Titanium is chosen for thin-wall work because it is strong enough to be thin. That is also what makes it difficult. On a wall of a millimetre or less, the margin between a full-penetration weld and a hole is small, and the metal conducts heat poorly enough that the heat stays where you put it.
On aluminium, heat disappears into the part and you chase it with more current. On titanium, the heat sits under the arc and builds. A puddle that looks correct for the first few seconds will, if you keep going at the same pace, sink through the wall. The welder's job is not to reach a temperature and hold it, but to keep the puddle moving so that no single point receives enough heat to collapse.
Every thin-wall titanium weld is controlled by what the pool is doing, not by what the machine says. A pool that is bright, wide and sluggish is about to fall through. A pool that is narrow and quick to freeze is telling you to slow down or add filler. Those two readings are the whole skill.
Machine settings matter, but they set a starting point rather than a guarantee. The same setting produces a sound weld on a flat seam and a hole on a tube-to-flange joint, because the heat sink behind the joint is different. Experience shows up as the ability to read the pool and change before the failure, not as a memorised setting.
A gap that has to be bridged with filler is a gap that will be welded hot and slow. Tight, consistent fit-up lets the arc run fast and keeps the heat input down, which on thin titanium is the same thing as quality. The best thin-wall welders spend more time on the fit than on the bead.
Butt joints should be square, deburred and butted without a visible gap. Where a slight gap is unavoidable, it should be uniform along the seam, because a gap that opens and closes forces the welder to vary travel speed, and variation is what produces the thin spot that later cracks.
Clamping does two jobs on thin titanium: it holds the joint closed and it pulls heat out of the part. Both are useful, and both can be overdone. A clamp that is too heavy creates a hard constraint, and the shrinkage that happens as the weld cools then has nowhere to go but into residual stress or a cracked bead.
Copper or aluminium chill bars behind the joint are the usual compromise. They support the weld, they draw heat away, and they can be shaped to follow the seam so the backing is consistent. The bar must be clean and free of any contamination that could be picked up by the hot metal, and it must not be so tight that it marks the surface.
Pulsing is the standard way to put heat in without letting it accumulate. The arc spends part of its cycle at a low level, which lets the pool stiffen slightly and the surrounding metal recover, then returns to full power to keep fusion. The effect is a series of small, overlapping pools rather than one continuous one, and the bead looks like a fine stack of dimes when it is done well.
Travel speed does the rest. A fast bead on thin titanium is not a shortcut; it is the technique. The arc should be moving continuously, with the pool following it, and any pause for adjustment should happen with the arc off. Stopping with the arc live is how thin-wall parts get holes.
Burn-through rarely arrives without warning. The pool first goes bright and slightly wider than the bead you intended, then the surface starts to sink, then a small dimple appears at the trailing edge. By the time a hole is visible, the warning was several seconds earlier.
The response at the first sign is to speed up and reduce the arc length, not to reduce current abruptly. Cutting current suddenly freezes the pool while the surrounding metal is still hot, and the resulting weld is usually undercut or lacks fusion at the edges. Smooth correction keeps the bead continuous; abrupt correction creates a defect you then have to repair.
A hole in thin titanium is repaired by stopping, letting the part cool completely, cleaning the area and then closing the hole with a small, controlled bead from the edges inward. Trying to close it while the surrounding metal is still hot is how a small hole becomes a large one.
Where the hole is bigger than a pinhole, a patch is often the better answer than filling. A patch spreads the heat over a larger area and produces a joint that is easier to shield and easier to inspect. On a visible part, the patch also has to look deliberate, which means cutting it to a shape that reads as part of the design rather than as a repair.
Thin titanium tube is springy and unforgiving. It does not want to sit in a V-block without rocking, and any rocking during welding shows up as an inconsistent bead. Soft jaws, shaped to the tube diameter, hold it without marking it and without forcing it into a shape it does not want.
The fixture also has to let the tube move axially as it shrinks. A tube clamped hard at both ends will either distort along its length or crack at the weld. One fixed end and one guided end is a better arrangement, and it is cheap to build into a fixture at the design stage.
Thin-wall titanium is priced on the assumption that the shop knows what it is doing with heat. The questions below separate a supplier who does from one who is learning on your parts.
Our own thin-wall work is mostly exhaust tube and heat-shield components. You can see the fabricated parts on our titanium fabrication components pages, the systems they belong to under titanium exhaust systems, and the welded assemblies under titanium TIG welding parts. Comparable stainless work is on the stainless steel exhaust systems and TIG stainless steel welding pages, and thin-wall tube sections are described under exhaust pipe sections.
