Why do the welding current and arc voltage have to be strictly matched during CO2/MAG/MIG welding?

In CO₂/MAG/MIG welding, a strict match between welding current and arc voltage is crucial for ensuring welding quality, stability, and efficiency. The following is a detailed analysis:

1. Arc Stability and Droplet Transfer Pattern

The Interaction between Current and Voltage:

Current determines the melting rate of the welding wire (the higher the current, the faster it melts), while voltage influences arc length (the higher the voltage, the longer the arc). If the two are mismatched:

Voltage is too high: The arc is too long, leading to unstable droplet transfer (such as large particle spatter), arc drift, and even arc failure.

Voltage is too low: The arc is too short, and the wire may dig into the weld pool, causing short circuits or frequent arc extinction.

Transfer Mode Requirements:

Short-Circuit Transfer (low current, low voltage): Precise voltage control is required to maintain a short arc and avoid spatter.

Spray Transfer (high current, moderate voltage): A higher voltage is required to maintain a stable arc and avoid excessively large droplets. 2. Weld Formation and Defect Control
Balance between Penetration and Width:
Current controls penetration (the higher the current, the deeper the penetration), while voltage controls width (the higher the voltage, the wider the penetration).
A mismatch can result in:
Excessive current + low voltage: Deep penetration but insufficient width, prone to undercutting or incomplete fusion.
Excessive current + high voltage: Excessive width but shallow penetration, leading to weld buildup and incomplete penetration.
Risk of Spatter and Porosity:
When voltage is too high, the oxidizing atmosphere produced by the decomposition of CO₂ gas exacerbates spatter; when voltage is too low, insufficient gas shielding can lead to porosity.
3. Shielding Gas and Process Characteristics
Specificities of CO₂ Welding:
As an active gas, CO₂ has a strong arc constriction effect, requiring a lower voltage to match the current to compress the arc. If voltage is too high, the arc spreads, reducing shielding effectiveness. MAG/MIG Gas Mixtures:
Different mixture ratios (such as Ar + CO₂) affect arc characteristics, requiring voltage adjustment to match current. For example, argon-rich gas requires a slightly higher voltage to maintain arc length.
4. Optimizing Welding Efficiency and Energy Consumption
Energy Input Matching:
The product of current and voltage (heat input) must match the base material thickness and welding speed. Mismatching can result in:
Excessive heat input: Burn-through or deformation.
Excessive heat input: Poor fusion.
Wire Utilization:
Excessive voltage increases spatter and wire loss; excessively low voltage can reduce wire feeding stability due to frequent short circuits.
5. Experience and Standardization of Process Parameters
Reference Welding Parameters Table:
Different materials, wire diameters, and shielding gas combinations have recommended current-voltage matching ranges (e.g., 200A for 1.2mm wire in CO₂ corresponds to 22-24V). Dynamic Adjustment Requirements:
During actual welding, the voltage needs to be fine-tuned based on the arc sound (a steady "hiss") and weld pool shape to achieve the optimal match.