GMAW welding: What it is & how it works

May 29, 2024
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What is GMAW welding?

GMAW welding, or gas metal arc welding, is a welding process that uses an electric arc between a continuous, consumable wire electrode and the weld pool. An inert or active gas shields the weld from contaminants.

Key components of GMAW welding systems

A GMAW welding system consists of several components that create an arc:

  • The power source is at the heart of the system and supplies the DC power needed for welding. Cables then conduct this power to the torch.
  • The torch holds a consumable electrode wire, typically made of steel, that feeds through the torch at a controlled speed. As you press the torch trigger, the power source sends current through the electrode, which arcs at the tip and melts the base metals. 
  • Shielding gas, like argon or carbon dioxide, flows through the torch to protect the weld pool from contamination.
  • The wire feeder pushes the electrode wire through the torch at a steady, predetermined speed. As the arc consumes the wire, more is automatically fed into place. The wire-feed speed, measured in inches per minute (IPM), helps determine how much heat and filler you put in. The resulting arc welds the metals together.
  • The ground clamp connects the workpiece to the power source, completing the electrical circuit and allowing current to flow. Proper grounding is essential for welding performance and safety.

Step-by-step GMAW welding process

Now comes the step-by-step part: 

  1. The first step is choosing an electrode wire that matches your base metal and the specific welding requirements. The wire is continuously fed through the welding gun during the process.
  2. Attach the grounding clamp to the workpiece to complete the circuit. Make sure it's firmly connected to bare metal.
  3. Adjust the flow rate of the shielding gas to protect the weld pool from contamination. The flow rate depends on factors like wire size and amperage. Typically, a flow rate of 20 to 50 cubic feet per hour is used.
  4. Set the voltage, wire feed speed, and travel speed on the wire feeder or welding machine. The correct parameters depend on the wire size and type of weld. It may take some testing to dial in the optimal settings.
  5. Hold the welding gun at a 10- to 15-degree angle and position the wire tip about 1/2 inch from the workpiece. Tilt the gun according to the direction that you’re welding in.
  6. Squeeze the trigger to start the arc and begin moving the gun slowly and steadily along the joint. Move the gun at an even speed in a smooth, straight line, or in small circles. Let go of the trigger to stop welding.
  7. Check that the weld penetrates fully into the joint and is slightly convex. Make additional passes as needed until the joint is filled to the desired reinforcement.

Types of GMAW welding

GMAW welding is a very versatile process with several distinct types, each suited for specific applications.

Welding types include: 

  • Short-circuit transfer: This method uses lower current and voltage, making it ideal for welding thin materials and all positions. The arc is repeatedly extinguished and re-established, creating a controlled and stable weld pool.
  • Globular transfer: Higher current levels cause larger droplets of molten metal to form and transfer to the workpiece. This method is excellent for thicker materials but can be prone to spatter.
  • Spray transfer: A high-energy arc produces a fine spray of molten metal, resulting in fast welding speeds and smooth welds. This method is best suited for flat and horizontal positions on thicker materials.
  • Pulsed spray transfer: This technique combines aspects of short-circuit and spray transfer, offering greater control and reduced heat input. It's more versatile for a variety of materials and thicknesses.

Applications of GMAW welding

Auto industry

GMAW welding is popular in the automotive industry because it’s ideal for welding auto bodies and frames where fit-up and high deposition rates are important. The GMAW welding process can quickly join thin materials while providing strong welds. Many vehicle components like doors, hoods, trunk lids, and wheel rims are also welded using GMAW.

Aerospace industry

The aerospace industry relies heavily on GMAW welding to manufacture aircraft, spacecraft, and components. The process can produce high-quality welds rapidly, an essential requirement for large-scale aerospace production.


In shipbuilding, GMAW welding joins large steel plates for hull construction. The high metal deposition rate and welding speed of GMAW make it efficient for long welds. GMAW also works well for welding in all positions, enabling welders to make vertical and overhead welds for hulls. 

General fabrication

GMAW is a very widely used process for general metal fabrication. It can weld a variety of materials including mild steel, stainless steel, and aluminum. The all-position welding capability, high welding speed, and low spatter of GMAW make it well suited to high-volume production and repair work.

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Advantages of GMAW welding

GMAW welding offers several benefits over other welding processes: 

  • Speed: The continuous wire feed allows for higher welding speeds compared to stick welding. This results in higher productivity and lower costs.
  • Less shape distortion: Since GMAW welding produces a small, highly controllable heat source, less heat transfers to the base metal. This means less warping and distortion. The lower heat also allows for better control of the weld pool, which leads to higher-quality welds.
  • Safer and easier to learn welding method: It does not require a welding slag to be chipped off and produces fewer welding fumes. However, proper ventilation is still required. The semi-automatic process is also simpler to pick up. With some practice, you'll be laying down high-quality welds in no time.
  • Versatile and portable: The GMAW process can weld a wide range of materials like steel, aluminum, and stainless steel. It can work in all positions — flat, horizontal, vertical, and overhead. GMAW equipment is also lightweight, portable, and suitable for field work.

Challenges and limitations of GMAW welding

GMAW welding may seem like an ideal process, but it does come with some big drawbacks to keep in mind: 

  • Equipment and gas requirements: GMAW requires specialized equipment like a welding gun, shielding gas, and a power source to generate an arc. This equipment can be expensive, especially if you need an industrial welding unit. The shielding gas also needs to be purchased, properly handled, and stored.
  • Limited welding positions: GMAW typically only allows for welding in flat or horizontal positions. Welding in vertical or overhead positions is more difficult and may require special techniques and equipment. 
  • Skilled operators: GMAW requires trained and certified welders to set up and operate the equipment properly. Improper use can lead to issues like porosity, cracking, or weak welds. Continuous training is needed as new welding techniques, gases, and standards emerge.
  • Porosity and cracking: If the GMAW process is not controlled carefully, defects like porosity (tiny holes) or cracking in the weld can occur. Issues like improper gas flow, contaminants in the weld zone, or a welding speed that’s too high can contribute to these defects. 
  • Limited material thicknesses: While GMAW is often associated with thinner materials, it's not strictly limited to 1/2 inch. Advances in technology and techniques have expanded its capabilities. With proper parameters and skilled welders, GMAW can be used for thicker materials, sometimes even up to several inches thick.

Safety considerations in GMAW welding

When GMAW welding, your safety should be a top priority:

  • Ventilation: Always weld in a well-ventilated area, such as an open garage or outside. The fumes from welding contain particles that can accumulate in your lungs over time. For welding indoors, use an exhaust fan to pull fumes away from the welding area. Wearing a respirator mask with filters specifically for welding also helps minimize fume inhalation.
  • Protective gear: You’ll want to protect your entire body during welding. Wear a long-sleeve shirt, welding jacket, welding helmet, welding gloves, and steel-toed boots. Your eyes also need safety goggles to protect from the intense UV radiation of the welding arc.
  • Fire safety: The extreme heat of welding can easily start fires if precautions are not taken. Never weld near flammable materials like paper, wood, chemicals, or fabrics. Have a fire extinguisher rated for electrical and grease fires readily available. Designate a fire watch — someone to watch for potential fires — when welding in areas where fire hazards may exist.

Summing up

Now you know the complete rundown on GMAW welding and how versatile this metal-joining technique is. With the right techniques and gear, you'll be laying down quality GMAW welds in no time.

Next steps

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