Page 34 - MetalForming December 2019

FABRICATION
Getting the Most From Your Weld-Shielding Gas
To optimize arc-weld quality, metal formers must understand the characteristics of the various shielding gases available, as well as their advantages and limitations.
BY ANDY MONK
Shielding gas plays a vital role in the performance and quality achieved in a gas metal arc weld- ing (GMAW) operation, preventing exposure of the molten weld pool from the atmosphere, where it can react with elements and lead to issues such as porosity and excessive spatter. Different shielding gases offer different weld- penetration profiles and arc stability; they also affect the weld’s mechanical properties.
Gas Selection
Many GMAW applications lend themselves to a variety of shielding gas choices. Shops should carefully eval- uate their welding goals to choose the best shielding gas for the job, account- ing for price, desired weld properties, and the base material. Also, consider productivity goals and the amount of
Andy Monk is product line manager, Bernard, Beecher, IL; www.bernard- welds.com.
Shielding gas prevents exposure of the molten weld pool to the atmosphere, thus play- ing a vital role in process performance and weld quality.
32 MetalForming/December 2019
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pre- and post-weld cleanup you are willing or able to accept.
Carbon dioxide (CO2) and argon find the most use in shielding gases, in addition to oxygen and helium. CO2 and oxygen are reactive gases—the electrons in these gases react with the weld pool, producing distinct charac- teristics. Argon and helium are inert gases; they do not react with the base material or the weld pool.
Shops can use CO2—less expensive than other shielding gases—in its pure form (100 percent) without adding an inert gas, making it an attractive choice for many welding operations. Using pure CO2 provides very deep weld pen- etration, useful for welding thick mate- rial, and it works well when welding mild or carbon steels. Limitations: Welders can only use pure CO2 in short- circuit welding processes; and the gas