Die Casting - Draft

Draft is the amount of taper or slope given to cores or other parts of the die cavity to permit easy ejection of the casting from the die casting die.

All die cast surfaces which are parallel with the opening direction of the die require draft (taper) for proper ejection of the casting from the die. This draft requirement, expressed as an angle, is not constant. It will vary with the type of wall or surface specified, the depth of the surface and the alloy selected.

The amount of draft required for holes, inside and out walls is different. Untapped holes require the most draft because the casting shrinks (while cooling) with great force around the die steel while forming the inside surface of the hole. Inside walls also are subjected to the casting shrinking onto the die steel that creates the surfaces of inside walls. Outside walls require the least amount of draft because the casting shrinks away from the die steel forming outside surfaces.

When proper draft is applied to a die casting it is much easier to open the die and also eject the casting from the die surfaces. A die that is easy to open and eject castings from will result in a more precise die casting with a higher surface quality.