Castability is the ease of forming a quality

casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or ...

. A very castable part design is easily developed, incurs minimal tooling costs, requires minimal energy, and has few rejections.Ravi, p. 2 Castability can refer to a part design or a

material property A material property is an intensive property of a material, i.e., a physical property or chemical property that does not depend on the amount of the material. These quantitative properties may be used as a metric by which the benefits of one ma ...

.Ravi, p. 1

Part design

Part design and geometry directly affect the castability, with volume, surface area and the number of features being the most important attributes. If the design has undercuts or interior cavities it decreases castability due to tooling complexity. Long thin sections in a design are hard to fill. Sudden changes in wall thickness reduce castability because it induces

turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to laminar flow, which occurs when a fluid flows in parallel layers with no disruption between ...

during filling;

fillet Fillet may refer to: *Annulet (architecture), part of a column capital, also called a fillet *Fillet (aircraft), a fairing smoothing the airflow at a joint between two components *Fillet (clothing), a headband *Fillet (heraldry), diminutive of the ...

s 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.Ravi, p. 4. Location of the mold's parting line also affects castability, because a non-planar parting line also increases tooling complexity. If a design requires a high degree of accuracy, fine

surface finish Surface finish, also known as surface texture or surface topography, is the nature of a interface (matter), surface as defined by the three characteristics of lay, surface roughness, and waviness.. It comprises the small, local deviations of a ...

or defect free surface it reduces the castability of the part. However, the casting process can be very economical for part designs that require intricate contoured surfaces, thickness variations, and internal features.Ravi, p. 3.

Quantitative analysis

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

\frac

Where V_c is the volume of the casting and V_b is the volume of the smallest box that the casting could fit in. :

\frac

Where V_c is the volume of the casting and A_c is the surface area of the casting :

\frac

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

Material properties

Material properties that influence their castability include their pouring temperature, fluidity, solidification shrinkage, and

slag The general term slag may be a by-product or co-product of smelting (pyrometallurgical) ores and recycled metals depending on the type of material being produced. Slag is mainly a mixture of metal oxides and silicon dioxide. Broadly, it can be c ...

dross Dross is a mass of solid impurities floating on a molten metal or dispersed in the metal, such as in wrought iron. It forms on the surface of low- melting-point metals such as tin, lead, zinc or aluminium or alloys by oxidation of the metal. Fo ...

formation tendencies.''Tool and Manufacturing Engineers Handbook'' (TMEH), 4th Edition, Volume 6, ''Design for Manufacturability'', Society of Manufacturing Engineers, 1992.

References

Notes

Bibliography