Plastic injection moulding isn't the right choice for every project. The production volume, component geometry, and required tolerances determine whether the mould investment will pay off. This article explains when injection moulding is indeed the most logical production method, and when you'd be better off choosing an alternative such as 3D printing or milling.
Volume as a starting point
The most important variable in the choice of Plastic injection moulding It is the production volume. A mould requires a one-off investment that quickly runs into the thousands of euros. This investment is spread across all the parts that come out of it. At low volumes, the cost price per unit remains high. At higher volumes, this cost price quickly drops to a level that other processes cannot achieve.
As a general rule, injection moulding starts to become interesting from around five thousand units per year. Above that, with tens of thousands or hundreds of thousands of parts per run, it is almost always the most cost-effective production method. For example, a connector housing that costs two euros per unit when milled can be reduced to fifteen cents through injection moulding at sufficient volume.
Eurotechniek assesses per application whether the volume justifies the mould investment. Sometimes an aluminium mould for a smaller series is the right interim solution. This is cheaper to purchase but less durable than a hardened steel mould for long-term production.
Reproducibility and measurement
Injection moulding produces the same part every cycle. That is the core of the process. If you need parts with tight tolerances that must be consistently maintained over thousands or millions of cycles, then injection moulding is the method of choice.
Suppose you are producing an enclosure that needs to make a clamp connection to a mating part. The fit must be correct every time. With milling, this depends on the settings per batch. With injection moulding, the geometry is in the mould and is reproducible by definition, provided the process parameters are stable.
This makes injection moulding popular in sectors such as medical technology, electronics, and automotive. In these fields, tolerances and repeatability are non-negotiable. Eurotechniek records a measurement protocol with every production run, ensuring dimensional traceability throughout the entire product lifecycle.
Material freedom as an advantage
A strong argument for injection moulding is the breadth of the material spectrum. Virtually any thermoplastic can be processed, from standard PP and ABS to high-performance engineering plastics like PEEK, PEI or PA-GF. This gives you the freedom to choose the material based on the functional requirements of your part.
Do you need a component that is resistant to high temperatures, chemicals, and mechanical stress? Then choose PEEK or PPS. Are you looking for a lightweight structural component with good impact resistance? Then PA66-GF30 is a solid choice. Different process parameters apply to each material, but the production method remains the same.
This is a direct advantage over metalworking. Metal gives you strength and rigidity, but not material choice that is specifically tailored for chemical resistance or electrical insulation. Injection moulding does give you that specific tailoring, without compromising on dimensional accuracy.
Complex geometries in one step
Injection moulding makes it possible to produce complex shapes in a single process step. Ribs, threads, snap-fits, cooling channels, and integrated mounting points can all be part of the mould design. What requires multiple machining steps in milling leaves the mould as one integrated part in injection moulding.
A good example is electrical switch housings. They have internal ribs for rigidity, external snap-fits for assembly, and sometimes inlays for metal contacts. All these functions are combined in a single injection moulding cycle. This saves assembly time and reduces the risk of assembly errors.
The 2K process adds another layer to this. In this process, two materials are combined in one cycle, for example, a rigid PA support structure with a soft TPE grip surface. During the design process, Eurotechniek assesses which geometry and process variant best meets the functional requirements of the part.
When injection moulding isn't the right choice
Honesty is important in this consideration. Injection moulding is not always the best option. For prototypes or small runs of fewer than five hundred units, the mould investment does not outweigh the returns. In such cases, 3D printing or milling is almost always cheaper and faster.
Injection moulding also encounters limitations with components that have extremely thick walls or entirely solid sections. The cooling time then increases significantly, and shrinkage problems become harder to control. For such applications, casting in polyurethane or a combined metal-plastic construction may work better.
Furthermore, injection moulding requires preparation time. The mould lead time ranges from four to twelve weeks depending on complexity. If you need parts tomorrow, injection moulding is not the solution. Eurotechniek helps determine the right production method, even if it's not injection moulding.
Design and mould: making the right choices early on
An injection-moulded part only functions correctly if the design takes into account the process's capabilities and limitations. Wall thickness, draft angles, rib positioning, and gate location are decisions made during the design phase. Retrofitting takes time and money.
A concrete example: a wall that is too thin in a section of the part can lead to short-shot during injection. A wall that is too thick without a rib structure leads to sink marks due to uneven shrinkage. Both problems can be prevented with a good DFM (Design for Manufacturability) process before the mould is built.
Eurotechniek routinely conducts a feasibility study for new product requests. This study suggests design modifications to enhance production stability and optimise cycle time. This way, you avoid costly mould modifications later on and ensure a smooth production start.
Frequently asked questions about plastic injection moulding
From what volume is injection moulding profitable?
As a guideline, a minimum volume of five thousand pieces per year applies for a standard two-part mould. For simple geometries and an aluminium mould, this can be lower, from approximately two thousand pieces. For complex moulds with multiple cavities or sliding mechanisms, a higher volume is required to recoup the investment. Eurotechniek calculates the break-even per request based on the mould type, the expected volume, and the desired cost per piece.
How long does it take for a new injection moulding project to go into production?
The lead time from design to first series production varies from six to sixteen weeks. This depends on the complexity of the mould, the availability of material, and the number of iterations in the validation phase. After the mould has been delivered, a T1 sample round follows, during which the dimensions and the process window are verified. Series production only starts after this. For time-critical projects, it is best to discuss this early in the process with Eurotechniek.
Can injection moulding also be used for small series?
Yes, but with adjusted expectations and a suitable mould type. For series of five hundred to three thousand pieces, an aluminium prototype mould is a realistic option. It is quicker to produce and cheaper than a hardened steel mould, but has a shorter lifespan. The parts are qualitatively equivalent to series production. This allows you to test functional parts under actual production conditions early in the product development process.
The right method for your part
Injection moulding is a strong process for those who combine volume, repeatability and material choice with complex geometries. The investment in the mould pays for itself through low unit prices, stable quality and an efficient production process.
Not sure if injection moulding is right for your application? Eurotechniek will help you think it through from the very first drawing. Get in touch via euro-techniek.nl and explain your situation.