Development of Automotive Hood Using Multi-Material Double Injection Molding

Introduction: The automotive hood is a critical closure component that must meet structural, safety, and styling requirements. Traditional metal hoods are increasingly being replaced or supplemented by polymer-based designs due to advancements in material technology and manufacturing methods. Among these, multi-material double injection molding presents a promising alternative to reduce production time and cost while achieving performance compliance. Aim: This study aims to develop an automotive hood using a hybrid plastic combination through a double-shot injection molding process. The focus is on evaluating the structural feasibility of such designs under regulatory and OEM-defined stiffness and crashworthiness performance targets. Purpose: The objective is to investigate the compatibility of different thermoplastic materials for outer and inner skin layers in achieving structural rigidity, impact resistance, and manufacturing efficiency. The approach targets the consolidation of part integration and reduction of assembly steps, without compromising functional durability and occupant safety. Methodology: A series of material combinations—such as polypropylene (PP), polyamide (PA), and glass fiber-reinforced variants—are assessed for bonding behavior, moldability, and structural interaction in a dual-shot injection environment. Finite element analysis (FEA) is used to evaluate hood performance under various loading conditions including torsional/bending/locking stiffness, pedestrian protection, and low-speed frontal impact scenarios. Simulation results are validated with lab testing of prototype hoods to verify bonding integrity and deformation behavior. The study with FEA and experimental results demonstrates that optimized multi-material designs can meet key stiffness and crash criteria while significantly improving production cycle efficiency.