09 Nov 2022
Pill case with living hinge

Living Hinges: What Are They & How Do They Work

Living hinges are a function built into some injection molded plastic parts. In this article we will learn more about live hinge design, live hinge material options, and other aspects of live hinge injection molding. 

What is a living hinge?

green injection molding with living hinge

A living hinge allows a plastic product to swivel at a certain point without requiring any extra hardware or inserts. It is quite simple to make a living hinge. Injection molding uses molds to shape parts, and the hinge is built into the shape of the mold by allowing a thin segment of material to separate the two halves that need to rotate together. This thin, flexible part area can efficiently function as a hinge without snapping, wearing down, or losing tension. 

How to design a living hinge

A living hinge is designed into a part by surrounding a thin flexible piece of plastic with a thicker piece, though this can be all part of the same mold. If your part needs to open and close and we think that a living hinge would be the best fit, our engineers will design it into the mold. When learning how to design a living hinge into a plastic part, it is important to get each specification right. A hinge that is too thick can limit mobility or functionality, and a hinge that is too small can break easier or not allow for enough material to flow to the rest of the part during production, which can lead to other issues. Finding the right balance will lead to a hinge that is integrated seamlessly into the part. 

Types of living hinge material

White injection molding with living hinge

A lot of materials are available when it comes to injection molding. But due to the specific needs of a living hinge, plastic material of only a couple types will work. Polypropylene is the most common living hinge material by far. This can be seen in products such as condiment bottle lids or clasps. Engineers use Polyethylene, though it is less common. An example of this would be a plastic toolbox.

How to make a living hinge

A living hinge is an easy way to add functionality to a part without the added cost or manufacturing process of an added hinge. In order to make a living hinge, the part and hinge are all one piece. This means that the thickness and location of the hinge, as well as the size and location of the gate must be just right to have proper material flow around the mold and to avoid knit lines.

Living hinge injection molding

Living hinges are just one efficient feature that we can design into a plastic part in injection molding. With experienced injection molders and engineers, we can bring your product to life. Designing something like a living hinge requires a precise and well-planned injection mold. When it is done right, you are left with a part that functions as it is intended to and will last a long time. 

How Rex Plastics can help

Rex Plastics has been in the injection molding business for over half a century. We have experienced engineers that can incorporate living hinges, or many other features into your part. Reach out to us for a quote today!