The fluid surface conveys much more information to

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Unformatted text preview: The fluid surface conveys much more information to the viewer than do the particles, in particular depth perception and variations in the surfaces are much easier to identify. In this case, it can be seen that the fluid separates from the front wall of the cylinder as it enters the runner producing a thinning sheet of fluid that flows into the gate. At the same time it spreads sideways and flows up the side walls of the runner to the top surface, giving a U-shaped profile in a cross section through the runner parallel to the gate. Figure 1: Cross section of the die. Concentrating on the flow after 28 ms when the horizontal section of the die cavity is beginning to be filled, the two views show the highly fragmented nature of the fluid and the three dimensionality of the fluid flow pattern. These features continue as the die cavity is increasingly filled, with many voids in the fluid. These voids move in an irregular and complex pattern and would lead to significant porosity in the final cast component. Die Cast Object The geometry of the die, the gate, the runner and the cylindrical plunger section is shown in Figure 3. In real die casting, the cylinder orientation would be horizontal and the part vertical but for the modelling we use a reference orientation as shown here. The fluid initially fills the cylindrical column and is pushed downward by a plunger at the top of the fluid moving at 15 m/s. In the simulation, a resolution of 1 particle per millimetre was used giving a total of 243,576 particles. Figure 5: Liquid metal surface (coloured by fluid velocity) as the fluid passes through the gate visualised using a surface mesh calculated from the SPH particles. Figure 3: A 3D mould with cylindrical plunger on the left leading to a divergent runner, through a curved gate into the die of a 3D machine component. Using another visualisation option, the particles are mapped to a rectangular grid which is then used to display the fluid surface. Figure 6 shows four views of the flow as die cavity fills. Note the introduction of the staircase artefacts in the surface. These are produced by the visualisation grid and are not present in the SPH data. This indicates that mesh based descriptions of the surface better represent the fluid than interpolation to an underlying grid. Two perspective views of the filling pattern at 3 different times are shown in Figure 4. The fluid particles are shown coloured by their speed. The first frame at 1 ms shows the system just as the fluid enters the runner. The second frame at 2.8 ms shows the fluid having mostly filled the runner and the leading fluid splashing through the gate. This leading material consists of fast moving fragments and droplets generated by splashing when the leading fluid flowed around the right angle turn as it entered the runner. In the final frame (4.52 ms) the fluid has entered the die proper and has split into separate jets around each of the 439 CONCLUSION In this paper, we have described the SPH method and the application of SPH to simulate the 3D die filling in high pressure die casting. The met...
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