Why use Draft Angle?

If you’ve ever wondered if draft angles were a must, we’ve got the answer for you

The justification for draft angles comes from the nature of the injection molding process, and the ever present issue of mold shrinkage. Injection molding is a high-pressure process. These high pressures force the plastic into intimate contact with all surfaces of a mold’s cores and cavities. This high-pressure packing of the cavities makes it difficult to get the part out of the mold, or “eject” the part.

Draft facilitates the removal of the part from the mold and is very important in injection molding where the molds are straight pull only (no side actions).

The guidelines associated with the number of degrees of draft required will vary with geometry and other part characteristics (e.g. surface texture requirements), but in general the more the better. Draft is your friend when building molds.

Here are some rough guidelines to follow:

• We ask for at least 0.5 degrees on all “vertical” faces
• 2 degrees works very well in most situations
• 3 degrees is minimum for a shutoff (metal sliding on metal). Without this, the
  mold would lock up and be unable to open
• 5 or more degrees is required for heavy texture

Remember, draft is your friend when designing molds.