Abstract
This paper uses computational fluid dynamics (CFD), in the form of the OpenFOAM software package, to investigate the forces on the salt core in high-pressure die casting (HPDC) when being exposed to the impact of the inflowing melt in the die filling stage, with particular respect to the moment of first impact—commonly known as slamming. The melt-air system is modelled via an Eulerian volume-of-fluid approach, treating the air as a compressible perfect gas. The turbulence is treated via a Reynolds-averaged Navier Stokes (RANS) approach. The RNG k-ε and the Menter SST k-ω models are both evaluated, with the use of the latter ultimately being adopted for batch computations. A study of the effect of the Courant number, with a view to establishing mesh independence, indicates that meshes which are finer, and time steps that are smaller, than those previously employed for HPDC simulations are required to capture the effect of slamming on the core properly, with respect to existing analytical models and empirical measurements. As a second step, it is then discussed what response should be expected when this force, with its spike-like morphology and small force-time integral, impacts the core. It is found that the displacement of the core due to the spike in the force is so small that, even though the force is high in value, the bending stress inside the core remains below the critical limit for fracture. It can therefore be concluded that, when assuming homogeneous crack-free material conditions, the spike in the force is not failure-critical.
Highlights
High-pressure die casting (HPDC) is an important process for the manufacture of high-volume and low-cost automotive components, such as automatic transmission housings, crank cases and gear box components [1,2,3]
The principal aim of these is to determine the magnitudes of the forces which act on the salt core, with a view to being able to infer whether an actual salt core would be able to withstand such forces in practice
Following the results of recently published articles on salt cores in high-pressure die casting [10,12,13,17], in almost every simulation where the core was treated as rigid, the signature peak mentioned in Section 1 appeared in a plot of the force exerted on the core as a function of time
Summary
High-pressure die casting (HPDC) is an important process for the manufacture of high-volume and low-cost automotive components, such as automatic transmission housings, crank cases and gear box components [1,2,3]. This complicates the task for the design engineer, who has to be sure about the viability of a process and manufactured parts before any budget is invested in tooling and machinery. One technological constraint to date is that there is no serial production, via HPDC, of parts with inlying hollow shapes or undercuts formed by lost cores, even though other casting techniques have employed lost cores for decades [1,4]. The basic idea of using salt cores is to block parts of the die volume by inserting cores as placeholders; in so doing, the melt will not penetrate into this space. The cores may be removed after solidification and one creates undercuts or hollow sections with them, which may later act as cooling or oil-flow channels [6,8,9]
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