When TIG welding ultra-thin gauge automotive sheet metal, what specific combination of amperage pulse frequency and duration is precisely controlled to minimize heat affected zone (HAZ) and prevent burn-through while achieving full penetration?

When TIG welding ultra-thin gauge automotive sheet metal, the precise control is achieved through pulsed TIG welding, a process where the welding current rapidly cycles between a high peak amperage and a low background amperage. The peak amperage is the higher current applied during the pulse cycle, responsible for achieving immediate fusion and initial full penetration, meaning the weld metal completely fuses through the thickness of the material. For ultra-thin material, this peak amperage is set high enough to ensure instant melting but carefully managed to prevent excessive melt. The background amperage is the significantly lower current applied during the pulse cycle. Its purpose is to maintain arc stability, keep the weld puddle molten without expanding, and allow the surrounding material to cool, thus preventing heat accumulation. The two specific parameters precisely controlled are amperage pulse frequency and pulse duration. Pulse frequency, measured in Hertz (Hz), defines the number of times the current cycles from peak to background and back to peak per second. For ultra-thin gauge, a high pulse frequency, typically ranging from 100 Hz to 500 Hz or even higher, is used. This high frequency creates a highly focused and stiff arc, promoting rapid agitation of the weld puddle and quick solidification, which minimizes the time the material is exposed to peak heat. This rapid cycling significantly reduces the heat affected zone (HAZ), which is the area of the base metal whose properties have been altered by welding heat but not melted, and minimizes distortion. Pulse duration, also known as peak time or on-time percentage, is the percentage of the total pulse cycle time that the current remains at the peak amperage. For ultra-thin gauge, a short pulse duration, typically set between 10% and 30%, is precisely controlled. This ensures the arc spends a very brief period at the high peak amperage, providing just enough energy for penetration, followed by a much longer period at the low background amperage for cooling. This combination drastically lowers the average heat input, which is crucial for preventing burn-through, the complete melting through of the material. By combining a high peak amperage with a very low background amperage, a high pulse frequency for arc focus and rapid solidification, and a very short pulse duration to severely limit the overall heat input, full penetration is reliably achieved with minimal HAZ and prevention of burn-through on ultra-thin gauge automotive sheet metal.