weld
forward with the tip of the torch, however that isn't always comfortable or a
good way to start learning. In the beginning it's perfectly fine to weld in
whatever direction/position that is comfortable and that works for you.
Once we finished
welding the pipe we were left with a big bump where the filler came in. You can
leave that if you like, or you can grind it flat depending on what you are using
the metal for. Once we ground it down we found one side where the weld didn't
penetrate properly. (See photo 3.) That means that we need to have more power
and more wire to fill in the weld. We went back and redid the weld so that it
was properly joined.
1. This was our first try. Not a bad weld, but we could probably
use a little more gas and a little less power. This weld penetrated pretty
1. This side of the square stock wasn't welded with enough power
because the weld didn't penetrate all the way through. Notice the blue hue to
the metal around the seam. That means that we were pushing too hard with the
angle grinder when we were grinding down the weld. Remember to keep the disc
moving and to resist the urge of trying to cut corners while grinding. It's
sometimes a slow process that requires patience.
7. GRINDING DOWN
If your weld
isn't on a piece of metal that will show, or if you don't care about how the
weld looks, then you are done with your weld. However, if the weld is showing or
you are welding something that you want to look nice then you will most likely
want to grind down your weld and smooth it out.
Put a grinding
wheel onto an angle grinder and get started grinding on the weld. The neater
your weld was the less grinding you will have to do, and after you have spent a
whole day grinding, you will see why it's worth it to keep your welds neat in
the first place. If you use a ton of wire and made a mess of things it's ok, it
just means that you might be grinding for a while. If you had a neat simple weld
though, then it shouldn't take too long to clean things up.
Be careful as
you approach the surface of the original stock. You don't want to grind through
your nice new weld or gouge out a piece of the metal. Move the angle grinder
around like you would a sander so as not to heat up, or grind away any one spot
of the metal too much. If you see the metal get a blue tinge to it you are
either pushing too hard with the grinder or not moving the grinding wheel around
enough. This is can happen especially easily while grinding thin sheets of
can take a while to do depending on how much you have welded and can be a
tedious process - take breaks while grinding and stay hydrated, (grinding rooms
in shops or studios tend to heat up, especially if you are wearing leathers).
Wear a full face mask when grinding, a mask or respirator, and ear protection.
Make sure that all your clothing is neatly tucked in and that you don't have
anything hanging down from your body that could get caught in the grinder - it
spins fast and it can suck you in!
When you have
finished you should end up with something similar to the photo on the right hand
8. COMMON PROBLEMS
It can take a
good amount of practice to start welding reliably every time, so don't worry if
you have some problems when you first stop. Some common problems are:
or not enough shielding gas from the torch is surrounding the weld. You can tell
when this happens because the weld will start splattering little balls of metal,
and will turn nasty colours of brown and green you can also see air bubbles on
top of the weld (porosity). Turn up the pressure on the gas and see if that
is not penetrating. This is easy to tell as your weld will be weak and won't be
fully joining your two piece of metal. Try more power and wire speed.
burns a while right through your material. This is caused by welding with too
much power. Simply turn down your welding power and it should go away.
much metal in your weld pool or the weld is sloppy like porridge. This is caused
by too much wire coming out of the torch and can be fixed by slowing down your
weld penetration, erratic weld. Check condition of earth clamp and ensure where
it fits to bench is clean and free from rust/paint. If earth clamp shows signs
of overheating fit new clamp or complete lead assy
torch spits and does not maintain a constant weld. This could be caused because
the torch is too far from the weld.
want to hold the tip of the torch about 1/4" to 1/2" away from the weld.
9. WELDING WIRE TO THE TIP/CHANGING THE TIP
Sometimes if you
are welding too close to your material or you are building up too much heat the
tip of the wire can actually weld itself onto the tip of your welding torch.
This looks like a little blob of metal at the tip of your torch and you'll know
when you have this problem because the wire won't come out of the torch anymore.
Fixing this is reasonably simple if you just pull on the blob with a set of
pliers. See photos below.
If you really
scorch the tip of your torch and fuse the hole closed with metal then you need
to turn the welder off and replace the tip. Follow the photo series below to see
how it's done.
tip is fused closed
Unscrew the welding shield cup.
Unscrew the bad welding tip
a new tip into place.
Screw the new tip on
6. Replace the welding cup
Listed below are
some features found on advanced MIG welders with their explanation.
This controls the penetration of the weld via a control knob on machine
(On older machines this was known as choke, you may have 2-3 connectors for the
Low setting = Less penetration and low splatter, used for thinner materials.
This really helps when welding car bodywork!
High setting = High penetration and more splatter (harsher weld), used for
This allows you to set an amount of time machine will weld when trigger
is pressed. When you press the trigger a spot weld is carried out and then
machine stops, release and press trigger again to produce another spot weld.
This is similar to spot welding but with the addition of stitch time
which sets the interval between spots. So as you press the trigger a spot weld
is done as set by spot welder control knob and then a delay set by the stitch
control knob and then another spot weld is produced, this will carry on until
the torch trigger is released.
Push Pull torch
This is a MIG torch used for aluminium welding. The torch head has a
pair of rollers driven by a motor which pulls the wire as well as the MIG welder
roller system pushing the wire. This ensures correct wire feed of the softer
alloy wire and prevents snags and wire feed problems. Generally used for
production alloy MIG welding.
When the trigger is pressed the wire comes out of the torch slowly
(slower than set wire feed speed), when the wire touches the work the arc is
started. The machine senses this and increases the wire feed to set speed. This
can stop torch jerk when starting a weld and also produces a better start to the
4-Roll Wire feed assembly
and DIY machines normally come with a 2-roll feed system, this comprises of a
bottom roller with grooves in and a top pressure roller which is flat and puts
pressure on wire as set by tensioners to drive wire when the rollers turn.
A 4-Roll system has two bottom rollers and two top rollers which give a more
stable wire feed and is better at feeding softer alloy wires than a 2-roll
system. Some MIG welders also have geared 4-roll systems which help to regulate
wire flow speed with great accuracy resulting in exceptionally smooth welds. The
pictures at the front of this guide show a 4-roll geared version – a common
feature on most
R-Tech MIG Welders.