How engineers can unlock the full potential of lightweight solutions
4 min read
Clichéd as it may sound, some of the best engineering minds in the world are thinking hard and losing sleep over the matter of getting more 'bang for their buck'.
Much of the talk these days centres on using materials to get lighter end products. In most cases this boils down to efficiency. We need to reduce the costs associated with various kinds of transit and transportation, which comes down to making fossil fuel go further. Engineers are increasingly being asked to work even smarter and, as resources shrink, most sectors will eventually have to get on board. The automotive and aerospace sectors are for now leading the field in many developments, so what advice can they pass on? "Our focus every day is on mass saving," says Patrick Wood, director and head of engineering and industrial operations at Astrium Satellites. "Customers are looking for very high reliability and very high performance. Space systems do not have the same aesthetic demands as other industries. Our customers just want highly-integrated engineering solutions." This emphasises the point that a lightweight solution is not simply a material in isolation, but a systems design philosophy that must take into account the inherent properties of materials from both a structural and manufacturing point of view. And lightweighting is not purely about technical hurdles. One of the biggest problems is cultural. Any engineer who designs and specifies a product to be made with an unfamiliar material in a completely different way that demands new tooling is going to see more than a few eyebrows raised along the way. One vital lesson that has been learned by both the aerospace and automotive sectors is that for lightweighting to really work, top-level management must buy into it and show solid support for its engineers. Aircraft manufacturers Boeing and Airbus have shown this buy-in and have made a sustained move toward lightweighting that has been implemented and supported from the highest levels of management. Both have now successfully developed primary composite structures for their next generation of aircraft, but both have also experienced significant problems and delays along the way, encountering unforeseen technical challenges and escalating costs. This is another key issue with lightweighting: while its implementation is essential, for the moment it is neither cheap nor easy. To the layman, the design of a civil airliner has not changed all that much in 50 years: it remains a cigar tube with low-mounted wings and a tail plane. Of course this is a gross oversimplification with the Boeing 787 Dreamliner and Airbus A350 showing some of the most advanced engineering capability of our day. However, the layout is fundamentally an evolutionary design based on a structure that was originally conceived to be made out of aluminium, not carbon fibre composites. Composite parts and structures now account for 50% and 52% of the Dreamliner and A350 respectively. The point is that while materials might seem to present fantastic new opportunities, it is important to be sure of each step forward and not get lost in the excitement. While military aviation has been more able to embrace new layouts enabled by material technologies, something like a blended wing body for the airline industry has been deemed too radical. Indeed, despite flying some scale prototypes, Boeing has shelved its development plans for a blended wing airliner. Colin Sirett, head of research and technology at Airbus, says: "Certainly in aerospace, we are at a watershed in terms of how we approach the design and build of aircraft. But, this is down to how we introduce new materials and manufacturing techniques. "It is not so much a question of whether the technology is here, but about the willingness of industry and companies to apply it. In a lot of cases we are asking for completely different methods and approaches. It is often the technology part that is the easy bit." The further use of composites could unlock as much as 20-25% latent improvement in Airbus' manufacturing capability. An example is the possibility of reducing the 60,000,000 holes Airbus UK alone drills each year. Composites allow the possibility of larger, single-skin parts and Airbus wants to achieve a smooth skin by eliminating the rivet heads and fasteners that are often visible on the outer surface. Aerodynamics is key for any material to be embraced by the aerospace industry, but this must be considered against manufacturability and structural design from day one. "You can't treat any one aspect in isolation," says Sirett. "It is pointless coming up with an application of a new material that is incredibly lightweight if you haven't got the tools to properly design, simulate or make it. What is absolutely key to a lightweight solution is a complete integrated design and manufacture process." Jaguar Land Rover has been at the forefront of the lightweight challenge and has been something of a trailblazer with the application of aluminium on its cars. However, it differs from the aerospace industry in that the aesthetics of its vehicles are absolutely vital. "Our products sell on how they look, that is fundamental," says Dai Jones, architecture leader – research (senior manager) at Jaguar Land Rover. "Our designs have been both evolutionary and revolutionary. The body construction used on the Range Rover has gone from steel to aluminium. So we still press them but there are considerations with the different performance of material through pressing and simulation. "We have the largest single-body side pressing on the front edge of the front door all the way to the rear tail lamps. That pressing made out of aluminium was traditionally made out of three or four pieces. Now it is made out of a single piece as the optimisation and simulation techniques have improved enough to allow us to do that." Lightweighting is not just about taking material considerations on board, but is also about optimising parts and components. Can several parts be integrated in to one or deleted all together, can anything be downsized, what has been over designed or designed with too much performance. For example, does a seat really need four or five motors to adjust its position? However, even with the best design engineering and materials, there are limits on how much economical optimisation is possible before a step change is necessary. Jones uses the analogy of wringing a flannel. "With the aluminium bodies now we have managed to wring 90% of the water out," he says. "Lightweighting raises the fundamental question of affordability. Most vehicles travel on average 18km a day in Europe. For probably 95-97% of the day cars are sitting on the tarmac unused. In the aviation industry it needs to be the other way round. You want it 2-3% on the tarmac and the runway. So the real question is what can you afford to put into lightweighting?"