SERVICE WELDING GUIDE MIG (GMAW) Gas Metal Arc Welding Caterpillar

Fundamentals of the Process

Definition

The Gas Metal Arc Welding process uses intense heat of an electrode arc to melt the filler metal and the base metal. The consumable bare solid electrode wire is continuously fed into the arc. The deposited weld metal is formed from metal melted off the end of the electrode wire and transferred through the arc to the work. Shielding gas protects the weld from contamination.

Slang names

Microwire/MIG/Wire Welding/Carbon Dioxide Welding.

Process Principles

1. Heat source - electric arc between electrode (wire) and the work.

2. Shielding - an external gas supply.

3. Filler metal - fed automatically from a spool or reel.

4. Flux - not applicable.

Figure 25

Transfer Modes with G.M.A.W.

Figure 26

* Short circuiting -

CO₂ or AR/CO₂, low amperage and voltage, all positions.

* Globular -

CO₂ or AR/CO₂, higher amperage and voltage, flat and horizontal.

* Spray -

AR/O₂, high amperage and voltage, flat and horizontal.

* Pulsed -

AR/O₂, Various amperage levels, spray transfer, all positions.

Figure 27

Bead on plat penetration diagrams for various shield gases.

Position Capabilities

* Grooves - all position capabilities.

* Fillets - all position capabilities.

* Limitations - type of transfer/skill of operator/wire size.

Electrical Requirements

Welding Circuit

Figure 28

Welding Current Types

* D.C.E.P. - normal type of current used.

* D.C.E.N. - can be used with special electrodes.

* AC - has not been successfully used.

Power Source Types and Characteristics

* Constant Voltage - 100% duty cycle with a flat volt/amp curve.

Other Equipment Requirements

Additional Equipment Necessary

* Wire feed system.

* Welding gun and cable assembly.

Mild Steel (Solid) Electrode Classification GMAW, GTAW, and PAW

Figure 29