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Fastener Selection, Development and Validation

April 8, 2010

In the development of many products, fastener selection is often neglected until the design is being finalized. In applications where fasteners are required, they should be among the first parts to be considered.

One of the first questions to ask is does the fastener have to carry load or is it only there to hold the part in a specific location? Either answer will raise another set of questions: What is the applied load? What materials are being clamped together? What are the environmental conditions? Depending on the application, other questions may need to be answered. Every answer is important, because if these issues aren’t addressed, the fasteners chosen could be inappropriate for the design.

During the development stage of the design, the selected fasteners should be tested for the appropriate torque and clamp load, using the parts that will clamped together. This will ensure that the torque specification developed for the manufacturing/assembly plant will work with the production parts. During the validation stage, when the design goes into final testing, the fasteners should be tightened to the specification and indexed for monitoring during duty-cycle testing.
Fasteners must be considered throughout the product development cycle. They should be part of the equation when developing the functional objectives for the product, as well as during design and development and validation testing. Obviously, fastener choice is key to efficient manufacturing and product assembly. Finally, fasteners are a vital concern in determining the aftermarket serviceability of a product.

Most fastener-related recalls are in the automotive industry, per the editor of the American Fastener Journal (12/2009). However, other products have had recalls due to fastener problems. One example is the recent recall of the Evenflo Envision High Chairs (April, 2009).

There is a great opportunity to significantly reduce the number of product recalls due to fastener problems if proper care is taken in fastener selection, development, and validation.

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