Gas-shielded welding is the welding process that is used most widely overall. It consists of an electrode surrounded by a shielding gas. The same shielding gas also surrounds the molten pool. This ensures a steady supply of heat and keeps the air—and its oxygen—out.
Gas-shielded welding can be performed both manually and mechanically. Compared to other welding methods, especially the Laser Welding, it's more affordable and more flexible at the same time.
How does gas-shielded welding work?
An electrically generated arc provides the heat needed to melt the materials. If the electrode melts during the process, it is the MIG or MAG process, depending on whether inert or active gases are used. If the electrode does not melt away during the process, it is TIG or plasma welding. In the latter two processes, a filler material must be added.
When using a consumable electrode, it is fed by a motor to replace the melting tip. The speed at which the wire is fed can be adjusted. The wire has a diameter of 0.8 to 1.2 millimeters and is made of the same material as the workpieces. At the same time, the shielding gas flows automatically through the torch at a rate of 10 liters per minute.
Choosing the Process—MAG or MIG?
The choice of process—MAG or MIG—depends on the material.
- Is this Steel, active shielding gases are used, and thus the MAG used.
- Is this Aluminum and other nonferrous metals, that must MIG be used.
In addition to the shielding gases and, consequently, the specific process, the arc itself can also vary. For thin sheets, a short arc is used. This involves a constant alternation between the arc and a short circuit. When welding thicker workpieces, however, a spray arc is used. Together with the shielding gas, the arc is highly focused and directed at the workpiece under high pressure. This allows even thicker walls to be melted down quickly.
TIG welding process
In TIG welding, the electrode does not melt away during the welding process. Therefore, the filler material must be fed in separately. The shielding gases used in this process are inert. This process is primarily used for non-ferrous metals and also for stainless steel. However, the TIG process also facilitates the welding of steel, with the inert gas enabling a very high-quality weld bead that prevents the formation of inclusions and pores.
For the TIG process, it is important that the electrode be protected by the shielding gas. Without it, the electrode comes into contact with oxygen, which destabilizes the arc and causes the electrode to fray. Therefore, the choice of shielding gas does not depend on the material being used, but rather on the use of inert gases.
Several measures can be taken to increase the melting rate. One option is to work with two wires—the dual-wire process, from which the tandem process was developed. This method uses two wires that can each generate an arc independently of one another, even with different intensities, and can be controlled individually. This allows for a deposition rate of up to 25 kg per hour. With a specific combination of cored wires, shielding gases, and parameters, this rate can be increased to 27 kg per hour—a process known as the T.I.M.E. process (Transferred Ionized Molten Energy).
Another variation involves a wire electrode that moves back and forth continuously. This makes it possible to work with less heat input. In addition, there are processes that combine this method with lasers to speed up the welding process.
How is gas-shielded welding performed in practice?
In practice, gas-shielded welding begins with thorough preparation of the necessary equipment.
Device Setup
The hose assembly, including all connections and the welding wire, should be checked and connected. Depending on the specific process, the polarity must also be connected accordingly at the welding site. The spool must be inserted into the inverter, and the delay time must be selected. Next, the wire must be loaded into the wire feeder, and the feed speed must be adjusted.
Every electric welding process generates heat, thermal radiation, and spatter. Therefore, it is essential to wear eye protection, gloves, and long-sleeved protective clothing.
Preparation of Weld Areas
The weld areas must be prepared: paint, rust, and other contaminants must be removed so that they do not adversely affect the weld later on. The parts must also be cut to size so that they fit together. Before the actual welding begins, they are placed together and checked for proper alignment.
Inserting the welding wire
The welding wire is adjusted in the gun—it should extend beyond the nozzle by one nozzle width and can be easily adjusted using nozzle pliers. An angle magnet serves as an aid, allowing the correct angle to be set and adhering magnetically to the workpieces. The choice of wire depends on the gas mixture for the material being welded and its thickness.
Inert Gas Volume
The flow rate of shielding gas per minute should be approximately ten times the diameter of the welding wire being used, in millimeters. For a wire with a diameter of 0.8 mm, this means you need 8 liters of shielding gas per minute. Disposable gas cylinders or rental cylinders can be used as the gas source. For frequent use, rental cylinders are more cost-effective than disposable cylinders, despite the higher initial investment.
What should be kept in mind when using the gas-shielded welding process?
Gas-shielded welding is the most widely used welding process for several reasons. Because it is so safe to use, it is often employed in hobby projects and for repairs. In practice, however, it is still a technique where a lot can go wrong. To protect your health and ensure a high-quality weld, the following points should be observed.
1. Take environmental conditions into account in the planning process
Every successful welding job begins with good planning that also takes environmental conditions into account. This includes the limits for humidity, air pressure, and the operating temperatures of the welding equipment used. If the humidity is too high, water can accumulate inside the welding equipment due to condensation and cause leakage currents. If the air pressure is too low due to high altitude, this impairs cooling. Temperatures that are too high or too low can cause electronic components to fail.
2. Set the shielding gas flow rate correctly
Too much gas can cause turbulence that draws air into the molten pool. Too little gas does not provide adequate protection—pores will form in the weld. The most important rules of thumb:
- MAG welding, short-arc, 0.8 mm wire: 10 liters per minute; for 1.0–1.2 mm wire: 12 liters per minute
- MAG welding, spray arc, 1.0–1.2 mm wire: 15 liters per minute; for 1.6 mm wire: 20 liters per minute
- MIG Welding (Aluminum), 1.0 mm Wire: 15 liters per minute; for 1.6 mm wire: 25 liters per minute
- TIG welding: at 100 A: 6 liters per minute; at 300 A: 10 liters per minute
If the inert gas contains helium, a flow meter calibrated for argon will indicate a lower-than-actual flow rate. With a helium content of 30 %, the meter will display a reading that is 28 % lower than the actual value.
3. Flush the supply lines
If the system is left unused for an extended period, condensation may form in the supply lines. When shielding gas is then passed through the lines, it absorbs the moisture—causing pores to form in the weld bead. This is particularly likely to occur when welding aluminum. Therefore, when resuming operation after a prolonged period of inactivity, a sufficient pre-flow time must be observed.
4. The gas nozzle must be clean
Splatters accumulate on the gas nozzle and prevent the molten pool from being adequately covered with shielding gas. Even a small buildup can create vortices that cause porosity in the weld. If splatters accumulate at the rear of the nozzle, there is a risk of arcing in the worst-case scenario. The nozzle should be cleaned during every welding break. Regular spraying with a release agent prevents buildup.
5. No drafts
Even a draft of just one meter per second can blow away the shielding gas curtain—caused by open doors, windows, fans, or heating vents. Without the shielding gas curtain, pores form in the weld. If the draft cannot be eliminated, the weld area must be shielded with protective screens or tents.
6. Protective Clothing for Welding
Welding poses risks from radiation, spatter, and electric shock. Gloves, long-sleeved protective clothing (e.g., a welder's jacket), and insulated shoes are essential. There are welding gloves that allow you to use all five fingers without compromising on the necessary protection.
7. Avoid chlorinated hydrocarbons
Chlorinated hydrocarbons are used to degrease metal parts. The UV component of the arc can break them down and produce phosgene—a highly toxic gas that can cause serious health problems and even death. Before welding, all chlorinated hydrocarbons must be completely removed—including any residues in crevices and cavities.
8. Ventilation in Enclosed Spaces
In basements, shafts, tunnels, or tanks, welding produces gases that can be harmful to health. Depending on the shielding gas used, this can lead to either an excess of oxygen (high flammability) or a lack of oxygen (impaired thinking or even a risk of suffocation). In spaces with limited air exchange, exhaust ventilation or mechanical ventilation is absolutely essential.
9. Protect the caterpillar
The shielding gas protects the work side. However, the underside—the other side—must also be protected from the ingress of harmful air. This problem occurs primarily when welding pipes or small containers, especially when using the TIG process on chromium-nickel and structural steel. The cavities can be flushed with shielding gas or forming gas. For longer pipe runs, shut-off balloons are suitable; branch lines can be fitted with end caps that have small holes.
10. Make Full Use of the Welding Machine's Capabilities
Welding machines offer adjustment options that should be used strategically. For MIG welders, these include balance and frequency controls: The balance control allows for a shallower or deeper penetration, as well as better penetration through the oxide layer. The frequency setting allows you to work with a stiffer arc. Even experienced welders should regularly refresh their theoretical knowledge by consulting technical manuals to avoid falling into the habit of using incorrect work methods.
FAQ: Frequently Asked Questions About Gas-Shielded Welding
The difference lies in the shielding gas used and, consequently, in the application. MAG welding (metal-active gas) uses active shielding gases—it is suitable for steel. In MIG welding (metal-inert gas), inert shielding gases are used—it is used for aluminum and other non-ferrous metals. Both are consumable electrode processes and are classified as gas shielded welding.
In TIG (tungsten inert gas) welding, the electrode does not melt away—it is made of tungsten and remains intact during welding. The filler material must be fed separately. This process is primarily used for non-ferrous metals, stainless steel, and high-grade steel, and produces particularly high-quality, porosity-free welds. The inert gases protect the electrode from oxidation.
As a rule of thumb, the gas flow rate in liters per minute is approximately ten times the wire diameter in millimeters. For example: 0.8 mm wire → 8 l/min. For MAG spray arc welding with 1.6 mm wire, 20 l/min is required; for MIG aluminum welding with 1.6 mm wire, as much as 25 l/min. For the TIG process: 6 l/min at 100 A, 10 l/min at 300 A.
Pores are mainly caused by inadequate shielding gas protection—whether due to an insufficient gas flow rate, drafts, condensation in the supply lines, or dirty gas nozzles. Prevention: Flush the supply lines before use, clean the gas nozzle regularly and spray it with a release agent, prevent drafts by using shields, and set the correct gas flow rate for the selected process.
The main hazards include: radiation (UV and IR), metal spatter and burns, electric shock, toxic welding fumes (especially phosgene when working with chlorinated hydrocarbons), oxygen deficiency or enrichment in poorly ventilated areas, and fire hazard. Protective measures: Welding helmet, gloves, protective jacket, insulated shoes, fume extraction, and mechanical ventilation in enclosed spaces.
The T.I.M.E. (Transferred Ionized Molten Energy) process is a further development of tandem welding. Using a special combination of filler wires, shielding gases, and optimized welding parameters, a deposition rate of up to 27 kg per hour can be achieved—compared to 25 kg/h with the standard tandem process. It is particularly well-suited for high productivity requirements in industrial applications.