Living Hinge Design

The Ultimate Guide

What is a living hinge?

A living hinge is a thin section of plastic that connects two plastic bodies together.

The use of a living hinge allow you to keep the two bodies connected while allowing

rotational movement

Living hinge example?A common example of a living hinge is a ketchup cap. The two sides are connected by a thin hinge. The cap can rotate out of the way while still being connected.

Living hinge

What are living hinges used for?

• Makeup compacts

• Candy container caps (Tic Tac mints)

• Condiments

• Shampoo and liquid soap

• Fishing tackle boxes

What are the benefits?• Eliminate assembly- Conventional hinges

need to be assembled. Living hinges do not

• Lower Cost- Lower cost though eliminating assembly steps and eliminate hardware

• Durability- properly design living hinges can last indefinitely

Conventional Hinges

Reason not to use a living hinge?

• Limited material selection- Living hinges require the use of Polypropylene PP or Polyethylene PE

• Limited load bearing- Living hinges can not handle much load parallel to the hinge.

• Added development time- Living hinges take effort and time to design.

Living hinge design considerations

Typical living hinge designs

Typical living hinge designs

• Flat hinge – the strait hinge is common and It consist of a landing in both sides and a thin hinge section.

• Double Hinge – A double hinge has two strait hinges separated by a narrow landing section.

• Butterfly hinge – A butterfly hinge is commonly used on dispensing caps.

• Bi-stable Hinge – this is very similar to the butterfly hinge only instead of one uniform living hinge there are three separate hinge sections.

Living hinge geometry

Living hinge geometry• Web thickness- Should range between 0.007” –

0.015” thick.

• No sharp corners – Every corner should have a radius in your design.

• Gate placement – RevPart will help you with this. The gate placement is very critical.

Hinge Material• Polypropylene aka PP- is the best resin by far for

living hinges. Use Homopolymer PP when possible.

• Polyethylene – Every corner should have a radius in your design.

• Gate placement – RevPart will help you with this. The gate placement is very critical.

FillersFillers are commonly added to plastic to meet physical or aesthetic requirements. Most fillers are not recommended for living hinges.

Molecular OrientationThe key to a quality living hinge is getting all the resin molecules to line oriented in

the same direction. This direction is in parallel to the flow though the living hinge.

Environmental Factors• UV exposure- UV light is brutal to all plastics in

varying degrees. Living hinges will not last very long with degraded plastic and fissures. UV additive is recommended in all outdoor applications.

• Chemical Exposure- It is important to take into account what chemicals the living hinge will come in contact with and see if the selected resin is applicable.

Prototyping a living hinge

• CNC Machining- RevPart has the expertise to CNC machine your living hinges out of Polypropylene.

• Prototype injection molding- RevPart can produce inexpensive prototype mold that let you test the real deal living hinge. This allow you to make revisions and ensure your design works before going to full scale production.

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