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Bentley unveils first fully 3D car

Ian Grant

The first Bentley to be designed and built completely in silicon will reach dealer showrooms within the next few months.

The £200,000 Mulsanne is also the first car the Bentley factory has designed and built purely of its own volition for 80 years. It marks a return to the traditional Bentley values of elegance, comfort and stomach-hollowing power in a big package.

These values have already won it pre-production orders of 800, roughly a year's production of the part-robot, part-hand-built vehicle at its home in Crewe, Cheshire.

The Mulsanne is a radical change in the way Bentley makes cars. Before one nut was ordered, the car was designed and built as a 3D digital model using Dassault Systèmes PLM software.

John Unsworth, head of computer aided design strategy at Bentley, said the company wanted to reduce the number and effect of late engineering changes in the production of vehicles. These cost vast sums because of the impact they have on all the preceding processes, related parts and assembly procedures. Reducing them cuts waste and improves profitability, he says.

This meant integrating all the information about the car, its components and assembly processes, and making it available to designers, engineers and production staff so that they could all work on parts and processes in parallel. Previously, all operations were sequential, and there was little or no communication between the departments until problems arose.

 


 

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Unsworth said, "We have one set of data accessed by all departments from styling, concepts, digital design, engineering and manufacturing. No longer do we manage separate data silos across departments."

Bentley is storing the data, including engineering change history, in a centralised Enovia database and feeding it with design data from the Catia v5 design suite. The system also takes in 3D information about the body surface shapes from a robot sensor. All the teams can access and author data from the Enovia database to make informed decisions without the need for a data preparation exercise, Unsworth said.

Engineers use the data with Dassault Systèmes' Delmia product lifecycle management tools to ensure that the factory can actually build the vehicle. Unsworth said it was crucial to test part-fit clearances, tool and hand access.

"Without the modelling tools we would not be able to verify processes in advance. But with it, we can verify and optimise the build process before any physical parts are available," he said.

For example, Bentley used Delmia to model how to fit a new floor in the boot of the vehicle. The only feasible way would have meant raising the back of the car six feet into the air. "Not an optimum solution on a production line," Unsworth said. So the engineers rethought the part to make it easier to fit.

Ian Swann, who was in charge of the virtual build, said it changed the way people worked, not least because it prompted Bentley to spend €27m on new kit and to revise its factory layout so that there was less physical distance between the different teams. This physical proximity has improved communication between the teams.

"We had a lot of review meetings," he said. "At first the production guys were sceptical, but when they saw that it was going to make their lives easier, they jumped in."

Can't build CAD car

According to Unsworth, the perfect computer-designed car could not be built. "There are always compromises to be made for style and parts," he said. Those compromises and the trade-offs they represented mark the difference between the car makers world-wide.

Despite Bentley's prestigious heritage, Unsworth happily admitted that the Mulsanne contains parts from other divisions of the parent VW empire. "If they represent the state-of-the-art or the best design, it would be wrong not to use them," he said, before adding, "but there are fewer than you might expect."

While access to the VW parts catalogue helped the engineers, it is the styling and trim designers that are the heart of Bentley, the custodians of its values, said Unsworth.

The Mulsanne consists of some 10,500 parts that take 831 processes at 30 stations to put together. And with more than a billion options available to buyers who wish to customise their car, it clearly requires a computer to trace and track those decisions from order to delivery.

"It's true that [working in CAD] you lose some of the tactile feeling," he said. But being able to check parts for clashes, for fit, for assembly procedure before they hit the production line more than made up for it.

Bentley will build all future cars in silicon before it starts physical production. The firm now has 500 Dassault Systèmes PLM seats, of which just more than half are used at any time.

It also plans to extend access to off-site suppliers and to the dealer network. "Having the data all in one place makes it easy to share," Unsworth said. This also proved true for making the dealer and owner manuals. This usually takes months and costs a fortune, but boiled down to an editing job, he said.

Unsworth paid tribute to Bentley's management. "Without their sponsorship we wouldn't have got off the ground," he said. But it has taken several life cycles of the CAD system to get to this point. "This [CAD] project will never be finished," Unsworth said.

Next steps are to bring the dealers on board and later to model the factory's machine tools, staff positions, and parts flow to work stations on the factory floor.


Custom quality

Conventional metal bending was unable to cope with the Mulsanne's front wing, which features very complex surface geometry. So Bentley adopted a manufacturing procedure from the aerospace industry called superforming to make the part. This involves heating aluminium sheets to 500ºC so that they become plastic, and vacuum-forming them onto a preformed shape.

This requires smart software to cope accurately with the changes in dimensions and material strength of the sheets as they are formed and cooled.

 

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