1) Battery enclosure concepts dominate the IABC agenda
2) Plan for bigger EV batteries & less expensive materials
3) Mixed materials are here to stay
4) Price parity by 2024: BEVs & ICEs
5) 3D roll-forming & 3D printing for innovative profiles
Body in White for 2020 Chevy Corvette
The biggest topic — by far — at the USA 2019 IABC Congress was battery enclosures for BEVs. To meet the need for increased BEV range, battery cells are getting heavier (Wh/kg) and much more energy dense (Wh/liter). For numerous reasons, it now makes business sense for OEMs to add more battery cells/modules to their BEVs.
However, the bigger and heavier batteries get, the more inventive Body in White (BIW) engineering has to become to safely protect the cells from any intrusion during a crash. Particularly challenging for BEV batteries is the side pole impact test.
Fortunately for designers, battery enclosures are also multifunctional: when combined with the rest of the BIW floor structure, they add stiffness and torsional rigidity, increasing it by over 30% when compared to ICEs (source: Caresoft Global Inc.).
Numerous battery enclosure concepts were presented, including the Docol EV Design Concept with its height-saving, 3D roll-formed beams.
Beyond 2020, lightweighting with aluminum will become more expensive than adding more battery modules, according to Don Malen, University of Michigan and Bloomberg New Energy Finance. And consumers definitely want bigger batteries for longer range and reduced “range anxiety.”
Bigger batteries will require BIWs using ultra high strength steels (UHSS) to absorb the increased energy from higher vehicle mass.
Aluminum battery enclosures are already at a cost disadvantage compared to enclosures made from AHSS and UHSS steels. Improvalue shows a $88 to $110 current advantage per vehicle in favor of an AHSS/UHSS battery enclosure vs. aluminum enclosure. (Assumptions: ideal plant, 200,000 vehicles/year; 5 years of production; and taking into consideration material costs, forming processes, assembly and e-coating.)
The IABC presenters noted that this price difference will likely become larger in the future as EV battery enclosures grow in size and designers become more innovative with AHSS/UHSS solutions. Their recommendation: don’t just carry over the aluminum enclosure design to steel. Instead leverage the specific advantages of AHSS steels for new designs that utilize your existing manufacturing processes — and consider some new steel forming processes, like 3D roll forming.
And even with bigger, more powerful — and heavier — EV batteries, lightweighting will still be critical. For one, OEMs will want to partially offset the additional weight of the bigger batteries. And lightweighting via AHSS/UHSS steels makes much more economic (and environmental) sense than GHG-intensive aluminum and CRFG. Hopefully in a few years we will start to see higher (energy) density solid-state batteries: they will be lighter than lithium-ion batteries but probably also more expensive, so designers will want to stay with economical AHSS/UHSS for the foreseeable future.
Some premium car models (like the Tesla X, S and 3, the BMW i3, and the Jaguar I-Pace) currently use high quantities of aluminum in their BIW, while more cost-conscious models (Renault Zoe, Nissan Leaf, Chevy Bolt) take a mixed materials, steel-intensive approach.
While some premium cars may continue to use high amounts of aluminum in their BIWs, the future seems to be opposite: the mix of materials in cars seems to be increasing, with specific materials solving specific optimization challenges.
For example, the materials list for the all-new platform for the 2020 Ford Explorer’s BIW is instructive:
Mild Steel 24.2%
High Strength Steel 21.4%
Advance High Strength Steel 13.1%
Ultra-High Strength Steel 9.2%
Press Hardened Steel 25.2%
Aluminum – Stamped 0.1%
Aluminum – Extruded 3.7%
Aluminum – Cast 2.1%
Magnesium – Cast 0.5%
Ford presented its BIW topology optimization approach, including their topology analysis of the “bone structure interpretation” for main load path, upper load path, tension beams and compression beams. Its “bionic” back-up structure in the 2020 Ford Escape/Kuga results in the transformation of impact loads into tension and compression — with minimal bending.
For the 2020 Escape/Kuga, key components — including the front structure, pillars, roof rail, and lower back structure — were individually engineered for each major regional market. While these components were specially tailored to meet regional performance requirements, as a group they all achieved optimal mass efficiency.
The 2020 Escape/Kuga is a lighter vehicle than its predecessors. Its design:
By 2024 — and without government tax credits — BEVs will reach price parity with ICEs across all models types and classes due to the falling costs of lithium-ion batteries. The big change that potential EV buyers have been waiting for is almost here: cheaper EVs, with longer range, and sustainable electricity rates
Looked at another way, by 2022, batteries will drop to about $100/kWh, making attractively priced BEVs with 380+ mile (610+ km) range more commonplace.
The 2020 Ford Explorer demonstrates Shape Corporation’s 3D Sweep Forming Technology, which sweeps in multiple planes and directions — all in-line with the roll-forming process. Feed rates are determined by the minimum feed rate for the line’s induction welder. In a single 3D roll-formed process, martensitic steel is custom formed into structural sectional tubing with 3-dimensional bends and an optimized closed profile for the 2020 Explorer.
The Shape 3D Sweep Technology can make sweeps as tight as R 400mm and requires only a minimum 100mm transition zone for the bender to change sweep radii. Bending is decoupled from the 3D roll-forming line to maximize roll forming efficiency and to leverage bender flexibility.
SSAB also highlighted 3D roll-forming in its Docol EV Design Concept for battery enclosures. 3D roll-forming creates the enclosure’s load-carrying bottom using beams that are one part fixed and one part flexible. Then one beam can be placed perpendicularly to a similar profile — that is, turned upside down and placed into a mesh pattern — without doubling its height in the Z-direction, saving space in the passenger compartment.
3D printing (aka additive manufacturing) dazzled conference attendees with highly intricate and innovative BIW components. One example was a steering knuckle, optimized and lightweighted to become 58% lighter when wire printed. Additive manufacturing continues — for now — to be best suited to low-volume models where the savings on both die costs ($250,000 and above) and component weight exceed the cost of 3D printing. Although still unacceptably slow for most components, wiring printing deposition rates are accelerating at a rate that promises the gradual disruption of many BIW component manufacturing processes.