Part Ejection

Protomold uses pins to eject parts from the mold during production. Designers should be aware of the need to accommodate such pins.

The Protomold Rapid Injection Molding process uses ejector pins of various sizes to push the plastic part out of the mold after it has solidified. The sizes and arrangement of these pins are selected to minimize the impact on your part design. 

Figure is an example of the illustration Protomold provides early in the process of designing the mold so that the location and size of both the gate(s) and ejector pins can be approved.

Figure: A typical Protomold-supplied gate and ejector pin layout submitted for customer approval.

Sometimes it is appropriate to adjust the design of the part to accommodate the need for ejection pins to push the part out of the mold. For example, Figure 2 illustrates how an injector pin "landing pad" has been integrated into the wall of a part design in order to provide sufficient material for the full diameter of the pin to meet the part. Landing pads may also be used to provide additional support for the ejection of thin curved walls, and in some cases the pins themselves can be contoured to fit the shape of the part. 

Of course, always remember to provide as much draft as possible so that the ejector pins can do their job, especially for applications where it isn't possible to use mold-release lubricants to help the part eject more easily. 

Each situation is different, but a good understanding of the use of ejector pins is important when designing a part to be Rapid Injection Molded.

Figure: The wall of this part has been increased to support the full impact of the ejector pin without damaging the part.

The mold core-cavity approach

Consider core-cavity approaches when possible

As an alternative to deep ribs, consider using the illustrated type of core-cavity approach to produce a similar geometry.

This mold will be faster and less expensive to manufacture, and the quality of the final part will be improved (polishing is much easier on core-cavity geometries than down inside deep ribs).

Deep Rib Approach

Box designed with walls as ribs. Higher cost to machine and polish cavity.

Core Cavity Approach

Box designed thru core-cavity method. Can get to features with bigger faster cutter. Easier and faster to polish.

Side Action Support for Simple Undercuts

The maximum side core dimensions are summarized in the following tables: 

Our process can support up to four side actions per mold, and they all need to be at the parting line. Side pulls must be perpendicular to the primary (A-B sides) pull direction. 

Side Action molds that support simple undercuts are available with our standard lead time of 10-15 business days. In some cases faster deliveries are available. 

A side action used to create a through-hole undercut feature.