How do you design a multi-material body-in-white optimizing weight, cost, and performance?

Multi-material BIW optimization involves: Material selection based on local requirements (mild steel for non-critical areas, AHSS/hot-stamped for crash, aluminum for mass-sensitive closures, composites for specific applications), joining strategy addressing compatibility, manufacturing process integration, and cost modeling. The optimization process uses topology optimization to identify material requirements, material substitution studies evaluating cost-benefit of each change, joining feasibility assessment, and manufacturing simulation. Total cost includes material, joining, tooling, assembly, and repair considerations. Successful designs achieve 100-200 kg body weight reduction with manageable cost premium.