Overmoulding techniques in medical device manufacture – what you need to know
Today’s medical devices often need to do things that a single material can’t deliver on its own – and the gap shows up in some very specific places.
For instance, the grip on a surgical instrument that needs to stay controlled through a long procedure. The housing on a wearable that has to be rigid enough to protect its internals and comfortable enough to sit against skin for hours. The overshield on an auto-injector that needs to compress predictably every time.
These aren’t unusual requirements – they’re the kinds of design challenges that land on development teams regularly, and overmoulding is often the most practical answer.
What is overmoulding and how does it work?
The process involves moulding one material over a pre-formed substrate to produce a single bonded component. The substrate goes into the tool first. A second material is then injected over or around it, bonding to form a unified part that behaves as one rather than two.
In medical device production, the most common form of overmoulding pairs a rigid thermoplastic substrate with a softer TPE or silicone overmould. The rigid layer provides structure, and the softer layer handles grip, cushioning or tactile feedback at the surface. Where a component needs to bring together more distinct functional properties, multi-material medical moulding can accommodate additional materials, each contributing something different to the finished part.
The result is a component that would be difficult or impossible to produce any other way, without secondary assembly operations and without the reliability risks that come with bonding separate parts together.
Benefits and applications in medical device production
The case for overmoulding in medical devices usually starts with ergonomics. Surgical instruments held for long procedures, handheld diagnostic devices and wearables worn directly against the skin – these are products where grip, comfort and control have a direct bearing on clinical outcomes. Overmoulding allows soft, tactile surfaces to be integrated precisely where they’re needed, producing ergonomic medical device design that would require multiple components and assembly steps to achieve any other way.
Durability is the other major gain. Assemblies held together with adhesives or mechanical fixings have weak points, and in clinical environments, those weak points get tested. Sterilisation cycles, repeated handling, demanding use conditions all put stress on joins that overmoulded medical components simply don’t have. The substrate and overmould bond structurally, producing a part that’s more reliable in the field and less likely to cause problems over its service life.
Beyond grip and durability, overmoulding opens up design options that matter in healthcare applications. Seals and barriers can be integrated directly into a component. Electrical insulation can be built in. Colour coding – useful for device identification or dosage differentiation – can be achieved without labelling. Connector housings, device grips, needle overshields, wearable housings and components for diagnostic equipment are all areas where custom overmoulded housings routinely deliver advantages over conventional single-material approaches.
Key considerations
Overmoulding produces excellent results when it’s specified correctly. Getting there requires some careful upfront thinking.
Material compatibility is the starting point. The substrate and overmould materials need to bond reliably – this depends on chemical compatibility, processing temperatures and surface preparation. Not all material combinations work, and selecting pairings that perform in both processing and end use is something that benefits from early involvement of an experienced medical plastic injection moulding company.
In healthcare applications, biocompatibility is non-negotiable. Both materials used in biocompatible overmoulding need to meet the relevant standards for their intended use – whether that’s skin contact, mucosal contact or implantation. This shapes material selection from the outset and has implications for the qualification and validation work required before a product can go to market.
The process also places real demands on tooling and process control. Wall thicknesses, gate positions and injection parameters all need to be dialled in to ensure the overmould bonds consistently and the finished part holds its dimensional tolerances across a production run. In medical applications, that consistency is a much a regulatory issue as it is a quality issue.
On cost and production, tooling for overmoulding is more involved than single-material moulding – two tools are typically required, and the moulding process takes longer. For high-volume programmes, the per-unit economics are generally strong. At lower volumes, it’s worth modelling the numbers carefully against the alternatives. Lead times also need to account for the additional validation steps that medical device production requires.
When does overmoulding make sense for your project?
Overmoulding is worth specifying when the design has genuine requirements that a single-material component can’t meet – structural complexity, integrated soft-touch surfaces, built-in sealing, or material properties that need to vary across a single part. Where those conditions exist, it’s a strong option. Where they don’t, the tooling investment and validation overhead may not be justified and a simpler approach may serve better.
For medical device designers and manufacturers working through those decisions, the process is easier with a medical plastic injection moulder in the UK that understands both the manufacturing side and the regulatory environment.
OGM: Expert medical injection moulder in overmoulding technique
OGM has been producing precision plastic injection moulded components for the medical and healthcare sector for over 60 years, with an ISO Class 7 cleanroom, full design for manufacture services and in-house tooling capability. If overmoulding is on the table for your next project, our team can help you establish whether it’s the right route – and deliver it if it is.