Designing with “L-” and “U-” Shaped snap Fits

Snap-fit designs for assembly of thermoplastic-based products provide many benefits. However, when the strain caused by the deflection of a typical cantilever snap fit cannot be designed below the allowable strain of the intended material, conventional designs must give way to alternative snap-fit designs. In these cases, a “U-” or “L-” shaped snap usually reduces the strain to an acceptable level without sacrificing the cost and performance benefits of the typical cantilever snap fit. These alternative designs can accommodate very large deflections without inducing high strains at the base of the snap-fit finger. Formulae for both the “L” and the “U” have been derived to allow for maximum deflection for a given geometry. Detailed examples of the application of these formulae, which were confirmed using finite-element analysis, are given in this paper.