13 April 2018
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Locked in battle

Manufacturers of heavy-duty equipment and fabricators of large metal structures have long embraced the practice of welding joints together. But lockbolts are now staking a powerful claim to this prized territory

For years, welding was seen as the only way to ensure the integrity of joints in demanding load-bearing or high-vibration structures. So, companies manufacturing heavy-duty equipment or fabricating large, metal structures continued to employ the universally accepted process of welding joints together. However, today there are alternatives to welding, one of the foremost being direct-tension installed, swaged lockbolts, such as the HuckBolts currently offered by Arconic Fastening Systems and Rings. These unique engineered fasteners, proven in such demanding applications as truck suspensions and chassis, railroad track crossings, and heavy defense vehicles, are now being used in a number of products and structures where welding was once the only option.


While welding is proven to be one of the surest processes for securing a joint, there are a number of issues relating to it. To begin, the welding process is very time consuming, particularly in situations where in-depth inspection procedures are required. Welding also requires skilled, often highly paid, technicians. And in some industries, such as oil and gas, quality welders are both difficult to find and to retain.

The heat generated by welding can often reduce the strength of the metals being joined, and damage critical surface coatings. In addition, welding dissimilar metals or pieces of varying sizes can be a challenge. Welding also often requires an on-going process of inspection, with many of these procedures being both costly and time consuming. And as most companies who make extensive use of welding as part of their manufacturing or fabrication process have discovered, the removal and/or rework of a weld can be problematic.

Last, but most assuredly not least, welding is a dirty, dangerous process. Safety is a critical issue, since many fires have been started by a random spark created while welding. At the same time, spent rods and other remnants of the welding process are an ongoing housekeeping issue in shops where welding is performed on a regular basis.


Engineered lockbolts have replaced welding in more and more heavy, demanding applications. For example, lockbolts such as Arconic Fastening Systems and Rings' HuckBolts fasteners can be found in a wide range of applications that once solely belonged to welding.

Structural HuckBolts, offered in a wide range of sizes (up to 1-3/8”) and materials, consist of a pin and a collar. These advanced fasteners are installed using a direct tension technique, in which the pin is pulled and the collar is simultaneously swaged into the locking grooves of the pin, deforming the collar into the grooves. Based on their design and unique direct tension installation, HuckBolts deliver consistent clamp for a strong, stable and vibration-resistant joint, states the company.

There are several reasons why many manufacturers of heavy equipment are actively investigating the possibility of using direct-tension lockbolts in their assembly process. “To begin with, even taking into consideration the need to drill a hole, installing a lockbolt is significantly faster than welding a joint. And a quick visual inspection is all that is required to confirm the accuracy and quality of the installation. In addition, an operator requires a minimal amount of training in order to be proficient in the installation of HuckBolts. One is no longer at the mercy of a limited pool of expensive skilled labour,” claims Arconic.

HuckBolts can be used with virtually any metal, while dissimilar metals with dissimilar coefficients of thermal expansion are said to present no problems. “Varying piece sizes in a joint are accommodated and surface finishes not harmed. And, most importantly, HuckBolts are proven to hold up over years of service in demanding high-stress, high-vibration environments.”

Also, employing lockbolts, such as the HuckBolt, in key joining applications is claimed to eliminate all of the housekeeping and safety issues integral to the welding process. HuckBolts are installed using a quiet, jolt-free swaging action, removing the potential for repetitive stress syndrome issues. There are no sparks to start fires or cause explosions, nor any debris on the floor that can lead to slips and falls.


There are several unique design elements of HuckBolts that also ensure their ultimate resistance to the effects of vibration, Arconic adds. “Compared to conventional nut and bolt installations, which can loosen in high-vibration environments, HuckBolts have proven to be impervious to the effect of vibration in a number of very demanding applications. The secret to this performance difference can be found in the unique HuckBolt design, in which the collar is fully swaged into the locking grooves of the pin.”

In contrast, it points out, conventional nut and bolt fasteners leave a slight gap between the crest and root of the threads when installed. “This gap becomes problematic when exposed to transverse vibration and can allow for rapid loss of clamp.”

Another key difference between HuckBolt and conventional fastener installations is found in the structure of the threads of each of the fastening systems. “Instead of the deep threads required to achieve a tolerance fit between conventional nuts and bolts, the HuckBolt pin requires only shallow locking grooves into which the collar is swaged. The shallow design of the locking grooves allows for a much larger pin root radius, which contributes significantly to the fatigue strength – up to five times that of a conventional nut and bolt. Overall, a HuckBolt lockbolt provides superior vibration resistance.”


For applications where only one side of the joint material is accessible, performance-engineered Huck structural blind fasteners can often meet design requirements. “These blind fasteners can deliver the shear and tensile strength to meet the demands of many heavy-duty applications. Available in diameters ranging from 3/16” to 3/4", these fasteners offer a combination of strength and vibration resistance, easy installation and a high level of safe operation,” says Arconic.

The company also readily notes that HuckBolts and Huck structural blind fasteners are not designed to replace all welds. “These fasteners can leave a protrusion, which may not be acceptable for some applications. However, there are many applications, where welding has been traditionally employed, in which these fasteners are a viable alternative. Engineered for easy installation and long, reliable life, these direct-tension HuckBolts and structural blind fasteners can be a faster, more cost-efficient and safer alternative to traditional welding processes.”


Brian Wall

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Related Companies

Arconic Fastening Systems & Rings Ltd


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