Steel Study Shows How To Lighten Up

A two-year study by this international steel company has come up with a specific array of parts—including the materials and processes needed to transform them into parts—that can achieve significant weight savings without an increase in cost.
#ArcelorMittal #body


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Obviously a steel company—and Arcelor-Mittal (arcelormittal.com) is nothing if not a steel company, as Roy Platz, director of Marketing, ArcelorMittal USA, says the firm is “the world’s number-one steel company,” with over 287,000 employees in more than 60 countries—would be interested in vehicle manufacturers continuing to make their cars with steel. (“Continuing” because, let’s face it, the vast majority of cars are primarily made of the ferrous material, aluminum and polymer-based products notwithstanding.) So it isn’t entirely surprising that ArcelorMittal has undertaken a two-year research program among its six automotive research centers (in France, Canada, and the U.S.), and in cooperation with Spanish hot-stamping expert Gestamp Automocion (gestamp.com) and Italian metalforming specialist Magnetto Automotive, named “S-in motion.” And, yes, the initial “S” stands for “steel,” but it goes beyond that to: saving weight; saving costs; sustain-ability; safety; service; strength; solutions.

While the program has come up with the materials, ways and means to create cars that check the boxes in terms of meeting worldwide crash and stiffness requirements at a low cost, in terms of the assessment made for a C-class body-in-white (BIW) using the developed approach compared with a baseline vehicle, one made with conventional materials and processes, Dr. Gregory Ludkovsky, head of Global R&D for the steel company, points out that the BIW cost for the S-in motion structure is cost-neutral.

And here’s a funny thing about that. They assessed four areas of cost: Tooling Amortization; Assembly; Process; Materials. So for the baseline car, the contributions of each of these to total cost are as follows:
• Tooling Amortization: 2%
• Assembly: 32%
• Process: 15%
• Material: 51%

And for the lightweight BIW they devised:
• Tooling Amortization: 3%
• Assembly: 34%
• Process: 18%
• Material: 45%

Yes: It may be more costly to build, but the cost of the materials on a comparative basis is less. Ludkovsky says, that this approach is “financially rational,” in that it provides structures that have “the weight of aluminum at steel cost.”

And Ludkovsky points out that (1) these advanced high-strength steels (AHSS) are either currently available and in commercial application at a car company or will be commercially available before the solution could be executed in a next-generation vehicle, not something that needs to be developed* and (2) the work they performed was not just analytical, but functional: they developed 43 parts for the C-segment car, including those for the front, side, rear, and door modules; hang-on parts; chassis components; and exhaust parts.

In the arena of creating the new AHSS materials, he says that they are “getting away from traditional metallurgy” that they are “bringing nanotechnology into steel.” While they are continuing to develop ferrous materials that are considered steel, they are doing it in a way that makes the material far more advanced than might ordinarily be considered “steel.” What’s more, Ludkovsky explains that the product development methodology they’re using to develop steels is “process-driven”: “There’s no more product development without high-caliber process engineers involved from day one.” He adds, “The only way we can find out how a steel can solve a problem is by understanding what the design and manufacturing problems are.”

The weight save on the optimized vehicle body-in-white (BIW) structure they developed is 57 kg. As Ludkovsky points out, “People are struggling to get pounds or grams out.” And they have achieved 57 kg. For example, they are taking 35 kg out of the structural parts, 5 kg from the roof panel and body sides, 1 kg from the bumper system, and 16 kg from the hang-on parts. This is achieved by using a majority of AHSS (including press-hardened steel, which is >1,300 MPa): materials with tensile strengths >450 MPa. For the body-in-white and bumpers, the total amount is 54%. By comparison, the baseline vehicle uses 36% AHSS.

And there are significant process changes, which help account for the before-mentioned cost shifts. That is, where is in the baseline structure there are four hot-stamped parts, eight parts that were stamped from laser-welded blanks, and one roll-formed part, the S-motion structure has 29 hot-stamped parts, 16 parts stamped from laser-welded blanks, and two roll-formed parts.

There are additional weight savings realized in the chassis on the order of 16 kg.

A goal of all this, of course, is to provide the means by which greater fuel efficiency can be realized (lighten the car and downsize the engine; get a power-to-weight ratio equal to or better than what had been the case). They’ve also performed a lifecycle analysis, which shows that the lighter vehicle has a 13.5% reduction in CO2 equivalent emissions during its use phase without compromising safety (e.g., they ran the virtual car through a series of virtual crash tests to determine whether it would meet Five-Star NCAP requirements, the FMVSS214s for door crash, and others, and it passed). And for those who are looking at CO2 emissions related to production, they calculated another 15% reduction there, as well.

*In addition to the array of advanced high-strength steels used, there were some other standard materials, such as stainless.