A plastic part moldability design resource

Moldability 101

The mission of this seminar is to help plastic part designers better understand injection molds, the design constraints imposed by the physics of molding, and the influence of molding mechanisms on part design.

Injection Mold Basics

Mold Standardization

MOLD BASES Mold base nomenclature The standardization and mass production of mold bases has resulted in naming conventions for basic mold parts that follow across all manufactured lines of moldbases and mold components.

Undercuts and Side Actions

UNDERCUTS Undercuts are those portions of the part that can not be pulled in the line of draw. If an undercut were to be machined into a mold without a mechanism to releive it, the part would be destroyed upon mold openi

Shutoff Angles

A shutoff angle has an entirely different reason for being than does a draft angle . A draft angle exists for purposes of part release, while a shutoff exists to prevent the two halves of the mold from crashing into one

Draft Angles

The purpose of draft is to first provide release from the cavity side of the mold upon tool opening. Then upon ejection, draft allows instant release of the plastic part without dragging. If plastic parts have completely

Parting Lines

The term parting line is a bit of a misnomer. Perhaps the term parting surface would be better. Many plastic part designers seem to have difficulty understanding that the parting line is not simply a vector that may be r

Shrinkage

as it applies to injection molding is the contraction of the molded part as it cools after injection. Most of the part shrinkage occurs in the mold while the molds internal cooling systems are solidifying the thermoplast

Steels

Following is a list of some of the most commonly used materials for mold construction. They include the following: P-20 Pre-hard steel. Rc 29-36. The most common tool steel used, it is a favorite among mold makers for it

Making Great Parts

Flaws and Defects

Many flaws and defects can be avoided by using good part and tool design techniques. As a part designer it is a very good Idea to be aware of your options in tooling and to consider those while designing your part. For e

Ribs and Bosses

The design of moldable ribs and bosses is outlined on the following two pages. Once you understand the 66% rule the design of ribs is pretty much straight forward. Bosses however seem to be the #1 feature that must be re