Injection molding

What is plastic injection moulding?

Plastic injection moulding is a moulding process in which molten plastic is injected under high pressure into a mould.
Once it has cooled, the plastic sets, the mould opens and the finished component is removed.

The following are characteristic features of plastic injection moulding:

• high dimensional accuracy
• consistent quality
• excellent reproducibility

This process is primarily used where technical components are required in medium to large production runs.

Classification of the proceedings

Plastic injection moulding within the plastics industry

Plastic injection moulding is a primary forming process and differs significantly from other plastic processing methods such as:

• Extrusion (continuous profiles)
• Thermoforming (shaping of semi-finished products)
• Blow moulding (hollow products)
• Moulding process (thermosetting plastics)

The main advantage of injection moulding lies in the combination of:

• complex component geometry
• high level of automation
• commercial-scale production

The injection moulding process

The injection moulding process follows a clearly defined, cyclical sequence:

1. Plasticising

The plastic granules are melted and homogenised in the machine’s plasticising unit by means of heat and mechanical agitation.

2. Injection

The molten plastic is injected into the closed injection moulding mould under high pressure.

3. Reprint

During the cooling process, additional pressure is applied to compensate for shrinkage and ensure dimensional stability.

4. Cool down

The plastic solidifies in the mould. The cooling time has a significant impact on cycle time and part quality.

5. Demoulding

The mould opens and the finished component is ejected.

In series production, this cycle is repeated automatically and with a very high degree of process stability.

Key terms in plastic injection moulding

Injection mould

A moulding tool, usually made of steel or aluminium, which forms the negative mould of the component.

Cavity

The mould cavity in the die that determines the final shape of the component.

Sprue

The channel through which the molten plastic enters the cavity.

Cycle time

The time taken for a complete injection moulding cycle (from injection to demoulding).

Shrinkage

Volume change in the plastic due to the material properties during cooling.

These terms are fundamental to understanding the entire injection moulding process.

Materials in plastic injection moulding

In plastic injection moulding, thermoplastics are predominantly used, supplemented by special thermosets and elastomers.

Typical groups of materials:

• Polyolefins (e.g. PP, PE)
• Engineering plastics (e.g. PA, ABS, PC)
• High-performance plastics (e.g. PEEK)

The choice of material affects:

• mechanical properties
• Temperature resistance
• chemical resistance
• Component costs

→ Further reading: Materials used in plastic injection moulding

Typical applications

Plastic injection moulding is used across a wide range of industries, including:

• technical functional parts
• Housings and covers
• Fasteners
• Precision components

The process is particularly suitable for components with:

• complex geometry
• tight tolerances
• high quality standards

Cost and influencing factors

The cost-effectiveness of plastic injection moulding is primarily influenced by:

• Tooling costs
• Component geometry
• Choice of materials
• Quantity
• Cycle time

Taking these factors into account at an early stage is crucial for an efficient production process.

Note: This page provides an impartial overview of the process. Information on the specific production and implementation can be found in the Services section.