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A single or multi-cavity mould: which is best for your project?

When manufacturing plastic products via injection moulding, you can use either a single or a multi-cavity mould. What is the difference between the two and how can you choose the best one for your injection moulding project? We will explain all this and more below.
What are sliding elements in a mould for? Sometimes, it is impossible to open a mould once it has been filled with the cooled plastic, e.g. because of apertures in the plastic or because of the product’s complex shape. The product is “locked” inside the mould, as it were. To get it out, the mould has to have one or more sliding elements. Undercuts are used in these locations.

The difference between single-cavity and multi-cavity moulds

A single-cavity mould produces a single product per cycle, while a multi-cavity mould produces more than one product per cycle. At this moment Rompa has a thirty-two-cavity mould that produces circa thirty-four million (!) plastic components per year.

What is cavity in moulding?

The sequence of events during the injection mould of a plastic part is called the injection moulding cycle. The cycle begins when the mould closes, followed by the injection of the polymer into the mould cavity. Once the cavity is filled, a holding pressure is maintained to compensate for material shrinkage.

Cycle time

Whether you need a single or a multi-cavity mould depends on the number of products you want to produce within a certain timeframe, and the cost advantage. If your product has a cycle time of one minute, you will never be able to produce one million products a year with a single cavity mould by injection moulding. After all, there are only 525.600 minutes in a year. On top of that, it takes time to optimally set up the injection moulding process. We also calculate time to conduct preventative maintenance to the mould. If your goal is to produce a million products per year, you will need a multi-cavity mould, e.g. a four- or eight-cavity mould. Rompa’s experts can help you make the right choice.

Shot guarantee

All our new moulds come with a shot guarantee. It guarantees the minimal operating time of the mould without costs for the customer. A single-cavity mould usually comes with a shot guarantee of one or two million shots, depending on the material, product design and tolerances. If you want to produce more products with the same mould, it is advisable to opt for a multi-cavity mould. For example, a four-cavity mould is capable of manufacturing four million products within the shot guarantee.

Pros of a multi-cavity mould

  • The desired number of products will be finished sooner because of the shorter lead time per batch;
  • You can produce more products with the same mould within the shot guarantee;
  • A four-cavity mould has, in most cases, a lower total cost of ownership (TCO) than four single-cavity moulds.
  • More efficient use of the cycle time;
  • Major scale benefits for stable processes;
  • Lower part price.

Cons of a multi-cavity mould

  • One multi-cavity mould requires a more substantial investment than one single-cavity mould;
  • A longer lead time for the mould manufacturer;
  • If there are any problems with one of the cavities, the entire mould will have to be taken out of the machine, which means the other cavities cannot be used either;
  • When using an automated process to operate a mould with a large number of cavities (thirty-two or more), each cavity will have to be absolutely perfect.

Let our injection moulding experts advise you

Would you like to know what the best mould for your project is? Our injection moulding experts can help you decide. As an injection moulding company, we are closely involved in the design of our moulds and we collaborate with you and the mould manufacturer to choose the best and most efficient option.