Snap-fit Joints

Snap-Fit and Press-FitJoints. Snap-fit joints offer the advantage that the strength of the joint does not diminish with time because of creep. Press-fit joints are simple and inexpensive, but lose hoi ding power. Creep and stress relaxation reduce the effective interference, as do temperature variations, particularly with materials with different thermal expansions. 

Mobay/Bayer Design Manual Snap Fit Joints in Plastics, Mobay Engineering Thermoplastics Bulletin, Bayer Chemical Corp., 1990. 

Visit plastics.bayer.com/plastics/emea/en/femsnap/index.jsp and examine the example snap-fit joint, noting the shape and stress distribution at maximum deflection. Find some examples of snap fit joints on consumer products and compare their design with that on the Bayer site. 

In all types of snap-fit joints, a protruding part of one component, such as a hook, stud, or bead, is briefly deflected during the joining operation, and it is made to catch in a de-... 

The maximum permissible deformation of the plastic hub in an annular snap-fit joint is limited by the maximum permissible strain or proportional hmit of the material. This limit is typically 50 percent of the strain at break for most reinforced plastics. It can be upwards of 60 to 70 percent of strain at break for more elastic polymers. 

These high-temperature thermoplastic materials are generally joined mechanically or with adhesives. The high modulus, low creep strength, and superior fatigue resistance make these materials ideal for snap-fit joints. 

Hoffman, J. M., Fundamentals of Annular Snap-Fit Joints, Machine Design, January, 6, 2005, p. 84. 

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