Injection Moulding

Injection Moulding UK

We are able to produce injection mouldings in a range of sizes from a few grammes, to over 4.5 Kilos in weight. Insert moulding is undertaken on the latest vertical Arburg machinery.

Materials are selected to suit the application range from the simplest of commodity materials such as Polypropylene or Polythene, to specialised engineering thermoplastics such as PBT and PPO. Our advanced materials selection processes ensure that components are tailored to specific applications.

When a reasonable volume of components are required, then DST moulding will produce parts at speeds approaching that of thermoplastic injection moulding. The materials used give exceptional electrical resistance coupled with good dimensional stability and rigidity. Materials processed include: Phenolics, Polyester, Urea, Melamine, Epoxy & DAP.

The Merriott Plastics Group consist of two UK manufacturing sites, one in Somerset and the other in Kent, that are highly equipped with a huge range of injection moulding machines and injection moulding tool making machinery. Our knowledge and experience of the injection moulding industry is second to none, allowing us to produce components with extreme accuracy, superb consistency and on time – every time. This experience is invaluable at the design and planning stage, giving you the benefit of our injection moulding experience to streamline the tooling process and therefore making the injection moulding run as perfectly as possible. If you have any queries please call us or make an enquiry via our contact page.

What is Injection Moulding?

Injection moulding is a manufacturing process for producing components by injecting material into a mould. Injection moulding can be performed with a host of materials, most commonly thermoplastic and thermosetting polymers. Material for the component is fed from a hopper into a heated barrel, mixed, and forced into a mould cavity, where it cools and hardens to the configuration of the cavity. Injection moulding uses a ram or screw-type plunger to force molten plastic material into a mould cavity; this solidifies into a shape that has conformed to the contour of the mould. Injection mouldings count for a significant proportion of all plastics products from micro parts to large components such as vehicle bumpers and wheelie bins.

The sequence of events during the injection moulding of a plastic part is called the injection moulding cycle. The cycle begins when the mould closes, followed by the injection of the polymer into the mould cavity. Once the cavity is filled, a holding pressure is maintained to compensate for material shrinkage. In the next step, the screw turns, feeding the next shot to the front screw. This causes the screw to retract as the next shot is prepared. Once the component is sufficiently cool, the mould opens and the part is ejected.

After a product is designed, usually by an industrial designer or an engineer, moulds are made by a mouldmaker (or toolmaker) from metal, usually steel or aluminum, and precision-machined to form the features of the desired part. Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars.

Components that will be produced by injection moulded must be very carefully designed to facilitate the moulding process; the material used for the component, the desired shape and features of the component, the material of the mould, and the properties of the moulding machine must all be taken into account. The versatility of injection moulding is facilitated by this breadth of design considerations and possibilities.

Thermoplastics are prevalent due to characteristics which make them highly suitable for injection moulding, such as the ease with which they may be recycled, their versatility allowing them to be used in a wide variety of applications, and their ability to soften and flow upon heating. For thermosets, typically two different chemical components are injected into the barrel. These components immediately begin irreversible chemical reactions which eventually crosslinks the material into a single connected network of molecules.

Pre-moulded or machined components can be inserted into the cavity while the mould is open, allowing the material injected in the next cycle to form and solidify around them. This process is known as insert moulding and allows single parts to contain multiple materials. This process is often used to create plastic parts with protruding metal screws, allowing them to be fastened and unfastened repeatedly. This technique can also be used for in-mould labelling, and film lids may also be attached to moulded plastic containers.

Injection moulding machines consist of a material hopper, an injection ram or screw-type plunger, and a heating unit. Also known as presses, they hold the moulds in which the components are shaped. Presses are rated by tonnage, which expresses the amount of clamping force that the machine can exert. This force keeps the mould closed during the injection process. Tonnage can vary from less than 5 tons to over 9,000 tons, with the higher figures used in comparatively few manufacturing operations. The total clamp force needed is determined by the projected area of the part being moulded.

Moulds or dies are the common terms used to describe the tool used to produce plastic parts in moulding. Since moulds can be expensive to manufacture, they are usually only used in mass production where thousands of parts were being produced. Typical moulds are constructed from hardened steel, pre-hardened steel or aluminum. The choice of material to build a mould from is primarily one of economics; in general, steel moulds cost more to construct, but their longer lifespan will offset the higher initial cost over a higher number of parts made before wearing out.

Two-shot or multi-shot moulds are designed to “overmould” within a single moulding cycle and must be processed on specialised injection moulding machines with two or more injection units. This process is actually an injection moulding process performed twice and therefore has a much smaller margin of error. In the first step, the base color material is moulded into a basic shape, which contains spaces for the second shot. Then the second material, a different color, is injection-moulded into those spaces. Push buttons and keys, for instance, made by this process have markings that cannot wear off, and remain legible even with heavy use.

Modern day injection moulding machines are controlled by a built-in computer. Acting on sensor fed information, it controls all the actions of the machine and ensures consistent output and shot to shot quality.

The Merriott Plastics Group has an extensive range of injection moulding machines to cover a very wide range of plastic component manufacture. Our experience in producing many millions of injection moulded plastic parts stands us in good stead when advising our clients on the optimum techniques to apply to your products. We are specialists in the key area of material selection to compliment the product and its applications, from highly durable rail components on both trains and their rails, to tiny widgets around the home and garden.

Contact us now to see how we can help your injection moulding projects run smoothly.

Merriott Plastics Group – your premier injection moulding company in the UK.


© Merriott Plastics Group Ltd  |  Somerset: +44(0)1460 72457  |  Kent: +44(0)1634 298500
Website design by Interface