Molding trials and injection phase simulations considering the impact of variable material properties from recyclates on flow front progression

Abstract This study explores how material-specific properties—namely dynamic viscosity, pressure–specific volume–temperature (pvT) behavior, and specific heat capacity—influence the development of the melt front during the injection phase. Simulations and experiments are conducted using various polymers under controlled flow rate conditions to focus on their effect on melt front progression. Dynamic viscosity and pvT behavior primarily control flow-front advancement and cavity-filling behavior. In contrast, variations in specific heat capacity, within realistic range observed for typical recycled materials, have a negligible effect. High-viscosity melts required injection pressures beyond the machine’s operational capacity, resulting in reduced flow rates and incomplete cavity filling. This issue is particularly relevant for recycled polymers with a high content of long-chain molecules. Assuming constant melt compressibility introduced measurable deviations in simulated flow behavior under constant flow rate conditions. To address this, a compensation strategy involving variable antechamber flow rates is proposed to ensure consistent cavity flow rates and filling times. These findings highlight the complex interplay between rheological properties and process control parameters. In conclusion, precise knowledge of dynamic viscosity and pvT behavior is essential for robust control of the injection molding process, especially when working with recyclates of uncertain or variable composition.