welder working on brompton bike frame welder working on brompton bike frame

Spotlight on: Tig Welding


Everything you need to know about Brompton tig-welded titanium frames.

All Brompton titanium framesets start their life as a set of tubes in our specialist TIG welding factory in Sheffield, 300 km north of our London Factory.

We built this dedicated space as titanium requires different skills, machinery, and process than steel. The city of Sheffield has a rich history and legacy of expertise in metalworking.

What is TIG welding?

TIG welding (Tungsten Inert Gas), also known as Gas Tungsten Arc Welding (GTAW), was first developed by the aerospace industry in the 1940s. We chose this technique for the high quality, clean welds it produces. And the exceptional precision it allows in hard to reach places.

TIG Welding requires a high level of skill and coordination between hand, foot and eye. Even the most experienced welders need time and intense focus.

welding helmets hanging on a wall

How does it work?

It's all in the name - Tungsten Inert Gas.
Our welders use a tungsten electrode (it looks a bit like a pen) to create an electric arc that produces intense heat. They manually guide the electrode along the join between the titanium pieces.

tig welding on a brompton bike

As the pieces start to melt, the welders introduce a commercially pure titanium wire rod to the mix. A molten pool of titanium is created. Once cooled, it forms a strong bond.

The skill of the welder here is to perfectly balance the pool of molten filler with the heat of the torch and the pace or motion of their hand.

molten filler used to create a strong bond

What about inert gas?

When you heat titanium to high temperatures, it chemically reacts with the oxygen and nitrogen in the air, compromising the strength of the weld. To get around this problem, we create an inert gas environment around the weld pool.

Inert gases, Argon, in this case, don't react under high heat – so you get a strong, clean weld as intended.

tig welding machinery in the brompton factory

Spotless tubes

It's not just oxygen and nitrogen that compromise the strength of a weld, even the tiniest bit of dirt contamination causes problems.

Before building the frames, we meticulously clean every titanium tube with acetone to make sure it's free of dust particles and fingerprints.

machinery used in tig welding to clean titanium tubes


Every joint of the frame is welded at a precise angle - there's no room for error as this dictates the final geometry of the bike.

To achieve the designed angles, our tooling engineering and manufacturing teams work together to develop and build bespoke jigs for each section of the frame.

These jigs hold the parts of the bike at the perfect angle while allowing the welder to move around and get up close.

bespoke jigs for tig welding

The beauty of the weld

TIG welded titanium joints have a silvery bead; at times, it almost appears to have a mirror finish.

Every TIG welder has a signature style making each weld unique. Their beauty is appreciated outside of engineering, with artists often choosing them for sculpture welding.

roller nut machine roller nut machine

The Brompton Roller Nut Machine

A man's tattooed hand unscrewing a hinge clamp on the T Line Brompton folding bike A person carrying a folded Brompton T Line bike in a studio
Our P Line and T Line Bromptons are made with titanium parts. Learn more about these lightweight folding bikes.

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