MIG welding, or GMAW (Galvano-Metal Arc Welding), is a popular type of welding that’s frequently used for welding low-alloy steels and is well suited for welding autobody parts and home repairs. It’s a simple process to learn, which is why so many hobby welders use it as their preferred method of welding. This MIG welding guide will teach you everything you need to know to start MIG welding.
The MIG Process
A MIG process is an arc welding process that joins metals together by heating them with an electric arc formed between a wire electrode and the workpiece. The wire electrode is fed through a MIG gun, which is connected to a MIG welder.
Benefits of MIG Welding
The one best thing about MIG welding is the increased productivity and reduced clean up time. You can save a lot of time by not having to change rods, brush the weld or chip away slag.
2. Reduced Costs
You can buy a high-quality welder for under $500, then spend some money on wire and gas and you can start welding. The increased productivity will also lower your welding costs and allow you to get more tasks completed, which is great if you’re running a small business.
3. Easy to Learn & Setup
The great thing about MIG welding is that anyone can learn how to do it. This is why it’s a good choice for home and hobby welders. Once you buy your MIG welder and get set up, welding is as simple as turning on a light switch. In the sections below we’ve outlined all the information you need to get started with your welds.
4. Good Quality
MIG welding uses shielding gas to protect the arc from atmospheric gases. This results in a good clean weld where you don’t have to remove any slag and being able to use both hands on the MIG gun helps with your control.
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How to Set Up to MIG Weld
Here is a simple illustration of how your MIG welding setup will look. Read the different sections to find out how to set up each component to get the best possible results.
You’ll need to install MIG wire into your welding machine so that it can feed through the MIG gun and into the weld pool, this is pretty straightforward once you get the hang of it.
Usually, your welder will come with a roll of flux cored wire, so you will probably have to buy some MIG wire. When you’re MIG welding, you’ll want to choose thicker wire for thicker metal. Also, if you want the best quality welds, you’re better off cranking the machine up on a thinner wire than having it really low on a thicker wire. Below are guidelines for which wire to choose, but make sure you check the door chart on the inside or your MIG welder to see their specific recommendations.
- 0.23″ wire – This is only for your small welding machines when you’re welding thin sheet metal from 24 gauge to around 16 gauge.
- 0.3″ wire– This wire will often come included with your MIG welder, this is also a good choice for sheet metal up to around 1/8″.
- 0.35″ wire – This does the job up to 1/4″ so is a good choice for your beginner welders.
- 0.45″ wire – This wire is best for 1/4″ and above so is more suited for industrial welding.
Installing MIG wire:
Once you have your MIG wire, you’ll want to install it into your welder. Here’s how to do it:
- Open up the cabinet.
- Make sure the cap is unscrewed from the spindle and slide the wire spool onto the spindle. Make sure the MIG wire faces in the direction of the drive roll and is on the bottom of the machine.
- Flick open the pressure release. If you press the trigger on the gun with this released, nothing will happen. You can also twist the pressure roll to adjust the tightness.
- Slowly feed the MIG wire through the drive roll entry making sure the wire is not bent.
- Put the cap on the spool of wire. Make sure the spring is in place before you attach the cap. Is you forget the spring the spool will keep rolling and damage the wire.
- Take off the MIG nozzle and contact tip with some pliers.
- Press the trigger to start feeding the wire through the gun.
- Put the nozzle and contact tip back on.
- Your MIG wire is set up!
If you’re MIG welding you will need to use welding gas to protect the weld pool from the atmosphere. Below we have detailed why gas is so important and which gas is best for your specific welding requirements.
Porosity is just another term for getting holes in your weld. This is something you really want to avoid because it makes the weld weak and not strong enough to hold the metal together.
When you MIG weld, you should use a shielding gas to protect the weld puddle from being contaminated by the gases in the atmosphere. If you don’t use gas, your weld will interact with the Oxygen and Nitrogen and become porous. This isn’t something you have to worry about when flux-cored welding, as the wire contains a core which shields the weld puddle.
When releasing gas from your cylinder you want to make sure that there is a good gas flow so that the weld bead is protected. However, if you release too much gas this will reduce the temperature of the weld pool. You need to find a balance between a high temperature and a good flow of gas. A good test for this is to place your hand 3 inches from the tip of the nozzle and release the gas.
You can use different types of gas when MIG welding. The two most popular are Carbon Dioxide and a mixture or Carbon Dioxide and Argon.
1. Pure Argon
Pure Argon gas is not recommended for welding steel, and it’s only suitable for non-ferrous metal like aluminum. Argon has a low thermal heat conductivity, which means it creates a narrow bead. You’ll have good penetration in the centre of the weld, but not enough penetration to effectively weld a steel joint.
2. Carbon Dioxide (CO2)
Carbon dioxide is popular for MIG welding and is the low-cost alternative to an Argon mix. The problem with CO2 is that it gives you a pretty wide arc that’s not stable and produces a lot of spatter.
3. Argon Mix
I prefer a mixture of argon and carbon dioxide for MIG welding because it produces the highest quality of weld. This is due to the fact that when you mix these gases together, you get a much more suitably sized arc stream which gives great penetration and minimizes spatter.
When handling a gas cylinder, be sure to read all the safety information that comes with it. Gas cylinders are high pressure, so if they fall over and knock the regulator off, it could fly across the room.
When you’re opening the cylinder to release gas, don’t stand on the same side as the regulator. If you suddenly yank it open this could release too much pressure in one moment and it could fly off. Make sure that your welding equipment is firmly tied down so it doesn’t move around. Welding safety is really important, so make sure you follow all the guidelines on your equipment and familiarize yourself with the basics of welding safety.
Nozzle & Electrode Stickout:
When you feed the wire into the MIG gun, the shorter your electrode stickout, the hotter your weld will be. For optimum results, make sure your electrode doesn’t stick out more than 3/8″ from the nozzle and that it’s at least 1/4″ long. If you’re welding really thin metal, you might want to go longer than 3/8″ if you’re concerned about straight through penetration.
To keep the nozzle clean and remove any spatter that sticks to it, make sure you keep the nozzle clean. If your nozzle has spatter stuck to it, this can reduce the flow of gas to the weld puddle and cause porosity. To prevent spatter sticking to your nozzle there is a range of sprays and gels you can apply to your nozzle to stop it sticking.
To MIG weld you need to have your MIG welder set up on direct current electrode positive (DCEP). Any MIG/Flux-cored welder will do this automatically. If you’re welding flux-cored, you will need to change the terminal on your welding machine to negative. This is pretty straightforward to do, although it is different on different welders so make sure you check the instruction manual before doing it. Usually, you will need to open the door of your MIG welder and switch over the polarity settings in the top right corner of the machine.
Front of Machine:
Usually, the front of your MIG welder will have a simple layout and there will be two main dials which control the wire feed speed and the voltage settings.
The voltage settings determine the temperature and height and width of the bead. For thinnest metals, you will start on the lowest setting and move up depending on thickness.
Wire feed speed:
Increasing the voltage setting will increase the wire speed. You’ll know when the wire speed is set correctly as it makes a sound like you’re frying bacon.
MIG Welding Techniques:
Now you’ve got your machine set up, you’re ready to start MIG welding. When welding there are so many variables: the position of the joint, the type of joint, the movement of the MIG gun—you name it. Below we’ve written guides to cover all common MIG welding techniques.
MIG welding isn’t just simply pushing across in a straight line, there are different types of movement suited to the type of joint and metal being welded. Clean the metal.
The most common welding position is a push weld in the forehand position. To get into this position, you need to hold the MIG gun at a 10° angle with the electrode pointed in the direction you’re looking to weld. You can decrease this angle and shift your body slightly so that the weld bead will look like one of the diagrams below:
When you’re in position, press the trigger and slowly move the MIG gun. Push it forward in the direction of the weld. One of the positives of this position is that you have a clear view of the weld joint. When you do this, make sure that your electrode points forward at the leading edge of the weld.
When you pull the weld, you use a backhand position and move the electrode towards your body. You use the same 10° angle and keep the electrode on the edge of the puddle. One of the positives of this technique is that it tends to get more penetration than when you’re pushing as the weld bead builds up. Sometimes you need to use both pushing and pulling techniques, but I feel that there’s more chance of contaminating the weld when you use a pushing technique so I tend to use it whenever possible.
Types of Bead:
A stringer bead is the most basic type of weld, in which you push or pull the MIG gun across a joint in a straight line. These are usually thinner than weave beads but are fine for your average butt weld.
The cursive “e” weld is a popular weave bead. To perform this, weld straight across the joint but use small circles which are linked together to form e shapes. This gives a really cool scaled effect and can look very smooth—especially when you overlap the weld beads to increase the deposit on your welds.
Similar to the cursive “e”, but this time you move the electrode side to side in a “v” shape which forms a zigzag shape. This is often used for overhead and vertical welds where you want to angle the bead upwards.
The flat position is the easiest position to lay your weld. In this position, your metal will lay flat on the table and you will usually approach the weld horizontally and above the joint.
Welds are often done horizontally. In a horizontal weld, the weld is performed across a horizontal surface that crosses a vertical piece of metal. A common problem with horizontal welds is that the weld bead can sag down, so you need to try and push the weld up so that you get a nice even weld. To do this, I place the nozzle at around a 45° angle to the joint and direct the electrode forward at about a 10° angle. Then I use the cursive “e” shape in the forehand position to push the weld up.
A vertical weld is when the weld’s axis is vertical or over a 45° incline. This is called either “vertical up” or “vertical down” depending on whether you’re welding from the top to the bottom of the joint or from the bottom to the top. For both these types of movement, I like to oscillate the MIG gun in a “u” shape and keep it pointing upwards at around 10° from horizontal.
When you’re performing a vertical down weld, hold the electrode so that it points upwards. Slowly bring the electrode down to the joint. This is a better choice for welding thinner metals because you’re not preheating the plate so you’re less likely to burn through the metal.
For a vertical up weld, hold the gun at the same angle but slowly push it up to the joint. This is better if you’re welding thick metal because it preheats the metal above it for increased penetration.
The most difficult position for a welder is overhead. You are facing a horizontal joint, but from below. This can be awkward and dangerous because of all the sparks falling on you. To avoid getting burned, cover up your body and head with a mask before beginning work.
When performing the weld, you should use the cursive “e” or “v” motion to stop the weld bead from dripping down. You should also maintain a short arc, keep it on low amperage if possible, and move fast! Keeping the nozzle as close as possible to the workpiece will help prevent you from getting wet.
Types of Welding Joint
There are a wide variety of different welding joints and combination joints you can perform. Below are the four most common joints that you need to know for almost any home welding task. If you learn these, you’ll be in a great position to perform almost any home welding task.
Butt joints are a great way to learn how to weld. A butt joint consists of two pieces of metal which are parallel to each other with the ends flush against each other. Once the edges are flush together, you simply weld right down the seam.
When two pieces of metal overlap, you can weld them together to create a lap joint. You can perform a single or a double lap joint; single is usually enough for most applications, but if your project will be under a lot of pressure then you may want to include both sides to make sure it’s strong enough.
When welding a lap joint, it can be harder to get good penetration on the bottom of the weld because heat rises and is lost quicker at the bottom of the weld. To counter this, aim your Mig gun towards the bottom piece of metal when performing a lap weld. You can also try welding in an ‘e’ or horseshoe motion.
A T-joint is formed when two pieces of metal intersect at a right angle to form a T shape; this is another type of fillet weld. If you weld it straight across, the force of gravity pulls the weld bead down so you should use a horseshoe or ‘e’ type motion to help push the bead up when moving across the joint. When looking at the finished weld side on, it shouldn’t be too concave or convex; it should be flat.
Corners are another common weld type. This one is formed when two pieces of metal meet at a right angle to form a letter L. Corners can be tricky when you get below 1/8″ thick metal, as the metal wants to melt away. The image shows an outside welded corner joint; however, you can also have a double welded corner joint for extra stability.
Depending on the thickness of the metal you’re welding, you may need to bevel the edge of the metal with a grinder. When making a bevel, you should grind a small 30° gap into the edge of the metal. This means that when you press two plates of metal next to each other, you’ll have a nice groove where you can create a weld pool. You can choose to weld just one of the plates on one side, up to both plates on both sides
For low-thickness welds of 1/8 inch or less, you’ll need to worry about bevelling the joint. Usually, I keep the electrode close to the joint as I’m welding so that I get good penetration, but you can keep it a little further away on thin metal where you’re at risk of burning straight through it.
If you’re working on a standard butt weld and the metal you’re working on gets over 1/8″ thick, you’ll be better off bevelling the edge of one of the pieces of metal. This will enable you to get the weld bead right down between the two metal plates, which will make your weld stronger than if you had a flat edge butt weld.
For even thicker pieces of metal, you can bevel both sides of the plate. This will not be applicable to hobby welders with 140A welding machines; however, if you’re an industrial welder this is a way of producing even stronger quality welds.
Most readers of this article will be beginning welders and won’t be welding really thick steel, but I’ve written about it so that you have an idea for the future if you decide to move on to thicker metals.
Here’s how you do the same thing with a thinner weld as you do with a thicker weld. Just flip it over and finish the other side once you’re done.
If you’re welding on thick metal, sometimes you’ll need to run a few passes before the joint is secure. If you do this, make sure you don’t leave any slag behind before moving on to the next pass. If there’s any slag it will just weaken your weld.
The following table shows the recommended type of joint for different thicknesses of metal.
MIG welding is a great way for beginners to start welding. Hopefully this guide has given you everything you need to know to get started on your own projects.
Manmohan HebbarAn Industrial Engineer by qualification and a Digital Marketer by profession.
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