Products and solutions, 2001-09-11, 02:00 AM
Lightweight steel car wheels reduce weight and fuel consumption
That steel wheels are not necessarily heavier than light alloy wheels is shown by the latest Ford Mondeo: for this model, Ford developed a lightweight 6½ J x 16 steel wheel weighing only 8.25 kilograms, not only almost 2½ kilos lighter than a conventional steel wheel but also 800 grams lighter than a cast aluminum wheel also proposed for the model. This breakthrough was made possible by using DP-W 600 and FB-W 45 high-strength steel grades from Thyssen Krupp Stahl.
The five wheels of a car account for around 3 percent of its curb weight, and the need to optimize their weight has been evident for some time. To this end Thyssen Krupp Stahl AG offers dual-phase steels with a soft ferritic microstructure interspersed with hard martensitic islands, along with ferritic-bainitic steels. These multi-phase steels owe their high strength and good forming properties to a tailored combination of hard and soft microstructure elements. The systematic use of these grades now means that lightweight steel wheels are generally lighter than comparable cast aluminum wheels.
Aluminum strip wheels are still around 20 percent lighter than steel wheels, but the material and manufacturing costs are considerably higher, making them at least three times more expensive than lightweight steel wheels. Added to this are design advantages: to meet today`s performance requirements, vehicles need bigger brake disks and calipers which in turn call for increased packaging space in the drop center of the wheel rim. The wall thickness of aluminum strip wheels is double that of steel wheels and thus restricts packaging space.
The remaining weight advantage of the aluminum strip wheel can be further reduced using Thyssen Tailored Strips® and Thyssen Engineered Blanks®, two innovative feedstock materials from ThyssenKrupp Stahl. Thyssen Tailored Strips® are made from two to three laser-welded sheets of varying thickness. When used as feedstock for rim production, the strips can be designed to be strongest at the points where the highest forces are exerted on the finished component. Thinner material is used in the remaining areas to reduce weight. Thyssen Engineered Blanks® offer the same advantages for wheel disks. These tailored blanks with non-linear welds can be tailored exactly to the loads acting on the finished component. Wheels with rims made from Thyssen Tailored Strips® and disks made from Thyssen Engineered Blanks® are only 500 grams heavier than a comparable aluminum strip wheel.
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