What is the difference between TIG and MIG welding?

The older acronyms, TIG (Tungsten Inert Gas) and MIG (Metal Inert Gas) are still used today but the correct terminology in North America is Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW) which we will use to explain the differences in the processes.

The GTAW process uses a non-consumable tungsten electrode to establish the arc between the tungsten electrode in the welding torch and the workpiece, as shown in Figure 1.  An inert gas such as argon, helium or a mixture of the two, is used to shield the weld pool, tungsten electrode and filler metal from contamination of oxygen and nitrogen in the atmosphere. The GTAW process uses a filler metal in the form of a solid rod, sold in lengths of 36 inches to be manually placed in the leading edge of the molten weld pool to form the weld bead. It can also be automated using a cold wire feeder, in which case if filler metal is required it will be delivered from a spool

This process can also be performed autogenously (without a filler metal) on some materials. The GTAW process is used to weld all types of metals and is especially chosen to weld thin gauge metals in carbon steel, stainless steel and, is best suited for aluminum.

Figure 1, Typical GTAW Welding Torch Operation

The complete setup of the GTAW system can be seen in Figure 2. The GTAW system consists of a constant current power source, a GTAW welding torch with 15 or 25-foot power cables, shielding/cooling gas hose or liquid-cooled hoses depending on the type of torch, work lead and a bottle of shielding gas.  The electrical current is generated from the power source by using a foot control (like a gas pedal in a car). Thus, the welder can operate the pedal and increase/decrease the amperage by pushing and letting off on the foot control pedal. This will also engage the shielding gas to start a pre-purge sequence for a selected time and then start the arc between the tungsten electrode and the workpiece.

GTAW torches are of two types, air-cooled for thinner materials and lower amperages and liquid-cooled for thicker materials where higher amperages will be in use. The process uses either direct current (DC) on steels and other ferrous metals and some nonferrous metals and alternating current (AC) on other nonferrous metals such as aluminum.

The GTAW process produces high-quality welds on all metals in all positions, but travel speeds will be slower than using GMAW thus slower production is the result. Welders who have mastered this process, and are productive, are generally in high demand for the precision metals fabricating companies.

Figure 2, Complete GTAW System

GMAW uses a consumable electrode in the form of a wire feed through a welding torch (or Gun as is sometimes called) to the workpiece where it creates the arc and transfers metal to form the weld bead. The GMAW process also uses a shielding gas to protect the weld pool, filler metal and workpiece from contamination from oxygen and nitrogen in the atmosphere see Figure 3.

Figure 3, Typical GMAW Welding Torch

The complete setup of the GMAW system can be seen in Figure 4. The GMAW system consists of a constant voltage power source, wire feeder, bottle of shielding gas, welding torch that operates with either a 10 or 15-foot lead. The GMAW welding torches also come in either air-cooled of liquid-cooled depending on the amperages used. Here the electrical current is started by pressing the trigger, Figure 5, on the welding torch that is connected to the wire feeder and power source.  This starts to move the filler wire from the wire feeder, which has a preselected wire feed speed, through a liner in the torch leads and out the goose neck. The wire then passes through the gas diffuser and the contact tube and will strike an arc once it reaches the workpiece. The power source senses the voltage between the contact tube and workpiece and generates amperage to melt the wire that eventually becomes the weld metal. The shielding gas is also engaged when the trigger is pressed, and the shielding gas is delivered through the leads to the nozzle on the gun and protects the welding zone from atmospheric contamination.

Figure 4, Typical GMAW system

The GMAW process works on DC electrode positive for all metals and can deliver three modes of metal transfer.

  • Spray metal transfer using a 100% argon or with oxygen or CO2 shielding gas mixtures. This is applied with higher voltage and wire feeder settings for high productivity on metals 3mm and above and, in the flat and horizontal positions producing high-quality welds.
  • Globular metal transfer is generally used with 100% CO2 or higher CO2 in Argon shielding gas mixes with high voltage and wire feed settings on thicker materials in the flat and horizontal positions, however this transfer generates lots of weld spatter and the quality of welds can be poor and welding productivity is low.
  • Short circuit metal transfer uses either 100% CO2 or mixtures of argon in CO2 or Oxygen. In the lower voltage and wire feed ranges this transfer can be used on all metals in all positions with minimal spatter and good quality welds. The productivity is much lower than the spray transfer mode.

However, the GMAW process in any transfer mode is still much more productive than the GTAW process.


Figure 5, Typical GMAW Welding Torch Parts

① Insulator
② Gas diffuser
③ Contact tube
④ Gas nozzle
⑤ Trigger
⑥ Gooseneck



 

Bill Eccles, VP
PPC and Associates