Reducing weight to increase the fuel economy of a vehicle is not a new concept. However, the topic of lightweighting has intensified as government regulation deadlines inch closer each day. Examining the regulations and the different options available for OEMs to achieve compliance, it’s easy to see why lightweighting is gaining in popularity.
A new standard in efficiency
Corporate Average Fuel Economy (CAFE) was enacted in 1975 with the purpose of reducing energy consumption by increasing the fuel economy of cars and light trucks. The National Highway Traffic Safety Administration (NHTSA) has recently set standards that will increase CAFE levels rapidly over the next several years, to improve the nation’s energy security and save consumers money at the pump.
The next major milestone by CAFE requires that automakers must deliver an average fuel economy across their passenger vehicle fleet of 54.5 miles per gallon by 2025. As an average, this requirement won’t mean that every car rolling off the assembly line must get 54.5 miles per gallon. CAFE is measured more generously than the numbers on the window sticker but increasing the CAFE standards does have a significant impact on the fuel economy of vehicles.
Many paths to explore
There are many different approaches to meet the upcoming fuel efficiency standards, including vehicle lightweighting, powertrain efficiency and electrification. OEMs typically use a combination of these three approaches (and a few others) to boost the fuel efficiency of their vehicles.
Vehicle lightweighting: lighter metals plastics composites
Vehicle lightweighting utilises different lightweight materials — including aluminium, magnesium, high-strength steel, plastics & carbon fibre – to replace components on a vehicle to reduce the total weight. A 10% weight reduction in a vehicle typically leads to a 6% to 7% increase in the fuel economy.
Powertrain efficiency: Turbocharging smaller engines advanced controls
New powertrain technologies can also lead to increases in fuel economy. OEMs are turbocharging smaller engines, adding friction-reduction measures throughout the engine and implementing advanced controls, such as, stop-start and regenerative braking systems.
Alternative energy: Hybrids electric vehicles fuel cells
Electrification of vehicles already exists in many forms and will continue to grow. They include conventional engines with supplemental electric motors, conventional hybrids, plug-in hybrids and fully electric vehicles.
The pragmatic choice
With all the different approaches available, OEMs are currently favouring lightweighting because of how relatively straightforward it can be. In its simplest form, lightweighting is basically just replacing existing parts on the vehicle with lighter versions of the parts that perform the same function. In contrast, powertrain technologies and electrification require large engineering investments, advanced vehicle controls and significant changes in the manufacturing process.
A new environmental philosophy
Producing more fuel-efficient vehicles conserves billions of barrels of oil, cuts carbon pollution, protects consumer choice and enables long-term planning for automakers. Over the lifetimes of the vehicles sold to the standards of model years 2017 to 2025, the CAFE program is projected to save approximately 4 billion barrels of oil and reduce Greenhouse Gas (GHG) emissions by 2 billion metric tons, with net benefits to society in the range of $326 billion to $451 billion. In addition, the use of recycled plastic and composite materials by the automotive industry has reduced waste. All these efforts combined will have a significant impact on the environmental footprint of new vehicles.
Why plastics & composites?
Although vehicle lightweighting is not a new concept, the materials and manufacturing processes involved in lightweighting applications are evolving. Cost reductions and advancements in materials are increasing the lightweighting opportunities within vehicles. Improved manufacturing techniques allow OEMs to push the limits and develop parts that were traditionally unfeasible. Plastics are already used in abundance within vehicles; they represent upwards of 50% of a typical vehicle’s volume, but as little as 10% of the vehicle’s weight. While plastics are abundant, many opportunities still exist for lightweighting utilising plastic and composite materials, due to the development of new materials and manufacturing processes.
There are more than 100 different types and grades of plastic used in an average vehicle. These are categorised by their appearance, resistance, rigidity, weight and cost. The three types that make up some 66% of the total plastics used in a car are polypropylene (32%), polyurethane (17%) and PVC (16%).
Increasing strength and stiffness
Plastics can also be reinforced with fibre materials for added strength and stiffness. This is commonly referred to as Fibre-Reinforced Polymer or Fibre-Reinforced Plastic (FRP). Fibre reinforcement generally comes in three basic forms: short fibre reinforcement, long fibre reinforcement and continuous fibre reinforcement.
Specifying the orientation of any of these reinforcing fibres can increase the strength and resistance to deformation of the polymer. Reinforced polymers are the strongest and most resistant to deforming forces when the polymer’s fibres are parallel to the force being exerted and are the weakest when the fibres are perpendicular. Compared to conventional steel, glass FRP composite systems can reduce mass by 25−30%, while carbon composite systems can reduce mass by 60–70%.
Continuous fibre reinforcement offers the greatest strength and stiffness properties, but doesn’t lend itself to intricate shapes, ribs, bosses, bolt locations, etc. To address these shortcomings, fields like multi-material injection moulding or overmoulding technologies (where one material is moulded into another one) are rapidly expanding. In addition, overmoulding is an excellent method to produce lightweight, technical parts and can help reduce production and assembly costs. Wider application of overmoulding plastics components are helping to meet the demands of the automotive industry and leading to many new and more modern design features.
Utilising plastic and composite materials for designs offers more advantages than just the weight reduction of parts. Plastics and composites can also be shaped and formed into very complex shapes and designs that would otherwise be impossible. In addition, opportunities exist to reduce the actual number of components in a design down to a single plastic part. Such components minimise part failure within assemblies, reduce tooling and assembly costs, provide watertight seals if required and can increase sound absorption and safety properties.
A wide variety of plastic materials exist which exhibit a vast range of desirable properties. They can be made with different levels of transparency, flexibility (soft, flexible, or hard), and in almost any shape, size or colour. They can even be heat, chemical and corrosion resistant. They are excellent thermal and electrical insulators but can alternately be electrically and thermally conductive. It is this versatility that makes plastic materials extremely cost-effective in so many different applications. Plastics can be formed using a variety of manufacturing processes, such as injection moulding, compression moulding, microcellular injection moulding, etc. This flexibility in the manufacturing process allows plastics to satisfy a wide range of requirements.
Simulation – key to successful manufacturing, testing and use
Traditionally, automotive designers have a strong experience in designing metal parts, but they tend to lack experience in designing for advanced materials. Additionally, there is a new push to further lightweighting efforts into structural components. Simulation allows designers to fully explore different lightweighting opportunities and gain confidence in their designs before making costly tooling and manufacturing investments.
In order to investigate different lightweighting opportunities within automotive designs, simulation software is essential. Physical prototyping and testing are very costly, time consuming, limiting and generally not feasible due to the demands of the automotive industry. Proper simulation will help ensure the manufacturability of the part and optimise the manufacturing process.
Tools designed for advanced materials
In order to get accurate simulations of advanced materials (like composites), the simulation software application must understand the material properties driven by the manufacturing process. The designer must also be able to calculate the orientation of the fibres that result from the manufacturing process. Fibre orientations controls the strength of the part, so without accurate, as-manufactured material properties, the results from simulations will yield false information and provide little value to the engineer.
Multiphysics/multi-domain analysis for advanced materials
Working with advanced materials requires special simulation tools that make reliable predictions about the performance of a part. The construction of these materials causes them to behave very differently than traditional materials and requires specialised analysis tools. For example, when loads are placed on continuous fibre composite materials, different failure modes can result in matrix cracking, fibre breakage or crushing and delamination. Capturing all these failure modes concurrently within a simulation can be very important for correctly capturing the behaviour of the laminate.
Accurately predicting how a part constructed from advanced materials will perform in practice can require analysis in more than one domain. For example, combining thermal, vibration and composite analysis could be required to get accurate simulation results and predict a part’s behaviour in a particular scenario.
Reducing the computational burden
Setting up multiple simulation studies using different materials and design iterations places heavy demands on local computer resources. One may not even be able to utilise their computer during most simulation studies, and the problem becomes exponentially larger as one increase the number of different materials and design iterations.
In order to reduce the computational burden on the local computer, one needs flexible solving options to simulate where and how one wants to reduce the computational burden, based on the needs. Many professionals use their local resources to iterate and optimise their setup for an analysis. Then, when they are ready to kick off a longer, more computationally intensive simulation, they use the power of the cloud and free up local resources for other tasks. Autodesk offers software tools and capabilities to assist manufacturers with creating accurate simulations for their lightweighting initiatives.
Courtesy: Autodesk Inc