MIG Welding Manufacturing and Materials Processes

(GMAW) MIG Welding Gas Metal Arc Welding (GMAW) is frequently referred to as MIG welding. Gas Metal Arc Welding (GMAW) is frequently referred to as MIG welding. MIG welding is a commonly used high deposition rate welding process. MIG welding is a commonly used high deposition rate welding process. Wire is continuously fed from a spool. Wire is continuously fed from a spool. MIG welding is therefore referred to as a semiautomatic welding process. MIG welding is therefore referred to as a semiautomatic welding process.

MIG Welding Benefits All position capability All position capability Higher deposition rates than SMAW Higher deposition rates than SMAW Less operator skill required Less operator skill required Long welds can be made without starts and stops Long welds can be made without starts and stops Minimal post weld cleaning is required Minimal post weld cleaning is required

MIG Welding Shielding Gas The shielding gas, forms the arc plasma, stabilizes the arc on the metal being welded, shields the arc and molten weld pool, and allows smooth transfer of metal from the weld wire to the molten weld pool. The shielding gas, forms the arc plasma, stabilizes the arc on the metal being welded, shields the arc and molten weld pool, and allows smooth transfer of metal from the weld wire to the molten weld pool.

The primary shielding gasses used are: Argon Argon Argon – 95% to 5% Oxygen Argon – 95% to 5% Oxygen Argon – 75% to 25% CO2 Argon – 75% to 25% CO2 Argon/Helium Argon/Helium CO2 is also used in its pure form in some MIG welding processes. However, in some applications the presence of CO2 in the shielding gas may adversely affect the mechanical properties of the weld. CO2 is also used in its pure form in some MIG welding processes. However, in some applications the presence of CO2 in the shielding gas may adversely affect the mechanical properties of the weld.

Welding Parameters and Techniques Welding current Welding current Wire electrode extension Wire electrode extension Welding voltage Welding voltage Arc travel speed Arc travel speed

WELDING CURRENT The welding current is the electrical amperage in the power system as the weld is being made. The welding current is the electrical amperage in the power system as the weld is being made. welding current is directly related to wire- feed speed (if the wire extension beyond the guide tip is constant). As the wire-feed speed is varied, the welding current will vary in the same direction. In other words, an increase (or decrease) in the wire-feed speed will cause an increase (or decrease) of the current. welding current is directly related to wire- feed speed (if the wire extension beyond the guide tip is constant). As the wire-feed speed is varied, the welding current will vary in the same direction. In other words, an increase (or decrease) in the wire-feed speed will cause an increase (or decrease) of the current..

WIRE ELECTRODE EXTENSION Wire extension or ”stick-out” is the distance between the last point of electrical contact, usually the end of the contact tip, and the end of the wire electrode. Wire extension or ”stick-out” is the distance between the last point of electrical contact, usually the end of the contact tip, and the end of the wire electrode.

WIRE ELECTRODE EXTENSION Controlling tip-to-work distance is important. Long extensions result in excess weld metal being deposited with low arc heat. This can cause poor bead shape and low penetration. In addition, as the tip-to-work distance increases, the arc becomes less stable. Controlling tip-to-work distance is important. Long extensions result in excess weld metal being deposited with low arc heat. This can cause poor bead shape and low penetration. In addition, as the tip-to-work distance increases, the arc becomes less stable.

WELDING VOLTAGE voltage setting directly controls the arc length. voltage setting directly controls the arc length. In addition, a certain range is required to maintain arc stability at any given welding current level. In addition, a certain range is required to maintain arc stability at any given welding current level.

ARC TRAVEL SPEED As the material thickness increases, the travel speed must be lowered. As the material thickness increases, the travel speed must be lowered. For a given material thickness and joint design, as the welding current is increased, so is the arc travel speed. The converse is also true. For a given material thickness and joint design, as the welding current is increased, so is the arc travel speed. The converse is also true. Higher welding speeds are attainable by using the forehand welding technique. Higher welding speeds are attainable by using the forehand welding technique.

WELDING TECHNIQUES Torch Position Torch Position Split the angle (90 degrees = 45 degree split) Split the angle (90 degrees = 45 degree split) 5 degree rake 5 degree rake

Good Weld Voltage to High Voltage to Low Too FastToo Slow

Less Stick Out