Twenty-five years ago, the first steel industry collaboration, the UltraLight Steel Auto Body Consortium, launched a global effort to demonstrate what was then the most advanced steels ever produced, High-Strength Steels (HSS). At the time, with just 11 HSS grades available, ULSAB reduced mass by 25% over benchmarks and featured cutting edge technology such as a tailor-welded body side outer that reduced part count from 3 or 4 pieces to one efficient structure (Figure 1). Tailor welding enables the joining of different material grades and thicknesses into one blank for stamping a part, thereby placing higher strength levels exactly and only where they are needed. A one-piece body side outer and tailor welding is commonplace today because of the efficiency it lends to vehicle design and manufacturing.
The four programs that followed ULSAB produced steel innovations that influenced vehicle design and manufacture for the past decades. Steel E-Motive follows this long history of global steel industry collaboration to demonstrate steel technologies that are expected to be commercially available in 2030 and beyond. With the portfolio of steel product and manufacturing processes already available and the addition of those forecasted for future commercial availability, we are expecting innovations that will be a roadmap for future mobility vehicle manufacturers.
Higher strength levels mean steel parts can be manufactured at minimum thickness while still meeting the strength requirements for crash and performance. The results are lighter and more environmentally efficient components because less material is used. But increasing strength and thinner gauges makes forming complex component shapes a challenge. 3rdGen AHSS have increased elongation as well as increased strength. Elongation is a material mechanical property that is the degree to which a material may be bent, stretched, or compressed before it breaks. With high elongation, complex vehicle component shapes can be formed and manufactured more easily, resulting in strong, efficient structures.
The global steel industry is investing significantly in product and fabrication development. High Strength and Advanced High-Strength Steels (AHSS) portfolios have grown from ULSAB’s 11 to more than 50 grades available for use in designing and optimizing Steel E-Motive’s autonomous EV architecture. Third Generation AHSS (3rdGen AHSS), which will have a prominent role in Steel E-Motive’s architectures, are taking strength levels ever higher while addressing manufacturability. Our members are producing 3rdGen AHSS that can be cold-formed with strength levels upwards of 1200 MPa, due to elongations of 20% and greater, which completely opens the manufacturing window of possibilities.
To further assist in the design and manufacture of efficient vehicle structures, new processes such as roll forming and hot forming help fabricate these stronger materials effectively, while often doubling material use efficiency. This means less material is produced for each component, resulting in a significant reduction in manufacturing emissions and, ultimately, an improved vehicle environmental footprint.
Roll Forming takes a flat sheet or strip and feeds it through a mill containing several successive roller dies, each of which incrementally bend the strip into the desired final shape. Incremental forming minimizes certain stresses and strains on the material that inhibit part formation with very high strength materials. Therefore, roll forming is well suited for generating many complex shapes from Advanced High-Strength Steels, even and especially for those grades with low total elongation. Unlike most forming operations which have various combinations of forming modes, the roll forming process is nothing more than a carefully engineered series of bends. Roll forming is appropriate for high-volume applications requiring long, complex sections held to very precise dimensions, such as a bumper, rocker or truck bed (See Figure 2 for more examples).
One of the traits that makes steel such a flexible, revolutionary material is the ability to change its very microstructure with various processes. One such process that is growing dramatically in vehicle manufacturing is hot stamping also known as press hardening. In this process, steel blanks are heated to over 900oC to change its microstructure to a fully austenitic, formable state. It is then transferred to a press where it is formed in its hot condition and then cooled rapidly while it is still in the die to achieve the required properties, i.e., another change to its final microstructure and shape. In this process, a material is made very formable by heating it up, but in the end the finished steel part can be as much as four times stronger than the original material. For instance, a 500 MPa material can become 2000 MPa in strength. Direct hot stamping is used for A and B pillars, floor tunnels and cross beams.
These are just two of many processes that will be a part of the materials and processes portfolio for manufacturing Steel E-Motive vehicle components. (See Figure 3 for more examples.)
The broad portfolio available to our engineering partner, Ricardo, ensures that there are ample configurations of materials and processes available, enabling the most efficient architectures to meet the design and manufacturing challenges of ride sharing, autonomous EVs. Steel has and continues to successfully reinvent itself with the family of Advanced High-Strength Steels (AHSS) and steel technologies, engineered to meet ever-changing vehicle design and manufacturing demands.
Steel’s characteristics of strength, manufacturability, durability, and recyclability align dynamically with the needs of next generation vehicles: the ability to meet or exceed vehicle weight, safety, environmental challenges and multiple use cases, while supporting optimal total cost of ownership