You need a component that must be produced thousands of times identically. Dimensions are critical, the material must have specific properties, and the cycle time must be low. Then the question is not whether injection moulding is the right method, but how to optimally set up the process. Eurotechniek explains step by step how plastic injection moulding works and what you need to know at each stage.

The die as the foundation of the process

Everything begins with the mould. Without a well-designed mould, it delivers Injection moulding no reliable results. The die determines the geometry, tolerances, and surface quality of each part that comes out of it.

A mould consists of two halves: the cavity side and the core side. Between these lies the cavity, which dictates the shape of the final product. For complex geometries, sliders or lifters are added to create undercuts without damaging the part during ejection.

The mould is typically manufactured from hardened steel or aluminium. Steel moulds last for millions of cycles. Aluminium moulds are cheaper and quicker to produce, but are suitable for lower volumes. Eurotechniek advises on mould selection based on your expected production volume and the required lifespan.

Material preparation and dosing

Before injection moulding begins, the plastic granules are prepared. Many technical plastics, such as PA or POM, are hygroscopic and must first be dried. Insufficient drying leads to air inclusions, surface defects or reduced mechanical properties in the final product.

The dried granules are loaded into the hopper of the injection moulding machine. A rotating screw transports the material forward, melting it through a combination of frictional heat and external heating. The screw simultaneously meters the correct amount of molten plastic for one cycle, known as the shot.

The screw geometry and the temperature zones along the cylinder are set for the specific material. For PEEK, the process parameters are different than for PP or ABS. An incorrect setting will cause degradation of the material and thus a loss of the desired material properties.

The injection phase: speed and pressure

Once the shot is ready, the screw moves forward like a plunger. The molten material is injected into the mould cavity at high speed and pressure through the sprue and runner. This injection phase typically lasts less than a second.

The filling speed and injection pressure are critical parameters. Filling too slowly leads to premature cooling and short-shot. Too high a pressure causes flash at the parting line. The optimal setting depends on the part wall thickness, material viscosity and runner geometry.

Following the injection phase is the post-moulding phase. The machine maintains a reduced pressure to compensate for shrinkage as the material cools and solidifies in the mould. Without sufficient holding pressure, sink marks or voids will form in thick-walled sections.

Cooling, ejection, and cycle time

The cooling phase takes up the largest portion of the total cycle time, sometimes sixty to seventy percent. Cooling channels in the mould dissipate heat and ensure controlled and uniform cooling. Uneven cooling causes shrinkage and distortion, also known as warpage.

Once the part has solidified sufficiently, the mould opens and ejector pins push the product out of the cavity. The positioning of these pins is part of the mould design. Incorrect placement will leave visible pin marks on functional or cosmetic surfaces.

After ejection, the mould closes and the next cycle begins. A typical cycle time for a thin-walled consumer product ranges from five to twenty seconds. For thick-walled technical parts, this can extend to over a minute. Eurotechniek optimises cycle time and cooling strategy during process preparation.

Specialised applications: 2k and insert injection moulding

Besides standard injection moulding, there are processes that add extra functionality to the end product. The 2k process injects two materials or two colours in one combined cycle. The machine rotates or shifts the mould after the first injection and adds the second material.

A practical example: a switch with a hard structural core of PA and a soft TPE grip surface. Both components are produced in one cycle. This eliminates an assembly step and increases the adhesion between the materials compared to gluing or clamping.

In insert injection moulding, metal components, such as nuts, bushings, or contacts, are placed into the mould before injection begins. The plastic encases the insert part, forming a strong mechanical bond. This process is widely used in connectors, electronic housings, and support structures in the automotive sector.

Quality control during production

A stable injection moulding process delivers the same result every cycle. However, process control requires continuous monitoring. Pressure, temperature, cycle time, and screw position are tracked in real-time. Deviations in these parameters are early indicators of quality problems.

First article inspections after the start of a production run are standard. During these checks, the dimensions, weight, and visual quality of the first products are inspected and compared to the drawing. Production only proceeds once the parts are within tolerance.

Eurotechniek works with fixed measurement procedures per production run. This ensures traceability and allows deviations to be quickly linked back to a specific process setting or mould component. This is particularly relevant for parts used in medical applications or safety-critical environments.

Frequently asked questions about plastic injection moulding

Which plastics are suitable for injection moulding?

Virtually all thermoplastics can be processed using injection moulding. Commonly used materials include PP, ABS, PA, POM, PC, and PEEK. The choice depends on the mechanical requirements, temperature resistance, chemical resistance, and the required surface quality. For high-quality technical applications, Eurotechniek provides advice based on the load specifications of your component.

Wat bepaalt de toleranties bij spuitgieten?

Tolerances are influenced by the material, mould accuracy, process parameters and the geometry of the part. Standard achievable tolerances are plus or minus 0.05 to 0.1 millimetre. Materials with high shrinkage, such as unreinforced PP, require wider tolerances than dimensionally stable materials like POM or PA GF. The expected shrinkage of the chosen material is already taken into account during mould design.

How long does it take for a mould to be ready?

The lead time for a new mould varies from four to twelve weeks, depending on the complexity. A simple two-part mould for a flat component is ready faster than a mould with slides, lifters, or multiple cavities. Eurotechniek monitors the tool shop schedule and will update you on the progress and delivery date.

Injection moulding in practice

Plastic injection moulding is a precise and repeatable manufacturing process if it is set up correctly from start to finish. The mould, material, process parameters and quality control together form a system. A weak link in that system is immediately visible in the final product.

Would you like to know if injection moulding is suitable for your part or do you have a specific application? Contact Eurotechniek or view the possibilities at euro-techniek.nl.