GMAW Basics – MIG Welding Set Up

Last updated on February 25th, 2019 at 02:38 pm

MIG welding process requires mainly three things, electricity to produce heat, an electrode to fill the weld, and shielding gas to protect the weld from air contamination.

Select the Wire Size

The wire is the filler material. MIG wire or electrode size is one of the considerations that you need to think of. The type of wire you use should match the type of metal you are trying to weld.

In general, for welding a thin material, you will need a thin wire. And for welding a thick material, you will need a thick wire. Also thicker wires conducts more electricity and burns more which allow for better penetration.

There are two common types of electrodes for welding steel;

  • ER70S-3 for all purpose welding.
  • ER70S-6 for welding on dirty or rusty steel when more deoxidizing is required.

These codes are standard codes that is set by the manufactures to identify the type of electrode.

Let’s take the code of ER70S-3 as an example;

ER – An electrode rod or filler wire used for welding.

70 – The amount of resistance of pressure. In this case, it;s 70,000 pounds of tensile strength per square inch.

S – Solid electrode type.

3 – The amount of deoxidizing and cleansing coating on the electrode.

  • Solid Wire

Generally, solid MIG wires range from .023” to .045” thickness. For industrial applications other wire sizes are also available. These are some guidelines for common wire size diameters;

  • 0.023” Solid – Good for welding thin metals from 24 gauge up to around 16 gauge. It leaves little filler material and reflects less heat. Which is required as to not burn through thin metals.
  • 0.030” Solid – Good for a wide range of common metal thicknesses from 22 gauge and up to around ⅛ inch.
  • 0.035” Solid – Good for beginners and can weld from 18 gauge and up to around ¼ inch. It leaves a high level of heat which is easy to use for thicker metals.
  • 0.045” Solid – Good for thicker metal welding of above ¼ inch.

Always make sure to check the size chart recommendations given by the manufacturer.

  • Flux Core Wire

Flux core wires on the other hand has few common choices for welding steel. Generally ranging from .030” to .045” thickness. Check the user manual of your welder to check the manufacturer’s recommendations for the wire size chart;

  • 0.030″ Flux Core – Good for welding a minimum of 18 gauge and up to around ¼ inch thickness.
  • 0.045″ Flux Core – Good for welding steel up to ½ inch thick.

Once your set with choosing the appropriate MIG wire. Then, you will need to install it into your MIG welding machine. This is pretty easy once you get the hang of it. As a result, in the welding process, the wire will pass through the rollers, then gets pushed through a set of hoses, which leads to the MIG gun. The set of hoses carry the electrode and the shielding gas.

Choose the Shielding Gas

The shielding gas protects the weld as it is forming as the atmosphere interferes with the quality of the weld. In fact, without the gas the welds will be less strong and will not look clean. The shielding gas also needs to match the wire electrode and base metal. It’s best to always seek input for recommendations on the proper shielding gas to match the wire used.

Always make sure you read all safety information and take maximum safety precautions. Gas tanks are squeezed under high pressure in the cylinder, and if it falls over and knocks the regulator off it will fly across the room. For safety reasons, try to keep your gas valve only half way open. This will not really affect the amount of gas released, but it will always be easier to turn off in case of emergency.

Pure gases or mixtures of gases are used for shielding with MIG or GMAW. Here are the common types of shielding gases;

  • Carbon Dioxide (CO2)

Most common and least expensive. Using 100% CO2 offers deep penetration and high spatter. You can use it in its pure form to weld thicker metals and achieve a deeper weld penetration on steel. As a result, it’s useful for welding thicker metals and would be difficult for thinner metals. Also using a mixture of CO2 and other gases can be used to make the arc more stable and minimize spatter.

  • Argon (Ar)

Argon is a more expensive gas. It has a high ability of shielding the weld from contamination as it has a higher density than air. However, using 100% argon offers a shallow penetration for welding steel. Argon can be used for welding almost any metal except steel. It’s good for welding non-ferrous metals such as aluminum, copper, magnesium, titanium, nickel,and alloys.

  • Helium (He)

Helium has the highest price. It’s also good for welding aluminum, copper, magnesium, and other non-ferrous metals. However, using 100 % helium leads to excessive spatter and can cause an erratic arc. As a result, sometimes helium and argon are mixed together to combine the qualities of both together.

  • Oxygen (O2)

This gas often gets mixed with other gases, especially argon or helium. It helps achieve deeper penetration and better arc stability.

  • Gas Mixtures

Argon and CO2 can be mixed for welding ferrous metals such as steel and stainless steel. The most common mixes of 75/25 blend is considered to be an all-purpose shielding gas for mild steel. Welding a thin metal sheet needs a higher percent of argon to achieve a flatter weld with less spatter. While the higher the carbon gas levels, the more spatter, achieving a higher penetration rate. Also, adding hydrogen (H) to the mix is good for welding stainless steel and nickel.

Having the right gas and electrode mixture varies depending on many factors. The three most commonly used gas and electrode combinations are;

  • Mild Steel – ER70S electrode with a 75% argon to 25% carbon dioxide gas mixture.
  • Stainless Steel – ER308L electrode with a 98% argon to 2% carbon dioxide gas mixture.
  • Aluminum – ER4043 electrode with 100% pure argon gas.

Depending on which gases you choose the metal transfer type changes too. If you are not familiar with transfer types then please read more below about MIG welders metal transfer types. This will definitely improve your welding knowledge and skills.

The Metal Transfer Types

There are four main methods for MIG. Each type is defined by the way in which the contact is made between the electrode wire and the parent metals. Below are the main methods explained;

  • Spray Transfer

Similarly to a fine water hose, in this method, welding machine creates a high current which passes through the electrode wire and out of the gun tip. Because the voltage runs so high for this method, the wire melts and explodes into these fine droplets, which bond together and cool rapidly, producing a clean, smooth weld.

The arc does not turn off during this method, which produces less spatter on the surface of the parent weld and works well with thick materials. This method usually uses high concentrations of argon shielding gas.

  • Pulse Spray Transfer

While very similar to spray transfer, this method varies in voltage currents, allowing for a cycle to cool and heat which forms a strong bond. What’s special about pulsed spray transfer is this inconsistency in the voltage. Consequently, as the voltage fluctuates, the welder actually experiences two types of welding, globular, and spray. Because the voltage needed to produce these efficient welds varies throughout the process, it doesn’t require a high amount of voltage to perform the weld.

Pulsed spray transfer can be used on thicker metals, due to its high average current, and can be used in more positions than spray transfer. The shielding gas used for this method is generally the same as the spray transfer. In pulsed spray transfer, the type of welder required is on a higher end than most traditional MIG welders. The reason these welders are more costly is due to the power needed to pulsate the voltage output.

  • Globular Transfer

When the electrode wire heats in globular transfers, the drops are larger than the diameter of the wire. Whereas in both pulsed and spray transfers uses small, finer drops to produce clean welds, globular produces some of the highest amounts of spatter compared to other methods of welding. This method collects melted wire on the tip of the gun. Similar to a leaking faucet you can’t seem to turn off all the way, drops of melted wire escape much slowly – two or three drops of metal per second – in comparison to spraying transfer and short circuit transfer. It uses relatively low welding current.

Instead of an argon heavy gas mix, globular uses pure carbon dioxide for shielding. The chemical compounds from pure carbon dioxide and carbon steel electrodes work well with carbon steel.

  • Short Circuit Transfer

In the methods mentioned above, drops of melted wire produce a weld pool, which cools and bonds the parent metals together. In short circuit transfers, the electrode wire actually touches the metal and causes a short circuit, which melts the wire and produces the weld. The wire is fed through the gun which, when touching the surface of the parent metal, completes a circuit. As a result, electricity courses through the wire and causes the metal to melt and drip on the surface. This method uses small diameter electrode wire and voltage high enough to melt the wire when it short circuits.

The shielding gas is a mixture of argon and carbon dioxide. The shielding gas penetrates thicker materials but produces less consistent results. It is also possible to burn through thinner metals since the penetration power is greater than argon-based shielding.

Set the Gas Flow Rate

Open the main valve of the tank and check the gauge level. Gas flow rate for MIG welding vary, but mostly starting off with 15 to 30 cubic feet per hour (CFH) is a good start. It depends on the materials, the conditions, the welding gun, and your skill level.

Not having enough shielding gas flow, will leave the weld porous. Just like a sponge with air void resulting in a weak weld. Too much or too little gas flow will cause the outside air to be pulled inside the bead or cause excessive spatter. Your ears are an excellent tool for setting the correct flow rate. If everything is set correctly, you should hear a hiss sound with no big popping or sputtering sounds.

Set the Wire Feed Speed

The wire feed speed controls how fast the wire is fed into the weld. As a result, controlling the amount of penetration to the weld and the amperage. A speed too slow may not be enough penetrate and too high can lead to burn through of the base metal. At the same time, the faster the wire feed speed gets, more amperage will be required so as to get a higher heat capability.

Wire feed speed is calculated in inches per minute (IPM). If a manual or weld specification sheet is not available, you can use the this multipliers rule. We are making this example using 120 amps;

  • 0.023 inch: multiply by 3.5 inch per amp used = 3.5 x 120 amps = 420 IPM.
  • 0.030 inch: multiply by 2 inch per amp used = 2 x 120 amps = 240 IPM.
  • 0.035 inch: multiply by 1.6 inch per amp used = 1.6 x 120 amps = 192 IPM.
  • 0.045 inch: multiply by 1 inch per amp used = 1 x 120 amps = 120 IPM.

Set the Voltage & Amperage

The type of metal to weld, the metal thickness, the wire diameter, the wire feed speed, the shielding gas, and the welding position are among other factors that will determine the amount of voltage you will adjust your machine to run at while welding.

The voltage determine the temperature and the width and height of the bead. To start welding, it’s better to start on the lowest voltage setting and move up depending on the thickness of the metal until the arc becomes unstable. A midway voltage between too low and too high to a point of a sloppy arc should be achieved.

To know the exact voltage required for a given thickness of metal, you need a convenient reference chart or manual. Most MIG welding machines will allow to select the wire diameter and the thickness of metal you are going to weld and it will automatically set itself to the amount of current, voltage, and even wire feed speed needed for the job.

Setting the proper amperage and wire size. This is an average reference for commonly used wire diameters with the appropriate amperage;

  • 0.023 inch: 30 – 130 amps.
  • 0.030 inch: 40 – 145 amps.
  • 0.035 inch: 50 – 180 amps.
  • 0.045 inch: 75  -250 amps.

As a guideline, each 0.001 inch of material thickness requires 1 amp.

Set the Welding Polarity

When MIG welding you to set the right polarity for the welder. MIG welding unlike most other welding processes, such as GTAW or stick welding, has one standard voltage type and polarity type which is DC current. Direct current (DC) flows in one direction, from the ( – ) negative to the ( + ) positive. Any MIG or flux-core welding machine will either run on direct current electrode negative (DCEN), or direct current electrode positive (DCEP).

Switching polarity for MIG solid wire requires you to set the terminal to positive. While for flux-core wires, you will need to change the terminal to negative. Although this is different on different welding machines so make sure you check the user manual.

The Welding Gun

The welding gun is where most of the action is going to happen. The start signal is triggered once you press the gun. By pressing the trigger, the welding electricity ignites, the wire feed moves, and the gas starts to flow. A replaceable contact tip takes welding current from the unit to the electrode. Tips are consumables like wires and shielding gases. The tip is located at the end of the welding gun. They vary in size and they must match the wire you are using for the weld. You should see a small piece of wire sticking out of the tip of the MIG welding gun.

While the gas nozzles is responsible for directing the shielding gas to the weld pool. Having the appropriate nozzle for the application will guarantee an appropriate shielding from contamination and will also avoid overheating of the consumable.

Connect the Ground Clamp

The ground clamp completes the circuit between the welder, the welding gun, and the workpiece. It should either be clipped directly to the metal workpiece or to a metal welding table. The grounding clamp should be making a good contact in order to establish a stable arc. As a result, make sure to grind off any paint or rust that may be preventing a connection. These surfaces do not allow for a proper welding current flow as they insulate electricity. Other signs of an improper grounding connection are cables or a ground clamp that are hot to the touch. So, always make sure to take the right steps towards a safe welding process.

Putting it All Together

Finally once everything is set together you will be able to produce the transfer type you wanted, produce enough heat to penetrate the metal, and get the proper shielding gas for protection. Resulting in no burning holes and a clean, high quality weld. It is the result of continuous tests and flaws that will ultimately allow you to set the machine the exact way you want. Unless you have a welding engineer or a ready procedure chart. Then, it’s time to look practice, practice, practice. Check our list of best rated MIG welders.

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