How Falcon Heavy rocket from Elon Musk's SpaceX company used technology invented by TWI
Steve Dodds explains how TWI at Granta Park pioneered technique now used in spacecraft, Tesla cars and the Apple iMac
If you’re going to launch the world’s most powerful operational rocket into space, then it must be reassuring to know that technology pioneered in the Cambridge region is holding things together.
So it was for Elon Musk, whose SpaceX company launched Falcon Heavy from Kennedy Space Center in Florida on February 6, and with it potentially a new space race powered by private companies.
Carrying the billionaire tech entrepreneur’s own midnight cherry Tesla Roadster as a dummy payload, complete with mannequin ‘Starman’ in the driving seat, cameras around it to capture some extraordinary scenes and David Bowie’s Space Oddity playing on a loop, Falcon Heavy has the capability of carrying 64 metric tons (141,000lb) – a mass greater than a 737 jet complete with passengers, crew, luggage and fuel.
Only NASA’s own Saturn V rocket, last flown in 1973, has delivered a heavier payload into orbit, opening up the possibility of launching larger US intelligence and military satellites, batches of satellites to help deliver global broadband, huge telescopes or bigger robots to Mars, Jupiter, Saturn and their moons.
SpaceX says it also restores the possibility of flying missions with crew to the Moon or Mars – and Falcon Heavy features cost-effective reusable launchers, which deployed retro-boosters to land back on Earth rather than being dumped in the upper atmosphere and breaking up over the oceans.
It’s an extraordinary – and extravagant – achievement, costing some half a billion dollars. And it employed some technology invented by TWI (The Welding Institute) at Granta Park in Great Abington back in 1991.
Friction stir welding was used on the first break-off tanks of Falcon Heavy and has become widely employed for space applications.
Steve Dodds, section manager for friction and forge processes at TWI, told the Cambridge Independent: “It’s a solid-state welding technique. When you see normal welding, you create a melt-pool – which is liquid between two plates – then you let it cool. It freezes and joins the two plates together.
“What we’re doing is completely different. We’re not getting it anywhere near as hot. We are rubbing the parts using a tool. We’re getting them so hot that they go soft, but they are still solid: it doesn’t flow. It’s a bit like Play-Doh or plasticine – it needs pushing around. We mix the two materials together.”
This viscoplasticity helps ensure a strong weld.
“Because you’re not turning it to a liquid state you are not causing anything like as much damage,” explained Steve.
“This is important because when you make a product, you normally make the weld to be the fattest part because you know it’s going to be the weakest. It has to be thicker to compensate for the weakness.
“But with the technique we invented, you’re not creating all that damage, so your whole product can be lighter and slender.”
This is ideal for space applications, of course, such as the Falcon Heavy launchers.
“More importantly for spaceships you can join materials that are really desirable that you can’t physically weld using a melting technique because they don’t stick together afterwards,” said Steve.
TWI patented the technology back in the 1990s. The patent expired after 20 years but the company has continued to evolve what is more properly referred to as a forging technique, rather than welding – think ‘fitting horseshoes’ rather than ‘flying sparks’.
“One of the first major advantages of friction stir welding was that it allowed the use of 2xxx-series aluminium for space flights,” said Steve. “These weren’t available before because you couldn’t join them in other ways so this totally opened up the use of lightweight, super-strong alloys for space flight.
“We worked very closely with Boeing on the Delta II rocket launcher tank, with the first super-size demonstrator tank here at TWI. It was the seminal use of it. From there, it spread like wildfire and we’ve helped the majority of rocket booster manufacturers.
“The latest is that we can friction stir weld titanium, which is very desirable. Once you get a satellite up there, you have to have a number of small tanks which hold the fuel to give it spurts of direction change to help it in orbit.
“Recently, TWI, the ESA (European Space Agency) and Airbus created the first friction stir welded propellant tank for satellites, and we’ve won awards for that.
“It’s extensively used in the structures of launch vehicles and spacecraft. Now you can get rid of rivets – you don’t have to drill a hole or fill it with a heavy material.
“Unlike the melting technique, you don’t have to put a wire in, you use the two plates as they are so you are not adding or taking away weight – it’s net neutral.”
Typically offering a lower cost, more environmentally-friendly and energy-efficient process, friction stir welding provides great tensile and fatigue strength.
Little wonder then that it has been adopted for a host of applications – including by the automotive industry. Elon Musk’s Tesla company transferred the technique and equipment from SpaceX to its electric cars.
“The automotive industry are very interested because there is a shift towards aluminium cars,” explained Steve.
“Normally you can only weld two of the same types of aluminium, but on a car you want the door to be stronger by the hinges, so you might need a thicker material with a bit more resistance, and in a more complicated part of the door you will want a formable material for aesthetic appeal.
“You can’t join these using standard techniques very easily. But friction stir welding opens up the opportunity for exploring the joining of very different metals together so you can do selective design or tailor-welded products, which put the right material in the right place for the right application.”
Also employed on jets such as the Eclipse 500, in ship building, on the Victoria Line on the London Underground, in high-end audio speakers, nuclear waste canisters and even in the Apple iMac, friction stir welds are now all around us.
“It’s extensively used around high-end, lightweight, elegant products,” said Steve, who added that TWI continues to develop the technique, with 16 staff in the section at Granta Park and in Sheffield.
“The advances that we’ve made are in the particular materials we can use. We can now friction stir weld steel, zinc, aluminium, titanium, copper and lead and we can even friction weld wood together,” he said.
It’s another global success story for TWI – or, now that SpaceX has used the technique, should that be galactic?