Gas Metal Arc Welding refers to:

Explanation:

Gas metal arc welding (GMAW) or Metal inert gas arc welding (MIG)

• In this process, the arc is formed between a continuous, automatically fed, metallic consumable electrode and welding job in an atmosphere of inert gas, and hence this is called metal inert gas arc welding (MIG) process.
• The shielding gases for MIG welding are mixtures of argon, oxygen, and CO₂, and special gas mixtures may contain helium. 
  

Electron beam welding 

• Electron beam welding joins metals by bombarding a specific confined area of the base metal with high-velocity electrons.
• The operation is performed in a vacuum to prevent the reduction of electron velocity.
• It allows fusion welds of great depth with a minimum width because the beam can be focused and magnified.
• As you can see in the above diagram that in electron beam welding is focused on the weld spot using the magnetic lens.

TIG Welding: 

• Tungsten Inert Gas (TIG) or Gas Tungsten Arc (GTA) welding is the arc welding process in which arc is generated between non-consumable tungsten electrode and workpiece.
• The tungsten electrode and the weld pool are shielded by an inert gas normally argon and helium.
• The principle of the tungsten inert gas welding process is shown below