What is Injection Moulding

In short: Injection moulding shapes plastic parts by injecting molten thermoplastic into a metal mould, the dominant process for high-volume plastic components. Carmo has injection-moulded in Denmark for more than 70 years, from single-use medical parts to HF-weldable technical components.

Injection moulding is one of the most common ways to produce plastic products. It is a fast process used to make large numbers of identical parts: from complex, high-precision components to single-use consumables. It works with a wide range of materials, including thermoplastics: the material is fed into a screw and melted by electric heating and friction, then injected into the cavity of a mould, where it cools and hardens to take the cavity’s shape.

Carmo brings 70+ years of advanced moulding experience, and shares it

Carmo has developed and produced injection-moulded parts for over 70 years, and we are glad to share that experience. We are experts in plastic moulding, with more than 70 years of hands-on experience designing, developing and producing high-quality components: for industries as varied as medical, marine, mining, agriculture and automotive.

If you need advice or a sounding board for your project, we are happy to talk. In our experience we add the most value when we are involved early, so material, geometry and technology are chosen for the best possible result.

Rapid prototyping: moulding combined with additive manufacturing

Carmo developed Carmo Print Moulding, a unique setup that combines additive manufacturing with injection moulding. It lets us design and produce highly complex components at tight tolerances, including in 2K, delivering prototypes in half the time and at half the cost of traditional prototyping. Read more about Rapid Prototyping and Carmo Print Moulding.

2K moulding

Using two or more injection units: also called 2K moulding: two or more materials fill the cavities at once, enabling very complex components. One example is Carmo’s range of sample-port connectors in PP, PVC and TPE, with properties tailored to the end product and to integration in the production line.

2K injection moulded part — 2K-moulded component

Overmoulding and insert moulding

Plastic can also be moulded over another part. Moulded over a part that was itself moulded first, usually plastic over plastic, that is overmoulding, used for soft grips, seals and two-colour parts. Moulded around a pre-made component, often metal, that is insert moulding: for example metal snap fasteners insert-moulded with PVC so they can be HF-welded onto projector screens, or surgical tips with an embedded aluminium wire and flexible TPE, enabling bend radii that were not possible before.

Frequently asked questions

Injection moulding basics

What is injection moulding?

Injection moulding is a manufacturing process that shapes plastic parts by injecting molten thermoplastic into a metal mould, where it cools and solidifies into the finished component. It is the standard way to make the same plastic part accurately and repeatably, in volumes from thousands to millions; the same tool can run for years, which is why injection moulding dominates high-volume plastic component production across medical, technical and consumer products. Carmo has moulded components this way for over 70 years. The range runs from HF-weldable technical components to single-use medical parts, which Carmo has supplied for more than 60 years.

How does injection moulding work?

In four steps: plastic granules are melted in a heated barrel; the melt is injected under pressure into a closed mould; the part cools and solidifies in the cavity; the mould opens and ejects the finished part. Then the cycle repeats. Cooling usually takes the most time, so wall thickness and material largely set how fast parts come off the machine.

What is an injection mould (the tool)?

The mould, also called the tool, is the precision-machined metal block that holds the cavities and cooling channels the molten plastic is injected into; it is what gives every part its geometry. Production moulds are cut from steel or aluminium to tight tolerances and built to run for years. The tool is usually the largest single cost in injection moulding, which is why tool-design decisions carry so much weight. For prototypes, Carmo 3D-prints mould inserts (Carmo Print Moulding) so functional prototypes arrive in days, in the production material.

What is cycle time in injection moulding?

Cycle time is how long one full moulding cycle takes (inject, cool, eject), and it sets how many parts a tool produces per hour. Cooling normally dominates it, so wall thickness, material and cooling-channel design drive the number. At volume, cycle time is one of the biggest levers on the price of each part. In Carmo’s production, cooling typically accounts for most of the cycle, which is why wall thickness is reviewed with the customer before the tool is cut.

What is clamping force?

Clamping force is the pressure the machine holds the mould closed with while plastic is injected, measured in tonnes. It has to exceed the force the injection pressure exerts on the part’s projected area, or the tool would open and the part would flash. Larger or higher-pressure parts need more clamping force; machines range from tens to thousands of tonnes.

What materials can be injection moulded?

Most thermoplastics, the plastics that melt and re-solidify repeatably, can be injection moulded, from commodity polymers like PP and PE to engineering and medical-grade materials such as PC, PA, TPE and PVC. Material choice drives strength, flexibility, chemical resistance and regulatory fit, so it is usually decided together with the part design rather than after it. At Carmo we mould these daily, from standard thermoplastics to medical grades, produced under Carmo’s ISO 13485 quality management system in Denmark.

Updated 1. September 2026