EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Thixomolding has emerged as environmental-friendly, technologically and economically competitive process for manufacturing lightweight components of magnesium alloys in consumer goods, sports, electronics and automotive industries. The beneficial process characteristics include comparatively low mold filling temperature and high injection pressure of the semisolid thixotropic metal slurry, which enables producing thin-walled complex-shaped parts with excellent dimensional accuracy. The fine-grained microstructure and the low porosity ensure particularly good fatigue and fracture behavior of the parts. Despite those benefits single-channel runner systems, which are nowadays standard in thixomolding, have been identified as unsuitable for producing large parts. In order to address this issue, the current work presents the design concept of a novel twin-channel hot-runner system. The concept is based on direct injection of the slurry from the runner into the steel mold via ingate nozzles. As gating channels between the runner and the mold become superfluous, the flow rate during mold filling increases and the amount of scrap, that must be recycled, decreases. The absence of gating channels also reduces the projected area on which the injection pressure acts. Thus, the force required for mold clamping decreases. Special attention was paid on design measures for ensuring tight sealing and for compensating displacements between the hot ingate nozzles and the comparatively cold mold due to thermal expansion during the process. Thermo-mechanical simulations using the Code Aster software were performed for predicting thermal expansion, and the design of the hot-runner system was optimized with mold filling simulations using the Magmasoft software. Based on the simulation-aided design a prototype of the novel twin-channel hot-runner system was manufactured and tested under industrial conditions.