What to consider when creating a plastic injection mould

Your design is finalised. You know the type of plastic needed. You worked out any bugs at the prototyping stage. Now you’re ready to begin manufacturing your part with plastic injection moulding

The next step is to make the mould, which is the most expensive part of the process, especially if it is geometrically complex, so you need to make smart decisions. By working with an experienced manufacturer, you can make sure that the mould you create suits your needs and provides return on your investment.

How is the mould made?

Some mould makers use Computer Numerical Control (CNC) machining. CNC machining uses computers to control the tools so it can make complex moulds with accurate details in less time than standard machining. Electrical Discharge Machining (EDM) is another process, which applies a voltage between tool and mould that causes spark erosion of the mould surface.

Each have their own advantages and, really, the best option depends on the mould you’re creating. Generally, EDM is a better choice for a complex mould, while CNC machining offers higher accuracy. A good manufacturer should be able to advise you on which option is the most cost-effective for you, while delivering the best results.

What needs to be considered when creating a mould?

During the injection moulding process, the material cools before shrinking from a liquid state to a solid. Your mould will need to accommodate this changed state, which is why cavities are scaled up. This allows the plastic to shrink back to the desired size.

Choosing whether your mould should be made from aluminium or steel is also an important decision. Aluminium costs less, but its production life is shorter. However, if your production run is short – and by short, we’re talking around 10,000 units – then it’s an ideal solution.

Modern hard aluminium can give you a longer production life of around 100,000 units or slightly more but only if the mould design is strong and is properly maintained.

For a production run that will last several years and include millions of parts, steel is your best option. It simply lasts longer and carries none of the risks of softer materials. Before you make that investment though, create a prototype with a softer mould, such as those commonly used in short production runs, to make sure the dimensions are correct.

What will a mould cost?

As the saying goes, how long is a piece of string? In addition to the material used, the number of cavities helps determine the cost. The more cavities, the more complex the mould, the more undercuts needed and so on, the costlier it is to make. However, investing the time and costs now will be sure to pay off in the long run if you get it right.

By talking to an expert from the beginning, you can make sure that the mould you create will meet your needs. We are experts at every stage of the process, from concept to manufacturing and distribution, and we can suggest ideas that will make the mould-making process easier and more cost-effective.