Focus B-pillar 'tailor rolled' to 8 different thicknesses

  • 24-Feb-2010 09:25 EST
focusBpillar.JPG

Colors indicate eight different thicknesses in the B-pillar post of the forthcoming Ford Focus. The right-hand color strip starts with the thinnest sections at the bottom (four shades of blue), rising to two shades of green and then one each of yellow and orange (thickest at 2.7 mm).

How important is the B-pillar in the new Ford Focus, which goes into U.S. production later this year? The answer is it's important enough to have Ford specify an ultrahigh-strength (boron) steel blank made at one German supplier with a highly developed cold-rolling process, where it is precision tailored to eight different thicknesses. Then it is shipped to another German supplier to be shaped and strengthened by a hot-stamping process and finally delivered to Ford for installation.

The new Focus is a world car, and its suppliers are worldwide, too, but the B-pillar certainly is not just an exercise in world sourcing. The design was intended to meet difficult Ford engineering objectives, specifically weight reduction while improving side-impact performance. The B-pillar has to contribute to passing federal procedures, of course, but particularly help with the very difficult dynamic side-impact tests run by Insurance Institute for Highway Safety (IIHS). The operating characteristics of the B-pillar are key factors in the results of those tests.

The new Focus B-pillar post starts as a "tailor rolled" blank from the process employed by German supplier Mubea, which produces strips that can be changed in thickness along their length by precision control of the gap between pairs of rollers. Mubea is able to execute smooth, quick transitions from one thickness to another along the blank, making a change of perhaps less than 0.2 mm (0.008 in), accurate to within 0.1 mm (0.004 in) overall—±0.05 mm (0.002 in)—at each step and from one end to the other.

As used for the Focus B-pillar, the eight thicknesses produced by the Mubea process range from a maximum of 2.7 mm (0.1 in) to as thin as 1.35 mm (0.05 in). The engineering of the shape puts the greatest thicknesses where they are needed for maximum strength in side impacts, and in the case of the B-pillar it's just above the midpoint (orange area in illustration), explained Mark C. Kaufman, Ford C-Segment Marketing Manager.

The thinnest sections will be at the bottom (blue in the illustration), and there actually will be four thicknesses in that area alone. Total weight of the B-pillar post is just over 7 kg (15.4 lb), a weight savings over a conventional design of 1.3 kg (2.9 lb), Kaufman added.

Tailored blanks produced by the rolling process permitted Ford to do more precise tuning of the shape than with the more conventional method of laser welding strips of different thicknesses, as is done with many body sections. There are two inherent advantages in tailor rolling: It is possible to get many stepped changes in the thickness of the part. And there are no weld seams—just a smooth transition at each change in thickness, which results in more uniformity overall.

The Mubea blanks will go to Benteler Automotive, which will do the finish-shaping and the hot-stamping that increases the material strength while maintaining shape accuracy.

The finished B-pillar post will be welded into position on the Focus body assembly line. The facing body section is shaped to mate up to the stepped thicknesses of the post.

To date, Mubea process blanks have been used in Europe for body structural parts by several German manufacturers, including General Motors' Opel. The Focus reportedly will be Ford's first U.S. application.

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