A Novel Concept to Manufacture Nano/Microcellular Foam Structures

Abstract Multi-material and multi-structure design, particularly the combination of metal-polymer and solid-foam, stands as a promising strategy to reduce component weight while increasing and diversifying their functionalities. However, adopting such design approaches faces significant challenges, primarily arising from the complex multi-stage manufacturing processes, necessitating multiple sets of equipment, tooling, and precise control at each production stage. In response to these formidable manufacturing hurdles, this paper introduces an innovative approach that integrates injection molding, forming, and foaming processes into a single hybrid process called Electromagnetic Forming Injection Foaming (EFIF). In this integration concept, the challenges related to the shrinkage and viscosity of polymer melt are addressed by utilizing supercritical fluid (SCF) foaming technology. Moreover, the incorporation of electromagnetic forming offers precise control over the foaming process, potentially enabling the creation of micro- to nanocellular structures in the injected polymeric material. As the proposed integration is a manufacturing innovation, with no available information in the literature directly relating to this concept, this study explores the basic principles, feasibility and effectiveness of the proposed integration in two preliminary studies. In the first study, the effects of pressure drop and drop rate on the cell nucleation and the morphology of the final foam structure are discussed along with various methods of creating pressure drop and drop rate in both conventional and hybrid foam injection molding processes. In the following, the experimental setup and study conducted to determine the impact of pressure drop and drop rate on the cell size and cell density are described, and the results are discussed. The second study focuses on the potential effects of integrating electromagnetic forming with the injection, forming, and foaming processes. A set of experiments is designed and conducted to evaluate the effect of the polymer layer on the electromagnetic forming. The initial evaluation shows that different boundary conditions, in this case, the adhesion of the polymer to the blank, significantly affect the forming result, which highlights the need for more fundamental research. In conclusion, this paper underscores the substantial potential of the EFIF concept to merge multiple commercially available technologies to find a scalable solution for manufacturing micro- to nanocellular polymer foams, which can eventually unlock the socio-economic benefits associated with the production of high-performance, multi-functional components.