Hollow castings produced by interrupted low pressure die casting

Abstract

Hollow aluminium castings have been produced by low pressure die casting where the pressure has been released when only a shell has solidified, thereby draining the liquid out of the centre of the casting. The influence of holding time of the melt in the die, the die temperature and the alloy type on the thickness and quality of the solidified shell has been investigated. It has been found that hollow castings can be produced reproducibly with constant wall thickness under constant process conditions. The casting wall thickness increases linearly with pressure holding time. The die temperature has less influence on the wall thickness. The roughness of the inner surface of the castings varies with alloy type. An Al–12 wt-%Si (AlSi12) alloy gives a very uneven rough inner surface whereas an Al–5 wt-%Mg (AlMg5Si) alloy gives a smooth, even surface. Grain refinement also improves the surface quality. Attempts to predict the wall thickness with a commercial casting software package had limited success; the calculations seem to overestimate the thickness.