Welding

What is GMAW Welding? How Does it Work?

Do you want to know more about welding? If so, you might be wondering: what is GMAW welding and how does it work? GMAW welding is a type of arc welding that uses electricity and gas to join metal pieces. It is also called MIG (Metal Inert Gas) welding.

In this blog post, I will explain the basics of GMAW welding, its pros and cons, and some common uses. You will learn how GMAW welding works, what kind of metals it can weld, what kind of positions it can weld in, what kind of quality and speed it can achieve, what kind of equipment and safety it requires, and what kind of applications it has in different industries.

What is GMAW Welding? When precision meets intensity, sparks are bound to ignite!

Takeaways:

  • GMAW uses an electric arc between a continuously fed wire electrode and a workpiece with shielding gas.
  • Benefits include speed, automation capability, and versatility for many industries/applications.
  • Techniques include short circuit, spray, pulsed, and globular metal transfer modes.
  • Must select suitable parameters like gas, electrode, voltage, and amperage for quality.
  • Critical to follow safety measures and troubleshoot defects through parameter tweaks.

Understanding the GMAW welding process

GMAW or MIG welding is a type of arc welding that uses an electric arc to melt the metal at the joint. The arc is between a wire electrode and the workpiece. The wire electrode is both the filler metal and the electricity conductor. The melted electrode forms a weld pool that joins the base metal.

The weld pool is protected by a shielding gas that comes from the welding gun. The shielding gas stops the air from affecting the weld quality and strength. The shielding gas can be inert (like argon or helium) or active (like carbon dioxide or oxygen). The type of shielding gas depends on the material, joint, and weld.

There are three types of GMAW welding: automatic, semi-automatic, and gasless (flux-cored). Automatic GMAW welding is when the machine controls everything. Semi-automatic GMAW welding is when the operator controls the gun movement. Gasless (flux-cored) GMAW welding is when the electrode has a flux core that makes its own shielding gas.

Advantages of GMAW welding

GMAW welding is a welding method that offers many benefits compared to other methods. One of the benefits is that it can produce more weld metal per unit time, which means it can reduce the overall welding time and cost. Another benefit is that it can be easily automated using robots or mechanized systems, which can improve the productivity and consistency of the welding process.

GMAW welding can also be used in various positions, such as flat, horizontal, vertical, or overhead, which makes it versatile for various applications. Moreover, GMAW welding can produce cleaner and more precise welds with minimal spatter, which means it can reduce the need for post-weld cleaning and grinding. It can also allow for better control of the weld bead size and shape, which can improve the appearance and accuracy of the weld.

Furthermore, GMAW welding can weld a wide range of metals with different thicknesses and compositions, such as carbon steel, stainless steel, and aluminium, which makes it suitable for various industries and applications.

Additionally, GMAW welding can adjust the heat input and penetration by changing the voltage, current, wire feed speed, and electrode diameter, which enables it to weld both thick and thin materials without distortion or burn-through. These are some of the advantages of GMAW welding that make it a popular and important welding method in the welding industry.

GMAW welding techniques

There are four main techniques or modes of metal transfer in GMAW welding: short-circuiting transfer mode, spray transfer mode, pulsed transfer mode, and globular transfer mode. Each mode has its own advantages and disadvantages depending on the material type, thickness, position, and application.

Short-circuiting transfer mode

Short-circuiting transfer mode is when the electrode touches the workpiece periodically and creates a short circuit that melts the metal. This mode uses low voltage (15 to 25 volts) and low current (60 to 200 amps) to produce small droplets of molten metal that transfer across the arc gap. This mode is suitable for thin materials (less than 3 mm), low heat input applications, out-of-position welding, and root pass welding. It produces less spatter, less distortion, good penetration, and good fusion.

Spray transfer mode

Spray transfer mode is when the electrode does not touch the workpiece but creates a stream of fine droplets of molten metal that spray across the arc gap. This mode uses high voltage (25 to 40 volts) and high current (200 to 400 amps) to produce high heat input and high deposition rates.

This mode is suitable for thick materials (more than 3 mm), flat or horizontal position welding, high-speed applications, and high-quality welds. It produces less spatter, less porosity, a smooth bead appearance, and excellent fusion.

Pulsed Transfer Mode

Pulsed-transfer mode is when the electrode alternates between high current pulses and low current background levels to create a controlled metal transfer. This model uses a variable voltage (15 to 40 volts) and a variable current (50 to 400 amps) to produce a combination of heat input and deposition rates.

This mode is suitable for all-position welding, medium to thick materials (1 to 12 mm), low spatter applications, and precise welds. It produces less spatter, less distortion, good penetration, and good fusion.

Globular Transfer Mode

Globular transfer mode is when the electrode does not touch the workpiece but creates large droplets of molten metal that fall across the arc gap. This mode uses low voltage (15 to 25 volts) and high current (200 to 400 amps) to produce high heat input and high deposition rates.

This mode is suitable for flat-position welding, thick materials (more than 6 mm), high-speed applications, and filler welds. It produces more spatter, more porosity, irregular bead appearance, and poor fusion.

Applications of GMAW welding

GMAW welding is widely used in various industries and applications, such as:

  • Automotive industry: GMAW welding is used for vehicle body and frame construction, exhaust systems and mufflers, and other parts that require high strength and durability.
  • Manufacturing and fabrication: GMAW welding is used for structural steel fabrication, sheet metal fabrication, metal furniture, appliances, and other products that require high quality and efficiency.
  • Construction and infrastructure: GMAW welding is used for pipelines and tanks, bridges and buildings, and other structures that require high reliability and safety.
  • Aerospace and aviation: GMAW welding is used for aircraft assembly and repair, engine components, and other parts that require high precision and performance.

Selection Of GMAW Welding Parameters

To achieve successful GMAW welding, it is important to select the appropriate parameters, such as shielding gas, filler material, voltage, current, and wire feed speed. These parameters affect the quality and characteristics of the weld, such as penetration, fusion, spatter, porosity, distortion, and appearance.

Choosing The Appropriate Shielding Gas

The shielding gas plays a vital role in protecting the weld pool from the air and influencing the metal transfer mode. The choice of shielding gas depends on the type of material, joint design, and desired weld characteristics. Some of the common types of shielding gases used in GMAW welding are:

  • Argon: Argon is an inert gas that does not react with molten metal. It produces a stable arc and a smooth spray transfer mode. It is suitable for welding aluminium, magnesium, copper, nickel, titanium, and their alloys.
  • Carbon dioxide: Carbon dioxide is an active gas that reacts with the molten metal. It produces a deep penetration and a short-circuiting or globular transfer mode. It is suitable for welding carbon steel, low alloy steel, and stainless steel.
  • Helium: Helium is an inert gas that does not react with molten metal. It produces a hotter arc and a spray or pulsed-transfer mode. It is suitable for welding aluminium, copper, nickel, titanium, and their alloys.
  • Oxygen: Oxygen is an active gas that reacts with the molten metal. It produces a higher heat input and a spray or pulsed-transfer mode. It is suitable for welding carbon steel, low alloy steel, stainless steel, and copper.
  • Mixed gases: Mixed gases are combinations of two or more gases that provide a balance of arc stability, penetration, spatter control, bead appearance, and cost. Some of the common mixed gases used in GMAW welding are:
    • Argon-Carbon dioxide: This mixture produces a moderate penetration and a short-circuiting or spray transfer mode. It is suitable for welding carbon steel, low alloy steel, stainless steel
    • Argon-Oxygen: This mixture produces a shallow penetration and a spray or pulsed-transfer mode. It is suitable for welding carbon steel
    • Argon-Helium: This mixture produces a high heat input and a spray or pulsed-transfer mode. It is suitable for welding aluminium
    • Argon-Helium-Carbon dioxide: This mixture produces a deep penetration and a spray or pulsed-transfer mode. It is suitable for welding stainless steel

Determining The Right Filler Material And Electrode

The filler material or electrode acts as both the conductor of electricity and the source of weld metal. The choice of filler material depends on the type of base material and the application requirements. The filler material should match or exceed the strength and corrosion resistance of the base material. Some of the common types of filler materials used in GMAW welding are:

  • Carbon steel electrodes: These electrodes are made of mild steel or low-carbon steel with small amounts of manganese or silicon as deoxidizers. They are suitable for welding carbon steel or low alloy steel with carbon dioxide or argon-carbon dioxide shielding gas.
  • Stainless steel electrodes: These electrodes are made of stainless steel with chromium or nickel as alloying elements. They
  • are suitable for welding stainless steel with argon, argon-helium, or argon-helium-carbon dioxide shielding gas.
  • Aluminium electrodes: These electrodes are made of aluminium or aluminium alloys with silicon or magnesium as alloying elements. They are suitable for welding aluminium or aluminium alloys with argon or argon-helium shielding gas.
  • Copper electrodes: These electrodes are made of copper or copper alloys with zinc, tin, or nickel as alloying elements. They are suitable for welding copper or copper alloys with argon, helium, or argon-helium shielding gas.

The electrode diameter affects the heat input and the deposition rate of the weld. A larger electrode diameter produces more heat input and more deposition rate, but also more spatter and distortion.

A smaller electrode diameter produces less heat input and less deposition rate, but also less spatter and distortion. The electrode diameter should be selected based on the material thickness, joint design, and welding position.

Adjusting voltage, amperage, and wire feed speed

The voltage, amperage, and wire feed speed are the main parameters that control the arc characteristics and the metal transfer mode in GMAW welding. The voltage affects the arc length and the stability of the arc.

A higher voltage produces a longer arc and a more stable arc, but also more spatter and less penetration. A lower voltage produces a shorter arc and a less stable arc, but also less spatter and more penetration. The voltage should be adjusted to maintain a consistent arc length and a smooth metal transfer.

The amperage affects the heat input and the size of the weld pool. A higher amperage produces more heat input and a larger weld pool, but also more distortion and burn-through.

A lower amperage produces less heat input and a smaller weld pool, but also less fusion and penetration. The amperage should be adjusted to achieve sufficient fusion and penetration without causing excessive distortion or burn-through.

The wire feed speed affects the deposition rate and the current of the weld. A higher wire feed speed produces more deposition rate and more current, but also more spatter and less control.

A lower wire feed speed produces less deposition rate and less current, but also less spatter and more control. The wire feed speed should be adjusted to match the travel speed of the welding gun and the desired weld bead size.

Safety considerations in GMAW welding

GMAW welding involves high temperatures, high currents, high pressures, and high radiation, which can pose various hazards to the operator and the environment. Therefore, it is important to follow proper safety precautions in GMAW welding, such as:

  • Importance of proper ventilation and extraction systems: GMAW welding can produce harmful fumes and gases that can affect the health of the operator and the quality of the weld. Therefore, it is important to have adequate ventilation and extraction systems in the welding area to remove these fumes and gases from the operator’s breathing zone and the weld zone.
  • Personal protective equipment (PPE) for GMAW welding: GMAW welding can expose the operator to various risks, such as electrical shock, UV radiation exposure, burns, eye injuries, noise, etc. Therefore, it is important to wear appropriate PPE for GMAW welding, such as:
  • Welding helmet with appropriate shade: The welding helmet protects the operator’s face and eyes from UV radiation, sparks, spatter, and flying metal. The helmet should have an appropriate shade level that blocks enough light without compromising visibility. The shade level depends on the type of material, current level, arc length, etc.
  • Protective clothing, gloves, and footwear: The protective clothing protects the operator’s body from heat, sparks, spatter
  • and flying metal. The clothing should be made of flame-resistant material, such as leather or cotton, and should cover the entire body. The gloves should be made of leather or rubber and should fit snugly. The footwear should be made of leather or steel and should have a closed toe and a high ankle.
  • Respiratory protection if required: Respiratory protection protects the operator’s lungs from inhaling harmful fumes and gases. The respiratory protection can be either a disposable mask, a half-face respirator, or a full-face respirator, depending on the type and concentration of the fumes and gases. The respiratory protection should be fitted properly and checked regularly for leaks and damage.
  • Understanding potential hazards, including electrical shock and UV radiation exposure: GMAW welding can cause various hazards, such as:
  • Electrical shock: Electrical shock can occur when the operator touches a live circuit or a grounded metal. Electrical shock can cause burns, muscle spasms, cardiac arrest, or death. To prevent electrical shock, the operator should:
    • Use insulated gloves and tools
    • Disconnect the power source when not in use
    • Avoid touching live wires or electrodes
    • Avoid working in wet or damp conditions
    • Use a ground fault circuit interrupter (GFCI) if available
  • UV radiation exposure: UV radiation exposure can occur when the operator looks at the arc without proper eye protection or when the arc reflects from shiny surfaces. UV radiation exposure can cause eye injuries, such as welder’s flash, cataracts, or blindness. It can also cause skin injuries, such as sunburn, skin cancer, or premature aging. To prevent UV radiation exposure, the operator should:
    • Wear a welding helmet with an appropriate shade level
    • Wear protective clothing that covers the entire body
    • Wear sunglasses or goggles when working near the arc
    • Avoid looking directly at the arc or its reflection
    • Use screens or curtains to shield the arc from others

Common defects and troubleshooting in GMAW welding

GMAW welding can produce various defects that can affect the quality and strength of the weld, such as:

  • Porosity and gas entrapment: Porosity and gas entrapment are when small holes or bubbles form in the weld due to trapped gas. They can reduce the weld strength and cause cracking. Some of the causes and prevention measures of porosity and gas entrapment are:
  • Contaminated base metal or electrode: The base metal or electrode can have dirt, oil, grease, rust, paint, moisture, or other impurities that can react with the molten metal and produce gas. To prevent this, the base metal and electrode should be cleaned thoroughly before welding.
  • Improper shielding gas: The shielding gas can have leaks, moisture, air, or other contaminants that can affect the gas flow and protection of the weld pool. To prevent this, the shielding gas system should be checked regularly for leaks and damage. The shielding gas type, pressure, and flow rate should be selected according to the material type, thickness, position, etc.
  • Improper welding technique: The welding technique can affect the gas entrapment in the weld pool. For example, too long an arc length can cause turbulence in the weld pool and trap gas. Too fast a travel speed can cause incomplete fusion and leave gaps for gas to escape. To prevent this, the welding technique should be adjusted to maintain a consistent arc length and a smooth metal transfer.
  • Incomplete fusion or penetration: Incomplete fusion or penetration is when the weld metal does not fuse properly with the base metal or does not penetrate deep enough into the joint. It can reduce the weld strength and cause cracking. Some of the factors contributing to incomplete fusion or penetration are:
  • Insufficient heat input: The heat input can be too low to melt the base metal adequately or create a large enough weld pool. This can be caused by low voltage, low current, low wire feed speed, large electrode diameter, etc. To improve fusion and penetration, the heat input should be increased by adjusting these parameters accordingly.
  • Improper joint design: The joint design can affect the accessibility and alignment of the weld pool with the base metal. For example, a gap or a mismatch between the joint edges can prevent the weld pool from reaching the root of the joint. A lack of bevel or groove on the joint edges can limit the penetration depth of the weld pool. To improve fusion and penetration, the joint design should be modified to ensure proper fit-up and gap control. A bevel or groove should be applied on the joint edges to increase the penetration depth.
  • Improper welding technique: The welding technique can affect the fusion and penetration of the weld pool with the base metal. For example, too fast a travel speed can cause the weld pool to move ahead of the arc and leave behind unfused areas. Too slow a travel speed can cause excessive heat input and burn-through. To improve fusion and penetration, the welding technique should be adjusted to maintain a balanced heat input and travel speed.
  • Spatter and burn-through: Spatter and burn-through are when molten metal splashes out of the weld pool and sticks to the surrounding area or when molten metal melts through the base metal and creates a hole. They can affect the appearance and integrity of the weld. Some of the causes and prevention of spatter and burn-through are:
    • High heat input: The heat input can be too high to cause excessive melting and boiling of the metal, which can result in spatter and burn-through. This can be caused by high voltage, high current, high wire feed speed, small electrode diameter, etc. To prevent spatter and burn-through, the heat input should be reduced by adjusting these parameters accordingly.
    • Improper shielding gas: The shielding gas can affect the stability and shape of the arc, which can influence the spatter and burn-through. For example, too much or too little shielding gas can cause arc instability and turbulence, which can produce spatter and burn-through. To prevent spatter and burn-through, the shielding gas type, pressure, and flow rate should be selected according to the material type, thickness, position, etc.
    • Improper welding technique: The welding technique can affect the spatter and burn-through of the weld pool. For example, too long or too short an arc length can cause spatter and burn-through. Too high or too low a torch angle can cause spatter and burn-through. To prevent spatter and burn-through, the welding technique should be adjusted to maintain a consistent arc length and a proper torch angle.

Conclusion

GMAW welding is a type of arc welding that uses an electric arc, a welding wire, and a shielding gas to join metal pieces together. It has many advantages, such as high speed, high quality, high versatility, and high suitability for various materials and applications.

It also involves different techniques, parameters, safety precautions, and troubleshooting methods that affect the weld characteristics and performance.

GMAW welding is a popular and important welding method in the welding industry, but it also requires proper training, practice, and technique to achieve successful results. Therefore, it is recommended to learn more about GMAW welding and its principles, advantages, techniques, applications, parameters, safety considerations, defects, and troubleshooting from various resources available online or offline. Thank you for reading! 😊

Thomas James

Thomas James is an experienced auto mechanic who enjoys writing comprehensive guides and offering valuable tips on various car issues.

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button