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Copper heat exchangers are demanding TIG work. Copper conducts heat away from the joint quickly, so a machine that handles thin stainless steel may struggle to start and sustain a weld on thicker copper. The right setup depends on the copper alloy, wall thickness, joint design, and whether the exchanger will see pressure or corrosive service. For many shop builds, a capable DC TIG welder is the practical choice; AC/DC is useful if the job also includes aluminum.
What the welder needs to do
For copper, look for stable DC output, a useful low-amp range, adjustable preflow and postflow, and enough current for the thickest joint you expect to weld. A machine rated around 200 amps gives headroom for heavier sections, but the rating alone says little about its duty cycle or arc behavior at low current. Check the manual for output at the duty cycle you need. A 200-amp welder with a 20% duty cycle at that output may require frequent cooling breaks during production work.
Most copper TIG work uses DC electrode negative (DCEN), not AC. Copper’s high thermal conductivity makes a large, clean joint more important than chasing a high amperage number. A good fit-up, short arc, and adequate torch access help keep heat in the joint. Use the copper alloy’s recommended filler; silicon bronze, for example, is not a universal substitute for filler intended for a pressure-bearing copper joint. Confirm filler and procedure requirements before fabricating a service-critical exchanger.
Choosing a machine type
| Machine type | Best fit | Trade-off |
|---|---|---|
| DC TIG inverter | Copper, steel, and stainless work | Does not provide AC for aluminum TIG |
| AC/DC TIG inverter | Mixed copper and aluminum fabrication | Costs more; AC features are unnecessary for copper alone |
| Small 120 V TIG machine | Thin copper, short welds, and light-duty shop work | Limited output and slower work on heavy sections |
If copper is the main job, a DC TIG machine is usually the sensible buy. Choose a 200-amp-class DC TIG welder when you need capacity for heavier parts or longer production runs. A lower-output machine can be fine for small exchangers made from thin tubing, provided the work is within its duty cycle and electrical supply limits.
Choose an AC/DC TIG welder if aluminum fabrication is also part of the plan. AC is valuable for aluminum, but it does not make a machine inherently better at copper. Compare low-end current control, included torch and pedal, warranty, and service access rather than paying for features you will not use.
Power, controls, and accessories
A 120 V machine can simplify setup, but household circuits commonly limit practical output. For thicker copper, a 240 V supply offers more headroom and reduces the chance that the welder will hit its limit before the joint is properly fused. Check the machine’s input requirements and the circuit capacity; do not rely on an extension cord or breaker upgrade as a substitute for correct wiring.
A foot pedal is useful when joint thickness changes or heat builds as you move along a seam. It lets you reduce current without breaking the arc. For repeatable work, a torch switch or preset process may be more convenient, but it offers less immediate control. High-frequency start avoids touching the tungsten to the copper, which helps prevent tungsten contamination. Postflow matters too: follow the tungsten size and current guidance in the machine manual, and give the electrode enough shielding gas to cool without oxidizing.
Plan for a TIG torch rated for the current and duty cycle, a gas regulator, and a clean supply of argon. A water-cooled torch is more comfortable for sustained high-current work, but adds a cooler, hoses, and maintenance; an air-cooled torch is simpler for intermittent fabrication. A compatible TIG foot pedal is worth considering if it is not included. Verify connector compatibility before buying accessories.
Copper technique and common failures
Clean the joint immediately before welding. Remove oil and oxide with a suitable solvent and dedicated stainless brush or abrasive; tools used on carbon steel can leave contamination. Fit the parts tightly and support thin walls, since gaps encourage burn-through and distortion. On copper, excessive travel speed can leave incomplete fusion because the base metal pulls heat away. Too much current or a long dwell can instead melt an edge, collapse a tube, or distort a thin header.
Use enough shielding gas to cover the puddle without creating turbulence. Excessive flow can draw air into the shield, while drafts can cause porosity and a rough, oxidized bead. Keep the torch angle modest and the arc short. If the puddle will not form consistently, check fit-up, cleanliness, gas coverage, and current before simply increasing amperage. Practice on offcuts of the same alloy and thickness; settings that work on copper sheet may not transfer to a tube-to-header joint.
Heat exchangers may operate under pressure, vibration, or corrosive fluids. A bead that looks sound is not proof of a leak-tight, code-compliant assembly. Use the specified welding procedure and filler, and arrange appropriate inspection and pressure testing. Never test with compressed gas unless the approved procedure and safeguards specifically permit it; stored energy makes a failure hazardous.
A practical buying decision
For occasional work on thin copper tubing, a modest 120 V DC TIG machine can be enough, especially if the parts are small and you can weld in short sessions. For thicker headers, more frequent fabrication, or a shop where downtime matters, favor a 240 V inverter with roughly 200 amps of output, a workable low-current range, pedal control, and a duty cycle that matches your workload. Add AC/DC only when aluminum TIG work justifies the extra cost.
Before ordering, confirm input voltage, duty-cycle specifications, torch rating, pedal compatibility, and local parts or service support. Those details affect whether the machine can complete the job more than a long feature list does.