Ejecting Miniature Parts via Ultrasonics
Instead of being ejected mechanically, moulded parts can also be ejected from the mould through use of ultrasonics. This approach leaves no marks on the plastic surface – an important benefit when producing microinjection moulded parts.
Conventional ejector systems leave witness marks on the moulded part that are often viewed as reducing quality. When moulding miniature parts in particular, the marks from ejectors can even be larger than the geometric details on the moulded part, since manufacturing limits are encountered when attempting to miniaturize ejector systems – the size cannot be reduced endlessly. As a result, they cannot always be used when producing microinjection moulded parts. In many cases, alternative ejection methods such as stripper plates, grippers or pneumatic systems do not provide satisfactory results either.
To eject miniature and microinjection moulded parts, the Plastics Technology Centre (Kunststoff-Zentrum) in Leipzig (KuZ) has developed an ejector system that employs ultrasonics. In contrast to the mechanical approaches taken to date, this technique leaves no quality-reducing witness marks on the moulded part.
The ultrasonic actuation system is incorporated into the standard ejector system in the mould. To eject the moulded part, the ejector of the injection moulding machine advances the ultrasonic system toward the mould parting line. Once it is in the forward position, the ultrasonic actuator is energized. This ejects the moulded parts from the mould. The control systems of the ultrasonic generator and injection moulding machine are linked to one another, so that a continuous injection moulding process is possible.
The patented ejector system is independent of moulded part geometry. It is suitable for thermoplastic materials and can be employed in single-cavity as well as multi-cavity moulds. This presents new possibilities regarding part design for miniature and microinjection moulded parts. This, in turn, opens up new fields of application for micromoulded parts.