Mould cavity layout can manufacture several castings in a single production mould. It is very economical as well as lot of material, labor and energy are saved. The costs of manufacturing tooling system is quite high, thus this technique is preferred only when the castings are very small as compared to the smallest size of production moulds and the production quantities are large. This process is usually taken up after selecting the casting orientation and parting.

Advantages :

• In this mould, less amount of material is utilized per casting.
• For improving and enhancing yield, more common feeders and gating system can be used.
• During manufacturing, the set up time is lower, used for mould preparation, pouring, shakeout and fettling per casting.

Remember :
It should be remembered that the minimum distance between cavities and from any cavity to the nearest edge of the mould must be set. Also, this minimum distance must be adequate to:

• Precluding damage to the mould.
• Offering enough heat transfer so that local hot spots are not formed in the portion of a casting close to another cavity.
• For medium sized castings, this minimum distance should be 50mm and for small sized castings, it vary from 25mm.

In regards of metal to sand ratio, the number of cavities in a mould has to be optimized by the following equation :


Metal to Sand Ratio Formula
In the above formula, density of casting and mould materials are required.
Nc: Number of casting cavities
Vc: Volume of a single cavity
Vf: Total volume of feeders
Vg: Total volume of gating
Vmould: Overall volume of the mould depending upon its dimensions

The high ratio must be averted as this may lead to poor heat transfer, in turn leading to defects related to casting solidification. Also, low value of ratio symbolizes poor usage of mould material. The recommended value of metal to sand ratio for ferrous castings is 1:1. However, this value can vary from 1:2 to 1:6. For varied sizes of mould, the process is repeated and the mould which gives the highest value of metal-to-sand ratio (but more than the minimum limit) is selected. This is possible to design the layout with different types of castings in the same mould. For example, a large casting (but not large enough for a good metal to sand ratio) can be combined with one or more small castings in the same mould.