Designing Snap Fit Components – Common Problems and Solutions
Snap-fit components present a quick and easy way of connecting two or more parts together. With the aid of an interlocking “snap and fit” mechanism, designing parts with these components can help you save time, cost and reduce the number of parts in an assembly.
In the simplest way possible, a snap-fit component may be described as a small stud, bead, hook or protrusion that is deflected during part assembly to match the depression from the coupling part. The mechanism is such that one part suffers a deflection, while the other part, its mate, keys into it in a snap-fit manner. Snap-fit components also present the possibility of faster assembly and disassembly in production. In earlier times, injection molding was the only feasible means for making snap-fit joints in production parts. Today, 3D printing is another technique that can be used in producing snap-fit joints. As easy as the mechanism may seem, a couple of challenges are still often encountered when making snap-fit components. This blog runs through the most common design challenges and how to get around them.
Stress Concentrations Snap-fit components are very susceptible to stress concentrations at sharp corners in the root of their cantilever. This stress, often results in accumulated fatigue on the part, causing it to shear off. Stress concentrations can be avoided in snap-fit components by using radii and chamfers to eliminate sharp corners that habour stress in the design. Also, consider adding a fillet in the base of the cantilever, use U or L-shaped snap-fits as their design have smoother and larger radii. U-shaped designs help to constrain the maximum amount of deflection that can result from the moving beam in the design contacting the backup surface of the part.
Stress Relaxation/Creep Creep refers to the gradual and progressive deformation of a material under the influence of stress. Unlike parts that are highly elastic, thermoplastic are susceptible to creep, experiencing permanent deformation that can render the mating components of the snap-fit useless over time. To prevent stress relaxations in your snap-fit components, design your mating parts in a way that they are not subject to tensile stress and prolonged bending after assembly. Where possible, use a chamfer on the tip of your mating snap insert and beam to facilitate the holding of the mating parts and allow for ease disconnection when pulled apart. Use support features like U-shaped cantilever designs for the tip of the beam to hold the snap-fit parts in place.
Repetitive loading failure/Fatigue Repetitive loading failure refers to the damage in the snap-fit components that results from the frequent assembly and disassembly of the snap joints in your design. This repeated stress on the joints results in fatigue in the snap-fit part, inevitably resulting in loading failure. To mitigate this risk, use fatigue-resistant materials using S-N curves. Also, consider the method of manufacture as 3d printed snap-fit components will generally have lesser cycles in them compared to injection-molded alternatives.
Inaccurate tolerances In some instances, parts may be designed with inaccurate tolerances that keep your snap-fit mating components from fitting into each other. To prevent tolerance issues, ensure that you keep a gap of 0.4mm for pivot joints and side fits, 0.3mm for close fit snap joints and 0.2mm for tight-fitting snap joints
Firstpart 3D Printing Solutions Firstpart offers a wide range of 3D printing solutions for both personal, commercial and industrial uses. Choose from a variety of printing options, filaments and finishes to produce high-quality parts that are suitable as production parts, prototypes or end-use devices. By simply contacting us, we can help you with incorporating living hinges, snap-fit and other fastening solutions into your design. We invite you to work with us and take advantage of our expertise in creating highly functional 3D design models that ensures an improved overall part performance, reduced risk of part failure and leverage the machining efficiency of CNC, injection molding and 3D printing machines for attention-arresting outcomes.