Constantly evolving, the medical industry requires OEMs to be forward-thinking in providing solutions that address trends and challenges. One such OEM, Smiths Medical, sought to change the design of its existing pulse oximetry portfolio to include enhanced functionality and improved manufacturability. At the project’s inception, they partnered with the U.S.-based injection molding experts at Kaysun to help refine and ultimately accomplish their goals.

The more companies learn about overmolding, the more they want to use this special plastic injection molding technology to add value to their product lines. Not only does overmolding improve functionality and performance, it lowers total production costs—that’s pretty rare these days.

Overmolding is a unique injection molding process that results in a seamless combination of multiple materials into a single part or product. It typically includes a rigid, plastic-base component overlaid with a thin, pliable, rubber-like thermoplastic elastomer (TPE) exterior layer or other materials using either a single-shot (insert molding) and two-shot (multiple-shot molding) technique.

Complex injection molding is a viable solution for many projects, but there’s often hesitation in using it because of confusion about which material matches the job. While “thermoplastic” and “thermoset” sound similar and both are appropriate for a wide range of applications, the material properties of these two resin categories and how they behave during processing ultimately reveal the best fit.

It’s a world of handheld devices we live in today: smartphones, tablets, GPS assistants and specialized power tools for the shop, lab, kitchen and garden. Medical facilities depend on portable digital devices to care for patients, contractors align studs with pocket-sized levels, troops perform safely in the field with reliable, high-performance equipment and gear, and households are stocked with all kinds of gadgets that make life easier.

Medical grade polymers are quickly becoming the preferred material for a broad range of surgical devices. In certain applications, the robust mechanical properties of medical molding polymers allow complete removal of metal from the surgical device design. In other instances, plastic and metal components can combine to create an enhanced product, with attributes that would not be possible in either an all-metal or an all-plastic device. 

Insert molding is a type of overmolding where a hard substrate component or “insert” is placed inside a mold cavity in an injection molding machine and then “overshot” with an exterior layer—typically a thermoplastic elastomer (TPE). The interaction between the insert and the TPE must be fully understood to create the strongest possible bond. The surface of the insert should also be free of contamination, including dust or even skin oil—even the slightest contamination can weaken the bond between the TPE and the substrate, leading to premature failure.  

The use of overmolding is popular across many manufacturing industries, from consumer products to medical devices, but possibly in no category more noticeable than portable devices. While in some applications, overmolding may seem to merely enhance the aesthetics of a device at first glance — a contrasting color or texture — the use of overmolding on portable devices intended for critical use is highly technical and sometimes highly regulated.

Overmolding is a value-added injection molding method for improving plastic and metal substrate performance and aesthetics. While seemingly simple, the process has a number of underlying complexities which must be carefully considered to ensure your overmolding project meets all goals and expectations.