New fastener provides conductivity solution for bonded metal sheets

Driven by the use of bonded sheets in lightweight vehicle assembly, EJOT UK has developed a self-piercing fastener that will maintain electrical continuity where metal sheets are glued, rather then joined.
The new EJOT E-connectivity screw uses pierce-point thread technology to create a fast installation that maintains conductivity – yet requires no pilot hole into the sheet.

Driven by the demand for lower emissions and increased fuel economy, lightweight vehicle assembly developments are creating challenges that question traditional techniques.

Automotive OEMs are reducing vehicle weights by bonding advanced thin sheet materials such as aluminium. Whilst effective, this can create issues where electrical continuity through areas of the vehicle structure needs to be maintained but is broken by the wafer thin sheet of glue between the metal sheets.

The obvious solution has been to 'drive' stainless steel fasteners through the sheets, not to add strength to the bond, but simply to reintroduce electrical pathways. However, the prerequisite of a pilot hole for each fastener makes this short-term solution time-heavy.

Shared Group technology and resource

EJOT UK has overcome this by utilising fastening technology originally developed for the EJOT Group's Building & Construction portfolio. Innovative twin thread geometry that displaces rather than cuts the metal, was adapted – making it possible to reduce debris whilst generating faster installation speeds. More significantly the screw is manufactured with a 'pierce-point' tip which eliminates the need for a pilot hole – significantly shortening installation time.

EJOT's R&D team then addressed the issue of corrosion resistance – with research pointing to a figure of 720 hours salt-spray resistance. Normally zinc plated fasteners require an organic coating to increase the corrosion resistance and to speed up installation. Adding an organic coat also drastically reduces conductivity by acting as an insulator. EJOT's Applitec R & D team found that by adding Nickel to the Zinc plating provides excellent salt spray resistance, works well as a lubricant – and successfully maintains electrical conductivity.

The resulting product has been named the E-connectivity fastener and is currently being trialed by several OEMs with an interest in light weight assembly processes. For more information about the EJOT E-Connectivity fastener visit www.ejot.co.uk/industry

Author
EJOT UK Ltd

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