BEVs are a major revolution in the automotive industry. In order to reduce weight, powertrain electrification, suitable materials and associated manufacturing processes must be considered early in the development phase. This is demonstrated by the example of hot form quenching (HFQ) using a high-voltage battery housing by FEV and Impression Technologies (ITL).
Even considering a more conservative scenario, the share of battery electric vehicles (BEVs) in major markets such as Europe, the United States, and China will increase significantly in the coming years, as shown in Figure 1. According to this scenario, 88% of vehicles sold in Europe alone will be battery-powered by 2040, while electrification in the United States and China is much slower.
It must be possible to integrate the traction battery, taking into account all the effects on weight and the vehicle package, including on ergonomics and modularity. From the traditional Cell-2-Module (C2M) to the highly integrated Cell-2-Vehicle (C2V) concept, choosing the right level of structural integration and the right conceptual approach needs to be a decision that needs to be made early in development and has a significant impact on the overall development and manufacturing strategy. The fully integrated C2V concept enables maximum potential for packaging and weight optimization. On the other hand, it significantly reduces modularity and flexibility and introduces certain new challenges in logistics, manufacturing and assembly processes, and certification.
Therefore, a structurally highly integrated Cell-2-Pack (C2P) approach can be a logical solution and compromise between weight-package and modularity-flexibility.
1. Efficient concept assessment
The FEV Concept Development Process (FCDP) is a combination of a synchronous engineering approach and efficient concept development, which, according to PUGH, uses morphological boxes and a decision-matrix approach to evaluate lean and efficient concepts at an early stage. Figure 2 depicts the three basic phases of concept evaluation. Early and strong involvement in computer-aided engineering (CAE CAD) can effectively assess structural performance and lay the groundwork for structural concepts, as shown in Figure 3. The master section process and simplified surface model reduce the design effort during the conceptual and evaluation phases, thus expanding the possible solutions that can be considered. Additional frontloading through early participation in the simulation of the manufacturing process ensures basic manufacturability from the first sketches and ideas.
2. Case analysis
To demonstrate the potential of thermite forming with the example of a high-voltage battery housing, FEV developed a concept with a C2P approach for HFQ manufacturing specialist ITL. In this case study, the concept development process FCDP approach is used for concept development combined with manufacturing process simulation to assess the manufacturability of an early design.
HFQ is a viscoplastic forming technology that encompasses alloy material clamping, design and simulation techniques as well as HFQ part production. It can form high-strength and ultra-high-strength, heat-treatable aluminum alloy sheets into complex shapes, making it ideal for vehicle lightweighting. HFQ has the highest possible higher formability, enabling downgauging, part integration, and tighter radii optimization. When considering part and layout design, vehicle design teams can use HFQ technology early and use the software plug-in HFQ module for forming simulations to gain confidence in the size, thickness, performance and formability of the formed part of their chosen alloy.
3. HFQ manufacturing process
The manufacturing process (fig. 4) involves heating the formed aluminum billet to solution temperature, followed by rapid prototyping and simultaneous in-mold quenching. This is followed by a second trimming or rapid manual aging operation necessary to achieve the desired strength of the assembled part and allow for a typical mechanical connection. The HFQ forming stage takes place at temperatures from 350 to 600 °C, depending on the alloy, with a cycle time of less than 25 seconds.
HFQ's formability facilitates the production of multiple parts at once from single or multiple blanks, further reducing press force requirements, material requirements, and operating costs – especially tooling capital expenditures of up to 60%. HFQ's extremely high formability enables the integration of a wide range of aluminum stamping parts in the automotive industry. Examples include high-strength superstructures, door closure interiors, track lines, rear wall interiors, light cans, battery housings, and seats. Compared to multi-piece cold-formed components, HFQ also reduces parts through multi-part production**: reducing material waste, part weight, design time, maintenance, and factory footprint by enabling more complex monolithic component designs to replace individual components.
4. Development projects based on HFQ
ITL operates an HFQ Technology Centre in Coventry, UK, where OEMs can find support from design feasibility assessments to full prototype and production part design.
This includes the delivery of HFQ tools and the management of mass production lines. One example is the high-strength 6XXX aluminum body safety unit of the Aston Martin DBX luxury crossover SUV.
The ITL Materials Evaluation Center focuses on the development of HFQ material cards for the HFQ process, working with leading companies to provide lubrication, cleaning and joining solutions. As an example of redefining material usability, Atlas Copco's HFQ 7XXX SPR connection solution can be listed.
High-strength aluminum brings benefits to the automotive industry by replacing cold-formed aluminum multi-piece components and providing a competitive alternative to boron steel, warm forming, and superplastic forming. Reducing the weight of components while maintaining strength is a clear advantage of HFQ. In order to create more space for the battery and thus further improve the range of pure electric vehicles, the advantages of packaging are attracting more and more attention.
HFQ** continues to grow globally through standard technology transfer and access agreements with HFQ's automotive production partners, including the Fischer Group in Germany, Jet Wagon in China, and Telos in the United States. These partnerships are important to provide OEMs with more options. The HFQ Partner Network was established to provide access to a range of equipment vendors and participants in the chain needed to mount aluminium plates onto vehicles.
The technical team developed by HFQ focused on pushing the limits of formability, deepening the draw, and tightening the radius, while reducing the size to accommodate a wider range of alloy grades. Alloy knowledge and the development of material cards that reflect the HFQ forming process are essential to solving OEM design problems. HFQ material cards can be used with commercial forming simulation software and build confidence in formability, damage**, and tool surfaces with the simulations they support. When combined with HFQ tooling and lubrication strategies, they play a key role in HFQ part production.
In 2021, ITL partnered with BMW, Volvo and Constellium to develop and produce large, complex-shaped battery housing covers for extrusion-based concepts, providing insight into the battery design process and where the design strategy of the time constrained packaging.
A recent exterior frame project with FEV demonstrates the type of freedom offered by using HFQ to find better design and packaging solutions.
5. The concept of exoskeleton of the battery shell
During the concept development of the aluminum battery housing, FEV also considered all relevant manufacturing processes, materials and connection technologies. In this project, the potential for the use of HFQ components in the right areas was clearly demonstrated. In general, the HFQ process allows for tight radii and low draft angles in the stamping process. These advantages of the battery housing component design enable the optimal packaging of the battery pack. In order to further increase the package size of the battery, FEV has adopted its patented outer frame concept for the battery housing. The concept takes into account the high structural performance of the outer area of the battery and the high structural integration of the battery housing, which is part of the vehicle's body-in-white (BIW) structure, as shown in Figure 5. Here, HFQ technology can improve structural performance, such as the reduction of the radius and draft angle of the enclosure top cover in the outer frame structure. This maximizes the gravimetric energy density.
Transferring the function and structural performance of the internal beams to the outer structure of the battery enclosure can provide a structural arrangement for the C2P approach, allowing for structural force-flow distribution below the battery pack as well as direct coupling of lower energy-absorbing structures to the BIW. This direct coupling of key structural elements enables efficient load transfer that is not possible with today's traditional battery enclosure technology. The internal space available for the battery cells of this battery pack is kept undivided by structural parts, thus providing the following advantages:
l Compared with existing solutions, the internal battery packaging is maximized and the complexity is lower.
l There are fewer restrictions on the choice of battery shape and type.
l Optimization of the connection between the BIW and the battery housing.
The latter is due to an additional lower battery load path, which optimizes load distribution.
The proposed design offers a level of flexibility that is not possible with other battery packs. By combining all the features of battery and structure integration with the base plate structure, the application of C2P or C2V battery integration is fully selectable without modifying the basic structure of the battery pack.
Six**Alloy.
Alloy vendors also want to know if HFQ has other advantages, whether their alloys are included in the HFQ material card and demonstrate their capabilities. A recent program with GR NGES demonstrated the formability of its 100% **6xxx alloy for automotive and aerospace parts. ITL is continuing to investigate opportunities to utilize higher levels of alloy 6xxx as well as the best materials available in the aluminium scrap market.
HFQ-R is a sustainable solution for aluminum sheet that reduces the broader impact of automotive production. In addition to a higher ** content, a smaller blank size, the possibility of integrating parts and the use of higher strength alloys with HFQ make it possible to produce stronger parts from thinner sheets – all with less carbon in the final product.
The goal of HFQ-R parts is to provide all the formability and performance benefits through super-recycled alloys as part of an OEM's low-cost solution.
SevenSummary.
As an independent engineering services provider, FE is committed to increasing the portfolio of design opportunities through new technologies and processes to design custom solutions for structural components. HFQ has implemented new complex designs and the conceptual development projects carried out have shown potential applications in the field of structurally integrated high-voltage battery solutions. Aluminium and its appreciability can support compliance with carbon emission limits for vehicles. HFQ can be an enabler of the introduction of low-carbon, high-strength aluminum into automotive production.
*：hog, m., kürten, c., offermanns, y. et al. integral battery housing design thanks to advanced simultaneous engineering and hfq. atz worldw 126, 60–65 (2024).
Translation and collation of automotive materials network.