Highly Optimized Advanced High-Strength Steel Rear Chassis Lightweight Rear Chassis Structure Jamal Alghanem PhD., Chrysler LLC Michael Gulas, ArcelorMittal Turi Solu, Altair Product Design May 13, 2009
Introduction Introduction Design Objectives Design Process Final Design 2
Objective Lightweight Rear Chassis Structure Design Objective Obtain a minimum mass reduction of 25% for a baseline passenger car rear chassis structure with no more than a 9% cost premium and with an equivalent baseline performance. 3
Project Plan Phase 1: Material Replacement Durability Optimization (Gage and Material) Stiffness, Modal and Forming Simulation Manufacturing and Physical Testing (10 parts) Phase 2: Clean Sheet Design Same Packaging Space Durability, Stiffness, Modal and Forming Optimization Cost Model Phase 3: Communication 4
Phase 1 Tests Bracket Fatigue Test Half-Rig Fatigue Test Modal Test Corrosion Trailer Test 5
Fatigue Method Development Weld Modeling Method Results Comparison (Normalized) Lab Test BS5400 Verity ======= ====== ==== Camber Bracket 1-1.8 0.7 1.4 Spring Bracket N/A 1 1.6 Toe Link N/A 1 9 FE (Verity) Results Physical Test Results 6
Phase 2 - Redesign The phase 2 redesign and process optimization created three unique concepts to choose from Tubular Hybrid Stamped Stamped Clamshel l 7
Optimizations Topology optimization was used to define the initial load paths which led to the clamshell style design. 8
Optimizations Topography Optimization Shapes Created Shape Optimization Many different types of optimization were utilized to further refine the design, including both topography and shape optimization. 9
Gauge Optimization It was determined gauge optimization yielded the best mass savings results. Numerous gauge optimizations were performed on the on the Phase 2 Preliminary Design. 10
Laser Welded Blanks Rear Longitudinal Lower Rails Upper Shell Front Lateral Member - Lower Shell Rear Lateral - Front Shell Rear lateral - Rear Shell The use of laser welded blanks was explored with all the major components. 11
Phase 2 Final Design After many gauge optimizations the final design was selected to have a 5 piece Upper Shell that utilized laser welded blanks. This design provides a mass reduction of 27% compared to the original baseline. 12
Material Selection After careful component level stress analysis, materials were selected for the components. Advanced High Strength Steels such as DP600 and TRIP780 were used. 13
Material Selection TRIP 780 DP 600 1.8 mm 1.7 mm 1.7 mm DP600 COATED 1.0 mm Front Lateral Member - Lower Shell Rear Longitudinal Lower Rails 1.7 mm 1.7 mm 1.0 mm TRIP 780 DQ DQ 1.7 mm 1.0 mm 2.1 mm Upper Shell 2.9 mm 2.7 mm 1.8 mm 1.9 mm 1.5 mm DP600 Rear Lateral - Front Shell Note: Coated sheet for all thicknesses <2.0mm Rear Lateral - Rear Shell The Advanced High Strength Steels selected allow us to use thinner gauges, which lowers part weight. 14
Fatigue Analysis Phase 1 Prototype Phase 2 Design Fatigue analysis was conducted to verify durability requirements. Phase 2 design met or exceeded all baseline performance. 15
Bracket Design Shape optimization was used to help redesign the bracket for local stiffness and increase overall weight savings. 16
Formability Study A formability study of the Upper Shell showed the laser welded blank to be formable. 17
Conclusions A mass reduction of 27% was achieved while meeting all stress and stiffness targets. This was made possible through the use of both laser welded blanks and Advanced High Strength Steel. MIT cost model indicates a 2.3% cost reduction. 18