CUMSA Comercial de Utiles y Moldes, S.A.

Angles stop negative areas from ‘undercutting’ injection process

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.

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.
n 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.

Discussing alterations with the component supplier

Once the moulder discovered the undercuts could be released by using the DH series vertical lifter from Cumsa, Maier contacted the supplier and learned that a number of modifications would be required. Some of them would be relatively easy, for example, merely an increase in the length of the pin. Others, however, were not. Some required the release of undercuts angles of up to 28 degrees from an ejection stroke of 13 mm.
Cumsa said it rose to the the challenge by modifying its lifters in quickly enough to allow Maier to develop two different solutions for the same problem. Maier manufactured two different moulds, one with traditional-style inclined lifters and the other with Cumsa’s devices.

Savings during mould construction and beyond

Cumsa said its system provides a range of advantages during the construction of the mould. Maier is quoted as saying that the system offers space savings, easier machining and simplicity of assembly. In addition, the system is expected to also reduce maintenance requirements for the entire life of the mould, so the savings are achieved not only in the initial phase but extend through the lifetime of the project. The moulder said the machining process has been simplified and plenty of space has been freed up in ejector plates. This makes possible, for instance, the addition of many more regular ejector pins, should they be required.

System also allows for improvements in processing

Moreover, with this new design, the required ejector stroke is reduced, which is said create faster cycle times that in turn provide cost savings. This can also be added to the time savings for mould construction, which is quoted at 40% thanks to the ability to machine less and easier. This system also reportedly allows two units to be assembled very closely together, which in the case of most conventional lifters is not possible.

Cumsa said it is also developing a completely new range of lifters based on this concept. These will target large moulds with deeper release movements.