MIG Welding Overview

Definition

• MIG stands for Metal Inert Gas welding.
• Also known as Gas Metal Arc Welding (GMAW) by the American Welding Society.
• Often referred to as wire welding.

Process Description

• Thin Wire Electrode: Acts as the electrode, fed from a spool.
  • Mounted on a gun or inside the welding machine.
  • Fed through a flexible tube and out of the nozzle.
• Continuous Feeding: Trigger on the gun feeds wire continuously.
  • Activates welding current and shielding gas.
• Electric Arc Formation: Between wire electrode and workpiece.
  • Heats metals above melting point, allowing them to coalesce and solidify.

Components

• Base Metal: Metal parts to be joined.
• Filler Metal: Metal from the melting wire electrode.
  • MIG welding always adds filler metal, as the wire electrode melts.
  • Described as a consumable electrode process.

Equipment Details

• Wire Feeder: Feeds wire through a flexible tube or conduit liner.
• Torch Nozzle: Wire is fed through a contact tip, coming out at the weld point.

Shielding Gas

• Fed through welding lead via a gas diffuser, flows out of the nozzle.
• Common Mix: Argon and CO2.
• Purpose: Protects molten metal from reacting with atmospheric elements such as oxygen and water vapor.
• Storage: In high-pressure cylinders, pressure reduced by a regulator.

Machine Controls

• Settings adjusted on the machine:
  • Polarity
  • Wire Speed
  • Voltage
• Trigger: Functions as an on-off switch.

Current Type

• Direct Current (DC): Similar to car battery.
  • One wire is positive and one is negative.
• DCEP: Direct Current Electrode Positive (Reverse Polarity).
  • Indicates the electrode is positive and workpiece is negative.
  • Current flows in a complete loop: from machine to torch, into work, and back to the machine.
  • Work Lead: Clamped to workpiece to complete the circuit.

Summary

• MIG welding is an electric arc welding process.
• Utilizes a consumable wire electrode.
• Filler metal is automatically added.
• Shielding gas is provided from a high-pressure cylinder.