Assessment of the Ejection Force in Tubular Injection Moldings

Abstract

The development and manufacture of injection molds for high quality technical parts is a complex task implying an integrated knowledge of the injection molding process and the material changes undergone during processing. In the case of the design of molds with deep cores (e.g. for boxes or tubular fittings), it is useful to know the force required to eject the parts for enabling the decision on the more efficient ejection system to be implemented in the tool, and for guaranteeing the integrity of molded parts. In this paper it is described a fully instrumented research mould, with six pressure/temperature sensors (three in the cavity and three in the core) and two load cells. Some experimental data with an amorphous material are included. The studies were carried out on tubular moldings (60 mm in diameter, 146 mm in length, and 2 mm in thickness). The injection unit cell is based on a 1 MN clamp force injection-molding machine. During the processing pressure, temperature and ejection force evolutions were recorded. The available data show that the holding conditions influence the ejection force and are related to the diametrical shrinkage.