TECH UPDATE EXCLUSIVE

Molders Get a Grip on Added Functionality of Overmolding

Stephanie Steward

That soft touch texture, great for handles of surgical instruments, used to be the reason to use overmolding. However, added functionality due to material advances and creative product development have resulted in a long list of reasons to use overmolding, including noise and vibration dampening, shock absorption, reduced assembly cost, and brand identification.

"New ideas are constantly coming forward that challenge our design and manufacturing engineers," says Paul Mazelin, sales and marketing manager for Specialty Silicone Fabricators Inc. (Paso Robles, CA). "We are seeing [overmolding used in] new areas today and I'm sure there will be more, especially with the development of more heat-stable thermoplastic materials."

The technique is also starting to be used to combine parts with flexible hinges, says Michael Hansen, senior technical development engineer for Mack Molding (Arlington , VT). "Another application is to mold-in functional features like ports, plugs, or hooks as part of the overmolded soft-touch area," he adds.

The multimaterial molding process allows manufacturers to take advantage of different materials' unique properties by combining them into a bonded unit. Selecting compatible materials is crucial to producing a secure bond. According to Hansen, compatibility is based on a number of factors, chemical affinity being the most important. In addition, the design process can be complicated.

"Companies don't choose overmolding right from the start unless there is some specific reason for it," says Mazelin. But advances in heat stability of thermoplastic materials, as well as plasma and corona etching treatments and primers that enhance adhesion, have benefited overmolding, Mazelin adds. Hansen concurs. "The overmolding grades bond to more substrates than ever before, including, if required, specially prepared metal substrates," he says.

Rob Gilman, plant manager for Plastics Engineering and Development Inc. (Carlsbad , CA), notes, however, that although materials have improved, finding equipment is still an issue. "There needs to be more two-shot mold makers and less-expensive two-shot machinery," he says.

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