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What matters when welding aluminum plate
Aluminum plate is a demanding TIG job because the metal conducts heat quickly, develops an oxide layer that melts at a much higher temperature than the base metal, and often needs substantial amperage. For a dedicated 240-volt circuit, look for an AC/DC TIG welder with high-frequency arc starting, adjustable AC balance, adjustable AC frequency, a proper foot pedal, and enough duty cycle for the plate thickness you actually weld.
A useful rule is roughly 1 amp per 0.001 inch of aluminum thickness, although joint fit-up, alloy, preheating, and heat sinking change the result. A 1/8-inch plate may require about 125 to 160 amps. A 1/4-inch plate commonly needs 200 to 250 amps, especially for a full-penetration joint. If you regularly weld thicker than 1/4 inch, a 300-amp machine or a different process may make more sense.
For most home shops, a 200-amp AC/DC inverter is the practical starting point. A 250- or 300-amp machine gives more headroom but usually costs more, weighs more, and demands a larger circuit.
The best TIG welder categories for a 240-volt shop
| Welder type | Best use | Typical strengths | Main compromise |
|---|---|---|---|
| 200-amp AC/DC inverter TIG | General aluminum plate, fabrication, repair | Efficient, portable, good arc control, often supports 120/240 volts | Limited output and duty cycle on heavy plate |
| 250- to 300-amp AC/DC inverter TIG | Frequent work on 1/4-inch aluminum and thicker | More penetration, longer high-output operation | Higher price and circuit requirements |
| AC/DC TIG with pulse | Thin plate, heat-sensitive assemblies, controlled appearance | Reduces heat input and can improve puddle control | Pulse is not a substitute for adequate amperage |
| AC/DC TIG with built-in water cooler | Long welds and high-amperage production work | Cooler torch, less hand fatigue, longer consumable life | More cost, plumbing, and maintenance |
For a serious aluminum setup, compare 200-amp AC/DC TIG welders first. They are often the best value when the work is intermittent and the material is 1/8 inch or thinner.
Sizing the dedicated 240-volt circuit
A dedicated circuit is a good idea because TIG welders can draw high current while a grinder, compressor, or heater on the same circuit can cause nuisance trips. Check the welder’s nameplate and manual rather than sizing the circuit from the advertised welding amperage. A 200-amp inverter may run on a 30-amp or 50-amp, 240-volt circuit depending on its input rating and duty cycle. A 300-amp machine may require 50 amps or more.
Use the manufacturer’s specified plug, receptacle, breaker, and wire size. Do not replace a breaker with a larger one to stop tripping unless the entire circuit has been designed for that rating. Have the installation checked by a qualified electrician, particularly in a detached garage or workshop. Voltage drop on a long, undersized run can cause poor performance and overheating.
Input power is another trade-off. Many inverter welders advertise a 240-volt output but still accept 120 volts at reduced amperage. That flexibility is useful for repairs, but it does not make a 120-volt circuit suitable for sustained aluminum plate welding.
AC controls that are worth paying for
AC balance controls the proportion of electrode-negative and electrode-positive time. More electrode-positive cleaning action can help break up oxide, but it also heats the tungsten and reduces penetration. Modern machines generally work well with a cleaning setting around 20 to 35 percent electrode-positive, then you adjust based on contamination, alloy, and surface preparation.
AC frequency changes the shape and focus of the arc. A higher setting, often roughly 100 to 150 Hz, produces a tighter arc that is useful near a joint or on thinner sections. Lower frequency gives a broader arc and can help spread heat over a larger area. The useful range varies by machine; a very high advertised frequency is not automatically better.
High-frequency start is preferable to lift start on aluminum. It starts the arc without touching the tungsten to the work, reducing contamination. A foot pedal or fingertip amperage control is also valuable because aluminum quickly pulls heat away at the beginning and then becomes hotter as the joint progresses.
Torch cooling and duty cycle
An air-cooled torch is adequate for occasional welding at moderate amperage. At 200 amps, however, a small torch can become uncomfortable during a long bead. A water-cooled torch is worth considering if you routinely weld above 180 amps, make long continuous welds, or work in a hot shop. Look for a package that includes the cooler, hoses, torch, and the correct power connector; adding those parts later can be expensive.
Duty cycle is usually stated as a percentage over a 10-minute period. A 60 percent duty cycle at 200 amps means six minutes of welding followed by four minutes of cooling at that rated output. Aluminum work often involves stops for repositioning and cleaning, so a modest duty cycle may be fine for a hobbyist. It is not fine if you are repeatedly making long production seams.
Setup for clean aluminum welds
Cleanliness matters more than many beginners expect. Degrease the plate with acetone, use a dedicated stainless-steel brush, and brush immediately before welding. Do not use a brush that has touched steel, galvanized metal, or oily work. Contamination can cause black soot, porosity, unstable arc behavior, and a dirty tungsten.
Use pure argon, generally around 15 to 25 cubic feet per hour indoors, adjusted for the cup size and drafts. Excessive gas flow can create turbulence and pull air into the shielding envelope. A lanthanated or ceriated tungsten is a practical choice; use a size appropriate to the amperage, commonly 3/32 inch for moderate current and 1/8 inch for heavier work.
For filler, 4043 is easy-flowing and forgiving for many common aluminum alloys. 5356 generally provides higher strength and better color match on some alloys, but it is less fluid and should be selected with the base alloy and service requirements in mind. Keep the arc short, add filler at the leading edge of the puddle, and travel steadily once the oxide layer breaks.
Common buying mistakes
Do not buy a DC-only TIG welder for aluminum plate; it cannot provide the required AC cleaning action. Be cautious with machines that list a high peak amperage but provide little information about duty cycle, input current, torch type, or AC controls. A cheap 200-amp unit can be perfectly adequate for occasional 1/8-inch plate, but it may struggle with 1/4-inch material and may have costly replacement accessories.
If your work is mostly thick plate, compare 250-amp water-cooled AC/DC TIG welders. If aluminum is occasional and thin, spend the savings on a good helmet, gas regulator, tungsten, and proper electrical installation instead. A dependable 200-amp inverter on a correctly sized 240-volt circuit will outperform a larger machine connected to an inadequate supply.