Seat Nut Analysis

Applied Kinetics determined that this bi-material seat nut had a serious design flaw.


Not all analysis projects are on large components.  Infact with modern miniaturization efforts more and more load bearing components are keeping up with the race to small.  This analysis was on a plastic automotive seat component with an over-moulded steel insert.




Seat Nut
 Category: Analysis




Plastic and steel


Moulded inserts have been growing in popularity for years.  The increased cost of metals and the increased performance of many new plastics has spurred many companies to push the boundaries of insert application.

Our customer was having component failures during testing of a seat nut.  It appeared that just the strength of the plastic alone should be enough to handle the test load in the area of failure, so what could be happening?  Even more perplexing, the component was failing in the steel insert before any distress was seen in the plastic.  A quick investigation by our customer into the quality of the components showed that they had excellent adhesion between the steel insert and the plastic mould.  The quality of the steel and plastic was also top notch.  That's where Applied Kinetics joined the project.

The constant time pressure in the automotive industry meant the problem had to be found immediately. Applied Kinetics did just that and in short order fully understood the problem.  A careful FEA analysis took this into account and helped to highlight the issue.  When two dissimilar materials are used in a load bearing application the more rigid material often takes a higher proportion of the load. In this case, the steel insert was bending to failure before any significant load reached the plastic, the plastic was simple bending out of the way. A quick redesign with this in mind fixed the problem and allowed the seat nuts to easily pass testing.


Improved Metal Insert


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