Once the material choices are manageable, economics become a large part of the equation. Depending on the geometry of the part, there are several manufacturing methods which may be considered. If the part is simple and symmetrical, it favors almost any manufacturing method, and is most desirable.
If the engineered plastics part is more complex, it may limit the manufacturing and tooling methods that would otherwise be available for consideration.
The raw material cost, the number of available cavities to mold the part, the part tolerances, aesthetics, and control methods will also have to be considered, as well as the tooling cost, which can vary widely, depending on many variables.
Perhaps the most impactful factor is the required volume of product, as considerable economies may come into play with larger volumes, but tooling may become an issue for smaller volumes.
The next step is to consider the “down-stream” elements of the project. These elements are generally more abstract and intuitive, and require considerable thought. For example, does the model you have developed lend itself to assembly? If you have the most economical model available with a dynamite material such as engineered rubber, but it is difficult to assemble in the application, it may not be worth going down this path.
Is it possible that proximity to other components may cause issues?
For example, ozone has a detrimental effect on many rubber materials, so everything else may be right on target, but the part will craze and crack due to ozone exposure.
How about aesthetics and/or marking?
If the part is to be assembled in any area which is visual for the customer, the engineered rubber and plastics must not leave a mark or create any crazing or cracking with mating parts. Some automotive OEM’s are demanding environmental compliance with ISO 14000, which calls for recyclable materials, and could create major constraints.
If the part is to be “pre-assembled” with the intent of the automotive OEM taking the part out of the box and assembling it, are the rubber and plastic components affixed to the unit in a way that will withstand the rigors of shipment?
Most automotive OEM’s will not accept a component if one if the parts has become dislodged, even if it is a simple refit process to put it back on. Slight modifications to the geometry of the part may be required to ensure that all downstream considerations are covered, but everything must be analyzed abstractly in order to head off potential problem.
Once the tooling is produced, it is very expensive to make changes.
When these considerations have been qualified, it’s time to review tooling. The complexity of the part will largely determine the tooling cost, and anything that can be done to avoid sharp corners and blind pockets will promote flow and avoid air trap between polyurethane o-rings, for example.
A smart engineer will go as far as to visualize parting lines in the mold, and work them into the solid model to create the splits and review the resulting tool. If there is any way to avoid undercuts (areas that prevent normal opening and closing of conventional tooling), it will pay large dividends.
If undercuts cannot be avoided, making them perpendicular to the parting line will soften the costs associated with tool construction, as core pulls and slides are easier to design and integrate. For additional information, please visit: http://www.real-seal.com/ to learn more.
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