How To Design A Living Hinge In Injection Molding?

In plastic injection molding, designing plastic parts is already a very difficult task, and design living is a part that can be folded and bent repeatedly, which can reduce the number of plastic parts and components and reduce product costs. So design living design is a very challenging job.

The living hinge is a piece of plastic sheet that links two thicker pieces of plastic, and can be folded or bent at a maximum of 180 degrees. But when a part is bent, it generates a strain called tensile stress. If the plastic is too thin, it may not have the necessary strength and the parts may tear. If it is too thick, too much stress will be generated and the part will break.

So, how to realize the design of living hinge in injection molding design? What issues need to be considered? Is the living hinge durable?

Recommended materials for living hinges

Polypropylene is the best material choice for living hinges. Polypropylene is the best material choice for its toughness and ductility. The well-designed injection molded PP hinge has almost unlimited service life and can be bent millions of times. Polyethylene is the second most common living hinge material, and its properties are similar to polypropylene.

How to design a living hinge

When working with customers, our living hinge design guidelines are 0.012 inches thick, with a pitch of about 0.060 inches, and the folded side of the part is reduced by 0.008 inches. On the other side where most of the tensile strain occurs, we recommend a radius of 0.030 inches to improve material flow and reduce strain. These recommended sizes provide a good starting point, but can be adjusted according to the application or part design.

Please note that the hinge should be bent several times immediately after prototype injection molding. This will cold-draw the plastic, thereby greatly extending its service life.