Draft Angles in Die Castings

Kinetic Die Casting Company discusses “Draft Angle in Die Castings” – “what is draft angle in an aluminum metal box casting?” or “why do I need a draft angle on my aluminum die casting box part?” The mechanical reply is, all aluminum die castings need a draft angle on the walls of die cast box parts perpendicular to the parting plane or parallel to the slide interfaces. Because I have been selling die cast parts for over 20 years, I find easy answers and give simple calculations for my clients. What does that have to do with the usual engineer (any engineer other than in tooling or mechanical) or professional buyer?

Most people do not have the need to worry about how things are made; only what is made, and will it be what is essential. “Have you ever observed on a cupcake the bottom diameter is smaller than the top diameter?” or “Have you noted that a cake pan has sides that slope in toward the middle of the pan?” That would be an extreme case of a draft angle. Aluminum die castings would stick inside the die casting tool, molds, or die casting die if there was not enough draft angle in the tool and part. The usual draft angle for an aluminum die casting part is two degrees per side. The calculation for that is easy if a anyone is acquainted with die casting production part design.

Imagine an enclosure (or Aluminum Box) lying on a counter with the open side up. The aluminum box is 2″ deep inside with the height and width 4″ each way on outside. The walls of the box are 0.10″ in width. Due to the wall’s thickness, a few things are obvious to a part designer regarding this seemingly simple box:

  • The general height of the box is 2.10″ tall.
  • The inside of the box at the top of the opening is 3.80″ x 3.80″.
    A 2 degree draft angle will alter the dimensions in the following on the interior and exterior and should be regarded if something needs to fit inside the box or outside the box:

  • The top inside dimension of the box will be 3.80″ and the bottom inside will be 3.664″
  • The top outside dimension of the box will be 4.00″ and the bottom outside will be 3.864″
    If the box was intended for the interior of 4″ x 4″ at the bottom: box:

  • The top inside box dimension needs to be 4.136″
  • The outside top box dimension will be 4.336″.

    See our die casting draft webpage: http://www.kineticdiecasting.com/draft.html

    Contact Kinetic Die Casting Company at 800-524-8083 for more information

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