The heat transfer and fluid flow in a GMAW weld pool are similar to that in a GTAW weld pool. The GMAW process can be used in combination with other welding processes such as plasma arc welding (PAW) or laser welding (LW) to improve deposition rate, welding speed, flexibility and productivity.
The total transfer of heat, H, (neglecting preheating) from the GMAW process to the weldment per unit time is given by:
Where E is voltage, I is current, and η is the heat-transfer efficiency. The rate at which heat is transferred to the weldment per unit length of weld is given by
- Where R is welding speed.
- Calorimeter-based heat-transfer experiments reveal that the heat-transfer efficiency for welding thick-section steel is nominally 80 to 90%.
- The total heat-transfer efficiency is altered somewhat by changing other parameters.
- For example, it increases slightly as the power supply open-circuit voltage is decreased (for a silicon controlled rectifier regulated power supply and it increases slightly with increasing contact tube-to-base metal distance. However, 85% is a reasonable estimate for most conditions.
Partitioning of Heat Transfer:
- In the GMAW process, the molten droplets of electrode material carry a significant portion of the total heat transferred to the weld pool.
- This is seen in calorimetry experiments, where the total heat transfer efficiency of the GMAW process is partitioned into those portions associated with transfer by the arc and by the molten droplets.
- At low electrode speeds, about 60% of the total heat transferred is associated with the arc