Cavity pressure sensor study of the gate freezing behaviour in aluminium high pressure die casting

Abstract

Free flowing of liquid metal through the gate during die filling and solidification is critical to the final product quality in aluminium high pressure die casting. Early close-off of the gate due to freezing detrimentally affects the pressure transmission from the injection system to the casting as it solidifies, resulting in poor soundness of castings due to improper feeding of the shrinkage.In this paper, piezoelectric cavity pressure sensors were employed to study the gate freezing behaviour in aluminium high pressure die casting. Metal pressure at the runner, gate and cavity was directly measured during casting. From the on-line measured metal pressure profile, a method was established for analysing the gate freezing time. The effect of process variables on the gate freezing time, such as intensification pressure and gate speed, as well as their relation to the mechanical properties of the produced castings, was studied in detail. It was found that the gate freezing time could be determined by the duration from the start of the cavity fill to the drop in pressure measured at a location just after the gate. The application of higher gate velocity and pressure assisted in keeping the gate open longer. As a result, sound castings were produced and mechanical properties were improved. The results indicate that the method developed in this work can be used to control and optimise the die casting process for the fabrication of high internal integrity components.