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059CLEA - Second International Conference on CFD in the...

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Second International Conference on CFD in the Minerals and Process Industries CSIRO, Melbourne, Australia 6-8 December 1999 437 THREE DIMENSIONAL MODELLING OF HIGH PRESSURE DIE CASTING Paul W. CLEARY and Joseph HA CRC for Alloy and Solidification Technology (CAST) CSIRO Mathematical and Information Sciences, Clayton, Victoria 3169, AUSTRALIA ABSTRACT This paper reports on the development of 3D smoothed particle hydrodynamics for high pressure die casting simulations. Numerical simulations of two realistic dies are presented. INTRODUCTION High pressure die casting (HPDC) is an important process for manufacturing high volume and low cost automotive components, such as automatic transmission housings and gear box components. Liquid metal (generally aluminium) is injected at high speed (50 to 100 m/s) and under very high pressures through complex gate and runner systems and into the die. The geometric complexity of the dies leads to strongly three dimensional fluid flow with significant free surface fragmentation. Crucial to forming homogeneous cast components with minimal entrapped voids is the order in which the various parts of the die fill and the positioning of the gas exits. This is determined by the design of the gating system and the geometry of the die. Smoothed particle hydrodynamics (SPH) has previously been used by Cleary and Ha (1998), Ha, et al. (1998) and Ha and Cleary (1999) to successfully predict two dimensional filling patterns in water analogue experiments for several dies of modest geometric complexity. Here we report the results of applying 3D SPH to the filling of two realistic dies. The methodology used to construct the simulation configuration starting from CAD input for the cast component through mesh generation to the SPH initial conditions will also be described. SPH is a Lagrangian method and it does not need a grid to compute the spatial derivatives. The particles are the computational framework on which the fluid equations are solved. SPH will automatically follow complex flows. This makes the method particularly suited for fluid flows involving complex free surface motion. The method only performs calculations in the regions where mass is located. No computational time will be spent in empty regions. These attributes allow the method to relatively easily to handle three-dimensional problem. It is often stated that it is relatively easy to write an SPH computer program and to change a 2D computer code to handle 3D computation. This is certainly true for certain problems, such as those that do not include physical boundaries or those which are geometrically simple such as in astrophysics applications where SPH originates (Monaghan, 1992). For problems of industrial and engineering interest, there are three areas causing significant additional complexity that must be addressed in the 3D simulation code. The major difficulties of changing from 2D to 3D are in the handling of boundary conditions, nearest neighbour search and the initial set-up. Although these difficulties also apply to 2D simulations, they are much more acute in 3D.
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