Abstract
During the injection molding process, the melt travels with a flow due to friction. As the velocity of the layers next to the wall is less than that of those flowing in the middle of the channel, a fountain flow is formed at the melt front. The temperature of the polymer surface decreases from the melt temperature to the contact temperature after contacting the mold surface. Based on all this, a complex shell–core structure is formed in injection-molded products, which can be influenced by the processing parameters and the surface of the tool insert. This paper focuses on investigating the effect of the microstructures replicated from the insert to the polymer product on its mechanical properties. During the research, two microstructured surfaces were created, with different effects on the melt flow formed by the femtosecond laser. These were compared with a ground insert to analyze the effects. For examining the effect of technological variables on the mechanical properties, an experimental design was used. The structure created by the femtosecond laser on the surface of the tool influenced the mechanical properties of the polymer products. Recognizing the effect of microstructures on the melt front and, through this, the change in mechanical properties, a predefined polymer product property can be achieved.
Highlights
During injection molding, the polymer in contact with the cavity surface typically has zero velocity, and at the center, it is maximum
The turbulent flow generated by these microstructures increases the pressure of the melt, as well as the shear stress
The turbulent flow generated by these microstructures increases the pressure of the melt, as well as the shear stress, and at the same time, decrease the melt velocity
Summary
The polymer in contact with the cavity surface typically has zero velocity, and at the center, it is maximum. The shear stress at the cavity wall decreases from its highest value, to near-zero at the center, influenced by the friction conditions. The microstructures cannot be replicated even when a high holding pressure is used To minimize this phenomenon, the mold can be heated before the material injection. The turbulent flow generated by these microstructures increases the pressure of the melt, as well as the shear stress. The flow instability, because of melt velocity and pressure variation, affects the fountain flow and the outer layer on the surface of the finished product [1,2]
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