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.
Highlights
The injection molding process is one of the most widespread processes for plastic part production
The possibility of replicating micro and nanostructures is related to the control of cavity temperature during the process; experimental results on an isotactic polypropylene confirmed that the replication accuracy is enhanced as the cavity surface temperature increases
The presence of a cavity characterized by macro-metrical dimensions, with a thickness in the order of few millimeters, and the features to be replicated in the order of few micros, is the main challenge in the simulation of the injection molding process
Summary
The injection molding process is one of the most widespread processes for plastic part production. The production of micro and nanopatterned surfaces in a single-step injection molding process has been proposed [10,11,12]. In this case, a patterned mold insert, previously obtained through lithography-based approaches, was located on the cavity surface, and the replication was assured through the optimization of process parameters, especially injection pressure and cavity temperature [13]. The possibility of modulating the cavity surface temperature during the process makes it possible to obtain micro and nanostructured surfaces with high geometrical accuracy [13,14]
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