Evaluation metrics for the rating and optimization of snap-fits

Current snap-fit design guides recommend sizing snap-fit features on the ba sis of insertion force and allowable strain during assembly. Retention forc e information in such guides is often inaccurate, although this is consider ed to be the primary attribute of the snap-fit after assembly. The authors contend that these (insertion force, allowable strain, retention force) are not the only critical performance criteria for snap-fit features. Designer s have to contend with several other constraints and design requirements. A dditional performance metrics for snap-fit features are proposed by drawing upon considerable experience with plastic part design issues. Locking rati o, dimensional and volumetric retention force. consideration of the charact eristic dimension of the joint and snap-fit, feature stiffness, required ov er-insertion and consideration of snap-fit strength relative to part streng th ai e proposed to supplement currently used metrics for evaluating and ra ting snap-fit designs. The applicability of these metrics is illustrated wi th real-life examples, and their merits and demerits discussed. A chart of achievable locking ratios for different snap-fit topologies is presented fo r use as a design tool for the initial selection of snap-fit topologies. It s use as a rational basis for selection and optimization of snap;fits is su ggested. Adoption of proposed metrics Mill allow designers to better quanti fy, and thereby optimize the performance of: snap-fit features. These ideas will be built upon in the future, and used as a basis for a comprehensive snap-fit selection and detailed design tool.