Copper TIG Welding: Settings, Filler & Techniques That Work

A fabricator once spent three hours cranking the amps on a chunky copper bus bar, only to get a cold, sitting-on-top bead while the rest of the plate turned a fire-engine red. The problem was never the machine or the welder’s skill—it was copper’s ability to whisk heat away faster than the arc could put it in. That single frustration is why copper TIG welding has a reputation, and why the fix is knowledge, not brute amperage.

Copper TIG Welding: Why This Metal Fights Back

A fabricator once spent three hours cranking up the amps on a chunky copper bus bar, chasing a weld that refused to sink in. The bead sat cold and proud on the surface while the surrounding plate glowed fire-engine red. The machine was fine and his hand was steady. The real culprit was copper doing what copper does best: pulling heat away from the arc faster than the arc can replace it.

That frustration is why copper TIG welding carries a reputation for being difficult. So let’s answer the principal question up front: yes, copper can be welded soundly with the TIG process, in production and in the repair shop alike. The difficulty is physical and metallurgical, not personal. Copper simply behaves differently from steel, and once you understand the three properties driving that behavior, most of the mystery disappears.

The Three Properties That Make Copper Hard

1. Thermal conductivity. Pure copper conducts heat at roughly 401 W/(m·K), the highest of any common structural metal apart from silver, and about five to eight times the conductivity of mild steel. Heat deposited into the puddle doesn’t stay put; it races outward into the surrounding base metal, which is why the plate beside your weld turns red while the joint itself refuses to melt. On a heavy section, copper behaves like a heat sink deliberately built to sabotage fusion.

2. High oxygen affinity. Copper grabs oxygen readily, and in grades that contain it, that oxygen creates porosity and can cause hydrogen-type embrittlement when it meets arc-generated hydrogen. This is a metallurgical problem rather than a heat problem, and it’s the reason filler selection and shielding gas discipline matter so much on oxygen-bearing grades. We’ll cover this in depth in the sections on alloys and fillers.

3. A melting point of about 1,084.62°C (roughly 1,985°F), followed by instant solidification. Copper melts at a lower temperature than steel, but the puddle freezes almost the moment arc energy drops. The window between fluid and solid is narrow, and if heat input falls even slightly as you travel, the puddle slumps, loses wetting, and sits on top of the joint instead of tying into it. High conductivity makes the collapse worse, because the heat that keeps the puddle alive leaks away on both sides of the weld simultaneously.

Why GTAW Is the Process of Choice

Since copper punishes uncontrolled heat, the ideal process is the one that lets the operator place energy precisely and change it instantly. That’s gas tungsten arc welding. A foot pedal lets you ramp amperage the second the puddle wets, then ease off as the joint fills, which is exactly the modulation copper demands. The arc is narrow and directional, dilution stays low, no flux is involved, and the welder can see the puddle forming clearly, critical when the puddle forms late and freezes fast.

Other processes have roles. GMAW deposits metal faster but gives far less heat control and a higher porosity risk on oxygen-bearing copper. Stick welding with AWS A5.6 copper electrodes works but introduces flux and slag into a metal that already resents contamination. Oxy-fuel spreads broad, soft heat and oxidizes the surface heavily, and braze-welding with silicon bronze filler is a genuinely useful lower-heat alternative for some joints. Even so, when a joint needs full fusion, tight tolerance and a clean visible puddle, TIG wins. The same logic applies to other heat-sensitive metals: if you have worked through an aluminum MIG welding guide, you already know how quickly a high-conductivity metal punishes sloppy heat control.

What This Article Will Cover

Copper TIG welding is a chain of decisions, and a chain only fails at its weakest link. This guide walks the whole sequence in order:

• Alloy identification — reading grades from C11000 ETP to C12200 DHP before you strike an arc
• Process choice — when TIG is right, and when brazing or soldering is the smarter answer
• Filler metal selection — matching AWS A5.7 classifications to conductivity, strength and corrosion requirements
• Gas and machine setup — polarity, tungsten, argon and argon-helium blends, flow rates
• Preheat and joint preparation — temperature ranges, cleaning, tacking and procedure paperwork
• Technique — running an actual bead from arc start to post-flow
• Troubleshooting — porosity, lack of fusion, burn-through, cracking and tungsten contamination
• Applications — bus bars, motor windings, heat exchangers, piping, art and dissimilar joints
• Fume safety — exposure limits, symptoms and the controls that keep you under them

If you have ever watched an alloy 20 welding procedure come together, you already appreciate that exotic alloys reward preparation, and copper is no different. The welder who identifies the grade, preheats deliberately, picks a filler that matches the service and lets the puddle tell him when to move will produce clean, fully fused copper welds — while the welder chasing amps on a cold bus bar keeps fighting a battle the metal was always going to win.

Know Your Copper First: Grades, Properties and Weldability

Before any amperage is dialed in or an electrode is struck, the single most important task for copper TIG welding is identifying the alloy in front of you. While two pieces may both be sold as “copper”, their weldability can be night and day. This comes down to chemistry, specifically oxygen content, and how it’s handled within each grade.

The Commercially Pure Coppers You’ll Actually Encounter

For the vast majority of fabrication work, you’ll be dealing with commercially pure coppers, which are represented by UNS numbers C10100 through C13000 by the Copper Development Association. Of these, only a select few are the ones that tend to cross a welder’s bench.

First is C11000 electrolytic tough pitch (ETP) copper. This is one of the most common forms of copper found in bus bars, sheets, and general stock. It typically contains roughly 0.02-0.04% oxygen. While this oxygen is harmless in electrical or mechanical service, under the arc it can combine with hydrogen to create porosity and hydrogen-type embrittlement. For this reason, ETP is considered weldable, but it’s often the most finicky of the pure coppers to get a sound, porosity-free TIG bead on.

Next are the oxygen-free grades. C10100 oxygen-free high-conductivity (OFHC) copper contains less than 0.0005% oxygen and carries a minimum conductivity of 100% IACS, as outlined by its alloy data. Its lack of oxygen makes it far less prone to the porosity issues seen in ETP, and as a result, it welds noticeably cleaner. Closely related is C10200 OFHC copper, which is also oxygen-free and welds very similarly, making both ideal choices when maximum electrical or thermal conductivity must be preserved.

Finally, there’s C12200 deoxidized high-phosphorus (DHP) copper. Instead of removing oxygen through vacuum processing like OFHC, this alloy uses phosphorus to scavenge it during melting. For this reason, C12200 DHP copper is phosphorus-deoxidized and is the standard alloy for copper tube to ASTM B88/B75. You’ll find it almost everywhere in plumbing, HVAC, and heat transfer tube. The phosphorus does an excellent job of preventing oxygen-related porosity, making it one of the most forgiving of the commercially pure coppers under the TIG arc.

Brasses, Bronzes, and The Need For Identification

Not every yellow or reddish piece of “copper” stock is a commercially pure copper at all. Brasses are copper-zinc alloys, and bronzes are typically copper-tin based alloys. These behave drastically differently under the arc than C10100, C10200, or C12200. Zinc in particular can vaporize at TIG temperatures, creating excessive fume, arc instability, and brittle weld metal. Because of this, the approach to filler, heat input, and even process selection shifts entirely. Much like the careful alloy identification needed when working with other non-ferrous materials, such as when following the principles for alloy steel welding electrodes, guessing is never an option here.

The practical rule is simple: identify the alloy before striking an arc. This can be done by checking for a part stamp, referencing a mill certificate, or performing a magnet-free density check for confirmation. Never rely on color alone. Two tube ends can be the same shade of copper, yet be C11000 and C12200 with completely different deoxidation practices.

At its core, weldability for pure copper boils down to this: the more oxygen present and left unscavenged, the more temperamental it becomes under GTAW. Oxygen-free and phosphorus-deoxidized grades grant the most leeway with heat control, whereas ETP demands the cleanest prep, best shielding, and the most disciplined heat management to achieve a sound joint. With that baseline established, every subsequent decision, from filler metal to preheat, will be dictated by the grade that you correctly identified to begin with.

Why TIG Is the Go-To Process for Copper (and When It Isn’t)

Process selection decides whether copper welding feels like a fight or a routine job. Copper tolerates almost no slack: the puddle shows up late, collapses the moment the arc moves, and pulls heat away in every direction at once. Any process that dumps heat in a fixed, uncontrolled dose leaves you guessing. That is the practical reason GTAW (TIG) has become the default answer for copper, and also the reason it is not always the right one. Knowing when to reach for something else is just as valuable as knowing how to run a TIG bead.

What GTAW Actually Gives You

The single biggest advantage is real-time heat control. A foot pedal or thumbwheel lets you add amperage while the puddle is forming and back off the instant it wets out, then swing back up when you move onto a heavier section. On a metal where the puddle forms late and freezes fast, that instant modulation is the difference between fusion and a bead sitting on top of the plate. The other benefits stack on top of it:

• Low dilution and precise heat placement. The arc is narrow and directed, so you can put energy exactly where the joint needs it instead of baking the whole part.
• No flux, no slag. Nothing to chip, no chloride or oxide residue to trap moisture, and full visibility of the puddle from start to finish. Visibility matters enormously when the window between “not enough heat” and “collapsed edge” is small.
• Clean, controllable filler addition. Dip-by-dip deposition keeps oxidation down and lets you compensate for copper’s shrinkage as you go.

The Alternatives, Honestly Compared

GMAW (MIG) deposits metal faster and is attractive for long production seams, but heat control is coarser: you set the machine and travel, rather than modulating continuously. Copper’s sensitivity to shielding disruption also raises porosity risk, and the shorter arc length gives less reaction time. For shop work where speed matters and the joint is simple, MIG is viable; for anything critical or heat-sensitive, TIG usually wins.

SMAW (stick) has a legitimate standard behind it: AWS A5.6/A5.6M covers copper and copper-alloy electrodes for shielded metal arc welding. Stick is portable and works overhead and in drafts, but the flux introduces slag and a cleaning step, and the fixed deposition rate removes the fine control copper rewards. It is a field-repair tool more than a precision one. If you want a broader look at when stick still outperforms wire processes, see our Advantages of Stick Welding: Why SMAW Still Wins guide.

Oxy-fuel delivers broad, soft heat and heavy oxidation at the surface. It is useful for heating, bending and brazing fittings, but for fusion welding structural copper it lacks the concentration and atmosphere control you need.

Braze-welding with silicon bronze is a legitimate, lower-heat alternative, particularly on thick, dirty or awkward sections where you would otherwise preheat heavily. It trades away conductivity and color match, which is why it never belongs on a bus bar with a conductivity spec.

Process	Heat control	Deposition speed	Best fit on copper
GTAW	Excellent (pedal)	Low	Critical joints, bus bars, tube, dissimilar joints
GMAW	Moderate	High	Long, simple production seams
SMAW (A5.6)	Moderate	Moderate	Field and repair work, out-of-position
Oxy-fuel	Broad, soft	Manual	Brazing fittings, heating, light repair
Braze-weld (SiBronze)	Forgiving	Moderate	Lower-heat joins where conductivity isn’t specified

Welding or Brazing? The Terminology Matters

Joining copper with a matching-melting-point copper filler is fusion welding, full stop. A filler that melts below the base metal is brazing, and AWS defines that threshold as below about 840 °C (1,550 °F). Bare filler rods used across GMAW, GTAW and plasma arc fall under AWS A5.7. This is not just pedantry: it changes your filler stock, your procedure qualification, your PPE and, in code work, which acceptance rules apply. For plumbing tube specifically, CDA and prevailing code practice still favor soldering or brazing over fusion welding, because those joints are faster, require no preheat, and stay out of the heat-affected zone. Specialty applications such as Alpha Laser Welding or friction stir welding enter where distortion must be near zero or where fusion welding would simply melt away the properties being designed for.

In practice, most fabricators settle into the same pattern: TIG for anything that must be sound, leak-tight or conductive; braze-welding where heat input is the enemy; and stick or MIG only when access, speed or field conditions make them unavoidable. With that decision made, the next question is choosing a filler that does not quietly defeat the purpose.

Choosing the Right Filler Metal (AWS A5.7 and Beyond)

If base-metal identification is step one of copper TIG welding, filler selection is step two, and it’s the step where good welds quietly go bad. Copper is unusual because the filler doesn’t just add strength; it can make or break the electrical conductivity, corrosion resistance, color, and serviceability of the finished joint. A bus bar welded with the wrong wire can look perfect and still fail its resistance spec. That’s why filler choice deserves as much thought as amps and gas.

The Governing Standard: AWS A5.7

Bare copper and copper-alloy welding rods and electrodes are classified under AWS A5.7/A5.7M. The current edition, AWS A5.7/A5.7M:2026, is the 8th edition of the specification, approved by ANSI in November 2025, and it sits within the work of AWS’s A5 Committee on Filler Metals and Allied Materials — the same committee behind the steel and stainless filler specs you may already use. Every wire discussed below carries an AWS classification, so the classification number, not the spool label, is what you match to your procedure.

ERCu: The Conductivity-Matching Choice

ERCu is a deoxidized copper filler with small additions of silicon, tin, or manganese to keep the puddle sound. It’s the correct choice whenever the finished weld has to retain the base metal’s electrical and thermal conductivity: bus bars, bus joints, motor hairpins, heat-exchanger tubes, and grounding hardware. Because its composition sits close to the base copper, the weld metal’s conductivity stays in the same neighborhood as the parent material instead of collapsing the way alloyed fillers do.

Think of ERCu as the default for anything carrying current or heat. As a practical analogy, choosing filler for copper follows the same logic as selecting alloy steel welding electrodes — you match the filler to the service, not to whatever is on the shelf.

ERCuSi-A (Silicon Bronze): The Forgiving Filler

ERCuSi-A, roughly 97% copper and 3% silicon, behaves completely differently. It flows beautifully at lower heat, wets out smoothly, and tolerates dirty or oxygen-bearing base metal that would fight a pure copper weld. Those traits make it a favorite for braze-welding, overlays, repairs, and decorative work where the joint isn’t expected to carry current.

The trade-off is real, however: the silicon drops both electrical and thermal conductivity well below the base copper, and the weld color doesn’t quite match polished copper. Where a conductivity specification exists, ERCuSi-A disqualifies itself no matter how nice the bead looks.

ERCuSn-A and ERCuAl: Bronze Fillers

ERCuSn-A, a phosphor bronze around 92% copper and 8% tin, is the go-to for overlays, bushings, bearing surfaces, and general bronze work where wear resistance and strength matter more than conductivity. ERCuAl aluminum bronzes push further toward strength and corrosion resistance, making them suitable for propellers, pump components, and seawater-exposed hardware. Both are legitimate copper-alloy fillers, but both abandon conductivity entirely.

Filler	Typical composition	Best for	Watch out for
ERCu	Deoxidized Cu with small Si/Sn/Mn	Bus bars, conductors, heat-exchanger tubes, joints needing conductivity	Less forgiving of dirty or oxidized base metal
ERCuSi-A	~97Cu-3Si (silicon bronze)	Braze-welding, overlays, repairs, decorative work	Reduced conductivity; color mismatch
ERCuSn-A	~92Cu-8Sn (phosphor bronze)	Overlays, bushings, bronze machinery work	No meaningful conductivity retention
ERCuAl	Aluminum bronze grades	High strength, corrosion and seawater service	Stiffer puddle, higher alloy content demands clean prep

Three Questions That Decide Your Filler

In practice, filler selection comes down to three checks:

• What is the base metal? ERCu matches C11000/C10100/C10200/C12200 copper best; bronzes and aluminum bronzes need matching alloys rather than plain copper.
• What must the joint do in service? Conductivity, strength, and corrosion resistance pull the choice in three different directions. Only one can win.
• Is this fusion welding or braze-welding? A filler melting below the base metal (below about 840°C/1,550°F by AWS definition) makes the joint a brazed joint, which changes the procedure, the inspection criteria, and sometimes the code you work to.

One last practical habit: buy filler from a heat-numbered or certified lot when the joint is critical, and store copper wire as carefully as you’d store a clean aluminum filler — copper wire that’s picked up oil, moisture, or marker ink will put porosity straight into a puddle that’s already sensitive to contamination.

Machine, Torch and Shielding Gas Setup

Copper conducts heat roughly 60% faster than steel and about eight times faster than stainless, so arc heat escapes the joint the moment it arrives. Every setting on your machine exists to fight that one fact. Get the setup right and copper behaves; get it wrong and you will chase amps all day, as in the bus bar story at the top of this guide.

Polarity: Run Straight Current

Use DC straight polarity (DCEN, electrode negative). In this configuration roughly two-thirds of the arc heat goes into the workpiece and only the remaining third sits in the electrode, which is exactly what you want when the base metal is trying to steal heat faster than the arc can supply it. Alternating current would split that energy and waste it heating tungsten you need intact.

Pair DCEN with high-frequency starts so you never touch the electrode to the copper to strike the arc, and fit a foot pedal or thumbwheel rather than a fixed-amperage switch. On copper, real-time amperage control is not a luxury; it is how you hold a puddle that forms late and freezes fast. For more on dialing in power sources, our Airgas Welding Equipment Guide walks through torch and machine choices in detail.

Tungsten: Keep It Clean and Sharp

A 2% thoriated (red band) or 2% lanthanated (blue band) electrode covers most copper work; mixed rare-earth alternatives such as ceriated or zirconiated tungsten also hold up at lower currents. Three habits matter more than the brand:

• Size the electrode for the current range you actually run, then step up one size if you are pushing heavy plate with helium mixes.
• Grind to a sharp point on a dedicated grinder, with longitudinal scratches running the length of the tip, and never reuse a contaminated end.
• Keep it clean. Copper vapor rises straight into a hot, exposed tip, and a single dip into the puddle transfers copper into the tungsten and sends the arc wandering.

Shielding Gas: Argon, Helium and the Blends

Pure argon is the default for material under about 6 mm (1/4 in.) because it gives a stable, easy-to-control arc at moderate amperage. Past that thickness copper’s heat sink wins, and helium becomes your lever. Helium ionizes at a higher voltage, so a blend raises arc voltage and therefore heat input without forcing you to raise the amperage you are already struggling to control. At 50% helium, arc voltage rises roughly 30–40% compared with pure argon at the same current.

Gas mix	Typical use	What it does
100% argon	Sheet and sections under 6 mm	Stable, cooler, most controllable arc
75Ar / 25He	Medium sections	Modest heat boost, still forgiving
50Ar / 50He	6–12 mm plate and heavy bus bar	30–40% higher arc voltage at the same amps
Helium-rich (75He/25Ar down to 100% He)	Heavy copper, thick sections	Maximum heat without adding amperage

Helium-rich mixes cost more, burn hotter, and demand better gas coverage, so they belong on thick work where they earn their keep. If sourcing blends locally is awkward, a supplier guide such as AllGas Welding Supply explains how these mixtures are specified and packaged.

Flow Rate, Gas Lens, Cup and Post-Flow

Coverage matters more on copper than on steel because the bead stays hot long after the arc leaves. A gas lens lets you run a lower, steadier flow, roughly 12–15 CFH instead of the 20 CFH you might use on a plain cup, while delivering a wider, more laminar column of shielding. It is the single best equipment upgrade for copper TIG work. Match cup size to joint geometry, keep pre-flow short, and extend post-flow, or fit a trailing shield, until the bead has dulled from bright orange down to a clean straw color rather than purpling. That last second of gas is what prevents sugaring and the discolored, weakened surface metal that follows it.

Amperage, Back-Pedaling and Pulsed Current

There is no trustworthy amperage chart for copper because thickness is only half the story; grade, clamping, backing and preheat change everything. Treat published figures as a test-run baseline: strike an arc on scrap of the same grade and thickness, start conservatively, then add current until the puddle actually wets both edges. Industry settings guidance from CK Worldwide on copper TIG amperage, preheat and filler reinforces the same approach: test, adjust, document.

Technique-wise, start the arc slightly ahead of the joint, let heat soak in, then back-pedal to hold the puddle as you move forward. On thin copper, switch to pulsed TIG: a higher peak current melts and wets the joint, then a background current lets the puddle solidify briefly between pulses. That breathing cycle keeps heat localized, reduces distortion, and makes the difference between a controlled bead and a hole you fill with filler. For the hand skills behind these settings, see our Aerospace TIG Welding guide on standards, technique and training.

With the machine configured, the next step is the joint itself: preheat, cleaning, and the procedure variables that decide whether your weld survives inspection.

Preheat, Joint Prep and Procedure Variables

If there is one step welders skip and then regret on copper, it is preheat. Copper pulls heat away from the arc so aggressively that a joint sitting at room temperature behaves like a heat sink with a puddle on top: the leading edge never gets hot enough to wet, while the surrounding plate climbs toward red. Preheat offsets that heat-sink effect, flattens out the steep thermal gradient that otherwise collapses the puddle the moment the arc moves, and gives the filler a chance to fuse rather than sit. In practical terms, you are not cooking the copper; you are taking away its ability to steal the arc’s energy.

Preheat also manages expansion. Copper’s coefficient of thermal expansion is roughly double that of steel, which produces a counterintuitive failure: a joint tacked snug at room temperature can close up badly by the time it reaches welding temperature. The tacks fight the shrinkage, the plate buckles, and the root gap you carefully set disappears or pinches shut. Fixturing and preheat together keep the geometry honest.

Practical Preheat Ranges and How to Verify Them

Treat these as starting guidance, not gospel, and confirm with a procedure trial:

• About 400–600°F (200–315°C) for material in the 1/4–1/2 in (6–12 mm) range.
• About 600–1,000°F (315–540°C) for material over 1/2 in (12 mm).
• Thick sections: an oven soak beats a torch every time, because it delivers uniform temperature through the whole part instead of a hot spot with a cold core.

Never guess. Check with a contact pyrometer, an infrared thermometer aimed at a non-shiny spot, or temperature-indicating crayons that melt at a set point. Experienced copper welders also talk about the same amperage-and-preheat logic in their own settings guides, and the pattern is consistent: preheat does more for fusion than raw amperage does.

Joint Prep: Clean, Fit, and Control the Heat Path

Start with the joint design. A square butt with a generous root face works for most moderate thickness; a slight bevel helps on heavier plate where full penetration is required. The root face stays generous because a knife-edge joint on a high-conductivity metal simply melts away before the root can fuse.

Cleaning is meticulous, not casual. Wipe or abrade with acetone and a clean emery cloth to remove oxide, drawing compounds, and oil. Fresh copper oxidizes almost instantly at temperature, so clean immediately before welding and keep gloves and pliers free of contaminants. The discipline is the same idea covered in how to prep aluminum right: the joint you are about to weld should be the cleanest surface on the bench.

Then control where the heat goes:

• Tack strategy: place tacks that accommodate expansion, sequence them symmetrically, and be ready to re-cut a tack that has pulled the root closed.
• Backing and chill blocks: a water-cooled or heavy copper-free chill backing absorbs excess heat on thin sections, while a clean inert-gas backing shield protects the root on tube.
• Fit-up: consistent root gap and land matter more on copper than on steel, because the puddle freezes fast and cannot bridge a sloppy joint.

Write It Down: Procedure Documentation

Repeatable copper welds come from a written procedure, not memory. A Welding Procedure Specification (WPS) in the ASME Section IX format captures the variables that actually decide the outcome: preheat under QW-406, shielding gas under QW-408, and electrical characteristics under QW-409. For copper alloys, the Copper Development Association’s procedure literature follows the same framework; notably, DHP copper tube (C12200) is listed as P-No. 107 in the CDA’s ASME-based brazing procedure, giving you a ready-made classification for procedure qualification. Standards literacy of this kind is the backbone of aerospace TIG welding work, where nothing is left to chance.

Interpass Temperature and Distortion Control

Get these variables under control and the next step, running the actual bead, becomes far less dramatic: the puddle arrives on time, the joint geometry stays where you put it, and fusion is a matter of technique rather than luck.

Running the Bead: Step-by-Step Technique

Settings get you to the starting line; the bead itself is where copper either forgives you or punishes you. Because copper’s heat races away almost as fast as the arc delivers it, the single most important habit is patience: wait for the puddle to actually wet the edges of the joint before you move, and never try to force fusion with another turn of the amperage dial. What follows is the sequence that works on the bench, in order.

The Eight-Step Walkthrough

1. Clean and fit the joint. Wipe both faces and the back side with acetone and fresh emery cloth until the copper is uniformly bright. Oxide, cutting oil and fingerprints are enough to seed porosity. Fit the joint tight, square and with no visible gap you did not plan for.
2. Preheat and confirm the temperature. Bring the area to the range called for by the material thickness, then verify it with a contact pyrometer or temperature-indicating crayons rather than guessing by color alone.
3. Purge or back-shield. On open tube, channels and any joint where the root will be exposed to air, flood the back side with argon. Oxide discoloration on copper is an early warning that shielding was inadequate, and on the root side of a tube it shows up as sugaring you cannot reach with a grinder.
4. Establish the arc slightly ahead of the joint start. Hold it there and let heat soak in until the puddle wets both edges on its own. This is the step most welders skip, and it is why beads sit on top of the plate instead of tying in.
5. Add filler in small, consistent dips, keeping the arc focused on the leading edge of the puddle. Let the puddle consume each dip before the next one.
6. Travel steadily. The working mantra is hot and fast: enough speed to keep heat localized, enough dwell to achieve real fusion. Excessive travel speed on unpreheated copper produces cold laps and lack of fusion that look acceptable but fail under load.
7. Backstep or skip-sequence long joints. Copper expands hard, so stitching the joint in short, reverse-order segments keeps cumulative shrinkage from pulling the assembly out of shape.
8. Hold post-flow or a trailing shield over the bead until the bright orange dulls. Copper oxidizes quickly at temperature, and the shield gas is still doing work after the arc is gone.

If you want to sharpen the underlying torch mechanics, a good aerospace TIG welding guide covers arc length, travel angle and filler rhythm in depth, and the same fundamentals transfer directly to copper.

Autogenous Welds and Pulsed Current

Autogenous TIG, welding without filler, is only sensible on clean, matched edges of OFHC (C10100/C10200) or DHP (C12200) copper in thin sections where the joint has no gap to fill. Any contamination or fit-up mismatch shows up as a joint that cracks or sinks as it cools. On everything else, add filler deliberately rather than hoping the base metal bridges the gap.

Pulsed current is the heat-management tool for thin copper. Instead of a constant stream, the machine alternates between a peak level that melts and a lower background level that lets the puddle solidify briefly between peaks. The result is a series of overlapping spot welds with far less total heat input, so sheet copper can be joined without burn-through. The peak should be high enough to wet the joint in about a second; if the puddle never forms, raise the peak before touching travel speed. Amperage, preheat and filler choices interact closely, and the CK Worldwide settings overview is a useful reference point when you are dialing in a new thickness.

What a Good Copper Bead Looks Like

A sound copper weld is smooth and slightly convex, with evenly spaced ripples and consistent tie-in along both toes. The surface should carry a straw to light-oxide color with a satin finish. Trouble signs are easy to read once you know them:

• Dull black or heavily sugared surfaces mean shielding was lost or the back side was never purged.
• Rough, lumpy toes with no wetting indicate the puddle was forced by amperage instead of allowed to soak.
• Gray, powdery deposits suggest contamination or an oversized gap burning through.

Run a test coupon on scrap of the same alloy and thickness before you touch the actual joint. Watch how long the puddle takes to wet, note the travel speed that produces full tie-in, and only then commit to the workpiece.

Common Copper TIG Problems and How to Fix Them

Copper TIG welding exposes weak setup instantly: a puddle that won’t wet, a bead full of pinholes, or a hole burned through within seconds. Almost every copper defect falls into one of two families, heat flow or oxygen. Diagnose which one you’re fighting and the fix usually follows.

Porosity: Bubbles Rooted in Oxygen

Porosity is the most common copper TIG defect, and the primary culprit is oxygen dissolved in the base metal. Electrolytic tough pitch copper (ETP, C11000) holds roughly 0.02–0.04% oxygen, which comes out of solution during solidification and leaves gas pockets—or, worse, causes hydrogen-type embrittlement when hydrogen from the arc meets that oxygen. Oxygen-free grades like C10100 OFHC copper (under 0.0005% oxygen) and deoxidized high-phosphorus C12200, where phosphorus scavenges oxygen, dramatically reduce the risk.

Your fixes, in order of impact:

• Change filler. Switch to ERCu, a deoxidized copper filler with small silicon, tin, or manganese additions that mop up oxygen in the puddle.
• Clean obsessively. Wipe the joint with acetone and scuff oxide off with fresh emery cloth right before welding. Oil, marker ink, and moisture all feed porosity. The same discipline carries across materials; our guide to aluminum cleaner for welding covers the why.
• Fix gas coverage. Check for draft, a leaking torch hose, a fouled gas lens, or an overextended stickout, then extend post-flow so the hot bead stays shielded as it freezes.
• Spec the right grade. Where the design allows, choose DHP or OFHC base metal and document it.

Lack of Fusion: The Sitting-on-Top Bead

A bead that looks fine in profile but never wetted the sidewalls is a heat problem, not a skill problem. The usual causes are insufficient preheat, amperage too low for the section’s heat sink, or travel speed that outruns puddle formation, especially at the coldest start of a joint. Raise preheat to 200–300°C (400–600°F) for 6–12 mm material, try an argon-helium blend to lift arc voltage and heat input without cranking current, and slow down at the start. Let the arc sit until the puddle wets both edges before you move.

Burn-Through on Thin Sheet

Thin copper has nowhere to hide heat. Drop amperage, step down to a thinner filler rod (1.6 mm works well on light gauge), and back the joint with a chill block or copper backing bar to pull heat out of the melt. Pulsed current is the single most effective tool here: the peak melts, the background lets the puddle partially solidify, and you control the window.

Hot Cracking and Shrinkage

Copper’s high coefficient of thermal expansion means the joint pulls itself closed as it heats, which is why room-temperature tacks distort badly and why underfilled roots crack. Fixturing and strongbacking, backstep or skip sequencing on long welds, and enough filler to leave a slightly convex bead all counteract shrinkage. Never starve the joint—it needs metal to absorb the movement.

Tungsten Contamination and Arc Wander

Copper vapor is unforgiving to electrodes. Once tungsten picks up copper, the arc wanders and sprays spatter. Grind fresh on a dedicated wheel, keep the stickout short, hold the arc tight, and if you do dip the electrode, stop and regrind rather than trying to burn through the contamination.

Sugaring and Oxide on Tube Backs

Open tube and channel joints oxidize violently on the unshielded side. Purge the interior with argon, use water-soluble purge dams, and keep purge flow low and steady—turbulent gas admits air. A trailing shield or extended post-flow protects the visible bead until it cools below the oxidation threshold. For purge gas sourcing, our AllGas welding supply guide covers cylinder and regulator basics.

Defect	Likely Cause	Quick Fix
Porosity	Oxygen in base metal, poor shielding	ERCu filler, acetone clean, restore gas coverage
Lack of fusion	No preheat, low amps, fast travel	Preheat, argon-helium mix, slow the start
Burn-through	Excess heat in thin section	Pulse current, chill backing, thinner rod
Hot cracking	Shrinkage, underfill, weak fixturing	Backstep sequence, fixture, slight overfill
Arc wander	Contaminated tungsten	Resharpen, shorten stickout
Back-side sugaring	No purge on tube	Argon purge with dams

Run a test coupon before the real joint. Ten minutes of scrap tells you more about your heat balance than an hour of guessing on the workpiece—and it keeps you from learning those lessons on a part that matters.

Real-World Uses: When to TIG Weld Copper — and When Not To

Knowing how to weld copper is only half the job. The other half is knowing when welding is actually the right answer. Copper TIG welding earns its reputation in a handful of demanding applications where nothing else gives you the combination of full fusion, clean aesthetics and precise heat placement. In plenty of other jobs, it is the slowest, most expensive and least code-friendly option on the board. This section walks through both sides so you can pick the process before you strike the arc.

Where Copper TIG Welding Earns Its Keep

Electrical bus bars and conductors. This is the classic application. Switchgear, transformer secondary connections, plating-plant bus work and large grounding straps all depend on copper’s conductivity, which is why the material gets specified in the first place. CDA technical resources consistently point to copper’s unmatched combination of electrical and thermal conductivity as the reason it dominates these designs. That creates a hard constraint on the weld: whatever filler you use has to protect that property. It pushes you toward ERCu rather than a convenient silicon bronze, because a bronze bead on a bus bar is a resistive heating element waiting to happen.

Electric motor hairpins and coil windings. Hairpin winding motors, common in modern EV drive units, use hundreds of formed copper bars that must be fusion joined quickly and consistently. The joints are small, the heat input has to be tightly controlled, and rejection rates matter. This is exactly the kind of work where a precisely controlled GTAW arc, sometimes automated or pulsed, outshines everything else.

Heat exchangers and condenser tubing. Shell-and-tube units, condenser plates and chiller assemblies need full-penetration, leak-tight welds that do not choke flow or trap oxide. Copper’s conductivity makes it a superb heat-transfer material, but that same conductivity means every joint is a heat-sink problem. Purged, back-shielded TIG root passes are the standard answer here.

Chemical and cryogenic process piping. Copper’s corrosion resistance and low-temperature toughness make it valuable in chemical handling and cryogenic lines, where welds must be sound, inspectable and free of porosity.

Artistic and architectural work. Sculpture, cladding, custom lighting and decorative furniture rely on TIG’s visibility and control. Color match, bead profile and minimal distortion are the acceptance criteria, and GTAW delivers all three.

Copper-to-Stainless and Copper-to-Steel Joints

Dissimilar joints are where filler choice gets interesting. Published experimental work on TIG butt joints between 2.7 mm copper and 316L stainless steel using ERCuSi-A (silicon bronze) filler found that around 135 A produced the most balanced fusion profile, with heat diffusing rapidly into the copper side because of its conductivity. That single detail explains why dissimilar copper joints are usually run hotter-looking on the steel side and why travel speed and preheat decisions must account for the copper acting as a heat sink. Silicon bronze is a sensible compromise filler for these joints because it wets both metals at a lower, more manageable temperature. The same logic applies broadly to joining copper to carbon or alloy steels; if you work regularly with alloyed steels, the fundamentals in our Alloy 20 welding procedures guide carry over to dissimilar-metal joint planning.

When Soldering or Brazing Beats Welding

For small plumbing, refrigeration and air-conditioning joints, welding is rarely the smart choice. Brazing and soldering are faster, need far less heat, cause less distortion, and are what the codes actually expect. The Copper Development Association’s guidance on soldering, welding and brazing copper reflects standard trade practice, and AWS A5.8 specification covers the BCuP family of copper-phosphorus brazing fillers used for these joints. Very thin decorative sheet is another case where a soft-soldered or brazed joint simply outperforms a fusion weld.

The Annealed Pressure Rating Rule

This one catches people out constantly. Hard-drawn copper tube gets much of its pressure rating from work hardening. Welding or brazing heat softens the tube in and around the heat-affected zone, so any welded tube run must be rated using annealed pressure values, not the hard- drawn numbers printed on the tube spec. Check the design basis before you weld structural or pressure-bearing tube.

The conductivity caveat. Even a perfect weld changes local microstructure. Fusion zones and heat-affected zones in copper can show reduced conductivity versus the parent metal, particularly when deoxidized fillers or alloyed bronzes are used. For bus bars, electrodes and heat-transfer surfaces, verify the finished joint against the design’s conductivity specification with a test coupon rather than assuming the bead behaves like base copper.

The short version: TIG copper where fusion quality, appearance, leak-tightness or dissimilar-metal control decide the job. Braze, solder or look for another process where speed, code acceptance or cost decide it.

Safety, Fume Control and Your Copper TIG Action Plan

Copper is forgiving on the body compared with a lot of welded metals, but “forgiving” is not “harmless.” Welding and brazing copper releases a fine metal oxide fume that irritates the eyes and airways, and enough of it will make you genuinely sick for a day or two. The good news: the limits are low, the symptoms are recognizable, and the controls are straightforward.

What the Exposure Limits Actually Say

Four numbers govern copper fume exposure. Both the OSHA permissible exposure limit and the NIOSH recommended exposure limit for copper fume are 0.1 mg/m³ as an 8-hour time-weighted average. ACGIH recommends a slightly higher 0.2 mg/m³ threshold limit value. For emergencies, NIOSH lists an IDLH concentration of 100 mg/m³ as Cu — the level considered immediately dangerous to life or health.

Organization	Limit	Averaging
OSHA PEL	0.1 mg/m³	8-hour TWA
NIOSH REL	0.1 mg/m³	8-hour TWA
ACGIH TLV	0.2 mg/m³	8-hour TWA
NIOSH IDLH	100 mg/m³ as Cu	Immediate danger

For context, those occupational limits are far below anything approaching the IDLH, which is exactly why steady, boring compliance with ventilation matters more than dramatic rescue scenarios.

Signs You’re Breathing Too Much

Overexposure usually announces itself in stages: eye and upper-respiratory irritation first, then a metallic or sweet taste in the mouth, then nausea. The classic endpoint is metal fume fever — chills, muscle aches, fever, a dry throat, cough and weakness. The catch is the timing: symptoms are typically delayed by several hours and can linger for a day or two, so welders often fail to connect Monday’s fever with Friday’s overtime. The NIOSH Pocket Guide to Chemical Hazards specifically notes that exposure can occur during welding of copper alloys, which is why this belongs in every copper TIG welder’s mental checklist, right next to preheat temperature.

Controls That Actually Keep You Under the Limit

Engineering controls come first, respirators second. That hierarchy is not negotiable under good practice, and it mirrors the guidance in OSHA’s welding fume fact sheet and the safety requirements of ANSI Z49.1, Safety in Welding, Cutting and Allied Processes.

• Local exhaust ventilation. A fume extraction arm or snorkel positioned at the arc captures the plume before it reaches your breathing zone. For copper TIG, closer is better — the plume rises fast over hot copper.
• Dilution ventilation. General shop airflow helps, but it should supplement extraction, never replace it. Confined spaces and interior chambers of tanks or tube bundles need dedicated thought.
• Respiratory protection. Where engineering controls cannot reach the limit, use NIOSH-approved particulate respirators. The NIOSH tables list N95, R95 and P95 options for concentrations up to 1 mg/m³ for copper fume — ten times the 8-hour PEL.
• PPE and hygiene. Eye protection against both UV and fume, gloves, and clean work clothes. Wash hands and face before eating or drinking so ingested copper dust doesn’t add to your absorbed dose.

If you already handle other metals, the same extraction habits transfer: the prep work matters as much as the process. See our guides to aluminum cleaner for welding and aluminum MIG welding for the same clean-surface, low-fume workflow applied to a different alloy family.

Your Copper TIG Action Plan

Everything in this article compresses into ten moves. Work them in order and copper stops being an enemy:

1. Identify the alloy. Confirm whether it is ETP, OFHC or DHP before striking an arc.
2. Choose matching filler. ERCu where conductivity matters; ERCuSi-A only where it does not.
3. Clean meticulously. Acetone and fresh emery cloth, right up to the moment of welding.
4. Preheat. 200–300°C for medium stock, higher for thick sections, verified with a pyrometer.
5. Select your gas. 100% argon under about 6 mm, argon-helium beyond it.
6. Set DCEN and prep tungsten. Sharp, clean, uncontaminated electrode.
7. Run a test coupon. Prove settings on scrap of the same thickness and alloy.
8. Control heat. Pulse where needed, backstep long joints, back-pedal to hold the puddle.
9. Inspect honestly. Straw-to-light colors, smooth and slightly convex, full edge wetting.
10. Control fumes. Extraction at the arc, correct respirator if needed, clean hygiene afterwards.

Do that consistently and you get copper welds that conduct, seal and hold — plus a shop where people feel fine on Monday morning.

Frequently Asked Questions

What amps should I use for copper TIG welding?

There is no universal amperage for copper because conductivity and thickness dominate the answer. As a starting baseline, scale current to thickness, then increase roughly 20-50% over what you’d use on mild steel of the same size, use an argon-helium mix on heavier stock, and validate with a test coupon. Foot-pedal control matters more than a fixed number.

Do you have to preheat copper before TIG welding?

Thin clean copper under about 6 mm can sometimes be welded without preheat using an argon-helium mix, but heavier sections almost always need it. Typical starting ranges are about 400-600°F (200-315°C) for 6-12 mm and 600-1,000°F (315-540°C) above 12 mm, verified with a pyrometer or temp crayons.

Which filler metal is best for TIG welding copper?

Use ERCu (AWS A5.7) deoxidized copper when the joint must retain the base metal’s electrical or thermal conductivity, such as bus bars and heat exchangers. ERCuSi-A silicon bronze is easier to run and more forgiving on dirty or oxygen-bearing copper, but it lowers conductivity. Confirm the filler against your design specification before welding.

Should copper TIG welding be AC or DC?

Copper is welded on DC straight polarity (DCEN), which pushes most of the arc heat into the workpiece. AC is reserved for aluminum and magnesium; there is no oxide-cleaning benefit to justify it on copper.

Why are my copper TIG welds porous or discolored?

Porosity almost always comes from oxygen in the base metal (common in ETP C11000 copper), contamination, or poor gas coverage. Fix it by switching to a deoxidized grade like C12200 or C10100, cleaning with acetone, using ERCu filler, and improving shielding with a gas lens or helium blend. Heavy black oxide or sugaring on the back indicates a need for argon purging.

Can you TIG weld copper to stainless steel or mild steel?

Yes, but the large differences in thermal conductivity and melting temperature cause asymmetric heating, with heat rushing into the copper and concentrating in the steel. Studies on copper-to-316L joints using ERCuSi-A filler found a moderate current around 135 A gave the most balanced fusion on thin plate. Expect to tilt the heat toward the steel side and control the puddle carefully.

Is TIG better than MIG for welding copper?

For most precision copper work, yes. TIG lets you adjust heat instantly and see the puddle, which matters on a metal that freezes fast. MIG can be productive on thicker copper but demands significant preheat, deoxidized wire, and strict gas control, and it is more prone to porosity and lack of fusion on thin material.

Is welding copper fumes dangerous?

Copper fume can cause eye and upper-respiratory irritation, a metallic taste, nausea, and metal fume fever—a flu-like illness with chills, muscle aches and fever that is often delayed several hours. The OSHA PEL and NIOSH REL are both 0.1 mg/m³ as an 8-hour TWA. Use local exhaust ventilation and, where needed, a NIOSH-approved particulate respirator.