The Weighting Game

Automotive researchers and engineers are looking for ways to knock the fat off nearly every part of a vehicle in their efforts to achieve higher fuel economy.

“Target the things that are—for lack of a better term—deadweight, because these are the things that drive mass into other subsystems,” says Dr Paul Krajewski, global manager and technical fellow for vehicle mass integration and strategy at General Motors.

Closure panels meet Krajewski’s deadweight designation. “Whatever material you use for door panels, the body should carry those loads. Ideally, get the deadweight first, because that allows you to hit everything else strategically,” he says.

Over the next decade, vehicles will get lighter on route to reaching stricter global fuel economy and emissions requirements.

Jay Baron, president and CEO of the Centre for Automotive Research, says cars are going to be 10-15% lighter by 2025, in comparison to a 2010 baseline.

“And that 10-15% represents several hundred pounds. So that’s a big deal, especially when you look at history. We’ve been adding weight to cars for the last 25 years, every year incrementally. We are clearly at a tipping point.”

Important conduits for engineering lightweight vehicles are the tools to model the various material choices. As Krajewsk points out: “If there isn’t a good material model, over-design can occur. When we were sourcing the composite parts for the new Corvette, it was difficult to get a ‘very good apples to apples’ comparison. Each supplier had a slightly different process and a different material. That made it challenging to be able to predict and optimise early on. This emphasises the need for standard material formulations and specifications in the composites industry.”

The 2015 full-size Ford F-150 marks the first time a high-volume pickup truck will use aluminium for exterior panels. Peter Friedman, Ford Motor Co’s manager of manufacturing research development, comments: “With the new F-150, we decided very early on that we were going to use lightweighting as an enabler to deliver both fuel economy and performance. The 2015 F-150 is aluminium-intensive in the front end, the cab and the box, and the frame is steel, with three times the amount of high-strength steel, compared to the outgoing model.”

According to Thomas Pilette, global vice president of product and process development at Magna Exteriors, multiple considerations factor into a material usage decision. “We’re very well aware of low-cost materials. But what we’re trying to mirror is the performance, cycle time and part quality expectations out of a single set of tools. So it’s really balancing material, process and performance with the understanding that nobody wants to pay more than the current material and the current process.”

Paybacks are proving to be one of the outcomes of industry collaboration. “The steel industry saw the headwinds of the lightweight materials coming and has done a really good job of buttoning down, aligning and working together through the Auto/Steel Partnership. That’s led to some great design solutions and development of new materials,” says Krajewski.

Meanwhile Pilette insists that the automotive industry needs to underscore the concept of reinvention. “We have to make sure that we keep sharpening our advanced development techniques, and make sure that we have the right material and process applications.”

One of the main goals of ThyssenKrupp’s InCar plus (phase 2) project, which the company claims is the largest manufacturer-independent development project by an automotive supplier, is weight reduction. Experts achieved that goal in many areas, including the A- and B-pillars.

The slim A-pillars offer a number of advantages, such as a significantly improved field of vision, high level of passive crash safety and about 10% less weight. The reduction in material usage and new manufacturing technologies ensure moderate lightweight costs of about .85/lb. Integration of the new A-pillar concept into a modular strategy offers possible cost advantages, the company notes. The B-pillars reportedly offer greater safety at lighter weight. A hot formed and roll-clad steel-composite material TriBond 1400 allows for a weight reduction of 2.82 lb (1.28 kg) per vehicle, compared to a tailored tempering B-pillar made of MBW 1500. (Pictured is TriBond 1400 three point bending test setup and result.) The design costs less than .85/lb.

Cold forming also can provide for lighter and cost-effective B-pillars. New materials, such as multiphase DP-K 700Y980T, open up further potential of lightweight design and cost advantages.

Ryan Gehm and Kami Bucholz

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