Die Casting Design
Draft is necessary on surfaces parallel to the direction of die draw because it facilitates ejection of the casting from the die.
It is not common practice to compute the draft angle for each feature on a component, and it is normally generalized with exceptions noted. Twice as much casting draft angle is generally recommended for inside walls or surfaces as for outside walls or surfaces. The reason for this is that as the alloy solidifies and shrinks onto the die features that form the inside surfaces (usually located in the ejector half in conventional cold chamber die casting), and away from the features that form the outside surfaces (usually located in the cover half in conventional cold chamber die casting).