Snap fits and living hinges both rely on a material that can flex repeatedly without cracking, and nylon happens to be one of the very best plastics for exactly that job. That makes SLS a natural fit for clips, latches, lids, catches and folding parts that have to survive being opened and closed many thousands of times over their working life without failing. The slightly flexible nature of sintered nylon gives these features room to bend and recover rather than snapping on the first hard flex.
Getting these features right comes down to choosing the correct nylon grade and following a handful of well established design rules. We help customers tune snap fits and hinges as part of every MJF & SLS printing and prototype development job, and a little attention at the design stage pays off enormously in durability.
Pick the right nylon
PA11 is the standout choice for flexing features because of its higher impact strength and greater ductility, which let it bend repeatedly without building up the kind of damage that eventually causes cracks. PA12 also works perfectly well for snap fits that only flex occasionally, but for a living hinge that opens and closes thousands of times, PA11 will last considerably longer and shrug off the cold knocks that would chip a stiffer grade.
The slightly softer feel of SLS nylon also gives a well designed snap fit a satisfying, positive click when it engages, which adds a quality feel to the finished product that customers notice even if they cannot quite say why. That tactile feedback is surprisingly important on consumer parts.
Design rules that matter
For snap fits, taper the cantilever arm so that stress is spread evenly along its length rather than concentrated at the base where it joins the part, and always add a fillet at the root to avoid creating a sharp stress riser that will become a crack. For living hinges, keep the hinge section thin and consistent in thickness so it bends along a single controlled line every time, rather than wandering and wearing unevenly.
Above all, avoid sharp internal corners anywhere a part is going to flex, because those corners concentrate stress and are almost always the first place a fatigue crack will appear and grow.
Sizing the deflection
A common mistake is asking a snap arm to deflect too far for its length, which overstrains the material and shortens its life dramatically. As a rough rule, a longer arm can safely deflect more than a short stubby one, so if a clip needs a generous amount of travel, give it the length to match rather than forcing a short arm to do all the work. A living hinge of around 0.3 to 0.5mm at its thinnest is a sensible starting point for most parts.
Orientation in the build matters too, since printing the flexing direction in the strongest plane gives the feature a little extra margin. When you submit a job, point out which features flex and how often, and we will orient the part to favour them.
Test before you commit
Because SLS needs no tooling at all, you can print several versions of a clip or hinge in a single build and then cycle each of them by hand to see which design holds up best in practice. That quick, cheap testing loop is far less painful than discovering a fatigue problem only after you have committed to production and shipped parts to customers.
- Choose PA11 for hinges and clips that flex thousands of times.
- Taper snap arms and fillet the root to spread stress evenly.
- Keep living hinge sections thin and consistent in thickness.
- Avoid sharp internal corners anywhere the part will flex.
- Print several variants together and cycle test before committing.