Assembly and Disassembly Mechanics of a Cylindrical Snap Fit

Abstract

Snap fit is a common mechanical mechanism. It uses the physical asymmetry that is easy to assemble but difficult to disassemble to provide a simple and fast link between objects. The ingenious combination of geometric shape, bending elasticity and friction of the snap fit is the mechanism behind the easy to assemble but difficult to disassemble disassemble. Yoshida and Wada (2020) has done a groundbreaking work in the analysis of the elastic snap fit. During our study of their paper, while we really enjoyed their research, unfortunately we detected several questioning formulations. After careful checking, we found that those formulations are not typographical, therefore it is necessary to make corrections. This paper reformulates the linear elasticity of a cylindrical snap fit, obtains an exact solution and proposes an accurate relation between the opening angle and bending tangent angle. Under the first order approximation, our formulations can reduced to the results of Yoshida and Wada and hence confirms the scientific correctness of Yoshida and Wada's work. Furthermore, this paper also derives a correct vertical displacement expression, and propose a new way of disassembly by bending for the first time and formulate a scaling law by data fitting. All formulations are validated by finite element simulation and experiment. The research here is helpful to the design of elastic snap fit or adjustable mechanical mechanism and metamaterial cell.

Assembly and Disassembly Mechanics of a Spherical Snap Fit

“…By data fitting, the correction coefficient is determined approximately as C = 2.95. Since the coefficient C should be greater than 1, it indicates that the spherical snap fit has a greater bearing capacity than the cylindrical snap fit [12,13], confirming our prediction in the preface. Eq.…”

“…Taking the spherical snap fit with two pairs of claws as an example, we use finite element method to study the assembly and disassembly mechanism of multi-jaw spherical snap fit, as shown in Fig. (13). We take the opening angle of Type I snap-fit φ = 2.3 rad and Type II snapfit φ = 2.7 rad as examples, and the simulation process is the same as above.…”

“…The multi-jaw spherical snap fit obtained by finite element simulation of single-jaw spherical snap fit still conforms to the law of mechanical asymmetry, but the snap fit force between multi-jaw spherical snap fit and single-jaw spherical snap fit is not a simple multiple relationship due to the influence of curvature and other factors, which requires to be further studied. This is another detailed study of snap fit mechanics in the context of thin structure physics [12,13], which helps to accurately predict the assembly and disassembly forces of spherical snap fits.…”

“…Although we often hear the "click" sound of the snap fit in our daily lives, there is very little research on the scientific mechanism of the snap fit mechanism. The snap fit appears everywhere in our daily lives because it is simple and reusable [1][2][3][4][5][6][7][8][9][10][11][12][13]. Two objects can be directly connected without welding, bolts, glue, or other means, and they can be assembled and disassembled repeatedly [1,12,13].…”

“…The snap fit appears everywhere in our daily lives because it is simple and reusable [1][2][3][4][5][6][7][8][9][10][11][12][13]. Two objects can be directly connected without welding, bolts, glue, or other means, and they can be assembled and disassembled repeatedly [1,12,13]. From receptor ligand interaction [2] in biochemistry to spacecraft docking [3], as well as zippers, Lego blocks, water pipe clamps, head massager claw etc., which are common in life, all use the principle of snap fit.…”