To meet stricter regulations aimed at significantly reducing emissions and improving fuel efficiency, automotive companies must drastically rethink the way vehicles are engineered and manufactured. Lightweighting has been identified by the industry as a critical way to comply with these government regulations. The impact of fuel economy regulations on car design is already evident in vehicles such as the 2015 Ford F150 truck, in which the use of riveted and glued aluminium has replaced a large percentage of the traditionally welded steel structure. These changes are removing barriers to entry for even more weight-efficient materials, such as composites, which cannot be easily introduced into a welding assembly line.
Lightweighting strategies will drive a shift to alternative materials and assembly methods radically different than those used in current steel-welded Body in White (BIW) structures. This seismic shift is unlike anything that the industry has seen in more than 50 years and is causing a fundamental change in vehicle designs. Automotive engineers will be forced to rely more on engineering tools than experience as these new materials and assembly processes are adopted.
Despite being seen as a top strategy for meeting the fuel efficiency regulations, lightweighting vehicles is also clearly viewed as being one of the most difficult strategies. In fact, the top strategy for achieving fuel efficiency and emission standards is reducing vehicle weight.
The spiral impact of decreasing weight
Reducing vehicle weight will be a challenge with respect to many parts of the vehicle, especially highly structural parts such as the BIW, which constitutes a significant portion of the overall weight. Weight reduction strategies cannot independently target individual components because optimal weight reduction can only be achieved with a systems approach to lightweighting. In addition, meeting weight reduction targets will require designing for lighter weight from the start.
Weight reduction of the BIW has a spiraling impact on overall vehicle weight reduction. When companies design for lightweighting, they can take advantage of the weight reduction spiral in which a lighter body results in a lighter chassis, which requires a smaller engine, less battery power or reduced fuel tank capacity, which in turn requires less braking, resulting in additional body weight reductions. Consider the redesign of Ford’s F150 truck with an all-aluminium riveted chassis. Ford was able to find a 450-pound reduction in the BIW, which helped result in a 750-pound reduction in overall vehicle weight with a corresponding 25% increase in fuel economy.
Making the case for composites
When considering alternative materials for lightweighting, carbon fibre composites is a very appealing material because it has low corrosion properties, is naturally light in weight and requires less material to achieve stiffness requirements and meet impact resistance needs, to name just a few of the benefits. But at the same time, there is uncertainty about designing and manufacturing new components with composites. Risks include the relative expense of carbon fibre, lack of composites design and manufacturing knowledge and long manufacturing cycle times for composites parts.
The use of composite materials is expected to grow over the next decade and, by 2025, automakers expect that 60% of their vehicles will be comprised of at least 20% carbon fibre.
The challenge of using composites
If properly designed, carbon fibre composites can offer significant improvement in performance-to-weight ratios compared to both aluminium and steel. For many years, the composite performance advantage has made it the preferred material in many aerospace applications, as recently demonstrated by the Boeing 787. Now automakers are either considering, or have started to develop the use of composites to help them meet their goals to reduce vehicle weight. However, the application of composites in high-volume automotive applications is significantly different from the way that composites are used in the aerospace industry.
Tight packaging requirements in automotive applications drive up part shape complexity relative to those encountered in the majority of aerospace applications. The shorter automotive product time-to-market means faster design cycle times and increasing the frequency of design changes. In addition, a greater variety of material forms and manufacturing processes, including forming, pultrusion and braiding, are also being considered to reduce cost. It is this combination of complex shape, material and process choice coupled with frequent design changes that make the engineering of composites especially challenging in high-volume automotive applications.
To meet such design challenges for automotive composite applications, a tighter coupling is required between analysis, design and manufacturing engineering. A bi-directional interface between the software tools used by analysts and design engineers is needed to facilitate the exchange of information, such as laminate configuration and fibre orientation. This will allow for the efficient assessment of the impact on part performance of changes to part shape material configuration and manufacturing methods.
Considering alternative materials
One of the most obvious ways to remove weight from a vehicle is to consider alternative materials that are lighter, yet strong enough to withstand the impact of a crash. Consequently, it is not surprising that 88% of automakers either have strategies or plan to develop strategies for using new materials.
When considering alternative materials for lightweighting and related material strategies, most companies are considering using a mix of materials. Whether it is an individual hybrid part combining plastic, metal and composites, or a mixed material assembly, a trend for the future is a BIW consisting of some combination of high-strength steel, aluminum, magnesium, plastics and composites.
Complexity of mixed materials
Such a mixed material strategy will also have an impact on engineering tools because software will be required to conduct part assembly complexity tradeoffs, helping determine appropriate joining methods, as well as assessing the balance needed between performance, cost and manufacturability.
As an example, consider a part/assembly design tradeoff in which a single all-composite part is used versus a mixed material assembly. Making the part entirely out of composites may not be feasible due to the complex shape geometry because composite material cannot conform to the shape without wrinkling. Alternatively, the simpler areas of the part could be made from composites, while the more complex portions may be made from metal. However, this comes at the expense of the added complexity of a new joint being added to the assembly process.
Appreciating the value of engineering software tools
Leveraging software to provide insight and guidance on design and manufacturing tradeoffs can save significant time and cost. The impact of joining method choices is critical with a mixed material strategy, and understanding the tradeoffs of joining methods is not insignificant. Consider that when using a single material you may have two or three joining options. If you have five or more material choices available, the potential joining method choices increase to 25 or more! The appropriate joining methods for a particular application will depend on the materials being joined, the relative cost, performance and structural requirements.
In the end, a new generation of engineering software applications that are tightly integrated with existing engineering applications will be required to help select the appropriate mix of materials, joining and assembly methods. The optimal choice will depend on how much a company is willing to pay for performance at a lighter weight. If high performance at a lightweight and high cost is tolerable, then the right choice may be unidirectional hand-laid prepreg composites, such as those used in F1 racing applications. If cost is the main design driver, and reducing weight is less of a consideration, then a traditional steel-welded structure may suffice. However, the appropriate material mix for applications between these two extremes will be more difficult to determine, but no doubt the next generation of engineering software tools will be invaluable in helping users figure that out.
Understanding the impact of vehicle lightweighting
Vehicle lightweighting drives fundamental changes to how cars are designed and built. As alternative materials are adopted for lightweighting, the impact will be felt not only in design, but across all disciplines, from earliest definition to the factory floor and beyond.
Vehicle repackaging with alternative materials will take place, such as in the BMW i3, in which the use of composites enabled a production design without a B pillar. New materials will have an impact on part manufacturing because new methods of part fabrication will be considered. A significant effect on assembly and joining will also occur because welding will be replaced by ‘no sparks’ joining methods, such as gluing, riveting and specialty fastening systems. Software technologies will have to evolve to help you analyse and simulate structural, crash, noise, vibration and harshness (NVH) and durability behaviours of structures that utilise alternative materials and joining methods.
The greatest change may be in the factory. Consider the possibility of a 50% reduction in floor space requirements resulting from more compact fabrication methods made possible by using materials such as composites. Composites may also eliminate the need for painting of some parts, resulting in a reduction of space required for the paint room, which can be a significant portion of a factory.
These changes will affect a variety of engineering software applications used from the earliest stages of analysis and design to detailed design, as well as to the tools used for manufacturing, simulation and PLM.
The automotive industry is facing a period of unprecedented change. New fuel economy and emissions standards are driving significant change across the industry. Producing lighterweight vehicles is one of the top strategies to meet these regulations, but it is also the one that is most challenging.
New material strategies, including the use of carbon fibre composites, will be critical for taking weight out of vehicles. The promise of lightweighting vehicles will only be fully realised if automakers adopt innovative manufacturing and engineering tools and processes that enable them to take full advantage of mixed materials, including composites.
Engineering processes and the supporting software applications must evolve to enable engineers to efficiently make the optimal design choices required to deliver cost-effective, lighter, more fuel-efficient products to market in a timely manner.
In the end, the optimal choice will depend on how much a company is willing to pay for efficiency and performance at a lighter weight. These considerations will help automotive companies achieve the success they need to meet upcoming regulations, creating a competitive advantage.