Learning MIG Welding Basics

Mig Welder Parts. Contact Tips, Nozzles, Diffusers, Liners, Fluxcore Wire, Hardwire, Flowmeter… What are these things?

If you are the owner of a MIG welder there is a point in time when you will have to replace some of the parts on your machine. Do you know what to call these parts? Do you know what they do?

This post is meant to inform the novice or newbie as to what not only the names of these parts are but to also inform as to what their purpose is. When you have this knowledge it is easier to troubleshoot some welding problems or converse with a welding professional about problems as they arise.

The pictures of the MIG consumables do not look exactly the same for all MIG welders but there are recognizable similarities enough as to know what they are. Being able to identify your parts makes purchasing parts easier and more efficient. All play an important part for MIG welding metal

The Contact Tip

Contact Tips. Such a Small Part Yet So Critical

When it comes to MIG gun parts, there is no “standard” tip and they are not interchangeable for the most part though there are some exceptions.

There are all sizes and shapes of contact tips but they all do the same thing. They provide a means of allowing the wire to be fed out the end of the gun while making electrical contact with the wire. This is why it is called a contact tip, or sometimes just called a tip.

It is important to remember that the tip size must match the wire size. If the tip doesn’t match you will be either sending a small wire through a larger orifice thus not making good electrical contact OR a larger wire through a smaller tip will not feed at all.

Contact tips are the least expensive of the MIG / GMAW consumables. They range in price from about $.75 cents to about $1.50 each. It is a good idea to keep a few of these on hand since they are subjected to the harshest of environments and do at sometime fail. It is especially important to have extras on hand if you own an off brand welder and parts are difficult to come by. Do not try and ream out the contact tip since this is where your electrical connection is to the welding wire and will either hurt performance or make the MIG welder totally inoperable

MIG Welding Diffuser

Holds the Contact tip and More

In MIG welding the Diffuser, also known as a contact tip adapter, has three or four purposes depending if you are using hard wire or flux cored wire.

Number one the diffuser holds the contact tip in place on the MIG gun. It is important that you keep the internal threads where the contact tip is screwed into diffuser clean so that there is a good fit for the contact tip.

Number two the diffuser is the part that connects to the goose neck of the gun.

Number three the diffuser is the part that the nozzle is attached to the MIG gun.

Number four the holes just above the threads are the ports that allow the shielding gas to reach the weld puddle. When the MIG nozzle is screwed onto the diffuser gas exits the small ports and is focused by the nozzle onto the weld puddle allowing for complete coverage from the ambient air.

Welding suppliers will stock these consumables. It is important to buy a major brand MIG welder so that the the parts are readily available.

MIG Nozzle

MIG Nozzle

The MIG nozzle is about as basic as it gets. It screws onto the diffuser and focuses the shielding gas over the molten weld puddle. Even though the design is basic it comes in different sized orifices as well as nozzles that are tapered to weld into corners.

Some nozzles are built with an insulator incorporated into it while others slide over a separate insulator that is screwed onto the diffuser. The nozzle will last quite a while but should be periodically cleaned by having the slag and spatter removed


The goose neck is a very basic part of the MIG gun. Very rarely will this part ever be replaced. The main function of the goose neck is to attach the gun to the diffuser and also create an angled pathway for the feeding of the wire.

There are only a couple of times it needs to be replaced. One is when the parts are attached incorrectly and the threads get damaged and two you want to change the welding angle of the gun. There are manufacturers that also make a bendable goose neck so that you can get into tight places but they do not fit all MIG guns.

MIG Gun Liner

The liner is a coil of wire that allows the wire to travel down the center of it from exiting the MIG welder leading to the diffuser or also known as a contact tip adapter. It looks similar to the linkage on a lawnmower from the control down to the carburetor.

Quite a few of feed problems are related to the liner. If the MIG welder is in a dusty environment the dust can be on the wire in the case and then drawn into the gun on the wire. The gun becomes filled with dirt and doesn’t allow the wire to move in the liner.

The main problem involving the liner is when there is a kink in it. It can be caused by someone stepping on the liner or creating a sharp bend in the MIG gun lead. The easiest way to tell if there are liner problems is to set up the machine and just pull the trigger and feel how the wire is being fed through the gun. If it feels like there is dragging or chattering remove the liner and check for irregularities that would cause the wire to drag. It can be a radical or slight bend in the liner. It doesn’t take much to make the wire drag inside the liner.

If you don’t feel comfortable changing the liner go to a reputable welding supply and they should do it for you.

Drive Roll System

Most wire feed welders will have the wire fed off of the bottom of the reel. The smaller MIG welders will only have one drive roll while some of the larger industrial MIG welders can have up to four drive rolls. Either way the wire feed system is basically the same.

To install the wire in the welder first remove the retaining device on the hub and installing the spool of wire. Check the contact tip making sure the wire diameter is the same in the machine as the diameter of the tip. If they do not match select a tip that will match the wire in the machine. Look at the side of the drive roll. Most will have the wire size stamped on the side of the drive roll showing which size groove will be handling the wire. If it does not match, turn it around and see what is stamped on the other side.

After installing the wire and double checking that the wire matches the tip and drive roll groove size, open tension knob and lift idler roller to allow wire to be fed. Now slowly draw the wire off of the spool and run through the inlet guide over the drive roll groove and into the inlet of the gun liner. Push wire into the gun about six inches. Now lower the idle roller over the wire pressing the wire into the grooves of the drive roll. Remove the tip and diffuser, turn on the machine and pull the trigger until the wire is fed out the end of the machine. Slide wire through the diffuser and tip and screw back into gun. Cut wire so that wire sticks out about 1/4 inch. This is referred to as, you guessed it, stick out.

Flow Regulators

Argon, Argon mixes, CO2

Flow Regulators

There are a lot of different regulators on the market for different gases. What makes a difference for a MIG application is that the outlet gauge is not measured in pressure / psi but as a flow rate.

The flow gauge regulator in the picture is made for a light to medium use application. These are commonly used with 110v wire feeds where large flow rates are not required.

Most often flow gauges are meant to use argon or argon and CO2 mixes. Straight CO2 gas requires an adapter for the 580 CGA fitting to fit a CO2 cylinder.

To increase the flow rate turn the T handle clockwise.

MIG Welder Polarity

It is important to use the correct polarity for the wire that is being used. If the wrong polarity is being used the weld will have excess spatter and have an unstable arc.

The correct polarity should be listed on the inside of the machine on a chart. If there isn’t a chart available just run a practice bead and see how it runs. If it is not running properly just reverse the polarity by switching the leads on the posts and try it again. It will not hurt the machine if the polarity is incorrect.

MIG Welding Wire

Hardwire or flux core?

There are so many different types of welding wire to choose from and for so many different uses. For this post I will keep to the very basics and that is for welding steel.

MIG or Metal Inert Gas uses what is commonly known as hard wire or ER70S-6. It will have a copper cladding on the wire to help prevent wire rust as well as aiding in the feeding of the wire.

It must have a shielding gas of CO2 or a blend of argon and carbon dioxide. This shielding gas protects the weld puddle from ambient contaminants so that a solid quality weld can be achieved. It is important when using a shielding gas that side drafts are reduced or eliminated so that your shielding gas does not get blown away. The lack of shielding gas usually results in what is called pinholes, worm holes or just plain porosity.

It is important that the polarity of the machine matches that which is needed for the wire being used. When using hard wire the cable coming off of the MIG gun block inside the machine must be hooked to the positive terminal. Not doing so will make a very bad weld.

Flux Core Wire

Also Known as cored Wire or E71T

The other type of wire is called flux core wire or the acronym FCAW. A shielding gas is not needed for this gas since it has the flux to protect the weld puddle in the center of the wire.

The main advantage of flux core is that you do not have to worry about being outdoors and having your shielding gas blown away. Flux core does smoke and spatter more than the hard wire and does require that the slag be removed from the bead as in stick welding. It also does penetrate more than hard wire.

Just as important as the hard wire polarity the flux core wire must be set up with the proper polarity as well. The cable to the MIG gun block must be hooked to the negative negative terminal and the ground lead to the positive. This is one of the most common mistakes people will make. I have talked to many a welder about this. They think it is a bad batch of wire but when reverse the leads it works fine.

Shielding Gas For Steel

Carbon Dioxide 75% Argon 25% Carbon Dioxide

When MIG welding steel the shielding gas that is most commonly used is 75% Argon 25% Carbon Dioxide GMAW. Argon is heavier than air and stays close to the weld puddle. The Argon portion of the mix allows for good arc stability.

Carbon Dioxide allows for good heat transfer but does not have the good arc stability. CO2 is used where more penetration is required. Conversely if you are welding on thin sheet metal you might experience burn through. With the mix you have more arc stability and good penetration.

Straight CO2 is cheaper than 75/25 and since it is pumped as a liquid it lasts longer.

It is important to weigh the options. Smooth stable arc or less expense and longer welding times. There are other

Argon Gas

Shielding Gas For Aluminum

Argon Gas

Two of the main things about how to weld aluminum is using 100% argon gas and to keep it as clean as possible. Unlike welding steel with argon/co2 using the dragging method you will want to push the weld making sure that the shielding gas is being pushed over the bead. If this is not done the bead will be blackened.

When welding aluminum you will also want to use a spool gun. It is possible to weld without a spool gun buy the MIG gun liner has to be changed to a Teflon or nylon liner so the soft aluminum wire will be able to move down the liner and out to the tip as smoothly as possible. If there are bends in the MIG gun the soft wire has a tendency to drag and then create a birds nest of wire back in the machine.


Anti-spatter prevents welding spatter from sticking to the nozzle, contact tip, diffuser and weld area which increases life of consumables and reduces clean up. It comes in to forms, spray and Gel.

When using the gel run a short bead to get the nozzle, tip and diffuser warm then dip it into the jar. The spray can is just applied as if spray painting the parts.

There are quite a few different brands of antispatter. Some have more toxicity than others and some are environmentally friendly. It just depends on the needs of the person. From talking with customers the environmentally friendly blends don’t quite work as well as the non “eco-friendly“. The decision is up to the user and the application they are working on.


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