By Allan Robinson
Updated Mar 24, 2022

Nordroden/iStock/GettyImages

Spot welding joins two metal surfaces by melting them together. In this process, a pair of electrodes clamp the workpieces and deliver a focused electrical current to a tiny spot—hence the name. With aluminum gaining traction in weight‑critical fields such as automotive manufacturing, mastering aluminum spot welding is essential.

Step 1 – Use Three‑Phase Power

Aluminum spot welding demands a high‑current pulse that lasts less than 0.1 s. A typical machine supplies 150 amps per phase on a 440‑volt supply. Because the power demand is concentrated into a short burst, three‑phase power is the standard for reliable operation. New machines range from $60 000 to $85 000, while rebuilt units cost between $25 000 and $35 000.

Step 2 – Opt for Capacitor‑Discharge Welders

Capacitor‑discharge units store energy in a capacitor bank and release it in a single, high‑current pulse. Their main advantage is a low steady‑state power draw, allowing smaller facilities to perform spot welding without upgrading their electrical infrastructure. This is especially valuable when welding thicker sections, as it prevents lighting flicker and maintains plant stability.

Step 3 – Account for Aluminum’s Physical Traits

Aluminum’s excellent conductivity means heat and current travel rapidly through the material. To avoid overheating, welds must be completed faster than with steel—typically two to three times the current and only a quarter of the weld time. Consequently, electrodes must be water‑cooled to dissipate the heat generated during the pulse.