Abstract

Traditional snap-fit design methods focus exclusively on design of an individual locking feature such as a cantilever hook or an annular lock. Location and orientation of other significant features on the two joined parts are not considered. This paper presents: (1) a comprehensive design methodology for nesting plastic parts via snap-fits and, (2) the concept of a part nesting table to encourage good design practices.

This nesting approach is based on relatively new methodologies and guidelines for arranging features on a plastic part. The authors advocate a nesting which is a statically determinate assembly and minimizes the use of snap-fit features. The advantages of such an assembly include robustness with respect to tolerance and warpage concerns, maximum utilization of existing “natural” part features, and a reduction in the number of locking features needed. The entire process is presented as an improved paradigm for attachment design and assembly.

It presents the concept of a part nesting table to help designers produce nested plastic assemblies. In this approach, degrees-of-motion to be removed are represented as columns in a table, and individual features are entered as rows. Advantages of this structured approach include recognition of under constrained and weakly constrained assemblies, identification of over constrained assemblies, and first-level optimization of lock location and assembly direction. Work is continuing on computer implementation of this approach so that force and moment values can be deduced at the feature level.

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