Design Tips for Rapid Injection Molding
As illustrated in figure 1, draft is the angle between the direction of ejection of a part from the mold and the surface of the part. Its traditional function is to facilitate the removal of the part from the mold, but in Protomold’s Rapid Injection Molding process, it also permits deeper geometries to be milled while reducing cost and insuring trouble free molding. Drafts of 1.0 degree and larger may result in lower costs with the Rapid Injection Molding process.
It is important that textured surfaces have adequate draft to prevent the part from sticking in the mold and to prevent “drag” marks. Protomold requires that lightly textured surfaces (T-1) have a minimum of 3 degrees of draft and that more heavily textured surfaces (T-2) have a minimum of 5 degrees of draft.
Another example of the importance of draft in the manufacturability of your design is illustrated in figure 2. In this case the draft not only helps the part eject from the mold more easily, but it also minimizes the amount of sliding required between the mold’s telescoping shutoff surfaces. A minimum of 3.0 degrees of draft is required for telescoping shutoff features.
Draft your way to a better part
©2007 Protomold. All rights reserved. Volume 1 n Draft your way to a better part n 3
It is important that textured surfaces have adequate draft to prevent the part from sticking in the mold and to prevent “drag” marks.
Figure 1: Draft definition.
Figure 2: Draft can also improve mold life.
No draft results in sliding parallel mold surfaces
Draft results in improved mold shutoff surfaces