Overmoulding is a versatile injection moulding manufacturing technique that involves applying a thin, additional layer of plastic over a moulded part to enhance functionality and comfort. The layer can be added to plastic, metal or other materials and offers several additional features. This is a solid, effective manufacturing method for parts and products that need to contain more than one type of plastic or material in order to facilitate different uses.
Thanks to the overmoulded layer, components can have reduced vibration for shock-absorbing applications, sealing moisture-sensitive products and improving the ergonomics and grip of a product. This versatility is brought about largely by choosing the right material selection for plastic overmoulding.
Overmoulding can be done using different methods: insert moulding (placing a pre-formed insert into the mould cavity and injecting the overmoulding material around it); two-shot moulding (injecting the base substrate material into the mould cavity, followed straight away by the plastic layer over the top) and over moulding with co-injection (injecting both types of plastic into the mould at the same time to improve the bond strength).
What characteristics should be considered in material selection for plastic overmoulding?
Getting the material selection for plastic overmoulding right is key to producing an effective, aesthetically pleasing and durable product. The main considerations for choosing which plastic to use include understanding how well the plastic adheres to the material underneath, along with the compatibility between the base substrate and overmoulding plastic – the bond must be durable and not prone to breaking under stress or regular use.
In addition, properties of the best plastic for overmoulding should include excellent chemical resistance in overmoulding. Materials chosen must also be able to stand up to solvents, oil, corrosion, exposure to UV, moisture and extreme temperatures. Many projects involving overmoulding and overmoulded connectors have stringent requirements around aesthetics – colour, texture, shape and finish. All of these are important aspects of material selection for plastic overmoulding projects. Finally, the materials must adhere to regulatory standards, eg for food safety, biocompatibility, electrical insulation or fireproofing.
What are some common choices of material selection for plastic overmoulding?
Material selection for plastic overmoulding is very important, as it ensures good plastic bonding strength, among other required characteristics. One decision to make is all about TPU vs TPE overmoulding. In other words, whether to use thermoplastic polyurethane (TPU) or thermoplastic elastomers (TPE) for the process. TPU offers strong resistance to abrasion, as well as excellent elasticity and durability.
The process of using TPU as the material selection for plastic overmoulding is common for applications requiring toughness and flexibility in equal measure. TPE are more popularly used for components needing a strong grip and good impact resistance, due to their softer nature and better flexibility. TPE materials bond well with a wide range of base substrates for a longer useful life.
Other common plastics used for overmoulding include polypropylene (PP), which offers good chemical resistance and excellent dimensional stability. It is a popular choice in medical devices. Polyethylene (PE) is very effective for plastic grips, handles and protective covers, thanks to its good impact resistance, lower costs and lighter weight.
Another option when considering material selection for plastic overmoulding is Acrylonitrile butadiene styrene (ABS) – a rigids, strong thermoplastic used a lot as a base substrate material over which the overmoulded plastic layer is bonded through plastic injection moulding techniques. This adds stability and strength to the overall component. Metals and other rigid plastics can also be used to form the base substrate – the choice of materials will depend entirely on the desired performance, aesthetics and features of the finished component or product.