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Holes Plastics One Injection Molding Holes are easy to produce in molded parts. Core pins that protrude into the mold cavity make the holes when the part is molded. Through holes in the molded parts are easier to produce than blind holes, which do not go all the way through a part. Blind holes are made by core pins supported on one end only. The pins can be deflected and pushed off center by the pressures of the molten plastic material during the molding process. A good rule of thumb: the depth of the blind hole should be about twice the diameter of core pins up to 3/16", and up to four times the diameter of core pins over 3/16". The guidelines for blind and through holes are seen below. Blind Hole (shown with draft) Through Hole (shown with draft) There are definite rules for the placement of cored holes in a molded part. If these minimum distances shown below are not followed, the holes will be egg shaped or the part will deform in the areas around the holes.
As depicted above, the distance from the edge of a hole to a vertical surface (i.e. rib) or the edge of a part should be twice the part thickness (or more), or at least one diameter of the hole. This same rule applies between holes - at least two part thicknesses or one hole diameter should be specified. |
