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Blind Fastener White Paper

Blind Fastener White Paper
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Technical White Paper The Case for Structural Blind Fasteners in Automotive Applications The call for lightweighting has led to significant advancements in how we design and construct vehicles. Technology gains have resulted in new and exciting possibilities, but they have also created unique problem sets. The move toward increased aluminum usage in vehicles is one example. While it is widely accepted that aluminum improves fuel economy and agility, aluminum also poses joint design challenges. The lessons learned while fastening steel bodies do not translate to the new aluminum joints, since aluminum behaves differently than steel. Based on this fact, even accepted practices like welding must be re-thought. Fortunately, proven technologies already exist to replace, and even improve upon, now incompatible practices. Enter structural blind fasteners. They have been used in many critical joint applications for decades, including widespread usage in aerospace, proving their reliability. The availability of carbon steel, aluminum, and stainless steel variations make structural blind fasteners a viable option for joining a multitude of materials, including aluminum. Installation of structural blind fasteners does not require the extensive training required for other joining technologies, and their captive subcomponents eliminate the “squeak-and-rattle” caused by other types of fasteners. You may ask: “Why try something new, when I know and trust adhesives or welding?” This article will explore the benefits and drawbacks of these technologies, and compare them to the benefits of structural blind fastening. Adhesives For manufacturers who must join dissimilar materials, adhesives are an attractive option. Application is usually simple and straightforward. These adhesives form consistent bonds between both similar and dissimilar materials, while only nominally adding to the weight of the structure. Additionally, adhesives can be applied along the perimeter of a joint to lend additional strength and provide a measure of protection from contaminants. One can choose from a broad selection of adhesive products for use in a number of applications. However, these options must be carefully evaluated, as many can be costly. Also, bonding times can be extensive, and if the adhesive is not applied consistently and cured properly, the resulting bond could be unreliable. When adhesives are used, a careful review of each joint must be performed. Adhesives can also be susceptible to degradation based on atmospheric conditions or contact with corrosive elements, raising long-term durability concerns for many applications. Lastly, the environmental impact of adhesives cannot be ignored. The disposal of residues from the application and cleaning up of adhesives can present problems, as can the recycling of end-of-life vehicles in which adhesives were used. 1|P

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Welding Welding is another widely accepted process for joining metals, having been used in various forms since the Bronze Age. The twentieth and twenty-first centuries have seen a growth in new welding technologies, many in response to lightweighting objectives and the introduction of new materials. The growing use of aluminum in the automotive industry has presented two major challenges for welding technology: electrical conductivity and surface preparation. The high thermal conductivity of aluminum means that heat must be applied four times faster than with steel in order to raise the...

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Structural blind fasteners offer similar benefits to those of non-structural blind fasteners, while also providing a distinct advantage: quantifiable and predictable shear and tensile strength. Unlike “pop” type rivets, structural blind rivets retain their mandrel after installation. This retention of the mandrel is made possible by the interaction of the mandrel and mandrel sleeve during the installation process. The presence of the mandrel accounts for a 60-80% increase in load-carrying ability in shear and tensile over conventional non-structural blind fasteners. Structural blind...

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Installed structural blind fasteners remain tight up to their minimum mechanical values, creating tight, vibration-resistant joints that are less susceptible to cracking. These versatile fasteners can also be used in conjunction with adhesives to ensure that a joint remains tight until the adhesives cure while also contributing additional supportive strength to the joint. Finally, the installed cost of structural blind fasteners tends to be lower than that of other joining options, with savings on time, labor, and complicated inspection processes resulting in overall savings and higher...

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Moving forward The automotive industry is under continued pressure to do more with less: less weight, less cost, and less time. The growing usage of aluminum and other exotic materials presents unique challenges in joint design. Understanding how different joining technologies function from the perspective of weight, cost, productivity, and reliability is crucial. While adhesives and welding are often the joining technologies of choice when trying to address weight concerns, structural blind fasteners should also be given strong consideration. Structural blind fasteners may add minimal...

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