Design for Manufacture – Yeah, it looks good, but can we make it competitively?
Design engineers wear more hats today than ever before. In the past, organizations had extensive staff that would support design projects, and engineers could specialize – not now. With more material choices than ever, design engineers have to consider not only the cost of the materials designed into a product or component, but they also have to consider the cost of manufacture to produce it. When it comes to rubber and plastic elastomer materials, Real Seal routinely provides design support to engineers to help navigate this path.
The 1st order of business is to narrow down the scope of choices for the Bill of Materials (BOM). Thermoset rubber materials generally still offer superior physical properties for sealing applications, but thermoplastics have improved considerably. For manufacturing consideration, thermoset rubber materials generally require more labor intensive processing for manufacture (which is why the vast majority are all molded in China now), while thermoplastics are more capital intensive, and are generally most competitively sourced in the US. Your best bet is to create a specification for the worst case environmental conditions that the component will see, and get quotes based on molders meeting the spec. Real Seal has a fully equipped rubber laboratory and polymer chemist, and routinely assists customers in developing engineering specifications for application.
Dimensions and tolerances must then be considered. Engineers tend to error on the side of caution, and ask for tighter tolerances than are really necessary, and in many cases, this can add considerable cost to the component. Elastometers in particular are engineered to deflect, so tighter tolerances than industry standard are normally not necessary. If the application absolutely must have the tighter tolerances, it is best to ensure that the part is dimensioned on the control document in a place that is measurable. If you indicate a control dimension, for example, from the center of one radius or diameter to another, how is the producer going to measure this feature? The best rule to follow is, “If you can’t measure it accurately, you can’t control it accurately”.
The next consideration is to review the geometry of the component, and determine if you can make it more “mold friendly”. Symmetry is preferred over asymmetry, and any “undercut” areas (areas of the component that would become trapped in the mold, thus making the part difficult or impossible to get out of the mold during process) should be avoided in order to streamline tooling and processing costs. Blind, sharp corners should be avoided, as they tend to trap air during molding and are expensive to cut in tooling, and the thickness of the part should be as consistent as possible in order to get the best results. For thermoplastic materials, the surface to volume ratio is important to consider, as the higher the StV is, generally the more difficult it is to mold. As a general rule, the more generous you can be with allowing for radii, the better molding results you can achieve. If you can live with a draft angle that will help to remove the part from the mold, this may also offer considerable cost savings.
When the general physical review is complete, actual production methods are determined, the focus should be on development of a control document. This document should achieve (3) primary things:
- Identify dimensions and tolerances which are critical to the performance of the unit
- Specify raw material(s) which are specific enough to ensure that the unit will perform as designed, but not so specific as to limit sources of raw material supply to the point where it is economically unfavorable
- Identify and specify any ancillary features for control, including flash allowance, surface finish, gate location restrictions, or aesthetic standards
Other things to consider may include identifying the cavity number with a small raised number on the surface of the part. This will help to identify issues in the mold which are cavity specific. It may also be to your advantage to identify the part with a specific raised part number, and/or include a distinct color, which would help to control the aftermarket if the component will be changed often over the life of the product it is engineered to perform in.
These considerations reflect a good basis for elastomeric component development, but there are literally hundreds of other possible options to consider. Real Seal has built a strong reputation for design support with our customers, and we bring the collective experience of more than 40 years of product development to the table. Give our website a look and see more specifics of the val
