Molding without melting: Investigation of thermoplastic polymers with regard to their suitability as mold material

Abstract

Context: The choice of material, manufacturing process, and molding tool significantly effects the quality, environmental impact, and cost efficiency of fiber reinforced polymer (FRP) components. Producing one-piece hollow profiles with smooth inner surfaces and undercuts presents major challenges for conventional mold concepts. A promising solution are shape memory polymers as tooling material. Objectives This study aims to identify thermoplastic polymers which are suitable as mold material in the FRP manufacturing process. The overarching objective is to develop a high-rate manufacturing process for one-piece FRP hollow profiles with undercuts. Methods First a manufacturing and curing process for an FRP is introduced. From this, boundary conditions for the mold material are defined. An assessment of the properties of thermoplastic polymers from literature research is carried out. An evaluation matrix allows the preselection of four polymers. PET, PPS, PA6 and PA66 are further analyzed by DSC and DMA. Results Semi-crystalline thermoplastics are more suitable as mold material than amorphous ones. When heated above their glass transition temperature (Tg) the elastomeric state allows for one-piece demolding. The material properties of 31 semi-crystalline polymers are assessed. PET, PPS, PA6 and PA66 are found as most likely suitable as mold materials for the introduced curing process. Their Tg is evaluated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Conclusion PET, PA6 and PA66 meet the process parameters of the defined FRP production process. Further research has to be carried out regarding their shape memory behavior and demolding capabilities.