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# Castability

[kast, kahst]
Castability is the ease of forming a casting. Castability can be thought of as how easy is it to cast a quality part. A very castable part design is easily developed, incurs minimal tooling costs, requires minimal energy, and has few rejections.

Castability can refer to a part design or a material property.

## Part design

Part design and geometry directly affects the castability. If the design has undercuts or interior cavities it decreases the castability due to tooling complexity. Location of the parting line also affects castability, because a non-planar parting line also increases tooling complexity. Long thin sections in a design are hard to fill. Sudden changes in wall thickness reduce castability because it induces turbulence during filling; fillets should be added to avoid this. Annulars in the path of flow should be avoided because they can cause cold shuts or misruns. A design that causes isolated hot spots decreases castability. An ideal design would have progressive directional solidification from the thinnest section to the thickest.

If a design requires a high degree of accuracy, fine surface finish or defect free surface it reduces the castability of the part. However, the casting process very economical for part designs that require intricate contoured surfaces, thickness variations, and internal features.

The castability of a design can be partially quantitatively determined by the following three equations. Better castability is denoted by a larger number.

$frac\left\{V_c\right\}\left\{V_b\right\}$

Where Vc is the volume of the casting and Vb is the volume of the smallest box that the casting could fit in.

$frac\left\{6\left(V_c\right)^\left\{2/3\right\}\right\}\left\{A_c\right\}$

Where Vc is the volume of the casting and Ac is the surface area of the casting

$frac\left\{1\right\}\left\{\left(1+n_f\right)^\left\{0.5\right\}\right\}$

Where nf is the number of features (holes, pockets, slots, bosses, ribs, etc.)

## Material properties

Material properties that influence their castability include their pouring temperature, fluidity, shrinkage, and slag/dross formation tendencies.

## References

### Bibliography

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