Smoothed Particle Hydrodynamics - Application
High pressure die casting into a 2D channel
High pressure die casting (HPDC) is used extensively to fabricate
complex-shaped objects using light metals. Liquid metal is injected at
high speeds under very high pressure. The resulting flow is extremely
complicated, with substantial droplet and fragment formation. HPDC
dynamics are not well understood; numerical simulation using SPH can lead
to an increased knowledge of the HPDC process.
The flow of liquid metal in a channel of width 2 mm has been computed
using two-dimensional SPH simulations. The Reynolds number - based on the
velocity through the gate of 50 m/s, and the gate width of 1 mm - is Re =
100. For this example, the liquid is assumed to be isothermal, and the air
initially in the mould is neglected.
The filling of the channel is observed in the plots below, which are
coloured according to local velocity magnitude. It can be seen that the
liquid metal enters and is forced upwards by the right wall without
contacting the left one. The jet then collides head-on with the top wall
and fragments. Most of the fluid moves to the right and forms an irregular
horizontal jet. The rest is forced back down along the left side of the
mould as a spray of droplets and is likely to trap air in the central gap
in the vertical section between the upward and downward jets. This takes
quite some time to fill with what would be partially solidified
irregularly shaped fragments and would be expected to produce fine scale
porosity and mechanical strength problems. Flakiness of the front surface
of such castings is actually observed here.
Velocity contours of the liquid metal at different
times
Meanwhile, the jet travels along the upper part of the short horizontal
section to the next bend where it is deflected downwards, again with the
formation of fragments. Similar behaviour is observed for the filling of
each of the mould sections. During the filling of the end vertical
section, multiple recirculations appear. Once filled, there is a back flow
and the lower part of the horizontal section fills. The region near the
lower wall of the top right section is the last to fill. Bubbles are
frequently observed here in real castings.
More details concerning this application can be found in [1].
Reference
[1] P.W. Cleary and J. Ha, SPH modelling of isothermal
high pressure die casting, Proceedings of the 13th Australasian Fluid
Mechanics Conference (Melbourne, 1998), pp. 663-666.
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