Fastening & Joining Components Roundup

Fastening and joining components are foundational elements in machine design, directly influencing the structural integrity, operational reliability and manufacturability of engineered systems. Although fasteners might seem commonplace, their selection, application and performance require specialized expertise to ensure optimal joint behavior.

Andrew Benson, an application engineer at Bossard, a fastening solutions provider, spoke with Machine Design about trends, failure diagnosis, supply chain considerations and advanced joint testing methodologies that are critical for modern machine design.

In complex assemblies, the right fastener choice extends beyond size and strength specifications, Benson said, noting that Bossard provides application engineering expertise to help users select the right fastener or resolve fastening issues, collaborating closely to ensure that designs perform well and meet market demands. They address issues such as environmental conditions, coatings, loads and potential failure modes early in the design process to help ensure reliable joints.

Emerging Trends in Fastening Technology

A major trend in fastening is the use of low-friction coatings, according to Benson. These coatings reduce assembly torque, easing the workload on operators and improving torque consistency. The coatings lower the friction coefficient to around 0.08 to 0.12 compared to higher values for standard zinc plating, facilitating better torque-to-clamp load control.

Conventional locking methods such as split lock washers are largely ineffective because they tend to flatten easily and lose their locking effect quickly, Benson said. He points out that preferred alternatives include wedge lock washers, lock nuts and pre-applied adhesive or nylon patches which simplify assembly and improve joint reliability without adding extra components.

Diagnosing Failures, Testing and Analysis

Fastener failures often result from improper installation or component selection. Benson describes that breakage can stem from using the wrong fastener type, over-torquing causing deformation or under-torquing leading to loosening and fatigue failure. Identifying the cause of failure typically requires inspection of fracture surfaces and review of torque application and operating conditions.

Bossard uses ultrasonic testing to measure clamp load directly without modifying the joint. The process involves lightly sanding the bolt on both sides, attaching a probe that measures clamp flow during tightening to allow for continuous load tracking. “That is more relevant than torque alone, since torque only indicates the means to achieve clamp load,” Benson said, adding that the objective is generally to keep bulk stretch within the elastic limit to allow reuse. Only in specific applications, such as engine bolts, is full stretching used to obtain maximum clamp load, he noted.

When asked about supply chain and manufacturing considerations, Benson spoke of the importance of sourcing flexibility and noted that Bossard works with manufacturers in both the U.S. and overseas to meet customer needs. He points out that given recent political changes, having diverse sourcing options helps provide the best solutions under varying conditions.

There are a host of fastening and joining components providers, and Machine Design has compiled a few here that address challenges in fastening reliability, assembly efficiency, thermal management and joint integrity. Additionally, you will find more fastening and joining components in Rehana Begg’s article “Hold it Together: Fasteners, Springs, Screws, Nuts, Bolts.”

Bimetal Face Seal Fittings for High Thermal and Chemical Performance

Designed to meet demanding requirements for thermal conductivity and chemical resistance, these bimetal fittings from Atlas Technologies offer a robust solution for secure, leak tight connections in aerospace and semiconductor applications. These fittings combine aluminum 6061-T6 bodies with stainless steel 316L seal faces, rated for tensile strength of 15,000 psi and vacuum leak tested to under 1 × 10−9 cc/sec helium. They are compatible with Swagelock VCR and Parker-Hannifin systems and available in a range of weld and mounting styles.

Integrated Keyless Fastening for Timing Pulleys

Offering a fastening solution that eliminates shaft machining while improving mounting precision, the Fairloc hub design from Stock Drive Products/Sterling Instrument (SDP/SI), a Designatronics brand, addresses concerns around joint security and assembly simplicity. This system integrates fastening directly into the pulley hub, enabling secure, precise mounting with reusability. There are no keyways or flats to machine, no holes to drill or tap and no additional components to purchase. They are available in aluminum and polycarbonate, supporting bore sizes up to 2 in. in multiple belt profiles, they are designed to reduce assembly time and parts count.

Nylon PCB Hardware and Tool-free Rivets for Efficient Assembly

With a focus on efficient, reliable assembly, Essentra's nylon PCB hardware and rivets are made to support rapid installation while protecting components from vibration and corrosion, aligning with trends in streamlined manufacturing. Their offering includes nylon hardware for insulation and vibration dampening, plus rivets designed for tool free installation. Components are made to resist corrosion and protect mating surfaces, enhancing assembly speed and joint durability.

Low Outgassing, Thermally Conductive Epoxy for Aerospace Applications

Thermal management and low outgassing are especially important in specialized machine designs. Master Bond’s EP53TC epoxy is made to provide an effective bonding and sealing option that meets strict aerospace standards. This two-component epoxy features flowable filler technology for efficient heat dissipation, meets NASA low outgassing ASTM E595 specifications, and maintains mechanical and electrical performance across a wide temperature range. Moderate heat cure is designed to maximize properties.