Snap Fittigns

Snap Fitting Defination: 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.[1] 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.

Design

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.

Annular

The annular snap-fit utilizes hoop-strain to hold into place. Hoop-strain is the expansion of the circumference of the more elastic piece as it is pushed onto the more rigid piece. In most cases the design is circular. Some popular examples are pen caps, ball and socket joints, Snap fasteners, and some water bottle caps. This kind of snap-fit can be used multiple times. However, permanent strain may develop, loosening the joint when it is used too often.

Cantilever

The cantilever snap-fit is the most commonly used snap-fit of the three.[6][7] A cantilever design can be multiple use or permanent. A multiple use snap-fit usually has a lever or pin to be pushed, in order to undo the snap-fit. However, on a permanent snap-fit there is no lever or pin. Attempting to undo a permanent snap-fit can result in the piece breaking.

Some potential problems with being able to undo the snap-fit is hyper-extending it past its breaking point. As a solution, some parts have a stopper in order to stop the snap-fit from breaking. One very popular example is a battery compartment lid.

Torsional

In a torsional snap fit, one must deflect, or force the protruding edges of piece B away from the insertion area. Piece A then slides in between the protruding edges until the desired distance is reached. The edges of piece B is then released and piece A is held in place. The snap-fits in this description are the protruding edges of piece B. These types of snap-fits may have a spring in place; so that when activated, the locked in piece is released and put into action.

Sample Types of Snap Fittings