But, whatever the exact balance, design is always at the heart of achieving a successful outcome.
Explains Kevin Moorcroft, MD at specialist fastener suppliers Challenge Europe: “Automation, in particular, places exceptional demands on a fastener above and beyond how well it does its job in service. For example, designs such as Torx and Torx Plus are less prone to slippage and wear in the assembly cycle; likewise, collated nails and screws for electric and pneumatic installation are ideal for the building/construction industry - similarly, self-piercing rivets, especially designed for fast joining of sheet metal.”
Many drive forms for threaded fasteners exist, each with a different relevance to assembly – eg, by hand, with power tools, semi-automatic, fully automatic and completely automated. Each also carries varying degrees of security when installed. “At the simple end, we have slot, cross head, socket, square and hex head forms,” states Moorcroft. “More complex, we have hex lobed (torx), tri-lobed (tri-wing), torq-set, triple square (12 point), polydrive, double hex (8 point), bristol, one way, splined, hex+pin, hexlobe+pin and pignose (spanner head/snake eye).”
It must be kept in mind that not all the above are freely available in a wide range of sizes, head styles or materials. Many were initially developed to meet specific applications and would be very expensive options, unless your demands ran into the hundreds of thousands.
In principle, the simpler drive forms are suited to lower speed assemblies, whereas the more specialist complex designs offer higher speed and higher torque capability. Types with centre pin or dual holes are primarily for security installations.
Where high-speed jointing of sheets is required on a continuous basis, then the investment in the specialist equipment for self-piercing rivets can prove a worthwhile exercise – no holes are required and a neat join is produced – it is essentially a single iterative process, which can be used on un-weldable materials and combinations of differing materials. There is minimal damage to coated sheets and it is a low impact process, in terms of environment: eg, zero fumes or heat, low noise levels and low energy usage.
