What do a leather wallet and a ketchup bottle cap have in common? You got it…they both implement the living hinge to bring the object to life through movement.

When speaking in terms of manufacturing, a living hinge is a thin flexible web of material that holds two rigid plastic pieces together. The living hinge concept has been around for years, but in terms of plastics, its full potential wasn’t realized until the inception of polypropylene in the late 1950’s.

So, what is the secret behind the “living” part of it?

It’s all in the design…

Injection Molding | Living Hinge Diagram | Quickparts.com
The key details to a successful living hinge include:

  • Hinge thickness
  • Radius
  • Recessed notch above the hinge feature

The hinge thickness controls the overall stiffness of the hinge; each application has its own requirements so make sure you find your part’s ideal thickness. Also, because the hinge plastic is so thin, it may be susceptible to tearing at the edges, so giving just the ends of the hinge extra thickness while adding radii will increase its tear resistance.

The overall radius applied will help to orient the plastic molecules flowing through the hinge, ensuring that the hinge bends along a straight line. This molecular orientation gives the hinge its strength and long life. Another way to ensure proper material flow and hinge operation is to choose a gate location that will place weld lines away from the living hinge feature.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200.