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Ultrasound injection molding has emerged as an alternative production route for the manufacturing of micro scale polymeric components, where it offers significant benefits over the conventional micro injection molding process. In this work, the effects of ultrasound melting on the mechanical and morphological properties of micro polypropylene parts were characterized. The ultrasound injection molding process was experimentally compared to the conventional micro injection molding process using a novel mold, which allows mounting on both machines and visualization of the melt flow for both molding processes. Direct measurements of the flow front speed and temperature distributions were performed using both conventional and thermal high-speed imaging techniques. The manufacturing of micro tensile specimens allowed the comparison of the mechanical properties of the parts obtained with the different processes. The results indicated that the ultrasound injection molding process could be an efficient alternative to the conventional process.

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The application of vacuum venting for the removal of air from mould cavity has been introduced in injection moulding with the intent to enhance micro/nano features replication and definition. The technique is adopted to remove air pockets trapped in the micro-features, which are out of reach for conventional venting technologies and can create considerable resistance to the melt filling flow. Nonetheless, several studies have revealed a negative effect on replication that could possibly arise from the application of vacuum venting. Although the incomplete filling of micro-scale features has often been attributed to poor venting, the limited research examining the application of vacuum venting has produced mixed results. In this work, the effect of air evacuation was experimentally investigated, monitoring mould and polymer temperature evolution during the micro injection moulding process by means of a high speed infrared camera and a sapphire window, which forms part of the mould wall. The results show that air evacuation removes a mould surface heating effect caused by rapid compression of the air ahead of the flow front and subsequent conduction of that heat into the mould surface. Hence, with the increase of the surface-to-volume ratio in micro-cavities, air evacuation has a detrimental effect on the cavity filling with polymers that are sensitive to changes of the mould temperature.

Low-friction mold surface coatings can be used to promote filling of thin-wall parts through reduction of the melt flow resistance by causing wall slip at the polymer-mold interface. This work investigates the effects of different mold coatings (DLC, CrN and CrTiNbN) on the flow resistance of molten polystyrene in thin-wall injection molding. The design of the mold allowed high-speed visualization of the molten polymer flow during the filling phase and measurement of the velocity profile across the cavity thickness. The evaluation of the speed profiles allowed the characterization of the wall-slip phenomenon, indicating the absence of conventional 'fountain-flow' filling mechanism.The results indicate that a DLC deposited on a chrome substrate can significantly reduce the flow resistance of polystyrene, by increasing the slip velocity of polymer melt in contact with the mold surface. Moreover, the contact angle of molten polystyrene over the considered coatings was found to be inversely proportional to the melt flow resistance, indicating the importance of the adhesion at the polymer-mold interface.