Step by Step: How to MIG Weld

The question "how to MIG weld" is becoming more and more common as hobbyists and professionals discover its' advantages. The equipment automates a good amount of the complexity making it a popular option that doesn't take the amount of practice associated with other methods. It also doesn't hurt that MIG welding is a faster process to apply.

MIG welding requires specialized equipment. Hobbyist machines can cost a few hundred dollars and run on regular wall current (110 volt electrical outlet). The gun used for MIG welding brings together the electrode, gas and current, also simplifying the process. Wire is fed via a feeder with the one needed dependent on the type of equipment and application. For example a 110 volt welding machine will work with a 110 volt feeder.

Some decisions are required before you start welding such as wire feed speed, voltage and recommended shielding gas. These can be calculated using the online tool recommended at the bottom of this page. They are also available as handy mobile apps.

GMAW How to Mig Weld Video

Tips and Equipment

GMAW Welding Equipment

GMAW wire feed motor (left) and power source (right)

Probably the most common How to Mig Weld question I get asked is - What wire welder (mig) should I buy for my small home shop ? 

It's a good question but what most people don't realize is that most small wire welders in the 110 volt range are very similar and it's probably the electrode choice, gas choice, duty cycle, input amperage and total output amperage that will matter most in the How to Mig Weld.

Let's discuss these items -

Electrode choice - Most of these small machines will come with flux cored wire. (The shielding flux is inside the wire and requires no shielding gas)

There are more than one kind of flux cored wire 

  1. flux cored without gas
  2. flux cored with gas

I will be honest, I have had the opportunity to use every type of flux cored wire sold in North America because of a small adult class research project including Lincolns new "dual Shield" wire and it's just my opinion that flux cored wires and small limited Amperage input/output hobby welders are not a match made in heaven.  

Don't get me wrong, flux cored wire has it's place. It is a high penetrating process that will not go away. But most hobby welders lack the know how to run it and don't care for it's weld appearance.

If you choose to run it I suggest the following:

  1. Increase your stick out (distance between the contact tip and base metal to 1/2" as this allows the core flux to melt and become gas and liquid in the molten puddle.
  2. Increase your voltage as most flux cored wires prefer a longer arc length and in wire welding voltage=arc length.  

When wire welding always remember - 

Voltage = Arc length (you can also think of it as weld width) Why? The higher the voltage, the longer the arc length, and,  the longer the arc length the wider the weld.

Use inline motions.

Inline motions (drag, 1/8" forward stop repeat ) allow the molten puddle to maintain heat and eliminate the chances of welding over flux already deposited.

We have small welders set up side by side for users to compare.

  1. flux cored without gas
  2.  flux cored with gas
  3.  solid core (Er70s6) with 75/25 gas   

When users try #3 they don't want to go back to #1 or #2. SO if you purchase one of these machines keep in mind that you might want to opt for the gas kit so you can make the switch and remember you'll probably have to .

HOWEVER, don't toss the flux cored wire in the trash can ! You might have some applications (ie.. outside in windy conditions, in the field where gas is not portable enough) to use it.

Gosh that took a long time ! The next ones are easier !

Gas Choice

  • CO2 - Carbon Dioxide is the least expensive, most penetrating of the 3 with the least weld flow and poorest weld appearance.
  • 75/25 - Argon/CO2 is the more expensive but will result in better weld appearance and quality. When carbon dioxide or oxygen is added to pure gas, it improves arc stability, reduces any undercut and porosity (pinholes in weld). 
  • Gas choices vary by type of metal being welded:
  • Argon for aluminum alloy, magnesium, nickel, Mondel, Inconel, Titanium, Silicon bronze and aluminum bronze
  • For aluminum and magnesium alloys use 75% helium, 25% argon
  • For Stainless steel use argon/oxygen mix
  • For deoxidized copper use 75% helium, 25% argon
  • For low alloy steel use argon with 2% oxygen
  • For mild steel use 15% argon, 25% carbon dioxide.  With deoxidized steel wire can also use 100% CO2

Duty Cycle

 The amount of time in 10 minutes a machine can perform (weld) at a given amperage. Example - 50% at 60 amps means you can weld 5 minutes out of 10 minutes at 60 amps.

Input Amperage

The required amperage delivered to a machine. This is a point that many people forget when purchasing a machine. If you purchase a 110 volt machine and plug it in to an outlet in your garage which has other items pulling from it you will have input amperage issues. It's a good idea to have a dedicated circuit for your welder or you will be tripping the breaker every time you weld.

Total output amperage - The Amps the power source will deliver for a given duty-cycle period. You just can't expect a 110 volt machine  to deliver more amps than it's capable of.

Don't get me wrong ! Small wire feed welders have a place in the world but you have to realize that they have the highest return rate of any welder on the market. Hopefully now you know why, and know if one belongs in your treasure chest of equipment in your shop.

Just my 2 cents

Good Luck !

How to MIG Weld

GMAW Push Technique
1. Check the contact tip and make sure that it is for the diameter of the welding wire.

GMAW Welding Nozzle

2.Check the feed roller
- Does the groove size of the feed roller match the diameter of the welding wire
- check for wear

3. Check the power

3. Connect work clamps
- If using DC power the positive lead connects to the torch and the negative to the work

4. Select electrode diameter and type
- as a general rule for same current, the arc will be more penetrating with decreases in the electrode diameter and as the deposition rate (rate at which metal is added to the weld)
- wire that is .045" and larger has a lower deposition rate, but will result in a wider bead

5. Turn on Power Supply

Prototypical GMAW Power Control Panel

6. Adjust gas flow

  • Check that the shielding gas regulator is in the right position before opening the main shielding gas cylinder
  • Adjust the pressure of the shielding gas to 2-3 kgf/cm(2) by controlling the pressure regulation knob of the shielding gas regulator
  • Turn the gas check switch to the "check" position on the control panel of the power source and adjust the gas flow rate according to the recommended standards of your welding equipment (see chart below for reference)
  • Return the gas check switch to the welding position

Gas Flow Rate Reference

Typical Flow rates for shielding gases. Find actual rate through manufacturer of equipment and experimentation

7. Adjust wire
- Feed the wire into the welding torch until it extends approx. 20mm from the tip of the contact tube

8. Adjust welding current and voltage

  • equipment should automatically adjust. Manual adjustment can be used to fine tune. If voltage is lower than what is required, the wire will stick to the base metal and make a crackling sound. If voltage is too high, the arc becomes a flame and will cause excessive spatter.
  • Most GMAW applications use DC power (also called DCEP). Each type of DC power (thyristor, tapped transformer type, sliding transformer) has operational features

7. Position the gun over the joint

GMAW Weld Direction and Position

8. Position face shield

9. Pull gun trigger and start to weld
- Maintain a distance between the contact tip and work surface between 3/8" to 1/2"
- Keep constant travel speed and angles

Tip: Check your travel speed by looking at the ridge, the point where the molten metal starts to solidify. The ridge should be approximately 3/8" behind the electrode

Nozzle to Work Distance

The proper nozzle to work distance depends on the welding current being used.

10. When the arc goes out release the gun trigger

11. To start again, back track a bit into the crater and then continue on.

12. When finished, close the shield gas cylinder, and discharge the shielding gas that is remaining in the passage between the gas regulator and the welding torch by switching the gas check switch to "check." Once the regulator shows zero pressure, return gas check switch to "welding."

13. Turn off the main power switch

Welding Performance Tips

  • Power sources work best when welding cables have a diameter of 5-10m. Use cables recommended by the weld equipment manufacturer.
  • Solid welding wires generate less slag and are better for multi-pass welding. Flux core wires have low spatter and create smooth beads.

Types and Characteristics of GMAW Flux-cored - FCW - and Solid Wires

Note that the performance of each wire type is dependent on the manufacturer. This table is only for general reference.

Useful Tools

If you are struggling with equipment settings needed when determining how to MIG weld, these MIG Welding Calculators will help to determine wire speed, recommended shielding gas and amperage.

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