Steel vs. Aluminum: ULSAC Executive Summary

1.1	Background

	The UltraLight Steel Auto Closure (ULSAC) program demonstrates the effective use of steel in producing lightweight, structurally sound automotive closure panels that are manufacturable in high volume and affordable. ULSAC began as a concept development program, producing innovative concept designs for doors, hoods, decklids and hatches that are up to 32 percent lighter than benchmarked averages and 10 percent lighter than best-in-class, while meeting stringent structural performance targets. These results were obtained through innovative steel design combining ultra-high strength steels with manufacturing technologies such as tailored blanks, hydroforming and laser welding. Like the UltraLight Steel Auto Body (ULSAB) study, the ULSAC program was commissioned by an international consortium of 31 sheet steel producers to assist their automotive customers with viable lightweighting solutions. The ULSAC Consortium contracted Porsche Engineering Services, Inc. (PES), Troy, Michigan USA, to provide design and engineering management for both the Concept and Validation Phases of the program.

1.2	Validation Phase - Door with Stamped Outer

	Following the successful Concept Phase, the ULSAC program proceeded to the validation of a frameless door design. The ULSAC Consortium chose to build and test the frameless door as a demonstration because it is representative of a range of closure concepts developed during the Concept Phase. The frameless door embodies most of the advanced concepts in structure, technology and steel usage developed in the Concept Phase designs and demonstrates their feasibility. Successful manufacture of the frameless door dramatically demonstrates the value and structural efficiency in combining innovative design, advanced technology and steel. In May 2000, the ULSAC Consortium released the Validation Phase results for a complete frameless door structure. The door structure featured a high and ultra high strength steel tubular frame and a stamped outer panel of 0.7 mm BH 260 steel. The complete door structure weighed 10.47 kg (normalized mass, 13.27 kg/m ). This is 22 percent lighter than the framed door best-in-class benchmark and 42 percent lighter than the average frameless door Validation Phase benchmark. This was achieved without compromising safety or structural performance and at no cost penalty.

1.3

Validation Phase - Door with Sheet Hydroformed Outer

Additional mass reduction also was investigated in the Validation Phase by manufacturing the outer panel, using the sheet hydroforming process. The process was intended to gain uniform stretch in the middle of the panel while maintaining dent resistance and oil canning performance at a lower mass.

Sheet hydroforming for complex parts, such as door outer panels, is a process under development. With completion of the Validation Phase, much more has been learned about the performance of differing grades and thicknesses and how stamping and hydroforming compare in dent resistance and oil canning, as well as overall door performance and cost, for the ULSAC door design.

A similar range of materials utilized for the manufacture of the stamped outer panels was used for the production of the test doors with sheet hydroformed door outer panels.

Oil canning and dent testing determined that 0.6 mm thick Dual Phase (DP) 600 steel material was the best choice among the sheet hydroformed outer panels to use in the demonstration hardware (DH) door structure. The validation door with a sheet hydroformed outer panel weighs 9.77 kg and meets all structural performance and safety targets at a slight cost increase of $3.72 per door, assuming an annual vehicle production volume of 225,000. With the 0.7 kg further reduction in weight, this door is 27 percent lighter than the best-in-class benchmarked door and 46 percent lighter than the average frameless door benchmark.

This research was conducted to explore the potential of the sheet hydroforming process for further mass reduction in auto body outer panels. The results indicate that, with further development to reduce cycle times, a sheet hydroformed outer panel could be used to effect additional weight reduction over the already significant achievement of the ULSAC door with stamped outer panels.

1.4	Information In This Overview Report

	This overview report contains the May 2000 results for doors using stamped outer panels and full details on the manufacture of the complete door structure. This report also contains a summary of the results from the manufacture of outer panels using the sheet hydroforming process. April 2000 and January 2001 ULSAC Engineering Reports are also available on the AISI website. These reports contain comprehensive details on the design, manufacture and results of the ULSAC program.

For further information, visit the American Iron and Steel Institute site.

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