Multi-Scale Simulation of Injection Molding Process with Micro–Features Replication: Relevance of Rheological Behaviour and Crystallization

Abstract

The possibility of tailoring key surface properties through the injection molding process makes it intriguing from the perspective of sustainability enhancement. The surface properties depend on the replication accuracy of micro and nanostructures on moldings; such an accuracy is enhanced with cavity temperature. The simulation of the injection molding process is very challenging in the presence of micro and nanostructures on the cavity surface; this does not allow for the neglect of phenomena generally considered not to influence the overall process. In this paper, a multiscale approach was proposed: in the first step, the simulation of the overall process was conducted without considering the presence of the microstructure; in the second step the outputs of the first step were used as an input to simulate the replication of the microfeature. To this purpose, a lubrication approximation was adopted, and the contribution of the trapped air, which slows down the polymer advancement, was accounted for. A modification of the viscosity equation was also proposed to describe the rheological behavior of isotactic polypropylene at very low temperatures. Concerning the microcavity filling simulation, the modification of the viscosity description at low temperatures consistently describes the process, in terms of polymer solidification. Concerning the replication accuracy, it increases with the cavity surface temperature, consistently with the experimental observations.

Evolution of the Deformation‐ and Flow‐Induced Crystallization and Characterization of the Microstructure of a Single Spherulite, Lamella, and Chain of Isotactic Polypropylene

“…[244] This system can investigate the rapid evolution of multiscale and multilevel structures of polymers under the complex thermomechanical field during injection molding simultaneously. [244,[257][258][259] The novel crystallization behaviors of iPP, such as the crystallization kinetics, polymorphism evolution, and growth and orientation of lamellar crystals, are revealed systematically and efficiently via this system (Figure 50). Meanwhile, the in situ characterization is successfully utilized to efficiently quantify the crystallization time under various injection molding processing conditions, and processing windows are established directly.…”

Polymer crystallization under external flow

“…Among them, the modeling for injection molding is relatively mature. Both Pantani [249,252,253] and Peters [168,254] have done great contributions to this field. Readers who concerned are suggested to read the reviews wrote by Pantani [249,252] for a systematic understanding.…”

Recent progress in flow‐induced polymer crystallization

“…[171][172][173] A combination of experiments and simulations is usually used to study and predict the morphological development of semicrystalline polymers during injection molding. 21,38,40,[174][175][176][177][178][179] In the injection molding, in addition to flow filed, other processing parameters such as mold temperature, melt temperature, packing pressure, packing time and cooling time also directly affect the morphology of the material. When the packing pressure increases, the effect of the flow field on the molecular chain orientation increases.…”