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Ketchup bottle cap featuring a living hinge design

Living Hinges: Benefits, Materials and Production Options

Living Hinges 101

Living hinges bring products to consumers and to easily useable, vivid life in a manor that is a designer’s dream: Simple and low cost. This easy, cost-effective method connects two rigid plastic parts with a flexible joint and can be used for everything from manufacturing soda bottles to ketchup lids to shampoo bottle caps to workshop storage containers to micro-electrical mechanical systems.

Plastic Living Hinges Defined

Their name may sound like something straight out of a sci-fi movie, but living hinges are very actual, very productive thin, flexible webs of plastic that connect two or more rigid sections of plastic. Most commonly, the larger rigid sections and the living hinge combine to make one continuous piece of plastic. Living hinges allow rigid pieces to bend along the line of the hinge.

The ease of manufacturing living hinges and their multi-usefulness for disposable packaging make their construction the easiest of plastic design surgeries. Living hinges and the connected rigid sections are manufactured as one part most commonly through injection molding. But their advantage over other flexible surfaces like cloth or leather only begin with their construction simplicity.

  • Big Bang For The Buck: Their simplicity makes living hinges a much cheaper option than other hinge types.
  • Built for the Long Haul: Living hinges are designed to be opened repeatedly, making them extremely durable. Living hinges experience very little friction when open and closed. Able to rotate on an axis 180 degrees or more, living hinges can potentially open and close for millions of cycles without breaking. This gives them a long life span that matches the lifespan of the part and makes even trees envious.
  • Component Compression: Living hinges turn five parts into one through their integration into one part. This eliminates the need for extra components and reduces part inventory.
  • Sharp-Dressed Parts: Unlike assembled hinges, snap fit connections and other parts, living hinges are a stylish and non-obtrusive connection method.

Living Hinges: A Product of Diverse Designs

There are living hinge designs for almost every needed function.

Straight or Flat Living Hinges

Straight hinges are the simplest type of living hinges and easiest to design. They can be long, short, continuous or segmented along the hinge line. For example. A short continuous straight hinge (also known a triple hinge) involves two plastic stops that act to arrest rotation at 180 degrees.

Butterfly Hinges

These classic hinges date back to 17th century cabinetry. A butterfly hinge snaps lids in open or closed positions. The webs on each side stretch, acting as a spring that pulls the lid to either the open or closed position.

Child-Safe Hinges

A must for any parent with an overly curious infant or toddler, this dual-action hinge is uniquely designed to prevent children from opening a container or lid.

Double or Triple Living Hinges

The use of multiple hinges in the same place offer enhanced security and stability when opening or closing an object.

Living Hinge Production

See in 3D

The best way to create a living hinge is to design the mechanism. 3D printed living hinges provide the perfect prototype for living hinges. 3D printed hinges verify the design needed before investing in expensive injection molding tooling.

Computer-aided design (CAD) pinpoint the desired hinge action, the needed size of the hinge and the desired range of motion. Once a design has been finalized, an injection mold tool can be used to manufacture the polypropylene part in volume.

These are the 3D printers that we use (and sell).

CNC Machining Living Hinges

Subtractive manufacturing is the best way to produce a single prototype product with a living hinge. For proofs on concept that require up to 10 prototypes, CNC machining is the proven way to go.

Injection Molding Living Hinges

The most affordable way to produce living hinges in high volume produces great performance and bottom line results.

Comparing the 3D and CNC Machining Advantages

3D printed living hinges replicate the qualities of polypropylene, but without the extreme durability. 3D printed hinges can fail when repeatedly bent. In contrast, CNC machining (which has the advantage of using strong, flexible polypropylene) develops a prototype for the same price as 3D printing without the drop off in quality.

Remember, the most important thing in living hinge design is proof of concept. Choose the production method that works best with your living hinge model.

The Ways Not To Hinge

Not all production methods perform equally. Living hinge production methods to avoid include screws and tape.

The Case For 3D Printed Living Hinge Modeling

For living hinge projects requiring a small number of cycles, 3D printed living hinges is the best, most affordable method of verifying the design. No expensive tooling is needed, the design does not need to incorporate features essential to injection molded parts like gates, runners or sprues.

3D designs can easily be altered to achieve the optimal design. Perhaps 3D’s most significant advantage: Its ability to produce parts quickly to accelerate the design process.

3D printing’s unique flexibility can allow your small prototype living hinge project to find its focus.

How to Bring Living Hinges to Life with CNC Machining

Start with one piece of polypropylene (PP) sheet stock. Progressively cut away plastic from the initial material block (subtractive manufacturing). For design verification and prototyping for 1-10 parts, cut prototype parts with living hinges out of polypropylene stock material.

How to Bring Living Hinges to Life with Injection Molding

Use a block of aluminum or steel with an internal cavity in the shape of your prototype. Since injection molding is designed for large volume living hinges, it is essential the sales sample of the prototype looks as much as the final project as possible. In large production cases, it is smart to first CNC cut prototypes to ensure the design is completely functional before making the investment in an injection mold tool.

The Living Hinge Design Truth

Remember, the number of living hinges needed should determine which production method you use. Knowing the volume and performance needs of your living hinge project will allow you to develop the smartest design. CNC Machining and 3D print modeling are the most effective options for small 1-10 hinge prototypes. For large mass production projects, injection molding is the best production route.

Knowing the best design road to take for your specific project will allow your living hinges to come to quick, fruitful, low cost and extremely useful and durable life.