Clinching the deal on cost

Louise Smyth

The world of fixings and fasteners has changed considerably, especially since the advent of self-clinching fasteners more than 70 year ago. Not only have the fields of application changed and expanded, the evolution of thinner sheet metals and increasing demands on serviceability and durability have put more traditional methods under scrutiny. 

As design engineers are forced to come up with ever more inventive assembly designs, sometimes traditional methods are not always the most suitable option. Welding has always been a staple fastening technology but with more complex designs, potentially incorporating dissimilar metals, welding is not always possible.

When serviceability is a key factor for an assembly, welding is out of the question and alternative options must be found. The use of welding still has its place in fixed assemblies that are hidden out of sight but when in plain view as the finished surface, the additional time and labour costs for removing scale and burn marks makes welding fasteners a less attractive option.

The tendency for favouring thin sheet metals also reduces the opportunities for employing welding as a fastening method as often the sheets are too thin to weld properly. Looking purely from a cost perspective the individual cost per fastener is less for welding but taking into account the additional final processes required, the additional manufacturing costs and QA procedures, welding overall is less cost effective than self-clinch.

Riveting is an alternative to welding as it addresses the concerns for attaching dissimilar or thin sheet metals. However, additional work is required when using rivets as they are not able to be installed flush without countersinking which involves secondary processes which cost both time and money. The use of rivets can also be cumbersome as valuable space is taken up by the rivet bulb.

The use of other loose hardware also carries potential concerns with a reduction in holding power over the lifecycle of the assembly, reduced thread integrity and the additional costs and time associated with additional handling of the fasteners prior to and during assembly.

The implications of not using the best joining method are damaging for brand reputations and as such self-clinching fasteners have continued to grow in popularity as they address all the weaknesses exposed with welding or riveting. Typically switching to self-clinching fasteners can offer savings of at least 27% compared to the use of loose fasteners, 40% for welded fasteners and up to 58% for rivet bushes depending on the existing fastener and the production process. These savings are achieved by replacing multiple inventory lines with a single fastener, general reduction in inventory costs and reducing the time and cost of assembly with fewer parts and fewer manual handling processes during production.

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