Voltage and Amperage in the Arc
Understanding electricity is essential for producing consistent welds. Amperage (measured in amps, A) controls heat input — higher amperage melts more metal and creates deeper penetration. Too little amperage produces cold, incomplete fusion; too much burns through thin material or creates excessive distortion. Voltage controls arc length in MIG and flux-core processes — higher voltage creates a longer, softer arc while lower voltage produces a short, crisp arc with faster freeze. In TIG and stick welding, the welder adjusts voltage indirectly by controlling torch/electrode distance from the work. Ohm's Law underpins all welding electrical behavior: Voltage (V) = Current (I) × Resistance (R). The welding arc itself is a plasma conductor; as arc length increases, resistance increases and voltage rises. Heat input to the weld is calculated as: Heat Input (kJ/in) = (Amps × Volts × 60) ÷ (Travel Speed in/min × 1000). This formula is critical in pressure vessel and structural welding codes that specify maximum heat input to prevent degradation of heat-affected zone properties.