Welding arc stiffness

Arc stiffness refers to the degree to which an electric arc remains straight along the electrode axis under the effects of thermal and magnetic contraction. This physical characteristic directly affects the stability of droplet transfer and weld formation quality during welding. For example, in arc additive manufacturing, insufficient arc stiffness can lead to spatiotemporal discontinuities in the morphology of the deposited layer affecting subsequent welding.

Main Influencing Factors:

Loop Inductance: The higher the inductance, the stronger the arc's anti-interference ability, especially at the moment of transition from short circuit to arc. High inductance helps maintain arc stability and facilitates rapid arc migration to the new spot.

Circuit Adjustment: Utilizing thermal inertia (such as in pulsed gas shielded welding) can compress the arc and improve stiffness. In pulsed welding, the arc is more concentrated, the molten pool has better fluidity, and the weld width is moderate.

Welding Machine Inverter Frequency: The higher the inverter frequency, the finer the arc control and the more precisely the arc stiffness can be adjusted.

External Magnetic Field: A longitudinal magnetic field can enhance arc stiffness, improve the weld penetration-to-width ratio, and increase droplet transfer stability. For example, a shrinkage effect can still be observed when the magnetic field strength reaches 0.01T.

Practical Applications: Plasma Arc: Due to mechanical, thermal, and electromagnetic compression, the stiffness of a plasma arc is significantly better than that of a free arc. It can maintain its shape and energy distribution over long distances, improving cutting or welding accuracy.

Testing Standards: Standards such as ASTM E207-2021 and ISO 5821:2019 are used to measure parameters such as arc current stability and voltage gradient to evaluate stiffness.