BHP unveils ultralight steel car body in Australia

The preview of the UltraLight Steel Auto Body (ULSAB) at the Melbourne International Motor Show yesterday offered an early insight into the future of automotive design.

The Australian preview of the ULSAB structure, ahead of its global release on March 4 in Geneva, takes the US$28 million international project, which involves 35 of the world's leading steelmakers, from a computer-generated concept to reality.

The major aim of the project is to prove steel can deliver significant weight savings in an age where fuel economy, environmental considerations and safety are equally prized, but without adding to the cost of the vehicle body.

Terry McDermott, national sales and marketing manager -- automotive, for BHP Coated Steel -- Australia, said the project represents one of the great breakthroughs in automotive design.

"The quest to achieve weight reductions in automotive bodies without compromising strength and road safety has been an on- going challenge for the last two or three decades," McDermott said.

The ULSAB project had its genesis in 1992, when the American Iron and Steel Institute began to study the possible weight savings on an existing steel body of a medium-sized car.

The results of the study, conducted by Porsche Engineering Services in the U.S., showed significant weight savings could be gained by starting with a clean sheet of paper.

Since then, BHP Steel as a member of the international consortium has developed a number of the latest-generation high- strength steels that could be immediately adapted by any carmaker.

"The ULSAB design uses advanced manufacturing processes and steels currently available, but not commonly used in automotive bodies," McDermott said.

"For example, ULSAB relies on high-strength steels, tailored blanks, hydroforming and steel sandwich material to provide lighter weight for maximum performance.

"These innovations presented unique challenges requiring close working relationships among design engineers, steel manufacturers and component fabricators."

Steel is the most recycled material in the world and all steel chosen for the ULSAB structure is recyclable.

"About 70 percent of a typical passenger car is iron and steel, 100 percent of which is recyclable," McDermott said.

"The ULSAB project proves that steel offers new directions in automobile manufacture and everyone will benefit from the advances it introduces."

The ULSAB design relies on advanced materials and manufacturing processes, including high-strength steels and assembly laser welding to provide lighter weight for maximum performance.

All ULSAB parts were manufactured from tools by component fabricators in Europe and the U.S. with no hand forming. Porsche Cars assembled the ULSAB structure in Germany.

Physical tests of the body show it is both stronger and stiffer than currently manufactured bodies, for improved levels of ride, handling and reductions in noise, vibration and harshness (NVH).

Computer modeling also demonstrates the ULSAB body structure meets international standards for a variety of crash tests while achieving better structural performance with less weight.

An independent economic analysis of the ULSAB body structure showed a design of a steel body structure can achieve light weight at no cost penalty and with potential cost savings.

"The project also embodies key environmental implications," McDermott said.

"Major benefits are fuel efficiency, reduced emissions and the use of fewer resources.

"ULSAB is lighter and stronger, and costs no more to manufacture than current automotive body structures. Clear proof that steel now emerges as a material of choice for designers to down weight vehicles."

Among the advanced technologies used in the ULSAB body in white are:

High strength steel

ULSAB uses high-strength and ultra-high strength steel for more than 90 percent of the body structure.

One challenge posed by these steels is that they form differently from the mild steel to which many component fabricators are accustomed.

High-strength steel has greater spring back and requires different draw angles so each different grade must be treated by the design engineer and manufacturing engineer as a unique material.

High-strength material specifications range from 210Mpa to 800Mpa yield strengths with thickness ranges from 0.65mm to 2.0mm.

Tailored blanks

ULSAB's body side outer is one of several parts that employs a fully laser-welded tailored blank with different thicknesses and grades of steels.

Careful placement of the seams in the tailored blank was critical for minimizing weight and facilitating forming.

This consideration was especially important in the body side outer because of its complexity, size, use of high-strength steels and the inclusion of a class A surface quarter panel. Almost half of the ULSAB mass consists of tailored blank parts.

Hydroforming

TO minimize weight and maximize structural performance, the project partners designed the tube from which the hydroformed side roof rail was created with an unusually thin gauge relative to its outside diameter.

The project partners had to develop methods for both manufacturing and forming this critical tubular part, which provides a unique load path for the body structure.

Steel sandwich

Again, to minimize weight, the program specified the skins of the steel sandwich material for the dash panel insert and spare tire tub to be extraordinarily thin. This requirement tested the project partners' ability to provide the width required.

Additionally, steel sandwich has different forming characteristics from regular sheet steel, requiring the project partners to treat it differently in the dies.

Manufacturability

To help ensure the feasibility of the designs created through the collaborative effort, the project partners performed detailed analysis on the most complex parts.

This included forming simulation to identify areas of unacceptable strain and adjustments to product design and tooling, and circle grid strain analysis to confirm the feasibility of parts for full volume production.

ULSAB is lighter and stronger, and costs no more to manufacture than the benchmarked average vehicle established in the project s concept phase -- clear testimony that steel emerges as a material of choice to down weight vehicles.