It all starts with titanium - and plenty of it.
"We had to buy about ten tonnes of high-strength titanium within one-and-a-half months, and receive it all in time and in perfect condition," says Steffen Zacharias of Germany's CP Autosport, one of the three manufacturers chosen by the FIA to be official suppliers of the new halo safety device.
'High strength' means Grade 5 titanium, which is used extensively in the aerospace industry owing to its near-optimal balance between structural stiffness and weight. But this comes at a cost, and not just in terms of expenditure on raw materials: titanium is a difficult and demanding material with which to work, which is why so few manufacturers made it through the tendering process.
"We have a long history in motorsport, having been involved since the 1990s, but we have an even longer background in aerospace materials and fabrication," says Zacharias. "We've been building titanium parts for aerospace and for outer space - for the EU's Ariane rocket programme - and this background is where we come from and it's how we ended up in Formula 1."
This experience put CP on pole when it came to producing the halo prototype for FIA testing. Alongside the UK's SSTT and Italy's V System, CP were tasked with building a prototype within 6.5 weeks to be tested at the UK's Cranfield Technical Centre in October 2017. They were the first company to pass the test and have been chosen by nine of the 10 F1 teams to supply halos this season - although some teams have purchased devices from all three companies.
It helps that CP's manufacturing facility was ideally suited to the task. "You need state-of-the-art machining parts to do the pre-machining and the post-welding final machining," explains Zacharias. "You need a welding chamber in a closed atmosphere for the welding process, and you need the supply chain for the material."
One of the key challenges with titanium is that it has to be heat-treated to achieve optimal strength before you start working it. CP generally receive forged blocks that have been pre-treated to an individual specification to help withstand the loads the finished device will face.
"Heat treatment is one of the technical tricks you need to bring in to make the parts work as they're supposed to" CP Autosport's Steffen Zacharias
"We've been given a challenging load case to which the halo should perform in the physical test," says Zacharias. "One thing to give a part function is the geometry, but when it comes to welding and metallurgy the heat-treatment process is one of the key drivers. With the heat treatment you set up the physical strengths of the part in combination with the geometry."
The next step is to pre-machine and gun-drill the tubes that will be welded together. The halo itself is built from five different parts. The half-ring at the top is made from two quarters of the circle. Then there are the two end pieces that attach to the back of the car and the centre pillar in front of the driver.
The welding process is performed in a closed chamber to prevent any foreign objects contaminating - and therefore weakening - the joins. The whole device then undergoes further heat treatment for additional strengthening before it's sent for testing.
"The challenge is in forming the tube in this titanium Grade 5 condition without weakening it," says Zacharias. "And then having the heat treatment in the right set-up. Heat treatment is one of the technical tricks you need to bring in to make the parts work as they're supposed to."
Only the reference production device is tested to destruction at Cranfield. Each subsequent device is made from an exact process sheet that is approved by the Global Institute for Motor Sport Safety, the FIA's safety research partner. But every device is geometry-checked, weight-checked and undergoes non-destructive testing, including x-rays and crack benchmarks.
"We do these in-house," says Zacharias. "Coming from the aerospace industry, we have a very intense testing area, including physical test benches and life-cycle testing. All our parts are tested in-house by certified people to an aerospace standard."
The x-ray test involves an approved engineer screening all of the welding seams, and this is followed by a dye-penetration test to check for any cracks in the material. Then an ultrasonic probe ascertains whether the wall-thickness of the tube is the same at every point. No area is left unchecked.
Once complete, the halo is manually shot-cleaned to create an abrasive surface that makes it easier for teams to attach any aerodynamic parts that are permitted by the FIA. This does not modify the strength of the material or put any stress on the parts.
All of these steps are essential to producing such a high-performance device. The halo has to withstand 125kN of force (equivalent to 12 tonnes in weight) from above for five seconds without a failure to any part of the survival cell or the mountings. It must also withstand forces of 125kN from the side. Without question, it's now the strongest element on an F1 car.
To achieve maximum effectiveness it has to be fitted to a chassis specifically designed to accept the kind of loads it might transmit
"It's been a task to bring it all together," says Zacharias. "We've been producing titanium structures for years, but to bring it all together - the machining, the gun-drilling of the material to produce a tube with such wall thickness, the welding process and geometry from all five parts coming together, and the heat-treatment process - to meet this precise window of technical function, that was the main task. Each field itself was like what we've been used to, but to nail it down in 6.5 weeks was the hardest task."
It helped that the F1 teams were fully supportive at every step of the way. "I've been in this business now for almost 20 years and I've never experienced such an open-door philosophy from the teams," admits Zacharias. "Every door has been opened."
Clearly the teams have been doing everything they can to help integrate the halo into the design of their cars. Although one priority during development was to minimise weight, it was inevitable - given the impact-resistance demands - that the halo would add bulk to the chassis. Each one weighs 7kg, which in itself isn't a great deal, and yet it's 7kg that wasn't previously positioned so high on the car.
"Adopting it has been a significant challenge," says Mercedes technical director James Allison. "It's several kilograms of titanium that needs to be put on the car, and all of the changes that we needed to do to accommodate it had to be made so that the overall car would still stay below the weight limit."
And although the halo functions like a bolt-on device, to achieve maximum effectiveness it has to be fitted to a chassis specifically designed to accept the kind of loads it might transmit. Allison explains: "We had to strengthen the chassis so that it would take roughly the weight of a double-decker bus sitting on top of the halo to make sure it's strong enough to withstand the type of event it's designed to protect the driver's head against."
That's why each team has bought several halos, some from all three suppliers, to evaluate during the design process. As always in F1, the pursuit of the perfect package is an unceasing whirl of marginal gains.
By the end of March, CP were expecting to have produced and shipped 100 halos. Not only are they supplying nine of the 10 F1 teams, they are also supplying the F2 and Formula E championships, which are then distributing to their teams. F2 is adopting the halo this year, while Formula E will feature it on the Gen2 car that makes its debut next season. Other series will follow. And this level of visibility will represent a new world for a company such as CP.
"We have 200 people working here and we usually produce parts that are underneath the car and covered up by carbon fibre," says Zacharias. "So to be able to show a physical part that's more visible to the public means our employees can say: 'This is what we've been working on, and this is what drives me to stay longer to fulfil my job and overcome obstacles that others may be stopped by.' So yeah, that really makes us proud."
First published in the FIA's AUTO magazine