Gas Metal Arc Welding (GMAW) is a versatile and efficient welding process that delivers high-quality welds across various applications. Unlike TIG welding, which can function without a wire feed, GMAW relies on a wire feeding mechanism to supply consumable electrode material to the weld pool. Understanding its metal transfer modes is key to achieving optimal results, as these modes affect weld appearance, penetration, and spatter levels.
This blog explores the four primary GMAW metal transfer modes, examining their characteristics, benefits, and ideal uses to help you select the best mode for your welding needs.
What Are The Four Modes Of GMAW Metal Transfer?
The four primary GMAW metal transfer modes are:
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Short circuit transfer
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Globular Transfer
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Spray Transfer
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Pulsed Spray Transfer
Source: https://www.aedmetals.com/news/mig-welding-transfer-methods
Short Circuit Transfer(GMAW-S)
Short Circuit Transfer, also known as "short arc," is a process that uses low welding currents and wire feed speeds to achieve efficient and controlled metal transfer. In this process, the welding wire repeatedly touches the weld pool, creating a short circuit which occurs between 90 and 200 times per second, melting the wire and transferring small droplets of metal into the weld pool. Due to the lower and colder settings it operates on, this mode requires a tighter and more consistent contact-tip-to-work distance (CTWD) to maintain stability and quality.
Its low heat input makes it particularly well-suited for welding thin materials, as it minimizes the risk of warping or burn-through. Additionally, the small weld pool allows for precise control, making it ideal for out-of-position welding tasks such as vertical and overhead welding. Short circuit transfer is generally not recommended for welding thicker materials due to its low heat input, which often leads to incomplete fusion or penetration.
Source:https://www.tiktok.com/@millerweldersofficial/video/7205342172919500074
A shielding gas mixture of approximately 75% argon and 25% CO₂ is typically used with this mode. This combination supports stable arc performance and minimizes spatter, further enhancing its suitability for precision welding applications. Wire diameter sizes for short circuiting transfer include: 0.020/0.023/0.025/0.030/0.035/0.045 in., offering flexibility for various welding tasks.
Globular Transfer
Globular Transfer operates at higher currents and voltages than Short Circuit Transfer, generating larger, irregular metal droplets that are transferred across the arc into the weld pool. These droplets are typically larger than the wire diameter, resulting in the most spatter among the four transfer modes and a less stable arc. The higher heat input of this mode makes it more suitable for welding thicker materials, such as those starting at 1/8 inch. Sometimes referred to jokingly as 'turning your wire speed up,' this mode adds a lighthearted touch to discussions about its characteristics, despite its practical limitations. *(The method typically is used to weld in the flat and horizontal positions because the droplet size is large and would be more difficult to control)
This transfer mode is often paired with 100% CO₂ shielding gas, which enhances penetration but contributes to the unstable arc and significant spatter. Although Ar/CO₂ gas mixes can also be used to achieve globular transfer, 100% CO₂ is more common due to its cost-effectiveness. The molten metal globs, combined with the higher amperage, create a highly fluid weld puddle that is difficult to control, limiting this method to flat or horizontal welding positions.
Compared to Short Circuit Transfer, Globular Transfer increases productivity by supporting higher wire feed speeds and voltages. However, the resulting weld appearance may be less appealing due to excessive spatter and potential metal escape from the weld joint. Operators must also manage challenges like slag removal when using gas-shielded flux-cored wires.
Globular Transfer is best suited for cost-sensitive projects where high deposition rates are needed and weld appearance is less critical, such as in heavy fabrication or industrial applications.
Spray Transfer
As current increases and argon shielding gas reaches 80% or higher, the mode transitions from Globular Transfer to Spray Transfer, a critical threshold known as the transition current. As the name suggests, this mode generates a fine spray of tiny molten droplets, smaller than the wire diameter, which are transferred across the arc into the weld pool. This results in a smooth welding process with minimal spatter.
Because of the high percentage of argon, Spray Transfer effectively minimizes spatter and produces a clean, aesthetically pleasing weld bead. Additionally, the high current and voltage required for this mode ensure deep penetration and consistent weld quality. However, these stringent requirements also limit Spray Transfer to flat and horizontal welding positions due to the fluidity of the weld puddle.
Source:https://www.thefabricator.com/thewelder/article/consumables/understanding-gmaw-transfer-modes-1
Spray Transfer is ideal for welding thicker materials, offering superior deposition rates and excellent weld appearance. It is commonly used in industrial applications such as heavy equipment manufacturing, structural fabrication, and pipeline welding, where productivity and precision are paramount.
Pulsed Spray Transfer(GMAW-P)
Pulsed Spray Transfer can be regarded as an advanced form of Spray Transfer. Like Spray Transfer, it requires a high percentage of argon in the shielding gas (generally over 80%) and produces tiny, axially directed droplets for minimal spatter and excellent weld quality.
What sets Pulsed Spray Transfer apart is its unique pulsing current, alternating between high peak current and low background current. During the peak current phase, the wire is heated and melted, pinching off a single droplet from the electrode and spraying it into the weld joint. This phase provides the energy necessary for efficient droplet transfer and deep penetration.
In the background current phase, the current remains at a lower level, maintaining arc stability. This lower heat prevents the wire from melting or forming droplets, allowing the weld pool to cool momentarily and reducing overall heat input. This alternation not only reduces heat input to prevent burn-through but also enhances control over the weld pool, making Pulsed Spray Transfer highly adaptable and precise.
The alternating current flow improves control over the weld pool, making Pulsed Spray Transfer an effective choice for thinner materials and out-of-position welding. While maintaining the deep penetration and efficiency of Spray Transfer, it offers enhanced adaptability for complex joint geometries and challenging positions, including vertical and overhead welding.
FAQs
Q: Why is Globular Transfer Generally Unpopular in MIG Welding?
A: Globular Transfer is an unstable mode characterized by a less smooth weld bead appearance and significant spatter production. The large, irregular droplets often cause cold lapping or incomplete fusion as they splash out of the weld puddle. This makes it undesirable for precision or aesthetic tasks, although it can be useful for cost-sensitive applications requiring high deposition rates in flat or horizontal positions.
Q:Are Metal Transfer Modes Exclusive to GMAW?
A:Metal transfer modes are primarily associated with GMAW. FCAW (dual shield) is often categorized as Globular or sometimes Spray transfer. For GMAW, the preferred modes are Short Circuit, Spray, or Pulsed Spray transfer.
Q: What is RMD (Regulated Metal Deposition)?
A: RMD is an advanced short-circuit transfer technology developed by Miller Electric. It provides precise control of the arc and weld puddle, reducing spatter and improving weld quality, particularly in root passes for pipe welding and thin materials.
