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 ...

. 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 materials property is an intensive property of a material, i.e., a physical 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 material versus another ca ...

.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

undercut Undercut may refer to: * Price slashing, a pricing technique designed to eliminate competition *Undercut procedure, a procedure for fair allocation of indivisible objects. * Undercut (boxing), a type of boxing punch * ''Undercut'' (film), a stunt ...

s 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 a 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 (cut), a piece of meat *Fille ...

s should be added to avoid this. Annulars in the path of flow should be avoided because they can cause

cold shut A casting defect is an undesired irregularity in a metal casting process. Some defects can be tolerated while others can be repaired, otherwise they must be eliminated. They are broken down into five main categories: ''gas porosity'', ''shrinkage ...

s or

misrun A casting defect is an undesired irregularity in a metal casting process. Some defects can be tolerated while others can be repaired, otherwise they must be eliminated. They are broken down into five main categories: ''gas porosity'', ''shrinkage ...

s. A design that causes isolated hot spots decreases castability. An ideal design would have progressive

directional solidification Directional solidification (DS) and progressive solidification are types of solidification within castings. Directional solidification is solidification that occurs from farthest end of the casting and works its way towards the sprue. Progressiv ...

from the thinnest section to the thickest.Ravi, p. 4. Location of the mold's

parting line A parting line, in industrial casting of molds, is the border line in which draft angles change direction. One can check the parting line in the mould or product which divides the two half, i.e; the core and the cavity of a molded part. It is so ...

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 surface as defined by the three characteristics of lay, surface roughness, and waviness.. It comprises the small, local deviations of a surface from the perf ...

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 Slag is a by-product of smelting (pyrometallurgical) ores and used metals. Broadly, it can be classified as ferrous (by-products of processing iron and steel), ferroalloy (by-product of ferroalloy production) or non-ferrous/base metals (by-prod ...

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. For ...

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

References

Notes

Bibliography