Mould design Angles stop negative areas from ‘undercutting’ injection process

Editor: Eric Culp

The more complex injection mould parts become, the more difficult it can be to remove them from the tool. A Spanish injection moulder called a component supplier for help.

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The problem with the Audi Q3 S-Type grille was threefold: the large angle of the undercuts, the large number of undercuts per bar and the high number of cavities in the mould.
The problem with the Audi Q3 S-Type grille was threefold: the large angle of the undercuts, the large number of undercuts per bar and the high number of cavities in the mould.
(Source: Cumsa)

Injection moulder and toolmaker Maier S. Coop, Guernica, Spain, decided to examine a completely new approach to one of the classic problems that arises during the design stage of a plastic injection mould: undercut release. In many plastic parts, negative or “undercut” areas need to be released in order to allow the part to be ejected. Sometimes it is not possible to do this by means of a conventional external slide core, so it is necessary to use an angled device actuated by the movement of the ejector plate that carries the ejector pins.

Abandoning tradition to find a better solution

The traditional solution to this particular problem has always been to use lifters or other similar angled mechanisms that convert the ejector plate movement into lateral part release, which allows the undercut to be freed. This, however, has always required difficult angled machining operations for the plates and inserts of the mould.

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See: Additive manufacturing of blow-moulding test tools

In the case presented here, the moulded products in question are the chrome-plated bars on an automobile’s front grille, namely that of the new Audi Q3 S-Type. The problem was threefold: the large angle of the undercuts, the large number of undercuts per bar and the high number of cavities in the mould.

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