Early prototyping benefits Bentley

Making the most of rapid prototyping technology early in the design process is bringing significant benefits to luxury car manufacturer Bentley Motors. Justin Cunningham reports.

Bentley Motors has a reputation for excellence when it comes to the design and engineering of luxury cars. So it is probably no surprise that it has been making use of rapid prototyping technology from the early days. It found that Laminated Object Manufacturing (LOM) allowed the production of under-bonnet parts that could actually be used for de-mist and air-conduit testing. The result was that the overall testing programme came in early and under budget.

The revelation meant that it wanted to expand its in-house RP capability, and made concerted effort to use the technology as early as possible in the procurement process. RP, for many firms, is an activity that can often happen at the end of the design process; to prototype. The physical representation is often used to proof a design before it becomes productionised for manufacture. However, Bentley, has found enormous benefit in bringing the process forward, and using rapid prototyping technology for much earlier design work.

David Hayward, operations and projects manager of the design studio at Bentley Motors, says: "We would have started the design process with a sketch and then worked through to a physical model at the end of the process. But that process has changed dramatically. Now, our rapid prototyping starts at the front end, as soon as we move from 2D into 3D."

The physical representations, albeit to scale, are critiqued and reviewed like never before in what Hayward describes as desktop reviews. As well as making use of things such as the 'Power Walls', wall-sized 3D projections of CAD models, the ability to hold a physical model, and compare physical scale models with competitors' cars is proving invaluable.

Until about 2010, most of the parts that were produced through rapid prototyping were outsourced to specialist firms. However, due to the increasing spend on rapid prototyping from around £75,000 to approximately £500,000, Hayward and his team wanted to bring that expertise in house. As a result it purchased an Objet Alaris printer specifically for the design studio.

"After we had the Alaris about a year, we thought we needed to do more with it," says Hayward. Using an optical scanning system from German-based GOM, the company would very accurately scan competitor vehicles, and then reproduce them as 1/10th scale models, for comparisons with its own conceptual designs.

He adds: "We were doing 1/3rd scale models later in process in clay, but what we now have is the ability to do 1/10th scale models that we use as desktop reviews."

Clay modelling has always played a big part in Bentley's design and production process, and continues to do so. However, rapid prototyping has significantly increased and RP parts are being used on both the interior and exterior of clay models to be more representative of how the product might finally look.

During the early design phase of what became known as the Bentley Mulsanne, the company used rapid prototyping on both the front and rear lamps of a clay scale model and also the wheels. Before this clay moulds were used. "Rapid prototyping tools give a much better and more representative look and to what the car will actually be like when we go in to a design review," says Hayward.

To further its capability the company has also recently brought an Objet Connex500 to enable the rapid prototyping of softer parts. "The whole purpose of us buying the Connex was the rubber side of it," says Hayward. "It means the design studio can start looking at the door seals and moulding those on the Connex machine to put on cars and scale models. This enables us to do things like water and moister tests and wind ingress tests. So we can start doing very early upfront testing and actually build that into the design process.

"We can also use it to make 1/10th and 1/3rd scale rubber tyres so the scale models can be much more representative in terms of what they will look like. The possibilities are endless in terms of the mixture of hard and soft materials."

Once the external themes have been finalised, the process then moves up to full scale representation. This might involve a full scale clay model of the exterior, but is increasingly involving the interior as well. This gives the distinct advantage of allowing the design teamto give early consideration to the ergonomics of the vehicle, long before its engineering and production departments have chance to get hold of the design.

"That gives people the opportunity to sit in the car and get a feel of what it is going to be like three to four months in to a program," says Hayward. "Already we are starting to look at the ergonomics and are using real parts."

About six months in to a project there is another design review. Although the same clay models are used, they are much more representative. To aid in this, 3D printing technology is used extensively to replace clay parts. The models also have a real painted finish so they give a very accurate depiction of what the final car design might look like on the road.

This is the same for the interior as well. More rapid prototyping is done; the seats recline, the rear consoles have air compact seats and although it is not functional to the full extent, it does give a good portrayal of the layout, which can be used by the designers.

Overall, RP enables engineers to be analytical and evaluative of the ergonomics, general layout and 'feel' so they can make changes. Although the changes might be subtle, these iterative improvements have perhaps in the past been the sort of thing you might see on MKII production models. But, the physicality of it all, makes the design improvements much more obvious when compared to a 3D CAD model. Having it there, in front of you, enables these subtle but important design steps to be taken earlier. And that is exactly what you would expect from a premium brand like Bentley.

"After 18-24 months that was usually the final stage for us," says Hayward. "Engineering came in, the design would be signed off and it would go forward to that team to look at the feasibility of the parts that we had designed. However, we are now able to go a phase further and actually produce a track vehicle.

"This has got a rollable chassis, is engine based, and although it doesn't do the 200mph that the production car will, it gives the board a representation of what this car is going to look like on the road."

To make the rolling chassis as representative as possible, the door handles, the door mirrors and exterior chrome, are all made from 3D-printed models. And many of these parts are fully-functional representations of how the production part is actually going to look and function.

"So many of the parts are made through RP processes," says Hayward. "And they actually function; the indicators and the headlamps work. Whereas before many of these parts were only ever moulded in clay on a static vehicle."

Justin Cunningham

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