How to Weld - MIG Welding

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Introduction: How to Weld - MIG Welding

This is a basic guide on how to weld using a metal inert gas (MIG) welder. MIG welding is the awesome process of using electricity to melt and join pieces of metal together. MIG welding is sometimes referred to as the "hot glue gun" of the welding world and is generally regarded as one of the easiest type of welding to learn.

**This Instructable is not intended to be THE definitive guide on MIG welding, for that you might want to seek out a a more comprehensive guide from a professional. Think of this Instructable as a guide to get you started MIG welding. Welding is a skill that needs to be developed over time, with a piece of metal in front of you and with a welding gun/torch in your hands.**

If you are interested in TIG welding, check out: How to Weld (TIG).

Step 1: Background

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 gun) and a cathode ( - the metal being welded).

The heat 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 metal.

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 heck your 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, aluminum, magnesium, copper, nickel, silicon bronze and other alloys.

Here are some advantages to MIG welding:

  • The ability to join a wide range of metals and thicknesses
  • All-position welding capability
  • A good weld bead
  • A minimum of weld splatter
  • Easy to learn

Here are some disadvantages of MIG welding:

  • 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 than arc welding which requires no external source of shielding gas
  • Produces a somewhat sloppier and less controlled weld as compared to TIG (Tungsten Inert Gas Welding)

Step 2: How the Machine Works

A MIG welder has a couple of different parts. If you open one up you will be able to see something that looks like what is pictured below.

The Welder

Inside the welder you will find a spool of wire and a series of rollers that pushes the wire out to the welding gun. 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 (this does happen from time to time) you will want to check this part of the machine out.

The large spool of wire should be held on with a tension nut. The nut should be tight enough to keep the spool from unraveling, but not so tight that the rollers can't pull the wire from the spool.

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 welder is set up to weld aluminum, so it has aluminum wire loaded into it. The MIG welding I am going to describe in this instructable is for steel which uses a copper colored wire.

The Gas Tank

Assuming you are using a shielding gas with your MIG welder there will be a tank of gas behind the MIG. The tank 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 tank and make sure that there is some gas in the tank. 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 gun you are using.

**It's a good rule of thumb to open all valves to all gas tanks in a shop only a half turn or so. Opening the valve all the way doesn't improve your flow any more than just cracking the valve open since the tank is under so much pressure. The logic behind this is so that if someone needs to quickly shut off gas in an emergency they don't have to spend time cranking down a fully open valve. This might not seem like such a big deal with Argon or CO2, but when your working with flammable gases like oxygen or acetylene you can see why it might come in handy in the event of an emergency.**

Once the wire passes through the rollers it is sent down a set of hoses which lead to the welding gun. The hoses carry the charged electrode and the argon gas.

The Welding Gun

The welding gun is the business end of things. It's where most of your attention will be directed during the welding process. The gun 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 gun is covered by a ceramic or metal cup which protects the electrode and directs the flow of gas out the tip of the gun. You can see the small piece of wire sticking out of the tip of the welding gun in the pictures below.

The Ground Clamp

The ground clamp is the cathode (-) in the circuit and completes the circuit between the welder, the welding gun 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 (we have two welders hence two clamps, you only need one clamp from the welder attached to your piece to weld).

The clip 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.

Step 3: Safety 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.

Safety Steps:

  • The 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 mask. I am wearing an auto-darkening welding mask below. They are really helpful if you are going to do a bunch 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.
  • Wear 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 whatever gloves 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!
  • If 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.
  • Do 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.

  • Weld 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.

Important Safety Warning

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 damage. This is not a joke. I have welded galvanized steel out of ignorance and immediately felt it's effects, so don't do it!

Fire Fire Fire

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.

Step 4: Prep for Your Weld

Before you start welding make sure things are properly setup at both the welder and on the piece you are about to weld.

The Welder

Check to make sure that the valve to the shielding gas is open and that you have around 20ft3/hr flowing through the regulator. The welder needs to be on, the grounding clamp attached to your welding table or to the piece of metal directly and you need to have proper wire speed and power setting dialed in (more on that later).

The Metal

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 randofo is using an angle grinder 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.

Step 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.

The pictures 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. Check out the image notes for the details.

The basic 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 gun to weave the two pieces of metal together.

First start 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 workpiece 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 gun is feeding a bunch of 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, almost like a bumble bee on steroids.

Step 6: Welding Metal Together

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 seem where they meet makes a small "v".

We are basically just taking the welder and making our sewing motion across the top of the seem. It's ideal to weld from the bottom of the stock up to the top, pushing the weld forward with the tip of the gun, 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 once 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.

Step 7: Grind Down the Weld

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.

Slap 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 thing sheets of metal.

Grinding welds 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 are done your piece of metal might look something like the one in the second photo pictured below. (Or maybe better as this was done by a few Instructables Interns at the beginning of the summer during their first welding experience.)

Step 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:

  • No or not enough shielding gas from the gun is surrounding the weld. You can tell when this happens because the weld will start splattering little balls of metal, and will turn nasty colors of brown and green. Turn up the pressure on the gas and see if that helps.
  • Weld 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.
  • Weld burns a while right through your material. This is caused by welding with too much power. Simply turn down your voltage and it should go away.
  • Too much metal in your weld pool or the weld is globy like oatmeal. This is caused by too much wire coming out of the gun and can be fixed by slowing down your wire speed.
  • Welding gun spits and does not maintain a constant weld. This could be caused because the gun is too far from the weld. You want to hold the tip of the gun about 1/4" to 1/2" away from the weld.

Step 9: Wire Fuses to Tip/Change 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 gun. This looks like a little blob of metal at the tip of your gun and you'll know when you have this problem because the wire won't come out of the gun anymore. Fixing this is pretty simple if you just pull on the blob with a set of pliers. See photos 1 and 2 for visuals.

If you really scorch the tip of your gun and fuse the hole closed with metal then you need to turn the welder off and replace the tip. Follow the steps and the overly detailed photo series below to see how it's done. (It's digital so I tend to take too many pictures).

1. (Photo 3) - The tip is fused closed.

2. (Photo 4) - Unscrew the welding shield cup.

3. (Photo 5) - Unscrew the bad welding tip.

4. (Photo 6) - Slide a new tip into place.

5. (Photo 7) - Screw the new tip on.

6. (Photo 8) - Replace the welding cup.

7. (Photo 9) - It's now good as new.

Step 10: Replace Wire Feed to Gun

Sometimes the wire gets kinked and won't advance through the hose or the gun even when the tip is clear and open. Take a look inside of your welder. Check out the spool and the rollers as sometimes the wire can become kinked in there and need to be re-fed through the hose and the gun before it will work again. If this is the case, follow these steps:

1. (Photo 1) - Unplug the unit.

2. (Photo 2) - Find the kink or jam in the spool.

3. (Photo 3) - Cut the wire with a set of pliers or wire cutters.

4. (Photo 4) - Take the pliers and pull out all of the wire from the hose through the tip of the gun.

5. (Photo 5) - Keep pulling, it's long.

6. (Photo 6) - Unkink the wire and feed it back into the rollers. To do this on some machines you have to release the tension spring holding the rollers down tight on the wires. The tension bolt is pictured below. It's the spring with the wing nut on it in it's horizontal position (disengaged).

7. (Photo 7) - Check to make sure the wire is properly seated between the rollers.

8. (Photo 8) - Re-seat the tension bolt.

9. (Photo 9) - Turn on the machine and depress the trigger. Hold it down for a while until the wire comes out of the tip of the gun. This can take 30 seconds or so if your hoses are long.

Step 11: Other Resources

Some of the information in this Instructable was taken from an online Mig Welding Tutorial from the UK. A bunch more of the info was gathered from my personal experience and from an Instructables Intern welding workshop that we held at the beginning of the summer.

For further welding resources, you could consider buying a book about welding, reading a knowledge article from Lincoln Electric, checking out the Miller MIG Tutorial or, downloading this beefy MIG Welding PDF.

I am sure that the Instructables community can come up with some other great welding resources so just add them as comments and I will amend this list as necessary.

Check out the other how to weld instructable by stasterisk to learn about MIG welding's big brother - TIG welding.

Happy welding!

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276 Comments

Very good guide! Thank You for sharing.

Great instructable! I just got a welder from Harbor Freight. It's a 90amp wirefeed flux core for $63 after using a 20% off coupon along with a sidewalk sale(reg $149.99 on sale for $79)!!! But, anyway, I haven't tried it yet and still need to learn a few more things. One question I have is what happens if your bare skin makes contact with the welding table or the piece of metal you are welding. Can you get a shock from that? I know, it's probably a dump question but I haven't seen it addresed anywhere. Thanks.

Hi,

I never thought about it to get shocked and I often welded with a friend who was holding one of the pieces to be weld. Never heard about getting an electrical shock during welding ....

I have NEVER been shocked by a welder unless I make contact with the ground AND the electrode , wire, or tungsten. You can weld electrode positive or negative and not get shocked by the ground clamp or anything attached to it.

Yep, I'd be willing to bet that you would be on the recieving end of a large and painfull shock. Basically MIG welding is a big electrical circuit and if the table is metal it will conduct electricity.

Any welding is a big electrical circuit.  However, remember the basic rule of electricity...it follows the shortest path to the ground.  And in welding, once it has a circuit established, it will follow it.  So if you do accidently touch the table that the metal is on, no, you most likely won't get a shock.   But I wouldn't try it!!  

NOT shortest, path of least resistance. Hell, I used to sit on submarine hulls and weld on them. The human body is a few hundred thousand ohms and the steel is near zero.

Theoretically, no you wont be shocked. The electrical current is looking for the easiest way to the ground (I know, an easy way to explain how electrons act) but since your table or material being welded is being grounded through the ground clamp, through the welder, and through the wiring in your house to the grounding rod installed outside it will pick to go through the ground clamp and not you, assuming you dont wear a wetsuit filled with water and golden boots all whole standing on a metal table directly grounded. Long as you aren't that dumb you should be fine.

Good article.
Just a notice: psi or cubic feet per second or so aren't official international mesures.

The "shield" gas is exactly that, a shield. It prevents gas molecules from the atmosphere from reacting with your molten metal. The term MIG stands for Metal Inert Gas; Inert- as in nonreactive. It is actually the Carbon Dioxide in the atmosphere that is the real problem.