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Using Rapid Manufacturing to Mitigate Design Risk in Overmolding and Insert Molding

Confirming your part design can be molded early in the design process can help reduce risks.

An insert-molded part with a brass insert. Image courtesy of Proto Labs.

Overmolding and insert molding are well established processes for combining two different materials in the same finished part. Such molding techniques are commonly used in medical device manufacturing, but there are still some "unseen risks," reports Becky Cater, global product manager for injection molding at Proto Labs. The company will be on hand to discuss such risks and potential ways to address them at the upcoming MD&M East expo in New York City June 13-15.

Overmolding can be used for enhancing the durability, tactility, or aesthetics of handles and other parts, Cater told Qmed. Insert molding typically involves a metal insert that is used to reinforce an outer plastic part. "Incorporating threaded metal inserts into a plastic part is the most common application of insert-molding," she said. Other overmolding applications include molded-in gaskets, which can later help save device assembly steps.

Given the investment historically needed for such molding processes, time and cost are at risk. "With the conventional molding process, it takes a significant commitment of money and time to develop a mold," explains Cater. "You often need to have months to spare as well as demand for 100,000 parts or more for the mold to pay for itself. Waiting months to get your first sample parts means that by the time design or manufacturing issues are discovered, it is often too late to make design modifications."

Another risk is material compatibility. "A key consideration in overmolding and insert molding is material compatibility to make sure the two materials stay joined," she said. "The best way to verify material bonding for a given part design is to manufacture parts early in the design process that are representative of the final production parts."

To help engineers address these risks and to make overmolding and insert molding more accessible, Proto Labs has developed what it calls "rapid overmolding," says Cater. "We can reduce the risks in design by confirming the part is manufacturable early in the design process and getting parts in the customer's hands quickly for design validation. We have greatly reduced the cost and lead time for overmolded and insert molded parts by automating the quoting and manufacturing processes, leveraging the digital thread by starting with a 3D model rather than a 2D drawing."

For instance, Proto Labs invites potential customers to upload their 3D CAD models to its Web site, and "they will know within a matter of hours whether their parts are moldable," Cater said. "We analyze their designs with our software to assess moldability and provide the feedback via an online interactive quote. Our team of application engineers is also available for a consultation to help work through any challenges."

Such feedback is particularly useful when it comes to material compatibility. "For materials that don't bond well chemically during the overmolding or insert molding process, we can work with the customer on ways to incorporate a mechanical interlock for additional bonding assurance," says Cater.

Once the design has been finalized, the company then employs automated software to make the molds. Leveraging this automation to dramatically reduce manufacturing time, Proto Labs can deliver between 25 to 10,000+ finished molded parts in 15 days or less. The company stocks hundreds of engineering-grade thermoplastics and liquid silicone rubber materials for prototypes and end-use production parts. "And If we don't stock the particular material the customer is looking for, we do accept most customer-supplied resins as well," said Cater.

For more details, visit Proto Labs at Booth #409 at MD&M East June 13-15. In addition to discussing rapid overmolding, the company will be highlighting recently introduced services such as like PolyJet and HP Multi-Jet Fusion 3D printing as well as pre-announcing some changes to its injection molding services.

Daphne Allen is executive editor of Pharmaceutical & Medical Packaging News and a contributor to Qmed. Reach her at and on Twitter at @daphneallen

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