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Overcoming traditional fastener challenges with self-clinching technology

09 September 2016

Self-clinching fastener technology has advanced significantly in more than 70 years since invention in the US and has enabled the development of ever-thinner, lighter and stronger end-product designs, marking a significant change in the story of joining sheet metal.

The anatomy of a self-clinching nut

Today, whether used in domestic appliances, automotive, marine or medical applications, the self-clinching fastener is one of the most versatile, effective and widely used fasteners in world. 

How fastener challenges have changed

Recognising that designers may have little or no choice when working with especially restrictive design envelopes, specific self-clinching fastener types have been developed to address the issues featuring smaller diameters and lower heights which permit shorter “edge of sheet” to “centre of fastener” distances.  

The increase in prevalence of serviceable sub-assemblies has had an impact on fasteners. Historically and still to this day, many sub-assemblies are riveted, but due to servicing and maintenance requirements and an increasing focus on safety, self-clinching fasteners allow for easier and faster servicing which is a major advantage, as loose hardware can be cumbersome and difficult to use. 

Comparison of self-clinching fasteners with traditional methods

Prior to self-clinching technology traditional methods such as riveting and welding were employed and still are today in certain industries. Given the nature of the modern fields of application, sometimes these traditional methods of fastening are no longer fit for purpose. For example, when an assembly requires servicing, as disassembly is required, if dissimilar metals need to be re-joined, designers cannot rely on welding as a fastening method. Yes, welding gives strength but it is almost impossible to weld dissimilar metals. In addition, if the welded surface is intended to be the finished surface, then additional finishing steps to compensate for burn marks and scale will be further required to create a presentable “cosmetic-friendly” assembly. Some sheets, of course, are just too thin to weld properly and it is not worth the risk given the increased use of thin sheet metals. When assessing the cost differentials, the individual fastener cost is less for welding but overall the cost for welding is far greater, making the use of self-clinching fasteners a more economical choice.

Riveting can work more effectively for attaching dissimilar thin materials, but rivets cannot be installed flush without countersinking or some other secondary operation, leaving unsightly metal bulging, often limiting their use to utilitarian assembly inside enclosures. Since standard rivets do not finish flush, attention must further be paid to the clearance necessary for the rivet bulb. The bulb can overly consume valuable ‘real estate’ especially in appliances where space is at a premium.

Other hardware such as sheet-metal screws can develop issues related to diminishing holding power over time, reduced thread integrity, loosening and falling out, and the time-consuming and unwieldy need to handle the screws before and during attachment operations.

Examples of typical self-clinching fasteners

Designers looking for a fail-safe solution need only turn to fasteners engineered to provide strong and reliable threads in thin metal assemblies. The benefits of all self-clinching fasteners essentially arise from their design incorporating an annular recess for permanently locking the fastener in place in thin ductile metal sheets and an element to prevent fastener rotation in service.

The main advantages of self-clinching technology

By nature, self-clinching fasteners become integral parts of an assembly and bring many benefits. Self-clinching fasteners have a high stress point, even in sheets with thickness as little as 0.5mm and strength is a key characteristic as it provides fastening solutions, even in sheets made from non-ferrous metals. Given the breadth of applications, some metal sheets require treatments and traditional fasteners may not be suitable for use. Thanks to their design, self-clinching fasteners will not damage treated sheets and the full integrity of a metal sheet can be maintained if a self-clinching solution is used.  

The use of traditional threaded fasteners can be limiting, so self-clinching fasteners provide additional benefits as they can withstand torque loading and linear forces which prevents the stripping of threads. With self-clinch, the thread is of a much greater quality and is far more reliable than threads that are tapped or extruded directly into the sheet metal.

As the complexity of assemblies is ever increasing and sizes decrease to allow for flexibility in design and application, self-clinch fasteners also have their part to play. Self-clinching fasteners are ideal for applications where high precision fitting is required. When all the right conditions are met, self-clinch fasteners also offer improved perpendicularity of the axis to the sheet level, creating a more aesthetic finish. This finish also has the potential to improve electrical conductibility between the metal sheet and the pressed part. 

As well as offering great strength, self-clinch fasteners also save time and money. The use of self-clinch reduces the need for extra hardware such as washers, this in turn reduces production cycles and assembly time. Fewer parts enable lighter designs, lower production costs, and optimised levels of end-product reliability. Time is also saved as the cut out hole for the fastener does not need special secondary treatment. In applications where regular servicing of an assembly is inevitable, self-clinching fasteners allow for easy component removal and re-attachment for access.

New developments in self-clinch technology afford designers and engineers expanding opportunities with the rise in popularity of thinner sheets and smaller assemblies. With manufacturing and production costs always in focus, the use of self-clinching fasteners provides a solution by reducing the number of loose fastenings needed and reducing labour time through the use of in-die production, both of which helps to reduce costs.

Finally, self-clinching fasteners provide product design engineers with an opportunity to bring to life products with a longer lifecycle that are more durable, easy to service and will stand the test of time. 

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