4.1 HOW ELASTIC INTERLOCKS WORK

An increasingly popular method of mechanical joining is "snap-fit fastening." While there are, indeed, fasteners that operate with what has come to be known as a "snap-fit" (see Section 4.2), most of the time when people speak of snap-fit fastening, the term is actually a misnomer because fasteners (i.e., supplemental devices specifically designed for joining parts together, without any other function) are not usually involved. Rather, elastic integral mechanical attachment features or elastic interlocks are.

As described in Chapter 2, Section 2.3, elastic integral mechanical attachments or elastic interlocks function by having a geometric feature on one part in a mating pair be designed so that it can and does elastically deflect when it comes into contact with a relatively more rigid geometric feature on the mating part. Once deflection of the elastic feature occurs and the insertion of the mating part, which is normally the one being moved, into the base part, which is normally the one that remains fixed or stationary, reaches a certain point, the designs of the deflecting and rigid features are such that some portion of the elastic feature clears some portion of the rigid feature and is able to recover at least partially, if not completely. When this recovery takes place, there is usually a distinctive "snap" that can be both heard and felt. This interesting and unique characteristic of these interlocks enables built-in quality assurance that successful part-to-part engagement and locking has occurred. In the...