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Overmoulding and insert moulding—additional injection moulding functionality

16th February 2017

Posted By Paul Boughton


Injection moulding is now even more versatile – when combined with overmoulding or insert moulding. Stephen Dyson explains how these services can improve part design, strength, functionality—in addition to reducing assembly time and costs

Overmoulding and insert moulding are low-cost ways to provide designers and developers with high-quality prototypes or low-volume end-use production parts as quickly as possible.

But there are some important differences between the two processes.

The greatest impact of the overmoulding or insert moulding processes is seen in products involving multiple injection-moulded components—and these can be made from a variety of plastics and metals.

If the finished item requires many parts and processes, overmoulding and insert moulding simplify their manufacture by reducing the number of components needed. So complex products become easier, faster and cheaper to complete. And with fewer parts, they have greater strength and stability.

A wide range of products, across multiple industries, have been made using either overmoulding or insert moulding or both.  

Cars, planes, power tools and medical equipment all benefit from the extra functionality, improved strength and lower assembly costs these techniques demand.

Overmoulding – adding texture and colour

Overmoulding is the injection moulding of one substance over another. The biggest benefit is that overmoulding lets you bind ‘soft-touch’ material to a product. This can improve grip and durability—for example, on a toothbrush handle. It can also add shock-absorbing properties and dampen vibration. Plus, the overmoulded material can be in a contrasting colour, enhancing the aesthetics of a product.

Designs for overmoulding involve three 3D CAD files: for the substrate, the overmould and the assembly. Each mould has an A side and a B side, and mould designers create the shut-offs and parting lines, along with the layout of the gate (or gates) and ejector pins—all customised to each specific part design. When the mould designs are approved and the moulds made, the overmoulded parts can be manufactured from a range of thermoplastic and liquid silicone rubber materials.

Insert moulding – integrating pre-formed components

Creating one integrated piece from two components, insert moulding involves loading a pre-made part—often metal—into a mould, and then overmoulding it with thermoplastic. Typical inserts include threaded components, bushings or metal bosses, all of which enhance a product’s functional or mechanical properties.

Insert moulding often results in stronger, lighter products, as the process helps add stability and strength without the need for multiple parts. For example, an electric lawn trimmer constructed in two halves is much more robust when the casing is held together with threaded inserts rather than with numerous fixings.

Which process to select? And when?

Both overmoulding and insert moulding make design and development quicker and easier, and improve products in different ways. When you need better grip or shock absorption, overmoulding is the ideal technique.

And when the secure interconnection of parts is essential, insert moulding is the choice for you.

Whether individually or together, insert and overmoulding create more design choices and more opportunities for enhancing performance. With its growing versatility, injection moulding will result in significant benefits and advancements for future manufacturing projects.

Stephen Dyson is Product Manager at Proto Labs.









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