Significance of viscous dissipation effect during the rapid filling process in the non-adiabatic mold: A full analytical and validating solution

Abstract

The thorough analysis of thermal effects in the interior of molds enhances the understanding of the role and evolution of flow-thermal interactions during injection molding. However, current methods that incorporate heating and insulation devices for detecting melt within molds do not accurately reflect actual manufacturing environments. The non-isothermal conditions in molds also complicate the quantitative analysis of thermal effects, posing challenges for in-mold analysis. In this study, we proposed a comprehensive analytical and validation approach to investigate the significance of viscous dissipation in a non-adiabatic mold during injection molding. Channel dimensions (fixed length of 25 mm, radii of 0.75–1.5 mm) and melt velocities (25–150 mm s⁻¹) were adjusted to observe pressure drop variations ($\Delta P_{\text{en}}$) in a special-designed mold. An equivalent pressure concept ($\Delta P_{\text{vis}}$) was proposed to assess temperature variations induced by viscous dissipation. Dimensionless indices related to channel dimensions ($I_{P\_R}$ and $I_{\text{Pcor}\_R}$) and melt injection velocities ($I_{P\_v}$ and $I_{\text{Pcor}\_v}$) were established to observe pressure drop ($\Delta P_{\text{en}}$) and corrected pressure drop ($\Delta P_{\text{cor}}$). The results indicate that the corrected pressure drop and viscosity curves ($\Delta P_{\text{cor}}$ and ${\eta }_{\text{cor}}$) show more consistent variations versus channel dimensions and melt velocities when the viscous dissipation effect is quantitatively incorporated into melt pressure and viscosity analyses ($\Delta P_{\text{en}}$ and $\eta$), aligning closely with observations under adiabatic conditions. Thermal-related dimensionless numbers (Eckert, Brinkman, and Peclet numbers) qualitatively confirm the significance of viscous dissipation. This study offers a comprehensive analysis and validation of thermal effects in mold, presenting a novel method for exploring specific melt behaviors and advancing the analysis of mold interiors in non-adiabatic environments.