Snap-fit designs can be an effective way to replace fasteners/hardware in injection-molded parts or products. There is growing interest by manufacturers in snap-fit because it can save time and money. Snap-fit connections are just as strong as fastened connections and can replace nuts, screws, washers, etc. No other adhesives, solvents, or fastening processes are needed. Snap-fit is designed right into the molding process, eliminating assembly steps and speeding up assembly and throughput. It also reduces material needs, saves on material costs, and makes the product lighter weight. An added benefit is environmental—because snap-fitted products are easy to take apart it’s easier to separate and recycle different materials.
For most applications, snap-fit connections are the simplest and most cost-effective way to assemble two parts—making them ideal for high-volume production because it is a quick and easy step to complete. This reduces the risk of improper assembly, which occurs more frequently during a step that requires more components (fasteners) and tools.
Which snap-fit is best for your product depends on the intended use and the material/design strength that is required to keep the snap-fit secure. Snap-fits can be engineered to be a permanent connection or allow frequent assembly and disassembly (like battery compartment covers in electronic products). Gas-tight and fluid-tight snap-fit connections can even be made when snap-fits are engineered to work with seals and O-rings.
Even though snap-fits are relatively simple in design and how they operate, incorporating them into product design does add complexity and cost to the molding process. This is because engineers have to consider the functional requirements of the connection and the product, assembly requirements, mechanical properties of the thermoplastic (strength, flexibility, recovery), and changes to the design of the mold (including part ejection). The design must ensure that the snap-fit has the proper “holding power” to keep the connection secure without bending too much, or breaking. These calculations become more complex, too, if the snap-fit application requires hundreds of openings and closings. Since most snap-fits require an undercut, a mold with side action is often needed.
Depending on the design and intended use of the product, snap-fit connections can increase the cost of molding and tooling. However, once the snap-fits are designed and production is underway, the extra cost of the molding process is usually quickly recovered by lower assembly costs, faster throughput, and less rework.