E-PAC® Design Guidelines

Uniform wall thickness;
In most cases, the minimum thickness of any portion of your E-PAC design should be 8mm. This is because E-PAC raw material is in the form of a pellet with a diameter of about 4mm. For the molding process to work, all areas of the part need to be at least two pellets thick. Another important design consideration is uniform wall thickness. E-PAC parts are most efficiently manufactured when there is minimal disparity in cross section thickness. Basically, the thicker the average cross section of an E-PAC part, the longer it will take to mold. If E-PAC parts have too much variation in wall thickness the thinner areas will over heat in the mold and some loss of surface quality might be seen.

Walls, flanges, ribs, or other protrusions whose height is more than three times their width should be avoided. In most situations tall, thin walls are difficult to fill during molding resulting in poor fusion of the E-PAC material. Care should also be taken to avoid narrow gaps between walls. Narrow gaps cause complications in the mold, which could decrease its efficiency.

Radii;
Radii aid in the molding process and should be added wherever practical. With the exception of the parting line, all corners and edges should be 0.3mm-radius at a minimum. Generally speaking, rounds and fillets are always preferable to corners and edges and the greater the radius the better. Consulting with Foam fabricators early in the design cycle will define the parting line where rounds and fillets are not possible.

Filling;
E-PAC molds are filled by blowing pellets into the mold with compressed air, unlike the injection molding process where liquid plastic is injected into the mold. Thin, complicated areas may be impossible to fill depending on their proximity to the filling orifice.

Filling orifices need to be placed on a flat plane parallel to the parting plane. These areas should be at least 20mm in diameter. Depending on part size and complexity, a part might need to be filled from several orifices. The location of these orifices can be critical to the moldability of the finished part. Consulting with Foam Fabricators early and often during the design will ensure proper placement of both fill and eject areas.

Draft Angles;
Molded parts generally require angled walls to aid in part ejection. The designer should be aware of this fact when creating an E-PAC part. The location of the parting line is essential to the placement and direction of draft angles. Establishing parting line and draft angles should be done with Premier Industries unless the designer is very experienced.

Undercuts;
E-PAC molds are usually not built with mechanical pulls or other moving parts. Care should be taken to avoid all undercuts unless they are absolutely necessary. If undercuts are unavoidable we can work with you to make sure they are designed in such a way that they can be molded.

Tolerances;
All molded parts will shrink to some degree when they are removed from their mold. Molded foam polymers do so to a greater extent than many materials. These shrink rates can affect part tolerances depending on the size of the molded part. E-PAC molds are designed with this in mind but E-PAC designers should keep in mind these values:

Dimension	Tolerance
0 - 40 mm	+ / - 0.4 mm
40 - 120 mm	+ / - 0.5 mm
120 - 400 mm	+ / - 0.8 mm
> 400 mm	+ / - 1.0 mm or .25%

Design Example:

Hewlett Packard Co. pioneered and patented the E-PAC process and now you can share in this new technology. The E-PAC design process utilizes a chassis made of custom molded resilient foam that holds components in a form-fit and form-locking manner.

Many current applications utilize a sandwich approach with top and bottom foam pieces that lock components between them. For example, instead of fastening a cooling fan to a wall or chassis with screws, use an E-PAC design to sandwich the fan and hold it in place. This not only eliminates fasteners, as the resilient foam chassis will also dampen vibration and noise created by the fan. Additionally, the use of fewer fasteners can lead to savings in assembly labor.

Improve the fan performance by utilizing the custom molding design feature of E-PAC, which allows you to incorporate an air duct into the fan enclosure, directing the cooling air to the location where it is most effective. At the same time, organize and protect wiring by providing wiring channels through the foam chassis. The end result is a quiet fan, operating more efficiently, and held in place with fewer fasteners.

This standard design suffers from vibration, undirected airflow and loose wires and its assembly requires fastners.(click this image to zoom in) This E-PAC fan assembly (shown here in red) system reduces fasteners, cuts assembly time and diminishes noise from vibration. E-PAC parts are easy to mold, allowing a custom-designed air duct and wiring channels to be incorporated into the assembly design. (click this image to zoom in)