Mould Design in Plastic Injection Moulding

Mould Design in Plastic Injection Moulding 

Injection Moulding is an extremely versatile procedure.  It can be utilised for virtually any product. Injection moulding is the industry standard for manufacturing components for products.

There are some limitation needs to consider. Here are the rules to follow when designing your product to make sure quality and durability:

Wall Thickness

Keeping your walls thin will ensure a faster cooling rate and less materials used. Lower cooling rate and less material used will result in a shorter cycle time. This allows you more parts in a shorter amount of time, for less production cost

To strengthen parts, ribs are more effective than thicker walls. Adding ribs at right angles to a wall will add considerably to its overall strength. It is a common mistake to thicken the walls of a design to achieve this effect when ribs are a cheaper and more effective option.

Ribs should be about half the main wall thickness. There can be some leniency here, but not too much or the ribs will be completely ineffective. Half is the generally accepted standard and is more than enough to increase a wall’s strength.

Try to make your design uniform throughout. That is, wall thickness, rib thickness and corner radii, for instance, should all be the same values. This will help the part to cool uniformly.

Corners & Edges

Corners could be an issue in a mould and will not come out flush. It is difficult to form plastic into a flawless corner. The outcome will look amateurish and messy, not to mention the power of the components can be compromised.

Corners and edges should be rounded wherever possible. Sharp edges do not always come out perfectly when the part is ejected from the mould.

Add a slight angle to the sides of your mould to allow easy release. A one- or two-degree angle should be applied to the mould on the face perpendicular to the parting line. This will allow for easy removal of the part from the mould.


These are structural factors for your component, utilised for general stability control. Ribs are thin wall protrusions which extend vertically from a plane or wall. Adding ribs instead of thicker walls will provide greater structural support.


These are empty, cylindrical protrusions. These are normally integrated in a style for accepting screws or other mating parts of your style. Making sure these are secured by attaching them a wall. Putting in ribs will means the bosses will stay straight as well as accommodate the part it was made for without an issue.

External Undercuts

A depression or protrusion in the exterior of the mould – the cavity half – could create issues if trying to divide parts from the mould. Adjust the parting line to lodge this.

Internal Undercuts and Overcuts

Related to external undercuts, these depressions or protrusions are within the mould – on the centre half. Adjust the parting line to lodge this.

Protrusions on the part that will snag on the mould core or cavity when it is opened can make it impossible to remove from the mould.


When your mould has a thread, always position it vertical to the parting column. This will make sure that the delicate thread isn’t damaged. It’s better, preferably, to not comprise a thread at all in the design. Making your design simple will lower the odd of something going wrong.

Injection moulding design makes a superior product. The myriad possibilities far outdo the limitations. Designing for an excellent injection moulded part is the core of the design process.  These restrictions are the guidelines for making a flexible end product.

Colour use
Where possible, use lighter colours for your moulds. The mould is already cool when the molten material is being injected. As such it begins the setting process immediately and will sometime leave setting patterns. Using lighter colours will help hide these patterns.

Injection moulding is the industry standard for creating lasting, quality parts. To be able to take advantage of this technology your design must meet its minimum requirements. Small considerations are all it takes and the result is a successful product that will meet all of your quality needs.

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