Vehicle lightweighting: The road to sustainability

In a world beset by climate change and multiple challenges, the automotive industry the world over is undergoing a radical transformation driven as it is by the twin imperatives of reducing its environmental impact and meeting stringent emissions and safety standards. While companies have been evaluating and adopting various measures to produce more efficient vehicles, lightweighting has emerged as a key methodology to slash vehicle weight.

The engineering mantra not only enhances fuel efficiency, particularly important in the era of Corporate Average Fuel Efficiency or CAFE norms that govern several global markets, including India, but it also directly contributes to reducing CO2 emissions. What’s more, it also enhances vehicle safety with the use of various advanced materials such as high-tensile and ultra-high-strength steel, that are lighter yet stronger.

EVs push the lightweighting envelope

As per industry studies, a 10 % reduction in a vehicle’s weight can result in 6-8% fuel economy improvement, as by the laws of physics, lighter vehicles require lesser energy to accelerate and maintain speed and therefore consume less energy. As automakers strive to comply with the ever-tightening CO2 emission targets, this drop in fuel usage directly correlates with a reduction in the vehicle’s greenhouse gas emissions, thereby making lightweighting a vital strategy to conform to the latest emission standards, as well as inch closer to the overarching goal of sustainability.

Furthermore, as the mobility ecosystem shifts towards zero-tailpipe-emission vehicles or EVs, the lightweighting methodology gains even more importance as range optimisation is amongst the biggest problems for engineers to solve in the EV domain. A lighter EV offers more out of every charge and, therefore, higher range is a key product USP to determine the market penetration of this emerging drivetrain technology in the automotive sector.

By reducing EV weight through optimised use of innovative light but strong materials like high-tensile, and ultra-high-tensile strength steel, and composites, manufacturers can either extend the range of their vehicles or even reduce the size and cost of the battery pack, required to achieve a certain range. A smaller battery makes EVs more affordable and practical, further accelerating the shift from internal combustion engine (ICE) vehicles to electric mobility.

In addition to environmental benefits, lightweighting also enhances the vehicle’s driving dynamics and safety as lighter vehicles typically exhibit better handling and acceleration due to the lower centre of gravity, thereby improving the overall driving experience for the consumer. The usage of certain advanced materials such as high-tensile- and ultra-high-tensile steel helps reduce vehicle weight, while maintaining or improving its crash performance.

Key challenges

Regulatory compliances around the world have set ambitious targets for fuel economy and emissions. For instance, while the European Union has mandated a fleet-wide average of 95 grams of CO2 per kilometre from 2022 to 2024 for the passenger vehicle segment, in India too, the CAFE-III norms that kick in from CY2027 mandate a similar emissions requirement.

According to CV Raman, Executive Committee Member, Maruti Suzuki India, “These stringent regulations mean that both the development time as well as complexity inside vehicles are increasing. Having said that, we must look at the problem not just from an efficiency perspective, but from a broader greenhouse gas (GHG) emissions perspective.”

Moreover, in comparison with compared with Europe, India’s GHG emissions from the transportation sector are significantly lower. While the transportation sector contributes 29% of the GHG emissions in Europe, in India it only stands at 13%. Furthermore, passenger vehicles in India only contribute 2.2% to the nation’s GHG emissions, while it is over 15% in Europe. “Therefore, for our unique challenges, we require India-specific solutions to solve the GHG emissions problem,” said Raman. It is here that to achieve the significant weight reduction required for sustainability goals, the automotive industry employs a range of strategies to slash the kilos and shed grams from every possible area of a vehicle by leveraging advanced materials, innovative design approaches, and cutting-edge manufacturing processes.

However, this rapid shift to such sustainable materials and products is also leading to a significant increase in the final cost of the vehicle, thereby making it a difficult task for them to be sold, particularly when they are targeted at price-sensitive buyers. According to Ritesh Agrawal, SVP and Head – Sourcing, Auto Sector, Mahindra & Mahindra, “Beyond a point, particularly when it is guided by stringent norms, one must bear the cost of lightweighting. It is a well-accepted fact that for every kilogram of weight reduction in a vehicle, there is a cost increase of up to five dollars.”

Optimising the supply chain is also a key concern when dealing with some innovative and advanced materials that might not necessarily be locally available in a geography. For example, ultra-high-strength steel (UHSS) which offers superior strength compared to regular steel, is gaining popularity in the automotive industry, but is locally unavailable in India due to the“lack of economies of scale,” as per Agrawal.

Advanced materials, design, lightweighting processes

Selection of materials plays a critical role in lightweighting, and some of the key materials widely accepted in the automotive industry include Aluminium, high-strength steel (HSS), ultra-high-strength steel (UHSS), magnesium, and carbon-fibre-reinforced polymers (CFRP), among others. While aluminium is widely used for its high strength-to-weight ratio, it is also increasingly replacing traditional steel in many automotive components such as engine blocks, crankshafts, and heads. However, there is a cost attached to this since aluminium is priced higher than steel. On the other hand, with a density about one-fourth that of steel, magnesium is one of the lightest structural metals available, and is also being used in applications such as transmission cases and steering wheels.

Carbon fibre-reinforced polymer composites, which offer dual benefits of very high strength and lightweight, are ideal for high-performance vehicles but are also expensive. Although traditionally CFRP has been used in high-end sports cars, advances in manufacturing techniques are making it more accessible for mainstream models as well. Despite material technology being a strong pillar of the lightweighting exercise, it is not complete without innovative design, which is also crucial in reducing vehicle weight. As a result, topology optimisation, which leverages computer algorithms to optimise the material layout within a given design space, helps improve the structural efficiency of a part, or monocoque, thus, reducing weight.

Moreover, multi-material design that deploys the strategy of combining different materials in a single component to leverage the strengths of each material also helps minimise weight. Furthermore, by integrating multiple functions of a vehicle into a single component, OEMs can reduce the total number of parts and, consequently, weight. For instance, several independent ECUs are now being replaced by a central ECU or a zonal architecture, particularly with the advancing E&E architectures in electric vehicles.

Lastly, advanced manufacturing processes are also essential for turning lightweight designs into reality. Some of these commonly adopted processes include hot stamping which involves heating steel blanks before stamping them into complex shapes. This process allows for the use of UHSS that are difficult to form at room temperature, thereby resulting in lighter, yet stronger components.

A recent entry into the lightweighting world is that of additive manufacturing or 3D printing, which enables the creation of highly optimised, complex shapes that would otherwise be impossible to produce with traditional manufacturing. Furthermore, hydroforming too, is an industrywide process that uses high-pressure hydraulic fluid to form metal parts into lightweight, and strong structures, often used in automotive chassis and body components. All in all, lightweighting — which is now a megatrend in the global automotive industry — is a critical strategy in OEM and component manufacturers’ quest to meet their sustainability targets. The adoption of advanced materials, innovative design approaches, as well as cutting-edge manufacturing processes are now facilitating significant weight reduction across the industry. This engineering methodology will continue to evolve in the coming years and continue to address the industry’s focus on reducing vehicle weight towards meeting the broader goal of mitigating climate change.

This feature was first published in Autocar Professional's June 1, 2024 issue.