Modified analytical method to calculate the assembly and separation forces of cantilever hook-type snap-fit

Abstract

In this study, a new analytical method to calculate the assembly force and separation force of cantilever hook type snap-fit was proposed. Finite element analysis and experimental measurement were performed to verify the new approach. It was found out that the conventional analytical method had a few limitations. The solution was only applicable when the retention face angle was small, and there existed a critical value of retention face angle where separation force unreasonably decreased with increase in deflection. The new approach considered large deflection of retention feature and resultant moment term in addition to the previous method, and the solution was obtained explicitly. The new analytical solution could be applied to large face angles without any divergence, and showed good agreement with finite element analysis results. When the face angle was relatively small, both conventional method and new method showed reasonable results; however, when the angle was large, only the new analytical method showed reasonable results. Experimental investigations of forces during assembly and separation showed that the measured forces were much smaller than the predicted values by analytical methods and finite element analysis. The forces were strongly dependent on the rigidity of the mating part and the magnitude of radius at the edges of beam and mating parts. It was found from experiment that the separation force nonlinearly increased as clearance decreased.

Assembly and Disassembly Mechanics of a Cylindrical Snap Fit

“…It can be seen from the deformation in Fig. 7 that the horizontal deformation relationship is where ∆ x represents the horizontal displacement driven by force F .Substitute expression ( 14) into (17) to get…”

“…The two objects can be directly connected without welding, bolts, glue and other means, and can be assembled and disassembled repeatedly [1]. There are vast varieties of snap fits ranging from receptor ligand interaction in biochemistry [2] to spacecraft docking in the space [3], as well as zippers, Lego blocks and water pipe clamps commonly used in life [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] . Although the buckle is not uncommon for snap fit, it implies a basic physical mechanism, that is, the buckle makes use of the mechanical asymmetry that is easy to assemble but difficult to disassemble.…”

Large deformation analysis of a backside-supported snap-fit with nonlinear behavior

“…A negative pressure stress can be observed at the root of the supporting bar. Note that a negative press stress (tensile pressure) promotes the yielding of polymer materials [ 8 ].…”

“…Notably, a small insertion face angle induces a low assembly force, whereas a large retention face angle induces a high separation force. Moreover, the friction between the mating part surface and the base part surface must also be considered [ [7] , [8] , [9] ].…”

Mechanics of A Thin-Walled Torus Snap Fit

“…[19,20], to receptor ligand interaction in biochemistry [27,28], and spacecraft docking [29], all use the principle of snap fit [19,20]. The snap fit seems simple, but it reveals how an operational asymmetry of snap fits (i.e., easy to assemble but difficult to disassemble) emerges from an exquisite combination of geometry, friction and elasticity [19][20][21][22][23][24][25][26][30][31][32][33][34][35][36][37][38][39].…”