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AIM Processing Small Plastic Parts Blog

A Brief Introduction to Living Hinges in Plastic Injection Molding

[fa icon="calendar"] Oct 26, 2017 10:17:00 AM / by Jon Gelston


If you’ve ever flipped open a bottle of ketchup or tube of toothpaste, you’ve used a living hinge. A living hinge is formed as an extension of the base and cap material, which in many cases is polypropylene plastic. This thin piece of material between the base and cap is flexible, allowing the cap to be bent out of the way as the contents of the container are dispensed and then returned to the closed position. Living hinges can be created in a number of ways, but one of the most cost-effective methods is plastic injection molding.

Types of Living Hinges

There are different types of living hinge, including:

  • Straight hinge. The simplest form of living hinge, these can be short or long, and can also be segmented (three short segments that work together as one hinge, for example).
  • Butterfly hinge. These hinges provide what is known as “bistable” hinge action. This means that the cap will snap either to the open or closed position. The advantage with this type of hinge is that when it is in the open position, it remains there without needing to be held by the user.
  • Child-resistant hinge. A living hinge can be combined with other features so that it is difficult for a child to open it
  • Double/triple hinge. In some cases, multiple types of hinge mechanism are used together to achieve the desired effect.

Key Considerations with Living Hinges

If you are thinking about incorporating a living hinge into your small plastic part design, here are some things to keep in mind:

  • Cost. Living hinges are created through the molding process, so no assembly steps are required. This means they are very cost effective to produce once a workable design has been created.
  • Adaptability. There are virtually unlimited options for the shape, size, and function of living hinges, so they can be adapted to almost any use.
  • Aesthetics. If a part is meant to be visually appealing (or at least not visually distracting), living hinges are ideal. They can be very small if appropriate, and they are an extension of the base/cap material so they blend right in.
  • Flexibility and range of motion. Living hinges have outstanding flexibility around their designed axis of rotation and are typically designed for 180 degrees or more of angular motion.
  • Frictionless. Because the base, cap, and hinge are one continuous part, there is effectively zero friction on the hinge as the cap is opened and closed.
  • Strength, durability, lifespan. Properly designed living hinges are exceptionally strong and durable, and can operate through countless cycles without failure. However, since the material is often flexible polypropylene, structural rigidity should be considered.

What Does Your Success Hinge On?

If a part for your next project needs to open and close smoothly for hundreds of thousands (if not millions) of cycles, and it has to be budget friendly, a living hinge may be just the solution you’re looking for. If that’s the case, our two decades of experience in plastic injection molding and the production of hinges of all kinds may mean we’re just the shop you’re looking for.

The best way to find out is to talk through your objectives. Contact us or stop by our facility in Longmont, Colorado, just north of Denver.


Talk to Our Plastic Parts Specialists!


Topics: Plastic Injection Molding, Small Plastic Parts

Jon Gelston

Written by Jon Gelston