Lightweighting has become a major preoccupation of all transportation manufacturers, whether an airplane, ship or passenger sedan is to be produced. Regulation to reduce carbon emissions affects all these industries globally, and engineers face new challenges in substituting new, lighter materials for conventional ones such as mild steel, and ensuring that these materials can be integrated into the overall design. The reduction in weight cannot compromise the safety and reliability of the vehicle; where possible it should improve it. The choice of materials varies from high-strength steel and aluminium, to organic fibres from plants such as bamboo and kenaf (Indian hemp).Complexity increases where these discrete materials are combined to form a composite material, such as plastic polymers using organic fibres. Understanding how these materials react under stress and how two parts composed of different materials can be joined have been described as “alchemy”, rather than engineering. Replacing heavier parts with lightweight materials is not mere substitution, lightweighting disrupts the whole product lifecycle, from design to end-of-life.
It’s Not a Perfect World
Under ideal circumstances, every manufacturer in the supply chain would be competing to bring the best and lightest product to market, either as a lightweight material, as a component or as a complete automobile. The reality is that cost determines how far an automobile manufacturer can apply mass reduction to any model. Carbon fiber is a vital material in lightweighting, but the slide below, taken from a presentation by Lucintel predicts that only 5% of light motor vehicles manufactured in 2025 will use carbon fibre extensively, while 95% will utilize very little or no carbon fiber due to its high cost. A cost reduction would have a major impact, but this depends on reducing costs. So while Lamborghinis and Audi R8s contain extensive carbon fiber, designers of the Toyota Yaris still have to look at other more affordable alternatives under the current price.
Source: Major Lightweighting Trends Shaping the Automotive Industry – Presentation by Lucintel at Composites Europe, November 2018.
Some might question whether the growing electric vehicle (EV) market will not render combustion engines redundant, but the reality is that petrol and diesel engines are still going to be around for the next decade. EV manufacturers are also involved in lightweighting, focusing on ways to reduce the weight of the battery, which is a major contributor to the overall vehicle mass, whether in EVs or in hybrids.
Another constraint is the ability to recycle the materials; the rise of the circular economy requires this, and producers that do not comply could be penalized. So the race is on to discover cost-effective materials, test their suitability under stress and over time and utilize them instead of the materials used in current models.
Concept and Design
The choice of a particular material has a dramatic impact on the design process. Before it can be successfully used, extensive testing must be done, most of which will use simulation software, complementing live testing of the material and prototypes. Providers of simulation applications have recognized that new simulation tools need to be added to the simulation toolkit. Altair, a leader in simulation software, has recently acquired Cambridge Collaborative’s SEAM® software. This software has been used by major companies to test for potential vibrations and noise, especially in the vehicle’s interior.
Autodesk University has training on what types of simulation are needed to test thermoplastic composites that contain fibers, where the testing for short and continuous fibers are different.
Testing of a material does not stop once a decision has been made to use it in the new design. Engineers are including sensors to monitor materials and parts in the field. This real-time data is then relayed back to the manufacturer during the lifetime of the product, usually to a digital twin of the part or even the entire vehicle. Any shortcomings can be identified in the virtual version and corrective action or improvements can be applied to the next model. Ansys, again a leader in simulation, has recently teamed up with PTC with their Teamworx IoT platform to support a digital twin solution.
Another new area of engineering is the discovery and design of new agents for bonding different materials and new fasteners where conventional nuts and bolts are unsuitable. Bonding parts, rather than using fasteners, also reduces vibrations and noise. Recent research has developed bonding agents for thermoplastics that are reversible; heat is applied to form the bond and when needed, for instance during a service, the bond id reheated to remove the bond. To re-bond the part, heat can be applied again. the researchers at Michigan University used nanotechnology for this innovation.
Rethinking the Assembly Line
The traditional linear process of the assembly line may be obsolescent. BMW are shifting to a new paradigm which is more flexible and agile. Rather than having a different assembly line for each powertrain, they have rethought the factory floor, so that a combustion engine, hybrid or fully electric car can be produced via a common assembly line. This gives them the ability to take customization up to a new level. Audi too has redesigned their shop floor to cater for future trends in manufacturing.
The use of digital twins facilitates proactive maintenance, impending defects and wear and tear are monitored by the various sensors embedded in the car and reported back to the dealer and company. The vehicle owner can be invited to bring his or her car in for maintenance and repairs as a result. This is already happening at Tesla, where each car produced has its own digital twin, and where a software download is the first prize for any problems, rather than the owner having to bring the car in for attention. When it comes to servicing and maintaining a vehicle, workers will need training in the new materials used and techniques like unbonding parts joined with a reversible bond. It is probable that this will be automated as much as possible, but workers who understand the process and materials will still be in demand.
The End of the Line
The days of cars being relegated to a scrap-heap at the end of their life are over. Parts need to be recyclable to reduce the load on the planet. This is where choosing the right materials during concept and design is important. While the parts must be durable and robust during the life of the vehicle, they must also be easily reclaimable. The energy consumed to achieve this should either be very low or should be offset by inherent qualities of the materials used. Indian Hemp or Kenaf is an example of a suitable material, it is carbon neutral, owing to its ability to extract co2 from the atmosphere and its quick growing cycle of 4 months. Malaysia has invested heavily in growing Kenaf, believing that there will be a vibrant market for kenaf in lightweight manufacturing.
The guesswork and research involved in understanding the new composites and their properties has been reduced by specialist organizations doing the research. Research giant Fraunhofer has created digital twins of materials, which are stored in a materials database accessible to manufacturers making a decision about what materials would work best for the problem at hand. While the intention was to support the additive engineering environment, it is equally effective for other manufacturing challenges.
The developments in lightweighting are not limited to automobiles and airplanes, any manufactured product, from domestic appliances to wind turbines, can benefit either from a reduction in weight and the associated risk for rotor blades. to new composite materials that are superior to those currently used. The reduction in the cost of sensors stimulates the use of digital twins to report on products in the field and creates a continuous improvement cycle.