Inline pvT Analysis for Precise Volume Dosing in Injection Molding: Addressing Variability in Recyclate Melts

ABSTRACT Precise volumetric dosing of polymer melts is essential for dimensional stability and mass consistency in injection‐molded samples, particularly when melt compressibility influences the effective volume delivered to the cavity. Conventional approaches rely on reference pvT curves or empirical correction factors, but these methods become unreliable for materials exhibiting variable compressibility, such as post‐consumer recyclates (PCR) with heterogeneous molecular‐weight distributions, fluctuating filler contents, and incomplete homogenization. This work presents an inline pvT‐based volume estimation method that couples real‐time pressure data during the injection phase to determine the instantaneous specific volume of the melt. The approach enables accurate dosing without requiring predefined reference curves and remains robust even when processing unspecified or compositionally varying recyclate melts. A comparative analysis demonstrates that the inline pvT method compensates for both thermal–mechanical material responses and batch‐to‐batch variability, thereby outperforming fixed pvT‐based correction strategies derived from patent‐established methods. Experimental validation on different polymer grades confirms that the proposed approach reliably predicts the effective melt volume despite significant variations in rheological behavior. The results show that integrating inline pvT characterization into machine control significantly enhances dosing accuracy, reduces dependence on material‐specific calibration, and supports stable processing of recyclates and virgin materials alike.