Snap hinge

Snap hinges are an advanced design of living hinges that have two stable end positions: open and closed. These hinges are characterised by the fact that they can snap into two fixed positions by means of a spring mechanism.

The functional principle of a snap hinge is based on a spring-loaded four-bar linkage. In addition to the hinge groove, which serves as the pivot point of the living hinge (pivot point 1), three additional hinge grooves and a spring element are used to achieve the two stable end positions. This design allows the hinge to be held in the end positions without any additional force being required.

Snap hinges are mainly used in injection-moulded parts made of polypropylene (PP). When designing such hinges, care must be taken to ensure that the spring element is almost relieved in both rest states – that is, in the "open" and "closed" end positions. This is an important requirement, as spring elements made of plastic can lose their spring force under load over the long term. It is therefore essential that the spring element is designed so that it is not permanently under tension in the end positions, in order to ensure a long service life of the snap hinge.