Sand casting is a manufacturing process in which liquid metal is poured into a sand mold, which contains a hollow cavity of the desired shape and then allowed to solidify.

Corners, angles and section thickness

Avoid using sharp corners and angles. 

Use fillets with radii ranging from 3 to 25 mm.

Using sharp corners and angles (act as stress raisers)  may cause cracking and tearing during solidification.

Risers

Chvorinov’s rule determines the minimum size of a riser. It is achieved by setting the cooling time of the riser longer than the casting. 25% is the standard time difference.

Triser = 1.25Tcasting

Absence of risers can lead to cavities due to shrinkage and defects within the casting material.

Parting Lines

Parting line is the line where parting surface meets with the casting surface of the mold.

The parting line should be wide, short, horizontally flat and placed as low as possible.

Change in parting line placement will affect core usage, gating placement, the weight of the cast and dimensional accuracy.

Shrinkage Allowance

To compensate the shrinkage during solidification, a pattern is made slightly larger than the actual dimensions of the finished casting.

Allowance for shrinkage, known as pattern maker’s shrinkage allowances, usually range from about 10 to 20 mm/m.

 If the shrinkage allowance is not managed, it can cause open shrinkage defects (pipe and caved surface) and close shrinkage defects (micro-porosity or macro-porosity) that lower the casting quality.