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Improving productivity through casting process modeling.

Casting engineers often design tooling based on their previous experiences. While this experience is invaluable, achieving the proper design using typical trial and error methods is time- and resource-consuming. Casting process modeling provides engineers a way to evaluate the effects of separate process variables on the quality of the resulting products in order to achieve the optimal process design.

In general, casting process modeling can be used by process engineers to develop new processes as well as optimize existing ones. This was the case for designing the mold and tooling for an automotive wheel made of A356 aluminum alloy. The wheel was cast via low pressure permanent mold with the tooling initially designed based on the past experiences of the engineers (Fig. 1). However, virtual inspection of the cast part revealed central shrinkage at the transition between the spokes and the well of the wheel casting (Fig. 2).


The part maker decided to redesign the cast tool using casting process modeling from Sutcast Technologies, Vancouver, British Columbia, Canada. Solidification modeling of the initial design showed a macro shrinkage defect in the same location and size where it occurred in the actual casting.

In order to remove the macro shrinkage and decrease the solidification time, mold design was modified through:

* application of padding for improvement of directional solidification guaranteed by modeling;

* insertion of a water-cooled copper chill;

* adjustment of the temperature distribution of different tool parts;

* tool heat transfer control with the application of different coating thicknesses.

The proposed geometry of the new tooling design is shown in Fig. 3. Casting process modeling of the new design showed no sign of microshrinkage or porosity inside the wheel. However, at 0.42 seconds, the temperature of the fluid distribution in the new design fell below the solidus temperature, and the filling was stopped before completion.


In the second step, initial conditions of the simulation were changed. Pouring temperature was set to 1,382F (750C), the mold initial temperature was increased to 572F (300C) and the contact surfaces with the metal were coated with various thicknesses. These changes resulted in increased temperature in the well of the wheel and, thus, complete mold fill.

Ultimately, process engineers were able to reduce lead time and avoid further casting process design by trial and error. Casting process modeling also allowed the cast wheel to be produced 2.5 times faster than the initial design.

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Publication:Modern Casting
Date:May 1, 2006
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Next Article:Tailor properties where needed using the CDC process.

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