What is Injection Moulding

Injection Moulding (or Molding to use the US spelling) ranks as one of the primary manufacturing processes for producing plastics articles. It is a fast process and is used to produce large numbers of identical items – from high precision engineering components to disposable consumer goods.

Injection moulding can be performed with a host of materials, including thermoplastics. Material for the part is fed into a heated barrel and melted by use of electrical heating and friction. The melted plastic is then injected (forced) into a mould cavity, where it cools and hardens to the configuration of the cavity.

Injection moulding tools (moulds)

The central part of the process is the die, or mould which contains the cavities and the cooling system. moulds are made by a mould-maker (or toolmaker) from metal, usually either steel or aluminium, and precision-machined to form the features of the desired part. A single tool can contain from 1 to several hundred cavities, depending on the size and complexity of the part.

Production quality moulds are made from hardened steel, the grade is chosen based on the type of plastic to be moulded, the surface finish required and the temperature at which the tool will run. Prototype moulds or those where production volumes are very low, are often made of aluminium or unhardened steel.

Carmo work together with a carefully selected group of toolmakers. The supplier for a particular mould is carefully chosen from the competences required, price and delivery deadlines. Our engineers work very closely with the toolmaker to achieve the optimal mould design for short cycle times and accurate part geometry.

Where to use Injection molding

Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars. Advances in 3D printing technology, using photopolymers which do not melt during the injection moulding of some lower temperature thermoplastics, can be used for some simple injection moulds.

Parts to be injection moulded must be very carefully designed to facilitate the moulding process; the material used for the part, the desired shape and features of the part, 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.

A thorough understanding of both the toolmaking and injection moulding process is a huge advantage in designing both cost effective and functional parts. It is often possible to combine several parts into one moulding process or assemble and print finished parts directly from the moulding machine. Carmo have a team of experts, with many years of experience, ready to explore possibilities with the customer, as early in the design process as possible.

2K injection moulding

By using two or more plasters, 2 or more materials can be used to fill cavities concurrently og sequentially, allowing for the realisation of very complex components. An example is Carmo’s range of sample port connectors featuring PP, PVC and TPE for tailored properties in the functionality of the end product, and the integration into the assembly line.

2K injection moulded part


It is also possible to mould plastic over other materials, even aluminum and steel. This opens up new possibilities for the part designer. For instance, metal snap fasteners overmoulded with PVC, enabling HF welding to projector screens. Or applicator tips used in operating theatres with inbuilt aluminium wire overmoulded with flexible TPE, enabling previously impossible bending radii.