Do you work with living hinges? If you’re in the consumer products space, it's likely that’s a “yes.”
Living hinges are found in plastic packaging, dispensing caps, thermoformed clamshell packaging and more. Manufacturing guidelines are easy to obtain for a variety of use cases. The hinge itself is simple—just a thin, flexible piece made from the same material as the rigid components it connects.
Living Hinge Prototypes
Prototyping living hinges, on the other hand, are not so simple. There are plenty of approaches—you probably have your own—ranging from using industrial tape to rigging up sheets of polypropylene as living hinge inserts. Building a hinge that closely mimics the real molded part is challenging.
Here’s where 3D printing can help. Creating living hinges that can last beyond a few bends is completely possible today, but you’ve got to use the right materials and techniques. The benefits are huge: turnaround times in hours and low run costs, while still producing a functioning hinge that closely matches the final part. You’re going to benefit from more design iterations and verification before committing to the expense and time of a true molded version of your design.
The Right Printers for the Job
To be clear, not every 3D printer is suited for functional prototyping of living hinges. So let’s look at three printer/material combos that work well:Lowest cost: Objet Using Endur Material
The Endur material is available on the Stratasys Object 30 Pro and higher 3D printers with PolyJet technology. With Endur, which is a simulated polypropylene, you’re getting good durability for living hinges and snap fit components.Highest performance: Objet Connex Using Endur Digital Materials
On Objet printers, with Connex dual- or triple-jetting technology, Endur can now be mixed as a Digital Material. Mixing Endur with flexible materials results in superior living hinge performance, plus the ability to have parts with rubber overmolding, transparency or other effects (depending on specific printer capability).
FDM high performance: Fortus Using Nylon-12 Material
While not as robust as using Endur Digital Materials, this solution is still very useful and is the best FDM-based solution. Running Nylon-12 requires a Fortus 360mc or higher, and results in a well-performing hinge using a single material throughout the part. This solution is what we’re focusing on for this blog post.
Here are some sample parts using the Fortus:
All of these parts were printed on the Stratasys Fortus 400mc (a commercial high-performance FDM 3D printer) using the Nylon-12 material. The parts were designed in SOLIDWORKS and transferred over to the Fortus software as STL files.
The parts have solid performance for the hinge, allowing for many bends before failure, and prove to be a very close match to the final part look and feel.
One of the biggest advantages is the ease of performing design iterations! In fact, you could easily print two or more variations of a design at once and choose the best after functional testing. Iterations only require minor changes to the CAD file and then just re-print.
Tips for Best Living Hinge Prototype Results
At TriMech, we regularly print sample benchmarks for all sorts of applications. We applied our expertise here to give a few simple guidelines for getting the best result.
- Choose the right build orientation. FDM printers tend to have parts with more strength in the horizontal build plane. Therefore it’s best to orientate the part so the hinge bend direction is also horizontal during the printing process. Often that will result in an overall “horizontal” part build, such as the box in the example image.
- Hinge design. The basics from traditional living hinge design apply even with 3D printed parts. Use a generous radius at the bottom of the hinge and a tight recess at the top to enable easy folding-over and prevent excess stress during folding.
- Layer thickness. Hinges work best when at least two FDM layers width are used. So using a 0.007” (7 mil/178 microns) print resolution, minimum layer thickness should be 0.015”. We found acceptable hinge results up to 0.020” for a maximum of 180-degree angles.
- Redesign if necessary. If your existing design or model has a hinge layer thinner than 0.015”, we recommend re-designing the prototype thicker to achieve a working hinge capable of one-hundred (100) or more bend cycles.
The Nylon-12 material we used is ideal for applications that demand high fatigue endurance, such as repetitive snap fits and friction-fit inserts. The key advantages of the performance and the power of 3D printing are clear: design proofs and verification that can be tested and in your hands within hours.
With 3D printing using Stratasys Fortus 3D printers and Nylon material, design tweaks are made in CAD and verified for performance using functional testing. Any design faults can be found early and fixed long before investing in full-scale production.