Complex injection molding: What you need to know

March 20, 2018 By Chris Newmarker

With careful planning, complex injection molding can reduce costs, optimize functionality and improve aesthetics in medical devices.

Ken Glassen, Kaysun Corp.

A robot picks up threaded metal inserts and metal spacers that will be placed in the injection mold tooling. Plastic will then be molded over the various inserts. [Image courtesy of Kaysun]

As medical device design evolves to provide ever-improving healthcare outcomes, manufacturers are partnering with full-service, experienced complex injection molders to gain the increased design freedom and process efficiencies necessary to keep pace with medical device advances. This partnership is a consistent value-add, from part and tooling design through material selection and process control, empowering many medical OEMs to address issues before they hit production or the bottom line.

Injection molding gives medical OEMs the latitude to integrate disparate materials — from dissimilar polymers to lenses, fastener threading, metal components and other non-plastics — to facilitate assembly, optimize functionality and increase durability.

The decision to use complex injection molding is commonly driven by several factors, including:

Many of the crucial decisions involved in complex injection molding should be made as early as possible in the design phase and with molder input. At this stage, adjustments have a reduced effect on the total cost and product timeline. When engineers are mindful of medical component design, tooling functionality and materials at the project outset, they can generally prevent missteps in three key areas:

Tooling development is at the heart of the injection molding process, the step from which everything else flows. The ultimate success of the part begins at the point when the engineering team selects the metal from which a tool is made, based on certain process criteria, including:

Ideally, choosing materials for the injection-molded part is a collaboration between the plastics engineer and the OEM to clearly define the project’s requirements and reach a mutual understanding of five defining factors:

Due to the unique nature of medical environments, it’s not uncommon for medical applications to have additional considerations that factor into materials selection, such as:

The high-heat resins required to withstand autoclaving, such as polysulfone (PSU), have their own set of process considerations. These materials are more difficult — and therefore costlier — to work with, mainly due to their higher melting points, which complicates everything from safety compliance to the molding process.

For instance, PSU has a melting point of 700°F, versus 500°F to 550°F for typical resins. These higher demands mean higher risks for both safety and deviation. Since the tooling itself can reach 325°F (as compared to 180°F for a water-heated tool) it is subject to higher levels of thermal expansion, which adds complexity to the overall tooling design process.

Complex injection molding can provide a medical device and equipment manufacturer with competitive differentiation in the progressive medical industry. Moreover, choosing to work with an experienced, full-service molder gives OEMs increased design freedom and process efficiencies that result in high-quality parts and devices that perform with optimum efficiency and at lower total production costs.

Ken Glassen is VP of engineering at Kaysun Corp. (Manitowoc, Wis.) — a provider of custom injection molding and engineering services. Glassen shares and applies his technical plastics engineering expertise to help OEMs in a variety of industries including medical, automotive and defense develop complex injection molding solutions.

The opinions expressed in this blog post are the author’s only and do not necessarily reflect those of MedicalDesignandOutsourcing.com or its employees.