January 2004 Design Tip

In-depth design considerations.

To fully exploit the use of Rapid Injection Moulding to manufacture your part, it is important to remember that the process uses three axis CNC milling equipment to machine the moulds.

Figure 1 : A ProtoQuote® illustration
showing a part wall thickness that is
below the minimum size that can be
milled at that depth.

Because the length of an end mill is typically limited to about eight to twelve times its diameter, it may not be possible to produce fine geometry details when a long tool is required. Figure 1 is a recent ProtoQuote® illustration that shows how we would bring this type of issue to the attention of the designer.

Secondly, all end mills have a finite length, so even the most accessible part features can only be machined to a given depth (see Figure 2).

Figure 2 : An illustration of a feature
on a part design that cannot be produced
due to excessive depth.

As noted in the Protomold Design Guide, the maximum part depth is 3 inches if the parting line can pass through the middle of the part or 1.5 inches if the parting line needs to be at one edge of the part.

And finally, just as draft helps in the mouldability of the part it can also help to provide access to deeper features. So be sure to draft your deep vertical walls as much as possible.

You can visit the Protomold Design Guide for other helpful Rapid Injection Moulding design information.