August 2003 Design Tip

Don't cut corners! Foci on your radii.


Figure 1 - Corner radii enhance part quality.

Whenever possible, a part to be injection moulded should be designed with generously radiused corners to enhance its quality and mouldability.

As illustrated in Figure 1, corners designed without radii can cause stress concentrations. These in turn may reduce the ability of the part to withstand load and/or cause warping in its geometry.


Figure 2 - Corner radii enhance mouldability.

Figure 2 illustrates how sharp corners might adversely affect the flow of resin during moulding, potentially causing incomplete fill. They also tend to cause the part to stick to the mould during ejection, which can cause a variety of problems.


Figure 3 - Corner radii can enhance mould life.

And in Figure 3 we show how the judicious use of fillets can also help to improve mould life by helping to minimize corner stresses at the bottom of tall, thin cores in the mould (at the entrance to deep thin holes in the plastic part). These fillets also help to enhance the ability of the mould to fill and further reduce internal part stresses.

See the Protomold Design Guide for more details.

Special thanks to Mr. Luther Lieh for this "Design Tip" suggestion. A package of Protomold goodies is on its way as a small token of our appreciation.