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CASE: Valve Housing

A simple example demonstrates how re-designing the shape of the component can dramatically increase castability and reduce costs. It also shows the possibilities of using simulation both in the machine shop and in the foundry, to optimise and iterate the design and manufacturing and the price of the casting.

The original shape of a duplex-steel valve housing used to have a constant wall thickness (13/16") in the axi-symmetric part. CastCHECK showed that the defects were spread all over the axi-symmetric part and close to the flanges (Fig.6). After this, the original shape was re-designed so that material was added to the outer side of the component in order to reach directional solidification towards the two flanges opposite each other. As a result, the defects were located close to the flanges mentioned before (Fig.7).
Fig. 6. CastCHECK- analysis for the original design. Black areas describe defects, which are spread all over the component.
Fig.7. CastCHECK- analysis for the re-designed component. The amount of defects is considerably lower than in the original version and they are located near the two flanges.
The risering system was designed for the redesigned component based on CastCHECK-analysis. Four risers with insulating sleeves and six chills were added to the system- two chills to each flange (Fig.9). CastCAE casting simulation program was used to check the functionality of the risering system. CastCAE clearly demonstrates that directional solidification is achieved towards the risers and the casting becomes sound (Fig.8, right side). The same risering system was also tested for the original design to find out if it works for it. As expected, it did not. A constant wall thickness in the axi-symmetric part of the component leads to simultaneous solidification which provides poor feeding conditions and causes porosity (Fig.8,left side).
Fig.8: CastCAE - simulation results for the original (left) and the redesigned (right) components. It can be clearly discovered that in the redesigned version directional solidification is achieved towards the risers while the original version solidifies smoothly in the axisymmetric part, resulting in porosity.
The risering system was further optimised to get the original design to produce a sound casting. Two additional risers with insulating sleeves and two extra segment chills had to be added to the system (Fig.10) The estimated manufacturing costs of the original, bad design would have been approximately 30% higher than in the case of the optimised, castable component. This does not include savings and profits resulted from a shorter lead-time.
Fig.9. CAD - model (form•Z RenderZone) of the casting including risering system. Moulding and cleaning are easy and fast to do for this version.
Fig.9. CAD - model (form•Z RenderZone) of the casting including risering system. Moulding and cleaning are easy and fast to do for this version.

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