Snap-fit

A Snap-fit (Integral Attachment Feature) is an assembly method used to attach flexible parts, usually plastic, to form the final product by pushing the parts' interlocking components together. There are a number of variations in snap fits, including cantilever, torsional and annular. Snap fits are an alternative to assembly using nails or screws, and have the advantages of speed and no loose parts. Snap fit connectors can be found in everyday products such as battery compartment lids, Snap fasteners and Pens.

Snap-together connectors have been used for thousands of years. The first ones were metal. Some of the oldest snap-fits found are snap fasteners, or buttons, shown on the Chinese Terracotta Army featuring soldiers from the late Warring States Period. Metal snap fasteners, spring clips, and other snap-type connectors are still in broad use today.

With the development of new flexible yet springy materials, such as molded plastic, and new manufacturing processes, many new variations in these types of connectors have been invented, and are commonly called snap-fits. They can be found in on our phones, laptops, keys, and other household devices. Engineers have studied and developed these snap-fits, creating formulae concerning the amount of deflection allowed on the components, amount of torque one can take, and the amount of space one can allow in order to be detached.

Molds of the parts are created and hot liquid plastic is poured into the molds. The molds contain the shape of the parts and the snapping component built in. However, one major risk when the cooling of the mold finishes is the product shrinking causing errors in the attachment parts.

Building a snap-fit design requires more precise engineering than a screw or nail assembly, and is often more expensive. When snap-fits are being made, the producer needs to determine where the stresses of the parts will be applied to when assembled, or they break during assembly. The high production costs are due to the amount of calculation and precision that must be done in order to create a strong snap-fit. Another reason is the creation of molds; they are more time consuming from the integration of parts in the product.

The design of the Snap-fit determines what it can be used for. There are three main types of snap-fits: annular, cantilever, and torsional. Most snap-fit joints have a common design of a protruding edge and a snap-in area. The specific name of the snap-fit is usually named after the type of stress or strain it utilizes; the torsional snap-fit uses torque to hold parts in place.

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Wikipedia