Investigation of shot sleeve distortion and oil cooling in high pressure die casting

Abstract

It is well known that thermomechanical distortion reduces the service life of shot sleeves in high pressure die casting (HPDC) processes. However, the underlying phenomenon which causes the distortion is still not well characterized. While finite element models (FEM) have been used to analyze shot sleeve distortion, these have typically used simplified 2D representations and do not consider the effect of transient molten metal flow on heat transfer. In the present study, a 3D finite element (FE) model based on ANSYS used a staggered approach to study the sources of shot sleeve distortion and the effect of active oil cooling. Transient flow behavior during pouring, settling, and slow shot phases was simulated using a computational fluid dynamics (CFD) based model after which the temperature field and internal pressure distribution were imported into a structural model which was used to predict shot sleeve distortion at selected instants during a representative steady-state cycle. The simulation results were validated using data obtained from an HPDC machine and demonstrated good agreement. A comparison of large and small internal diameter (ID) shot sleeves showed that the former distort the most and that cooling channels are only moderately effective at minimizing distortion. Based on the complex 3D nature of shot sleeve distortion, the use of total indicator runout (TIR) is also proposed as a metric for minimizing distortion in shot sleeve designs. In addition to distortion, the thermal gradient in the shot sleeve was analyzed and it was noted that the largest source of heat loss is through the mounting flange attached to the HPDC machine frame, which is not an area typically considered for thermal management.