Design Considerations in Grinding-

In general, the design consideration for grinding operations are

similar to those for machining but certain special considerations are

required. Since these are finishing operations, the amount of material

to be removed for archiving the required tolerance and surface finish

should be kept to a minimum. Further, the design should allow the entire

grinding operation to be completed without repositionning of the

workpiece. Also, operations requiring frequent wheel dressing should be

avoided. This is particulerly important for form grinding.

Solidification and cooling-

After pouring the molten metal into the mould cavity, it is allowed to freeze and cool before the casting in taken out. The solidification process is extremely important since it dictates the structure of the cast metal and hence controls the properties of the casting.
The cooling curve of a metal depicted that the liquid metal cools quickly to the freezing point and then remains at a constant temperature until the metal loses its heat of fusion and solidifies completely. Further cooling occurs only after the solidification process is complete.
In casting, the temperature of the molten metal reaches freezing point first at the mould walls and then the solidification front moves towards the center through the liquid metal.

Pouring time-

The pouring time or the pouring rate of a casting depends upon the casting material and the configuration of casting since the cooling rate varies form material to material and is significantly affected by the volume and surface area of casting. If the pouring rate is low, the molten metal may start solidifying before the mould cavity is filled. On the other hand, higher pouring rate may cause erosion of mould cavity and turbulence. The pouring rate is, however, chosen to ensure complete filling of mould cavity before solidification starts.

Pouring Temperature-

In general, the higher the pouring temperature, the higher is the fluidity of molten metal because of decreased viscosity. But at higher pouring temperature, the amount of dissolved gases increases significantly. Therefore, the pouring temperature should be kept low to avoid defects due to trapped gases. It is clear that gas solubility and fluidity are two conflicting requirement. The pouring temperature is, however, decided on fluidity consideration alone and the temperature of the molten metal at the time of pouring is so chosen that every corner of the mould cavity is filled before solidification begins.

Design of Riser-

Risers are designed and located in such away that the volume of riser is sufficient to compensate for shrinkage and that it solidifies after the casting. A riser volume of approximately three times the shrinkage volume is usually
Considered adequate. The location of riser is selected to promote directional solidification. Invariably, more than one riser is required and the number and their locations depend upon the configuration of the desired casting.