In a plastic injection moulding project, the mould usually represents the largest initial investment. However, its influence extends far beyond the cost of the tooling.
The mould design directly affects cycle time, surface quality, dimensional stability, material consumption, machine productivity and, ultimately, the cost of each part produced.
For this reason, selecting the correct type of mould is one of the most important decisions during the industrialisation of a plastic component.
At Gestión de Compras, we design and manufacture plastic injection moulds for sectors such as the automotive, construction, agriculture, furniture and industrial equipment industries. Our experience shows that many opportunities for optimisation arise even before the first mould is manufactured, when it is still possible to adapt the component’s design to the most efficient solution.
There is no single type of mould that is suitable for every project. The choice depends on striking a balance between investment, production volume, geometric complexity and industrial strategy.
Single-cavity moulds: maximum flexibility for small production runs
Multi-cavity moulds: productivity and reduced cost per part
As production volume increases, the priority shifts from the cost of the mould to the cost per part.
Multi-cavity moulds allow several parts to be produced in a single cycle, improving productivity and making better use of the injection moulding machine’s capacity.
However, this solution also increases technical complexity.
Flow balance, cooling, simultaneous filling of all cavities and dimensional stability become critically important.
Even a minimal difference between cavities can result in parts with different weights or dimensions.
For this reason, the design of a multi-cavity mould requires much more advanced engineering than the simple repetition of cavities.
Family moulds: a solution with advantages… and limitations
Family moulds allow several different parts to be produced during a single injection cycle.
This strategy can be very advantageous when different components form part of the same assembly and are always used in the same proportion.
However, they also have significant limitations.
Different geometries may require different material volumes, filling times or cooling rates, making it difficult to balance the process.
For this reason, family moulds are usually recommended only when there is a high degree of compatibility between the parts.
Cold runner or hot runner: a decision that affects costs for years to come
One of the factors that has the greatest influence on process efficiency is the mould feeding system.
Cold runner moulds produce a sprue that must be separated from the part after each cycle. Although their initial cost is lower, they increase material consumption and, in certain cases, require additional operations.
Hot-runner systems virtually eliminate this waste, keep the molten material flowing right up to the gates and significantly reduce plastic consumption.
The initial investment is higher, but it is usually recouped quickly in medium and high-volume production runs.
Therefore, the choice between the two solutions should be made by considering the expected volume over the entire lifetime of the project, and not solely the initial cost of the mould.
Cooling: the least visible element and one of the most important
Regardless of the type of mould selected, there is one factor that directly affects productivity: the cooling system.
In many injection moulding processes, more than half of the cycle time is devoted exclusively to removing heat from the material.
Well-designed cooling reduces cycle time, improves dimensional stability and minimises the risk of warping.
Conversely, poor thermal management can turn a technically sound mould into an uncompetitive process.
This is precisely why cooling must be considered from the very start of the mould design process and not treated as a secondary consideration.
The importance of designing the mould with manufacturing in mind
One of the most common mistakes is to design the part and then try to adapt it to the mould.
The most efficient strategy is precisely the opposite.
Designing the part whilst taking into account the behaviour of the injection moulding process allows for the simplification of the mould, a reduction in manufacturing times, the minimisation of secondary operations and an improvement in process repeatability.
Aspects such as wall thicknesses, draft angles, the position of ribs or the location of parting lines have a direct influence on the complexity and cost of the mould.
Gestión de Compras’s experience
At Gestión de Compras, we design and manufacture plastic injection moulds for a wide variety of industrial sectors, playing an active role from the earliest stages of industrialisation right through to mass production.
Our experience shows that the decision on the type of mould cannot be made in isolation. It must be analysed in conjunction with the part design, the anticipated production volume, the selected material and the overall manufacturing strategy.
This approach enables us to propose solutions that not only meet technical requirements but also optimise the cost per part, improve productivity and ensure process stability throughout the mould’s service life.
Conclusion
Choosing an injection mould is not simply a matter of deciding how many cavities it will have or which feeding system to use.
It means defining how a component will be manufactured over thousands — or even millions — of production cycles.
Therefore, the decision must be made by considering not only the initial cost of the mould, but also the impact it will have on productivity, quality, material consumption and the competitiveness of the final product. In plastic injection moulding, the mould is not merely a tool. It is the element that determines the efficiency of the entire manufacturing process.