Plastics and metals over molded with elastomers are becoming very popular in the marketplace. A quick walk through virtually any store will yield many examples of products with this construction. Product designs combining two different materials most often use a metal or a commodity hard plastic over molded with a low cost elastomer to make the part efficiently and with low cost. The metal or plastic imparts structural integrity to the product and the elastomer typically provides comfort to the end user or protection to the plastic in end use. Advances in elastomer raw materials utilizing adhesion promoter technology have aided processing and lowered production costs. In large volume applications, the trend has been to go to single step co-injection molding to again promote low cost production. In lower volume applications or products where the material choices are more limited due to functional requirements, two step insert over molding remains an accepted and popular processing choice. In all cases, when designing a product, the benefits of over molded parts should be weighed carefully keeping the cost and technical challenges of multi-material constructions in mind.
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