3ERP
In the following post, Ronan Ye, a manufacturing specialist from 3ERP, looks at the ways in which using fibre-reinforced and filled materials offers manufacturers of injection moulded components new opportunities for stronger parts.
Injection moulding is a manufacturing process that produces strong and durable parts in giant quantities. It is one of the most cost-effective manufacturing processes and works with a wide array of plastic materials, including thermoplastics and thermosets.
You can, of course, even mould plastic components over other materials using overmoulding and insert moulding.
Sometimes, however, typical injection moulding plastics will not suffice for a part that demands greater strength, durability, or stiffness, and this can make it tempting to use a metal manufacturing process instead of a plastic process.
Fortunately, there is a simpler alternative within the realm of injection moulding. By using fibre reinforced or fibre-filled resins, it is possible to make stronger parts without resorting to metals or an alternative manufacturing process.
Fibre composite materials possess excellent material properties, and many of them can be manufactured just like ordinary injection moulding plastics.
What is a fibre-reinforced/fibre-filled material?
In injection moulding, fibre-filled materials are plastic resins mixed with glass fibres, carbon fibres, silicon fibres, ceramic fibres or natural fibres. These fibres — which are spread more or less evenly throughout the plastic matrix — can be long or short, and they provide advantages such as toughness, strength and a high specific modulus.
Plastics mixed with fibres in this way are known as bulk moulding compounds. Glass fibres are the most widely used in compounds for IM, and can be mixed with plastics like polyamides (nylons) and polycarbonates.
But materials with added fibres are also used in other manufacturing processes besides injection moulding. In fact, the molten plastic used in injection moulding is not an ideal repository for, e.g. carbon fibres, for which a uniform direction of fibres is needed to make truly strong parts.
With the injection moulding process, you cannot control the orientation of fibres when they are mixed into liquid resin, because they end up simply floating within the plastic matrix. For glass fibre-filled parts, this random orientation of chopped fibres still results in strong and useful parts, but it is not a particularly effective use of carbon fibres, which are very expensive and better used in other ways.
Creating continuous fibre-reinforced parts — where fibres are oriented in the same direction for maximum strength — is easier with processes like extrusion or some new forms of additive manufacturing, where the fibres can be easily oriented.
That being said, it is possible to achieve fibre-reinforced moulded parts by lining a mould with a fibre-reinforced fabric then injecting resin into the cavity.
What are the fibre materials used for?
Injection moulding with fibre-filled materials or fibre-reinforced materials can produce parts suitable for many industries. At present, common applications include automotive and aerospace, particularly with regard to lightweight, as well as architectural and industrial parts.
Glass-filled plastics can be used as a metal substitute, with parts such as nuts and bolts, brackets and levers.
The ratio of plastic to fibre also determines the possible uses and applications of composite fibre material. For example, glass-filled polyamide may contain 10, 20, 30, or more than 30 per cent glass fibres.
A recent report from MarketsandMarkets found that the most widely used mix of nylon and glass fibre is the 30 per cent variety, which is often used in the automotive industry because of its high strength and rigidity.