Die Casting Design
Some features, such as undercuts, bosses and holes, require either subsequent machining or retractable core slides in the tool, because these features are not oriented in the direction of die draw. Retractable core slides can substantially increase the cost of manufacturing and maintaining a tool, and also increase the casting cycle time. Furthermore, they also tend to cause flash on exterior surfaces and attract additional costs for subsequent removal.
Examples of component die redesign to eliminate core slides are shown below.
Movable cores are required in (1), due to the outside features, whereas the casting can be made without movable cores or core slides in (2).
Eliminating Undercuts Beneath Bosses
Undercuts beneath bosses form features that prevent the casting being ejected from the die. In these cases, careful redesign can eliminate the subsequent machining required or the additional core slides required in the tool. Die design alternatives that eliminate an undercut formed by an interior boss are shown below.
The original housing design is shown in (1). The bosses create undercuts that cannot be cast. An alternative is shown in (2) where the bosses are relocated on the outside of the box, eliminating the undercuts. In (3) the original design has the bosses cored by providing an opening through the bottom wall. In (4) the bosses are extended to the bottom wall of the enclosure, eliminating the undercut. However, without the additional coring shown in (5), an excessive mass of metal will be present.
The die parting line location may be important to the application because of the line left on the die casting where the die halves meet. If required, the casting must be trimmed along this line and the trim die must be configured to it and maintained. Simplification of the parting line configuration will reduce the cost of manufacturing and maintaining the trim die. In some cases, a simplified parting line may negate the need for clean-up operations on external surfaces.