Raise your hand if you want to save time, money, and reduce the number of part failures when you 3D print? One way to do this is with 3D printed living hinges. 3D printed living hinges can help eliminate the need for multiple moving parts to be fastened together after printing, they also allow for the connection of two separate bodies with a thin flexible region. If designed properly, these sections can be 3D printed all in one piece.
So, what exactly is a living hinge and why is it important for product design? Well, living hinges are used in just about every category of product — from the lid of a ketchup bottle to the washer fluid cap in the engine bay of your car, or on your children’s pencil box. The purpose is simple: enable the movement and connection of two separate bodies, with as little complexity as possible.
When should you use a living hinge?
Like anything, it’s essential to use the right tool for the job. Despite the many benefits that a living hinge can provide, it’s not perfect for every application. So, when should you use one?
For a housing or case that must open and close, such as custom packaging for lab instruments or an electronics housing.
For prototyping the lid or cap to a bottle or container that must be easily removed and ideally tethered (such as condiment or shampoo bottle).
For soft robotics or wearables where controlled flexibility or mechanical operation is needed.
For an integrated latch to keep something fastened or held closed, like a battery enclosure or craft box.
For rapid assembly when you need to improve production times by printing flat and assembling vertical components.
What are the pros and cons of 3D printing living hinges?
Pros:
3D printing gives the ability to rapidly test numerous hinge designs before more expensive and time-consuming processes like CNC (computer numerical control) or IM (injection molding).
Reduce part complexity by printing parts as one piece rather than separate parts.
Less challenges with print tolerances compared to separate mechanical hinges that must be fastened together.
Better surface finish as parts should be optimized for printing flat on the bed without needing as much support material.
If these are end use parts, no need for tooling.
Cons:
Material options limited to PP (polypropylene), PE (polyethylene), TPU (thermoplastic polyurethane), and PA (polyamide or nylon).
Not all parts can be printed in an ideal orientation to allow for a living hinge and must be printed as separate pieces.
Fewer cycle times than molded hinges.
What 3D filament should you use?
Polypropylene (PP) filament is an ideal choice for living hinges due to its toughness and ductility. Where other 3D materials might fail after a few cycles, PP can be repeatedly flexed back and forth without weakening. PP creates durable and functional parts that can be used for longer periods of time compared to less ductile materials like Nylon or ABS (Acrylonitrile butadiene styrene), which may degrade more quickly. Other options include TPU or EVA (ethylene-vinyl acetate) for parts which require either extreme impact resistance, or flexibility. Direct drive 3D filament feed systems are typically used for these softer more flexible materials.
How do you 3D print a living hinge?
There are two main considerations when printing a living hinge: hinge design and part orientation. Both are essential for creating parts that not only function properly, but last for a long time.
Hinge design
Similar principles apply from injection molded hinge designs to 3D printed designs. When bending, the inner surface is compressed, while the outer surface is placed under tension and stretches. So, a long, curved outer surface, and short inner surface can help to prolong hinge life especially in smaller flat or butterfly style hinges. In hinges such as the one shown below, a long thin area can be used to bridge a lid to a housing and can even be “kerfed” where narrow cuts perpendicular to the fixed bend direction of the hinge are added to increase stability without decreasing flexibility. Keep in mind that the width and thickness of the hinge, or material bridging the two components, greatly impacts the flexibility. For parts printed with a .4mm nozzle, we suggest at least three layers. Don’t be afraid to experiment, each design is unique and prototyping is ideal to dial in the proper feel!
Print orientation
The way in which a part is oriented on the build plate of an FDM (Fused Deposition Modeling) 3D printer will also greatly affect its performance. Orient your parts in the direction where the layers of the hinge are running across the hinge, not in-line with it. This creates strength in the same way that the woven layers of carbon fiber give a composite part its uniform performance. Also be sure to use 100% infill when printing your living hinge this will help maximize the cycle time and durability of your hinge design.
So, whether you’re looking to consolidate a design into fewer parts, simplify the assembly of a product, or even lower the risk of part failures, try experimenting with living hinges and polypropylene filaments. Braskem PP filament is formulated specifically for 3D printing, is easy to print, excellent bed adhesion, minimal warping, and fast print times, making printing living hinges that much easier.