♦ What Are the Different Metal Transfer Modes in MIG Welding?
By Chatchai Innumat, Product Manager, Thermal Mechanics Co., Ltd.
“Changes in welding parameters can alter the metal transfer behavior of the welding wire into the workpiece, which significantly affects the appearance and properties of the weld bead…” This article will help you achieve better welds in MIG welding.
Key Summary
MIG welding has four main metal transfer modes: Short Circuit, which is suitable for thin sheet metal and all-position welding; Globular, which offers high productivity but produces a lot of spatter; Spray, which creates a smooth weld bead and deep penetration for thick materials; and Pulse Spray, which provides the best heat control and is suitable for aluminum and thin materials. The choice of transfer mode depends mainly on workpiece thickness, welding position, and shielding gas type.
For welders or users of MIG welding machines, commonly called CO2 welders in Thailand, it is already familiar that achieving a stable and smooth arc requires proper adjustment of wire feed speed and welding voltage. This cannot be done by adjusting welding current alone, as in shielded metal arc welding with flux-coated electrodes.
In MIG welding, more welding parameters must be adjusted than in stick welding. Welding current is controlled by increasing or decreasing the wire feed speed, and it must also be matched with welding voltage. In addition, the type and size of welding wire, shielding gas composition, electrode stick-out, and the distance between the contact tip and the workpiece (CTWD) must all be properly controlled during welding. These factors directly affect the metal transfer behavior of the welding wire into the workpiece.
Welders may notice that increasing wire speed or changing any welding parameter alters the way molten metal transfers to the workpiece. This significantly affects weld appearance, weld properties, and travel speed. In general, MIG welding has four transfer modes:
- Short Circuit Transfer.
- Globular Transfer.
- Spray Transfer.
- Pulse Spray Transfer.
Short Circuit Transfer
MIG welding is a process in which the welding wire is fed from the machine to the workpiece at a constant and steady speed. When the wire is fed until it touches the weld pool or the workpiece, an electrical short circuit occurs and metal transfer takes place. The wire then melts into the workpiece, forming a weld bead, as shown in Figure 1.
In short circuit metal transfer, the wire tip repeatedly touches the weld pool in a continuous and stable cycle, which may occur as often as 20 to 200 times per second. This mode uses low welding current and low voltage, resulting in a low deposition rate. As a result, welding speed is not very high, and the molten pool solidifies quickly. Therefore, it is suitable for welding thin sheet metal, usually less than 3 mm thick, in all welding positions, or for tack welding with a wide gap.
Normally, MIG welding using short circuit transfer produces spatter when the molten droplet separates from the wire. Spatter can be reduced by adjusting the machine inductance or by selecting an appropriate shielding gas. The shielding gas composition significantly affects the surface tension of the molten metal in the weld pool. Changes in shielding gas composition affect the size of the droplet contacting the weld pool during short circuiting and also affect the duration of each short circuit. In addition, the shielding gas also affects arc characteristics and weld penetration. For example, if CO2 is used as the shielding gas, the weld will have more spatter but deeper penetration than when argon or helium is used.
To balance spatter and penetration, a shielding gas mixture of argon and CO2 is a good choice for welding carbon steel or low-alloy steel. A typical mixture is 75–80% argon and 20–25% CO2. Helium mixed with argon can also help increase penetration when welding non-ferrous metals.
However, short circuit transfer can also be used for thicker workpieces. Because it uses low welding current and voltage, incomplete penetration may occur. On the other hand, this low heat input also helps reduce thermal distortion. From a technical perspective, short circuit transfer is easy to control. Because the weld bead cools quickly, upward welding may require weaving and proper maintenance of the contact tip to workpiece distance.
Globular Transfer
Globular transfer occurs in the parameter range between short circuit transfer and spray transfer. It happens when the end of the wire melts into a large molten droplet that falls through the arc into the weld pool during welding. In general, this droplet is irregular in shape and larger than the wire itself. This type of transfer occurs because the welding current and wire feed rate are higher than in short circuit transfer. It allows high travel speed and high productivity, but it also produces a large amount of spatter, making post-weld cleanup more difficult.
Globular transfer is used in flux-cored arc welding with 100% CO2 shielding gas for carbon steel materials 3 mm thick and above. It is a relatively low-cost welding process, but flux-cored welding produces slag that must be removed after welding.
From a technical standpoint, globular transfer uses high current and voltage, which results in high heat input to the workpiece. Therefore, the contact tip to workpiece distance should be maintained between 3/4 and 1 inch. If the distance is too short, the large droplet may contact the weld pool, become overheated, and break apart, creating unwanted spatter. It is therefore important to maintain enough distance so that the droplets can fall freely through the arc.
Spray Transfer
Spray transfer uses high welding current and voltage. The wire is melted by the high current and is propelled by arc force as fine droplets smaller than the wire itself, continuously moving at high speed into the weld pool. This results in a very high deposition rate and enables faster travel speed and higher productivity than both short circuit and globular transfer.
In terms of quality, spray transfer produces a fully fused weld bead with deep penetration. Since there is no chance of short circuiting between the wire and the workpiece, spatter is minimal, and the weld appearance is excellent.
Because spray transfer uses high current and voltage, it is suitable for welding materials 3 mm thick and above. It is also suitable for aluminum, stainless steel, and carbon steel using solid wire or metal-cored wire. For steel welding, an argon-rich shielding gas mixture should be used, with more than 80% argon, such as 80% argon and 20% CO2. For stainless steel, a mixture of 98% argon and 2% oxygen can be used, while aluminum welding typically uses 100% argon.
Pulse Spray Transfer
Pulse spray transfer is an intermittent form of metal transfer rather than continuous like normal spray transfer. This mode requires a specially designed welding machine that supports pulsed current output. During welding, it is easy to recognize by the sound produced, which differs from other transfer modes because of the special characteristics of the machine.
In pulse spray transfer, the machine supplies current in two levels, alternating between a high peak current and a low base current at a rate of 30 to 400 pulses per second. The peak current provides enough energy to melt the wire and transfer metal in spray form through the arc into the weld bead. The base current maintains a stable arc without melting the wire. During this interval, the weld cools down, preventing excessive heat input. This mechanism makes MIG pulse spray welding highly effective for heat control, preventing excessive heat from entering the workpiece and reducing the risk of burn-through. It is therefore very useful for welding metals with low melting points such as aluminum, or for thin materials.
From a production standpoint, pulse spray transfer offers very high travel speed while generating very little spatter compared with other transfer modes. Beyond these two advantages, pulse spray also provides a very high deposition rate, especially when used with metal-cored wires, which further improves productivity. The shielding gas used for this transfer mode can be the same as that used for conventional spray transfer.
*** Read more: “Aluminum – Weld with Ease Using a MIG Pulse Machine”
Comparison Table
| Transfer Mode | Current / Voltage | Suitable Thickness | Spatter | Penetration | Suitable Applications |
|---|---|---|---|---|---|
| Short Circuit | Low | < 3 mm | Moderate to high, can be reduced by inductance/gas | Low to medium | Thin sheet metal, all-position welding, tack welding |
| Globular | High | ≥ 3 mm | High | Medium to high | Low-cost FCAW, jobs where appearance is not critical |
| Spray | High | ≥ 3 mm | Low | High | Aluminum, stainless steel, thick carbon steel |
| Pulse Spray | Alternating high-low, 30–400 times/sec | Thin to thick, broad range | Very low | Well controlled, prevents burn-through | Aluminum, low-melting-point metals, thin materials |
How to Choose the Right Mode
Users should study the type of welding wire they are using and determine which metal transfer mode is suitable for that wire. Understanding the advantages and limitations of each transfer mode will help welders achieve better weld quality. Each mode has different strengths and constraints. Welding should always be performed using the proper parameters, and the transfer mode should be selected and adjusted to match the application for the best results.
Choosing MIG Transfer for Your Job
Check the workpiece thickness. If it is thinner than 3 mm, consider short circuit or pulse spray. If it is thicker than 3 mm, consider globular or spray transfer.
Check the welding position. For multi-position work, including vertical and overhead welding, short circuit or pulse spray is generally preferred.
Check the metal type. For aluminum and low-melting-point metals, pulse spray is recommended to control heat and prevent burn-through.
Check the shielding gas composition. An argon/CO2 mixture of 75–80% / 20–25% is suitable for general carbon steel, while pure argon is suitable for aluminum.
Check the contact tip to workpiece distance (CTWD). Adjust it appropriately for the selected mode to reduce spatter and control penetration.
Check total cost. Consider not only wire cost, but also welding speed, spatter cleanup, and consumables.
FAQ: Common Questions About MIG Welding
Q: What is the difference between a MIG welder and a CO2 welder?
A: Technically, they are the same process.
Q: Which transfer mode should be used for thin steel sheet welding?
A: For steel thinner than 3 mm, short circuit transfer or pulse spray transfer is recommended.
Q: Why does my MIG weld produce a lot of spatter, and how can I fix it?
A: The main cause is incorrect welding parameters. Spatter can also be reduced with anti-spatter chemicals.
Q: Which transfer mode is recommended for MIG welding aluminum?
A: Pulse spray transfer is recommended.
Q: What shielding gas mixture is suitable for carbon steel welding?
A: In general, an argon-rich mixture of 75–80% argon is recommended.